E. Zanetti
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Hydrogen Pipeline Compressor Substation
A Physics-Based Optimisation Framework for Hydrogen Pipeline Compressor Substation Design: Configuration Selection, Intercooling, and Heterogeneous Train Dispatch
Hydrogen pipeline networks require compressor substations to overcome frictional pressure losses over long transport distances, yet no established design methodology exists for translating hydrogen’s distinct thermodynamic and safety properties into a substation configuration. This thesis addresses the research question: how can hydrogen compressor substation design be quantitatively optimised using a physics-based model under thermodynamic, operational, and safety constraints?
A python-based model combining the Leachman equation of state (via CoolProp), polytropic compression and intercooling relations, mechanical and utilisation-based feasibility filters, and a Casey & Robinson elliptic-curve representation of off-design centrifugal compressor behaviour was developed and applied to a representative case of 40 to 80 bar boundary conditions. A three-layer optimisation architecture reduces the combinatorial space of 4094 candidate configurations, first through independent mechanical and thermodynamic feasibility screening, then a joint SLSQP-based pressure-ratio and intercooler- placement optimisation, and finally a mass-flow-allotment optimisation across heterogeneous parallel trains, cutting the number of required thermodynamic property evaluations by 94%.
Three intercoolers (K = 3) emerged as the unambiguous optimum across all evaluated stage counts and both impeller tip speeds (450 and 600 m/s), driven by rapidly diminishing marginal cooling benefit against a fixed intercooler pressure drop. Stage count was found to affect mechanical and capital cost but not thermodynamic performance; optimising the pressure-ratio distribution across stage groups, rather than assuming a uniform split, yielded a modest 0.263% reduction in specific work, with most of the achievable efficiency gain instead coming from intercooler count and placement. Heterogeneous train dispatch was shown to substantially widen the usable operating window relative to an equal-split strategy, though the tightest surge/choke margin identified across the design space narrowed to approximately 1.19 times the design flow coefficient at the final stage of the (N=12, K=4) configuration.
The techno-economic evaluation, benchmarked against a Class 4 (AACE, ±30%) accuracy correlation, placed total CAPEX at 1421.95 and 1932.64 million euros for the titanium- and composite-impeller configurations respectively, though this comparison is confounded by the two configurations also differing in stage count and tip speed.
This work’s primary contribution is the layered optimisation architecture itself, together with the demonstration that heterogeneous train sizing offers a meaningful operational flexibility benefit over homogeneous dispatch. The framework’s predictions were compared against published elliptic-curve calibration data and existing compressor performance maps, though full off-design validation against independent experimental or vendor data was outside this thesis’s scope. As a decision-support tool for early-stage compressor substation design, the model is positioned to guide configuration selection ahead of detailed engineering, rather than to replace it. ...
A python-based model combining the Leachman equation of state (via CoolProp), polytropic compression and intercooling relations, mechanical and utilisation-based feasibility filters, and a Casey & Robinson elliptic-curve representation of off-design centrifugal compressor behaviour was developed and applied to a representative case of 40 to 80 bar boundary conditions. A three-layer optimisation architecture reduces the combinatorial space of 4094 candidate configurations, first through independent mechanical and thermodynamic feasibility screening, then a joint SLSQP-based pressure-ratio and intercooler- placement optimisation, and finally a mass-flow-allotment optimisation across heterogeneous parallel trains, cutting the number of required thermodynamic property evaluations by 94%.
Three intercoolers (K = 3) emerged as the unambiguous optimum across all evaluated stage counts and both impeller tip speeds (450 and 600 m/s), driven by rapidly diminishing marginal cooling benefit against a fixed intercooler pressure drop. Stage count was found to affect mechanical and capital cost but not thermodynamic performance; optimising the pressure-ratio distribution across stage groups, rather than assuming a uniform split, yielded a modest 0.263% reduction in specific work, with most of the achievable efficiency gain instead coming from intercooler count and placement. Heterogeneous train dispatch was shown to substantially widen the usable operating window relative to an equal-split strategy, though the tightest surge/choke margin identified across the design space narrowed to approximately 1.19 times the design flow coefficient at the final stage of the (N=12, K=4) configuration.
The techno-economic evaluation, benchmarked against a Class 4 (AACE, ±30%) accuracy correlation, placed total CAPEX at 1421.95 and 1932.64 million euros for the titanium- and composite-impeller configurations respectively, though this comparison is confounded by the two configurations also differing in stage count and tip speed.
This work’s primary contribution is the layered optimisation architecture itself, together with the demonstration that heterogeneous train sizing offers a meaningful operational flexibility benefit over homogeneous dispatch. The framework’s predictions were compared against published elliptic-curve calibration data and existing compressor performance maps, though full off-design validation against independent experimental or vendor data was outside this thesis’s scope. As a decision-support tool for early-stage compressor substation design, the model is positioned to guide configuration selection ahead of detailed engineering, rather than to replace it. ...
Hydrogen pipeline networks require compressor substations to overcome frictional pressure losses over long transport distances, yet no established design methodology exists for translating hydrogen’s distinct thermodynamic and safety properties into a substation configuration. This thesis addresses the research question: how can hydrogen compressor substation design be quantitatively optimised using a physics-based model under thermodynamic, operational, and safety constraints?
A python-based model combining the Leachman equation of state (via CoolProp), polytropic compression and intercooling relations, mechanical and utilisation-based feasibility filters, and a Casey & Robinson elliptic-curve representation of off-design centrifugal compressor behaviour was developed and applied to a representative case of 40 to 80 bar boundary conditions. A three-layer optimisation architecture reduces the combinatorial space of 4094 candidate configurations, first through independent mechanical and thermodynamic feasibility screening, then a joint SLSQP-based pressure-ratio and intercooler- placement optimisation, and finally a mass-flow-allotment optimisation across heterogeneous parallel trains, cutting the number of required thermodynamic property evaluations by 94%.
Three intercoolers (K = 3) emerged as the unambiguous optimum across all evaluated stage counts and both impeller tip speeds (450 and 600 m/s), driven by rapidly diminishing marginal cooling benefit against a fixed intercooler pressure drop. Stage count was found to affect mechanical and capital cost but not thermodynamic performance; optimising the pressure-ratio distribution across stage groups, rather than assuming a uniform split, yielded a modest 0.263% reduction in specific work, with most of the achievable efficiency gain instead coming from intercooler count and placement. Heterogeneous train dispatch was shown to substantially widen the usable operating window relative to an equal-split strategy, though the tightest surge/choke margin identified across the design space narrowed to approximately 1.19 times the design flow coefficient at the final stage of the (N=12, K=4) configuration.
The techno-economic evaluation, benchmarked against a Class 4 (AACE, ±30%) accuracy correlation, placed total CAPEX at 1421.95 and 1932.64 million euros for the titanium- and composite-impeller configurations respectively, though this comparison is confounded by the two configurations also differing in stage count and tip speed.
This work’s primary contribution is the layered optimisation architecture itself, together with the demonstration that heterogeneous train sizing offers a meaningful operational flexibility benefit over homogeneous dispatch. The framework’s predictions were compared against published elliptic-curve calibration data and existing compressor performance maps, though full off-design validation against independent experimental or vendor data was outside this thesis’s scope. As a decision-support tool for early-stage compressor substation design, the model is positioned to guide configuration selection ahead of detailed engineering, rather than to replace it.
A python-based model combining the Leachman equation of state (via CoolProp), polytropic compression and intercooling relations, mechanical and utilisation-based feasibility filters, and a Casey & Robinson elliptic-curve representation of off-design centrifugal compressor behaviour was developed and applied to a representative case of 40 to 80 bar boundary conditions. A three-layer optimisation architecture reduces the combinatorial space of 4094 candidate configurations, first through independent mechanical and thermodynamic feasibility screening, then a joint SLSQP-based pressure-ratio and intercooler- placement optimisation, and finally a mass-flow-allotment optimisation across heterogeneous parallel trains, cutting the number of required thermodynamic property evaluations by 94%.
Three intercoolers (K = 3) emerged as the unambiguous optimum across all evaluated stage counts and both impeller tip speeds (450 and 600 m/s), driven by rapidly diminishing marginal cooling benefit against a fixed intercooler pressure drop. Stage count was found to affect mechanical and capital cost but not thermodynamic performance; optimising the pressure-ratio distribution across stage groups, rather than assuming a uniform split, yielded a modest 0.263% reduction in specific work, with most of the achievable efficiency gain instead coming from intercooler count and placement. Heterogeneous train dispatch was shown to substantially widen the usable operating window relative to an equal-split strategy, though the tightest surge/choke margin identified across the design space narrowed to approximately 1.19 times the design flow coefficient at the final stage of the (N=12, K=4) configuration.
The techno-economic evaluation, benchmarked against a Class 4 (AACE, ±30%) accuracy correlation, placed total CAPEX at 1421.95 and 1932.64 million euros for the titanium- and composite-impeller configurations respectively, though this comparison is confounded by the two configurations also differing in stage count and tip speed.
This work’s primary contribution is the layered optimisation architecture itself, together with the demonstration that heterogeneous train sizing offers a meaningful operational flexibility benefit over homogeneous dispatch. The framework’s predictions were compared against published elliptic-curve calibration data and existing compressor performance maps, though full off-design validation against independent experimental or vendor data was outside this thesis’s scope. As a decision-support tool for early-stage compressor substation design, the model is positioned to guide configuration selection ahead of detailed engineering, rather than to replace it.
Analysis of SOFC-GT Architectures with Heat Recovery for Primary Aircraft Propulsion
Influence of Heat Exchanger Configuration and Size on the Performance of a Hydrogen-Powered Hybrid Turboshaft Engine
Master thesis
(2026)
-
V. Ļaļikova, A. Gangoli Rao, R.P. Sampat, D. Chatterjee, E. Zanetti, F. De Domenico
Aviation requires propulsion concepts that improve efficiency while reducing reliance on hydrocarbon fuels. This study investigated hydrogen-fuelled solid oxide fuel cell-gas turbine (SOFC-GT) architectures with heat recovery for primary propulsion in a regional turboprop application, with particular attention to the influence of the heat exchanger placement and size on the steady-state design performance. PW127-based turboshaft model was developed in OpenMDAO-pyCycle and extended with an intermediate-temperature SOFC, electric motor and compact counterflow plate-fin heat exchanger. Four hybrid architectures were investigated, with the heat exchanger hot stream placed downstream of the low-pressure turbine, high-pressure turbine, burner and SOFC cathode exhaust. The effects of SOFC power contribution and turbine inlet temperature on the hybrid engine were evaluated, resulting in maximum efficiencies of 55.35\%, 49.91\%, 47.32\% and 48.73\% compared to the hydrogen-fuelled baseline cycle efficiency of 26.64\%. The heat exchanger model was additionally used to examine rectangular and triangular channel shapes and identify designs satisfying the established pressure drop constraint. The architecture with post-low-pressure turbine heat recovery achieved the highest efficiency, but no geometry that satisfies the set constraint was identified. The architecture with post-burner heat recovery provided the most compact heat exchanger, the architecture with post-high-pressure turbine heat recovery offered an intermediate compromise, while the architecture with post-SOFC heat recovery demonstrated feasible operation only with high SOFC power contribution.
...
Aviation requires propulsion concepts that improve efficiency while reducing reliance on hydrocarbon fuels. This study investigated hydrogen-fuelled solid oxide fuel cell-gas turbine (SOFC-GT) architectures with heat recovery for primary propulsion in a regional turboprop application, with particular attention to the influence of the heat exchanger placement and size on the steady-state design performance. PW127-based turboshaft model was developed in OpenMDAO-pyCycle and extended with an intermediate-temperature SOFC, electric motor and compact counterflow plate-fin heat exchanger. Four hybrid architectures were investigated, with the heat exchanger hot stream placed downstream of the low-pressure turbine, high-pressure turbine, burner and SOFC cathode exhaust. The effects of SOFC power contribution and turbine inlet temperature on the hybrid engine were evaluated, resulting in maximum efficiencies of 55.35\%, 49.91\%, 47.32\% and 48.73\% compared to the hydrogen-fuelled baseline cycle efficiency of 26.64\%. The heat exchanger model was additionally used to examine rectangular and triangular channel shapes and identify designs satisfying the established pressure drop constraint. The architecture with post-low-pressure turbine heat recovery achieved the highest efficiency, but no geometry that satisfies the set constraint was identified. The architecture with post-burner heat recovery provided the most compact heat exchanger, the architecture with post-high-pressure turbine heat recovery offered an intermediate compromise, while the architecture with post-SOFC heat recovery demonstrated feasible operation only with high SOFC power contribution.
