New technologies are being developed to produce electricity cleaner and more efficient. A promising technology among these is the solid oxide fuel cell (SOFC). It electrochemically converts chemical energy into electricity. This process is highly efficient and several types of fuel are suitable. Furthermore, the SOFC operates at a high temperature, thus producing high quality excess heat which can be converted into electricity in a thermodynamic power cycle to increase the efficiency. Commonly this is done by a directly coupled gas turbine (GT). The supercritical carbon dioxide (sCO2) Brayton cycle has recently received attention for its potential as a next generation power cycle. It combines the advantages of the steam Rankine cycle and air Brayton cycle. So far, two heat sources are mainly considered for this cycle: Nuclear and concentrated solar power (CSP). The aim of this study is to investigate the potential of integrating a SOFC with a sCOs Brayton cycle. A thermodynamic model of the SOFC- sCOኼ Brayton cycle hybrid system (SSHS) is developed to explore and analyze different concepts that effect the integration of both systems. Methane is converted to syngas in an indirect internal reforming (IIR) setup. The steam required for this process is either fed by a heat recovery steam generator (HRSG) or supplied by recirculating anodic exhaust gas. Both options are considered. Recirculating the exhaust of the cathode is another options that is explored and analyzed. Two sCO2 cycle setups are analyzed in combination with the SOFC system: A simple recuperative cycle and a recompression cycle. Different setups of the SSHS are compared on efficiency, complexity of the system and size of the exchangers. For comparison, a directly coupled solid oxide fuel cell (SOFC)- GT hybrid system is considered as well. It is found that the recompression cycle in combination with SOFC system is more efficient than the simple recuperative cycle but significantly increases the complexity of the heat exchanger network, recirculating cathodic air decreases the size of the heat exchangers and increases the efficiency and supplying steam through a HRSG decreases the efficiency. Compared to a directly coupled SOFC-GT system the SSHS is a significantly more complex system. However, it does not require a pressurized SOFC since the sCO2 Brayton cycle is indirectly coupled to the SOFC. The most efficient setup of the SSHS, combining the recompression cycle with cathode recirculation, has a higher LHV efficiency than the directly coupled SOFC- GT hybrid system, 66.58% over 62.38%. This setup of the SSHS is rather complex though. Other setups of the SSHS show efficiencies similar to that of the directly coupled SOFC- GT hybrid system. A promising result, but the practical feasibility of the SSHS is something that should be carefullyconsidered in future research and practice.

The global energy demand is growing, while climate change is demanding a sustainable way of generating this energy. Ocean Thermal Energy Conversion (OTEC) can be a part of the solution for this problem. OTEC generates electricity by using the temperature difference between the surface water of the ocean and the water at 1000 meters depth as a driving force. As this temperature difference is present all year round, there is no need for energy storage, which is the case for wind- and solar energy. An OTEC system utilizes an Organic Rankine Cycle (ORC), which uses ammonia as a working fluid. A lot of research is conducted on this cycle, all assuming steady-state. However, as the system is constantly changing its state, either by a changing temperature difference or by variations in the operating conditions of components, more research is required to investigate the impact of these changes. Therefore, a dynamic model has been developed. In order to cope with these changes and to ensure the optimal power output at all times, a control strategy is developed and implemented on the model. As the system has been developed with the use of a control system as a boundary condition, a model is adapted which prioritises computational time over accuracy, but, according to literature, is still accurate enough for the small transients. This model has been implemented for the OTEC cycle and improved from normal dynamic models by including pressure drops and storage tanks. Allseas, in cooperation with the TU Delft, has built an experimental set-up of an OTEC cycle. Experiments conducted on this set-up were used to compare the model with reality, both steady-state and dynamically. It has been proven that the steady-state values matched the experiments within 1%, and the  dynamics matched the experiments almost perfectly. As a next step, the system has been scaled to match the desired 3MW output. With this scaled model, realistic scenarios were simulated to check the response on larger transients. The scenarios consists of a start-up and shutdown of the system, a changing inlet temperature, pumps being shut off and a number of heat exchangers that are decoupled from the system, for example when a number of heat exchangers need maintenance.  The outcome proved that, from a dynamic perspective, the influence of a seawater temperature change was negligible. As the temperature changes per second are very small, the net output scales linearly with the temperature difference. A start-up and shutdown of the system was successfully simulated, which is the largest possible transient in the system. The influence of pumps that are stopped and heat exchangers being turned off for maintenance have been simulated, which showed just a slight decrease in net output. It also showed that the system, when running at the nominal conditions of the pump and turbine curve, was not running at an optimum. Therefore, a control strategy was developed by conducting a sensitivity analysis and, after using an optimisation to find the optimum point, the resulting control strategy was implemented. This new strategy resulted in an increase of 15% in the net output, compared to the nominal conditions. This proves that an OTEC cycle could greatly benefit from using a dynamic model to predict its dynamic performance and the implementation of a control system.

