Modeling and Performance Analysis of Alternative Heat Exchangers for Heavy Vehicles

Abstract: Cross flow heat exchangers made from aluminum are common as radiators in vehicles. However, due to the increasing power requirement and the limited available space in vehicles, it is extremely difficult to increase the size of heat exchangers (HEXs) placed in the front of vehicles. Placing the heat exchanger on the roof or at the underbody of vehicles might offer opportunity to increase the size of the heat exchangers. A new configuration of heat exchangers has to be developed to accommodate the position change. In this study, a countercurrent heat exchanger is proposed for the position on the roof of the vehicle compartment. Furthermore, a new material, graphite foam having high thermal conductivity (1700 W/(m•K)) and low density (0.2 to 0.6 g/cm3), is introduced as a potential material for those heat exchangers in vehicles. In order to find an appropriate configuration of fins with high thermal performance and low pressure loss on the air side for a countercurrent flow HEX, the main-flow enhancement and the secondary-flow enhancement methods are employed to analyze different configurations of fins. The main-flow enhancement cases included are (1) aluminum: louver-, wavy-, and pin fin; (2) graphite foam: corrugated-, wavy corrugated-, pin-finned-, and baffle fin. The secondary-flow enhancement cases included are graphite foam: rectangular fin, rectangular fin with one-side dimples, and rectangular fin with two-side dimples. The computational fluid dynamics (CFD) approach is applied for the comparative studies by using the ANSYS FLUENT software. Moreover, the simulation results are verified by experimental results from literature. After comparing the performance among different configurations of fin, it is found that the aluminum louver fin shows better performance than the wavy fin and pin fin. Also the graphite foam wavy corrugated fin presents higher heat transfer performance and lower pressure drop than the corrugated-, pin-finned-, and baffle fin. On the other hand, the graphite foam rectangular fin with two-side dimples exhibits better performance than the fin with one-side dimples. The cross flow HEX (made from aluminum) is compared with countercurrent flow HEXs (made from aluminum or graphite foam), in terms of the coefficient of performance (COP), power density (PD), compactness factor (CF), and energy saving efficiency. Due to the high power density and high compactness factor in the countercurrent flow HEXs, the overall size and weight of the countercurrent flow HEXs are much lower than those of the cross flow HEX. Moreover, the graphite foam wavy corrugated fin provides higher power density and higher compactness factor than an aluminum louver fin because of the high thermal conductivity and low density of the graphite foam. Furthermore, a graphite foam fin with two-side dimples exhibits higher coefficient of performance than an aluminum louver fin, and it becomes very efficient in energy saving. However, due to the high pressure loss in the graphite foam wavy corrugated fin, the air pumping power for the countercurrent flow graphite foam wavy corrugated fin HEX is much higher than that of the cross flow aluminum louver fin HEX. Based on the presented studies, useful recommendations are highlighted to promote the development of countercurrent flow HEXs and the graphite foam HEXs in vehicles.