The transient thermal response of a 15-cell, 48 volt, lithium-ion battery pack for an unmanned ground vehicle was simulated with ANSYS Fluent. Heat generation rates and specific heat capacity of a single cell were experimentally measured and used as input to the thermal model. A heat generation load was applied to each battery and natural convection film boundary conditions were applied to the exterior of the enclosure. The buoyancy-driven natural convection inside the enclosure was modeled along with the radiation heat transfer between internal components. The maximum temperature of the batteries reached 65.6 °C after 630 seconds of usage at a simulated peak power draw of 3,600 watts or roughly 85 amps. This exceeds the manufacturer's maximum recommended operating temperature of 60 °C. The pack was redesigned to incorporate a passive thermal management system consisting of a composite expanded graphite matrix infiltrated with a phase-changing paraffin wax. The redesigned battery pack was similarly modeled, showing a decrease in the maximum temperature to 50.3 °C after 630 seconds at the same power draw. The proposed passive thermal management system kept the batteries within their recommended operating temperature range.

Managing the thermal loads inside a non-airbreathing hypersonic vehicle is particularly difficult. The heat generated by the power electronics, avionics, etc. must be removed so that the components do not exceed their maximum temperatures. These vehicles cannot dump the waste heat into fuel or ram air because they carry no fuel and do not have provisions for ram air. This means that the thermal energy resulting from the heat generated must be dumped into an onboard heat sink. Existing solutions to this problem have been passive systems based on solid-liquid phase change materials (PCMs), which store thermal energy as they melt. Since space is at a premium, a heat sink must store a lot of energy per unit volume, while keeping components below their maximum temperature. In this project, three heat sink concepts are tested, i.e., one based on PCMs, a second on thermal to chemical (TTC) energy storage, and a third on a hybrid combination of the first two. For the first, three different PCMs are tested and for the second a single endothermic chemical reaction. The hybrid PCM/TTC concept consists of a single PCM which plays the dual role of PCM and reactant in the endothermic chemical reaction of the TTC energy storage. To enhance heat sink performance, the use of thermoelectric generators (TEGs) and a local coolant loop are investigated. The advantage of the former is that they transform waste heat into usable electricity, reducing the amount of thermal energy that needs to be stored by the heat sink. The advantage of the latter is that it results in a more uniform cooling of the heat source and more uniform heating of the heat sink. Prototypes of each of the heat sink concepts and the coolant loop are designed, built, and tested. Experimental results indicate that all the solutions tested in this project outperform widely used paraffin heat sink technologies on an energy per unit volume basis. Our experiments also show that a local coolant loop is indeed advantageous and that current off-the-shelf thermoelectric generators do not generate enough power to offset the power requirements of the coolant loop. Significant improvements in the ZT factor of the thermoelectric materials used by the TEG would be required. / Master of Science / All electronics produce waste heat and have a maximum operating temperature above which they fail due to overheating. Heat sinks absorb the waste heat and prevent overheating. Non-airbreathing hypersonic vehicles do not have natural heat sinks like intake air or liquid fuel which are commonly used as heat sinks in airbreathing vehicles. Heat cannot be transferred to the environment due to the high temperatures caused by the friction of hypersonic air travel. This means that all waste heat must absorbed by an onboard heat sink. Existing heat sinks in non-airbreathing hypersonic vehicles use paraffin based solid-liquid phase change materials (PCMs) which store thermal energy as they melt. Three novel heat sink options are evaluated in this project, hydrated salt PCMs which absorb energy as they melt, a chemical reaction which absorbs heat as it reacts, and a hybrid system which incorporates one of the hydrates salt PCM as a reactant in the chemical reaction. Because space is at a premium, these options are evaluated by the amount of energy they can absorb (kilojoules) per unit volume (in3) while keeping the electronics below their maximum temperature. To enhance heat sink performance, the use of thermoelectric generators (TEGs) and a local coolant loop are investigated. The advantage of the former is that they transform waste heat into usable electricity, reducing the amount of thermal energy that needs to be stored by the heat sink. The advantage of the latter is that it results in a more uniform cooling of the electronics and more uniform heating of the heat sink. Prototypes of each of the heat sink concepts and the coolant loop are designed, built, and tested. Experimental results indicate that all the solutions tested in this project outperform widely used paraffin heat sink technologies on an energy per unit volume basis. Our experiments also show that a local coolant loop is indeed advantageous and that current off-the-shelf thermoelectric generators do not generate enough power to offset the power requirements of the coolant loop. Significant improvements in the state of the art of thermoelectric materials would be required for TEGs to generate enough electricity from our waste heat load to power the local coolant loop.