In conventional compressor technology, high pressure ratios are often achieved by multiple, successive compression stages. This is done to avoid high temperatures due to the adiabatic nature of most compression processes which deteriorates the working of oil lubrication. The aim of this work is to reduce a conventional four-stage system to only two stages as this may improve the size and expenses of the system. This goal combined with a long desired lifetime, makes that a compressor is developed that operates based on gas bearing technology. The design is focused on two main subjects. Firstly, the load capacity of the gas bearings is significantly lower than oil lubricated bearings due to the reduced viscosity. To avoid mechanical contact and wear of the components this has been thoroughly analysed using finite element methods. The oscillating nature of the loads in the system enhances the squeeze effect from the Reynolds equation. Secondly, the sealing function of gas bearings opposing internal leakage is evaluated carefully to obtain a desired efficiency. Based on these simulations, the mechanical design of the compressor is optimized to improve the manufacturing of the compressor components.

The maritime sector is important for the facilitation and growth of global trade. Currently, about 90% of the goods are transported by ships and as a result, the number of ships has risen, increasing the emissions related to shipping. Pollution caused by exhaust gas, especially the sulphur oxide emission, from marine diesel engines has become a global concern in recent years. Therefore, the International Maritime Organisation limited marine fuel sulphur content in both Emission Control Areas to 0.1%w/w since 2015 and globally to 0.5%w/w since January 1st , 2020. It is anticipated, that the newly implemented IMO regulations will help to mitigate negative impact of ship emissions on public health and the environment in the coastal areas. The wet scrubber system is a reliable technology for flue gas desulphurisation in marine applications and can achieve a sulphur dioxide removal efficiency of 98%. The operating costs are low, however the capital cost for installation are high and a scrubber system requires space for installation while maintaining ship’s stability. Wet scrubber systems operating in a closed loop and using caustic soda may operate without discharge to the sea and thus are allowed to operate in ports. The use of caustic soda also makes it possible to use the scrubber in areas with low seawater alkalinity. However, scrubber systems generally operate at 100%, even when the engine operates at lowload. This results in an increase of the fuel consumption and carbon dioxide emissions. Themain objectives of this research are to examine the influence of water evaporation on the sulphur dioxide removal efficiency and the (response of the scrubber) effect of dynamic loads on the scrubber efficiency. A dynamic model of a closed loop wet scrubber operating with fresh water and caustic soda also known as sodium hydroxide was created and verified. The scrubber model consists of three resistance elements, namely the venturi scrubber, the tower scrubber with a packed bed and the demister and two volume elements (lower and upper) to connect the resistance elements. The absorption of SO2 is mainly taking place in the packed bed and the two phase flow of exhaust gas and scrubbing liquid was modelled in this section. The Nerst film theory was used and extended to a two film theory in which the exhaust gas and scrubbing liquid phases come into contact through an interface and exchange both heat and mass. The gas flow in the packed bed could be modelled with a combination of resistance and volume elements as this phase is compressible. The liquid flow and liquid film thickness in the packed bed were modelled based on the conservation of mass and the liquid holdup theory developed by Billet and Schultes. A feedback control system controls the scrubbing liquid flow based on the sulphur dioxide to carbon dioxide ratio. The system includes a time constant to account for the inertia of the scrubber’s pump and pipe system. The verified model was integrated with engine data and used to run several static and dynamic simulations. The inclusion of evaporation in the packed bed leads to an increase of the scrubber efficiency in all engine loads. The extra vapour added dilutes the gas phase and reduces the mass fraction of sulphur dioxide. When evaporation is included in the analysis, the sulphur dioxide to carbon dioxide ratio leaving the scrubber is 1.88, equal to a fuel sulphur content of 0.043% on a mass base (from 3.5% in the fuel) for 100% engine load. When evaporation is not included in the analysis the previous values are 2.3 and 0.053% respectively. To increase the precision concerning the amount of water that evaporates, a higher discretisation of the packed bed is required. High engine load fluctuations and/or high input frequencies lead to overshoots and higher liquid supply, in order to keep the scrubber system efficient. In the transition from 25% MCR to 100% MCR the liquid supply exceeds the nominal value of 94 kilogram per second by by 5.3 kilogram per second (or by 5.6%). In the transition between 75%MCR to 100%MCR, for the frequency of 50 seconds the liquid supply is equal to 92.9 kilogramper second. Increasing the input frequency 5 times results in an increase of the liquid supply to 96.1 kilogram per second. The sulphur dioxide to carbon dioxide ratio leaving the scrubber was always below the ECA sulphur limit and was fluctuating around the set point, but most of the time below it. A combination of feed forward and feedback and/or a more advanced control may result in a more stable control of the scrubber, but this has to be investigated. The model functions, but more research is required for the venturi and the demister models, but also for the packed bed model. In the venturi a three phase flow is required and in the demister an analytical and dimensional analysis is required. Also, the packed bed model needs to be further developed to include the condensation effect and a more precise approach for the liquid phase. Further research can be done on the integration of the model with a diesel engine and SCR model. Also, seawater can be examined as a scrubbing liquid as this may reduce the operational costs of the scrubber. Finally, because space requirements of the scrubber are high, a structured packed bed could be an alternative to the dumped and reduce the space occupied by the wet scrubber.

