Thermal convective effect on the performance of thermally regenerative electrochemical cycle against self-discharge

•TRECs were incorporated with flow channels to study the thermal convective effect.•TREC performance was examined using experimental and numerical approaches.•Time constant analysis was carried out with respect to flow rates.•The self-discharge effect depends on the convective heat transfer. The effect of convective heat transfer on low-grade heat recovery in thermally regenerative electrochemical cycles (TRECs), which were operated on the basis of electric double-layer capacitors, was investigated at varying flow rates of fluid flowing from thermal reservoirs. Although the TREC performance is primarily determined by the magnitude of an open-circuit voltage rise driven by a temperature difference, it can be significantly restricted by spontaneous charge losses due to self-discharge. To investigate the convective heat transfer effect against self-discharge, cycle performance was evaluated through experiments at flow rates ranging from 56 to 184 mL/min, and further estimated at extended lower flow rates to 14 mL/min through numerical calculations. When TRECs were operated between 20 and 60 °C, the highest net work was obtained to be 81.3 μJ at 184 mL/min, corresponding to 34 % conversion efficiency relative to the Carnot efficiency. Unlike the high flow rate conditions, the TREC performance below 56 mL/min significantly decreased with reduced the flow rate due to the considerable charge loss by self-discharge. This shows the stronger flow dependence of the TREC performance. This study provides a novel approach to estimate energy loss through a time constant analysis, thereby enabling better TREC designs concerning energy efficiency.