Today’s necessity- and goal to reduce carbon emissions in tandem with finite fossil resources and rising oil prices, demand for an alternative and cleaner energy source to power the world dredging fleet. In parallel, recent research in naval architecture iterates the potential role for nuclear-based propulsion on board of ’energy-intense’ merchant vessels (approx. 20 MWe+ installed power) [16][20][23]. Powering a (large) trailing suction hopper dredger (30.000m3+) by an on-board small modular nuclear reactor would cut direct greenhouse gas emissions by 100%.

The power demand on board of trailing suction hopper dredger is fluctuating continuously. A reactor is typically applied for supplying constant power. The objective of this thesis was to research the transient load capabilities of a nuclear-powered trailing suction hopper dredger.
First, for the on-board nuclear installation, a graphite-moderated high temperature gas reactor was opted for which is cooled by helium gas. This reactor type has a technology readiness level of 9 and small-modular-reactor concepts of this type are being developed. Both the open- and closed helium Brayton cycle concepts show greatest potential for power conversion. It was shown that the reactor, the heat exchangers and the turbomachinery play an important role in both the overall efficiency of operation and the transient load limits of the system as a whole.

Second, a thermodynamic model was built to be able to simulate the effects of different control mechanisms in realising load-following. Bypass- and compressor throttling control performed best and allowed the reactor to ramp down at lower rate, which is a favourable feature. For a 100% reduction in power output, the reactor would have to ramp down to 47% and 34% of nominal power respectively.

Third, it was investigated how the limitations in load-following would effect the operational profile of a HTGR-powered TSHD. The suggested closed helium Brayton cycle cannot perform adequate load following to the fluctuating demand of a conventional TSHD today without an auxiliary source of energy. When keeping reactor ramping rates below 10%/minute, a 25MWe HTGR-powered TSHD would see peaks in power imbalance up to 10 MW. However, a 3MWh ESS was considered to perform power take-in and power take-off. In presence of such auxiliary power source, the operational profile of a TSHD would not have to be changed.

Looking ahead, it is crucial to investigate the impact of repetitive power transients on the controllability and lifespan of both the reactor and other components within the power cycle. Additionally, a more in-depth study of the aerodynamic characteristics of the helium turbomachinery is necessary. Lastly, incorporating supplementary nuclear kinetics analysis could help validate the findings presented in this report. ... Read more

Latent heat storage using phase change materials (PCMs) is a promising technology for storing and recovering waste heat. PCMs offer high energy density and can be tailored for specific melting temperatures, making them suitable for various applications, including temperature stabilization in buildings and thermal management of electronics and batteries. However, a significant disadvantage of PCMs is their low thermal conductivity, which slows the process of charging and discharging thermal energy. This work explores a novel approach to enhance the melting rate of PCMs by incorporating thermally conductive objects (TCOs) within the PCM. The TCO density lies between the solid and liquid PCM densities and is designed to follow the solid-liquid interface. First, an analytical model based on the Stefan problem formulation and a numerical model developed using Ansys Fluent, with locally modified thermal conductivity at the solid-liquid interface, were created to simulate the thermal behavior of the PCM with the addition of TCOs. An experimental setup, consisting of a rectangular enclosure with an organic paraffin as the PCM and hollow aluminum cylinders as the TCOs, was employed to validate these models under purely conductive melting conditions, with heating from the top and cooling from the bottom. Experimental results indicate that the addition of cylinders increased the melting rate by 19% under purely conductive conditions compared to the scenario without cylinders. However, the cylinders enhanced heat flux only within the first 12 mm, beyond which the thermal resistance of the liquid PCM became dominant, preventing further heat flux improvements. During solidification, the cylinders did not move with the solid front and were engulfed at the bottom. In the second part of this work, the developed Fluent model is used to study hypothetical scenarios where a TCO is added to the PCM, but heating comes from the side walls and melting is driven by convection. In this scenario, the inclusion of a TCO at the solid-liquid interface acts as a moving fin, increasing the melting rate by 62% and enhancing thermal power dissipation from 26.5 W to 75.4 W. Future research should focus on experimentally validating this scenario under convective melting, exploring methods to mechanically return the TCO to its starting position for repeatability, and conducting an energy analysis to determine whether the benefits of an enhanced melting rate outweigh the energy required to move the object and the increased manufacturing costs of the latent heat storage system. ... Read more

There is currently a resurgence of interest in nuclear propulsion within the maritime sector, which is reflected by the ambition, as mentioned in the Dutch maritime sector report "No Guts, No Hollands Glorie", to develop a standardized, modular nuclear reactor for ship integration within 10 years. Nuclear energy has the potential to reduce the maritime sector’s contribution to climate change, as it does not emit CO2 during operation. Additionally, in contrary to many other renewable energy sources, nuclear energy offers a high-energy-density power source capable of providing sufficient energy for longer periods of operation. Not only would this improve the strategic autonomy of the Royal Netherlands Navy, but it would also be a solution for the increasing energy demands of additional unmanned systems or advanced combat systems, like high power radars and rail guns.

