Experimental study of thermal energy storage system for solid particles/ heat transfer oil in shell and tube heat exchangers with H-shaped fins

Abstract

The solid-state sensible heat storage method is cost-effective, technically simple, and works well across wide temperatures. Using return fines (RFs) as the heat storage medium (HSM) can ease problems like RFs in excess and high energy consumption in the sintering process. This article first characterizes the thermal properties of RFs. Results show a specific heat capacity of 0.67–0.97 kJ/(kg·°C) within 20–380 °C, with stable thermal properties from 100 to 1000 °C. Then, the heat transfer performance of RFs and heat transfer oil (HTO) in a shell and tube heat exchanger is experimentally investigated. H-shaped fins are added to enhance the heat transfer. Stacking solid particles on the shell side can avoid direct contact between the HSM and HTO, the tiny size limitations of HSM particles, and cracking problems caused by thermal expansion. The thermal energy storage (TES) unit operates within 170–270 °C. Effects of different flow rates (30, 20, 10 L/min) and charging/discharging temperatures (300/160, 290/150, 280/140 °C) on system performance are explored. Increasing the HTO flow rate and charging temperature and lowering the discharging temperature can reduce charging/discharging time and enhance average power. Cycle efficiencies for flow rates of 30, 20, and 10 L/min are 86.9%, 85.2%, and 79.5% respectively. The 30 L/min working condition shows the best performance. Remarkably, system performance improvements are relatively limited compared to the 20 L/min setting. Regarding charging/discharging temperatures of 300/160, 290/150, and 280/140 °C, cycle efficiencies stand at 73.3%, 85.2%, and 70.6%, respectively, with the 290/150 °C setting displaying the most favorable characteristics, including the shortest total charge and discharge time of 59.3 min and the highest cycle efficiency. Efforts to enhance the system's insulation and maintain a substantial temperature differential between HTO and HSM are pivotal in accelerating the charge/discharge process and minimizing heat loss.