The European commission has in the Energy Performance of Buildings Directive from 2010 decided that its member states were required to ensure that all new buildings by the end of 2020 were nearly zero-energy buildings. These buildings require small amounts of energy compared to its performance in example by keeping a pleasant indoor climate. To achieve these goals there is an option for integrating phase changing material into building material.   The purpose of this project was to determine which kind of PCM is suitable for use in building materials to increase its fire resitance, taking inspiration from the report Fasomvandlingsmaterial: Risker och möjligheter written by Michael Försth, Alexandra Byström and Jonathan Wolf. In particular, the aim was to observe if the application of PCM, in pure powder form, into pure concrete could increase the time until it reaches it critical temperature of 500 °C. The choice of PCM to be used was decided by a literature review and initial thermal tests, and in this case, Magnesium Carbonate Hydroxide Pentahydrate, MCHP, was used as a substitute for the cement, in this project.    The project has been carried out through a literature review and laboratory experiments. The laboratory experiments were performed in different stages. First, the thermal properties of the PCM were decided by using a DSC (differential scanning calorimeter) and a TGA (Thermogravimetric analysis). Three kinds of PCMs (Magnesium hydroxide, Aluminium hydroxide and MCHP) were tested from the results of the literature review. The DSC gave a variation in results between the three tested PCMs. MCHP showed two melting phases which produced different kind of fire-retardant products and theoretically would give two instances of stopping the heating of the concrete. With that MCHP was then chosen as the most appropriate one to be incorporated into concrete. From there, pure concrete samples and with PCM mixed in, with different weight percentage varying between 2-10 weight percent (wt.%) of the cements weight, with a thermocouple embedded in the bottom were manufactured. Thereafter, a cone calorimeter was used with the constant heat flux of 50 kW·m-2 as a source of heat radiation.   The results shows that the application of the PCM in the concrete by replacing the cement does not give any noticeable increase in its fire resistance by increasing the time until it reaches 500 °C. Neither did it show any signs of the heating curve to flatten out, which in theory would have occurred during melting of the PCM. This could depend on the way the heat transfers down through the concrete and melts the PCM along the way towards the bottom and the thermocouple measuring the temperature. Making the thermocouple only register the heating of the concrete in close proximity to it. Therefore only a small amount of PCM melts and the required energy is not enough to halt the heating. Theoretical calculations performed showed that the melting of the PCM in the case with 5 and 10 wt.% gave an improvement by increasing the time until critical temperature is reached with 4 % and 7.3 %, compared to a pure concrete sample. The melting of the PCM is responsible for 1 % respectively 2 % of that time increased compared to the pure concrete sample. The rest of the increase in time comes from the PCMs thermal properties which is higher than the cement. The literature study shows that there exist many suitable PCM for increasing a building material’s fire resistance, some of which are already used as fire retardants. It also shows that PCM can affect a material’s fire resistance in more ways than just the heat storage (latent heat) in the melting phase.    The conclusion of this report is that substituting concrete with MCHP in powder form is not suitable and does not affect the concretes fire resistance. But the usage of PCM in concrete should not be dismissed. There exist different ways to implement the PCM into the concrete which could give a desirable result.