Implementing nuclear propulsion in future (naval) vessels presents challenges, particularly regarding the dynamic power profile of ships during operation. Land-based nuclear reactors typically operate as stable power sources, which contrasts with the fluctuating power demands of ships, especially naval vessels. This research aims to find a solution for these dynamic power requirements, without the use of energy storage capabilities, like batteries, for peak shaving capabilities.

Based on the expected implementation of a small modular reactor (SMR) by 2034, the Future Air Defender and the Amphibious Transport Ship were selected as potential vessel types of interest for the Royal Netherlands Navy to implement an SMR. Additionally, the high-temperature gas-cooled reactor (HTGR) and the supercritical carbon dioxide (sCO2) recompression power conversion cycle were selected for the nuclear power plant. A dynamic model of the selected SMR and its energy conversion system has been developed to compare its ramp rate with those of conventional naval prime movers, such as diesel engines and gas turbines.

The simulation results indicate that the reactor dynamics alone are insufficient to meet common ramp rates of naval vessels, demonstrating that relying solely on reactor control is not a viable control strategy. However, the implementation of the turbine bypass valve, while operating the reactor at a constant load, provides dynamic power behaviour comparable with diesel engines and even gas turbines. Potential drawbacks include reduced cycle efficiency at part load, as well as significant pressure and temperature gradients within the heat exchangers. The unacceptable temperature increase at the reactor’s inlet was addressed by incorporating a dump cooler into the primary circuit. This research therefore concludes that an HTGR, in combination with an sCO2 cycle and a bypass valve, is capable to provide the dynamic power requirements of a naval vessel.
... Read more

This report analyses the improvement potential of zeotropic refrigerant mixtures on the performance of vapour compression heat pumps integrated into industrial dryers. The report reviews the scope of total global energy consumption and the percentage of this attributable to industry to demarcate application area.

It proposes that by targeting industrial process heating, significant reductions to energy consumption and carbon emission by industry can be achieved. Heat pumps are introduced as the preferred system to accomplish this for temperatures up to 200 ◦C. A performance limitation is identified in the form of heat transfer between process streams that reject and receive heat at non-constant temperatures.

Zeotropic refrigerant mixtures are introduced in heat pumps to improve the interaction with non-isothermal heat sources and-sinks. The considered mixture compounds are limited to future-proof refrigerants and the mixtures are limited to binary ones. Humid air encountered in industrial drying is targeted as one such non-isothermal process stream with a large potential for waste heat recovery. The most prominent industries that use dryers are identified and evaluated as to provide representative operating conditions at which a heat pump integrated dryer would have to work. Heat pump cycles are described both on a cycle scale as well as per component and the most important design aspects and considerations are presented. The methods used to allow heat pumps to interact favourably with temperature glides are presented namely zeotropic mixtures and trans-critical heat pump cycles.

A modeling strategy is proposed to simulate heat pump integrated dryers in large numbers in order to investigate the effects of dryer inlet and outlet conditions as well as refrigerant mixture composition both in terms of constituents and mixing ratio. The total process flow diagram is given and divided into definable thermodynamic states for both the (humid) air as well as the refrigerant. Governing equations for each component are presented and the calculation method for the thermodynamic states is discussed in terms of known state variables and used thermodynamic libraries. Finally a novel heat pump cycle is proposed, motivated by a desire to decouple the glide matching in the evaporator from that in the condenser, that attempts to use the fractionation risk present in zeotropic mixtures as an advantage instead. The criteria placed on refrigerant are presented both within the context of the future-proof limitation, legislative limitation as well as those introduced by the process requirements.
The most promising refrigerant candidates from literature are presented for applications in the defined process conditions. Finally a selection is made of 13 refrigerants namely water, ammonia, (iso)butane,
(iso)pentane, methane, ethane, propane, CO2, propylene, ethylene and hexane. The thirteen refrigerants are combined into 78 refrigerant pairs and modelled using the described modeling strategy. The modelling reveals that using zeotropic mixtures does improve the COP for many refrigerants when compared to their pure cycle performance. For drying at 180 ◦C two heat pumps are proposed at different outlet temperatures. The cycles use 87.5%mol Isobutane mixed with Ethane and 87.5%mol NH3 mixed with Propane for a high temperature and lower temperature outlet respectively. COPs of 3.38 and 3.44 were calculated with PRs of 16.53 and 6.84 for the Isobutane-based and NH3-based cycles respectively. A lower drying temperature of 120 ◦C was explored and here CO2-based mixtures were identified as highly desirable refrigerants due to their non-toxic, non-flammable nature as well as low global warming and ozone depletion potential. The mixtures 87.5%mol CO2-Isopentane and 90%mol CO2-Isobutane were proposed, both feasible with single stage compression and possessing a COP of 3.96 and 4.02. Zeotropic mixtures improved the COP in at least 48 out of 78 possible refrigerant combinations when compared to the pure cycle COPs and allowed the dampening of flammability and toxicity where the pure refrigerant possesses those properties.

