Date of Award
Master of Science (MS)
Phase change materials can increase the efficiency of many energy-intensive applications, such as solar power plants, solar heating and cooling systems, heat recovery systems, photovoltaic electricity systems, and Earth satellite systems. In several proposed thermal management systems for high power electronic equipment, PCMs change phase and absorb latent heat at peak energy loads during operation, then dissipate this energy later to prevent overheating. More specifically, composite PCM’s, consisting of an organic material (e.g., paraffin) and an inorganic material (e.g., metallic alloys or salt hydrates), provide a superior balance of thermal conductivity and latent heat for thermal management. Organic PCMs have low thermal conductivity but high latent heat, whereas salt and metallic PCMs have comparatively high thermal conductivity but low latent heat. While most reported PCM composite experiments have used only one phase change material, here we evaluate a composite with two phase change materials. The inorganic material used was Field’s Metal (FM: a eutectic alloy of bismuth, indium, and tin), and the organic material was paraffin wax. Common variables for evaluating PCM thermal performance, which include the cooling capacity figure of merit, energy density, and thermal conductivity, were found to be larger when the Field’s Metal and paraffin composite was embedded in high conductivity materials, such as aluminum, graphite carbon fiber, and copper. We compared the thermal conductivity of our PCM model with that of other well-known numerical PCM models and found it most closely resembled that of a parallel model. The parallel model was then used to calculate the optimal volume fractions of copper, aluminum, and graphitic carbon fiber with varying volume fractions of PCM. The optimal cooling capacity was reached at a 50% v/v fraction of high conductivity material and PCM, where 50% of the PCM composite is Field’s Metal. Compared to two-material composites, this three-material composite better distributes heat throughout the geometry. The percentage increases in the figures of merit of the composite PCM material, compared to a single PCM incorporated in high thermal conductivity material, are 68.9% for copper, 73.2% for aluminum, and 72.8% for graphitic carbon fiber. These results advance the understanding of how a composite PCM, in which both the organic and metallic components change phase, can benefit various thermal management.
Dr. Damena Agonafer
Dr. David Peters Dr. Ramesh Agarwal