The increasing demand in renewable energy motivates the search for new renewable energy sources. The ocean is a vast energy source of both thermal and kinetic energy, however methods to harness this energy haven’t reached maturity yet. Ocean Thermal Energy Conversion (OTEC), a method to harness the thermal energy of the ocean, could change this. In order to get to this stage of maturity, experimental and numerical research on the OTEC power cycle was done by Goudriaan [12] and Kuikhoven [23]. However, the numerical model developed showed inaccuracy for the condenser and lacked physical insight into the processes of heat transfer. The condenser and consequently, the cold water pipe, are a significant part of the investment costs of an OTEC plant. Therefore, the goal in this research was to increase the accuracy of the performance calculations of the condenser and to gain more knowledge on the physical phenomena in the condenser heat exchanger. Two different methods were tested in order to improve the condenser model. In the first part a heat transfer correlation is fitted to the experimental data. A literature study was done on two phase heat transfer correlations to investigate what phenomena occur in two phase condensation flow. Relevant dimensionless quantities were chosen accordingly. The quantities used are the conventional Reynolds and Prandtl number. The mass transfer that occurs through absorption was represented by the Schmidt number. The resulting correlation fit was tested on accuracy using the experimental data obtained by Goudriaan [12] and Kuikhoven [23]. To be able to compare the results of this research with their research, the in-depth validation was done for the same working fluid mass flow of 0.010 kg/s that was used by Goudriaan [12] and Kuikhoven [23]. The Schmidt number showed a positive effect on the accuracy. The correlation was extrapolated for other working fluid mass flows as well. It was found that the correlation fit is a useful tool for the working fluid mass flows that have a large amount of experimental data available (the cases 0.007, 0.010 and 0.013 kg/s) but isn’t as accurate for working fluid mass flow with a small amount of experimental data available (0.005 kg/s). In the second part of the report a detailed condenser model was developed using the method of Fernández- Seara et al. [10]. This model was used to provide more physical insight into the two phase mixture behaviour in a condensation process. The model is also capable of predicting the required pressure on the working fluid side to provide full condensation. Literature research was done on different aspects of the condensation process in a plate heat exchanger. Film thickness correlations were tested. Different heat transfer correlations developed for plate heat exchangers were investigated. Flow pattern theory and flow pattern maps were used to predict the flow behaviour. The method of Fernández-Seara et al. [10] was used to predict mass transfer through the vapor-liquid interface in the working fluid. A pressure iteration loop was added to predict the condenser pressure on the working fluid side. The initial results were slightly off compared to the experimental measurements. The reason for the inaccuracy is expected to be the neglection of surface tension effects on the wettability of the working fluid. Dry surface voids are expected to occur in the liquid film with decreasing concentration. A correction factor based on surface tension was added to include this effect. The 0.010 kg/s case was validated in detail and showed decent accuracy. At 0.007 kg/s working fluid mass flow deviations were slightly more significant but the trends of the characteristic variables were similar to the experimental data. The mass transfer iteration loop showed inaccuracies and instabilities at the working fluid mass flows of 0.005 and 0.013 kg/s. The model showed that for the range tested the condenser performs better with increasing concentration of ammonia. The non-linear behaviour of the mass diffusivity decreases the mass transfer coefficients at decreasing concentrations. The surface tension correction factor also adds to the decrease in performance, however, if the mass flux of the working fluid would be higher, this correction factor might not be valid because the dry surface voids might not occur any more. The overall heat transfer coefficient increases towards the outlet of the condenser.

