Wamei Lin

Vehicle Cooling Systems for Reducing Fuel Consumption and Carbon Dioxide: Literature Survey

The number of vehicles in use is increasing from year to year. It causes more fuel/energy to be consumed, and more carbon dioxide or other exhaust gases are released to the environment. But the legislations on carbon dioxide emissions have become stricter than before. In the overall effort to achieve sustainability, advanced technological solutions have to be developed to reduce fuel consumption and carbon dioxide emissions from vehicles. More than half of the energy in vehicles is lost as heat to the different cooling systems (engine cooling system, air conditioning, frictional components cooling) and exhaust gas. Reducing the amount of energy lost in vehicle cooling systems will enhance the fuel efficiency of the vehicles. This paper presents a literature survey of different cooling systems in vehicles, which includes the engine cooling system, air conditioning of the compartment, the electronic cooling system and cooling of frictionally heated parts. The usage of exhaust gas in some cooling systems is also included. Some methods or factors are presented for these different cooling systems. Flow field and thermal management are important factors in designing the engine cooling system. Whereas the exhaust gas can be circulated back to the engine, or used for driving air conditioning units. Reducing the thermal resistance can improve the electronic cooling performance. The flow field will affect the cooling of the frictional components. This literature survey is offering a starting point for future research in the vehicle cooling systems.

Comparison and Analysis of Heat Transfer in Aluminum Foam Using Local Thermal Equilibrium or Nonequilibrium Model

Aluminum foams are favorable in modern thermal engineering applications because of the high thermal conductivity and the large specific surface area. The present study aims to investigate an application of porous aluminum foam by using the local thermal equilibrium (LTE) and local thermal nonequilibrium (LTNE) heat transfer models. Three-dimensional simulations of laminar flow (porous foam zone), turbulent flow (open zone), and heat transfer are performed by a computational fluid dynamics approach. In addition, the Forchheimer extended Darcys law is employed to evaluate the fluid characteristics. By comparing and analyzing the average and local Nusselt numbers, it is found that the LTNE and LTE models can reach the same Nusselt numbers inside the aluminum foam when the air velocity is high, meaning that the aluminum foam is in a thermal equilibrium state. Besides, a high interfacial heat transfer coefficient is required for the aluminum foam to reach a thermal equilibrium state as the height of the aluminum foam is reduced. This study suggests that the LTE model can be applied to predict the thermal performance at high fluid velocities or for the case with a large height.

Graphite Foam Heat Exchanger for Vhielces

Because of the high thermal conductivity (1700 W/(m.K)) and the low density (0.2 to 0.6 g/cm 3 ), the graphite foam is a good option for heat exchangers in vehicles. However, there is a high pressure drop through the foam due to the open cells of the foam. In order to evaluate the performance of graphite foam heat exchanger, a simulation comparison between a convectional aluminum louver fin heat exchanger and a corrugated graphite foam heat exchanger is carried out in this paper. The aim of the comparison is to investigate the coefficient of performance (COP), power density (PD), and compactness factor (CF). Useful recommendations are highlighted to promote the development of graphite foam heat exchangers in vehicles.

Performance Analysis of a Countercurrent Flow Heat Exchanger Placed on the Truck Compartment Roof

Due to the increasing power requirement and the limited available space in vehicles, placing the heat exchanger at the roof or the underbody of vehicles might increase the possibility to handle the cooling requirement. A new configuration of the heat exchanger has to be developed to accommodate with the position change. In this paper, a countercurrent heat exchanger is developed for position on the roof of the vehicle compartment. In order to find an appropriate configuration of fins with high thermal performance on the air side, the CFD (computational fluid dynamics) approach is applied for a comparative study among louver fin, wavy fin, and pin fin by using ANSYS FLUENT software. It is found that the louver fin has high thermal performance and low pressure drop. Thus, the louver fin is chosen to be the configuration of the countercurrent heat exchanger, which presents higher heat transfer coefficient than a cross flow heat exchanger. For a specific case, the overall size and the air pumping power of the countercurrent flow heat exchanger is lower than that one for a cross flow heat exchanger. Several suggestions and recommendations are highlighted. (Less)

Performance Analysis of Aluminum and Graphite Foam Heat Exchangers Under Countercurrent Arrangement

Due to the increasing power requirement and the limited available space in the vehicles, a countercurrent heat exchanger (HEX) is proposed for the position on the roof of the vehicle compartment. Furthermore, a new material, graphite foam with high thermal conductivity and low density, is a potential material for HEXs in vehicles. In order to evaluate the performance of the graphite foam HEX, the CFD computational fluid dynamics (CFD) approach is applied in a comparative study between the graphite foam and the aluminum HEXs under countercurrent flow condition. The analysis is conducted for the thermal performance (heat transfer coefficient) and the pressure loss. The simulation results show that the graphite foam HEX proves higher thermal performance than the aluminum HEX. However, due to the high pressure loss in the graphite foam HEX, the coefficient of performance in the graphite foam HEX is much lower than that of the aluminum HEX. A specific case study is carried out to evaluate the performance of graphite foam HEX as well. Useful recommendations are highlighted and provided to promote the development of the countercurrent flow HEXs in vehicles.

A Review of Cooling Systems in Electric/Hybrid Vehicles

Due to increasing oil demand and serious global warming, a green power generation system is urgently requested in transportation. Electric/hybrid vehicles (EV/HEV) have been considered as a potential solution with great promise in achieving high energy/power efficiency and a low environmental impact. The important electric and electronic equipment in EV/HEV are the battery, inverter and motor. However, because of the high power density in the inverters or the low working temperature of batteries, the cooling problems affect significantly the working performance or the lifetime of electric and electronic equipment in EV/HEV. This paper views different cooling systems including the battery cooling system, inverter cooling system and motor cooling system. A general introduction to the EV/HEV and the electric and electronic equipment working processes are briefly presented at first. Then different methods for the battery cooling system, the inverter cooling system and the motor cooling system are outlined and discussed in this paper. Among other things, the means of using phase change material, or electro-thermal modules are significant for the battery cooling system. Finally, some conclusions or recommendations are presented for the cooling systems, in order to promote the EV/HEV development. (Less)