Structure optimization of a polygonal automobile exhaust thermoelectric generator considering in-vehicle compatibility

Polygonal heat exchangers (HEXs) are more applicable to automobile exhaust thermoelectric generators (AETEGs) due to their symmetrical structure and low backpressure, but their structural parameters will directly affect the systems' performance. For the sake of accurately predicting the AETEG performance based on a polygonal HEX inserted with sickle-shaped fins, a comprehensive fluid-thermal-electric coupling model was established, and the effects of HEX widths and lengths on its fluid field, thermal field, and electric properties were numerically investigated. Results indicate that increasing HEX widths reduces the pressure drop, output power, and conversion efficiency of the AETEG system while increasing HEX length increases its pressure drop and decreases the conversion efficiency. According to the designed in-vehicle compatibility index considering temperature uniformity, backpressure, output power, and conversion efficiency, the optimal structural parameters for HEX are H = 130 mm, Nw = 1 row, and NL = 8 columns. At an exhaust flow rate of 40 m/s and an input temperature of 600 K, the conversion efficiency, highest power, temperature uniformity, and backpressure of the AETEG system are 0.97 %, 118.24 W, 98.97 %, and 868.67 Pa, respectively. The findings provide an efficient approach to optimize the structural parameters of AETEGs with reduced backpressure in the future.