Research On Thermal Management System Cooling Modeling And Battery Thermal Control Strategy

The Vehicle thermal management system(VTMS)is an important means to ensure the high efficient power output and energy saving.The research methods on the VTMS are in the continuous progress.The approach of the multi thermodynamic systems simulation can couple the heat exchangers,power battery,power systems and analysis together.It can be used to analysis the system association on the basis of solving the heat transfer optimization and performance determination.So it can be as one of the main approaches on the thermal management system research.Under the framework of this approach,many problems need to be solved in this approach.These problems include the heat exchanger performance determination and three-dimensional(3D)characterization,the power battery temperature control strategy,the system simulation model and the integration of the CFD simulation model.In order to solve these problems,the researches are carried in this paper under the support from NSFC(National Natural Science Foundation of China)under the grant No.51376079.Firstly,the simulation approach coupling one-dimensional(1D)simulation and three-dimensional(3D)simulation are combined to establish the simulation experiment approach of the multi thermodynamic systems.The 1D simulation is mainly about the relevance of systems and thermodynamic system cycle.The 3D simulation is mainly about the structure change.The matlab routine is used to compile the 1D model program and the combination module.The Fluent software is used to compute the 3D simulation model in the multiple thermodynamic systems models.The combination module has the functions that include the 3D model combination and 1D relevance.Through the examples,the comprehensive ability of integrated analysis is discussed.The characteristics of heat interaction are discussed between the engine cooling,the air conditioning and the charged air cooling.Moreover the comprehensive analysis is used to discuss the heat flow variation characteristics and the transient relevance characteristics of system circulation.In order to solve the problem of equivalent representation of 3D simulation model of heat exchangers in multi thermodynamic systems,a mathematical simulation approach based on the typical structure of louver fins heat exchangers is proposed to solve the problem that the single or several louvers can not accurately represent the heat transfer characteristics of the overall heat transfer performances.This approach combined with 1D calculation program and 3D simulation of the typical structure of louver fins heat exchangers.The overall heat transfer performances can be obtained by the similar method.For the thermal management system of power battery pack in multi thermodynamic systems,the liquid heat exchange plate is placed in the bottom of battery.And it is as the basic flow heat transfer structure of the battery pack.On this structure,the effects of flow temperature,flow rate and discharge rate on the temperature consistency and uniformity are analyzed.Through effects,the evaluation method is established.For the improving the temperature uniformity of the power battery pack,the comparison between the liquid plate at the bottom,the liquid plate at the one side,and the liquid plate at the one side with the heat conduction enhancement is carried out.Among the liquid plate at the one side with the heat conduction enhancement,the comparative analysis is carried out between the aluminum slice and the graphite slice.The results show that the graphite slice can be used to improve the temperature uniformity on the surface of the battery when the weight is same to the aluminum slice.Based on the liquid plate at the one side with the 0.6mm graphite slice,the schemes of linear cooling and heating are proposed.The effect of the cooling and heating rate is analyzed.The results show that the linear cooling scheme with a relatively long cooling time can ensure the uniformity of the battery surface temperature.And the linear heating scheme with a relatively long cooling time can also ensure the uniformity of the battery surface temperature.The efficient operation of the power battery pack depends on the thermal management system which is maintaining the temperature in the highly efficient operating temperature range and ensuring the temperature consistency and uniformity.In this paper,the thermal control strategies in the different temperature zones are proposed.The idea is that the battery working temperature range is divided into the high temperature zone,the normal temperature zone and the low temperature zone.The different thermal control strategies can be used to the different temperature zones.This can achieve the purpose of keeping the power battery pack in the high efficiency operation temperature.Among these strategies,the thermal control strategy in high temperature zone is that the large circulation linear cooling mode is used to cool the power battery pack to the stable temperature.The cooling slope of the linear cooling mode is closely related to the temperature range of battery.The thermal control strategy in normal temperature zone is that the small circulation and the large circulation are combined to make the battery temperature maintained at the stable temperature.First the small circulation is used to increase the battery temperature to the stable temperature.And the large circulation is used to adjust the fluid temperature into the battery and make the battery temperature maintained at the stable temperature.The thermal control strategy in the low temperature zone is that the thermal control strategy in normal temperature zone is used when the battery temperature is increased to the minimum value of the normal temperature zone with heat pump.In order to deal with the change of discharge rate,the adjustment range of liquid temperature should be adjusted according to the discharge rate.Through the CFD models of under-hood and battery pack,the interaction analysis is made on the battery radiator and motor radiator.