Numerical investigation on paraffin/expanded graphite composite phase change material based latent thermal energy storage system with double spiral coil tube

Latent thermal energy storage (LTES) by using phase change material (PCM) is a promising technology which can solve the temporal and geographical mismatch problems between energy supply and demand in utilization of solar thermal energy and industrial waste heat, However, until now, it is still challenging to provide LTES systems with high energy storage efficiency because of the low thermal conductivity of the PCM and suboptimum structure of heat exchanger. In this work, a novel LTES system with paraffin/expanded graphite (EG) composite PCM and double spiral coil tube as heat-exchange tube was constructed. The radius of the double spiral coil-shaped tube was determined by means of the quasi steady state method. And the effects of heat transfer fluid (HTF) inlet position and the ratio of the heat-exchange area between the inner and outer coil tube on the latent heat storage performance of this system were investigated. Compared with single coil tube, LTES system with double spiral coil tube could reduce the time to finish latent heat storage.