Performance evaluation and parametric optimization strategy of a thermocapacitive heat engine to harvest low-grade heat

A novel Stirling-like irreversible electrochemical thermo-capacitive regenerative cycle operating between a heat reservoir and a heat sink for harvesting low-grade heat is proposed, in which the main irreversible losses are considered. Expressions for the efficiency and power output of the cycle are derived. The inherent regenerative heat loss of the cycle is revealed. The influences of several important parameters, such as the capacitance of the supercapacitor, charge ratio, endpoint voltage of the charging process on the power output of the cycle are discussed. The maximum power output and corresponding efficiency are calculated. The results show that when the charging endpoint voltage of the electrochemical thermo-capacitive regenerative cycle is 10 V, the maximum power output is 31.9 W and the efficiency at the maximum power output can reach 12.8%, which is 51.2% of the Carnot efficiency. The optimal values for several parameters at the maximum power output are determined. The parametric optimum selection criteria of the cycle are provided. The results obtained can ensure the cycle to operate in the optimum states.