Influence of natural convection during melting and solidification of paraffin in a longitudinally finned shell-and-tube latent thermal energy storage on the applicability of developed numerical models

Abstract

In this paper, melting and solidification processes in the shell-and-tube type latent thermal energy storage (LTES) with longitudinal fins have been numerically studied in order to determine an accurate and time-effective model for describing charging and discharging processes. Two mathematical models, one including natural convection in the liquid phase of the phase change material (PCM) and one neglecting it, have been developed. They both describe the transient three-dimensional problem of fluid flow and phase change heat transfer in the LTES. The computations, carried out using ANSYS Fluent 18.2 software, are based on an iterative, finite volume numerical procedure that incorporates enthalpy formulation for simulation of the phase change phenomenon. Results from both numerical models have been compared with data obtained by experimental investigations during melting and solidification, performed on the test LTES tank with paraffin RT 25 as the PCM and water as the heat transfer fluid (HTF). Numerical results of the model with natural convection have shown good agreement with experimental measurements, which indicates that the models could be used to accurately simulate phase change problems, while results obtained by model without natural convection have shown good agreement for solidification processes. Since numerical results obtained by both models are similar for solidification and significantly different for melting, it can be concluded that the model neglecting natural convection, with notably shorter calculation time, could be used for solidification modeling, while the model including natural convection in the liquid phase of the PCM should be used for melting modeling.