Energy storage within hypersonic aircraft is becoming increasingly important with the development of more sophisticated electronic components and is an integral piece of expanding their overall capabilities. Hypersonics not only produce large external thermal loads, but also an abundance of internal thermal loads from components such as power electronics, avionics, and batteries. Additionally, limited volume within such vehicles introduces additional constraints. Thus, having efficient heat sinks that are capable of storing much of these heat loads is imperative. Passive thermal management systems, i.e., heat sinks, are preferable in most applications because they do not require power input to operate, and they are typically smaller than active systems such as coolant loops. In identifying and developing heat sinks with increased energy storage capability, an exhaustive search of available phase change materials (PCMs) is conducted. PCMs have been used in hypersonic vehicles in the past as a means of energy storage. Additionally, the use of energy-consuming endothermic reactions is considered. An innovative PCM-endothermic reaction hybrid approach is also developed. Both thermodynamic and transient/quasi-stationary models are developed for each of these proposed heat sink technologies. Prototypes are then developed for the best candidates to validate the models and draw conclusions on each heat sink's performance. Both the thermodynamic modeling and experimental results presented in this paper suggest that PCMs, endothermic reactions, and, especially, the hybrid system show greater energy storage capabilities than what is being used in hypersonic vehicles currently. / Master of Science / Hypersonic vehicles are an important topic of interest in the aerospace and defense industries. To be classified as hypersonic, a vehicle must travel at or above Mach 5, which is at least five times the speed of sound. Hypersonic vehicles often travel at high altitudes and a common application of the technology is in missiles. One major hurdle in developing hypersonic technologies at lower altitudes is that because of the high speeds, the outside skin temperature of the vehicle can reach thousands of degrees. Clearly, these temperatures can affect the heat load on the inside of the vehicle as can the thermal energy release of internal components such as the power electronics, the avionics, etc. To deal with these internal heat loads, innovative energy storage solutions are needed to efficiently and effectively store the thermal energy released internally. One approach considered here is the use of phase change materials (PCMs) as a storage medium. Melting such a material requires large amounts of energy and occurs at constant temperature. This is much more advantageous than heating a material in which only the temperature rises. Another approach considered in this thesis is that of using a chemical reaction, which requires energy input to proceed. Such a reaction is called an endothermic reaction and often results in a temperature decrease. Thus, simply mixing a set of reactants and adding energy helps cool the system. A final approach considered is a hybrid one, which combines a PCM material and an endothermic reaction. Such an approach combines the advantages of both. Each of these approaches are modeled thermodynamically to better understand how devices based on them work. Physical prototypes are then designed, built, and tested to confirm their performance. Both the modeling and experimental results presented in this thesis suggest that these devices show significantly improved energy storage capabilities over the devices currently used in hypersonic vehicles.

Thermal energy storage (TES) consists in storing heat for a later use, thereby reducing the gap between energy availability and demand. The most diffused materials for TES are the organic solid-liquid phase change materials (PCMs), such as paraffin waxes, which accumulate and release a high amount of latent heat through a solid-liquid phase change, at a nearly constant temperature. To avoid leakage and loss of material, PCMs are either encapsulated in inert shells or shape-stabilized with porous materials or a nanofiller network. Generally, TES systems are only a supplementary component added to the main structure of a device, but this could unacceptably rise weight and volume of the device itself. In the applications where weight saving and thermal management are both important (e.g. automotive, portable electronics), it would be beneficial to embed the heat storage/management in the structural components. The aim of this thesis is to develop polymer composites that combine a polymer matrix, a PCM and a reinforcing agent, to reach a good balance of mechanical and TES properties. Since this research topic lacks