The drainage time of liquid-filled PET bottles can be greatly reduced by pre-rotating the bottle with a certain angular velocity. Depending on the magnitude of the angular velocity, up to four different flow regimes can be distinguished during the emptying of a bottle: bubble regime, transition regime, vortex regime and the swirl regime. At zero or low pre-rotation, the flow is in the so-called bubble regime in which the intermittent downward liquid flow is accompanied by an upward motion of irregularly shaped air bubbles into the bottle. At sufficiently high pre-rotation, the picture is completely different. After initial transient behaviour in which the flow is first in the bubble regime, the flow undergoes transition towards a so-called vortex regime. This is characterized by regular downward motion of liquid along the bottle wall in a free-surface vortex and accompanying upward motion of air through the nozzle core. Finally, close to the end of the drainage process another transition towards a so-called swirl regime takes place, in which the last bit of liquid swirls around in the bottle before being slowed down sufficiently to exit the bottle through the nozzle opening. Dimensional analysis indicates that for a specific bottle geometry the non-dimensional total drainage time td/td,0, where td,0 is a characteristic drainage time scale for stationary low-viscosity fluids in the bubble regime, depends primarily on 3 non-dimensional numbers: (1) the rotation number, Π (2) the Morton number, Mo, and (3) the E¨otvos number, Eo. The former represents the characteristic ratio of centrifugal to hydrostatic forces inside the liquid phase. The objective of this study is to determine the relationship between the non-dimensional drainage time and Π and gain insight in the influence of E¨otvos and Morton onto this. To this purpose, a parametric CFD study of a model PET bottle has been conducted and the results have been compared with previous preliminary experiments performed in our group. The numerical study is divided into three categories, each discussing the influence of one of the dimensionless parameters. The influence of the Π-number was studied by altering the initial rotational velocity of the bottle. It was found that at some critical Π-number, the drainage time was minimal. A further increase beyond the critical Π-number resulted in a longer drainage time, due to the stronger centrifugal force acting on the liquid layer. It was found through an analytical solution and verified with the numerical results that the rate at which the Π-number grows in relation to the dimensionless drainage time is to the power 3 for the laminar case and to the power 3/2 for the turbulent case. Below the critical value, the flow is expected to remain in the so-called bubble regime, also increasing the drainage time. Furthermore, the onset of the vortex regime was expected to occur at a constant value of Π. This was also verified with the numerical results and a strong correlation was found between the onset and the corresponding local Π-number. The influence of the Morton number is also discussed, where an increase in the Morton number was realized with an increase in viscosity. It was found that the drainage time got substantially reduced with an increase in viscosity. The effects of viscous dissipation resulted in a bigger effective area and higher axial downward flow velocity. However, increasing the Morton number excessively would result in the flow regime remaining in the bubble regime. Therefore, the critical Πnumber shifts depending on the different fluid compositions. When varying the E¨otvos number, by both changing the viscosity and the surface tension, it was found that the latter had negligible effect on the generation of the air-core or the drainage time.