Assessment of Integrated Solar-Based Residential Energy Systems with Seasonal Thermal Storage
Development and Evaluation of SOLSTICE V2 with a Focus on High-Temperature Aquifer Thermal Energy Storage
The transition to low-carbon energy systems requires the electrification of residential heating using renewable electricity. However, renewable electricity generation, of which solar electricity forms an important share, and residential heat demand are strongly mismatched across the seasons. This thesis critically evaluates and further develops the Solar Storage in Diverse Climates (SOLSTICE) modelling framework into SOLSTICE V2, an accessible and transparent hourly Excel-based model for the early-stage assessment of residential energy systems. The model is intended to enable users such as policymakers and planners to compare system configurations and explore energy-system behaviour without requiring advanced simulation software or specialised modelling expertise. SOLSTICE V2 combines photovoltaic or photovoltaic-thermal collectors, heat pumps, electrical battery storage, and high-temperature aquifer thermal energy storage. The existing component representations were assessed and adapted where necessary, with particular attention given to plane-of-array irradiance, duty-specific heat-pump operation, electrical battery losses, photovoltaic-thermal and heat-pump coupling, and the physical representation of useful heat stored in the aquifer. The resulting framework uses hourly weather, demand, and electricity-price data to simulate energy flows and compare system configurations under different climatic conditions.
The results show that converting excess summer solar electricity into directly usable winter heat can achieve electrical self-sufficiency above 90%. For the Berlin reference case, adding high-temperature aquifer thermal energy storage to the photovoltaic and electrical battery configuration reduced annual grid import from 2024 kWh to 450 kWh per household. Replacing photovoltaic modules with photovoltaic-thermal collectors further improved system performance because the higher heat-source temperature significantly increased heat-pump performance. In Berlin, the investigated system used approximately 25 m² of solar collectors per household and a shared effective hot-well volume of 230,000 m³ for 1000 households. Under the higher solar irradiation and lower heating demand of Madrid, comparable performance was achieved with approximately 13 m² of solar collectors per household and an effective hot-well volume of 100,000 m³. The results demonstrate the complementary roles of short-term electrical storage and seasonal thermal storage, as well as the importance of climate-specific system sizing.
...
The results show that converting excess summer solar electricity into directly usable winter heat can achieve electrical self-sufficiency above 90%. For the Berlin reference case, adding high-temperature aquifer thermal energy storage to the photovoltaic and electrical battery configuration reduced annual grid import from 2024 kWh to 450 kWh per household. Replacing photovoltaic modules with photovoltaic-thermal collectors further improved system performance because the higher heat-source temperature significantly increased heat-pump performance. In Berlin, the investigated system used approximately 25 m² of solar collectors per household and a shared effective hot-well volume of 230,000 m³ for 1000 households. Under the higher solar irradiation and lower heating demand of Madrid, comparable performance was achieved with approximately 13 m² of solar collectors per household and an effective hot-well volume of 100,000 m³. The results demonstrate the complementary roles of short-term electrical storage and seasonal thermal storage, as well as the importance of climate-specific system sizing.
...
The transition to low-carbon energy systems requires the electrification of residential heating using renewable electricity. However, renewable electricity generation, of which solar electricity forms an important share, and residential heat demand are strongly mismatched across the seasons. This thesis critically evaluates and further develops the Solar Storage in Diverse Climates (SOLSTICE) modelling framework into SOLSTICE V2, an accessible and transparent hourly Excel-based model for the early-stage assessment of residential energy systems. The model is intended to enable users such as policymakers and planners to compare system configurations and explore energy-system behaviour without requiring advanced simulation software or specialised modelling expertise. SOLSTICE V2 combines photovoltaic or photovoltaic-thermal collectors, heat pumps, electrical battery storage, and high-temperature aquifer thermal energy storage. The existing component representations were assessed and adapted where necessary, with particular attention given to plane-of-array irradiance, duty-specific heat-pump operation, electrical battery losses, photovoltaic-thermal and heat-pump coupling, and the physical representation of useful heat stored in the aquifer. The resulting framework uses hourly weather, demand, and electricity-price data to simulate energy flows and compare system configurations under different climatic conditions.
The results show that converting excess summer solar electricity into directly usable winter heat can achieve electrical self-sufficiency above 90%. For the Berlin reference case, adding high-temperature aquifer thermal energy storage to the photovoltaic and electrical battery configuration reduced annual grid import from 2024 kWh to 450 kWh per household. Replacing photovoltaic modules with photovoltaic-thermal collectors further improved system performance because the higher heat-source temperature significantly increased heat-pump performance. In Berlin, the investigated system used approximately 25 m² of solar collectors per household and a shared effective hot-well volume of 230,000 m³ for 1000 households. Under the higher solar irradiation and lower heating demand of Madrid, comparable performance was achieved with approximately 13 m² of solar collectors per household and an effective hot-well volume of 100,000 m³. The results demonstrate the complementary roles of short-term electrical storage and seasonal thermal storage, as well as the importance of climate-specific system sizing.
The results show that converting excess summer solar electricity into directly usable winter heat can achieve electrical self-sufficiency above 90%. For the Berlin reference case, adding high-temperature aquifer thermal energy storage to the photovoltaic and electrical battery configuration reduced annual grid import from 2024 kWh to 450 kWh per household. Replacing photovoltaic modules with photovoltaic-thermal collectors further improved system performance because the higher heat-source temperature significantly increased heat-pump performance. In Berlin, the investigated system used approximately 25 m² of solar collectors per household and a shared effective hot-well volume of 230,000 m³ for 1000 households. Under the higher solar irradiation and lower heating demand of Madrid, comparable performance was achieved with approximately 13 m² of solar collectors per household and an effective hot-well volume of 100,000 m³. The results demonstrate the complementary roles of short-term electrical storage and seasonal thermal storage, as well as the importance of climate-specific system sizing.
This thesis addresses the urgent challenge of decarbonizing large-scale industrial process heating with limited available electricity grid capacity. An integrated energy system is developed combining solar heat generation with thermal storage coupled to a high-temperature heat pump for industrial process heating up to 150 ℃ This work involves the development of individual component models capable of high temperature (100--150 ℃) operation and the integration of these components into a numerical energy system model. The model is evaluated for two industrial sectors, Food & Beverage (130 ℃) and Paper & Pulp (150 ℃), under northern and southern European climate conditions. The developed integrated model is added to the PVMD Toolbox, an advanced modeling tool developed by the Photovoltaic Materials and Devices research group at TU Delft.
Through dynamic hourly simulations over a full year, the theoretical feasibility of the integrated energy system has been demonstrated. The thermal efficiency of the solar thermal collectors averages 40% and 50% in Delft and Seville respectively. Significant reductions in peak electricity grid consumption of 70% and 100% can be achieved for northern and southern European climates respectively. Solar thermal collector count is the most important performance variable over all scenarios and seasonal heat storage is essential for peak load reductions in northern European climates. The system can be economically competitive compared to a natural gas boiler reference (80 €/MWh) in Seville, achieving a minimum LCOH of 66 €/MWh. For Delft the lowest LCOH is 119 €/MWh, not yet competitive under current gas prices but considerably less exposed to fossil fuel price volatility. ...
Through dynamic hourly simulations over a full year, the theoretical feasibility of the integrated energy system has been demonstrated. The thermal efficiency of the solar thermal collectors averages 40% and 50% in Delft and Seville respectively. Significant reductions in peak electricity grid consumption of 70% and 100% can be achieved for northern and southern European climates respectively. Solar thermal collector count is the most important performance variable over all scenarios and seasonal heat storage is essential for peak load reductions in northern European climates. The system can be economically competitive compared to a natural gas boiler reference (80 €/MWh) in Seville, achieving a minimum LCOH of 66 €/MWh. For Delft the lowest LCOH is 119 €/MWh, not yet competitive under current gas prices but considerably less exposed to fossil fuel price volatility. ...
This thesis addresses the urgent challenge of decarbonizing large-scale industrial process heating with limited available electricity grid capacity. An integrated energy system is developed combining solar heat generation with thermal storage coupled to a high-temperature heat pump for industrial process heating up to 150 ℃ This work involves the development of individual component models capable of high temperature (100--150 ℃) operation and the integration of these components into a numerical energy system model. The model is evaluated for two industrial sectors, Food & Beverage (130 ℃) and Paper & Pulp (150 ℃), under northern and southern European climate conditions. The developed integrated model is added to the PVMD Toolbox, an advanced modeling tool developed by the Photovoltaic Materials and Devices research group at TU Delft.
Through dynamic hourly simulations over a full year, the theoretical feasibility of the integrated energy system has been demonstrated. The thermal efficiency of the solar thermal collectors averages 40% and 50% in Delft and Seville respectively. Significant reductions in peak electricity grid consumption of 70% and 100% can be achieved for northern and southern European climates respectively. Solar thermal collector count is the most important performance variable over all scenarios and seasonal heat storage is essential for peak load reductions in northern European climates. The system can be economically competitive compared to a natural gas boiler reference (80 €/MWh) in Seville, achieving a minimum LCOH of 66 €/MWh. For Delft the lowest LCOH is 119 €/MWh, not yet competitive under current gas prices but considerably less exposed to fossil fuel price volatility.
Through dynamic hourly simulations over a full year, the theoretical feasibility of the integrated energy system has been demonstrated. The thermal efficiency of the solar thermal collectors averages 40% and 50% in Delft and Seville respectively. Significant reductions in peak electricity grid consumption of 70% and 100% can be achieved for northern and southern European climates respectively. Solar thermal collector count is the most important performance variable over all scenarios and seasonal heat storage is essential for peak load reductions in northern European climates. The system can be economically competitive compared to a natural gas boiler reference (80 €/MWh) in Seville, achieving a minimum LCOH of 66 €/MWh. For Delft the lowest LCOH is 119 €/MWh, not yet competitive under current gas prices but considerably less exposed to fossil fuel price volatility.
Large-Scale Hydrogen Liquefaction: Cryogenic Cooling and Boil-off Gas Recovery
Process Modeling and Techno-Economic Analysis of Catalytic Plate-Fin Heat Exchangers and Ejector-Driven Cycles
Hydrogen is at a turning point in the global energy transition. Its high specific energy makes it attractive for weight- and range-constrained sectors such as long-distance transport and aviation, where liquid hydrogen (LH2) provides the required compact storage medium. Liquefaction, however, remains the main challenge, as industrial plants consume 12-15 kWh per kilogram of liquid hydrogen, roughly three to four times the thermodynamic minimum. Conceptual designs promise to reduce this consumption, but they rest on idealized models. This thesis quantifies two of these idealizations for an 86 tonnes-per-day reference process. The first is the property and kinetic modeling of the cryogenic catalytic plate-fin heat exchanger (PFHX). The second is the assumption of full liquid yield, which ignores the boil-off gas (BOG) generated during storage and truck loading. An ejector-driven recovery cycle is then proposed and assessed for the BOG.
For the cryogenic cooling stage, the helium-neon refrigerant is modeled with an improved equation of state (SAFT-VRQ-Mie) and residual entropy scaling. This replaces the dilute-gas correlations used in earlier studies. The revised thermal conductivity diverges from those correlations by a factor of two at 30 K and underpredicts the measured mixture property by 20-22%. Because the cold-side heat transfer scales as the two-thirds power of conductivity, this increases the required heat exchanger length by about 30% to 7.8 m, and the updated ortho-para conversion kinetics push it to the 8.2 m single-unit manufacturing limit.
