Thermal energy storage systems, precisely latent thermal energy storage (LTES), are systems capable of recovering and storing thermal energy from waste processes, including hot exhaust gases out of combustion engines, or even renewable sources of energy like solar energy. LTES rely on phase change materials (PCMs) to store a significant amount of thermal energy in a relatively small volume. With limited volume and at almost constant temperature, they are capable of storing a large amount of thermal energy, mainly latent energy. Studies of LTES systems have focused primarily on system and process optimization including transient behavior as well as field performance. A major drawback in the development of the use of PCM in LTES has been the low thermal conductivity characteristic of most PCMs. Thus, there is a need to enhance heat transfer using reliable techniques, with the goal of reducing the charging and discharging times of PCM in LTES systems. Some approaches that have been studied in the past include use of finned tubes, insertion of metal matrix into PCM, and microencapsulation of PCM. The performance of TES configurations in forced convection have been characterized using Reynolds numbers (Re), and Stefan numbers (Ste) of the heat transfer fluid (HTF) for different enhancement techniques. The goal of this study is to experimentally investigate the effectiveness of corrugated PCM panels with high surface-to-volume ratio in forced convection as a function of HTF mass flow rate, charging temperature, and flow direction through a corrugated TES unit. The PCM (octadecane) has been segmented using sealed corrugated panels containing several channels immersed in the HTF stream. With this approach, the author expects that the charging and discharging times will be substantially reduced due to the high surface-to-volume ratio of the PCM panel for heat transfer. Of the three conditions examined, the HTF direction influenced the charging and discharging times the most with significant reductions in these times observed when the HTF flow direction through the TES was upwards. Buoyancy effects, observed at high Stefan numbers, were important during the charging (melting) process and greatly influenced the temperature profiles along each channel. Results indicate that the devised TES is more effective than some other TES systems in the literature.

The objective of this research is to synthesize and characterize microstructures and some elastic properties of bioactive glasses subject to relaxation and/or devitrification treatments. We synthesize two kinds of bioglasses, i.e. P-richer 45S5 and P-poorer 55S4.3. After tempering, the as-prepared bioactive glasses are transparent, 55S4.3 being colorless while 45S5 pale pink in color. The thermal events in DTA analysis indicated that the crystallization of 45S5 and 55S4.3 starts at 620oC and 680oC, respectively. The two bioactive glasses became ivory upon heating at 715oC, and the degree of being opaque increases with dwelling time. The crystalline phase for 45S5 is Na2CaSiO4 -derived Na2Ca2Si3O9 or Na4CaSi3O9. By XRD traces and polarizing optical micrographs, we conclude that the crystal is based on simple cubic structure with a=7.5054Å and space group P213 (198). Due to poor crystallization rate, the crystal in P-poor 55S4.3 glass was not investigated in detail. However, according to the similarity of Raman spectra for devitrified 45S5 and 55S4.3, we suggest that the crystal is similar for the two devitrified glasses. Raman spectra indicated that the relaxed 45S5 has predominant Q2 and Q3 species and the Q3/Q2 ratio decreases with firing time at 715oC. As for relaxed 55S4.3, the major structural unit is Q3, and the intensity of Q3 is higher for 55S4.3 than 45S5. As the Na+/Si4+ ratio increases, the intensity of 946 (or 947) cm-1 increases while bands near 1100 cm-1 decrease. Based on the Raman spectra of devitrified 45S5 and 55S4.3, the crystals in the two glasses have a common structural unit of SiO32- (Q2). The elasticity measurement by Brillouin scattering indicated that the moduli for devitrified glass 45S5 are greater than undevitrified 45S5 and 55S4.3 glass. The elasticity of the present bioactive glasses is lower than hydroxyapatite and fluorapatite.

