| Heat exchanger such as intercooler,radiator and oil cooler are widely used in all kinds of vehicles.CFD technology can effectively reduce the required experimental work,production costs,and improve the efficiency of research and development,if it was employed in the accurate simulation of heat exchanger.At the same time,the simulation results can also provide the foundation for optimizing the microstructure of heat exchanger,which is of great engineering significance and economic value.In this paper,the resistance and heat transfer performance of intercooler and oil cooler are studied on CFD software Fluent by the porous media and multi-scale method.The simulation data exhibit small errors as compared to the experimental data,which proves that the simulation methodaccurately predict the overall performance of the heat exchanger well.In addition,the non-linear programming method is employed to optimize the fin structure of the oil cooler.In the case of intercooler simulation,firstly,the equations of air physical parameters about temperature are fitted under the two test conditions of relative,i.e.,humidity of 80%,absolute pressure of 280 k Pa,and relative humidity of 0%,absolute pressure of 101 k Pa to improve the simulation accuracy.On this basis,the simulation data of 90 groups of local fine structure models are studied,and the equations reflecting the overall pressure drop and heat transfer characteristics of the intercooler are obtained.Secondly,it is found that the relative errors of pressure drop and heat exchange of the intercooler are 1～12%and 4.8～6.5%,respectively,as comparing with the simulated results by software Fluent with with the experimental test results.Finally,the simulation results of the intercooler under the constant and variable physical property models of air are analyzed.It is found that the pressure drop of the variable physical property model is almost the same as that of the constant physical property model.However,the heat exchange of the variable physical property model is increased by 5%～8%compared to the constant physical property model.For oil cooler simulation,the local periodic fine structure of oil cooler is simulated under 256 groups of different conditions.The pressure drop of per unit length(ΔP_h)and the average heat flux(HF)of fin surface are recorded under each simulation condition.Then,the correlations ofΔP_h and HF on the inlet temperature and inlet speed are established.Finally,the pressure drop and heat transfer performance of the oil cooler are simulated by modifying the porous medium heat transfer model.It is found that the relative error of pressure drop is between 7.3%and 9.9%and the relative error of heat transfer is between 2.4%and 9.6%under different conditions as compared with the test data.As for optimizing fin structure,the main purpose is to optimize the wave distance(L_d),wave height(L_h)and cut width(L_w)of a offset strip fin.Firstly,13 groups of fins with different L_d、L_hand L_w are produced by using the control variable method.Then,the 13 groups of fins are simulated under different inlet boundary conditions and the corresponding pressure drop of per unit length(ΔP)and the surface heat transfer coefficient(h)of the fins are recorded.Then,the correlations ofΔP and h with L_d、L_hand L_w are established by using the regression method.Finally,the effects of L_d、L_hand L_w and inlet velocity onΔP and h are analyzed,and the fin structure is optimized by nonlinear programming.The results show that theΔP is reduced by 4.59%and h is increased by 1.39%of the optimiazed fin in compasion with the original one.Acoordingly,the comprehensive performance of the optimized fin is improved by 6.26% as compared with the original fin. |