a systematic investigation in the scientific literature, a wide range of polymer/PCM/reinforcement combinations were studied in this thesis, to highlight the effect of PCM introduction in a broad range of matrix/reinforcement combinations and to identify the best candidates and the key properties and parameters, in order to set guidelines for the design of these materials. The thesis in divided in eight Chapters. Chapter I and II provide the introduction and the theoretical background, while Chapter III details the experimental techniques applied on the prepared composites. The results and discussion are then described in Chapters IV-VII. Chapter IV presents the results of PCM-containing composites having a thermoplastic matrix. First, polyamide 12 (PA12) was melt-compounded with either a microencapsulated paraffin (MC) or a paraffin powder shape-stabilized with carbon nanotubes (ParCNT), and these mixtures were used as matrices to produce thermoplastic laminates with a glass fiber fabric via hot-pressing. MC was proven more suitable to be combined with PA12 than ParCNT, due to the higher thermal resistance. However, also the MC were considerably damaged by melt compounding and the two hot-pressing steps, which caused paraffin leakage and degradation, as demonstrated by the relative enthalpy lower than 100 %. Additionally, the PCM introduction decreased the mechanical properties of PA12 and the tensile strength of the laminates, but for the laminates containing MC the elastic modulus and the strain at break were not negatively affected by the PCM. Higher TES properties were achieved with the production of a semi-structural composite that combined PA12, MC and discontinuous carbon fibers. For example, the composite with 50 wt% of MC and 20 wt% of milled carbon fibers exhibited a total melting enthalpy of 60.4 J/g and an increase in elastic modulus of 42 % compared to the neat PA. However, the high melt viscosity and shear stresses developed during processing were still responsible for a not negligible PCM degradation, as also evidenced by dynamic rheological tests. Further increases in the mechanical and TES properties were achieved by using a reactive thermoplastic matrix, which could be processed as a thermosetting polymer and required considerably milder processing conditions that did not cause PCM degradation. MC was combined with an acrylic thermoplastic resin and the mixtures were used as matrices to produce laminates with a bidirectional carbon fabric, and for these laminates the melting enthalpy increased with the PCM weight fraction and reached 66.8 J/g. On the other hand, the increased PCM fraction caused a rise in the matrix viscosity and so a decrease in the fiber volume fraction in the final composite, thereby reducing the elastic modulus and flexural strength. Dynamic-mechanical investigation evidenced the PCM melting as a decreasing step in ’; its amplitude showed a linear trend with the melting enthalpy, and it was almost completely recovered during cooling, as evidenced by cyclic DMA tests. Chapter V presents the results of PCM-containing thermosetting composites. A further comparison between MC and ParCNT was performed in a thermosetting epoxy matrix. First, ParCNT was mixed with epoxy and the mixtures were used as matrices to produce laminates with a bidirectional carbon fiber fabric. ParCNT kept its thermal properties also in the laminates, and the melting enthalpy was 80-90 % of the expected enthalpy. Therefore, ParCNT performed better in thermosetting than in thermoplastic matrices due to the milder processing conditions, but the surrounding matrix still partially hindered the melting-crystallization process. Therefore, epoxy was combined with MC, but the not optimal adhesion between the matrix and the MC shell caused a considerable decrease in mechanical strength, as also demonstrated by the fitting with the Nicolais-Narkis and Pukanszky models, both of which evidenced scarce adhesion and considerable interphase weakness. However, the Halpin-Tsai and Lewis-Nielsen models of the elastic modulus evidenced that at low deformations the interfacial interaction is good, and this also agrees with the data of thermal conductivity, which resulted in excellent agreement with the Pal model calculated considering no gaps at the interface. These epoxy/MC mixtures were then reinforced with either continuous or discontinuous carbon fibers, and their characterization confirmed that the processing conditions of an epoxy composite are mild enough to preserve the integrity of the microcapsules and their TES capability. For continuous fiber composites, the increase in the MC fraction impaired the mechanical properties mostly because of the decrease in the final fiber volume fraction and because the MC phase tends to concentrate in the interlaminar