Thermal and exergetic analysis of shell and eccentric-tube thermal energy storage

The selection of artificial cylinder boundary is of vital importance in the simulation of multiple-tube thermal energy storage (TES). This paper is intended to design and compare the accuracy of the concentric and eccentric artificial cylinder boundary, which is used to simplify the geometry of multiple tubes thermal energy storage system in the numerical computation. The eccentric artificial cylinder boundary shows the higher accuracy due to fully considering the development of buoyancy-driven convection. Based on the single tube TES with eccentric artificial cylinder boundary, the effects of multiple phase change materials (PCMs) and gradient copper foam on the thermal behavior and exergetic efficiency were investigated. The field synergy principle was employed to illustrate the heat exchange process in TES. The results indicated that both the exergetic efficiency and heat transfer efficiency could be significantly improved by gradient copper foam. The layout of multiple PCMs with various melting points could remarkably reduce the complete melting time. However, the application of multiple PCMs had a little effect on the exergetic efficiency because of the large entropy generation. Besides, the results indicate that the lower inlet temperature of the heat transfer fluid (HTF) results in the higher exergetic efficiency. The outcomes of this paper help design and optimize multiple tube TES.