It is clearly demonstrated that future-proof binary zeotropic mixtures increase the performance of VCHP-integrated dryers across all relevant temperature ranges, by as much as 21.47%. The highest COPs are found when zeotropic refrigerant mixtures are used together with trans-critical operation. It is concluded that zeotropic mixtures improve the COP of vapour compression heat pump integrated dryers and should be utilised for non-isothermal processes like drying. ... Read more

In recent years, a considerable amount of research has been directed towards making energy generation more efficient to combat global warming. To aid this goal, the use of supercritical fluids (SCFs) is gaining a lot of traction. SCFs have only one phase and experience a sharp variation of thermophysical properties when heated sufficiently. These facts can be exploited to gain several advantages over conventionally used sub-critical fluids. However, the strong property variation in heated SCFs also complicates the flow Physics considerably if the wall heating is strong enough. Further, the flows in such settings are often turbulent and spatially developing. For these flows, a strong variation of properties can lead to a modulation of turbulence, which the conventional turbulence models can not predict well. This thesis is an attempt to better understand how spatially developing heated supercritical turbulent flows behave and use this understanding to improve turbulence model predictions.

In this thesis, we investigate two supercritical heated developing turbulent flows from Nemati et al. (2015). One case is oriented horizontally and the other is oriented vertically. The latter has an additional effect of buoyancy resulting from its vertical orientation and strong density variation near the wall. We analyze how the strong property variation modulates the turbulence in both cases. Then, we assess if Semi-Local Scaling (SLS) and Apparent Reynolds Number (ARN) theories can characterize the modulated turbulence. Further, we propose a methodology to make use of ARN by itself, and in combination with SLS to improve turbulence model predictions.

The results indicate that ARN theory provides a robust way to sensitize conventional turbulence models to the additional effects arising in supercritical heated developing turbulent flows due to property variation. Additional research in turbulent heat flux modeling is deemed necessary to improve the model performance further. ... Read more

As a big contributor to the the global emissions, the maritime sector strives to bring down its greenhouse gasses and hazardous emissions by enforcing increasing strict rules on the exhaust gasses. This gives major challenges to the maritime sector to develop greener modes of transportation. This report investigates the in-cylinder starting conditions of spark ignited gas engines, as the starting conditions have a large influence on the efficiency and NOx emissions of gas engines. The investigation is based on experiments performed on a Caterpillar G3508 gas engine. These experiments gave an insight on the starting temperature, pressure and residual mass. With the acquired knowledge on the starting conditions, we improved the induction and volumetric efficiency prediction of a state of the art 0-dimensional engine model [15]. Another contribution of this paper is the development of a way to establish the volumetric efficiency from the amount of oxygen in the exhaust gas, for a natural gas engine. We used this method to check the improvements made to the engine model. Out of the performed experiments, we concluded that the induced inlet mass temperature decreases with increasing power or mass flow. The insight found about the starting pressure for this engine is that the trapped pressure increases in relation to the manifold pressure with increasing power or mass flow. Together with an improved residual mass prediction, these insights resulted in an increase of the volumetric efficiency prediction accuracy by 2% at low powers and 10% at high power. ... Read more

To achieve the emission goals set out by the International Maritime Organization in 2018. Low or zerocarbon fuels will have to be used. Ammonia is considered to be a possible candidate since it doesn’t contain carbon. This thesis will attempt to study two methods that characterize the closed-cylinder process of an internal combustion engine; the Seiliger approach and Wiebe function. Two things are the main focus of this thesis. Namely, the application of these methods and how this process will be different for ammonia-diesel combustion compared to diesel combustion. The application will be done for a two-stroke compression ignition engine. The operating conditions that are considered are four load points 20%, 40%, 60%, and 100% at a constant engine speed. The application of this method means building an anti-causal and causal simulation model using Matlab Simulink. Both models simulate what happens in one cylinder during the closed-cylinder process, require the engine parameters as input, and produce the same results. The anti-causal model processes the pressure as a function of the crank angle to determine the combustion reaction rate. The causal model simulates the combustion reaction rate using a Wiebe function to determine the pressure. The Wiebe function is determined based on the reaction coordinate produced by the anti-causal model. By using the Wiebe function, the causal model produces smoother results than the anti-causal model. The Seiliger parameters are determined by using a Newton-Rhapson solver with the maximum pressure, maximum temperature, indicated work, and heat input as equivalence criteria. The results produced by this thesis generally show that the constructed method can produce accurate results. However, this accuracy is correlated to the operating conditions of the engine. As for the changes necessary for ammonia-diesel combustion. These changes have been provided on a conceptual level, with conceptual meaning in terms of equations and assumptions. These changes have not been implemented into a computer model that has been verified and validated. The fundamental difference for the constructed method according to this thesis is the fact that the combustion parameters; start and end of combustion for the two fuels have to be incorporated in the combustion model used for the anti-causal and causal model. This change has to be made, along with assumptions that the injected fuel evaporates and combusts almost simultaneously. This assumption is considered to be highly questionable for ammonia. ... Read more

The Nuclear Research and consultancy Group (NRG) performs CFD simulations to improve the safety of nuclear installations and conducts research leading to new computational methods. One of the problems encountered in nuclear installations is that vital parts of the reactor, such as the fuel rod bundle, corrode over time. Corrosion leads to roughness elements on the surface which affect the heat transfer. To increase safety and reduce costs, it is of paramount importance to predict the heat transfer accurately when the surface is rough. The effect of roughness on a flow is an increase in both skin friction and heat transfer. Current models rely on the Reynolds analogy to calculate the heat transfer. Because in most applications pressure has no effect on heat transfer, it is often overestimated. In this thesis the accuracy of RANS modelling with respect to predicting heat transfer rates from or to a rough wall has been investigated.