All energy, wind, water, biofuel and fossil fuel besides nuclear- and tide power originates from the sun. It’s very hard to take full advantage of the huge amount of energy hitting the earth each day from the sun. The suns highest radiation appears often when the energy need reaches its lowest. That’s why it’s very important to be able to store energy over time when the sun doesn’t shine. A large part of energy storage is thermal energy storage, which can either be done sensible, latent or chemical. Another possible thermal storage is a combination of sensible and latent. This exam was aiming to investigate different types of energy storage methods available on the market and a much more detailed analysis for different storage methods with phase change materials (PCM). A new method was designed for a new storage tank suitable for Absolicon Solar Collector AB and their energy park in the city of Härnösand. The methods for this exam were to create a theoretical storage tank suitable to Absolicons Energy Park with some simple calculations. The criteria for the storage tank was to create a storage tank that could provide the district heat in Härnösand with 160 degrees pressurized water and create 160 degrees steam to the industry. The dimensions of the storage tank where chosen by the conditions in Härnösand and from the specific data of Härnösands district heat and from Absolicons new solar collectors. The work temperature of the system were set to 160 degrees which meant that the storage tank would be able to work in those conditions with high temperature. A suitable phase change material and methods for encapsulation of the phase change material suitable for this system was to be found. Small tests were made with a new type of encapsulation for phase change materials in higher temperature. Simple calculations of two types of storage tanks were made. The first storage tank was made with a PCM from PCM products named A164. This PCM was encapsulated with special bags that could handle temperature up to 200 degrees with surrounding rapeseed oil and a copper loop that handled the heat transfer. The second thank was made with the same PCM and encapsulation but with water glycol surrounding the PCM and two types of heat exchangers for the heat transfer. The results from the first tank were that it didn’t work with the district heat. Because a wrong calculation with the schematic of the system made it impossible to connect into the district heat of Härnösand. The only good thing was that it didn’t need to be pressurized because of the rapeseed oil but the bad heat transfer between oil and water made a pressurized tank of water more profitable. The results from the second tank showed that it could produce 160 °C to the district heat for 2 h and 7 minutes. The schematic connection worked and the tank would in the near future be able to connect into the district heat. The result for the encapsulation showed that the bags were able to stand temperatures up to 190 degrees for a short period of time.

A mathematical model is developed to describe the micro/nano-scale fluid flow and heat/mass transfer phenomena in an evaporating extended meniscus, focusing on the transition film region under nonisothermal interfacial conditions. The model incorporates thermocapillary stresses at the liquid-vapor interface, a slip boundary condition on the solid wall, polarity contributions to the working fluid field, and binary mixture evaporation. The analytical results show that the adsorbed film thickness and the thin film length decrease with increasing superheat by the thermocapillary stresses, which influences detrimentally the evaporation process by degrading the wettability of the evaporating liquid film. In contrast, the slip effect and the binary mixture enhance the stability of thin film evaporation. The slip effect at the wall makes the liquid in the transition region flow with smaller flow resistance and thus the length of the transition region increases. In addition, the total evaporative heat flow rate increases due to the slip boundary condition. The mixture of pentane and decane increases the length of the thin film by counteracting the thermocapillary stress, which enhances the stability of the thin film evaporation. The polarity effect of water significantly elongates the thin film length due to the strong adhesion force of intermolecular interaction. The strong interaction force restrains the liquid from evaporation for a polar liquid compared to a non-polar liquid. In the experimental part, laser induced fluorescence (LIF) thermometry has been used to measure the microscale temperature field of a heated capillary tube with a 1 mm by 1 mm square cross section. For the temperature measurement, the calibration curve between the temperature and the fluorescent intensity ratio of Rhodamine-B and Rhodamine-110 has been successfully obtained. The fluorescent intensity ratio provides microscale spatial resolution and good temperature dependency without any possible bias error caused by illuminating light and background noise usually encountered in conventional LIF techniques. For the validation of the calibration curve obtained, thermally stratified fields established inside a glass cuvette of 10 mm width were measured. The measurement result showed a good agreement with the linear prediction. The temperature measurement in a 1 mm capillary tube could provide the feasible method of temperature measurement for the thin film region in the future.