For the LH2 storage stage, validated two-phase models show that the loading process dominates the boil-off losses and vents about 2.3% of each delivered load. A one-dimensional ejector model then shows that this BOG, together with the separator flash vapor, can be entrained and returned to the cycle in a single pass. This raises the net liquid product from 86 to 104 tonnes per day. In the adapted cycle, the binding constraint is the downstream PFHX and not the ejector. At the original 75 bar feed pressure, the heat exchanger exceeds the 8.2 m single-unit limit. Only when lowering the feed pressure to 40 bar, which also removes one feed-compression stage, it becomes buildable as a single unit at 8.19 m.
A techno-economic analysis of the isolated cryogenic section quantifies the cost of this recovery. Capital cost rises by 24% and specific energy consumption by 56%. The specific liquefaction cost increases from 0.432 to 0.593 USD per kilogram, an increase of 37.4% that holds across all tested cost assumptions. Ejector-based BOG recovery is therefore technically feasible and increases liquid yield, but it is not economically justified within the cryogenic boundary on its own. ...
For the cryogenic cooling stage, the helium-neon refrigerant is modeled with an improved equation of state (SAFT-VRQ-Mie) and residual entropy scaling. This replaces the dilute-gas correlations used in earlier studies. The revised thermal conductivity diverges from those correlations by a factor of two at 30 K and underpredicts the measured mixture property by 20-22%. Because the cold-side heat transfer scales as the two-thirds power of conductivity, this increases the required heat exchanger length by about 30% to 7.8 m, and the updated ortho-para conversion kinetics push it to the 8.2 m single-unit manufacturing limit.
For the LH2 storage stage, validated two-phase models show that the loading process dominates the boil-off losses and vents about 2.3% of each delivered load. A one-dimensional ejector model then shows that this BOG, together with the separator flash vapor, can be entrained and returned to the cycle in a single pass. This raises the net liquid product from 86 to 104 tonnes per day. In the adapted cycle, the binding constraint is the downstream PFHX and not the ejector. At the original 75 bar feed pressure, the heat exchanger exceeds the 8.2 m single-unit limit. Only when lowering the feed pressure to 40 bar, which also removes one feed-compression stage, it becomes buildable as a single unit at 8.19 m.
A techno-economic analysis of the isolated cryogenic section quantifies the cost of this recovery. Capital cost rises by 24% and specific energy consumption by 56%. The specific liquefaction cost increases from 0.432 to 0.593 USD per kilogram, an increase of 37.4% that holds across all tested cost assumptions. Ejector-based BOG recovery is therefore technically feasible and increases liquid yield, but it is not economically justified within the cryogenic boundary on its own. ...
Hydrogen is at a turning point in the global energy transition. Its high specific energy makes it attractive for weight- and range-constrained sectors such as long-distance transport and aviation, where liquid hydrogen (LH2) provides the required compact storage medium. Liquefaction, however, remains the main challenge, as industrial plants consume 12-15 kWh per kilogram of liquid hydrogen, roughly three to four times the thermodynamic minimum. Conceptual designs promise to reduce this consumption, but they rest on idealized models. This thesis quantifies two of these idealizations for an 86 tonnes-per-day reference process. The first is the property and kinetic modeling of the cryogenic catalytic plate-fin heat exchanger (PFHX). The second is the assumption of full liquid yield, which ignores the boil-off gas (BOG) generated during storage and truck loading. An ejector-driven recovery cycle is then proposed and assessed for the BOG.
For the cryogenic cooling stage, the helium-neon refrigerant is modeled with an improved equation of state (SAFT-VRQ-Mie) and residual entropy scaling. This replaces the dilute-gas correlations used in earlier studies. The revised thermal conductivity diverges from those correlations by a factor of two at 30 K and underpredicts the measured mixture property by 20-22%. Because the cold-side heat transfer scales as the two-thirds power of conductivity, this increases the required heat exchanger length by about 30% to 7.8 m, and the updated ortho-para conversion kinetics push it to the 8.2 m single-unit manufacturing limit.
For the LH2 storage stage, validated two-phase models show that the loading process dominates the boil-off losses and vents about 2.3% of each delivered load. A one-dimensional ejector model then shows that this BOG, together with the separator flash vapor, can be entrained and returned to the cycle in a single pass. This raises the net liquid product from 86 to 104 tonnes per day. In the adapted cycle, the binding constraint is the downstream PFHX and not the ejector. At the original 75 bar feed pressure, the heat exchanger exceeds the 8.2 m single-unit limit. Only when lowering the feed pressure to 40 bar, which also removes one feed-compression stage, it becomes buildable as a single unit at 8.19 m.
A techno-economic analysis of the isolated cryogenic section quantifies the cost of this recovery. Capital cost rises by 24% and specific energy consumption by 56%. The specific liquefaction cost increases from 0.432 to 0.593 USD per kilogram, an increase of 37.4% that holds across all tested cost assumptions. Ejector-based BOG recovery is therefore technically feasible and increases liquid yield, but it is not economically justified within the cryogenic boundary on its own.
For the cryogenic cooling stage, the helium-neon refrigerant is modeled with an improved equation of state (SAFT-VRQ-Mie) and residual entropy scaling. This replaces the dilute-gas correlations used in earlier studies. The revised thermal conductivity diverges from those correlations by a factor of two at 30 K and underpredicts the measured mixture property by 20-22%. Because the cold-side heat transfer scales as the two-thirds power of conductivity, this increases the required heat exchanger length by about 30% to 7.8 m, and the updated ortho-para conversion kinetics push it to the 8.2 m single-unit manufacturing limit.
For the LH2 storage stage, validated two-phase models show that the loading process dominates the boil-off losses and vents about 2.3% of each delivered load. A one-dimensional ejector model then shows that this BOG, together with the separator flash vapor, can be entrained and returned to the cycle in a single pass. This raises the net liquid product from 86 to 104 tonnes per day. In the adapted cycle, the binding constraint is the downstream PFHX and not the ejector. At the original 75 bar feed pressure, the heat exchanger exceeds the 8.2 m single-unit limit. Only when lowering the feed pressure to 40 bar, which also removes one feed-compression stage, it becomes buildable as a single unit at 8.19 m.
A techno-economic analysis of the isolated cryogenic section quantifies the cost of this recovery. Capital cost rises by 24% and specific energy consumption by 56%. The specific liquefaction cost increases from 0.432 to 0.593 USD per kilogram, an increase of 37.4% that holds across all tested cost assumptions. Ejector-based BOG recovery is therefore technically feasible and increases liquid yield, but it is not economically justified within the cryogenic boundary on its own.
Multi-Objective Optimization of Precooling Stage in Hydrogen Liquefaction
A Process Modelling Approach to Harmonize Technical and Economic Trade-Offs
Hydrogen is getting great attention as a key energy carrier for a cleaner energy future, with demand projections up to 20% of global energy demand by 2050. However, the low volumetric density of hydrogen leads to a challenge for storage and transport purposes, making liquefaction a promising solution that also ensures high purity. However, at the current time, the high energy consumption of liquefaction remains a major obstacle. Within this process, the precooling stage is the second most energy-intensive step, covering the broadest temperature range but offering flexibility in terms of refrigerant choice, cycle configuration, and operating conditions.
However, most of the study of the hydrogen precooling omits economic analysis, refrigerant freeze-out discussion, and employs a portion of a non-environmentally sustainable substance as the refrigerant. This study focused on addressing the gap by conducting multi-objective optimization (MOO) on specific energy consumption (SEC) and levelized precooling cost (LPC) to find out the optimal trade-off between the technical and economic competitiveness of the precooling stage, while ensuring the freeze-out risk in the streams was avoided and using environmentally friendly mixed refrigerant (MR) mixtures.
Two cycles, namely single mixed refrigerant (SMR) and dual mixed refrigerant (DMR), are modeled in Aspen HYSYS V12, where the configurations are defined based on freeze-out consideration. Nine MR mixtures for SMR and DMR are defined based on their thermophysical properties. A Non-dominated Sorting Genetic Algorithm-II (NSGA-II) algorithm was used for MOO through the pymoo library package in Python, which was then coupled with Aspen HYSYS. The decision variables to be optimized include MR composition, MR flow rate, compressor discharge pressure, and JT valve outlet pressure. Several constraints are also introduced, such as vapor fraction at the inlet compressor, minimum internal temperature difference (MITD) of heat exchangers, JT valve temperature difference, and several temperature constraints to ensure thermodynamic behavior is not violated.
In this study, Mixture 8 (for SMR) and Mixture 6 (for DMR) appear to be the top-performing mixtures, achieving specific energy consumptions (SEC) of 1.25 kWh/kgH2 and 1.13 kWh/kgH2, respectively, with levelized precooling costs (LPC) of €0.47/kgH2 and €0.60/kgH2. The study indicates that aligning the boiling points of mixed refrigerant components to enhance temperature glide, combined with tuning of operating conditions, is the key to achieving both energy efficiency and cost competitiveness. Furthermore, the optimized results in DMR also suggest that the intermediate-compression stage in the MR2 cycle could be removed.
From the sensitivity analysis, it was observed that as the precooling temperature target increased, the gap in SEC between the SMR and DMR configurations narrowed. Starting from 95 K, both systems reached similar SEC values, highlighting equal technical performance. However, the LPC further SMR dominant over the DMR. This indicates that beyond this temperature target, DMR was no longer economically competitive. Additionally, variations in pressure drop across heat exchangers and coolers had a stronger impact on the SMR configuration. The percentage increase in SEC and LPC was more severe due to the accumulation of pressure losses within a single-loop cycle. In contrast, the DMR system distributes losses across two separate loops, making it less sensitive to pressure drop effects. ...
However, most of the study of the hydrogen precooling omits economic analysis, refrigerant freeze-out discussion, and employs a portion of a non-environmentally sustainable substance as the refrigerant. This study focused on addressing the gap by conducting multi-objective optimization (MOO) on specific energy consumption (SEC) and levelized precooling cost (LPC) to find out the optimal trade-off between the technical and economic competitiveness of the precooling stage, while ensuring the freeze-out risk in the streams was avoided and using environmentally friendly mixed refrigerant (MR) mixtures.
Two cycles, namely single mixed refrigerant (SMR) and dual mixed refrigerant (DMR), are modeled in Aspen HYSYS V12, where the configurations are defined based on freeze-out consideration. Nine MR mixtures for SMR and DMR are defined based on their thermophysical properties. A Non-dominated Sorting Genetic Algorithm-II (NSGA-II) algorithm was used for MOO through the pymoo library package in Python, which was then coupled with Aspen HYSYS. The decision variables to be optimized include MR composition, MR flow rate, compressor discharge pressure, and JT valve outlet pressure. Several constraints are also introduced, such as vapor fraction at the inlet compressor, minimum internal temperature difference (MITD) of heat exchangers, JT valve temperature difference, and several temperature constraints to ensure thermodynamic behavior is not violated.
In this study, Mixture 8 (for SMR) and Mixture 6 (for DMR) appear to be the top-performing mixtures, achieving specific energy consumptions (SEC) of 1.25 kWh/kgH2 and 1.13 kWh/kgH2, respectively, with levelized precooling costs (LPC) of €0.47/kgH2 and €0.60/kgH2. The study indicates that aligning the boiling points of mixed refrigerant components to enhance temperature glide, combined with tuning of operating conditions, is the key to achieving both energy efficiency and cost competitiveness. Furthermore, the optimized results in DMR also suggest that the intermediate-compression stage in the MR2 cycle could be removed.
From the sensitivity analysis, it was observed that as the precooling temperature target increased, the gap in SEC between the SMR and DMR configurations narrowed. Starting from 95 K, both systems reached similar SEC values, highlighting equal technical performance. However, the LPC further SMR dominant over the DMR. This indicates that beyond this temperature target, DMR was no longer economically competitive. Additionally, variations in pressure drop across heat exchangers and coolers had a stronger impact on the SMR configuration. The percentage increase in SEC and LPC was more severe due to the accumulation of pressure losses within a single-loop cycle. In contrast, the DMR system distributes losses across two separate loops, making it less sensitive to pressure drop effects. ...