Increase in global energy demand has brought to a massive rise in greenhouse gases emissions. In particular, the continuously increasing atmospheric concentration of carbon dioxide is a major concern among the scientific community. This paved the way for an intense research of CO2 emissions mitigating technologies. Those ones including carbon capture, storage and utilisation are seen as part of the solution for this global problem. In this framework, Zero Emission Fuels (ZEF), a startup company located in Delft (The Netherlands) set the ambitious goal of developing a micro process plant producing methanol from ambient air and sunlight only. Part of the process involves direct capture of carbon dioxide from the atmosphere (direct air capture) with the use of a pure tetraethylenepentamine (TEPA) absorbent. ZEF sets itself aside from the rest of the industry developing an absorber which collects CO2 with no support structure by continuously flowing TEPA inside open channels. Previous research shows how this approach brings limitations connected to slowly diffusing CO2 molecules in the absorbent liquid film in proximity of the gas-liquid interface. In this framework, circulation of TEPA particles from the gas-liquid interface into the bulk of the flowing absorbent is seen as a viable solution to improve the process. This thesis focuses on investigating this hypothesis by inducing mixing on the liquid side. That is done by building two experimental setups investigating both passive and active mixing. Experimental results show that active mixing can be used to improve the rate of CO2 absorption, while passive mixing does not bring significant advantages. Results from the passive mixing experiments are further investigated by modelling the fluid dynamics of the process through a Direct Numerical Simulation of the particular Stokes’ flow in the engineered absorption channel. The process is characterised with the definition of a theoretical framework describing mass transfer in the liquid side. Following an analogy with ice formation on top of a frozen lake, this theory, also known as the ”Ice-Sheet” theory, shines some light on the way this diffusion limitations are happening at a molecular level. In particular, a highly viscous, heavily loaded layer of sorbent on the gas-liquid interface is believed to be the cause for observed CO2 diffusion limitations. This theory is backed-up by defining its mathematical equivalent in the form of a mass transfer model. Comparing the results of the model with experimental results, a very good agreement is observed. That is believed to add credibility to the proposed theory. Moreover, that is also found to be in line with the latest knowledge available in literature about CO2 absorption in TEPA films. Finally, the experimental results and the developed models are used to engineer a new iteration of ZEF’s absorber on a cost reduction basis.

As the world population is increasing and cities grow faster than before, food scarcity becomes a bigger issue. To depend less on import and decrease CO2 footprint, food should be produced nearby its consumers. A good solution for food production is a greenhouse which provides a steady high yield throughout the year. Some of the world's fastest growing cities are in Subtropical climates. Subtropical climates are characterized by high temperatures, abundance of sun and high humidity. Due to the high temperatures, cooling in greenhouses in subtropical climates is necessary, but evaporative cooling is not sufficient due to the high humidity. Outside air can be dehumidified by a liquid desiccant to cool the air further with an extra evaporative cooling step. After dehumidifying the air, the absorbed moisture from the air in the desiccant must be removed from the desiccant solution for re-use. This requires a lot of energy, which makes this cooling technique for greenhouses in subtropical climates not economically feasible. The proposed solution is to remove moisture from the desiccant by making use of the hot air that can be collected in the top of the greenhouse. The potential of this solution is assessed in this study. To predict the transfer of mass and heat between air and a calcium chloride solution as desiccant, a mathematical model of the process of mass and heat transfer over a structured cardboard pad is made. An experiment is conducted to validate the mass and heat transfer coefficients of the model. The model is used to evaluate the workings of the proposed system of regeneration. Results show that dehumidification can significantly lower the inlet temperature of the air in the greenhouse, provided that the inlet temperature of the desiccant is low. Regeneration of the desiccant solution with hot air is also possible, provided that the air in the greenhouse is significantly heated by the sun and pre-heating of the desiccant before regeneration is beneficial. The direct coupling of these two systems is not sufficient due to the big difference in temperature of the desiccant that is required at the inlet of the dehumidifier and regenerator. In future work attention should be paid to this temperature difference which is currently limiting the performance of the system. Then it's possible for the concentration of the desiccant to be brought back to the starting conditions for the dehumidifier.