region, thereby lowering the interlaminar shear strength. On the other hand, a small amount of MC enhanced the mode I interlaminar fracture toughness (Gic increases of up to 48 % compared to the neat epoxy/carbon laminate), as the MC introduced other energy dissipation mechanisms such as the debonding, crack deflection, crack pinning and micro-cracking, which added up to the fiber bridging. Chapter VI introduces a fully biodegradable TES composite with a thermoplastic starch matrix, reinforced with thin wood laminae and containing poly(ethylene glycol) as the PCM. The wood laminae successfully acted as a multifunctional reinforcement as they also stabilized PEG in their inner pores (up to 11 wt% of the whole laminate) and prevent its leakage. Moreover PEG was proven to increase the stiffness and strength of the laminate, thereby making the mechanical and TES properties synergistic and not parasitic. Finally, Chapter VII focused on PCM microcapsules. The synthesis of micro- and nano-capsules with an organosilica shell via a sol-gel approach clarified that the confinement in small domains and the interaction with the shell wall modified the crystallization behavior of the encapsulated PCM, as also evidenced by NMR and XRD studies and confirmed by DSC results. In the second part of Chapter VII, a coating of polydpamine (PDA) deposited onto the commercial microcapsules MC. The resulting PDA coating was proven effective to enhance the interfacial adhesion with an epoxy matrix, as evidenced by SEM micrographs. XPS demonstrated that the PDA layer was able to react with oxirane groups, thereby evidencing the possibility of forming covalent bond with the epoxy matrix during the curing step.

The effect of using high voltage DC and AC on the heat transfer process during the melting of a Phase Change Material (PCM) in a rectangular enclosure was studied experimentally and numerically. The experiments were conducted for two configurations: (a) a horizontal rectangular enclosure in which the initial melting process is governed by heat conduction, (b) a vertical rectangular enclosure in which the initial melting process is governed by heat convection. The level of heat transfer enhancement was quantified by using a novel experimental facility for the horizontal configuration. The experimental methodology was verified first against non-EHD melting cases and then was further expanded to include the EHD effects. The experiments showed that EHD forces can be used to enhance a conduction dominated melting up to a maximum of 8.6-fold locally and that the level of enhancement is directly related to the magnitude of the applied voltage. It was found that the main mechanism of enhancement in these cases can be attributed to the electrophoretic forces and that the role of the dielectrophoretic forces is minimal under the applied voltages. In the vertical configuration, the effect of the magnitude of the applied voltage, the applied voltage wave-form, the gravitational Rayleigh number, Stefan number and the aspect ratio of the enclosure on the heat transfer enhancement were investigated experimentally. A novel shadowgraph experimental measurement system was developed and verified against the analytical correlations of natural convection in rectangular enclosures and the non-EHD melting performance was verified against the bench mark experiments of Ho (1984). The shadowgraph system was used to measure the local heat transfer coefficient across the heat source wall (the heat exchanger surface). The local heat transfer measurements along with the melting temporal profiles were used to explain and visualize the coupling between the Electrohydrodynamics (EHD) forces and the gravitational forces. It was found that the EHD forces could still enhance the melting process even for an initially convection dominated melting process. The mechanism of enhancement was found to be a bifurcation of the initial convection cell into multiple electro-convective cells between the rows of the electrodes. The shadowgraph system was used to assess the interaction between the electrical and the gravitational forces through the visualization of these cells and quantifying their size. The EHD heat transfer enhancement factor was found to increase by the increase of the applied voltage, reaching a 1.7 fold enhancement at the lower gravitational Rayleigh number tested and 1.45 fold for the highest gravitational Rayleigh and Stefan number. The effect of the polarity of the applied voltage was tested for the different cases and it was found that there was no significant difference between the positive and the negative polarities when the magnitude of the applied voltage was below 4 kV. At higher voltages- 6kV- the negative polarities showed better level of enhancement when compared to the positive applied