Preparation And Test Of Latent Functional Thermal Fluid Based On Microencapsulated Phase Change Material And Its Application In Power Battery Cooling

Under the dual pressure of energy crisis and environmental pollution,the global new energy automotive industry has developed rapidly.Among them,pure electric vehicles have gained high market recognition due to their simple structure,no pollution and high energy conversion efficiency.However,with the growing market,the cooling of power batteries is a key problem to be solved urgently.Phase change energy storage materials have great latent heat and constant temperature characteristics in the process of phase change,which can absorb heat at a higher temperature,so that the temperature of the battery remains at the optimal value.It is a new type of battery cooling method with high efficiency,environmental protection,low cost and great promotion value.However,in the phase change process,the phase change material has the problems of leakage and low thermal conductivity,which greatly restricts its practical application.Therefore,in the battery cooling system,strengthening the heat transfer performance of phase change materials and efficient packaging of phase change materials are very important.This paper will develop phase change microcapsule composite phase change material which is suitable for battery cooling to improve its thermal stability,temperature regulation and thermal conductivity,and prepare it into latent heat type functional fluid for experimental study.On this basis,a flow channel variable cross-section phase change coupling liquid cooling battery cooling method is designed to study its effect on battery cooling performance.The main research contents and key conclusions of this paper are as follows :(1)In this paper,the melamine-urea-formaldehyde encapsulated octadecane and dodecane microencapsulated phase change material were prepared by the original polymerization method.Through the study,it was determined that when the weight ratio of octadecane and dodecane was 1:2,the melting temperature of microcapsules was 39.8°C,the latent heat value was 107.6J/g,and the melting peak width was 17.9°C,which could effectively expand the phase change temperature of materials,thus providing a good basis for the thermal cooling of power batteries.(2)In order to improve the thermal conductivity of microencapsulated phase change material,this paper studied the effects of the type,addition position and addition amount of thermal conductive reinforcement materials on their thermal properties.Experiments show that the thermal conductivity of microencapsulated phase change material can be increased by 1.32 times by using nitrogen doped carbon nanotubes.Compared with the addition of thermal conductive materials to the microencapsulated phase change material,the addition of shell material does not affect the thermal conductivity of the material but reduces its latent heat value.At the same time,the more thermal conductive materials are added,the higher the thermal conductivity of microencapsulated phase change material is,but the latent heat value will also decrease,and the minimum value is only 96.4J/g.(4)The cooling plate that can simultaneously use microencapsulated phase change materia and latent functional thermal fluid was designed and used for phase change coupled liquid cooling scheme,and a cooling performance test bench for the battery was built.At ambient temperature of 30°C,the cooling performance test of 3C discharge in battery pack under natural cooling,phase change cooling and phase change coupling liquid cooling was studied.The results show that the temperature of the battery pack is kept within 49 °C by the coupling cooling method of microencapsulated phase change material and latent functional thermal fluid.After four cycles of charge and discharge,the maximum temperature of the battery pack rises to 45.8 °C,showing good cooling performance.