| Efficient and accurate battery temperature control solution is an important guarantee for thermal management and thermal safety of electric vehicle power batteries.Enhanced heat transfer and increased thermal safety requirements promote hydronic circulation thermal management,direct refrigerant cooling and heating,emergency evaporative cooling,and innovation and enhancement of composite integration technology.Therefore,we continue to explore the innovation of thermal management control of power battery systems,as well as the mechanism of integrated thermal system interaction management and control,especially the strengthening and synergy research the heat transfer of liquid direct cooling for battery.Through enhanced and coordinated management and contro l,the thermal management and thermal safety requirements of multi-variable working conditions and multi-heat sources system are realized,and the energy distribution and utilization of electric vehicles are achieved,and the integrated heating and cooling control of the whole vehicle is formed,promoting the advancement of electric vehicles with high safety,high reliability,low energy consumption and high comfort.Under the support of the National Natural Science Foundation of China(No.U1864213 and No.51376080),this article carried out the research on the key technologies and scientific problems about heat transfer enhancement and collaboration of hydronic circulation thermal management for battery.Meanwhile,this article combined with the structural design of the battery cooling device components and the formulation of a reasonable temperature control strategy under the precise temperature control of the power battery system.Further,we also explored the collaborative problem battery system and the HVAC system.To evaluate battery thermal control performance comprehensively,the simulation platform of battery thermal management system for vehicle dynamic conditions,the battery cell electro-thermal model and the power battery system heat flow transmiss ion model based on AMEsim and FLUENT have been established.The 1D vehicle dynamic model can analyze discharge characteristic of the battery system on the basis of power and torque matching between the electric motor,mechanical drive system and battery system.As fed with battery system discharge characteristic by TXT,the 3D battery electro-thermal model can calculate the heat generation characteristic.As compiled with the battery heat generation characteristic by UDF,the 3D battery system model can explore thermal control performance.This method can calculate the dynamic driving conditions for the later simulations.In terms of expanding the limitation of heat transfer permeability,a liquid cooling heat transfer structure using the pneumatic component was proposed.The cooling capacity was extended by improving the gas pressure gradient in the discrete space of the battery module,increasing the aerodynamics of the flow rate in the space.This article proposed the integrated thermal management of mixed flow with air circulation cooling method.Based on the analysis guidelines,many parameters,such as average temperature change of battery system,average temperature change of cells in high and low rows,the temperature uniformity coefficient and temperature difference coefficient,the fan position,fan installation height,and fan series-parallel connection,have been optimized.This article introduced the orthogonal experiment with four factors and three levels to sift out the weights of main in FLUENT factors for different optimization targets.As concluded,the coolant inlet temperature had a great influence on the average temperature change of cells in high row,and the fan aerodynamic characteristic heavily affected the battery system temperature consistency.In order to further enhance the effect of liquid thermal management and the heat transfer capacity,as well as simplify the liquid flow system,the evaporative direct cooling of the integrated heat pump was studied.While avoiding the heat exchange between the heat pump refrigerant and the heat transfer fluid,low temperature and emergency cooling can be achieved.The system studied the heat transfer characteristics of battery heat exchanger plates and combined the dynamic conditions of the vehicle,and designed the high discharge rate and heat transfer structure to explore the pressure drop characteristics and heat transfer characteristics of the refrigerant gas-liquid two-phase boiling flow.Based on summary characteristics of gas-liquid two-phase flow boiling heat transfer and pressure drop characteristics,a three-unit parallel-flow type evaporator had been proposed,which owned a medium pressure drop,a low wall temperature and a high heat transfer coefficient.Additionally,the effects of thermo-fluid parameters(e.g.refrigerant inlet saturation temperature,flow rate,subcooling,ambient temperature and battery discharge rates)on evaporator outlet vapor,pressure drop,wall temperature and battery thermal control had been obtained,which can provide significant guidance for battery evaporative cooling under various vehicle dynamic conditions.In addition,under the dynamic condition,the typical compressor control characteristics were set,and the refrigerant flow was used as the element to further ensure the temperature control of the power battery under high temperature condition.The characteristics of the refrigerant flow rate and the evaporative direct cooling temperature under the relevant structure were studied.Characterized by a simple linear flow variation,the evaporator outlet vapor,pressure drop,and wall temperature and battery thermal control of the evaporative heat transfer plate was studied by using the different flow rate with the time-varying slope.Among several typical variations,comparative analysis showed that the temperature drop and temperature uniformity of the battery system under high load and high power output conditions can be effectively improved,thereby providing greater control of dynamic process optimization potential cooperative control.In the thermal management based on heat pump integration,it is necessary to accurately ensure the temperature control of the electric system and meet the heat load requirements of the air-conditioned passenger compartment,and to coordinate the control in time under different dynamic conditions to compensate for the difference.This is a breakthrough and attempt in research and control in integrated management.A collaborative study based on supply and demand was proposed,which was based on real-time demand and dynamic envelope of thermal management heating and cooling supply system.To this end,taking the variable frequency control refrigerant flow as an example,this paper attempted to study the synergistic characteristics and impact relationships of the vehicle's energy optimization allocation and comprehensive utilization.In detail,on the basis of active,passive and timely priority integration,especially avoiding the violent fluctuation of the passenger compartment te mperature,and the parallel evaporator air conditioning system was designed to coordinate with the thermal management of the direct cooling and the passenger cabin thermal comfort.It was proposed that the battery side temperature drop and temperature average were prioritized,and the refrigerant distribution scheme that the battery side evaporator using a small flow rate,and the passenger compartment evaporator using a large flow rate was determined.The principle of thermal flow coordination between the direct cooling battery and the passenger compartment was established.The research showed that the temperature of the battery pack under the typical power load condition can achieve a good temperature rapid decrease.And the average temperature drop rate was greater than 1.7K/min,and the temperature uniformity within 4K~8K can still be guaranteed.At the same time,it effectively avoided the excessive fluctuation of the air supply temperature of the passenger compartment,which was basically stable in the range of 285K~288K,and the PMV thermal comfort evaluation index PMV met the recommended range by ASHARE.Obviously,the control boundary based on dynamic cohesive provided control multi-component synergy and complementation for the heat pump system,which was conducive to the precise guarantee of battery temperature control and passenger cabin comfort.Therefore,on the basis of researching efficient heat transfer,further solving the optimal utilization and distribution of vehicle energy,improving the integrated heat transfer performance of vehicle multi-heat system,improving power,energy saving,safety and comfort are the key to future thermal management of electric vehicles. |
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