Numerical validation and assessment of vertical and horizontal latent heat energy storage system during a melting process

Abstract

Passive enhancement techniques have been widely adopted in thermal energy storage applications such as the phase change material (PCM) based latent heat energy storage systems to improve the thermal performance of these systems with minimal complexities. Recent studies have shown high interest in investigating the effect of different system orientations as a passive technique to improve the performance of thermal energy storage systems. This paper, thus, seeks to fill the research void in developing a numerical model that can be applied to assess the thermal effectiveness of the vertical and horizontal LHESS as a heat exchanger in addition to the melting dynamics of the PCM. This paper discusses a detailed numerical investigation using Computational Fluid Dynamics (CFD) simulation that was developed based on an experimental study. This paper displayed the numerical validation of the temperature profiles and heat exchanger effectiveness of both vertical and horizontal LHESS with insight into behaviour of the phase change material within the systems. The simulation results displayed the trends of the temperature profile and effectiveness were well captured against the experimental study. The numerical model displayed that the horizontal LHESS was more thermally effective than the vertical LHESS which was attributed to its superior free convective heat transfer behaviour and transient supply temperature of the heat transfer fluid. The horizontal LHESS reduced the PCM melting duration by 23 %, 13.3 %, and 33.3 % in comparison to the vertical LHESS for the HTF flow rates of 1.4, 0.7, and 0.35 l/min, respectively. It was observed that at all HTF flow rates, the rate of melting at the horizontal LHESS slowed down after approximately 85 % of the PCM have been melted which was caused by the absence of natural convection, resulting in the remaining PCM to melt mainly by conduction.