Carbon dioxide emission into the earth’s atmosphere by maritime activities are a concern for the people within and outside the industry. This is because of the environmental impacts that are caused by these greenhouse gas emissions which changes the very chemistry of this planet. These impacts can be mitigated by reducing the CO2 emissions which can be achieved by several design and/or operational means. Waste heat recovery (WHR) technology is one such means that is capable of reducing emissions. This is achieved by improving the overall fuel efficiency of marine engines which reduces the fuel consumption of the vessel. This improvement is realised by harnessing the heat energy that is expelled by the engine through waste heat sources such as exhaust gas, etc.  Organic Rankine cycle (ORC) is one of many WHR technologies that is capable of harnessing that waste heat energy from the fuel which cannot be utilised by the engine operation alone. ORC as a WHR system (WHRS) is widely implemented in land based applications due to its fluid choice flexibility, plant simplicity and net efficiency. However, it is rather new to the maritime industry because WHRS on-board ships are predominantly based on steam Rankine cycle or turbo-compounding. These systems have their own advantages but ORC-WHRS may outweigh them in certain applications on-board ships. This is especially for electrical power generation from low and medium temperature waste heat sources. However, ORC in marine application encounters challenges unlike seen in land based applications. These challenges are caused by the physical & geometrical constraints, operational profile of the vessel or uncertainties caused at sea.  In this thesis, the implementation of ORC-WHRS to marine engines for exhaust gas is investigated and studied to understand how such an application can be beneficial. Unlike steam Rankine cycle, an ORC system has flexibility in choosing an organic fluid that is suitable based on the application. This flexibility in fluid choices are confronted by the above mentioned maritime related challenges. Hence, a screening methodology is devised in this thesis that finds a suitable fluid based on the waste heat source profile and selection parameters. These selection parameters are necessary to filter out functioning organic fluids that can be limited due to the mentioned challenges. In this thesis, the power density of the ORC plant is the selection parameter used.As mentioned earlier, the ORC-WHRS may often be subjected to off-design conditions due to the operational profile of the vessel or by uncertainties at sea. Hence, off-design performance is analysed to study the ORC system when designed at several discrete engine load points. These analysis are carried out in plant models modified from an existing steam based dynamic model and developed into a simple-ORC and a recuperative-ORC dynamic plant models. Sensitivity analysis of these models are also performed to understand uncertainties in the model output corresponding to uncertainties in model input parameter. This analysis is followed by analysis of the dynamic behaviour of the ORC plant model to varying load step functions and step duration for plants designed at discrete engine load points.  This thesis can be extended, not only to study how ORC can be used to meet future regulations on CO2 emissions, but also on operability limitations imposed on ships. The fluid screening approach used here can also be modified based on parameters, such as toxicity, flammability, cost, specific power etc. This can present a realistic approach to an end product that can be safely and economically operated on board.

This study provides suggestions to decrease hot utility use and impact on the environment of a skim milk powder (SMP) processing plant. These suggestions are based on the integration of waste streams with processes in the production of SMP. To identify appropriate waste and process streams, process integration has proven to be a successful method. This concept addresses the issue of waste heat of a process by pointing out to the importance of the relation between unit-processes. In this study, the integration of waste streams is accomplished by heat exchangers, heat pumps and a zeolite wheel. The general assumption underlying this research, is that recovering heat from unused waste streams decreases hot utility use. Multiple methodologies were used in this study. To accomplish process integration, the pinch analysis forms an essential tool. This analysis was used to identify potential heat recovery schemes in the SMP plant. Furthermore, to fully understand these schemes, a thermal, environmental and economical analysis was done. These analyses were based on mass and energy balances, (in)direct CO2 emissions and investment and operational costs. Several conclusion can be drawn from the pinch analysis. First, the pinch temperature is 50◦C. This represents the dividing line between processes which require heating and cooling. Second, the heating and cooling demand is known. The SMP production process requires 6.8 MW of external heating and 1.7 MW of external cooling. Third, the amount of recoverable heat is equal to 5.3 MW. Fourth, appropriate heat sink and sources are identified. The heat sources, i.e. waste streams, are the spray dryer exhaust and the the condensate streams from two evaporators. The supply temperatures of the exhaust and the condensate streams are respectively 77, 65 and 55◦C. The appropriate heat sinks are the spray dryer air inlet and the evaporator product inlet streams. The target temperature of the spray dryer inlet and evaporator inlet streams are respectively 190, 75 and 70◦C. Seven heat recovery setups are proposed. In terms of saved energy, the spray dryer exhaust has the most potential for heat recovery. The zeolite wheel is the best performing heat recovery technology in the spray dryer process, with a recovery of 3.5 MW. Furthermore, a heat exchanger-heat pump combination and a stand-alone heat exchanger recover respectively 1.8 and 1.6 MW. In contrast, the evaporation process has less potential for heat recovery. The best performing configuration is a heat pump, recovering 1.4 MW from the evaporator condensate. The environmental performance is strongly related with the amount of energy saved. This is because the most decisive parameter in the environmental analysis is the carbon intensity of natural gas and electricity. The best performing configurations in terms of saved CO2 emissions are the zeolite wheel (3806 ton/yr), the heat exchanger-heat pump combination (1934 ton/yr) and the stand-alone heat exchanger (1593 ton/yr) in the spray dryer process. In the evaporation section, the heat pump saves 1485 ton CO2 per year. The total annual costs are derived from the equivalent annual costs of the asset, carbon savings and utility savings/costs. The best performing configuration is the heat pump in the evaporation process. This technology has an annual return of 145 ke per year. Other configurations with a high return are the stand-alone heat exchanger (143 ke/yr), the heat exchanger-heat pump combination (128 ke/yr) and the zeolite wheel (123 ke/yr).

