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.

The substantial energy consumption driven by industrial and technological advancements, coupled with rapid global economic growth, has led to significant environmental issues, necessitating investment in energy-saving mechanical devices. Compression resorption heat pumps (CRHPs) are particularly important due to their efficiency across a wide temperature range and superior heat recovery via resorption. The twin-screw compressors in these heat pumps play a critical role, with wet compression often used to manage temperature and prevent overheating through heat transfer from vapor to evaporating water droplets. Understanding the complex turbulent multiphase flows within these compressors requires both experimental and numerical approaches.

This research simplifies the geometry of twin-screw compressors to focus on key features such as suction and discharge fluid domains and screw rotors, omitting external leakage and heat loss due to internal friction. Stationary fluid domains are meshed using Ansys Meshing and Fluent Meshing, and their grid quality and compatibility with Ansys CFX are compared. The narrow and irregular screw domains are meshed in TwinMesh using a ”mixed” method, fixing nodes on the female rotor while allowing movement on other curves. The combined meshed domains are then imported into Ansys CFX, where rotational reference frames and boundary conditions are set, preparing for mesh independence studies and flow analysis of both single-phase airflow and ammonia-water multiphase flows to verify the effectiveness of wet compression. Additionally, the influence of gap seals with changeable diameters, which partially recirculates the outlet mass flow back into the suction chamber, on global pressure and mass flow rate is discussed. The simulated results of volumetric efficiency and compressor power consumption are compared with Marina’s experimental data to further verify its reliability.

The study delves into the critical necessity of long-duration energy storage to ensure the consistent reliability of electricity derived from renewable sources. Numerous technologies have emerged to address this need, enabling the storage of surplus energy generated by renewables in diverse materials, taking the forms of sensible or latent heat. The comprehensive analysis explores these various techniques in detail, providing a thorough examination of their respective advantages and disadvantages. High-temperature TES emerges as a pivotal component, particularly within CSP. This storage capability becomes imperative for maintaining a seamless and predictable power generation process, especially during periods of limited or intermittent sunshine, coinciding with high electricity demand and costs. Presently, CSP plants predominantly employ sensible energy storage in molten salt, which requires substantial salt volume, two large tanks, or a single tank system. A detailed study is conducted on a similar type of TES system using a PCM as an insulation to minimize the heat losses from the storage tank. The impact of the PCM layer in minimizing the heat loss is analyzed via an analytical model and CFD simulations. The cost incurred for the PCM is further compared with the cost of electrical heating.

The utilization of waste heat from data centers in low-temperature district heating networks has emerged as a promising trend in the pursuit of enhanced energy efficiency, sustainability, and environmental stewardship. Data centers, known for their significant energy consumption and associated greenhouse gas emissions, have the opportunity to transform into energy providers rather than mere consumers by utilizing their waste heat. This innovative strategy has already gained traction in the Nordic regions, where the waste heat from data centers is harnessed to heat buildings and communities, thereby decreasing reliance on fossil fuels and cutting carbon emissions. Through leveraging waste heat, data centers can markedly reduce their environmental impact, thus aiding in the promotion of a more sustainable future. This transition towards waste heat utilization is essential for the data center sector to reach its net-zero energy targets, alleviate its environmental footprint, and support the global transition to a low-carbon economy. By optimizing energy efficiency, data centers can become a crucial component of sustainable urban development, fostering a healthier environment for future generations.
This report investigates the potential of utilizing residual heat that is continuously produced by the data centers by incorporating low-temperature district heating systems in the Amsterdam neighbourhood. The research highlights the possibility of data centers as a dependable source of waste heat and its integration into low-temperature district heating networks. This will thereby contribute to a more sustainable and energy-efficient future. The study scrutinizes the feasibility of waste heat utilization in a detailed manner, down to the component level. The results from the study presented here are discussed at a component as well as, a system-wide scale. Moreover, the paper elaborates on the potential of low-temperature district heating networks in Amsterdam neighborhoods undergoing upcoming refurbishments involving improving the housing insulation and a shift towards addressing energy poverty. The conclusions drawn from this research have the potential to encourage similar research endeavors aimed at large data centers across diverse regions.

Coolworld Waalwijk, a cooling machines rental service experiences marginal growth due to the rise of cooling systems for temporarily use. Their testing facility is heavily occupied for testing systems up to 800 kW. Besides the willingness to more sustainable practices, the urge rises for implementation of new energy solutions to their 500 MWh annual consumption for both heat and electrical demand.

