| With the development of electric vehicles to the high range,high safety and short charging time,the performance and life of power batteries have become the key constraints.It is very important to develop an efficient and reliable power battery thermal management system.Because power battery can maintain high performance and long life only when operating at the appropriate temperature,high performance thermal management becomes crucially important.In this paper,a power battery thermal management system based on a U-shaped plate heat pipe is proposed.The flow characteristics and heat transfer mechanism of the U-shaped plate heat pipe were studied in detail through experiments,and the performance of the battery cooling system equipped with U-shaped plate heat pipe was further studied by using the analog battery module.Firstly,the effects of filling rate and heat flux on the heat transfer performance of the U-shaped plate heat pipe were studied experimentally.The results showed that the filling rate of the U-shaped plate heat pipe could be divided into three ranges:unbalanced filling rate,oscillating filling rate and thermal equilibrium filling rate.In the thermal equilibrium filling rate,the temperature at the hot end of the heat pipe is almost unchanged at the filling rate of 56%-63%,and then increases with the increase of filling rate in the range of 63%-98%.Through thermal resistance analysis,it was found that the performance of the U-shaped plate aluminum heat pipe is the best when the filling rate is 63%.With the increase of heat flux,Thermal resistance of heat pipes has the minimum value when the heat flux is 0.35 W/cm2.Then,the U-shaped plate heat pipe visualization experiment was conducted by using quartz glass tubes,and the flow characteristics and heat transfer mechanism of vapor-liquid working fluid in different working stages were studied.Before the start-up of the heat pipe,three kinds of vapor-liquid states of the working fluid were observed,namely vapor tubes,liquid tubes and vapor slug-liquid slug co-existent tubes,which correspond to the slug flow,the annular flow and the liquid cylinder oscillation in the circulation flow respectively.The experimental results showed that the heat transfer capacity of slug flow and annular flow is much greater than that of liquid cylinder oscillation.When the working fluid circulates in the heat pipe,three stages of bubble formation were observed at the hot end:bubble detachment,bubble fusion,and change of slug;and the process of annular flow changing into slug flow or churn flow were observed at the elbow bend.It was found that the start-up of U-shaped plate heat pipe is aroused by the vapor plug produced in the liquid tube.The number of liquid tubes increased with the increase of the filling rate.Therefore,there is an optimum filling rate range,which makes the heat pipe easy to start and show strong heat transfer capability.The start-up of U-shaped plate heat pipe is also related to the heat flux.With the increase of heat flux,the start-up temperature difference of heat pipe will decrease.Experiments on different working fluids show that the heat transfer performance of U-shaped plate heat pipe with R134a as working fluid is better than that of R113.Finally,the analog battery module equipped with U-shaped plate heat pipe was tested to simulate the charging and discharging conditions of power batteries.It was found that the U-shaped plate heat pipe can significantly reduce the temperature difference of battery module and improve the temperature homogeneity between the cells.Under the simulated 1C charging and 1C discharging conditions,the maximum temperature of the battery module decreases from 61.74? to 36?,and the proportion of heat pipe heat dissipation reaches more than 60%of the total generated heat value of simulation battery module.When charging at different rates,it was found that U-shaped plate heat pipe coupling water cooling solution can control the maximum temperature of the battery module at 36.2 ? under the charging rate of 1C. |
PDF Full Text Request