Encapsulated PCM-carbon nanotube based composite for thermal control of transient pulsed power loads

The key challenge faced in the design of modern high power electronics is the requirement of effective thermal management techniques. The situation becomes even more conspicuous due to certain issues associated with contemporary electronics such as; nano/micro scale developments, pulsed heat inputs, and interfacial resistance. These issues further intensify the problem of heat dissipation and pose serious challenges in the design of thermal control (TC) systems with capability to keep device operating temperatures under safe limits for their efficient and sustained working.;The present work is focused on the design of a composite TC system with particular significance for thermal protection of electronics against transient pulsed power heat loads. Three types of materials; paraffin wax, carbon nanotubes (CNTs), and carbon-carbon (CC) composites are used in a novel design configuration to produce the composite TC system design. The composite system consists of multiple layers of paraffin wax separated by partitions and enclosed in a casing of high thermal conductivity CC composite sheets. An optimum design configuration is achieved for the composite TC system by performing three separate studies to account for the critical thermal management issues.;An experimental setup consisting of a test rig enclosed in a vacuum chamber is designed and fabricated for a comprehensive thermal analysis of the TC composite. The TC composite samples are tested for three different cases: TC composite (a) without CNT additives and TIM, (b) with CNT additives and (3) with CNT additives and TIM. For each case the samples are subjected to two types of heat loads; uniform power condition and two types of varying power conditions; (a) varying power with high intensity pulses (b) varying power in stand alone mode. The TC composites samples caused a greater reduction in the heater and junction temperatures for case-b as compared to case-a. However, the samples revealed a huge damping in heater and junction temperature values for case-c as compared to case-a and b.;A geometric optimization is next performed based on the principle of constructal theory for optimizing the TC composite dimensions. The model is used to find an optimum geometry for the TC composite sample based on its heat dissipation and total energy rate and sample weight. This optimized geometry is later used to predict maximum junction temperature for the TC composite. The maximum junction temperatures are reduced further substantially for all the heat loads by using optimized dimensions for the TC composite as compared to its original size used for the experiments.;The TC composite system thus designed and analyzed represents an optimized structure built by performing a pretesting optimization to obtain a best design configuration and thermal properties enhancement. The composite system is able to control the maximum junction temperature below 55°C a requirement for portable electronics corresponding to low order of uniform (12, 24 W) and pulsed (15-55 W, 24-0, 30-0 W cycle) heat loads. It also maintained the maximum junction temperature well below 85°C for high order of uniform (30 W) and pulsed (15-75 W, 15-95 W, 48-0 W cycle) heat loads. Thus, the designed TC composite has the capability for low to high power thermal management applications. The geometric optimization routine reduced the size, weight and global thermal resistance of the TC composite and further increased its temperature damping and control ability.