Currently, investments in solar-generated energy have become cheaper than fossil fuel alternatives and the rise of newly developed technology such as PVT panels is ever-increasing. This is especially relevant when considering the PV energy generation losses that occur when exposed to high temperatures. This is where Coolworld comes in. In seeking a sustainable alternative energy resource, their residual cold could actively cool solar panels, enhancing their performance.

This master's thesis aims to gain insight into the energy-intensive processes and losses at Coolworld Waalwijk's testing facility and to identify sustainable solutions. With the outcome, an Energy Management Strategy (EMS) will be created, Additionally, it includes an analysis of a PV/Thermal system, with Coolworld as a case study.

The growing consumption of fossil energy resources increases greenhouse gas emissions (GHG). To meet the industry sector's target of reducing GHG emissions by 49% in 2030, relative to the levels in 1990, there is a need for energy storage. Energy storage offers a potential solution to enhance the utilization of renewable energy, by addressing the intermittent nature of these sources. This study includes a conceptual design for three Thermal Energy Storage (TES) materials, steel slag, phase change salt, and molten salt, able to generate steam in the industry (4-20 bar). Moreover, this study attempts to contribute to faster commercialization of the phase change materials, by aiming to contribute to a thermal conductivity improvement method. The thermal conductivity limits the discharging and charging ranges nowadays.

The concept designs are based on a fluctuating steam demand pattern provided by Arcadis. Two storing modes are extracted, a stand-alone thermal energy source which can meet a 12-hour steam demand and an energy source intended for peak shaving. Based on literature, the storage configurations, with the associated key parameters are extracted, for each material, to attain an estimation of the dimensions and losses. Due to the inflexibility of literature on phase change salt, a semi-empirical model is developed. With this model, the temperature of the heat transfer fluid (HTF) temperature at the outlet of the storage can be calculated based on various input parameters. The input parameters include the type of phase change salt, type of HTF, mass flow rate of the HTF, and the dimensions of the storage. The HTF outlet temperature in combination with the mass flow determines the discharge power. Based on the output of the TES, an economically optimized design, of a shell and tube steam generator, using AspenEDR software, is conducted.

The results for the stand-alone case showed almost similar volumes for the steel slag and phase change salt. The molten salt storage solution was larger based on the requirement of two tanks, a hot and a cold one. Furthermore, phase change salts resulted in the highest total stored energy, which is a measure of the inability to completely discharge the phase change storage in combination with a maximum temperature drop of the HTF outlet temperature. An increase in the thermal conductivity of the phase change salt can reduce this problem. Another advantage is the possibility of using any HTF for charging and discharging the phase change salt. Due to diffusion inside the TES upon partly charging and discharging, steel slag and phase change salt seemed not suitable for peak shaving.

Next, the focus is on increasing the thermal conductivity of the phase change salt. A readily available, stainless steel, wire mesh implemented in the phase change salt, at the shell side of a shell and tube storage, already yields a 10% increase in overall discharging performance. A graphite coating, applied on the mesh, could enhance the corrosion resistance, thereby enabling the the use of a higher conductive steel, such as carbon steel. Furthermore, could a graphite coating increase the overall thermal performance, by generating highly conductive pathways parallel to the mesh. A suitable graphite coating is obtained by exploring graphite coatings in various application areas. Together with the requirement of this coating, the first choices are made regarding the components of the coating. In addition, various experimental results are conducted to determine a potential coating composition and application method.

Results showed that a graphite coating consisting of graphite, Polyvinylidene Fluoride (PVDF) and N-Methylpyrrolidone (NMP), applied with the use of a dip coater, followed by drying, could be attached to the carbon steel with a thickness of 2 mm in four layers. The influence of the graphite coating is estimated with the use of a resistance model.

Further research should focus on quantitatively determining the influence of the graphite coating application in combination with the evaluation of the corrosion resistance of the coating.

The world is witnessing unprecedented climate changes, which have worsened over the past couple of years. Despite significant progress in renewable energy, achieving a reduction of global warming remains challenging. Renewable energy sources like solar, wind, and hydroelectric technologies offer promising solutions, but challenges persist due to their intermittency and geographical dependency. Green hydrogen, generated through electrolysis using renewable energy, has come up as a solution for storing electric energy and providing a constant energy supply.

