Phase Change Materials (PCM) absorb and release heat at preset temperatures. Due to their relatively high values of latent heat, they are capable of storing and releasing large amounts of energy during phase change. When a PCM is in its solid phase, it will absorb heat as the external temperature rises. The temperature of the PCM will mirror the external temperature until the melting point of PCM is reached. At this stage, the PCM will begin to melt with almost no change in its temperature. PCM plays an opposite role when the external temperature drops. It releases the stored energy back while going through phase change from liquid phase to solid phase. The present work is a numerical study towards fundamental understanding of the impact of using PCM on enhancement of heat and mass transfer in several scenarios. A numerical analysis has been carried out to determine the impact of presence of PCM on the insulating characteristics of paper board packaging. Two different cases of a layered PCM and uniformly dispersed PCM within the packaging wall are considered. The numerical results illustrate significant reduction in exchange of heat between the exterior and the interior of the packaging. Specifically, the unique concept of utilizing PCM in drying of paper is proposed and a numerical investigation is performed to determine the corresponding transport characteristics. The results indicate that the PCM acts as a heat source and a heat sink alternatingly throughout the conventional paper drying process, enhancing the drying energy efficiency. This study also included presence of gas-fired infrared emitters in the drying process as well for which the spectral absorption coefficient of PCM was measured and incorporated into the theoretical model. Finally, the impact of the presence of PCM in convective air-drying of moist paper is numerically investigated. The hot air ow is generated by an in-line jet nozzle. The air impinges on the exposed surface of the moist paper while the other side is considered to be perfectly insulated. The results provide the corresponding air flow field as well as air temperature distribution in between the nozzle exit and the surface of the moist paper. The results also reveal the enhancement of drying rates with PCM, fundamentally confirming the role of PCM on enhancing the energy efficiency of convective drying of moist paper.

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.

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.

Smart textiles especially Phase Change Materials (PCMs) are getting attention because these materials can provide regulation of wearer’s body climate and provide comfort in the temperature fluctuations during the physical activity like sports. These materials have the advantage of latent heat energy storage that can absorb and release high amount of energy over a narrow temperature range around the human’s body temperature to provide thermal comfort. Phase Change Materials (PCMs) absorb energy during the heating process as phase change takes place and release energy to the surroundings during the reverse cooling process. The types of phase change materials that are suitable for sports applications are hydrated inorganic salts, linear long chain hydrocarbons, Poly Ethylene Glycol (PEG). The concept of thermal comfort and working of PCMs in the textiles garments are important for determining the functionality of PCMs. Phase Change materials are micro capsulated in the shells by “Situ polymerization technique before application to sportswear and garments. The PCMs microcapsules are incorporated in the sportswear and garments by fiber technology, lamination, foaming and coating. The testing of clothing containing micro capsulated PCMs is discussed after the incorporation of PCMs in textiles. Quality parameters that are key for getting good results are mentioned i.e. particle size, thermal conductivity, fire hazard treatment, durability and performance of micro capsulated PCMs and clothing. In the last section findings, suggestions and conclusion are discussed. / Program: Magisterutbildning i Applied Textile Management

Chalcogenide phase change (PC) materials can be reversibly transformed between the high resistivity (~ 1 Ω∙m) amorphous state (OFF-state) and low resistivity (~ 10-6 Ω∙m) crystalline state (ON-state) thermally, both are stable at the room temperature. This makes them well suited as reconfigurable RF switches and non-volatile memories. This work will present the understandings of two key characteristics of PC materials, the crystallization dynamics and the threshold voltage (Vth), as they determine performance limitations in these applications. Crystallization dynamics describe the correlations of the states, temperature and time; the Vth is the trigger of the threshold switching which leads to the “break down” of PC materials from OFF-state to ON-state. The four-terminal indirectly-heated RF switches with high cut-off frequency (> 5 THz) has advantages over other technologies but its programming power (~ 1.5 W) is yet to be reduced. Measuring the maximum allowed RESET quench time in the crystallization dynamics is critical for designing low power switches. As a major contribution, this work provides a universal methodology for accurate heater thermometry and in-situ crystallization measurements for this study. On the other hand, understanding the Vth is essential for high power handling applications as it determines the maximum power that an OFF-state switch can withstand without being spontaneously turned on. This work will discuss new observations and learnings from Vth measurements including the geometry dependent Vth variations which provide insights into the threshold switching mechanism. Unlike RF switches, faster crystallization is desired for memories to improve the write speed. The non-Arrhenius crystallization needs to be explored to achieve short crystallization time (< 10 ns) at high temperature (> 700 K). As another major contribution, this work will present a nano-scale (~ 100 nm) high-speed (thermal time constant < 5 ns) PC device for assessing the crystallization time in this regime, and provide a comprehensive learning for the crystallization dynamics from 300 K to 1000 K by developing a unified framework based on the fragility model and growth-dominated crystallization. This can be used to accurately simulate the crystallization process for any device geometry and estimate the RF switches power and Vth.

