Optimum Design, Heat Transfer and Performance Analysis for Thermoelectric Energy Recovery from the Engine Exhaust System

Abstract

Thermoelectric waste heat recovery can improve the thermal efficiency of internal combustion engines and reduce CO2 emissions. In this study, a mathematical optimization using a genetic algorithm method is applied to obtain the optimal fin parameters of a rectangular offset-strip fin heat exchanger, used with an automotive thermoelectric generator (TEG) system. Three fin parameters are considered (fin spacing, fin thickness and fin height). Their effect on the exhaust pumping power, the exhaust heat transfer coefficient and the system performance is explored. The main goal is to maximize the net power output of the system. Results show that fin spacing has the most significant effect on the system performance. Moreover, when fin spacing is reduced below 0.5 mm, a negative net power output is obtained. By comparing the performance of stainless-steel (SS) and copper heat exchangers, it was found that the SS heat exchanger requires smaller fin spacing and fin height, which induces a higher pressure drop. TEGs with higher maximum operating temperature will allow further utilization of the exhaust heat, without a decline in performance due to overheating. Finally, a maximum net power output of 553.3 W is achieved using the copper heat exchanger and commercial bismuth-telluride (Bi2Te3) thermoelectric modules.