Firing industrial installations, like boilers, with a cogeneration gas turbine instead of a classic burner have several beneficial aspects. A cogeneration system allows for a more efficient utilization of energy and lowered emissions. What makes such a system especially interesting is that the revenue of the generated electrical power can outweigh the extra costs required to operate a gas turbine for producing a specific amount of thermal energy. The technical challenge, covered in this thesis, consists of improving a gas turbine for cogeneration applications relative to a classic burner. The solution can be found in reduction of the high stack losses, as these comprise the main disadvantage of firing a boiler with a gas turbine. This research focuses specifically on cogeneration with the PowerBurner, a gas turbine developed and manufactured by Innecs Power Systems, located in Ter Aar, the Netherlands. The goal of this study was to identify, analyze and conceptualize methods that reduce the stack losses of a PowerBurner used for the production of steam. Implementation of such methods should allow the PowerBurner to become a more attractive alternative for steam production compared to a conventional burner. Four concepts were identified which could improve operation of a cogeneration gas turbine: Steam injection, flue gas recirculation, supplementary firing and implementation of a boiler in the combustion chamber, the Velox boiler. A thermodynamic model of a gas turbine was created in Thermoflex. The model was based on the design point specification of the PowerBurner, from which it deviates less than 1% at any point in the process. Implementation of steam injection was able to induce the largest increase the electrical efficiency, from 10.5% to 20%, whereas flue gas recirculation resulted in the highest increase in total efficiency, from 85% to 95%. With supplementary firing and the Velox-type boiler, the thermal capacity and -efficiency could be increased the most, from 2 MW to 6.8 MW and from 74% to 90%, respectively. The profitability of each setup compared to making use of a conventional burner for an equal thermal output was determined. Supplementary firing allows for the most profitable operation. A qualitative cost analysis showed that supplementary-fired setup required the least capital expenditures. From a combination of the thermodynamic and economic characteristics, the supplementary-fired PowerBurner was chosen to be the best alternative for replacing a conventional burner for the production of steam. A conceptual design of a burner for such an application was created in ANSYS Fluent. The design was able to operate with fuel inputs of at least 0.485 MW up to 4.85 MW. 100% Combustion efficiency was achieved over the full range. Pressure losses over the burner are low at 1.6 mbar. Whether the current burner design results in a stable flame cannot be determined from the model. A NOX analysis in Fluent indicated that the emissions of NOx are over the Dutch regulation standards for gas turbines, but the accuracy of this result is not known. Therefore, future research is required to determine flame stability and pollutant emissions.

In some countries, drying processes use up to 20% of the total energy consumption. Within the agriculture sector, drying of food and flowering products is a necessary step in production. A lot of companies make use of hot air dryers where the heat is gained by burning natural gas. A novel method is to use a heat pump assisted drying systems instead. Heat pump assisted drying realises a better product quality due to the ability of humidity and climate control of the drying medium: air. Additionally, there are possibilities for energy savings up to 50%. This thesis project is mentioned as the first step for an initiative to introduce heat pump drying into the horticulture sector. The project started almost 1 year ago and is still far from finished. Main goal was to get a good understanding of the product drying behaviour, drying capacities and the system requirements and footprints. Conclusions should determine whether there is a possibil-ity for market implementation or not. The results in this report are promising. Heat pump drying is a trending research topic in science, where new developments on predicting the dynamic drying behaviour of agricultural products show up every month. This study involves a computational model, where the dynamic process of drying flower bulbs is simulated. This model is validated by measurements on existing drying in-stallations. Building this model resulted in a good understanding about the flower bulb characteris-tics and the necessary drying capacities. Additionally, Heat pump drying systems are evaluated and a dynamically modelled. When both models are the drying process of FB’s can be optimized. The first protype of the HP drying system that will be used in further research will be shortly discussed. Conclusion of this report is that heat pump drying is a promising technique for drying of FB’s. The combination of technical advantages with energy savings, could lead to better product quality and lower production costs. The business case is strengthened by future perspectives where energy efficiency and reduction of CO2 emissions will more and more important due to climate change.

