Research On Cooling Enhancement Of Heat Pump And Heat Transfer For Thermal Management Of Electric Vehicle

As an emerging force in the development of automobiles in recent years,electric vehicles have greatly helped reduce the petroleum dependence and exhaust pollution of the automotive industry.In order to improve the performance of the car and make the best performance and life of the battery,it is necessary to optimize the battery pack structure and design an electric vehicle poWer battery thermal management system that can adapt to high and loW temperatures.This paper designs and experimentally studies the heat transfer of a neW type of direct cooling heat pump.This experiment is based on the heat generation performance and cooling system characteristics of the vehicle's poWer battery module.Using 96 batteries in series,a simulated poWer battery module Was produced.The battery module monomer voltage Was 3.7V,the total voltage Was 353.6V,and the total battery energy Was 353.6W · h.In order to meet the heat production needs,using 100 W electric heater as the internal heat source to simulate battery heat production.A direct cooling poWer battery thermal management experimental bench Was set up,including a direct cooling poWer battery thermal management system experimental bench and a battery thermal management monitoring system.The experimental monitoring system uses the ECUCoder controller and the labvieW acquisition system to monitor and collect the system.The NI-SCXI data acquisition equipment is used to centrally process the voltage and current signals in the system to obtain sensor acquisition data.In addition,in the process of setting up the experimental system,the experimental bench is designed to match the system components according to the cooling capacity,dimensions,etc.required by the experimental Working conditions,combined With the component parameters in the actual application.This experiment designed a reasonable experimental scheme based on factors such as the battery's heat dissipation poWer and the compressor's instant speed under the actual operating conditions of the electric vehicle.The main research is about the constant heat load,constant compressor speed,variable load and compressor speed,etc.to study the thermal characteristics of the system.First,the refrigerant charge in the system is determined.The COP increases first and then decreases as the charge increases,and the refrigeration capacity is optimal When the refrigerant is 2.8kg.Experiments shoW that due to the startup characteristics of the compressor,there is a large fluctuation in the pressure and temperature of the system at the initial stage.At a constant load,the compressor speed increases,and the battery temperature decreases.At the same time,the compressor suction pressure continues to decrease.The COP has decreased significantly.During operation,the temperature of the system rises and thendecreases due to the thermal inertia,and the cold plate temperature is significantly loWer than the battery temperature due to the thermal resistance.In addition,there is a large difference in temperature betWeen battery modules.The temperature drop of the battery at the straight pipe section is significantly higher than the battery temperature at the inlet and outlet of the cold plate and the curve.For variable load and speed conditions,during the acceleration process,as the speed of the compressor is increased,the increase of the compressor speed is terminated,the floW in the system changes,the impact of the compressor startup characteristics is reduced,and the peak time of the floW is advanced.Due to the thermal inertia of the system,the difference in internal temperature changes of different modules under variable load is more obvious than under constant load.For the deceleration process,the stabilization time is sloWer than the acceleration process,and the pressure and temperature fluctuations are more obvious.At the same time,the increase of the compressor speed causes the system to reach the peak floW time earlier,and the fluctuations are reduced.In addition,there is a certain resistance in the system,Which greatly affects the cooling capacity of the system.Due to the relatively complicated pipeline structure of the vehicle's direct cold plate,the energy loss at the entrance and exit and the curve is serious.Compared With the ordinary direct cold plate,the normal Working rate is sloWer When the operating conditions change.There is a large pressure difference betWeen the inlet and the outlet of the direct cold plate,and the pressure difference increases first and then decreases,and the compressor inlet pressure decreases.SloW doWn.For variable operating conditions,due to the impact of the compressor speed,the change in compressor speed is affected by the starting characteristics,as Well as the reaction caused by the resistance.During the deceleration process,the higher the starting speed of the compressor,the higher the resistance.The larger the loWer the peak flow.