Solar assisted heat pump (SAHP) systems have been widely applied in domestic hot water (DHW) production due to their sustainability and stability in operations. However, their performance efficiency requires further improvement using advanced technologies such as energy storage with phase change materials (PCM) and optimal system controls. Undoubtedly, employing PCMs for latent heat storage (LHS) application has a great potential to improve a solar thermal application performance. Despite this fact, the use of PCM in this area is quite limited due to the poor thermal conductivity of available PCMs. Therefore, heat transfer enhancement is one of the essential strategies that can overcome this obstacle. Accordingly, a test rig of a new indirect expansion solar assisted heat pump (IDX-SAHP) system has been designed, built and instrumented. The system can handle heating capacity up to 9 kW. The IDX-SAHP system consists of three operational loops: solar thermal, solar-air assisted heat pump and load profile. A 2 kW PCM heat exchanger (HX) was purposely designed and installed in the system solar thermal loop to store solar energy, when applicable, and release heat when required by the heat pump. The PCM HX is employed with a novel heat transfer enhancement method. The maximum coefficient of performance (COP) of the IDX-SHAP system reached 4.99 during the sunny day with the PCM (HX) integration. However, the maximum energy saving was achieved during the cloudy day with the PCM HX integration. Moreover, the proposed heat transfer enhancement method has been modelled through CFD package and validated with the experimental results. This allows a clear understanding of the reasons for the longer discharging process compared with the charging process. Furthermore, the inlet flow rate and temperature variation of the PCM HX was simulated during charging and discharging processes. The optimum inlet flow rate for this application was found at 0.1 kg/s while the optimum inlet temperature was found at 40°C. Meanwhile, the whole system was modelled by the coupling of TRNSYS, EES and CFD to investigate the potential and advantages of using the system in locations with rich solar intensity such as Cairo and Madrid. The simulation shows that the solar thermal operation loop was called more frequently in these locations. This had a significant impact on the system energy consumption, especially during winter. The maximum COP and solar performance factor (SPF) of the modelled system were 5.3 and 0.83 respectively.

The present study has focused on the use of coil heat exchangers (CHEs) with microencapsulated phase change material (MPCM) slurries to understand if CHEs can yield greater rates of heat transfer. An experimental study was conducted using a counterflow CHE consisting of 3 helical coils. Two separate tests were conducted, one where water was used as heat transfer fluid (HTF) on the coil and shell sides, respectively; while the second one made use of MPCM slurry and water on the coil and shell sides, respectively. The NTU-effectiveness relationship of the CHE when MPCM fluid is used approaches that of a heat exchanger with a heat capacity ratio of zero. The heat transfer results have shown that when using a MPCM slurry, an increase in heat transfer rate can be obtained when compared to heat transfer results obtained using straight heat transfer sections. It has been concluded that the increased specific heat of the slurry as well as the fluid dynamics in helical coil pipes are the main contributors to the increased heat transfer.

There is a renewed interest to use material as wood to construct large multi-storey buildings in Sweden, but lightweight material tends to increase the indoor temperature fluctuations during days with large changes in outdoor temperature. The problem can be resolved by integrating phase change material (PCM) in the construction. This increases thermal inertia which mitigates the fluctuations.           The scope of the study is to develop a simulation model in COMSOL Multiphysics, to validate the model experimentally and to determine the optimal position and thickness of a PCM layer in a multi-layer wall. The model, representing a building with the shape of a box, consists of two versions. The first version, called the test box, is modeled with 5 sides of pure gypsum and 1 side of PCM-gypsum composite. The second version without PCM, called the reference box, is modeled with 6 sides of pure gypsum. Since the study is focused on reducing the cooling load, the PCM gypsum composite material should function effectively during summer conditions in northern Sweden. The experimental part includes two real-life boxes, the experimental test box and reference box, built of the same type of material that is chosen for the simulation model boxes. A climate chamber is utilized for the temperature control of the two boxes while performing measurements to validate the simulation model. The simulation model showed deviations from the experimental measurements. The temperatures inside the climate chamber, at all five points of measurement, were lower than the equivalent points in the simulation. It was possible to compensate by adjusting the overall ambient temperature down with 0.6 °C in the simulation, resulting in smaller errors. The PCM positioning resulted in recommendations to place the PCM closest to the interior space. The testing of different PCM thicknesses showed the best heat storage for the thickest PCM layers, but the PCM storage efficiency should have been considered as well.

No description available.

The ability to pattern in the nanoscale to drill holes, to draw lines, to make circles, or more complicated shapes that span a few atoms in width is the main driver behind current efforts in the rapidly growing area of nanomanufacturing. In applications ranging from the microprocessor industry to biomedical science, there is a constant need to develop new tools and processes that enable the shrinking of devices. For this and more applications, nanomanufacturing using electron beams offers a window of opportunity as a top-down approach since electrons, unlike light, have a wavelength that is in the order of the atomic distance. Though the technology based on electron beams has been available for more than twenty years, new concepts are constantly being explored and developed based on fundamental approaches. As such, a tool that utilizes electron field-emission from carbon nanotubes was proposed to accomplish such feats. A full numerical analysis of electron field-emission from carbon nanotubes for nanomachining applications is presented. The different aspects that govern the process of electron field-emission from carbon nanotubes using the finite element method are analyzed. Extensive modeling is carried here to determine what the effect of different carbon nanotube geometries have on their emission profiles, what energy transport processes they are subject to, and establish what the potential experimental parameters are for nanomachining. This dissertation builds on previous efforts based on Monte Carlo simulations to determine electron deposition profiles inside metals, but takes them to next level by considering realistic emission scenarios. A hybrid numerical approach is used that combines the two-temperature model with Molecular Dynamics to study phase change and material removal in depth. The use of this method, allows the determination of the relationship between the amount of energy required to remove a given number of atoms from a metallic workpiece and the number of carbon nanotubes and their required settings in order to achieve nanomachining. Finally, the grounds for future work in this area are provided, including the need for novel electron focusing systems, as well as the extension of the hybrid numerical approach to study different materials.