Many regions in the world depend heavily on expensive desalinated water for fresh water consumption, in particular tropical areas. Current mainstream desalination technologies (Reverse Osmosis and Multi-Stage Flash Evaporation) are quite energy intensive and thus costly. Today’s challenge is to design a desalination system that could run with local available renewable energy and provide affordable fresh water, even in the most arid environments. A potential fresh water production method that differs from mainstream technologies is Ocean Thermal Water Production (OTWP). This method makes use of high temperature and high relative humidity air in the tropics and condenses it against a cooled fresh water loop in a packed bed column. The system is expected to deliver fresh water at a competitive level once built at a larger scale. This master thesis project improves a previously researched OTWP model and validates the model by testing its output values against experiments done using an experimental setup at the TU Delft P&E laboratory. Taking into account the previous work done during the thesis of van der Drift [49] and Lopez [30], the theoretical background for building an OTWP model has been further described and expanded in this thesis. Three different direct contact condensation theories have been thoroughly examined. The first two theories suggest that heat and mass in the DCD are transferred through a constant laminar film on the packing [38] [1] [4]. The third theory is an add on to the laminar film model, and suggests that heat and mass is also transferred through the creation and dynamics of small droplets within packings [34]. The model and its 4 main submodels are fine-tuned to be able to reproduce the thermodynamics occurring in the experimental setup. The model is tested under different steady state conditions using experiments, to provide insight on the model’s robustness and reliability. The final improved simulation model is used to present conclusions on heat transfer, mass transfer and water production rates for the experimental setup. A brief economic analysis of the system is performed to arrive at an energy price of water for the OTWP experimental system. Although the final energy price for the OTWP setup is quite unfavorable, 14 kWh/m3 as opposed to 2-3.5 kWh/m3 for current desalination systems, tips to improve a possible future pilot facility are proposed. Here high yield and low cost are key requirements, and the design of a future pilot facility needs to be optimized using these two pillars.

This thesis project aims to enable Bluerise to create a 3 [MW] plant for their OTEC system. The current model and lab setup used to create insight into the systems working mechanisms are based on a Kalina cycle configuration. This method uses a working fluid mixture of water and ammonia. After evaporation, the liquid and vapor are separated and the heated liquid is used in a recuperator to retain (some of) the heat and increase the efficiency of the system. The first 3 [MW] test plant that is planned to be built will be using an ORC configuration. This method solely uses ammonia as a working fluid and doesn’t use a recuperator to retain heat. Understanding the effects of liquid separation and re-circulation are important aspects while using this configuration. The working method of the current OTEC off-design model and lab setup will have to be altered to accommodate the ORC configuration. An extensive study on both available literature, the current OTEC off-design model and OTEC Demo lab setup lead to conclude that a gear pump will be implemented to drive the liquid re-circulation from the separator back to the evaporator. Parallel to the gear pump, a one-way valve is installed into the cycle so natural re-circulation experiments can also be conducted. From literature, a hypothesis is made on what the effect on the evaporator heat transfer rate could be by changing the re-circulation rate. The re-circulation rate must not be too high, because increased amounts of vapor bubbles increase fluid mixing and thus heat transfer. The re-circulation rate also must not be too low, because dry-out in the evaporator will occur, reducing the heat transfer rate. The OTEC off-design model that currently exists at Bluerise B.V. is used and expanded upon to accommodate the ORC configuration. The evaporator is changed in more detail, adding a heat transfer correlation and the possibility to calculate the evaporator pressure drop through two phase pressure drop correlations. After implementing the gear pump liquid re-circulation technique, the OTEC Demo can be used to create experimental data. From experiments, it is found that the re-circulation rate does not significantly change the evaporator heat transfer rate between 1.2 to 2.9 re-circulation rate. This is a remarkable result but can be explained by the low flow velocities in the evaporator, which indicate that the heat transfer process in the evaporator is mostly driven by pool boiling heat transfer mechanisms over flow boiling heat transfer mechanisms. Knowing that the re-circulation rate does not affect the evaporator heat transfer rate, liquid re-circulation can also happen naturally, by the liquid column driving force in the separator. Using this technique, a comparison with the Kalina cycle configuration using pure ammonia is made. The evaporator performance is higher in the Kalina cycle configuration, but the ORC configuration net power output is slightly higher. The main reason for this phenomenon is a lower required pumping power for the ORC configuration. The OTEC off-design model in ORC configuration is validated to the experimental data collected. The two phase heat transfer correlations used show to be very mass flux dependent, and applicable to flow boiling evaporative heat transfer. The correlations proposed by Taboas and Han et al. have the best fit to the experimental data. The correlation proposed by Taboas is used to validate the full cycle model. This two phase heat transfer correlation has a consistent negative deviation from the experimental data, causing the full cycle model to be conservative in the cycle performance it calculates. Finally, a scaling analysis is made in support of the efforts by Bluerise to create a 3 [MW] OTEC plant. Using the geometries supplied by Bluerise it is concluded that a 3 [MW] net power output could be achieved, but it heavily depends on the water side pump power needed and the turbine efficiency, which are not investigated in the current research.