Hydrogen is getting great attention as a key energy carrier for a cleaner energy future, with demand projections up to 20% of global energy demand by 2050. However, the low volumetric density of hydrogen leads to a challenge for storage and transport purposes, making liquefaction a promising solution that also ensures high purity. However, at the current time, the high energy consumption of liquefaction remains a major obstacle. Within this process, the precooling stage is the second most energy-intensive step, covering the broadest temperature range but offering flexibility in terms of refrigerant choice, cycle configuration, and operating conditions.
However, most of the study of the hydrogen precooling omits economic analysis, refrigerant freeze-out discussion, and employs a portion of a non-environmentally sustainable substance as the refrigerant. This study focused on addressing the gap by conducting multi-objective optimization (MOO) on specific energy consumption (SEC) and levelized precooling cost (LPC) to find out the optimal trade-off between the technical and economic competitiveness of the precooling stage, while ensuring the freeze-out risk in the streams was avoided and using environmentally friendly mixed refrigerant (MR) mixtures.
Two cycles, namely single mixed refrigerant (SMR) and dual mixed refrigerant (DMR), are modeled in Aspen HYSYS V12, where the configurations are defined based on freeze-out consideration. Nine MR mixtures for SMR and DMR are defined based on their thermophysical properties. A Non-dominated Sorting Genetic Algorithm-II (NSGA-II) algorithm was used for MOO through the pymoo library package in Python, which was then coupled with Aspen HYSYS. The decision variables to be optimized include MR composition, MR flow rate, compressor discharge pressure, and JT valve outlet pressure. Several constraints are also introduced, such as vapor fraction at the inlet compressor, minimum internal temperature difference (MITD) of heat exchangers, JT valve temperature difference, and several temperature constraints to ensure thermodynamic behavior is not violated.
In this study, Mixture 8 (for SMR) and Mixture 6 (for DMR) appear to be the top-performing mixtures, achieving specific energy consumptions (SEC) of 1.25 kWh/kgH2 and 1.13 kWh/kgH2, respectively, with levelized precooling costs (LPC) of €0.47/kgH2 and €0.60/kgH2. The study indicates that aligning the boiling points of mixed refrigerant components to enhance temperature glide, combined with tuning of operating conditions, is the key to achieving both energy efficiency and cost competitiveness. Furthermore, the optimized results in DMR also suggest that the intermediate-compression stage in the MR2 cycle could be removed.
From the sensitivity analysis, it was observed that as the precooling temperature target increased, the gap in SEC between the SMR and DMR configurations narrowed. Starting from 95 K, both systems reached similar SEC values, highlighting equal technical performance. However, the LPC further SMR dominant over the DMR. This indicates that beyond this temperature target, DMR was no longer economically competitive. Additionally, variations in pressure drop across heat exchangers and coolers had a stronger impact on the SMR configuration. The percentage increase in SEC and LPC was more severe due to the accumulation of pressure losses within a single-loop cycle. In contrast, the DMR system distributes losses across two separate loops, making it less sensitive to pressure drop effects.
However, most of the study of the hydrogen precooling omits economic analysis, refrigerant freeze-out discussion, and employs a portion of a non-environmentally sustainable substance as the refrigerant. This study focused on addressing the gap by conducting multi-objective optimization (MOO) on specific energy consumption (SEC) and levelized precooling cost (LPC) to find out the optimal trade-off between the technical and economic competitiveness of the precooling stage, while ensuring the freeze-out risk in the streams was avoided and using environmentally friendly mixed refrigerant (MR) mixtures.
Two cycles, namely single mixed refrigerant (SMR) and dual mixed refrigerant (DMR), are modeled in Aspen HYSYS V12, where the configurations are defined based on freeze-out consideration. Nine MR mixtures for SMR and DMR are defined based on their thermophysical properties. A Non-dominated Sorting Genetic Algorithm-II (NSGA-II) algorithm was used for MOO through the pymoo library package in Python, which was then coupled with Aspen HYSYS. The decision variables to be optimized include MR composition, MR flow rate, compressor discharge pressure, and JT valve outlet pressure. Several constraints are also introduced, such as vapor fraction at the inlet compressor, minimum internal temperature difference (MITD) of heat exchangers, JT valve temperature difference, and several temperature constraints to ensure thermodynamic behavior is not violated.
In this study, Mixture 8 (for SMR) and Mixture 6 (for DMR) appear to be the top-performing mixtures, achieving specific energy consumptions (SEC) of 1.25 kWh/kgH2 and 1.13 kWh/kgH2, respectively, with levelized precooling costs (LPC) of €0.47/kgH2 and €0.60/kgH2. The study indicates that aligning the boiling points of mixed refrigerant components to enhance temperature glide, combined with tuning of operating conditions, is the key to achieving both energy efficiency and cost competitiveness. Furthermore, the optimized results in DMR also suggest that the intermediate-compression stage in the MR2 cycle could be removed.
From the sensitivity analysis, it was observed that as the precooling temperature target increased, the gap in SEC between the SMR and DMR configurations narrowed. Starting from 95 K, both systems reached similar SEC values, highlighting equal technical performance. However, the LPC further SMR dominant over the DMR. This indicates that beyond this temperature target, DMR was no longer economically competitive. Additionally, variations in pressure drop across heat exchangers and coolers had a stronger impact on the SMR configuration. The percentage increase in SEC and LPC was more severe due to the accumulation of pressure losses within a single-loop cycle. In contrast, the DMR system distributes losses across two separate loops, making it less sensitive to pressure drop effects.
Enabling Scalable Direct Air Capture With Concentrated Solar Power
Process Modelling and Techno-Economic Analysis
This thesis explores the integration of solid sorbent direct air capture (DAC) with two types of concentrated solar power, to create a renewable and scalable approach for carbon dioxide removal. Parabolic trough collector (PTC) and solar power tower (SPT) systems are modelled dynamically on an hourly basis, combined with the energy requirement and performance of the DAC model. Because system output is highly sensitive to climatic conditions, two high-irradiance locations in Almeria, Spain and Alice Springs, Australia are evaluated using typical meteorological year data.
The results show that SPT outperforms PTC in achieving the lowest levelised cost of CO2 removal (LCOD), primarily due to its lower thermal energy storage costs. The configuration optimised for LCOD involves significant oversizing of the solar field and storage, far larger than the configuration optimized for cost of heat. This increases the capacity, and utilises the CAPEX-intensive DAC installation to a greater extent. These DAC costs are the main cost driver accounting for 68% of the cost for a conservative scenario. A sensitivity analysis reveals that lowering the DAC costs is found not to change the optimal configuration significantly, allowing the LCOD of a lower CAPEX scenario to be determined accurately from the results.
The weather conditions in Alice Springs result in a reduction of the LCOD by up to 27% compared to Almeria, due to higher and more constant solar availability combined with lower humidities. While PTC systems have higher LCOD, they require significantly less land. Overall, the combination of CSP and DAC is technically viable and it offers a scalable, land efficient alternative to nature based carbon dioxide removal methods. ...
The results show that SPT outperforms PTC in achieving the lowest levelised cost of CO2 removal (LCOD), primarily due to its lower thermal energy storage costs. The configuration optimised for LCOD involves significant oversizing of the solar field and storage, far larger than the configuration optimized for cost of heat. This increases the capacity, and utilises the CAPEX-intensive DAC installation to a greater extent. These DAC costs are the main cost driver accounting for 68% of the cost for a conservative scenario. A sensitivity analysis reveals that lowering the DAC costs is found not to change the optimal configuration significantly, allowing the LCOD of a lower CAPEX scenario to be determined accurately from the results.
The weather conditions in Alice Springs result in a reduction of the LCOD by up to 27% compared to Almeria, due to higher and more constant solar availability combined with lower humidities. While PTC systems have higher LCOD, they require significantly less land. Overall, the combination of CSP and DAC is technically viable and it offers a scalable, land efficient alternative to nature based carbon dioxide removal methods. ...
This thesis explores the integration of solid sorbent direct air capture (DAC) with two types of concentrated solar power, to create a renewable and scalable approach for carbon dioxide removal. Parabolic trough collector (PTC) and solar power tower (SPT) systems are modelled dynamically on an hourly basis, combined with the energy requirement and performance of the DAC model. Because system output is highly sensitive to climatic conditions, two high-irradiance locations in Almeria, Spain and Alice Springs, Australia are evaluated using typical meteorological year data.
The results show that SPT outperforms PTC in achieving the lowest levelised cost of CO2 removal (LCOD), primarily due to its lower thermal energy storage costs. The configuration optimised for LCOD involves significant oversizing of the solar field and storage, far larger than the configuration optimized for cost of heat. This increases the capacity, and utilises the CAPEX-intensive DAC installation to a greater extent. These DAC costs are the main cost driver accounting for 68% of the cost for a conservative scenario. A sensitivity analysis reveals that lowering the DAC costs is found not to change the optimal configuration significantly, allowing the LCOD of a lower CAPEX scenario to be determined accurately from the results.
The weather conditions in Alice Springs result in a reduction of the LCOD by up to 27% compared to Almeria, due to higher and more constant solar availability combined with lower humidities. While PTC systems have higher LCOD, they require significantly less land. Overall, the combination of CSP and DAC is technically viable and it offers a scalable, land efficient alternative to nature based carbon dioxide removal methods.
The results show that SPT outperforms PTC in achieving the lowest levelised cost of CO2 removal (LCOD), primarily due to its lower thermal energy storage costs. The configuration optimised for LCOD involves significant oversizing of the solar field and storage, far larger than the configuration optimized for cost of heat. This increases the capacity, and utilises the CAPEX-intensive DAC installation to a greater extent. These DAC costs are the main cost driver accounting for 68% of the cost for a conservative scenario. A sensitivity analysis reveals that lowering the DAC costs is found not to change the optimal configuration significantly, allowing the LCOD of a lower CAPEX scenario to be determined accurately from the results.
The weather conditions in Alice Springs result in a reduction of the LCOD by up to 27% compared to Almeria, due to higher and more constant solar availability combined with lower humidities. While PTC systems have higher LCOD, they require significantly less land. Overall, the combination of CSP and DAC is technically viable and it offers a scalable, land efficient alternative to nature based carbon dioxide removal methods.
This MSc thesis investigates the performance of a sintered-powder wick copper-water heat pipe by focusing on two primary areas: a hypothetical exploration of the inner dynamics under high-acceleration conditions, specifically the effects of sloshing, and the detailed mathematical & computational modeling of its steady-state operation. The effects of a sloshing motion were analyzed through a series of analytical ”thought experiments.”
These investigations defined and modeled potential phenomena, including, but not limited to, pressure-induced liquid ”leakout” from the wick and the re-wetting of the undersaturated wick. A 2D axisymmetric computational model of the heat pipe was also developed in COMSOL Multiphysics for simulating steady-state operation. The model solves the coupled equations for heat transfer and fluid flow, accounting for the solid casing, the liquid-saturated porous wick, and the compressible vapor core. The dynamic analysis revealed that under high accelerations, significant wick dryness can occur, with its severity being highly dependent on wick permeability. Furthermore, the theoretical results indicate that the leaked liquid can shorten the re-wetting period of the wick, possibly leading to a rapid recovery of thermal performance. The steady-state computational model was also successfully validated against existing literature, demonstrating accurate predictions of temperature, pressure, and velocity profiles. The study successfully provides a validated steady-state model and a preliminary mathematical framework for understanding the complex physics of sloshing in heat pipes. While the final objective of coupling the dynamic and steady-state models was not achieved, this work lays the critical groundwork for future transient multiphysics simulations of heat pipes. ...
