abstract
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Conventional cooling techniques, such as the use of heat pipes and forced convective cooling can be inadequate for many high performance electronic chips or when the operating ambient temperature is high. In such cases, there is a need for active cooling of the chip to keep its operating temperature below the design point. Thermo-Electric coolers (TEC) provide an attractive option in such instances and have been developed and used for thermal management in electronic packaging systems. Such systems, however, can have a low overall coefficient of performance since the TEC needs to be kept on even at low heat load conditions. In this thesis a hybrid thermal management system is considered that incorporates a TEC based active path in parallel with a conventional heat pipe based passive path. A thermal resistance network model is developed for the hybrid system that takes into account the governing thermo-physical equations for the TEC. The advantage of this hybrid system is that the passive path can transport the heat from the chip at moderate thermal conditions keeping the TEC electrically off while the TEC modules can be turned on when.the conditions become adverse. A higher overall system coefficient of performance can be achieved compared to a system consisting of only TEC module(s). One important design parameter is the fraction of the total heat sink area dedicated to each path, which will depend on the rated heat dissipation from the chip, thermal resistance of the entire heat sink and the operational ambient temperature. Controlled experiments were performed to validate the hybrid thermal management model for an example case of electronic package. The experimental facility consisted of a flexible heater to simulate the chip. The heat sink in the experiments was a cooling loop and the ambient temperature was controlled by changing the temperature of the water flowing through the cooling loop. The thermal resistance of the heat sink was simulated by acrylic glass. Experiments were performed for different fraction of the heat sink area dedicated to the heat transfer paths for a range of ambient temperatures. An operating envelope was presented to compare different hybrid thermal management configurations with a heat pipe based passive system and an only TEC system. The model predictions were in good agreement with the experimental results. Parametric studies were performed to analyze the effect of different variables on the system performance. The hybrid model can be used for other thermal management systems involving TEC modules.