In the last decades, the excessive increase in average global temperature related to a massive rise in greenhouse gas emissions showed the world how the fossil fuel society we live in today is drastically modifying and destroying the world we live in and is turning it in an un-habitable planet. Scientist all over the world made it clear that if we stay on the current patterns and we don't reduce drastically our greenhouse gas emissions, we are gonna end up with the extinction of the human species. The urgency of the problem seems to be clear to most people, what we need now are immediate actions to drastically reduce our greenhouse gas emissions. Among all different sectors, the residential sector is one of the biggest contributors to greenhouse gases (GHG) emissions and most of the energy is used for space heating (SH) and electrical appliances. In the specific case of the Netherlands, most energy provided to the residential sector is produced by means of natural gas, and the goal of the country is to replace natural gas with net-zero CO2 solutions. In this thesis work, a solar-assisted ground-source heat pump (SAGSHP) system for space heating for a typical Dutch terraced house is thoroughly investigated. In particular a 115 m2 house with 3 people living in it. The main different components of the system are investigate by looking at the state-of-the-art technology to understand what are the different system components that would be more convenient to use in the Netherlands in terms of efficiency, costs, etc. After the different system components have been selected and a general layout of the system is determined, the different components are designed and modelled using Matlab or Simulink environment. Finally, the whole system is assembled together and simulated in a Simulink environment. The simulation runs over a period of one year using a simulation time step of 6 minutes (0.1 hours). In particular two different cases have been used for the simulation. The base case used is an year where the ambient conditions used (ambient temperature and irradiance intensity) are values averaged over a period of twenty years (1991-2020). The second case is the simulation of a very cold year to see how the system performs in extreme cases. The simulated year is the year 2010. The obtained results are presented and discussed to draw conclusions and future work recommendations. The final goal of this work is to understand the competitiveness of the system with respect to a traditional gas boiler in terms of CO2 emission reduction, performance and costs. From this work it was possible to conclude that the chosen SAGSHP system performs slightly better in colder climates where a higher heat load requirement is needed. From the base case study used in this work, it was concluded that the modelled SAGSHP system can achieve a system seasonal coefficient of performance (SSCOP) of about 3.8 and it can significantly reduce the amount of CO2 emissions generated, up to about 2.8 ton of CO2 every year. From an economical point of view, the system levelized cost of energy (LCOE) is still higher than the LCOE of a traditional gas boiler system due to the high initial investment associated with SAGSHP systems.

To tackle the expected increase in fresh water shortage in the world, alternative water production methods are required. One such a possible method is Ocean Thermal Water Production (OTWP). This thesis continues on the innovative concept of the use of OTEC waste water as a cooling fluid for atmospheric water production introduced in previous work. In this thesis, an experimental study on a structured packed bed condenser column is presented. This work was carried out on an experimental OTWP set-up installed in the Process & Energy lab at the Delft University of Technology. Additionally, a numerical Python model was used to investigate the heat transfer and condensation characteristics of the packed bed column. The condenser function of the Python model was used to compare the prediction performances of different mass transfer coefficient and hydraulic correlations. The Python model simulations were compared both to the predictions of Aspen plus, an established chemical process software, and to the experimental results. The correlation by Olujic et al. (1999) was chosen as the most suitable for the transfer rate and hydraulic behavior predictions for the Python condenser model. A mean average error in the mass transfer predictions of 2.5 % and in the hydraulic predictions of 16.9% was reached in relation to the experiments. outperforms the Aspen plus model, that has respective mean average errors for the mass and pressure drop predictions of 9.5% and 13.0 % for the correlation proposed by Rocha et al. (1993). The Python model was extended with functions that calculate the pressure drop over the remaining necessary equipment for an OTWP plant. The aim of the developed model was to predict the processes in the OTWP condenser column and design a pilot-plant. The model was used to perform a sensitivity analysis on a large-scale column. A preliminary economic analysis identified that reducing the diameter of the condenser column reduces the cost of water production but increases the energy requirement. For an OTWP pilot-plant with a production of 25 m3/day, the chosen column diameter of 6.6 m leads to a system energy requirement of 3.5 kWh/m3 and a levelized cost of water production of 8.08 $/m3. Those production costs can be reduced by an optimization study of the full OTWP pilot-plant.