Alkaline water electrolysis has emerged as one of the most promising electrolysis methods due to its large-scale operation, long durability and low costs. This does not come without challenges, one of them being leakage currents, which reduces the efficiency of the electrolyser. Leakage currents occur when not all current is used for hydrogen production, but some of it leaks into, for example, the produced hydrogen stream. To reduce these leakage currents, more research into the origins is needed. The first step is modelling the electrolysis while considering as much as possible of the physics happening inside the system. Current models of alkaline water electrolysers are either modelled using only mathematical equations or neglect the operating parameters, which makes the results highly variable per system. Other models do use analytical methods with experimental results, but these models only comprise one electrolysis cell rather than a full stack.

This work consists of developing two three-dimensional models, validating them using experiments, and using them to predict the effect of changes in geometry. The first model was made using COMSOL Multiphysics software and used to research the water electrolysis stack, which comprised one or eight cells using electrochemical relations and physical data. It was found that a model could be made that fitted the experiments within the error margin of the experiments (<2.5%). It lacked flexibility but overall showed good results for an electrolyser stack of one or eight cells. The second model was made using an equivalent electrical circuit (EEC) of the electrolyser in Python via the PySpice module. A steady-state model, including the leakage currents, could be developed by calculating all system resistances, namely the cell, inlet/outlet, and manifold resistances. This model overestimated the performance of the electrolyser by 10-15% for low current densities and 2-4% for high current densities. Nevertheless, it was highly adaptable for different scenarios, making it valuable for research into optimising the electrolysis stack. Both models were used to predict the effect of changes in geometry; the effect of the length of the inlets, and the number of cells. This showed that the EEC model was better suited for this research.

As the energy transition gains momentum, the development of effective energy storage technologies is crucial. Among these technologies, batteries are of utmost importance as they store chemical energy that can be converted into electrical energy. The operation of batteries is a complex process that involves the interplay of material technology, multiphysics transport phenomena, and mechanical effects. While experiments can reveal new and unexpected features of batteries in various conditions, simulation models offer a costand time-effective way to gain valuable insights across a wider range. However, the accuracy and fidelity of mathematical models are directly proportional to the complexity of describing all the relevant phenomena. To date, equivalent-circuit models have been the dominant framework for industrial applications due to their simplicity and low computational cost. However, these models treat batteries as black boxes, which limit users’ ability to interpret the results. In contrast, physics-based models that couple electrochemistry, conservation laws, and heat equations can produce high-fidelity models that capture the intricacies of battery operation. The Multiphase Porous Electrode theory (MPET) provides a useful framework for integrating these phenomena and enables users to modify parameters that can significantly impact simulation results. In this study, experiments in different operating temperatures were conducted and analysed, and based on these outcomes, the accuracy and validity of MPET was tested. The root mean squared error between the simulation and experimental results was smaller than 5% in all cases. The correlation between the high temperature (50 ◦C) discharge curve and the ambient temperature discharge curve showed the high dependence of temperature to the state of charge of the battery which was confirmed by the experiments. Furthermore, a possible degradation mechanism could have an impact in the final results. The main research outcomes were the exponential relation between the temperature and the rate constant and between the particles conductivity and the temperature. Using these two relations, the model could reproduce the same trend and equal maximum capacity with the experiments. This shows the flexibility of the model in completely different operating conditions. After the validation, the active particle population model can be used to understand the coccurent or particle by particle intercalation and gives indentifications of hotspot in a battery. The final part was a sensitivity analysis about capacity optimization taking into account not only different C-rates but also different temperatures. Because the whole study was in an experimental coin cell, a relation to bigger battery systems should be built in the same manner using this software so as to facilitate the development of more effective energy storage technologies. Keywords: Li-ion batteries, phase separation materials, temperature dependency, parameter estimation, optimization, machine learning, physics-based models.

Buoyancy-driven plumes are natural phenomena that occur in widespread applications, such as geological flows or pollutant dispersion from a chimney. One characteristic of plumes is the entrainment process, where the plume stream drags in ambient fluid and mixes with the ambient fluid, and classic plume theory has used an entrainment coefficient to describe the entrainment process. Literature research reveals that there is a general lack of experiment data on the entrainment process of an axisymmetric plume, and there is little consensus on the entrainment coefficient. The aims of the thesis are to address the problem of insufficient experimental evidence and to investigate the entrainment coefficient using two theories (classic entrainment theory and new energy-consistent theory).

The thesis’s method is experimental. Buoyancy-driven plumes with different initial conditions were created in a water tank, and the velocity field and buoyancy field were measured using particle image velocimetry (PIV) and laser induced fluorescence (LIF). In addition, a new combination of urea and sodium sulfate was proposed to perform the refractive index matching (RIM), which is a crucial step for accurate velocity and buoyancy measurements.

