Research Of Power Battery Cooling System Based On Porous Media

Temperature has a very significant effect on performance of power batteries of electric vehicles.Existing cooling technologies have their own limitations.Open porous media has the character of high specific surface area and light weight.It can improve fluid turbulen,enhance the cooling effect and make the temperature distribution more uniform.Considering the heat dissipation demand of electric vehicle power battery and the heat transfer characteristics of porous media,the battery cooling model based on the porous media is proposed.At first,flow and heat transfer mechanism of porous media is studied.Then the key factors of design about the system based on porous medium are determined.At last,the influence factors of heat dissipation performance of the system are analyzed and studied.The main research conclusions are summarized as follows:1.Heat transfer mechanism in porous media is studied.Temperature distribution of heat conduction in the porous media and Nu number expressions of forced convective heat transfer are derived.According to Brinkman-Darcy extension model and local thermal non-equilibrium model,the expressions of dimensionless velocity,dimensionless temperature and Nu number is deduced respectively,in the two cases of flat channel filling with porous media and clean channel.Influence law of various dimensionless parameters on heat transfer process is analyzed,such as the Da number,Bi number,the effective thermal conductivity ratio k,porosityεand so on.2.Flow and heat transfer in the narrow gap vertical channels filling porous medium is researched by numerical simulation.Through the analysis of the velocity distribution in narrow gap vertical channel filling the porous media,resistance criterion equation is fitted.Through the effect of channel width height ratio,inlet velocity and porosity on the channel wall temperature,the convective heat transfer coefficient and Nu number,heat transfer characteristics criterion equation is fitted.By exergy transfer theory,convective heat transfer exergy transfer characteristics of narrow gap vertical channel filling the porous media are analyzed,and the convective heat transfer exergy transfer equation is set up.The expression of exergy transfer Nu number owing to temperature difference heat transfer Nu_eTT and the lost exergy transfer Nu number owing to flow friction Nu_eP are further derived.Exergy critical Re numbe is defined,and Exergy critical Re number at this research condition is 2147.5.3.Heat transfer law in narrow gap vertical channel filling the porous media is researched by experimentation.Experimental platform is set up and experimental procedure is designed.Temperature measuring point is arranged uniformly.The temperature of each point is measured under different inlet velocity,heat flux,and porous materials.Then convective heat transfer coefficient and the average Nu number are obtained.Direct measurement error analysis and indirect measurement error analysis are carried out for direct and indirect measurement of experimental data,respectively.In order to prove the influence of different porous materials and porosity on heat transfer,the cheap iron shavings materials and foam copper are choose in this study.Difference of wall temperature of narrow gap vertical channel filling the porous media and narrow gap vertical clean channel are compared and analyzed in different inlet velocity and heat flux.4.Application of porous media in power battery cooling system is studied.Design process of system based on porous media is set up.Key factors of design process are determined,and the influence factors of heat efficiency of the system are analyzed.Design goal of temperature,the filling length,porosity and housing materials are researched respectively.The law of temperature distribution are analyzed in the case of different ambient temperature,inlet speed and speed of vehicle.The velocity distribution uniformity index and temperature distribution uniformity index are analyzed in the different location,quantity and shape of the inlet and outlet.According to the analysis and research of the battery arrangement and the distance between the battery and the box,the optimization scheme of the box structure is proposed.In conclusion,combination field of flow and heat transfer in porous media and field of mechanical design,design of cooling system and flow and heat transfer in porous media in the system are studied by theoretical derivation,experiment and numerical simulation methods.The research results and methods can provide theoretical guidance and reference for the study of flow and heat transfer in porous media and the design and application of power battery cooling system.