Experimental study of solid particles in thermal energy storage systems for shell and tube heat exchanger: Effect of particle size and flow direction

The solid particle thermal energy storage method offers cost-effective, simple, and high-temperature suitable solutions. It effectively resolves chemical compatibility and thermal stress issues in shell-and-tube heat exchangers. This work studies the quartz sands' particle sizes and flow direction's impact on heat exchanger performance. The results show that heat conduction and natural convection heat transfer mechanisms exist on the particle side. Flow direction minimally affects charge/discharge time and stored energy but significantly impacts delivered/recovered energy and exergy and energy and exergy efficiencies. Optimal performance is achieved when HTO enters from the top during charging and from the bottom during discharging, creating a transparent thermal gradient of “Top Temperature High, Bottom Temperature Low”. This distribution minimizes natural convection losses, resulting in a 15–17 % increase in energy efficiency and an 11–13 % increase in exergy efficiency compared to reverse flow. Smaller particles show slightly faster temperature rise due to lower energy storage density. Large and medium particles perform well, achieving energy efficiencies of 81.5 % and 81.0 % and exergy efficiencies of 62.1 % and 61.8 %, respectively. Small particles have an energy efficiency of 79.0 % and an exergy efficiency of 60.4 %, possibly due to higher porosity and increased heat losses.