voltage. It was again found that the main mechanism of enhancement is attributed to charge injection from the high voltage electrodes. A scaling analysis was conducted based on the previous conclusions and the dominant mechanism of enhancement to describe the problem in non-dimensional form. An electrical Rayleigh number was introduced and its magnitude was correlated to the magnitude of the injected current. The melt volume fraction was then represented against the non-dimensional parameter (n+1)(H/W)Fo.Ste.RaE^0.25 and the melt fraction temporal profiles for the different voltages collapsed well against this parameter. Finally, a numerical analysis was conducted on the role of the dielectrophoretic forces during the melting of Octadecane and when they would become of significant importance. The results of the numerical model supported the experimental findings and suggested that a minimum of 15 kV is needed in order to realize the effect of the dielectrophoretic forces. The numerical model was used to understand the interaction between the gravitational and the dielectrophoretic forces at different ranges of both gravitational Rayleigh number and electrical Rayleigh number. The model was complemented with scaling analysis to determine the governing scales of the problem and the dielectrophoretic Rayleigh number was deduced from the study. / Thesis / Doctor of Philosophy (PhD)

A framework that presents a new methodology for design-evaluation of active solar collection systems was developed. Although this methodology emphasizes the importance of detailed modeling for accurate prediction of building performance, it also presents a process through which the detailed modeling results can be reused in a simplified iterative procedure allowing the designer the flexibility of revising and improving the preliminary design. For demonstration purposes, the framework was used to design and evaluate two case studies located in Blacksburg (VA) and Minneapolis (MN). These locations were selected because they both represent a cold weather region; presenting a need for using solar energy for heating and hot water requirements. Moreover, the cold weather in Blacksburg is not as severe as in Minneapolis. Therefore, the two cases will result in different thermal loading structures enabling the framework validation process. The solar collection system supplying both case studies consisted of a low temperature flat plate solar collector and storage system. Thermal performance of the case study located in Blacksburg was conducted using detailed modeling evaluation techniques; while thermal performance of the case study located in Minneapolis was conducted using a simplified modeling evaluation technique. In the first case study, hourly evaluation of the thermal performance of the solar collection system was accomplished using finite element (FE) analysis, while hourly evaluation of the building thermal performance was made using Energy Plus software. The results of the finite element analysis were used to develop a statistical predictive design equation. The energy consumption for the second case study was calculated using the heating design day method and the energy collection for that case study was calculated using the predictive design equation developed from the first case study results. Results showed that, in the case of the building located in Blacksburg, the solar collection system can supply an average of 85% of the building's heating and hot water requirements through out the year. In the case of the building located in Minneapolis, the solar collection system can supply an average of 56% of the building's heating and hot water requirements through out the year given no night time window insulation and using similar insulation thicknesses for both cases. / Ph. D.

Irreversible electroporation has recently emerged as an effective focal ablation technique. When performed clinically, the procedure involves placing electrodes into, or around, a target tissue and applying a series of short, but intense, pulsed electric fields. Oftentimes, patient specific treatment plans are employed to guide procedures by merging medical imaging with algorithms for determining the electric field distribution in the tissue. The electric field dictates treatment outcomes by increasing a cell's transmembrane potential to levels where it becomes energetically favorable for the membrane to shift to a state of enhanced permeability. If the membrane remains permeabilized long enough to disrupt homeostasis, cells eventually die. By utilizing this phenomenon, irreversible electroporation has had success in killing cancer cells and treating localized tumors. Additionally, if the pulse parameters are chosen to limit Joule heating, irreversible electroporation can be performed safely on surgically