Predicting when a neonate will fall victim to an infection or a disease allows prevention through early medicine administering. Such physiological conditions can be made visible using infrared thermography (IRT). This is a technique for measuring heat emitted in the infrared spectrum and transforming them into visible signals that can be recorded photographically. This thesis will contribute to the prediction of infection in (pre)term neonates by quantifying the interaction between IRT and a neonatal incubator without (and with) a neonate in it.  A system was designed that consisted of three modules: a measurement (incubator and IRT camera), back-end (embedded system and server), and front-end module. The scope of this thesis is limited to the measurement module and the embedded system of the back-end module. Minimum camera requirements were set up which required the camera to: be inexpensive (i.e. ≤ €1000,-), be mobile, be open-source (for Linux), have a minimum frames-per-second of 5, have a resolution of at least 160x160 pixels with a field of view (FOV) of 27°, sensitivity of < 0.1°C, and safe to the patient. Such a camera was found in the FLIR One Pro. For this thesis a different FLIR camera was used due to lack of budget, namely the FLIR A305sc, which was already available at the TU Delft. The A305sc is not open-source, which required a work-around. The Aravis Open Source Project allowed for communication with the camera. Internal camera parameters had to be determined to calculate temperature based on analogue-to-digital values. ExifTool was used on a file stored by the camera to extract these parameters. This calculated temperature was compared to the temperature as determined by FLIR’s software and led to a difference in the range of 1·106°C. An open-source application was written that can connect with this IRT camera that has a GenICam interface using Aravis. Additionally, this application implemented the temperature calculation based on the internal camera parameters. The hood of the incubator is opaque to infrared, which required the design of a measurement setup to circumvent this. Three different setups were discussed, with the final choice falling on placing the camera in front of an opened incubator porthole on a tripod, and sealing this porthole with high or low density ethyl polyethylene (HDPE/LDPE). Regular H/LDPE used for construction site was found to have a attenuated transmissivity as found in literature. To quantify the interaction between IRT and a neonatal incubator, the IRT measurements were to be compared against the current golden standard sensor, namely thermistors. These sensor values were to be read out from the incubator as this would also be used in the final product. Code was written which allows for automatic detection between the GE GiraffeTM Omnibed and the Dräger Caleo® incubator, automatic connecting, and manipulation of all sensors values to a standard string which allows for easy uploading to the InfluxDB database on the server. To be allowed to perform measurements on human subjects, approval had to be acquired by the human research ethics committee (HREC) of the TU Delft and the respective hospital. A “non-wet medisch wetenschappelijk onderzoek met mensen” (nWMO) request was submitted and approved, which resulted in 25 recorded sick and healthy neonates in incubators divided over two hospitals (the JKZ in The Hague, and the RDGG in Delft), with over 25 hours of recording material. Simultaneously, measurements were performed on an empty incubator to gain an understanding in the behaviour of an incubator when actors from outside interacted with the internal environment. Measurements that were performed included determining the reflected apparent temperature (RAT) for every possible opened porthole and for both incubator types. The RAT for the Caleo was found to be higher for every measurement for the GE. The accuracy of the IRT and hospital skin temperature sensors was compared against a calibrated Pt-100 sensor, which show that the Pt-100 sensor measures an equal value as the hospital skin temperature sensor, whereas The IRT camera measured .6°C higher. The effect of changing the distance on IRT values was measured, which shows that for a distance of 0.2m to 1.2m the accuracy of the IRT camera is within the specified accuracy. Finally, the effect of opening additional portholes on IRT was measured, the effect of the airboost setting on IRT, and the measurement of opening additional portholes was repeated with a different IRT camera. Overall the IRT camera measures a higher temperature than the hospital skin temperature sensors, but follows the skin temperature sensors’ pattern.    

Rising concentration of CO2 in the atmosphere has become a significant concern, paving the way for worldwide research on mitigation techniques like carbon capture and storage (CCS) and carbon capture and utilization (CCU). Zero Emission Fuel (ZEF), an aspiring startup based in the Netherlands, aims to develop a micro plant that produces methanol from just solar energy and air. Their process involves capturing CO2 and H2O directly from the air, splitting H2O to obtain H2 and producing methanol by reacting CO2 with H2. The focus of this research is on the absorption process of ZEF's direct air capture unit. Instead of capturing CO2 and H2O through a widely used batch direct air capture process, ZEF chooses to side with a novel continuous absorption and desorption process involving a flow of bulk polyamines without any conventional support structures. Polyethyleneimine (PEI-MW-600) and Tetraethylenepentamine (TEPA) are used as absorbents to achieve a target of capturing 825 grams of CO2 in 8 hours every day from a single direct air capture unit. Preliminary investigations show that the viscosity of PEI-600 is significantly higher than that of TEPA. An increase in CO2 concentration increases the viscosity of both polyamines significantly. In comparison, increasing H2O concentration leads to a maximum viscosity point in both polyamines and subsequent decrease in viscosity with a further increase in H2O concentration. Although, compared to CO2, H2O has a smaller effect on viscosity. Moreover, premixed samples of PEI-600 and TEPA with H2O show an increase in the CO2 absorption rate when pure CO2 is bubbled through the samples. In order to study and characterize the novel absorption process, an experimental setup facilitating a flow of absorbent is developed, and experiments are conducted following an experimental approach to calculate the mass transfer rates and average concentrations of CO2 and H2O. Fourier-transform infrared spectroscopy is used to estimate these concentrations. Experiments are performed on different initial concentrations of PEI and TEPA. TEPA is found to have a better absorption performance with an average CO2 absorption rate that is two times higher than PEI-600. Contrary to preliminary investigations done by bubbling CO2 into polyamines, absorbents with premixed water flowing down a channel were found to have lower CO2 absorption rates than pure polyamines. A multiple regression viscosity model, heat model, and a model of absorption column is developed using the data collected to estimate average viscosity, the heat of absorption of water, and characteristics of the absorption process. Diffusion of CO2 through the absorbent layers is found to be the primary limiting factor, while mass flow rates of absorbent and air are also found to influence the absorption process. Finally, a design of the absorption column is made to meet ZEF's requirement taking into account various performance characteristics studied during the thesis.

