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

Abstract

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 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.