(689i) Enhanced Heat Transfer for Phase Change Materials Engine in Unmanned Underwater Vehicles

Phase change materials (PCM) such as paraffins have been used in the thermal engine of some unmanned underwater vehicles (UUVs) because it can provide a potential infinite energy storage solution without the limitation of battery capacities as for the current UUVs. Developing PCM and a thermal engine with enhanced heat transfer rates and increased power generation per profile for UUVs is necessary to enable more advanced sensing and ocean exploration activities. We improved the dispersion of some additives with high thermal conductivity and used them to increase the thermal conductivity of paraffin PCMs. Also, the composition of various PCM was controlled to adjust the melting temperature and heat of fusion and to achieve reduced melting time. Thermal conductivity and melting time for the PCM mixtures with additives were quantified using an off-the shelf thermal conductivity analyzer and home-made melting time test set up to correlate the relationship with the concentration of the additives, composition of PCM mixtures over the full operating temperature range. The impact of thermal conductivity and melting temperature of the PCM mixtures on the melting time were simulated using computational fluid dynamic modeling, and fin structures added to the thermal engine were proposed and evaluated to further accelerate the phase change process. Potential power generation per profile for UUVs using the modified PCM mixtures and fin structures of the PCM engine was determined based on the rate of thermal energy collection.