It was found that a model for Low Reynolds Number meshes showed promising results. A downside of a RANS simulation on a Low Reynolds Number mesh is the increased amount of computational time due to fully resolving the velocity and temperature profiles compared to one on a High Reynolds Number mesh where wall functions are used. Therefore the model has been applied on several High Reynolds Number meshes and was compared to DNS results from literature. The results clearly showed that the mesh size was of influence on the predictions. However, a possibility was identified to reduce the mesh size dependency. The damping function was found to be responsible for this dependency and was reformulated using DNS data, resulting in a fitted equation for two different Prandtl numbers. The calibrated damping function which was made for a Prandtl number of 0.7 was validated with experimental results. It was found that the adjusted model could predict the Stanton number accurately and that the mesh size dependency was greatly reduced.

For future research it is recommended that the damping function should be calibrated for other Prandtl numbers as well, so the different damping functions could be combined in a single Prandtl dependent equation. ... Read more

In this master thesis several novel DEIM formulations are proposed that enable the construction of non-linearly stable hyper-reduced order models (hROMs) of the incompressible Navier-Stokes equations. The hROMs have the same mass, momentum and energy conservation properties as the previously proposed ROM, but they do not suffer of prohibitively expensive computational scaling when the number of POD modes is increased. The first of the proposed methods is the least-squares discrete empirical interpolation method (LSDEIM), which is based on a constrained minimization. The second method is the Sherman-Morrisson discrete empirical interpolation method (SMDEIM), which applies a rank-one correction to the conventional DEIM to conserve energy. The third method is the decoupled least-squares discrete empirical interpolation method (DLSDEIM), which is a generalization of the LSDEIM that allows increasing the size of the measurement space. All methods result in structure-preserving DEIM formulations that have an equivalent computational scaling as the conventional DEIM, but provide provably stable, structure-preserving hROMs. Furthermore, the use of the principal interval decomposition (PID) in the construction of the reduced and DEIM spaces is considered to beat the Kolmogorov barrier. ... Read more

To anticipate for future demand of sustainable liquid fuels, Zero Emission Fuels B.V. develops a solar powered micro plant which produces methanol from water and carbon dioxide captured from outside air. An intermediate step in this process is the electrolysis of water to create hydrogen which reacts with carbon dioxide to methanol. This study encompasses an integration of the pressurised alkaline electrolysis system, in which problems observed in previous generations of the electrolyser have been solved and functionalities have been added. In addition to that, electrolyte samples are taken after different periods
of operation to investigate electrolyte deterioration over time.

A new Balance of Plant (BoP) has been designed, realised and tested. Eight new features to the system can be distinguished, two of which are included to add functionality: the degasser to decontaminate the carbon dioxide-rich
feed water and the pressure booster to replenish the consumed water at system
pressure. The other features are integrated to enlarge the operational envelope, the determination of which was central to the experiments conducted in this research.
Experiments are conducted to find and characterise the four limitations to the operational envelope: the relative valve opening duty (RVOD), flow stagnation, temperature control and crossover.

The RVOD experiments showed deviations from the modelled valve opening cycles, attributed to additional pressure drops, valve opening interference and smaller discharge volumes. Subsequently a corrected model is presented to improve valve cycle time predictions.
Flow stagnation was investigated at various current densities, pressures and temperatures using camera images and a characteristic temperature response to establish flow stagnation. The results showed a minimum volume flow rate decrease in comparison to the previous system, expressed in parameter 𝑋 which decreased from 3.4 to 0.74 A K bar^-1 cm^-2. The minimum volume flow rate decrease is attributed to the larger number of cells and the increase of the height difference between the stack and buffer tanks.
In the temperature control experiments, steady state temperatures were monitored at different current densities, with and without crossflow fan operation. This resulted in a temperature control map, in which the reachable temperatures for different current density are depicted. Furthermore, electrolyte mass flows are determined and pressure dependency of temperature control was investigated at low current densities, concluding that steady state temperatures are independent from pressures in the 10 bar to 50 bar regime. 
Hydrogen crossover was tested by taking gas samples at different operating conditions and subsequent gas composition analysis in a gas chromatograph; oxygen crossover was determined by an oxygen sensor implemented downstream the hydrogen exhaust. All steady state crossovers values were found to be below the safety limits, concluding that crossover is not limiting in the acquired system on all possible operating points. Overnight diffusion crossover experiments showed that maintaining the system under pressure overnight, keeps crossover values below the safety limit.
In addition to the operational envelope, complementary general characteristics such as power consumption and efficiency are presented and compared to industry and literature. On top of that, unexpected findings, design deficits and other relevant phenomena are described to complete the perspective on system performance and behaviour of the electrolysis system. Due to the electrolyte mist purged into the degasser and pressure booster, the electrolyte deterioration experiments are deemed inconclusive. Moreover, a demister is found to be an essential system feature to include in the next generation electrolyser, because both degasser and pressure booster were damaged by the electrolyte spill. ... Read more