inoperable tumors located next to major blood vessels and nerves. As with all technologies, there is room for improvement. One drawback associated with therapeutic irreversible electroporation is that patients must be temporarily paralyzed and maintained under general anesthesia to prevent intense muscle contractions occurring in response to pulsing. The muscle contractions may be painful and can dislodge the electrodes. To overcome this limitation, we have developed a system capable of achieving non-thermal irreversible electroporation without causing muscle contractions. This progress is the main focus of this dissertation. We describe the theoretical basis for how this new system utilizes alterations in pulse polarity and duration to induce electroporation with little associated excitation of muscle and nerves. Additionally, the system is shown to have the theoretical potential to improve lesion predictability, especially in regions containing multiple tissue types. We perform experiments on three-dimensional in vitro tumor constructs and in vivo on healthy rat brain tissue and implanted tumors in mice. The tumor constructs offer a new way to rapidly characterize the cellular response and optimize pulse parameters, and the tests conducted on live tissue confirm the ability of this new ablation system to be used without general anesthesia and a neuromuscular blockade. Situations can arise in which it is challenging to design an electroporation protocol that simultaneously covers the targeted tissue with a sufficient electric field and avoids unwanted thermal effects. For instance, thermal damage can occur unintentionally if the applied voltage or number of pulses are raised to ablate a large volume in a single treatment. Additionally, the new system for inducing ablation without muscle contractions actually requires an elevated electric field. To ensure that these procedures can continue to be performed safely next to major blood vessels and nerves, we have developed new electrode devices that absorb heat out of the tissue during treatment. These devices incorporate phase change materials that, in the past, have been reserved for industrial applications. We describe an experimentally validated numerical model of tissue electroporation with phase change electrodes that illustrates their ability to reduce the probability for thermal damage. Additionally, a parametric study is conducted on various electrode properties to narrow in on the ideal design. / Ph. D.

This master thesis deals with problematic of the heat convection in phase change materials (PCM) and PCM with nanoparticles. The derivation of stationary and non-stationary equations for 1D, 2D and 3D heat convection are described in detail. The finite element volume method is used for solution to these equations, of which principle is described carefully. The aim of this thesis is model development for 2D solution to temperature distribution at heat convection in PCM and influence assessment of nanoparticle implementation into material on given temperature distribution. Software MATLAB was used for model development, solution and plotting graphs.

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: Solar energy is a time dependent, high-temperature radiant energy resource. The utility of a solar thermal energy system increases if the hot temperature source is available when it is needed most. This is realized by the thermal storage of the solar energy. Thermal storage gives greater versatility to a solar energy system by decoupling the heat source from the heat sink. A large quantity of energy may be stored during the melting process in a phase change material (PCM) within a small temperature range. This molten PCM can then deliver its absorbed heat at a constant temperature in a heating application. In this study a phase change storage system (PCS) is developed and proposed for a solar water heating application. This PCS system stores more heat per unit mass than would be possible with water across the same temperature range. The heat transfer rate in and out of many PCMs is slow because of the low thermal conductivity of the PCM. However, heat transfer enhancers (HTE), such as heat pipes and fins may be added to enhance heat absorption and heat removal rates. Heat pipes have the inherent capability to transfer heat at high rates across large distances, even where the temperature difference is small. In this thesis a description is given of a PCS system consisting of paraffin wax as the PCM and which uses rectangular heat pipes in conjunction with aluminium fins to enhance heat transfer. The storage design is modular and each module has the characteristic that enhanced heat transfer in and out of the PCM is possible when the module is heated or cooled. It also has the capability to quickly absorb