Effects of thermophysical properties on optimal selection of phase change material for a triple tube heat exchanger unit at different time scales

Abstract

The multi-criteria decision making (MCDM) method has been widely applied to select phase change material (PCM) for various applications. However, the relationship between the thermophysical properties of a PCM and the optimization objective, as well as the effect on different time scales for specific applications, has not been addressed in the selection process of the optimum PCM. In this study, to solve the above two issues, first, an orthogonal experiment with five factors and four levels is designed to explore the effect of the thermophysical properties of PCMs on the heat storage ratio of a triple tube heat exchanger (TTHX) unit based on a numerical simulation. Then, the criteria weights are determined based on the range analysis at different time scales, and finally, the technique for order performance by similarity to an ideal solution (TOPSIS) method is employed to perform the ranking and selection. The results indicated that the thermophysical properties have a significant influence on the heat storage rate. When the melting time was 20 min, the PCM density and thermal conductivity had higher weights and PlusICE-S117 was selected as the optimal PCM. However, when the melting time was 150 or 250 min, the PCM density and melting enthalpy were the primary criteria to consider, and the best choice was Urea-NaCl. Furthermore, the reliability and effectiveness of the proposed PCM selection method were verified through a comparison with the TOPSIS-entropy method.