Capturing CO2 directly from the air has gained wide attention as it is one of the possible solutions to mitigate the risks of climate change. Zero Emission Fuels (ZEF) is a start-up in Delft that develops a small-scale plant to produce methanol from sunlight and air only. CO2 and H2O are captured from the air by a direct air capture unit that operates continuously by means of an absorption and stripping column. Liquid amines are investigated as chemical sorbent. In this work, the stripping column is characterized and optimized for the liquid amine tetra-ethylenepentamine (TEPA). A vapor-liquid equilibrium based stage-by-stage stripper model was established using mass and energy balances for each stage individually. A number of input parameters was specified to understand the effect of those parameters on the performance of the stripping column. The parameters include; composition, temperature and mass flow rate of the feed, number of stages, H2O reflux ratio, temperature of the reboiler and absolute pressure of the column. The mass balance was solved according to the Rachford-Rice equation while using bisection as numerical root finder. To validate the stripper model, experiments were performed for varying configurations regarding the input parameters mentioned above. For this, a trayed stripping column with bubble caps, was build and adjusted according to the experimental plan. Furthermore, single stage kinetic experiments were performed at 115 °C and 950 mbar to find the limitations of the desorption process inside the column. Subsequently, the Damköhler number was estimated to understand the effects of reaction rate and diffusion during the process. Sensitivity analyses were performed to find the effect of input parameters on the performance of the stripping column. The effect was measured in terms of; CO2 concentration in the outlet stream, cyclic capacity of the liquid solvent, CO2 and H2O vapor ratio in the top stage of the column and energy demand per desorbed mol of CO2. Based on the results, a tool to predict the performance of the stripper in an elementary way was produced. Based on the kinetic experiments, it was found that a typical hold up time that is required for the system to reach equilibrium was measured at 600 s. This number was used to estimate the liquid hold up volume per stage in the final stripper design. The experimental and model results were combined in a new stripper design considering the operating conditions stated by ZEF. The 5 stage column operates at 1000 mbar and a reboiler temperature of 120 °C. The feed was preheated up to 105 °C and the mass flow rate was determined at 0.31 g/s resulting in a hold up volume of 187 ml per stage. The cyclic capacity of the system equals 3.3 mol CO2 per kg TEPA and the energy demand was found to be 279 kJ per mol CO2. In addition, a new design for ZEF's direct air capture system was presented where the absorption column is modelled as a black box. An heat exchanger was implemented to minimize the energy demand of the system, which resulted in a lowest energy demand of 2319 kWh per ton of CO2. This is slightly higher than the DAC energy demand of companies like Climeworks, Carbon Engineering and Global Thermostat, but could potentially decrease when optimizing the system. ... Read more

The process in which a smooth laminar flow transits to a chaotic to a chaotic, turbulent state, is a topic of particular interest in the sectors of energy technology and aerodynamics. To study the different paths that can be followed during the transition process, various tools and methods have been developed. A preliminary investigation of the response of a laminar flow to an internal or external disturbance can be performed by applying Linear Stability Theory principles. In the recent years, the Direct Numerical Simulations of flows offer a more insightful method to study the transition process, since the flow fields are numerically solved using high computational power. Previous research has primarily focused on the stability and transition of Ideal Gas flows, with little attention to the effects of a highly Non-Ideal behaviour. The present work aims to develop a DNS code that can be used to investigate the stability of compressible boundary layers in the vicinity of theWidom Line. For the initialization of a DNS, a two dimensional base flow profile is required. For the calculation of the base flow, a self-similar solution is obtained, using a MATLAB script that has been developed for the purpose of this study. The DNS code is developed in FORTRAN. An inviscid characteristic wave analysis is utilized for the implementation of the boundary conditions, along with numerical sponges to avoid reflections. To trigger the instabilities, periodic suction and blowing is incorporated. For the simulations of non-ideal fluids, a thermodynamic table interpolation tool is incorporated. For the validation of the results obtained by the DNS code, an in-house MATLAB script is used to for the calculation of the growth rate and fluctuation amplitude profiles using LST. Initially, the FORTRAN code is used on ideal-gas simulations, to investigate how different computational parameters will affect the flow field. The parameters are related to mesh resolution, boundary conditions and numerical sponges. To investigate the stability of non-ideal fluids, cases of different free-stream temperatures and Eckert numbers are simulated. The free-stream temperature is altered to control the non-ideal gas effects, whereas the Eckert number is used to control the compressibility effects. In general, the flow is stabilized as non-ideal gas and compressibility effects become more prominent. However, a second unstable mode is observed in the case where the temperature profile crosses the pseudo-critical point. This second mode has a higher growth rate of instabilities, compared to the first mode. All the results are validated using the LST predicted profiles. ... Read more

