Experimental investigation of the performance attributes of a thermal energy storage unit using different system configurations

Abstract

One of the goals engineers pursue in the energy production and recovery field is to design a heat exchanger that can store a large amount of thermal energy in a shorter time. This work practically tests the performance attributes of a latent heat thermal energy storage system in a vertical shell-tube heat exchanger configuration. Water flows in the tubes that are arranged as circular layers at certain radii in the shell, which is occupied by organic paraffin phase change material (RT60). The experiments consider the effects of the tube area ratio, layer radius ratio, number of tube layers, and distribution of the tubes (inline/staggered), besides incorporating semi-circular tubes instead of complete circular ones. These experiments are conducted by employing heating water (65 °C to 75 °C) during the charging process and cooling water (25 °C) during the discharging process. The key findings from this work are that increasing the radius ratio from 1/3 to 2/3, employing semicircular tubes instead of complete ones, increasing the area ratio from 2.4% to 4.3%, and distributing the same number of tubes in two layers rather than one layer provide reductions in the charging time of 7.2%, 7.3%, 17.6%, and 11%, respectively. The corresponding augmentations in the charging/discharging effectiveness are 8.1%/2.6%, 7.4%/3.3%, 19.7%/5.7%, and 8%/4.5%, respectively. Moreover, by applying a staggered distribution of the tubes instead of an inline one, the charging effectiveness is amplified by 5.3%. Finally, a set of experimental correlations is developed to predict the charging effectiveness of the storage system.