Thermophysical properties analysis of graphene-added phase change materials and evaluation of enhanced heat transfer effect in underwater thermal vehicles

Abstract Underwater vehicles are one of the most important tools for ocean observation and exploration, whose duration and range of underwater vehicles can be significantly extended by harvesting and utilizing ocean thermal energy. Generally, most underwater vehicles use the thermal engine to harvest ocean thermal energy. The phase change material (PCM)is the most important component of the thermal engine, the heat transfer performance of which directly affects the performance of the underwater vehicle. Enhancing the thermal conductivity of phase change materials is an effective way to improve the heat transfer rate of underwater thermal vehicles. The heat transfer performance of thermal engine can be effectively improved by incorporating graphene into PCM. In this paper, the molecular dynamic simulations of PCM with different addition ratio of graphene were carried out. Then the models of temperature-pressure-density, temperature-pressure-thermal conductivity and pressure-heat capacity were established for different simulation systems. On this basis, the internal connection between the additive ratio of graphene and the heat transfer rate of the thermal engine was revealed by using the phase change heat transfer model considering pressure conditions. The simulation shows that the appropriate addition of graphene is beneficial to the heat transfer rate of thermal engine at 0.1 MPa. Under the pressure condition of 20 MPa, the thermal engine can achieve the highest the heat transfer rate when the addition ratio is 1.2%, which also shows the best performance under simulated ocean conditions. The melting time can be reduced by 11.97% compared with the thermal engine without added graphene.