These investigations defined and modeled potential phenomena, including, but not limited to, pressure-induced liquid ”leakout” from the wick and the re-wetting of the undersaturated wick. A 2D axisymmetric computational model of the heat pipe was also developed in COMSOL Multiphysics for simulating steady-state operation. The model solves the coupled equations for heat transfer and fluid flow, accounting for the solid casing, the liquid-saturated porous wick, and the compressible vapor core. The dynamic analysis revealed that under high accelerations, significant wick dryness can occur, with its severity being highly dependent on wick permeability. Furthermore, the theoretical results indicate that the leaked liquid can shorten the re-wetting period of the wick, possibly leading to a rapid recovery of thermal performance. The steady-state computational model was also successfully validated against existing literature, demonstrating accurate predictions of temperature, pressure, and velocity profiles. The study successfully provides a validated steady-state model and a preliminary mathematical framework for understanding the complex physics of sloshing in heat pipes. While the final objective of coupling the dynamic and steady-state models was not achieved, this work lays the critical groundwork for future transient multiphysics simulations of heat pipes. ...
This MSc thesis investigates the performance of a sintered-powder wick copper-water heat pipe by focusing on two primary areas: a hypothetical exploration of the inner dynamics under high-acceleration conditions, specifically the effects of sloshing, and the detailed mathematical & computational modeling of its steady-state operation. The effects of a sloshing motion were analyzed through a series of analytical ”thought experiments.”
These investigations defined and modeled potential phenomena, including, but not limited to, pressure-induced liquid ”leakout” from the wick and the re-wetting of the undersaturated wick. A 2D axisymmetric computational model of the heat pipe was also developed in COMSOL Multiphysics for simulating steady-state operation. The model solves the coupled equations for heat transfer and fluid flow, accounting for the solid casing, the liquid-saturated porous wick, and the compressible vapor core. The dynamic analysis revealed that under high accelerations, significant wick dryness can occur, with its severity being highly dependent on wick permeability. Furthermore, the theoretical results indicate that the leaked liquid can shorten the re-wetting period of the wick, possibly leading to a rapid recovery of thermal performance. The steady-state computational model was also successfully validated against existing literature, demonstrating accurate predictions of temperature, pressure, and velocity profiles. The study successfully provides a validated steady-state model and a preliminary mathematical framework for understanding the complex physics of sloshing in heat pipes. While the final objective of coupling the dynamic and steady-state models was not achieved, this work lays the critical groundwork for future transient multiphysics simulations of heat pipes.
These investigations defined and modeled potential phenomena, including, but not limited to, pressure-induced liquid ”leakout” from the wick and the re-wetting of the undersaturated wick. A 2D axisymmetric computational model of the heat pipe was also developed in COMSOL Multiphysics for simulating steady-state operation. The model solves the coupled equations for heat transfer and fluid flow, accounting for the solid casing, the liquid-saturated porous wick, and the compressible vapor core. The dynamic analysis revealed that under high accelerations, significant wick dryness can occur, with its severity being highly dependent on wick permeability. Furthermore, the theoretical results indicate that the leaked liquid can shorten the re-wetting period of the wick, possibly leading to a rapid recovery of thermal performance. The steady-state computational model was also successfully validated against existing literature, demonstrating accurate predictions of temperature, pressure, and velocity profiles. The study successfully provides a validated steady-state model and a preliminary mathematical framework for understanding the complex physics of sloshing in heat pipes. While the final objective of coupling the dynamic and steady-state models was not achieved, this work lays the critical groundwork for future transient multiphysics simulations of heat pipes.
Magnetic refrigeration is a highly investigated topic with great potential in cooling and heating applications. Its promising efficiency and environmentally friendly operation make it an attractive and resilient solution. The modeling of such thermodynamic systems is a central research focus, due to the high costs of manufacturing and testing real-life designs. To achieve the maximum capabilities of magnetic refrigerators, the tuning of their design parameters is essential. The complexity of magnetic refrigeration applications results in a high-dimensional design space that is difficult to solve analytically.
In this thesis, a surrogate model-based optimization framework was developed and validated for near-room-temperature Active Magnetic Regenerators (AMRs) that balance second-law efficiency against magnet mass. The framework combines a Multi-layer Perceptron (MLP) surrogate model with a genetic algorithm to efficiently explore a design space defined by more than eight parameters: length, width, and height of the regenerator, number of magnetocaloric material (MCM) layers, individual layer thicknesses, Curie temperature per layer, porosity of MCM layers, applied magnetic field, and void spaces. The surrogate model approximates a computationally expensive 1-D thermodynamic AMR model, reducing evaluation time and paving the way to multi-dimensional complex optimization AMR problems. The results demonstrate that with sequential model-based optimization (SMBO), the model can predict with higher accuracy the efficiency of each design, eventually leading to various design configurations with high efficiency and within the desired cost limits. The effect of SMBO is captured every training round by the mean absolute error (MAE) metric.
The optimal AMR configuration identified through this framework for a 15 K temperature span features 8 MCM layers with Curie temperatures spanning 274.8 K to 291.8 K, a regenerator geometry of 68 mm × 25 mm × 29 mm (length × width × height), 23% porosity for the MCM blocks, and operates under a 1.3 T magnetic field. This configuration represents a practical balance between hermodynamic performance and manufacturing feasibility for near-room-temperature magnetic refrigeration applications. ...
In this thesis, a surrogate model-based optimization framework was developed and validated for near-room-temperature Active Magnetic Regenerators (AMRs) that balance second-law efficiency against magnet mass. The framework combines a Multi-layer Perceptron (MLP) surrogate model with a genetic algorithm to efficiently explore a design space defined by more than eight parameters: length, width, and height of the regenerator, number of magnetocaloric material (MCM) layers, individual layer thicknesses, Curie temperature per layer, porosity of MCM layers, applied magnetic field, and void spaces. The surrogate model approximates a computationally expensive 1-D thermodynamic AMR model, reducing evaluation time and paving the way to multi-dimensional complex optimization AMR problems. The results demonstrate that with sequential model-based optimization (SMBO), the model can predict with higher accuracy the efficiency of each design, eventually leading to various design configurations with high efficiency and within the desired cost limits. The effect of SMBO is captured every training round by the mean absolute error (MAE) metric.
The optimal AMR configuration identified through this framework for a 15 K temperature span features 8 MCM layers with Curie temperatures spanning 274.8 K to 291.8 K, a regenerator geometry of 68 mm × 25 mm × 29 mm (length × width × height), 23% porosity for the MCM blocks, and operates under a 1.3 T magnetic field. This configuration represents a practical balance between hermodynamic performance and manufacturing feasibility for near-room-temperature magnetic refrigeration applications. ...
Magnetic refrigeration is a highly investigated topic with great potential in cooling and heating applications. Its promising efficiency and environmentally friendly operation make it an attractive and resilient solution. The modeling of such thermodynamic systems is a central research focus, due to the high costs of manufacturing and testing real-life designs. To achieve the maximum capabilities of magnetic refrigerators, the tuning of their design parameters is essential. The complexity of magnetic refrigeration applications results in a high-dimensional design space that is difficult to solve analytically.
In this thesis, a surrogate model-based optimization framework was developed and validated for near-room-temperature Active Magnetic Regenerators (AMRs) that balance second-law efficiency against magnet mass. The framework combines a Multi-layer Perceptron (MLP) surrogate model with a genetic algorithm to efficiently explore a design space defined by more than eight parameters: length, width, and height of the regenerator, number of magnetocaloric material (MCM) layers, individual layer thicknesses, Curie temperature per layer, porosity of MCM layers, applied magnetic field, and void spaces. The surrogate model approximates a computationally expensive 1-D thermodynamic AMR model, reducing evaluation time and paving the way to multi-dimensional complex optimization AMR problems. The results demonstrate that with sequential model-based optimization (SMBO), the model can predict with higher accuracy the efficiency of each design, eventually leading to various design configurations with high efficiency and within the desired cost limits. The effect of SMBO is captured every training round by the mean absolute error (MAE) metric.
The optimal AMR configuration identified through this framework for a 15 K temperature span features 8 MCM layers with Curie temperatures spanning 274.8 K to 291.8 K, a regenerator geometry of 68 mm × 25 mm × 29 mm (length × width × height), 23% porosity for the MCM blocks, and operates under a 1.3 T magnetic field. This configuration represents a practical balance between hermodynamic performance and manufacturing feasibility for near-room-temperature magnetic refrigeration applications.
In this thesis, a surrogate model-based optimization framework was developed and validated for near-room-temperature Active Magnetic Regenerators (AMRs) that balance second-law efficiency against magnet mass. The framework combines a Multi-layer Perceptron (MLP) surrogate model with a genetic algorithm to efficiently explore a design space defined by more than eight parameters: length, width, and height of the regenerator, number of magnetocaloric material (MCM) layers, individual layer thicknesses, Curie temperature per layer, porosity of MCM layers, applied magnetic field, and void spaces. The surrogate model approximates a computationally expensive 1-D thermodynamic AMR model, reducing evaluation time and paving the way to multi-dimensional complex optimization AMR problems. The results demonstrate that with sequential model-based optimization (SMBO), the model can predict with higher accuracy the efficiency of each design, eventually leading to various design configurations with high efficiency and within the desired cost limits. The effect of SMBO is captured every training round by the mean absolute error (MAE) metric.
The optimal AMR configuration identified through this framework for a 15 K temperature span features 8 MCM layers with Curie temperatures spanning 274.8 K to 291.8 K, a regenerator geometry of 68 mm × 25 mm × 29 mm (length × width × height), 23% porosity for the MCM blocks, and operates under a 1.3 T magnetic field. This configuration represents a practical balance between hermodynamic performance and manufacturing feasibility for near-room-temperature magnetic refrigeration applications.
Large-Scale Hydrogen Liquefaction Based on Brayton Cycle Concept
Process Modelling, Viability and Techno-Economic Analysis
The viability of hydrogen as a sustainable energy carrier is significantly affected by the costs linked to its transportation and storage. Transporting and storing hydrogen in its liquid form offers remarkable advantages, as liquid hydrogen has unique characteristics, including lower weight and volume, as well as a higher energy content compared to gaseous hydrogen. However, current industrial hydrogen liquefaction processes face significant challenges related to efficiency and cost, with a second-law efficiency of less than 25% and costs ranging from 2.5-3.0 US$/kgLH2.
Large energy storage systems can address the issue of energy demand fluctuations in renewable energy grids by storing excess energy produced and compensating for any energy shortfalls. The development of hydrogen energy storage systems will thus support the advancement and increased utilization of renewable energy sources. The demand for liquid hydrogen is expected to rise in the near future, driven by environmentally friendly applications and use in mobility sector. As a result, large-scale hydrogen liquefaction (LHL) plants will become increasingly important in the clean energy efficient hydrogen supply chain.
This thesis aims to develop a Large-scale Hydrogen Liquefaction (LHL) plant based on the Brayton cycle concept of 86 TPD. The plant is modeled using Aspen HYSYS, with preliminary designs for key equipment—such as compressors, turbines, and plate-fin heat exchangers, ensuring compatibility with current technological constraints. State properties of the fluid used in the design of compressors and turbine equipment were obtained from REFPROP software, utilizing the Peng-Robinson Equation of State (EOS). For the design of plate-fin heat exchangers, Aspen Exchanger Design and Rating (EDR) was employed. Subsequently, a techno-economic analysis was conducted using the Aspen Process Economic Analyzer (APEA) to estimate both capital and operating expenditures, based on the process simulation model and preliminary equipment designs.
The specific energy consumption (SEC) of the plant, accounting for power recovery from turbine shafts, is determined to be 6.9025 kWh/kgLH2. The plant’s exergy efficiency is calculated at 43.665%, and the specific liquefaction power is found to be 3.014 kWh/kgLH2. Assuming an electricity price of 0.1 €/kWh, modelled 86 TPD Brayton-cycle concept yielded specific liquefaction cost (SLC) of 1.57 €/kgLH2.
A sensitivity analysis was conducted to identify the parameters that influence the specific liquefaction cost (SLC) of the plant. The analysis focused on two key parameters: 1) electricity price and 2) feed pressure. The results reveal that fluctuations in electricity prices have a substantial impact on the plant’s economic performance. Additionally, the analysis indicates that the plant’s efficiency and economic viability are significantly sensitive to decreases in feed hydrogen pressure. ...
