Numerical study of electrochemical thermocells for harvesting low-grade waste heat

Experimental studies on electrochemical thermocells or thermogalvanic cells have demonstrated their potential for lowgrade heat utilisation, but the numerical studies on these systems are lacking. In this study, a mathematical model is developed to simulate the transport and electrochemical processes in the thermocells. After model validation, parametric simulations are conducted to understand the effects of various operational and structural parameters on thermocell performance. The studied parameters include the concentration of redox couples, temperature difference between anode and cathode, size of thermocell and the thickness and location of the separator. It is found that a higher concentration of redox couples and larger temperature difference between the two electrodes benefit thermocell performance. It is also interesting to find that vertically arranged thermocells produce a higher power density than that of horizontally arranged thermocells by 13.85%. Besides, the power density is increased by approximately 30% if the separator is attached to the cathode in comparison to the non-separator condition. Optimal values of the structural parameters are identified. This research clearly demonstrates that the performance improvement of thermocells depends on not only electrochemistry and materials, but also engineering design optimisation.