The thesis’s results highlighted that the entrainment coefficient is approximately 0.11, despite large variations when using the classic theory to determine the entrainment coefficient, which may help explain different values in previous literature. In addition, the existence of a refractive index field was observed to affect both the velocity and buoyancy measurements. Specifically, the refractive index field caused PIV and LIF to overestimate the velocity field and underestimate the buoyancy field, respectively.

Metal additive manufacturing has enabled great diversity and design freedom in heat exchanger design. However, these benefits cannot be adequately realised without optimizing its ancillary components as well, specifically the inlet and outlet manifolds. Optimizing the manifolds can significantly improve the flow distribution inside the heat exchanger core. This in turn will improve the heat exchange performance and reduce flow obstruction. More importantly, it can reduce the size of the setup, which makes for much cheaper and faster manufacturing. Literature on optimization of flows is quite vast and extensive, but experimental validation is lacking. It is not well understood whether 2D optimized parts hold up to 3D validation, and whether it differs for laminar and turbulent regimes. In this work, a manifold is numerically optimized in 2D and 3D for various flow regimes including both laminar and turbulent flow. The ideal set of assumptions for each specific case is then prescribed based on the results. Validation is performed for some of the geometries after manufacturing them via 3D-printing.

Gasketed Plate Heat Exchangers (GPHEs) are a sub-class of heat exchangers that enable heat transfer between 2 fluids via metal plates. A common problem encountered in all heat exchangers is fouling. Fouling can be described as the deposition and accumulation of unwanted materials such as scale, algae, suspended solids and insoluble salts on a heat transfer surface. Despite the widespread use of GPHEs and the common occurrence of fouling in heat exchangers, fouling is not clearly understood in GPHEs. Scale, one of the several types of fouling, has the most harmful effect on heat exchangers out of all fouling mechanisms and is the most common problem encountered in cooling water systems. When formed on heat-exchanging surfaces, scale retards heat exchange, accelerates fouling, promotes certain types of corrosion and microbial growth, and increases pumping back pressure. These, in turn, result in decreased plant efficiency, reduced productivity, schedule delays, more downtime for maintenance, and increased costs for equipment repair and replacement. Since Alfa Laval is an active part of this project, and a large portion of the GPHEs they sell are used in cooling water applications, the focus of this project is to understand the effect of flowrate, inlet temperature and GPHE duty on scaling in GPHEs. The most common scale deposited on heat exchangers is calcium carbonate (CaCO3), and therefore this study will only focus on CaCO3 scaling.

In order to quantify the effect of changes in a parameter on scaling tendency and GPHE performance, an experimental setup is built. The experimental design ensures that when altering one parameter, all other operating conditions of the GPHE remain constant, thereby attributing any changes in scaling tendency solely to the test parameter. Throughout each experiment, media temperatures are monitored, and the overall heat transfer coefficient and fouling resistance are plotted against time to observe changes in GPHE performance. Additionally, since the deposited scale initially increases the performance of the GPHE, a time for ’onset of scale’ is also determined for each experiment, where ’onset of scale’ is defined as the moment when the deposited scale is detrimental to GPHE performance. Moreover, following each experiment, the GPHE is disassembled, and the scaled plates are weighed to determine the quantity of scale deposited on the plates. Finally, images of the scaled plates are compared with those of a clean plate to observe the distribution of scale on the plate surface.

After performing and analysing the results from all experiments, it can be concluded that all 3 parameters have a significant influence on GPHE performance. It was observed that higher flowrates led to a smaller amount of scale deposits on the plate and result in a greater duration to achieve the onset of scale condition. Conversely, higher inlet temperatures and GPHE duty led to a greater amount of scale deposits and result in a shorter time to achieve the onset of scale condition. The results also indicated that a change in GPHE duty has the greatest influence on scaling from all 3 parameters, provided the flowrate is greater than 250 kg/hr. However, for flowrates below 250 kg/hr, the flowrate of the test solution has the biggest impact on scaling tendency and GPHE performance. Additionally, an optimal performance region which would result in minimal scale deposition on the plates is determined for the current system. Finally, to predict the amount of scale deposited on the plates as a function of the test parameters, regression analysis is performed on the data and a 5th-degree polynomial function is established.

