The Flow And Heat Transfer Coupling Analysis And Construction Modification Of Vehicular Cooling Models Based On Field Synergy Principle

The cooling system of vehicle is an important assistance system to ensure the stability of the vehicle, and it has a direct effect to energy-saving and emission reduction. Recently the heat dissipation environment of vehicles is gradually deteriorating due to the emergence of high-density and high-power engines, as well as the application of many new technologies and systems. As a result, new demands have been raised on the volume, weight, efficiency and intellectualization of cooling systems. Meanwhile, the profit rate of automobile industry keeps decreasing so that it becomes an important direction to work out the optimization of cooling system with economical and effective measures.Based on field synergy principle, together with the application of CFD and the combination of wind tunnel techniques, the paper completed the research on the flowing and hear transfer characteristics of vehicle cooling modules, including that of the unit and module, partial and whole, micro and macro. The main contents are as follows:1. The research on flowing and heat transfer characteristics is completed on local heat exchanger unit, single heat exchanger, heat exchanger assemble and the combination between heat exchanger and fan, according to the establishment of the CFD 3-D simulation model.2. The microscopic analysis and integral simulation of single heat exchanger was completed based on multi-scale coupling.3. The wind tunnel experiment platform was built up to examine the effectiveness of simulation model according to the experiment data.4. According to the possible conditions in real situation, the original model and boundary conditions are adjusted to analyze the effect of uneven flow of both hotter and colder medium on the heat transfer process.5. The inside and outside flowing characteristics of single heat exchanger was analyzed, the optimization method was raised based on the analysis of effect of factors such as structure and the distribution regulation coolant.6. The analysis is completed on the effect of the relative position and distance, and the flow of hotter medium on the heat transfer process of heat exchanger module.7. The air flowing characteristic is researched when driven by suction fan. The effect of different fan configuration on the heat transfer performance of cooling module was compared by the combination between cooling module and fan.8. According to the field synergy principle, the results of research mentioned above was proved and explained, and the measure to enhance the heat transfer or structure optimization were designed.Conclusions from the researches above are as follows:As for the hear transfer process with air as media, considering the media property changing during calculation, the temperature difference between hot and cold side will decrease slightly, the pressure drop on the cold side will increase, and the pressure drop on the hot side will obviously decrease, compared with constant property simulation model.For the heat transfer of partial unit, the heat transfer capacity of the unit will decrease when the velocity distribution of hot medium is not homogenous, especially the velocity of hot medium decreases along with the flowing direction of cold one. If the temperature of cold medium decreases along the flowing direction, the temperature field synergy between hot and cold media is relatively better, thus showing better heat transfer performance, otherwise the heat transfer effect will get worse. If the velocity of cooling medium increases along the flowing direction of hot medium, the temperature will decrease due to the rise of velocity, and temperature field synergy between hot and cold media could be better, thus improving the heat transfer performance, otherwise the heat transfer will also get worse.As for the single heat exchanger, the application of multi-scale coupling method could raise the calculation accuracy, however the operation process would be complex. With reference to the vehicle heat exchangers, the inhomogeneous distribution of hot medium is an important factor to lower the working efficiency of intercooler. As a result, it is an effect optimization to improve the structure of heat exchanger, thus allowing a homogeneous distribution of hot medium in channels. Besides, the temperature of cold medium in low-temperature section could be lower if the flow rate of cold medium in low-temperature was increased, and the temperature field synergy could be better, thus realizing the enhancement of heat transfer.As for the adjacent cooling module, the change of the relative position of the core would have slight effect on heat transfer performance without the consideration of heat radiation factors. However, when the distance between cores reached a certain value, the increase of core distance would not affect the heat transfer performance. Changing the hot medium flowing direction of upper heat exchanger could achieve a more homogeneous distribution of flow rate and temperature in hot channels, thus improving the efficiency evidently, but it will meanwhile worsen that of the lower exchanger.When driven by suction fan, the velocity distribution in upper area of fan is inhomogeneous, the flow velocity was high at blades, especially at blade tips, and the velocity in center and edge was relatively lower. It is a key factor for the efficiency improvement of fan if the heat exchanger and fan were sealed. For typical water tank exchanger on passenger vehicles, the combination of a larger fan and two smaller fans, compared to traditional fan configuration, could obtain better heat transfer effect under the same static pressure.