Performance evaluation of cascaded storage system with multiple phase change materials

Abstract

The charging enhancement of latent heat thermal energy storage system is of great significance for the efficient transfer of non-uniform thermal sources. In order to solve the problem of long charging time caused by the low thermal conductivity of phase change materials (PCMs), multiple PCMs - uneven fins combination as a compound enhancement approach was proposed to improve thermal storage rate. The transient heat transfer and melting process of PCMs was numerically studied by the finite volume method and enthalpy-porosity method. Firstly, the filling ratio of high melting point PCM to high melting point PCM was optimized as 60%: 40%. Under the optimal ratio, the charging time was reduced by 29% and the thermal storage rate was increased by 9%. Then, the effect of natural convection on multiple PCMs melting characteristics was analyzed. Finally, the thermal storage performance of multiple PCMs - uneven fins combination was investigated. The results indicated that the reasonable fin arrangement (upper dense - lower sparse fins) strengthens the local convection and improves the melting uniformity, which reduces the melting time by 16% and increases the thermal storage rate by 7%. Therefore, multiple PCMs - uneven fins combination can obviously reduce the charging time and increase the thermal storage capacity, which contributes to promote efficient utilization of fluctuating thermal energy.