The content of this thesis encompasses the fundamentals, modelling, chip design, nanofabrication process, measurement setup, and experimental results of devices exploiting the optical properties of phase-change chalcogenide materials. Special attention is paid to integrated Si₃N₄ nanophotonic circuits for optical switching and memory applications, as well as to multilayer stacks for colour modulation. Herein, the implementation of the first robust, non-volatile, phase-change photonic memory is presented. By utilising optical near-field effects for Read, Write and Erase operations, bit storage of up to eight transmission levels is demonstrated in a single device employing Ge₂Sb₂Te₅ as the active material. These on-chip memory cells feature single-shot read-out of the transmission state and switching energies as low as 13.4pJ at speeds approaching 1GHz. The capability to readily switch between intermediate states is also demonstrated, a feature that requires complex iteration-based algorithms in electronic phase-change memories. This photonic memory is not only the first truly non-volatile memory---a long-term elusive goal in integrated photonics---but could also potentially represent the first multi-level memory, including electronic counterparts, that requires no computational post-processing or drift correction. These findings provide a pathway towards solving the throughput limitations of current computer architectures by eliminating the so-called von-Neumann bottleneck and portend a new paradigm in all-photonic memory, non-conventional computing, and tunable photonic devices. Finally, novel capabilities in electro-optic colour modulation using phase-change materials are demonstrated. In particular, this thesis offers the first implementation of Ag₃In₄Sb₇₆Te₁₇-based optical cavities for colour modulation on low-dimensional multilayer stacks. Moreover, "gray-scale" image writing is demonstrated by establishing intermediate levels of crystallisation via voltage modulation. This finding, in turn, corresponds to the first demonstration of nonvolatile colour-depth modulation in the emerging phase-change materials nanodisplay technology, featuring resolutions down to 50nm. Furthermore, a comprehensive comparison is carried out for two types of materials: growth- (Ag₃In₄Sb₇₆Te₁₇) and nucleation-dominated (Ge₂Sb₂Te₅) alloys in terms of colour, energy efficiency, and resolution. These results provide new tools for the new generation of bistable and ultra-high-resolution displays and smart glasses while allowing for other potential applications in photonics and optoelectronics.

Accessibility to clean water which is necessary for a healthy lifestyle is a problem that spans the globe. Many societies that lack clean water are also without the energy resources such as electricity or gas that are used for purification. This project is on the development of a solar powered water purification system with Phase Change Material (PCM) energy storage and experimental studies on the system. Water distillation was achieved and analyses were performed on the effects of weather conditions on the distillate production. Solar systems are affected by limited sunshine which occurs only during daylight hours. A second part of the research involved adding a PCM heat exchanger to the system to extend distillation beyond the daylight hours. The analyses evaluated distillate production against outdoor conditions such as temperature, wind speed, and use of the PCM heat exchanger, to determine how they affect the performance of the system. Results show that increased outdoor temperature and clear atmospheric conditions yield greater distillate production. The effects of wind speed were less conclusive. Use of the PCM heat exchanger shifted production to later in the day, but overall, resulted in lower daily production than when the heat exchanger was bypassed. The most definite indicator of distillate production was the temperature differential between the water entering the still and the outdoor temperature.

