Numerical investigation of heat transfer characteristics in a shell-and-tube latent heat thermal energy storage system

Abstract

This paper presents the numerical investigation for a shell-and-tube latent heat thermal energy storage system (LHTES) employing numerical modeling and simulation with the FLUENT software. The LHTES consist of coilers where the heat transfer fluid (HTF) flows and a cuboids shell filled with phase change material. The unsteady N-S equation and energy equation using enthalpy measurement to deal with the latent heat of melting/solidification are solved. The effect of the tube diameter on the heat charging performance is examined, and the result shows that the functional relationship between the diameter of the tube and phase-change-rate is not monotonic. The optimal diameter of the tube at 20mm is used in all the subsequent computations. The influence of natural convection on charging and discharging processes is analyzed with positive tube pitch, and the result shows that natural convection plays a crucial role in the charging process and significantly accelerates the melting process; thermal conduction is dominant in the discharging process during the phase change stage which makes the discharging process much slower than the charging. The effects of the initial inlet temperature and velocity of HTF on the charging and discharging processes are studied in the case while PCM has a specific initial temperature. The result indicates that the inlet HTF velocity does not show a significant effect on the charging and discharging processes; the inlet HTF temperature shows a substantial effect on both processes. The temperature changing processes with time at different locations are also analyzed to dig more profound characteristics of the phase change process.