As the shipping industry needs to become greener, it has to move away from fossil fuels. For deep-sea shipping, ammonia is marked as a high potential fuel. The AmmoniaDrive concept feeds the anode-off gas from a Solid Oxide Fuel Cell (SOFC) and additional ammonia into an Internal Combustion Engine (ICE). The exhaust gas coming from the ICE can contain relatively large amounts of NOx, NH3 and N2O. This research focuses on reducing all these substances using Selective Catalytic Reduction (SCR) in steady-state conditions. A 1-d single-channel model is used to model a Vanadium, Iron and Copper catalyst. The levels of pollutants entering the atmosphere are compared to the current legislation for ships, where NOx emissions are limited. Furthermore, new legislation is proposed that also limits the NH3 and N2O emissions of the powerplant. Meeting these limits is much more complicated than meeting the current legislation. The presence of N2O in the exhaust can be problematic as only the Fe catalyst can reduce N2O with temperatures above 350/400 degC. The Cu based SCR has the highest potential for AmmoniaDrive as it can meet the newly proposed limits with exhaust temperatures below 200 degC, this allows for an efficient driveline. ... Read more

Organic Rankine Cycle (ORC) Power Plants can be of greatimportance in the energy transition as they are suitable for converting wasteheat to power and can utilize renewable energy for their operation. To improvethe efficiency of ORC Power Plants, the physical phenomena inside thesemachines must be understood. Understanding the boundary layer of complexorganic fluid flows in these systems is crucial, as it is estimated to beresponsible for one-third of the losses in turbomachinery. n this thesis, two-dimensional steady state boundarylayer flows of nonideal gas have been investigated numerically. The objectivewas to find the influence of complex fluid nonideality, characterized by idealgas departure, on boundary layer flows. In particular, a high-speed densevapour expansion of organic fluid Hexamethyldisiloxane (MM) inside a de Lavalnozzle test section has been studied. The nozzle is part of a measurementcampaign to collect experimental data with the purpose of validation andcalibration of Non-Ideal Compressible Fluid Dynamics (NICFD) software.  MATLAB program was developed for solving thetwo-dimensional steady state boundary layer equations including generalthermophysical properties. Transition prediction methods, the algebraicCebeci-Smith turbulence model (CS-model), and state-of-the-art thermophysicalmodels were implemented. The program was verified and validated for air withliterature. The turbulence model was validated with experimental data oflarge-scale zero pressure gradient adiabatic flows. The results match for theentire Mach-number range from 0.2 up to 2.8. The program also proved to becapable of predicting the turbulent boundary layer along a flat wall inside ade Laval nozzle expanding air. Deterministic simulations of the boundary layer along thecurved wall surface of the aforementioned nozzle expanding MM were performed.The results showed a larger decrease in the newly defined property C_e inthe core flow along expansion compared to air. In contrast, the propertygradients; namely density ratio c and Chapman-Rubesin parameter C,inside the boundary layer were found to be negligible. Furthermore, the resultsshow that the influence of the pressure history upstream of the nozzle throatis relatively small or even negligible in the diverging nozzle section. Theboundary layer displacement thickness for both laminar and turbulent flow wasfound to be negligible compared to the nozzle cross section, which results in anegligible effect on the nozzle core flow. The program needs further validation for flows departingfrom ideal gas. First, the flow condition in de Laval nozzles, laminar orturbulent, needs to be obtained by conducting experiments. Then, sensitivitystudies need to prove if the inviscid nozzle design is a robust design forviscous flows too; namely, being insensitive to changes in total inputconditions, uncertainties in closure coefficients, and variations in upstreampressure history. ... Read more

