Enhanced waste heat recovery from automotive engine exhaust gas using a novel spiral fin-and-tube heat exchanger

This study experimentally investigates the exhaust gas-side heat transfer and flow characteristics of a novel spiral fin-and-tube heat exchanger (SFTHX) designed for automotive exhaust waste heat recovery. The heat exchanger consists of a helically coiled stainless-steel tube fitted with L-footed spiral aluminum fins. Exhaust gas flows over the finned tube, while water flows inside the tube. The effects of exhaust gas frontal velocity, water flow rate, inlet water temperature, and damper position on the heat transfer rate, heat exchanger effectiveness, and pressure drop are examined. The results show that the heat transfer rate and pressure drop increase with increasing exhaust gas velocity, while a higher water flow rate improves the heat exchanger effectiveness. Decreasing the inlet water temperature enhances both the heat transfer rate and effectiveness. Compared with the fully open damper, the fully closed damper increases the heat transfer rate by 40–55%, with a negligible effect on pressure drop. A maximum waste heat recovery rate of approximately 8 kW is obtained with the damper fully closed at a water flow rate of 10 LPM and engine speeds ranging from 2,000 to 3,000 rpm. The use of a helically coiled tube with L-footed spiral fins represents a new configuration for engine exhaust waste heat recovery. The experimental results confirm its potential to improve heat recovery and energy efficiency in automotive applications.