Heat transfer phenomena in foams infiltrated with phase change materials: Applications to cooling for electronics and energy storage devices

With the extremely rapid progress in developing new micro-electronic devices and the urgent need to harvest and store energy, designing a new generation of heat sinks and energy storage devices has become important. The materials used in these applications should possess high heat capacity and high thermal conductivity. Phase Change Materials (PCMs) have a huge heat capacity but low thermal conductivity. On the other hand, foams exhibit high thermal conductivity, low weight, and good mechanical properties.; A composite of a PCM infiltrated inside a high thermal conductivity foam was used in designing a heat sink and an energy storage device. First, a novel numerical technique was developed to solve the conservation equations of mass, momentum and energy in such a composite. A two-energy equation model was used to tackle the local thermal non-equilibrium between the two phases. The conservation equations were formulated in non-orthogonal curvilinear coordinates to accommodate both regular and irregular geometries. Second, an experimental test rig was built to measure the thermal conductivity of the foam materials and to capture the temperature and the melting evolution of the PCM inside aluminum and carbon foams. The numerical model predicted the temperature field and the location of the solid-liquid interface during the melting process accurately compared to the experimental results.; Then, the numerical model was used to make a design optimization for the heat sink and the energy storage. Generally, it was found that using such high thermal conductivity foams significantly enhanced the performance. The performance of the heat sink for steady heat generation electronics enhanced with decreasing foam porosity, increasing foam pore size, and with activating the foam surface energy. Changing the geometry and inserting internal fins also showed little enhancement, while changing the heat sink orientation made the biggest impact on the performance. For electronics subjected to fluctuating energy spikes, the presence of the PCM showed a tremendous reduction in the heat sink resistance. For energy storage design, it was found that using high thermal conductivity foams showed significant improvements of the storage output power. The output power improved with increasing foam thermal conductivity and foam pore size.