Heat Transfer Performance of a Double Tube Type Light Duty Exhaust Heat Recovery Heat Exchanger

In this paper, a light-duty exhaust heat recovery heat exchanger prototype is proposed to enhance the heating capacity of an automobile cabin. Even though the prototype is a small and simple structure of offset fins installed on a double tube, it showed a heat recovery capacity of more than 800 W. Therefore, the prototype is expected to be used in vehicles such as recreational vehicles and light utility vehicles with a cabin roof. The prototype was compared with a mass-produced model in tests of heat transfer and pressure drop performance by using hot air and a coolant. The results showed that the overall heat transfer coefficient for the prototype exceeded that for the mass-produced model for a Reynolds number of less than 1500. The heat transfer coefficients of the hot air on the inner tube walls were calculated by assuming laminar flow of hot air on the offset fin walls and the value for the prototype was much higher than that for the mass-produced model especially at low Reynolds numbers and the slope of its curve was smaller. Hot air pressure drop approximations were obtained by assuming laminar flow on the fin walls and the calculated values showed good agreement with the test results.