The effect of conical shell and converging/diverging tube on the charging performance of shell and tube latent heat thermal energy storage system

Abstract

Latent heat storage is a promising method to overcome the problem of the intermittent nature of renewable sources. However, the main challenge in utilizing phase change materials is their poor thermal conductivity which leads to the slow charging and discharging of latent heat thermal energy storage tanks. Geometric optimization is a passive method to enhance the charging and discharging rate. In this paper, the geometric optimization of a shell and tube storage tank is studied numerically. Different configurations, including conical shell and tube, cylindrical shell and diffuser, cylindrical shell and nozzle, and a combination of conical shell and diffuser with different tilting angles is investigated. The height of all cases is assumed to be a constant number. The melting process is modeled by the enthalpy-porosity method, and the Boussinesq approximation is employed to consider the effect of natural convection. The governing equations are solved by a spatially and temporally second-order finite volume method. It is found that the main determining parameter is the cross-sectional area ratio of the phase change material at the top to its value at the bottom of the tank. By increasing this ratio, the effect of conductive heat transfer is attenuated, but natural convection is augmented. Since the charging rate is affected by these two heat transfer mechanisms, an optimum value of around 10 is obtained for this shape factor which results in an increased storage rate of 25 % compared to the case of cylindrical shell and tube storage tank. The optimum shape factor can be obtained either by a conical shell and tube or by combining a conical shell and a diffuser.