or alternatively to supply heat at a nearly constant temperature during the phase change of the module. A rectangular module was designed and built. The module was then analysed under controlled heat absorption and heat removal cycles. The heat up experiment involved an electrical kettle as the hot temperature source. The heat sink was a mains water heat exchanger. The experimental results were compared to those of a transient numerical model, which calculates theoretically how the module will perform thermally under the given test conditions. The numerical model of the experimental set-up was validated when it was found that the numerical model results resemble the experimental results. The numerical model was then adapted to simulate a novel solar water heater (SWH) with an additional PCS container. The improvement over previous designs is that the additional storage container can be heated to a higher temperature than the allowable geyser temperature. The system also heats up and cools down at a faster rate than would be possible without the HTEs. From the numerical simulation the size and performance of such a system is determined. This numerical analysis indicated that a phase change storage system in a SWH application will increase the hot water delivered by a given solar collector and geyser by increasing the storage capacity and by heating up the geyser overnight for early morning hot water use. / AFRIKKANSE OPSOMMING: Son energie is ‘n tyd afhanklike, hoë temperatuur radiasie energiebron. Die bruikbaarheid van ‘n sontermiese energie sisteem verhoog indien die hoë temperatuur bron beskikbaar is wanneer dit die meeste benodig word. Dit kan verwesenlik word deur die sonenergie termies te stoor. Termiese storing bied groter veelsydigheid aan ‘n sontermiese stelsel deur effektief die hittebron te ontkoppel van die hitte sink. ‘n Groot hoeveelheid energie kan, gedurende die smeltingsproses in ‘n faseveranderingsmateriaal binne ‘n nou temperatuurband gestoor word. Hierdie gesmelte materiaal kan weer op sy beurt in die waterverhittingstoepassing, die geabsorbeerde hitte teen ‘n konstante temperatuur oordra. In hierdie studie word ‘n sonwaterverwarmer stelsel wat aangepas is deur ‘n addisionele latente hittestoor daaraan te heg, voorgestel. Hierdie faseverandering hittestoor kan meer hitte stoor as wat water in dieselfde temperatuur band sou kon. Die hitteoordrag tempo na en van baie van die faseveranderingsmateriale (FVM) is egter as gevolg van die lae termiese geleidingskoëfisient, stadig. Hierdie eienskap kan gelukkig verbeter word deur hittepype en hitteoordrag verhogings materiaal soos vinne by te voeg. Hittepype het die inherente eienskap om hitte teen ‘n hoë tempo oor groot afstande, oor te dra, selfs oor ‘n klein temperatuurverskil. In hierdie tesis word ‘n ondersoek rakende ‘n faseverandering storingsisteem wat bestaan uit paraffien was as die FVM en reghoekige hittepype wat te same met met aluminium finne gebruik word om die hitteoordragtempo te verhoog, beskryf. Die stoorontwerp is modulêr en elke module het die kenmerk van hoë hitteoordrag na en van die FVM. Die module het verder ook die eienskap om vining hitte te absorbeer of hitte af te gee. Dit gebeur teen ‘n konstante temperatuur gedurende die faseverandering van die FVM. Presies so ‘n reghoekige module is ontwerp en gebou en onder beheerde hitte absorbering- en hitte verwyderingsiklusse analiseer. Tydens die verhittings eksperiment is ‘n elektriese ketel van gebruik gemaak wat gedien het as die hoë temperatuur bron. Die hitte sink was ‘n hitteruiler wat kraanwater van ‘n konstante hoogte tenk ontvang het. Die resultate van die volledige toets is met die resultate van tydafhanklike numeriese model vergelyk. Hierdie numeriese model bereken teoreties wat die module se storing verrigting onder gegewe toets omstandighede sal wees. Die numeriese model se resultate het goed vergelyk met die resultate van die eksperimente. Die numeriese model van die module is toe aangepas om ‘n sonwaterverwarmer met addisionele stoortenk wat fase verandering materiaal gebruik, te simuleer. Hierdie ontwerp is anders as vorige ontwerpe in die sin dat hoër temperature as wat die warmwatertoestel kan hanteer, in die faseverandering storingstenk, bereik kan word. Die sisteem kan ook as gevolg van die hitteoordrag verhoging materiaal, vinniger verhit of afkoel en teen ‘n vinniger tempo. Die simulasie van die sonwaterverwarmer met FVM word gebruik om die grootte en verrigting van die sisteem te bepaal. Hierdie numeriese model toon aan dat wanneer ‘n addisionele faseverandering storingstelsel in ‘n sonwaterverwarmer toepassing gebruik word, die warm water wat die verbruiker uit die sisteem kan verkry, kan verhoog. Die rede hiervoor is dat meer hitte gestoor kan word, wat beskikbaar gemaak word aan die warm water tenk.