This master thesis introduces a recently surfaced method to produce hydrogen and oxygen using alkaline water electrolysis. A hydrophilic porous diaphragm is used that can feed electrolyte laterally to two porous electrodes that are placed against it. Consequently, hydrogen and oxygen are produced directly at the electrodes without any bubble formation. More specifically, this master thesis aims to investigate the thermal behaviour of such a capillary-fed electrolyzer and the limits to which capillary-fed electrolysis can be sustained.
A small scale capillary-fed cell and a larger segmented cell are manufactured during the project. Both cells are used to perform experiments at constant current. Capillary rise in diaphragms with and without compression deviate from the Lucas-Washburn model for capillary rise. Particularly the polyethersulfone material outperforms the diaphragms that were studied. It follows the Lucas-Washburn equation relatively well and exhibits two times deeper penetration under compression. Furthermore, experiments have been performed studying the relation between electrolytic concentration and capillary wicking. Although more highly concentrated KOH solutions for electrolytes increase conductivity over time, it has shown that for the utilised diaphragm a KOH solution surpassing 3 moles per litre shows problematic capillarity. Contact angle experiments with 6M KOH have shown a hydrophobic contact angle of ̄Θ=78.14° compared to complete imbibition, i.e Θ = 0°, for 1,2 and 3M KOH solutions. The origin of these extremely large contact angles on the polyethersulfone substrate is not fully understood. 
The study has culminated in performing experiments at constant current and low concentration KOH utilising flushing and dilution techniques to prevent precipitation at the electrodes. The small cell reached an overall heat transfer coefficient of h = 121 W/m²K, showing very large heat production for a relatively small surface area. For the segmented cell, electrolyte supply with a bottom-up feed resulted in h = 19.13 W/m²K in which precipitation occurred. The top-down feed showed that the top segment has the largest areal heat dissipation. The heat transfer coefficient equates to h = 25.73 W/m²K. A final enhancement has been made by introducing Nickel Felt Fiber conducting layers into the cell to improve electronic conductivity. This resulted in an increased range of current densities that could be reached at lower overpotentials compared to absence of these conductive layers. This resulted in the bottom most segment to exhibit the largest areal heat dissipation. The heat transfer coefficient here equates to h = 43.86 W/m²K.
This study takes another important step into the regime of capillary-fed electrolysis and alternative electrolysis methods in general. Introducing an alternative design, assessing this design from experimentation and reporting on subsequent steps that can be taken.

Electrification and decarbonization of industrial process heat is an important next step in the energy transition to reduce greenhouse gas (GHG) emissions. This study provides an in-depth analysis of how in the current industrial landscape the combination of commercially available electric heating technologies with the implementation of thermal energy storage (TES) can realize the electrification of
medium-temperature industrial process heat on the short-term. Moreover, it explores what potential novel high-temperature heat pump (HTHP) technologies, specifically the supercritical CO2 (sCO2) reversed Brayton HTHP, have to realize this electrification even more efficient in terms of electricity demand in the future. Thereby, it also briefly highlights the opportunities and challenges to combine HTHP technology and TES in the future to realize an optimal electrification.

In order to reduce greenhouse gas (GHG) emissions, fleets of medium- and heavy-duty vehicles are transitioning from conventional fossil fuels to fully electric drivetrains. To utilize these medium- and heavy-duty electric vehicles (MHDEVs) without significantly disrupting their operations, Megawatt Charging Systems (MCS) are being developed, which enable charging rates up to 4.5 MW. However, these charging rates are associated with substantial heat generation in the vehicle’s battery pack. To regulate the battery temperature and maximize battery lifetime, performance, and safety, the development of a battery thermal management system (BTMS) for this application is crucial.