Large energy storage systems can address the issue of energy demand fluctuations in renewable energy grids by storing excess energy produced and compensating for any energy shortfalls. The development of hydrogen energy storage systems will thus support the advancement and increased utilization of renewable energy sources. The demand for liquid hydrogen is expected to rise in the near future, driven by environmentally friendly applications and use in mobility sector. As a result, large-scale hydrogen liquefaction (LHL) plants will become increasingly important in the clean energy efficient hydrogen supply chain.
This thesis aims to develop a Large-scale Hydrogen Liquefaction (LHL) plant based on the Brayton cycle concept of 86 TPD. The plant is modeled using Aspen HYSYS, with preliminary designs for key equipment—such as compressors, turbines, and plate-fin heat exchangers, ensuring compatibility with current technological constraints. State properties of the fluid used in the design of compressors and turbine equipment were obtained from REFPROP software, utilizing the Peng-Robinson Equation of State (EOS). For the design of plate-fin heat exchangers, Aspen Exchanger Design and Rating (EDR) was employed. Subsequently, a techno-economic analysis was conducted using the Aspen Process Economic Analyzer (APEA) to estimate both capital and operating expenditures, based on the process simulation model and preliminary equipment designs.
The specific energy consumption (SEC) of the plant, accounting for power recovery from turbine shafts, is determined to be 6.9025 kWh/kgLH2. The plant’s exergy efficiency is calculated at 43.665%, and the specific liquefaction power is found to be 3.014 kWh/kgLH2. Assuming an electricity price of 0.1 €/kWh, modelled 86 TPD Brayton-cycle concept yielded specific liquefaction cost (SLC) of 1.57 €/kgLH2.
A sensitivity analysis was conducted to identify the parameters that influence the specific liquefaction cost (SLC) of the plant. The analysis focused on two key parameters: 1) electricity price and 2) feed pressure. The results reveal that fluctuations in electricity prices have a substantial impact on the plant’s economic performance. Additionally, the analysis indicates that the plant’s efficiency and economic viability are significantly sensitive to decreases in feed hydrogen pressure. ...
The viability of hydrogen as a sustainable energy carrier is significantly affected by the costs linked to its transportation and storage. Transporting and storing hydrogen in its liquid form offers remarkable advantages, as liquid hydrogen has unique characteristics, including lower weight and volume, as well as a higher energy content compared to gaseous hydrogen. However, current industrial hydrogen liquefaction processes face significant challenges related to efficiency and cost, with a second-law efficiency of less than 25% and costs ranging from 2.5-3.0 US$/kgLH2.
Large energy storage systems can address the issue of energy demand fluctuations in renewable energy grids by storing excess energy produced and compensating for any energy shortfalls. The development of hydrogen energy storage systems will thus support the advancement and increased utilization of renewable energy sources. The demand for liquid hydrogen is expected to rise in the near future, driven by environmentally friendly applications and use in mobility sector. As a result, large-scale hydrogen liquefaction (LHL) plants will become increasingly important in the clean energy efficient hydrogen supply chain.
This thesis aims to develop a Large-scale Hydrogen Liquefaction (LHL) plant based on the Brayton cycle concept of 86 TPD. The plant is modeled using Aspen HYSYS, with preliminary designs for key equipment—such as compressors, turbines, and plate-fin heat exchangers, ensuring compatibility with current technological constraints. State properties of the fluid used in the design of compressors and turbine equipment were obtained from REFPROP software, utilizing the Peng-Robinson Equation of State (EOS). For the design of plate-fin heat exchangers, Aspen Exchanger Design and Rating (EDR) was employed. Subsequently, a techno-economic analysis was conducted using the Aspen Process Economic Analyzer (APEA) to estimate both capital and operating expenditures, based on the process simulation model and preliminary equipment designs.
The specific energy consumption (SEC) of the plant, accounting for power recovery from turbine shafts, is determined to be 6.9025 kWh/kgLH2. The plant’s exergy efficiency is calculated at 43.665%, and the specific liquefaction power is found to be 3.014 kWh/kgLH2. Assuming an electricity price of 0.1 €/kWh, modelled 86 TPD Brayton-cycle concept yielded specific liquefaction cost (SLC) of 1.57 €/kgLH2.
A sensitivity analysis was conducted to identify the parameters that influence the specific liquefaction cost (SLC) of the plant. The analysis focused on two key parameters: 1) electricity price and 2) feed pressure. The results reveal that fluctuations in electricity prices have a substantial impact on the plant’s economic performance. Additionally, the analysis indicates that the plant’s efficiency and economic viability are significantly sensitive to decreases in feed hydrogen pressure.
Large energy storage systems can address the issue of energy demand fluctuations in renewable energy grids by storing excess energy produced and compensating for any energy shortfalls. The development of hydrogen energy storage systems will thus support the advancement and increased utilization of renewable energy sources. The demand for liquid hydrogen is expected to rise in the near future, driven by environmentally friendly applications and use in mobility sector. As a result, large-scale hydrogen liquefaction (LHL) plants will become increasingly important in the clean energy efficient hydrogen supply chain.
This thesis aims to develop a Large-scale Hydrogen Liquefaction (LHL) plant based on the Brayton cycle concept of 86 TPD. The plant is modeled using Aspen HYSYS, with preliminary designs for key equipment—such as compressors, turbines, and plate-fin heat exchangers, ensuring compatibility with current technological constraints. State properties of the fluid used in the design of compressors and turbine equipment were obtained from REFPROP software, utilizing the Peng-Robinson Equation of State (EOS). For the design of plate-fin heat exchangers, Aspen Exchanger Design and Rating (EDR) was employed. Subsequently, a techno-economic analysis was conducted using the Aspen Process Economic Analyzer (APEA) to estimate both capital and operating expenditures, based on the process simulation model and preliminary equipment designs.
The specific energy consumption (SEC) of the plant, accounting for power recovery from turbine shafts, is determined to be 6.9025 kWh/kgLH2. The plant’s exergy efficiency is calculated at 43.665%, and the specific liquefaction power is found to be 3.014 kWh/kgLH2. Assuming an electricity price of 0.1 €/kWh, modelled 86 TPD Brayton-cycle concept yielded specific liquefaction cost (SLC) of 1.57 €/kgLH2.
A sensitivity analysis was conducted to identify the parameters that influence the specific liquefaction cost (SLC) of the plant. The analysis focused on two key parameters: 1) electricity price and 2) feed pressure. The results reveal that fluctuations in electricity prices have a substantial impact on the plant’s economic performance. Additionally, the analysis indicates that the plant’s efficiency and economic viability are significantly sensitive to decreases in feed hydrogen pressure.
Interest in incorporating renewable energy systems into current infrastructure has surged as a result of the growing need for sustainable energy solutions in urban settings. This thesis investigates the optimization of a heating and cooling system designed for residential and commercial buildings, with a focus on Dutch climate conditions. The system consists of photovoltaic thermal (PVT) collectors, aquifer thermal energy storage (ATES), heat exchanger and heat pumps. By using these technologies, buildings will be able to satisfy energy demand sustainably without the need for fossil fuels.
Through dynamic simulations, the research aims to optimize the energy system's performance while taking into account a range of operational scenarios and parameter values. Critical components, including the ATES and PVT collectors, are modeled to evaluate their working and performance with heat pumps to provide heating and with heat exchanger for cooling.
The Photovoltaic Materials and Devices research group at TU Delft uses the PVMD Toolbox, a sophisticated modeling tool. Few models from the toolbox are utilised in developing an integrated model, which is later implemented in the toolbox. Later on, it is optimized to improve its effectiveness through dynamic sizing of collectors and aquifers, and implementation of operational modes, making overall the integrated system more robust and redundant. The performance of the integrated system is then studied for a base scenario with 10 PVT collectors and 27,000 m^3 aquifer volume for the current scenario. It showcases promising results. To assess its applicability, the system is analysed under various scenarios. The first scenario is a season-wise performance assessment, where it is showcased that PVT produce energy during summer months and the rest of the year there is a consistent performance by ATES. On comparing the performance of different insulation levels of the buildings, it is found that the future scenarios require half or one-fourth of the energy as compared to the current scenario and the system performs better for them in terms of power consumption by heat pumps. The system's performance under different flow rates of water from PVT and ST is assessed. It is found that at a higher flow rate, a higher amount of energy is generated by both of the collectors, while ST shows better performance than PVT.
For the case when the system provides underfloor heating, it shows that the heat pumps require almost 25% of the energy required for radiator heating. The integrated system is then compared to that of conventional energy systems, demonstrating similar costs but almost no environmental impact and better energy efficiency.
The research findings present a compelling argument for the implementation of such energy systems in urban environments, as they indicate the possibility of substantial energy savings and a decrease in carbon emissions. The report also offers suggestions for future work, such as the application of advanced software, location feasibility studies, and various ATES to precisely model and scale such systems in various real-world circumstances.
This thesis contributes significant insights into the subject of renewable energy systems and lays the groundwork for further study and development of sustainable heat networks by offering a thorough analysis of an innovative method of sustainable energy management. ...
Through dynamic simulations, the research aims to optimize the energy system's performance while taking into account a range of operational scenarios and parameter values. Critical components, including the ATES and PVT collectors, are modeled to evaluate their working and performance with heat pumps to provide heating and with heat exchanger for cooling.
The Photovoltaic Materials and Devices research group at TU Delft uses the PVMD Toolbox, a sophisticated modeling tool. Few models from the toolbox are utilised in developing an integrated model, which is later implemented in the toolbox. Later on, it is optimized to improve its effectiveness through dynamic sizing of collectors and aquifers, and implementation of operational modes, making overall the integrated system more robust and redundant. The performance of the integrated system is then studied for a base scenario with 10 PVT collectors and 27,000 m^3 aquifer volume for the current scenario. It showcases promising results. To assess its applicability, the system is analysed under various scenarios. The first scenario is a season-wise performance assessment, where it is showcased that PVT produce energy during summer months and the rest of the year there is a consistent performance by ATES. On comparing the performance of different insulation levels of the buildings, it is found that the future scenarios require half or one-fourth of the energy as compared to the current scenario and the system performs better for them in terms of power consumption by heat pumps. The system's performance under different flow rates of water from PVT and ST is assessed. It is found that at a higher flow rate, a higher amount of energy is generated by both of the collectors, while ST shows better performance than PVT.
For the case when the system provides underfloor heating, it shows that the heat pumps require almost 25% of the energy required for radiator heating. The integrated system is then compared to that of conventional energy systems, demonstrating similar costs but almost no environmental impact and better energy efficiency.
The research findings present a compelling argument for the implementation of such energy systems in urban environments, as they indicate the possibility of substantial energy savings and a decrease in carbon emissions. The report also offers suggestions for future work, such as the application of advanced software, location feasibility studies, and various ATES to precisely model and scale such systems in various real-world circumstances.
This thesis contributes significant insights into the subject of renewable energy systems and lays the groundwork for further study and development of sustainable heat networks by offering a thorough analysis of an innovative method of sustainable energy management. ...
Interest in incorporating renewable energy systems into current infrastructure has surged as a result of the growing need for sustainable energy solutions in urban settings. This thesis investigates the optimization of a heating and cooling system designed for residential and commercial buildings, with a focus on Dutch climate conditions. The system consists of photovoltaic thermal (PVT) collectors, aquifer thermal energy storage (ATES), heat exchanger and heat pumps. By using these technologies, buildings will be able to satisfy energy demand sustainably without the need for fossil fuels.
Through dynamic simulations, the research aims to optimize the energy system's performance while taking into account a range of operational scenarios and parameter values. Critical components, including the ATES and PVT collectors, are modeled to evaluate their working and performance with heat pumps to provide heating and with heat exchanger for cooling.
