Numerical investigation of using helical fins for the enhancement of the charging process of a latent heat thermal energy storage system

Abstract

This paper is focused on the enhancement of the thermal performance of a vertically oriented shell and tube latent heat thermal energy storage (LHTES) system by using helical fins. In order to see the improvement made by using the helical fin in a LHTES unit, the performance of the helically finned LHTES system has been compared with those of axially finned LHTES system, and no finned LHTES system. The length of the helical fin in the helically finned LHTES system is considered equal to the total length of the four axial fins used in the axially finned LHTES system and the net volume of the PCM is supposed to be identical for all studied cases. Three different temperatures of 345 K, 355 K, 365 K have been considered for the inner tube wall. Results revealed that for the helically finned TESS, the total melting time of the PCM can be reduced up to 18.25%, 21.5% and 16.75% in comparison with axially finned LHTES system for the inner tube wall temperatures of 345, 355 and 365 K, respectively. The presence of a helical fin causes the penetration of the heat into the core of the PCM inside the container and the motion of the molten PCM will be affected by the result of the buoyancy forces and the centrifugal force. Thus, there will be both transverse convection and longitudinal convection for the helically finned LHTES system. Besides, for the helically finned LHTES system, the PCM receives the needed heat for its full melting (charging) in less time compared to the axially finned LHTES system. This is due to the helicity of the molten PCM and also the formation of the vorticities due to the existence of the helical fin which contributes to deeper penetration of the heat and melt front.