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.

Recent advancements in the field of nanotechnology have proven to offer viable alternatives for energy production, transport, and storage. As far as thermal energy is concerned, nanofluids have emerged as a novel method to enhance heat transfer. Indeed, nanofluids exhibit superior thermal capabilities, which may be able to meet the requirement of high heat dissipation rate in limited space advanced by various high-tech industries. In particular, boiling heat transfer is an efficient heat removal mechanism that may be further improved by using nanofluids. Indeed, it has been reported that nanoparticles play a crucial role in affecting the parameters which have major impact on the boiling process (i.e. thermophysical properties of the fluid, heating surface morphology, near-surface hydrodynamics). Being boiling very sensitive to surface characteristics, the latter factors have been found to have a significant influence on the boiling heat transfer coefficient. Hence, the aim of the present research is to elucidate the physical mechanisms underlying pool boiling of nanofluids. Based on this framework, a pool boiling test facility has been designed and validated, thus enabling to conduct a comparative study on boiling of a pure fluid (water) and a water-alumina 0.1% 𝑤𝑡 nanofluid. The pool boiling experiments were performed on six aluminium samples, which were characterized by SEM (scanning electron microscopy) and WLI (white light interferometry) before and after boiling in order to highlight the change in surface topography. The research efforts were targeted at correlating the trend of the boiling curves and the surface parameters of the corresponding sample. Nonetheless, due to the limited dataset and the inconsistencies in the behaviour of the tested nanofluid, further investigation is required to assess the potential of nanofluids as more efficient heat transfer media.

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.