The study provides a methodology that adopted a system engineering approach for the design of a BTMS for the application of MHDEVs which utilize MCS. The study defined the requirements for the BTMS which include the optimal temperature range for battery cells and determined the battery heat generation rate when using MCS. Furthermore, the study investigated the magnitude of temperature gradients in battery cells as a result of MCS.
Subsequently, two assessment stages have been proposed to assess BTMS strategies, which include forced air BTMS, immersion cooling BTMS, cooling plates with coolant BTMS, and cooling plates with refrigerant BTMS. This assessment resulted in design requirements for heat transfer areas and mass flow rates to maintain the battery cells below 35 ℃. Moreover, the concepts of utilizing cooling plates with refrigerant in a vapor-compression refrigeration system and storing charging session heat by thermal energy storage (TES) have been developed. This included the dimensioning of a condenser and compressor for the vapor-compression refrigeration cycle and included the dimensioning of the required mass and volume of TES medium for the TES system. The study found that these two BTMS strategies are the most favorable. Thermal energy storage with hydrated salt as phase change material (PCM) appeared as the most effective and feasible option subsequent to conducting comparisons with immersion coolant and paraffin PCM. However, a BTMS with a vapor compression refrigeration system might be needed when the BTMS is used for both driving and charging. Analysis of refrigerants R717, R134a, and R1234yf, indicated that R717 is the most effective in this BTMS with a COP of 3.52 and a lower required mass flow rate and compressor power consumption, however, is associated with several safety considerations that must be addressed when selecting R717 over other refrigerants. Lastly, the study utilized a MATLAB Simulink model to identify the effects of dynamic phenomena that occur during operation of the BTMS and the study determined the impact of BTMS weight on MHDEV driving range.

Recommendations for future research are given related to the need for increased fidelity of heat generation prediction and BTMS models. Furthermore, future research should be conducted on combining the BTMS with other thermal management systems in the vehicle to maximize overall effectiveness.

The ever-increasing power demand, the high scarcity of fossil fuel resources and the growing environmental pollution have pushed the development on technologies related to sustainable energy systems. Maximizing the energetic performance of industrial processes is a key aspect in this quest for sustainable
energy management. A large share of waste heat below 100°C is rejected into the environment during industrial processes. This low temperature industrial waste heat can be a relevant heat source, reducing the consumption of fossil fuel and the emission of CO2 into the atmosphere. While these lower temperatures may not be suitable for direct industrial use and their capture may not be economically justified, the implementation of a heat pump allows for the elevation of these stream temperatures to levels that can support a wide range of industrial processes.
Heat pumps can be utilized to upgrade waste heat streams from low to higher temperature levels
which can then be used as energy supply for other industrial processes. State-of-the-art heat pumps are still restricted to temperature levels below 120°C due to long payback periods and technical limitations regarding the compressor. The application of heat pumps in industry could become more widespread if the technology would allow for a higher temperature output. Compression-resorption heat pumps (CRHPs) are a promising option to upgrade waste heat streams since they combine the advantages of absorption heat pumps (working with a mixture having non-isothermal phase transitions and low environmental impact) and vapor-compression heat pumps. CRHPs can operate both under dry and wet compression conditions. One of the main issues in reaching high temperatures with dry compression is the degradation of the oil, which leads to a reduction of the performance. Employing wet compression, the liquid can function as a lubricant avoiding both oil contamination and irreversibility caused by the superheating of the vapor. As pointed out by several researchers, a crucial point for the feasibility of high temperature CRHPs is a good value of isentropic efficiency for the compressor. As such, since a technological solution is currently not commercially available, the diffusion of CRHPs in the industrial processes is inhibited.
This research thesis develops a numerical model of the compressor in which the liquid phase and
the vapor phase are at non-equilibrium conditions. The model incorporates heat transfer between
the phases, yielding new insights and results. The validated model serves as a tool for analyzing
optimal operating conditions to maximize compressor efficiency. A case study within the dairy industry was considered. The results indicate a 60% reduction in operating costs and a saving of 104 tonnes of emissions if a single heat pump substitutes a traditional boiler. The substitution of fossil fuel fired boilers with heat pumps becomes increasingly necessary in light of the EU Renewable Energy Directive, ratified in 2023, which targets a 45% renewable energy share by 2030. The development of such next generation heat pumps could be a major breakthrough for optimizing energy management in industrial processes.

This study aims to develop a methodology for upscaling commercially available latent thermal energy storage systems using salt-hydrate HS48 as a phase change material, with a focus on determining optimal design parameters for different sizes and energy demands. The paper begins with a comprehensive review of phase-change materials' properties, theories, and practical applications in various energy storage systems, including integration into hot water storage tanks with diverse configurations. Subsequently, a research method is introduced, based on heat transfer principles and commercial heat battery specifications, providing a scalable simulation model validated through experimental setups. The model emphasizes two different scales and demonstrates non-linear charging time increases with PCM mass. After optimization, the model is scaled to match a commercially available heat battery's power output, evaluating various configurations based on key independent variables. Results favor the configuration, which consist of twice the number of parallel tubes, as the optimal design for reducing PCM mass, system size, and charging time. While the study shows promising outcomes, it also highlights areas for improvement, such as refining assumptions about phase change behavior and addressing specific application requirements like domestic hot water supply