Microencapsulated Phase Change Materials for Energy Storage and Thermal Management
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The continuous increase of greenhouse gas emission, the climb in fuel prices, and the limited natural resources drive human beings to utilize energy more effectively. Changes are required in energy storage and thermal management systems, particularly through the advanced technologies and systems of thermal energy storage and heat dissipation. Phase change materials (PCMs) have received considerable attention for these applications. As a novel technology to utilize PCMs, microencapsulated phase change materials (microPCMs) have drawn great interest due to their high heat capacity and easy manipulating and operating, and thus are potentially applicable in various industries. This dissertation provides results of a systematic investigation on the design, synthesis, characterization, and applications of microPCMs. With either solid-solid PCM or liquid-solid PCM as the core material, microPCMs have been synthesized with wet-chemical methods using colloidal solutions as the reaction media. To begin with, the thermophysical properties of colloidal systems were investigated, especially the change of thermal conductivity with the concentration of surfactant. Two types of microPCMs were then synthesized using emulsion techniques, and the synthesis parameters were manipulated to enhance the thermophysical properties of the microPCMs and suppress the supercooling of encapsulated PCMs. To enhance their thermal conductivity, microPCMs with large latent heat capacity and suppressed supercooling were coated with a metal layer. The as-synthesized phase changeable and thermal conductive microPCMs were applied in a heat transfer fluid to enhance the heat transfer performance. This work was focused on the following aspects. The first aspect is the thermophysical properties of colloidal solutions, such as thermal conductivity, at low surfactant concentrations around the critical micelle concentration (CMC). The second aspect is the synthesis of microPCMs in the colloidal systems with solid-solid PCM neopentyl glycol and liquid-solid PCM n-octadecane as the core material. The third aspect is the enhancement of thermophysical properties (e.g., heat capacity, supercooling,) of the microPCMs, which was achieved by manipulating the parameters of the environment of chemical synthesis. The fourth aspect is the elevation of the thermophysical properties of the microPCMs, such as thermal conductivity, after the microPCMs were produced. The fifth and final aspect is the applications of the as-produced microPCMs, e.g., to enhance the heat transfer in bulk solid materials for latent heat storage and heat transfer fluids for heat dissipation with the aid of microPCMs, with or without coating with thermal conductive silver layer.