This thesis describes the investigation of the dynamics of turbulent shear flows over non-smooth surfaces. The research was conducted in two parts, related to the experimental facility used in combination with the applied functional surface. The first part describes the experiments of a turbulent Taylor-Couette flow over a riblet surface. The Taylor-Couette facility proves to be an accurate measurement device to determine the frictional drag of surfaces under turbulent flow conditions. Sawtooth riblets are applied on the inner cylinder surface and have the ability to reduce the total measured drag by 5.3% at Res=4.7x104.  Under these conditions, a small shift is observed in the azimuthal velocity profile that indicates the change in the net system rotation, which on its turn affects the quantity of drag change, the so-called rotation effect. A model based on the angular momentum balance is proposed and quantifies the drag change due to the rotation effect. Using the total measured drag change, the model accurately predicts the velocity shift in the azimuthal direction. In addition to the steady operational conditions, periodically driven Taylor-Couette flows were investigated by modulating the velocity between the two cylinders as a sinusoidal function, while maintaining RΩ = 0. The main scaling parameters are the shear Reynolds number Res, the oscillation Reynolds number Reosc and the Womersley number Wo, such that the required power to overcome the frictional drag becomes equal to <Pd> = f(Res,Reosc, Wo). Large velocity amplitudes A = Reosc/Res > 0.10 induce the growth of frictional drag due to the additional turbulent fluctuations. The required power to overcome the frictional drag is given by <Pd> = <Pd,0>(f(A)+ K*Wo4A2). The first term represents the analytical quasi-steady state solution with the accompanying velocity modulation, while the second term involves the magnitude of the boundary acceleration with the associated velocity fluctuation, where K* is the conditional scaling-factor between the additional drag and the dimensionless acceleration. Riblets are still able to reduce the frictional drag under small accelerations of the periodically driven boundaries, but the effect declines drastically or even enhances the frictional drag when the boundary acceleration becomes more significant.   The second part of this thesis describes the assessment of the applied water tunnel and the interactional behavior between a compliant coating and a turbulent boundary layer flow in the tunnel. In the assessment of the water tunnel, the Clauser chart method showed to be a suitable procedure to quantify the local wall shear stress τw. The interaction between a compliant wall and the near-wall turbulent flow was examined by applying in-house produced visco-elastic coatings with three different stiffnesses.  Two typical flow-surface interaction regimes were identified; the one-way coupled regime and the two-way coupled regime. The one-way coupled regime is valid when the turbulent flow initiates moderate coating surface deformation, while the fluid flow remains undisturbed. All of the three coatings exhibited the one-way coupled interactional behavior, where the surface modulations ζ were smaller than the viscous sublayer thickness δv and scale with the turbulent pressure fluctuations over the coating shear modulus, i.e. ζrms ~ prms/|G*|. In this regime, the surface waves have the propagation velocity in the order of cw = 0.70-0.80 Ub, indicating a strong correlation with the high-intensity pressure fluctuations in the turbulent boundary layer away from the wall. The two-way coupled regime has only been observed for the coating with the lowest shear modulus when Ub > 4.5 m/s, indicating significant surface deformation accompanied by additional fluid motions (u',v') and an increase in the local Reynolds stresses. The velocity profile shifts downwards Δu+ in the log region, which verifies the drag increase due to the significant surface undulations. The visualizations of the surface deformation showed the formation of wave-trains with high amplitudes originating from the initial surface undulations caused by the pressure fluctuations in the turbulent boundary layer (i.e. one-way coupling). When these early surface undulations start to protrude the viscous sublayer, the turbulent flow is capable of transfering more energy towards the coating and initiates the wave-train with high amplitudes. The wave-trains dominate the coating surface incrementally with increasing bulk velocity and propagate with a wave velocity of cw = 0.17-0.18 Ub. The 1-way/2-way regime transition is estimated to occur around ζrms > δv/2. The turbulent flow along the slow-moving wave-trains resembles the classical phenomenon of a turbulent flow over a rigid wavy surface, with a local acceleration and deceleration of the fluid. When the wave-trains start to dominate the coating surface, a linear correlation determines the abovementioned downward shift Δu+, based on the wall-normal velocity component dζ/dt. No frictional drag reduction under turbulent flow conditions was found in this study with this type of visco-elastic compliant coatings.   @en

This thesis focused on designing and constructing a deoxygenation reactor through a modular experimental setup for Catalytic Hydrogen Combustion (CHC). The developed system aims to enhance hydrogen purification techniques. The setup enables testing various catalysts and conditions to remove oxygen down to 5 ppm in a hydrogen stream. The experimental system was designed from the ground up due to the lack of detailed information on existing systems. The design includes gas treatment, the catalytic reactor, and a post-process system, with several iterations for modularity and safety. The final setup successfully removed oxygen in an initial test and allowed flexible reactor configurations for various catalyst tests. The system operated smoothly, maintaining gas composition and ensuring safe operation. The oxygen sensor performed reliably, providing data that aligned with the 1D model after adjustments. In summary, this thesis lays a strong basis for further CHC research. The developed experimental setup is a robust and adaptable tool for researchers and engineers aiming to improve hydrogen purity for industrial applications.