Absorption refrigeration cycles are energy saving as they can be driven by waste heat instead of electricity. By doing so, they reduce the use of fossil fuels, resulting in a reduction of emissions. However, many challenges exist for the traditional working fluids of the cycle, such as the crystallization problem of the water-lithium bromide pair and the difficulty in separating ammonia from the ammonia-water working pair. Ionic liquids, as novel absorbents in absorption cycles, have attracted considerable attention because of their unique properties like negligible vapor pressure, negligible flammability, thermal stability, low melting temperatures, liquid state over a wide temperature range and good solubility. In this thesis, a thermodynamic model of the ammonia based double-effect absorption cycle in series configuration was used to predict the performance and suitability of nine ionic liquids as potential absorbents. The performance of the ammonia-ionic liquid systems was compared with that of ammonia-water systems and the influence of the operating conditions and the design parameters on the performance was investigated. Furthermore, a method to experimentally determine the excess enthalpy of ammonia and ionic liquid mixtures is proposed and the suitability of using absorption refrigeration on a fishing ship, with ionic liquids as absorbents, is studied. The results show that the ionic liquids [Bmim][BF4], [Mmim][DMP] and [Emim][SCN] used as absorbents in the investigated absorption cycle reached the best performance and could be a promising replacement of water in the ammonia-water working pair. The best performing ionic liquid, [Bmim][BF4], was found to be a better performing absorbent than water in the double-effect cycle.

Of the global energy demand, 20% can be allocated to residential energy demand. Most of this energy is produced by fossil fuels, which raises the importance of energy production in a more sustainable way. In order to do this on the level of residential heating applications, the Dutch government aims to make its residential neighborhoods natural gas-free. An often considered solution is making residential areas all-electric. However, when considering the heating of these households based on electricity, high peaks may occur in the electricity grid due to simultaneous heating at times of high demand. This could cause problems regarding the capacity of the electricity grid. Subsequently, the generation of electricity is nowadays associated with relatively high CO2 emissions, raising the awareness for alternative methods of heating. One of these methods is district heating coupled to (more) sustainable energy sources. A problem occurring with this combination is a possible discrepancy between the supply and demand of energy. Therefore, it could be beneficial to implement thermal energy storage in district heating. This research assesses the feasibility of different configurations of thermal energy storage integrated into district heating. For this research, a case study is conducted in which district heating for a residential area coupled with thermal energy storage is modeled. The model is based on the thermodynamic equilibrium of the network and is able to compute the required characteristics and key performance indicators of the district heating network. For the case study, multiple scenarios have been created which assess different distribution characteristics and heat sources. For reference, an all-electric scenario has been designed as well. The results of the case study show that the implementation of thermal energy storage in district heating is able to lower peak loads on the heat source by two-thirds. This implementation goes paired with an increase in levelized cost of energy of 10-16% and 8-73% higher CO2 emissions, compared to district heating without storage and depending on the characteristics of the district heating net and its heat source. However, for certain heat sources, the advantages of thermal energy storage outweigh the drawbacks or thermal energy storage might even be considered to be inevitable. This is especially the case for renewable heat sources, of which its share in the future energy market is considered to be substantial. Also, the results show that every scenario considering district heating performs better on levelized cost of energy and CO2 emissions than the all-electric scenario. When designing new DH projects, it is key that different available heat sources will be considered and that an accurate trade-off is made between the advantages and drawbacks of thermal energy storage. This research is based on the comparison of various scenarios for a case study. Therefore, it does not focus on finding the optimal parameters for either district heating or thermal energy storage. For finding these optimal parameters, future research must be conducted.

The research presented in this thesis focuses on the use of hydrate slurries in the air conditioning and refrigeration areas. Both experimental and mathematical methods have been used. Hydrate slurries have been suggested as promising cold storage materials that can be used in air conditioning systems due to their high latent heat (193 kJ/kg and 387 kJ/kg for the hydrates studied in this thesis) and positive phase change temperature (12.5 °C and 8.0 °C for the hydrates studied in this thesis). However, large scale industrial applications of hydrate slurries are still very limited. This suggests that more research efforts should be devoted to the demonstration of its advantages.@en