Today’s renewables, wind and solar power, have a fluctuating nature, making the grid less stable.However, with the increasing share of intermittent sources of renewable power, novel options have to be created to stabilize the power grid. One of these options is energy storage via the conversion of excess power to hydrogen, during periods of high generation from wind and/or solar. In periods of power shortages hydrogen is converted back to power. In the literature fossil fuelled turbine cycles have been studied extensively, furthermore multiple fuelcell turbine cycles have been modelled. However, models with hydrogen and oxygen fuelled turbine cycles and fuel cell turbine cycles are scarce, leaving opportunity for further optimization of modeled hydrogen and oxygen fuelled cycles. The application of pressurized H2/O2 can lead to several improvements over conventional thermodynamic cycles and fuel cells. In this work, a number of high efficiency hydrogen and oxygen fuelled thermodynamic cycles, based upon the Graz cycle and the Toshiba Reheat Rankine cycle, both a coupled closed Brayton cycle with a Rankine cycle, are investigated. urthermore, the following thermodynamic improvements are proposed to fit the Graz cycle: an increased TIT (turbine inlet temperature), the use of a reheat combustor (the inclusion of a second combustor), condensate preheating and hybrid cooling (a combination of open loop and closed loop cooling) of the high temperature turbine blades. All upgrades together lead to an efficiency of 75% LHV. The rise of efficiency of the individual upgrades summed up is lower than the rise off all upgrades together. This is due to the fact that adding reheat and increasing TIT introduce extra high temperature turbine blade cooling needs and losses, which an improved cooling method counteracts. For this reason, the cooling method used is rather influential. Therefore, two cooling methods, open loop cooling and hybrid cooling, used in the Graz and Toshiba cycle respectively, are studied in this thesis.Next to the thermodynamic improvements, an electrochemical improvement is studied, by adding fuel cell systems to the turbine cycles. Multiple fuel cells combinations are studied: a single low temperature solid oxide fuel cell (SOFC) and a low temperature, intermediate temperature and high temperature SOFC in series. Moreover, the type of fuel cell cooling is investigated, both cooling by adding steam to the cathode and recirculating excess oxygen in the cathode are studied. The addition, of a triple SOFC cooled by oxygen recirculation, to an upgraded Graz cycle leads to a potential efficiency of 84% LHV. This efficiency is reached at a relatively low fuel cell fuel utilization of 58%. In this study the turbine cycle is not fully adapted to the fuel cell system or vice versa. Both systems are adapted to each other, leading to the unique triple fuel cell system operating in series, which is more easily coupled to a turbine cycle and can operate at an overall higher SOFC utilization, compared to a single fuel cell. However, from the fuel cell side 2 of the 3 fuel cells are less electrochemically favorable, as only one of the three fuel cells can operate in the best conditions. The overall system efficiency of the combined multiple fuel cell in series system with a turbine cycle, however is most efficient. ... Read more

Energy storage systems are an emerging field of interest for the future of electrical grids. With the rapid growth of renewable but intermittent sources of electricity, energy storage systems can help smooth the variations, making the grid more stable and reducing the need for maintaining an overcapacity of power production infrastructure. Among energy storage solutions, power-to-chemical storage is of particular interest due to the high energy density of chemicals and seasonal storage capabilities. Developments made in power-to-chemical technologies can also go a long way towards making the transportation and chemical industries sustainable. The chemical considered in this work is ammonia (NH3), which has advantages of being an easily liquefiable fuel, and has also been in industrial use for over a century. This thesis project aims towards the development of an efficient power-to-ammonia energy storage system using reversible solid oxide cells. The system designed in this thesis is based on direct ammonia utilisation in fuel cell mode, and steam electrolysis coupled with Haber-Bosch ammonia synthesis in the electrolysis mode. A steady state process model is designed in Aspen Plus. This is followed by extensive thermodynamic exergy analysis, used as the basis for the further design and optimisation of the system, with a goal to maximise the round trip efficiency. Exergy analysis is used to identify the sources with most scope for improvement.
The final system can attain a maximum round trip efficiency of 61.20 %, improved from a basic system efficiency of 19.79 %. The maximum round trip efficiency is comparable to values reported in recent times for thermodynamically studied models from literature using other fuels, such as 56.72 % for methanol. The optimised system attains high efficiencies without the need for thermal energy storage or an afterburner. Further, it is demonstrated that the designed system is efficient enough that heat integration across modes with high temperature energy storage does not provide any significant benefit. ... Read more

Heat transfer via thermal radiation is a common occurrence in industry; be it in flue gas, boilers, reactors, or in supersonic combustor such as in a scramjet propulsion.
Numerous studies have been done regarding the phenomena interacting with thermal radiation in different types of turbulent flows.

For compressible flows the effect of thermal radiation on the turbulent field via Turbulent Radiation Interaction (TRI) has been research to a lesser degree than for incompressible flows. Therefore, a more in-depth study on the impact of optical thickness in compressible flows should help create a better understanding regarding this.
This study consists of an investigation into the effect of thermal radiation in a non-reacting supersonic channel flow where the optical thickness of the fluid is changed.
The fluid dynamics is simulated using a Direct Numerical Simulation (DNS) code for compressible turbulence and for the thermal radiation a grey-gas Finite Volume Method is used. A fictitious fluid is used with two different Planck numbers (Pl = 0.1, 0.01). Furthermore, for cases with Pl = 0.01 the constant absorption coefficient is varied between κ = 1, 5, 10.

The effects of thermal radiation on the temperature and density fields are discussed. Changing the optical thickness via the absorption coefficient shows a strong change in the behaviour of the fluctuating fields.
Compressibility is shown to be affected by thermal radiations, where a stronger thermal radiation characterized by a high optical thickness and low Pl number show characteristics of an incompressible flow while being supersonic.

