Investigation On Temperature Uniformity Of The Flat Heat Pipe In Compound Liquid Cooling System

With the rapid development of electric vehicles,the requirement for the battery thermal management system is more and more strict.An effective power battery thermal management system can not only control the battery temperature within the appropriate operating range,but also keep the battery module a certain temperature uniformity,with a view of prolonging the cycle life of the power battery and to ensure the endurance and safety performance of the electric vehicles.The flat heat pipe has the features of easy assembly structure and high thermal conductivity.The transport of working medium in vapor chamber makes the heating surface maintain better temperature uniformity and thermal diffusivity.Therefore,it is of great engineering significance to investigate the effect of the flat heat pipe on the uniformity of battery temperature distribution.In the paper,aiming at the disadvantages of the traditional liquid cooling plate channel design and large flow resistance,as well as the complexity of the three-stage heat pipe cooling system,a compound liquid cooling system for the battery thermal management,composed of a grooved aluminum vapor chamber and a one-through liquid cooling plate was proposed.The temperature homogenization performance of flat heat pipe sandwiched between the traditional cold plate and the power battery is used to improve the temperature difference on the heating surface caused by the temperature rising of coolant along the path.Compared with the traditional three-stage heat pipe cooling system,the compound liquid cooling system presented in this paper is featured with more compact structure,simple liquid cooling channel design,and better heat transfer and temperature uniformity.To investigate the two-phase flow and heat transfer inside the vapor chamber and the coupled heat transfer with the coolant,a three-dimensional CFD model was established in this paper based on the actual size for the coupled heat and mass transfer characteristics in the compound liquid cooling system.The model was numerically solved by the VOF method and the Mixture method,respectively,and the numerical results were verified by experimental data.The research showed that the computed results with the VOF transient model are similar to that with the Mixture steady model,and the temperature distribution of the heating surface and cooling surface is in good agreement with the experimental results.According to the numerical results revealed that there is a cycle of the two-phase flow beneficial to the performance of the temperature uniformity inside the vapor chamber and it’s affected by the temperature difference on the heating surface.The influence of coolant flow,heating power and titling angle of flat heat pipe on the heat transfer performance of compound liquid cooling system was investigated.The numerical results show that the inhibition rate of temperature difference increases with the decrease of coolant flow on the heating surface,and the temperature uniformity can be maintained on the heating surface though the coolant flow is small.With the increase of heating power,the boiling intensity in the chamber increases,and the strengthening effect of boiling and condensing inhibits the temperature rise of the heating surface,so that the heating surface maintains a good temperature distribution uniformity.Tilting angle has an obvious effect on heating surface temperature difference,compared to horizontal placement,the temperature difference of the heating surface increases and the inhibition rate decreases when the flat heat pipe is inclined with negative titling angles.On the contrary,the buoyancy force and the temperature difference drive are beneficial to the heat and mass transfer in the chamber when the tilting angle is positive,and the temperature difference inhibition rate increases obviously.The flat heat pipe shows the best temperature uniformity under +20° titling angle.