Numerical Study on Thermal and Flow Characteristics of Divergent Duct with Different Rib Shapes for Electric-Vehicle Cooling System

The cooling performance of the air-conditioning system in electric vehicles could be enhanced through the geometrical optimization of the air ducts. Furthermore, it has been proven that the heat-transfer performance of divergent channels is better than that of conventional channels. Therefore, the present study investigates the thermal and flow characteristics of divergent ducts with various rib shapes for the cooling system of electric vehicles. The thermal and flow characteristics, namely, temperature difference, pressure drop, heat-transfer coefficient, Nusselt number and friction factor, are numerically studied. Divergent ducts comprising ribs with the different shapes of rectangle, isosceles triangle, left triangle, right triangle, trapezoid, left trapezoid and right trapezoid arranged symmetrically are modeled as the computational domains. The thermal and flow characteristics of divergent ducts with various rib shapes are simulated in ANSYS Fluent commercial software for the Reynolds-number range of 22,000-79,000. The numerical model is validated by comparing the simulated results with the corresponding experimental results of the Nusselt number and the friction factor, obtaining errors of 4.4% and 2.9%, respectively. The results reveal that the divergent duct with the right-triangular rib shape shows the maximum values of the heat-transfer coefficient and Nusselt number of 180.65 W/m(2)K and 601, respectively. The same rib shape shows a pressure drop and a friction factor of 137.3 Pa and 0.040, respectively, which are lower than those of all rib shapes, except for the trapezoidal and right-trapezoidal rib shapes. Considering the trade-off comparison between thermal and flow characteristics, the divergent duct with the right-triangular rib shape is proposed as the best configuration. In addition, the effect of various conditions of the inlet air temperature on the thermal characteristics of the best configuration is discussed. The proposed results could be considered to develop an air-duct system with enhanced efficiency for electric vehicles.