The Photovoltaic Materials and Devices research group at TU Delft uses the PVMD Toolbox, a sophisticated modeling tool. Few models from the toolbox are utilised in developing an integrated model, which is later implemented in the toolbox. Later on, it is optimized to improve its effectiveness through dynamic sizing of collectors and aquifers, and implementation of operational modes, making overall the integrated system more robust and redundant. The performance of the integrated system is then studied for a base scenario with 10 PVT collectors and 27,000 m^3 aquifer volume for the current scenario. It showcases promising results. To assess its applicability, the system is analysed under various scenarios. The first scenario is a season-wise performance assessment, where it is showcased that PVT produce energy during summer months and the rest of the year there is a consistent performance by ATES. On comparing the performance of different insulation levels of the buildings, it is found that the future scenarios require half or one-fourth of the energy as compared to the current scenario and the system performs better for them in terms of power consumption by heat pumps. The system's performance under different flow rates of water from PVT and ST is assessed. It is found that at a higher flow rate, a higher amount of energy is generated by both of the collectors, while ST shows better performance than PVT.
For the case when the system provides underfloor heating, it shows that the heat pumps require almost 25% of the energy required for radiator heating. The integrated system is then compared to that of conventional energy systems, demonstrating similar costs but almost no environmental impact and better energy efficiency.
The research findings present a compelling argument for the implementation of such energy systems in urban environments, as they indicate the possibility of substantial energy savings and a decrease in carbon emissions. The report also offers suggestions for future work, such as the application of advanced software, location feasibility studies, and various ATES to precisely model and scale such systems in various real-world circumstances.
This thesis contributes significant insights into the subject of renewable energy systems and lays the groundwork for further study and development of sustainable heat networks by offering a thorough analysis of an innovative method of sustainable energy management.
Through dynamic simulations, the research aims to optimize the energy system's performance while taking into account a range of operational scenarios and parameter values. Critical components, including the ATES and PVT collectors, are modeled to evaluate their working and performance with heat pumps to provide heating and with heat exchanger for cooling.
The Photovoltaic Materials and Devices research group at TU Delft uses the PVMD Toolbox, a sophisticated modeling tool. Few models from the toolbox are utilised in developing an integrated model, which is later implemented in the toolbox. Later on, it is optimized to improve its effectiveness through dynamic sizing of collectors and aquifers, and implementation of operational modes, making overall the integrated system more robust and redundant. The performance of the integrated system is then studied for a base scenario with 10 PVT collectors and 27,000 m^3 aquifer volume for the current scenario. It showcases promising results. To assess its applicability, the system is analysed under various scenarios. The first scenario is a season-wise performance assessment, where it is showcased that PVT produce energy during summer months and the rest of the year there is a consistent performance by ATES. On comparing the performance of different insulation levels of the buildings, it is found that the future scenarios require half or one-fourth of the energy as compared to the current scenario and the system performs better for them in terms of power consumption by heat pumps. The system's performance under different flow rates of water from PVT and ST is assessed. It is found that at a higher flow rate, a higher amount of energy is generated by both of the collectors, while ST shows better performance than PVT.
For the case when the system provides underfloor heating, it shows that the heat pumps require almost 25% of the energy required for radiator heating. The integrated system is then compared to that of conventional energy systems, demonstrating similar costs but almost no environmental impact and better energy efficiency.
The research findings present a compelling argument for the implementation of such energy systems in urban environments, as they indicate the possibility of substantial energy savings and a decrease in carbon emissions. The report also offers suggestions for future work, such as the application of advanced software, location feasibility studies, and various ATES to precisely model and scale such systems in various real-world circumstances.
This thesis contributes significant insights into the subject of renewable energy systems and lays the groundwork for further study and development of sustainable heat networks by offering a thorough analysis of an innovative method of sustainable energy management.
With the adoption of the Paris Agreement, 196 countries worldwide committed to the limitation of the global temperature rise. In order to achieve this goal more energy needs to be produced in a sustainable way. However, the industrial sector is still mainly fossil driven and therefore has to adapt to be able to utilize sustainable produced power, which most often is in the form of electricity. More than a quarter of the total heating demand is in the 100 ◦C to 200 ◦C range. In this temperature range heat pumps are a strong alternative to fossil fuels. Heat pumps can absorb energy from a low temperature heat source and deliver it at a higher, usable temperature. Various technologies for waste heat recovery were investigated in this thesis. It was identified that existing heat pump technologies are suitable to upgrade waste heat, but are limited to lower temperatures of around 120 ◦C. This limitation is mostly due to the high compressor discharge temperatures, which degrade the lubrication oil. Compression resorption heat pumps utilizing wet compression (CRHP’s) limit the superheating during compression and are able to operate oil free, because the working fluid acts as a lubricant. This increases the achievable compressor discharge temperature. The wet compression however is not yet a mature technique and an isentropic efficiency of 70% is required to be competitive with existing technologies. Absorption cycles show promising results for upgrading waste heat due to their non-isothermal heat source and sink, which can be matched to the waste heat temperature. At the Process and Energy lab experiments have been performed on a wet compressor using an ammonia water mixture. This thesis proposes a new method of analysing existing experimental data through a cycle energy balance model. In order to create a model of the experimental setup, four limitations of the setup were identified. First the influence of the gap seal flow, which is the flow from the high pressure to the lower pressure side of the compressor. Second, the mixture inside the compressor can not be assumed homogeneous, which means that both phases are not in equilibrium. Third, there is cooling oil flowing through the compressor housing which cools the process side, this results in a non-adiabatic compression. Finally the pressure drop on the high pressure side is not measured, resulting in an error when calculating the composition of the working fluid. In order to model these limitations a model of the experimental setup was created in Aspen Plus. This model was supplemented with Matlab code to account for the non-equilibrium compression as well as the pressure drop and gap seal flow. Empirical relations were used to determine the heat and mass transfer between the phases during compression. The isentropic efficiency of the modelled compressor was varied until the output matches the input indicating that the steady state solution has been found. The influence of the non-adiabatic compression and the gap seal flow seem to have a significant impact on compressor performance. It was found that the compressor has the highest volumetric and isentropic efficiency when the inlet vapor quality is around 0.85 and the performance decreases with higher vapor qualities. Isentropic efficiencies of up to 0.88 were calculated. The results were compared against previous analysis of the same experimental data which used different assumptions and did not consider the whole cycle. Finally, a case study was performed to analyse the applicability of heat pump technology to upgrade waste heat in a paper recycling plant. A conventional vapor compression heat pump (VCHP) and an electric boiler were compared to a CRHP. To deal with the uncertainty of wet compression performance a range of isentropic efficiencies were considered as well as different ammonia concentrations. The CRHP proved to be energetically and economically viable and outperformed both the VCHP and electric boiler in this case study.
...
With the adoption of the Paris Agreement, 196 countries worldwide committed to the limitation of the global temperature rise. In order to achieve this goal more energy needs to be produced in a sustainable way. However, the industrial sector is still mainly fossil driven and therefore has to adapt to be able to utilize sustainable produced power, which most often is in the form of electricity. More than a quarter of the total heating demand is in the 100 ◦C to 200 ◦C range. In this temperature range heat pumps are a strong alternative to fossil fuels. Heat pumps can absorb energy from a low temperature heat source and deliver it at a higher, usable temperature. Various technologies for waste heat recovery were investigated in this thesis. It was identified that existing heat pump technologies are suitable to upgrade waste heat, but are limited to lower temperatures of around 120 ◦C. This limitation is mostly due to the high compressor discharge temperatures, which degrade the lubrication oil. Compression resorption heat pumps utilizing wet compression (CRHP’s) limit the superheating during compression and are able to operate oil free, because the working fluid acts as a lubricant. This increases the achievable compressor discharge temperature. The wet compression however is not yet a mature technique and an isentropic efficiency of 70% is required to be competitive with existing technologies. Absorption cycles show promising results for upgrading waste heat due to their non-isothermal heat source and sink, which can be matched to the waste heat temperature. At the Process and Energy lab experiments have been performed on a wet compressor using an ammonia water mixture. This thesis proposes a new method of analysing existing experimental data through a cycle energy balance model. In order to create a model of the experimental setup, four limitations of the setup were identified. First the influence of the gap seal flow, which is the flow from the high pressure to the lower pressure side of the compressor. Second, the mixture inside the compressor can not be assumed homogeneous, which means that both phases are not in equilibrium. Third, there is cooling oil flowing through the compressor housing which cools the process side, this results in a non-adiabatic compression. Finally the pressure drop on the high pressure side is not measured, resulting in an error when calculating the composition of the working fluid. In order to model these limitations a model of the experimental setup was created in Aspen Plus. This model was supplemented with Matlab code to account for the non-equilibrium compression as well as the pressure drop and gap seal flow. Empirical relations were used to determine the heat and mass transfer between the phases during compression. The isentropic efficiency of the modelled compressor was varied until the output matches the input indicating that the steady state solution has been found. The influence of the non-adiabatic compression and the gap seal flow seem to have a significant impact on compressor performance. It was found that the compressor has the highest volumetric and isentropic efficiency when the inlet vapor quality is around 0.85 and the performance decreases with higher vapor qualities. Isentropic efficiencies of up to 0.88 were calculated. The results were compared against previous analysis of the same experimental data which used different assumptions and did not consider the whole cycle. Finally, a case study was performed to analyse the applicability of heat pump technology to upgrade waste heat in a paper recycling plant. A conventional vapor compression heat pump (VCHP) and an electric boiler were compared to a CRHP. To deal with the uncertainty of wet compression performance a range of isentropic efficiencies were considered as well as different ammonia concentrations. The CRHP proved to be energetically and economically viable and outperformed both the VCHP and electric boiler in this case study.
Master thesis
(2024)
-
D. Martinez Aguilera, R. Santbergen, Z.U.A. Ul Abdin, I.M.F. Gordon, E. Zanetti
Photovoltaic-Thermal (PVT) modules, alongside Solar Thermal (ST) and Photovoltaic (PV) technologies, offer solutions to energy demands such as electrical consumption, space heating, and domestic hot water of residential buildings. This research employs a model-based approach to analyze how building insulation, solar collector configurations, and seasonal heating modes impact system design. Enhanced insulation scenarios demonstrate potential space heating demand reductions up to 70\%, highlighting the relevance of proper insulation selection.
The findings identify that using a PVT/PV configuration with one module per string is optimal, reducing roof area usage while achieving balanced thermal and electrical energy exchange. The analysis further reveals that higher indoor temperature settings substantially increase heating demands, suggesting significant energy savings potential through temperature set point adjustments. Operational heat supply strategies are adapted to seasonal variations, optimizing the use of solar energy and effectively incorporating aquifer thermal energy storage (ATES) systems as seasonal storage for winter months. But notably, the integration of PVT modules with heat pumps emerged as the primary driver of heat supply, contributing approximately 67\% of the total heat demand. ...
The findings identify that using a PVT/PV configuration with one module per string is optimal, reducing roof area usage while achieving balanced thermal and electrical energy exchange. The analysis further reveals that higher indoor temperature settings substantially increase heating demands, suggesting significant energy savings potential through temperature set point adjustments. Operational heat supply strategies are adapted to seasonal variations, optimizing the use of solar energy and effectively incorporating aquifer thermal energy storage (ATES) systems as seasonal storage for winter months. But notably, the integration of PVT modules with heat pumps emerged as the primary driver of heat supply, contributing approximately 67\% of the total heat demand. ...
Photovoltaic-Thermal (PVT) modules, alongside Solar Thermal (ST) and Photovoltaic (PV) technologies, offer solutions to energy demands such as electrical consumption, space heating, and domestic hot water of residential buildings. This research employs a model-based approach to analyze how building insulation, solar collector configurations, and seasonal heating modes impact system design. Enhanced insulation scenarios demonstrate potential space heating demand reductions up to 70\%, highlighting the relevance of proper insulation selection.