Thermal switch is very important in today’s world and it has varies of applications including heat dissipation and engine efficiency improving. The commercial thermal switch based on mechanical design is very slow and the structure is too complicated to make them smaller. To enable fast thermal switch as well as to make thermal switch more compact, I try to use second-order phase transition material to enable our thermal switch. Noticing the transition properties of thermoresponsive polymer for drug delivery, its potential in thermal switch can be expected. I used Poly(N-isopropylacrylamide) (PNIPAM) as an example to show the abrupt thermal conductivity change of thermoresponsive polymer solutions below and above their phase transition temperature. A novel technique, transition grating method, is used to measure the thermal conductivity. The ratio of thermal switch up to 1.15 in transparent PNIPAM solutions after the transition is observed. This work will demonstrate the new design of using second-order phase transition material to enable fast and efficient thermal switch. / Master of Science / Controllable thermal conductivity (thermal switching) is very important to thermal management area and useful in a wide area of applications. Nowadays, mechanical thermal conductivity controller device suffers from large scale and slow transition speeds. To solve these problems, I tired the phase transition thermoresponsive polymers to create quick thermal switching because the thermal conductivity will change with the phase. Thermoresponsive polymers show sharp phase changes upon small changes in temperature. Such polymers are already widely used in biomedical-like applications, the thermal switch applications are not well-studied. In this work, I tested Poly(N-isopropylacrylamide) (the abbreviation is PNIPAM) as an example to show the quick thermal conductivity changing ability of thermoresponsive polymer when the transition was happened .I used a novel approach, called the TTG, transient thermal grating. It has easy setup and high sensitivity. The thermal conductivity switching ratio as high as 1.15 in transparent PNIPAM solutions after transition is observed. This work will give new opportunities to control thermal switches using the phase change of thermoresponsive material or abrupt other phase change material in general.

No / Convergence properties are established for the piecewise linear heat balance integral solution of a benchmark moving boundary problem, thus generalising earlier results [Numer. Heat Transfer 8 (1985) 373]. A convergence rate of O(n¿1) is identified with minor effects at large values of the Stefan number ß (slow interface movement). The correct O(n¿1/2) behaviour for incident heat flux is recovered for ß ¿ 0 (pure heat conduction) as previously found [Numer. Heat Transfer 8 (1985) 373¿382]. Numerical illustrations support the theoretical findings.

This thesis makes a novel contribution to the state-of-the-art literature on EHD melting enhancement of PCMs showing the effects of electroconvection flow and solid extraction during the melting process. The details of the contribution made by this work have been disseminated in the form of three journal publications, which have been integrated into this sandwich Ph.D. thesis. / Latent heat thermal energy storage plays an important role in bridging the gap between the energy supply and consumer demands. The latent heat storage systems use phase change materials (PCMs) which are characterized by their high latent heat and therefore lead to higher energy densities. However, one major disadvantage of PCMs is their low thermal conductivities which affects the rates of charging and discharging. Electrohydrodynamics (EHD) offers an opportunity as an active heat transfer enhancement method which can significantly enhance the melting rates while being able to control the heat transfer as per the system’ needs with a very low power consumption. The application of EHD in two-phase solid liquid systems results in generating electroconvection flow in the liquid medium which increases the heat transfer coefficient and decreases the melting time. The main objective of the current work is to study the heat transfer enhancement and the role of EHD forces during the melting of phase change materials (PCMs) under constant temperature boundary conditions. There are two main investigations performed in the current study. First is experimentally studying the EHD melting enhancement of PCMs while applying high voltages through two rows of electrodes embedded inside the PCM. Moreover, in the experiments, solid extraction was investigated using high-speed imaging conducted at various locations with respect to the electrodes. In the second investigation, PCM melting in a rectangular cavity under the effect of EHD and constant temperature boundary conditions is studied numerically. The flow field, temperature field, and phase field are simulated during the melting process until a steady state condition is reached. Additionally, the effect of the applied voltage and temperature boundaries on the electroconvection flow is illustrated. Experimentally, the EHD melting enhancement of paraffin wax is examined under different applied DC voltage magnitudes and polarities, and different temperature gradients. In addition, the role of EHD forces was investigated by applying DC and AC square waves with different frequencies and offset values. The results showed that the melting enhancement increases with a nonlinear relation with voltages, wherein the maximum effective thermal conductivity was found to be 0.95 W/m-K at -10 kV in comparison with the value of 0.2 W/m-K for the pure liquid paraffin wax, with an enhancement ratio of 4.75. The Coulomb force was concluded to be the dominant EHD force in the study while the dielectrophoretic effect was negligible. Characterization of solid extraction was performed by measuring the intensity of extraction, and the size and velocity of dendrites after extraction at different applied voltages and temperature boundaries for different phase change materials having different mushy zone thickness. For paraffin wax, solid extraction was detected for all the applied DC voltages. Small dendrites were observed to be pulled out from the mushy zone melt front and rise upwards in a rotational manner. The extraction intensity was found to be high at locations of high Coulomb force near the electrodes. In addition, solid extraction measurements showed that the size and velocity of the extracted dendrites increase alongside the applied voltage while the velocity decreases at higher temperature boundaries. Finally, it was found that the existence of a large mushy zone results in higher solid extraction intensities. A numerical model was conducted using the finite element method to investigate the EHD melting of PCMs. In the model, the non-autonomous charge injection assumption is used with the Coulomb force being the only electrical body force considered. First, phase-change modeling is conducted to simulate the melting of paraffin wax without EHD under constant temperature boundary conditions until a steady-state condition is achieved. Next, the whole set of coupled EHD equations is introduced to the model to simulate the EHD melting process. The results revealed that two electroconvection cells were generated between each two successive electrodes in the liquid PCM. The EHD flow leads to the redistribution of the temperature field which enhances the heat transfer. EHD melting continues until a steady-state condition is regained after one hour of EHD time, at which point the enhancement ratio was found to be 2.33 at 6 kV. The influence of the applied voltages and temperature boundaries on the electroconvection flow showed that the fluid velocity increases significantly by increasing the voltage while it decreases under higher temperature gradients across the liquid region. This thesis makes a novel contribution to the state-of-the-art literature on EHD melting enhancement of PCMs showing the effects of electroconvection flow and solid extraction during the melting process. The details of the contribution made by this work have been disseminated in the form of three journal publications, which have been integrated into this sandwich Ph.D. thesis. / Thesis / Doctor of Philosophy (PhD)