A model to determine the fluctuating incident radiation developed for high optical thickness incompressible flows is applied to this study as-is to investigate if the model is suited. It is shown that the assumptions made for the model, especially regarding thermal structures size, do not hold for compressible fluids and a different approach is needed.
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Large quantities of heat stored in geothermal aquifers can be of interest to satisfy above-ground heating demands. With the use of heatpipes, placed into the aquifers, heat may be passively extracted. Vertical two-phase thermosiphons are considered in this study. As a result of a local increase in the saturation temperature in liquid pools, heat can only be transferred in the falling liquid film. The aim of this work is to investigate film heat transfer and its limitations at varying boundary conditions in the evaporator of a vertical experimental setup. An initially homogenized film is studied in a separate film heating section, in which a specific distribution of controlled band heaters and temperature transmitters enables the sensing of local film heat removal behaviour in the heatpipe. With increasing degrees of wall superheating, the mean film heat removal rate has been found to increase. Locally, beyond some degree of superheating, the heat transfer rate stagnates with increasing Jakob numbers, possibly as a result of film dry-out. As a result of such local behaviour, the slope of the mean heat transfer rate curve decreases with increasing Jakob numbers. The onset of dry-out, characterized by an increase in the intermittency of the results, has been studied by varying the initial liquid flow rate to the heated section. Both the initial film flow rate and the degree of superheating have been found to be of significance for the onset of film dry-out. Film dry-out takes place at flow rates less than some critical flow rate. The local heat removal rate decreases significantly if the initial film flow rate is decreased beyond the critical flow rate. The critical flow rate has been found to increase with increasing rates of superheating. The significance of the saturation temperature on the film heat transfer rate has also been studied in this work. The film heat transfer rate has been found to decrease with decreasing saturation temperature, for all in this study considered degrees of superheating. The steepest decline in heat transfer rates with decreasing saturation temperature is found for the smallest degree of superheating in the analysis. At last, the possibility of film re-distribution following dry-out has been considered. Melamine foam homogenizer rings, inserted in the film flow path, have been found to decrease the degree of film thickness variation in initially inhomogeneous films to some extent. Homogenized films were found to be able to transfer a greater amount of heat than films that had not been re-distributed.
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Heat pipes are typically used in the semiconductor industry. This means that the scale of these heat pipes is typically in the order of centimeters. Zijm suggests that heat pipes could be used for geothermal applications, but literature is lacking. To further investigate the geothermal application of heat pipes, a large scale heat pipe is built. This thesis gives an insight in the typical design challenges that one faces when constructing a heat pipe of this scale. The heat pipe that is constructed can support a heat flow of 10 kW. The heat pipe is constructed from mainly 54 millimeter copper and glass pipes. The evaporator section is 1.5 meters long and facilitates controlled electric heating. Then follows a 4 meter long adiabatic section. The condenser section is 2.5 meters long. The total length of the heat pipe is 9 meters. The individual sections are held together by EPDM connectors. The dimensions of the heat pipe are compared to the operational limits posed by the Engineering Sciences Data Unit. Then the thermal resistances of the heat pipe sections are calculated and afterwards validated. The interfacial thermal resistance between the electric heaters and evaporator wall was reduced by applying thermal conduction paste to the band heaters. It was found that at coolant flows of 1000 l/h and higher, the vapour temperature in the heat pipe drops significantly. The drop in temperature facilitates a higher heat flow through the heat pipe. Also, the resistance across the evaporator and the condenser section gets smaller for higher coolant flows. The results found are supported by theory and formulae from the Engineering Sciences Data Unit. ... Read more

Tata Steel employs physical vapour deposition (PVD) as a novel galvanization technique in their line production to prevent corrosion. In this process, zinc is evaporated in a vapour distribution box (VDB) and directed via nozzles into a vacuum where it is deposited on a steel substrate. In order to reduce stray deposition, achieve high and uniform mass flow rate from the nozzles and avoid condensation, understanding of the flow phenomena in the VDB and nozzles are necessary. Seeing that the PVD process is carried out at high temperatures in vacuum which makes it infeasible to experimentally characterise the flow for optimization purposes, thus, this research utilizes computational fluid dynamics (CFD).

In this study, the flow behaviour of the zinc vapour in the VDB and nozzles are investigated by solving the fluid governing equations numerically using finite volume method (FVM) in openFOAM. This analysis is done using the pressure-based sonicFoam solver to cope with the subsonic flow in the VDB and supersonic flow in the nozzles. The mass flow rate was compared to the ideal isentropic expression and experimental results. Regions in the set-up with high probability of condensation was investigated using a four coefficient Antoine equation.

A uniform pressure build-up in the VDB enabled uniform deposition. Around the corner of the inlet channel, a stable recirculation pattern affected the nozzle flow, however, this effect reduced as the outlet pressure decreased. The simulated total mass flow rate was greater than the experimental data by a factor of four possibly as a result of numerical errors and experimental stray depositions. And the simulated nozzle mass flow rate was less than the analytical isentropic expression by a factor of five due to the nozzle viscous boundary effect, and VDB wall heating. The mass flow rate from the nozzles decreased with increase in distance from the inlet channel. However, the nozzles far away are less likely to form zinc droplets as compared to those close to the inlet stream. For scale-up under the same conditions, it is expected that non-uniformity would be pronounced and the effect of the small eddies would become more significant. Thus, the simulation of the PVD process gives a qualitative description of the flow and a first approximation for the mass flow rate. To further improve the mass flow prediction, the sensitivity of the mass flow rate depending on the melt temperature and inlet velocity boundary condition should be studied in future works. ... Read more