This thesis focused on designing and constructing a deoxygenation reactor through a modular experimental setup for Catalytic Hydrogen Combustion (CHC). The developed system aims to enhance hydrogen purification techniques. The setup enables testing various catalysts and conditions to remove oxygen down to 5 ppm in a hydrogen stream. The experimental system was designed from the ground up due to the lack of detailed information on existing systems. The design includes gas treatment, the catalytic reactor, and a post-process system, with several iterations for modularity and safety. The final setup successfully removed oxygen in an initial test and allowed flexible reactor configurations for various catalyst tests. The system operated smoothly, maintaining gas composition and ensuring safe operation. The oxygen sensor performed reliably, providing data that aligned with the 1D model after adjustments. In summary, this thesis lays a strong basis for further CHC research. The developed experimental setup is a robust and adaptable tool for researchers and engineers aiming to improve hydrogen purity for industrial applications.

Prediction of heat transfer phenomena and resulting temperature distributions is crucial among many appliances in the industry sector. In a vacuum, the dominant mode of heat transfer is conduction. The resulting temperature drop at the body’s interface is dependent on a parameter known as Thermal Contact Conductance (TCC) or, alternatively, Thermal Contact Resistance (TCR). During the literature study, it was found that several parameters are mainly affecting the heat transfer performance between the samples: surface roughness, contact pressure, material properties, and environmental conditions. The Thesis project is accomplished in cooperation with Philips Engineering Solutions (PES). For the Thesis, it is proposed to explore the TCC phenomenon through a combined study. The first part is investigating newly manufactured samples with a modified experimental setup in vacuum conditions. Before the Main Test Campaign started, the experimental setup and old laboratory samples were tested to mark the way. Also, several more samples were tested alongside the Main Tests to extend the TCC database. Another important study goal is to perform thorough surface analysis using a Digital Microscope. The analysis results in a surface roughness evolution study and reconstruction of the surfaces using MATLAB © software. The surfaces are then matched together to simulate and predict the parameter known as the real contact area. The study ends with a section summarizing the investigation and proposing recommendations and possible further research.

Energy efficiency is a key goal for the Quooker system. To further increase the energy efficiency of the Quooker system, this study investigates a possible heat integration system where the waste heat from the refrigeration cycle for chilled drinking water is implemented to preheat water before entering the boiling water reservoir. Due to the intermittent nature of both the supply of heat, which is coupled to the control scheme of the chilled water reservoir and the demand for heat, which is determined by the user, a thermal storage system is required. Literature showed that the best refrigeration system for this application was a vapour compression system using a natural refrigerant such as isobutane. The most efficient heat storage could be done using organic phase change materials (PCM). Using a PCM allows the system to retain more energy in the same volume due to the latent heat in the system. To enhance the heat transfer between the fluid streams and the PCM, a fin-and-tube heat exchanger concept was designed. This concept, coupled with existing Quooker system demands, leads to a preliminary set of design requirements as well as a set of variables left to be optimised by modelling. The heat transfer from the refrigerant to the tubes was modelled using known correlations for condensation in tubes. The heat transfer between tubes and fins was modelled using a two-dimensional finite difference scheme. The heat transfer between the tubes and the water was modelled using forced convection models. The models gave dimensions for the size of the PCM container, the number of passes for each fluid stream and the thickness and spacing of the heat transfer fins. An experimental setup based on the optimal design was created to validate the models. The results showed that PCM storage is an effective manner to store thermal energy. Heat transfer was significant in the regions surrounding the tubes. Further away from the tubes, the fins did not provide enough heat transfer to utilise the whole storage capacity effectively. In its current design state, the system would have an economic payback time of around 20 years. With small design improvements, such as increasing the fin thickness and decreasing the fin distance, the payback period can be brought down significantly. The added product value from being a more efficient product makes the concept promising for future implementation.

