Thermal Management And Experiment On Refrigerant-based Direct Cooling For Battery Module

With the continuous development of electric vehicles,as well as the requirements of the power performance,specific energy,safety and service life of power batteries,the power battery system urgently requires an efficient thermal management system.In this paper,the refrigement-based direct cooling thermal management system is emphatically studied.In this paper,the basic functional test bench of the refrigement-based direct cooling heat management system is constructed with reference to the air conditioning system of electric vehicles.And the corresponding design calculation is carried out on the basis of the cooling demand of the system designed.At the same time,referring to the calculations,match the components of the refrigeration system and build the experimental bench of the refrigetant-based direct cooling thermal management system.First,construct the data acquisition and control system around the refrigetant-based direct cooling thermal management test bench.Take NI-SCXI data acquisition equipments as the core of the data acquisition system,and design the virtual instruments to centrally monitor and process the temperature,pressure refrigerant flow and other data in the whole experimental system.The RapidECU rapid prototyping controller is used as the system control core to achieve the control of compressors,fans and other controllable devices in the experimental system.Secondly,For the thermal characteristics of the refrigetant-based direct cooling battery thermal management system,the effects of compressor speed and condensing wind speed and the cooling structure of the battery module are separately explored.In the experiment,the compressor speed and the condensing wind speed were adjusted separately,and other factors were unchanged.The results show that the cooling effect of the refrigerant-based direct cooling thermal management system is related to the compressor speed and the condensing wind speed.The higher the compressor speed and wind speed,the more obvious the cooling effect.Under the influence of the refrigerant pressure loss in the direct cooling plate,the transverse temperature difference of the battery module increases when the compressor speed increases.High thermal conductivity graphite and copper plates were used as heat dissipation fins of the experimental module.Under the influence of thermal properties of high thermal conductivity graphite fins and copper fins,the graphite fins have better cooling effect and temperature uniformity under low load conditions.The cooling effect of copper fin is more obvious when the module heat production load is larger.Then,according to the start-up characteristics of the direct cooling process,the influence characteristics of the compressor speed and the condensing wind speed in different heat generating conditions were investigated respectively.The speed of the compressor and the speed of the condensing wind are adjusted respectively under the condition of stable load.The results show that the surface temperature difference of the direct cooling plate is related to the compressor speed and the condensing wind speed.The higher the speed of the compressor,the larger the maximum temperature difference on the surface of the direct cooling plate,and the shorter the duration of the large temperature difference.The cooling wind speed mainly affects the maximum temperature difference on the surface of the direct cooling plate.When the speed of the compressor and the condensing wind speed is coupled in the variable load condition,it is found that when the rate of change of the compressor speed and the condensing wind speed is the same or close to the rate of change of the thermal load,the surface temperature of the straight cooling plate has the best consistency.Finally,aiming at the problem of the timeliness in the heat pump regulation,the experimental studies on the refrigeration system's early start,immediate start and delayed start were carried out respectively.In the experiment,the start-up time of the direct cooling system was adjusted based on the load time of thermal load.The experiment shows that different cooling measures should be taken according to the different initial temperature and heating state of the battery.Starting the refrigeration system in advance can reduce the energy consumption of the system,prevent the battery from heating up sharply in the heavy load condition with high initial temperature,and prevent the battery from exceeding the optimal operating temperature range.When the module temperature is low but the heat production load is large,the cooling system should be started later to prevent the rapid drop of battery temperature.