The findings identify that using a PVT/PV configuration with one module per string is optimal, reducing roof area usage while achieving balanced thermal and electrical energy exchange. The analysis further reveals that higher indoor temperature settings substantially increase heating demands, suggesting significant energy savings potential through temperature set point adjustments. Operational heat supply strategies are adapted to seasonal variations, optimizing the use of solar energy and effectively incorporating aquifer thermal energy storage (ATES) systems as seasonal storage for winter months. But notably, the integration of PVT modules with heat pumps emerged as the primary driver of heat supply, contributing approximately 67\% of the total heat demand.
The findings identify that using a PVT/PV configuration with one module per string is optimal, reducing roof area usage while achieving balanced thermal and electrical energy exchange. The analysis further reveals that higher indoor temperature settings substantially increase heating demands, suggesting significant energy savings potential through temperature set point adjustments. Operational heat supply strategies are adapted to seasonal variations, optimizing the use of solar energy and effectively incorporating aquifer thermal energy storage (ATES) systems as seasonal storage for winter months. But notably, the integration of PVT modules with heat pumps emerged as the primary driver of heat supply, contributing approximately 67\% of the total heat demand.
The electrification of industrial process heat
Implementation of thermal energy storage and the potential of novel high-temperature heat pump technologies
Electrification and decarbonization of industrial process heat is an important next step in the energy transition to reduce greenhouse gas (GHG) emissions. This study provides an in-depth analysis of how in the current industrial landscape the combination of commercially available electric heating technologies with the implementation of thermal energy storage (TES) can realize the electrification of
medium-temperature industrial process heat on the short-term. Moreover, it explores what potential novel high-temperature heat pump (HTHP) technologies, specifically the supercritical CO2 (sCO2) reversed Brayton HTHP, have to realize this electrification even more efficient in terms of electricity demand in the future. Thereby, it also briefly highlights the opportunities and challenges to combine HTHP technology and TES in the future to realize an optimal electrification. ...
medium-temperature industrial process heat on the short-term. Moreover, it explores what potential novel high-temperature heat pump (HTHP) technologies, specifically the supercritical CO2 (sCO2) reversed Brayton HTHP, have to realize this electrification even more efficient in terms of electricity demand in the future. Thereby, it also briefly highlights the opportunities and challenges to combine HTHP technology and TES in the future to realize an optimal electrification. ...
Electrification and decarbonization of industrial process heat is an important next step in the energy transition to reduce greenhouse gas (GHG) emissions. This study provides an in-depth analysis of how in the current industrial landscape the combination of commercially available electric heating technologies with the implementation of thermal energy storage (TES) can realize the electrification of
medium-temperature industrial process heat on the short-term. Moreover, it explores what potential novel high-temperature heat pump (HTHP) technologies, specifically the supercritical CO2 (sCO2) reversed Brayton HTHP, have to realize this electrification even more efficient in terms of electricity demand in the future. Thereby, it also briefly highlights the opportunities and challenges to combine HTHP technology and TES in the future to realize an optimal electrification.
medium-temperature industrial process heat on the short-term. Moreover, it explores what potential novel high-temperature heat pump (HTHP) technologies, specifically the supercritical CO2 (sCO2) reversed Brayton HTHP, have to realize this electrification even more efficient in terms of electricity demand in the future. Thereby, it also briefly highlights the opportunities and challenges to combine HTHP technology and TES in the future to realize an optimal electrification.
Master thesis
(2023)
-
J.K. Dijkhuis, K. Hooman, A.M.J. Felden, E. Zanetti, J. Hermans, D. Palanisamy, R. Shah
In order to reduce greenhouse gas (GHG) emissions, fleets of medium- and heavy-duty vehicles are transitioning from conventional fossil fuels to fully electric drivetrains. To utilize these medium- and heavy-duty electric vehicles (MHDEVs) without significantly disrupting their operations, Megawatt Charging Systems (MCS) are being developed, which enable charging rates up to 4.5 MW. However, these charging rates are associated with substantial heat generation in the vehicle’s battery pack. To regulate the battery temperature and maximize battery lifetime, performance, and safety, the development of a battery thermal management system (BTMS) for this application is crucial.
The study provides a methodology that adopted a system engineering approach for the design of a BTMS for the application of MHDEVs which utilize MCS. The study defined the requirements for the BTMS which include the optimal temperature range for battery cells and determined the battery heat generation rate when using MCS. Furthermore, the study investigated the magnitude of temperature gradients in battery cells as a result of MCS.
Subsequently, two assessment stages have been proposed to assess BTMS strategies, which include forced air BTMS, immersion cooling BTMS, cooling plates with coolant BTMS, and cooling plates with refrigerant BTMS. This assessment resulted in design requirements for heat transfer areas and mass flow rates to maintain the battery cells below 35 ℃. Moreover, the concepts of utilizing cooling plates with refrigerant in a vapor-compression refrigeration system and storing charging session heat by thermal energy storage (TES) have been developed. This included the dimensioning of a condenser and compressor for the vapor-compression refrigeration cycle and included the dimensioning of the required mass and volume of TES medium for the TES system. The study found that these two BTMS strategies are the most favorable. Thermal energy storage with hydrated salt as phase change material (PCM) appeared as the most effective and feasible option subsequent to conducting comparisons with immersion coolant and paraffin PCM. However, a BTMS with a vapor compression refrigeration system might be needed when the BTMS is used for both driving and charging. Analysis of refrigerants R717, R134a, and R1234yf, indicated that R717 is the most effective in this BTMS with a COP of 3.52 and a lower required mass flow rate and compressor power consumption, however, is associated with several safety considerations that must be addressed when selecting R717 over other refrigerants. Lastly, the study utilized a MATLAB Simulink model to identify the effects of dynamic phenomena that occur during operation of the BTMS and the study determined the impact of BTMS weight on MHDEV driving range.
Recommendations for future research are given related to the need for increased fidelity of heat generation prediction and BTMS models. Furthermore, future research should be conducted on combining the BTMS with other thermal management systems in the vehicle to maximize overall effectiveness.
...
The study provides a methodology that adopted a system engineering approach for the design of a BTMS for the application of MHDEVs which utilize MCS. The study defined the requirements for the BTMS which include the optimal temperature range for battery cells and determined the battery heat generation rate when using MCS. Furthermore, the study investigated the magnitude of temperature gradients in battery cells as a result of MCS.
Subsequently, two assessment stages have been proposed to assess BTMS strategies, which include forced air BTMS, immersion cooling BTMS, cooling plates with coolant BTMS, and cooling plates with refrigerant BTMS. This assessment resulted in design requirements for heat transfer areas and mass flow rates to maintain the battery cells below 35 ℃. Moreover, the concepts of utilizing cooling plates with refrigerant in a vapor-compression refrigeration system and storing charging session heat by thermal energy storage (TES) have been developed. This included the dimensioning of a condenser and compressor for the vapor-compression refrigeration cycle and included the dimensioning of the required mass and volume of TES medium for the TES system. The study found that these two BTMS strategies are the most favorable. Thermal energy storage with hydrated salt as phase change material (PCM) appeared as the most effective and feasible option subsequent to conducting comparisons with immersion coolant and paraffin PCM. However, a BTMS with a vapor compression refrigeration system might be needed when the BTMS is used for both driving and charging. Analysis of refrigerants R717, R134a, and R1234yf, indicated that R717 is the most effective in this BTMS with a COP of 3.52 and a lower required mass flow rate and compressor power consumption, however, is associated with several safety considerations that must be addressed when selecting R717 over other refrigerants. Lastly, the study utilized a MATLAB Simulink model to identify the effects of dynamic phenomena that occur during operation of the BTMS and the study determined the impact of BTMS weight on MHDEV driving range.
Recommendations for future research are given related to the need for increased fidelity of heat generation prediction and BTMS models. Furthermore, future research should be conducted on combining the BTMS with other thermal management systems in the vehicle to maximize overall effectiveness.
...
In order to reduce greenhouse gas (GHG) emissions, fleets of medium- and heavy-duty vehicles are transitioning from conventional fossil fuels to fully electric drivetrains. To utilize these medium- and heavy-duty electric vehicles (MHDEVs) without significantly disrupting their operations, Megawatt Charging Systems (MCS) are being developed, which enable charging rates up to 4.5 MW. However, these charging rates are associated with substantial heat generation in the vehicle’s battery pack. To regulate the battery temperature and maximize battery lifetime, performance, and safety, the development of a battery thermal management system (BTMS) for this application is crucial.
The study provides a methodology that adopted a system engineering approach for the design of a BTMS for the application of MHDEVs which utilize MCS. The study defined the requirements for the BTMS which include the optimal temperature range for battery cells and determined the battery heat generation rate when using MCS. Furthermore, the study investigated the magnitude of temperature gradients in battery cells as a result of MCS.
Subsequently, two assessment stages have been proposed to assess BTMS strategies, which include forced air BTMS, immersion cooling BTMS, cooling plates with coolant BTMS, and cooling plates with refrigerant BTMS. This assessment resulted in design requirements for heat transfer areas and mass flow rates to maintain the battery cells below 35 ℃. Moreover, the concepts of utilizing cooling plates with refrigerant in a vapor-compression refrigeration system and storing charging session heat by thermal energy storage (TES) have been developed. This included the dimensioning of a condenser and compressor for the vapor-compression refrigeration cycle and included the dimensioning of the required mass and volume of TES medium for the TES system. The study found that these two BTMS strategies are the most favorable. Thermal energy storage with hydrated salt as phase change material (PCM) appeared as the most effective and feasible option subsequent to conducting comparisons with immersion coolant and paraffin PCM. However, a BTMS with a vapor compression refrigeration system might be needed when the BTMS is used for both driving and charging. Analysis of refrigerants R717, R134a, and R1234yf, indicated that R717 is the most effective in this BTMS with a COP of 3.52 and a lower required mass flow rate and compressor power consumption, however, is associated with several safety considerations that must be addressed when selecting R717 over other refrigerants. Lastly, the study utilized a MATLAB Simulink model to identify the effects of dynamic phenomena that occur during operation of the BTMS and the study determined the impact of BTMS weight on MHDEV driving range.
Recommendations for future research are given related to the need for increased fidelity of heat generation prediction and BTMS models. Furthermore, future research should be conducted on combining the BTMS with other thermal management systems in the vehicle to maximize overall effectiveness.
The study provides a methodology that adopted a system engineering approach for the design of a BTMS for the application of MHDEVs which utilize MCS. The study defined the requirements for the BTMS which include the optimal temperature range for battery cells and determined the battery heat generation rate when using MCS. Furthermore, the study investigated the magnitude of temperature gradients in battery cells as a result of MCS.
Subsequently, two assessment stages have been proposed to assess BTMS strategies, which include forced air BTMS, immersion cooling BTMS, cooling plates with coolant BTMS, and cooling plates with refrigerant BTMS. This assessment resulted in design requirements for heat transfer areas and mass flow rates to maintain the battery cells below 35 ℃. Moreover, the concepts of utilizing cooling plates with refrigerant in a vapor-compression refrigeration system and storing charging session heat by thermal energy storage (TES) have been developed. This included the dimensioning of a condenser and compressor for the vapor-compression refrigeration cycle and included the dimensioning of the required mass and volume of TES medium for the TES system. The study found that these two BTMS strategies are the most favorable. Thermal energy storage with hydrated salt as phase change material (PCM) appeared as the most effective and feasible option subsequent to conducting comparisons with immersion coolant and paraffin PCM. However, a BTMS with a vapor compression refrigeration system might be needed when the BTMS is used for both driving and charging. Analysis of refrigerants R717, R134a, and R1234yf, indicated that R717 is the most effective in this BTMS with a COP of 3.52 and a lower required mass flow rate and compressor power consumption, however, is associated with several safety considerations that must be addressed when selecting R717 over other refrigerants. Lastly, the study utilized a MATLAB Simulink model to identify the effects of dynamic phenomena that occur during operation of the BTMS and the study determined the impact of BTMS weight on MHDEV driving range.
Recommendations for future research are given related to the need for increased fidelity of heat generation prediction and BTMS models. Furthermore, future research should be conducted on combining the BTMS with other thermal management systems in the vehicle to maximize overall effectiveness.