In this dissertation, an increased thermal capacitance (ITC) and thermal storage management (TSM) system was simulated to reduce building energy consumption, specifically energy related to heating, cooling and domestic hot water. An increased thermal capacitance allows phase shift and amplitude reduction of heat flow fluctuations associated with the building’s internal temperature response due to weather. An adaptive allocation and control of the added capacitance through TSM significantly improves the benefits of the extra capacitance. This dissertation was conducted in three parts: (1) a first-order analysis of the ITC/TSM applied to a micro-building; (2) a transient simulation of the ITC/TSM with PCM implementation for tank volume control; and (3) a parameter study on the ITC/TSM system with added complexities such as the inclusion of DHW and a multiple story residential building. The first-order analysis was used for transient simulation comparison, as simple models are much more suitable for real time implementation in actual control systems. A first order study on a small residential building is also used to establish the merit of the ITC/TSM concept before integrating into a more complex analysis. This study determined that the ITC/TSM could potentially provide savings but required a very large thermal mass. The ITC/TSM system was then coupled with phase change materials (PCMs), which enable thermal energy storage volume reduction. The transient energy modeling software, TRNSYS, is used to simulate the building’s thermal response and energy consumption, as well as the ITC/TSM system and controls. Four temperature-controlled operating regimes are used for the ITC/TSM operations: building shell circulation, heat exchanger circulation, solar panel circulation, and storage. After this, 125 simulations were conducted to design and optimize the ITC/TSM. The three parameters of interest were: tank volume size, solar panel size, and mass flowrate. Domestic hot water usage was also included as another energy savings opportunity. Results for the parameter study showed that savings are optimized when the solar panel and the hot water tank are size together. If they are not sized simultaneously, the temperature of the large thermal capacitance is not adequately controlled. For all simulations conducted in the parameter study, the building energy usage was reduced significantly.