The production process of milk powder consists of multiple stages. This report focuses on the falling film evaporator, which role in the production process is to evaporate the water content from the milk. A falling film evaporator is a large vertically-placed vessel whereby the inside is filled with smaller tubes. Steam enters the vessel and heats up the outside of the smaller tubes. The milk flows in a thin layer only along the inside perimeter of the smaller tubes, so these tubes are not completely filled. The advantage of this flow is that a thin layer of liquid is continuously in contact with the wall so the heating process is equal along the tube. The thin layer is called a falling film because the thickness compared to the length of the flow is very small. The objective of this research is to determine theoretically the local overall heat transfer coefficient of the falling film and to investigate experimentally the applicability of heat flux sensors by determining the local overall heat transfer coefficient. By investigating the falling film, it is not allowed to disturb the falling film. Once a falling film is disturbed, the falling film will proceed at a different path. Heat flux sensors allow for local non-intrusive measurements. The overall heat transfer coefficient gives information about the thickness of the falling film. Theoretically the overall heat transfer coefficient is calculated by taken the thermal resistances of each component. Experimentally, the overall heat transfer coefficient is measured by the heat flux and the temperature difference between the bulk temperature of the fluid and the sensor at the outside of the tube. Before the heat flux sensors are used in practice on the falling film evaporator, a setup has been built to experimentally determine the applicability of the heat flux sensor. This setup has been made for a tube filled with water and to create a falling film. The tube filled with water is well-described in theory and used as a reference. The results of the experimental setup show that the Danfoss 'Koperpasta tube AT' is in good comparison with the theoretical approach. The theoretical overall heat transfer coefficient difference, caused by the mass flow difference of 0.01 kg/s in the falling film evaporator, can be detected by the heat flux sensors taking into account the error margin of the heat flux sensor and temperature sensor.

The freeze plug is a key safety component of the molten salt fast reactor (MSFR), one of six next-generation nuclear reactor technologies being developed under the Generation IV International Forum (GIF). It should be designed to melt if an accident occurs, allowing the MSFR to drain before it incurs structural damage. Two freeze plug concepts have been considered in recent years, in which the plug is melted either through the decay heat produced in the core, or through heat generated by special heating rings and stored in steel blocks adjacent to the freeze plug. Variations consisting of both a single freeze plug, and multiple smaller plugs contained in a metal plate, have been proposed. This work seeks to evaluate the feasibility of these designs and study how parameters such as the sub-cooling of the plug affect melting times. Additionally, an alternative, wedge-shaped freeze plug design is proposed for increased reliability.  Simulations performed in COMSOL showed that the decay heat plug melts within 600 s only if placed within 0.01 m of the mixed core flow. Because such a placement makes the plug vulnerable to temperature and velocity fluctuations in the core during regular operation of the reactor, this design is considered unfeasible and is not recommended for further study. On the other hand, melting times under 600 s were possible with the heating ring design for a range of sub-cooling amounts and plug configurations, suggesting that this design is promising. A thin frozen layer was shown to form on top of the metal grate in the multi-plug configurations, preventing heat transfer through the top of the plate. Although the melting behavior of this layer warrants further investigation, its insulating effect was found to generally cause the single-plug designs to melt faster than the multi-plug designs. A simplified, isothermal model of the wedge-shaped plug was simulated using the enthalpy-porosity approach to account for convection. To model the sinking of the wedge, an extended Darcy term approach was developed based on an analytical solution which was validated experimentally, with good agreement. This model shows that melting of the wedge is unsteady, and that melting times depend linearly on the wedge angle and sub-cooling. Unfortunately, melting times of the wedge plug could not be estimated with realistic, non-isothermal, time-dependent boundary conditions. For future study, a customizable numerical solver such as OpenFOAM is recommended, which would allow the sinking of the solid phase to be modeled more robustly through an immersed boundary method.

Heatpipes are promising devices for geothermal energy extraction owing to their effectiveness to transport heat. The goal of this research is to validate an analytical heatpipe model with experiments and to investigate the difficulties in designing and constructing geothermal heatpipes. There is a lack of literature and research concerning the operation, performance limits and construction of heatpipes suitable for geothermal heat extraction. A prototype heatpipe is designed based on specifications for geothermal energy extraction and constructed in a laboratory set-up with sensors and data acquisition. The prototype setup collects experimental data and is used to evaluate important parameters, requirements and practical design difficulties. This research shows the difficulties in designing a geothermal heatpipe taking into account fluid choice and physical limitations as well as complications in constructing a properly sealed heatpipe under the influence of repeated heating and cooling. Furthermore it shows the limitations of the analytical model by comparing the model predictions with experimental data.