Study On Heat Transfer Performance And Basic Application Of Two-phase Closed Thermosyphon With Binary Mixed Working Fluid

Thermosyphon is a passive heat transfer element with simple structure and high heat transfer efficiency.The binary mixed working fluid can improve the thermal performance of the thermosyphon by adjusting the ratio of different substances.In this paper,the heat transfer characteristics of binary mixed working fluid thermosyphon were tested and the basic research on its application in battery thermal management were carried out.The research results can provide theoretical and data support for the practical engineering application of thermosyphon.In this paper,different specifications of thermosyphon were designed and processed,and a heat transfer performance test system of thermosyphon were constructed.The thesis studied the influence of five kinds of heat flux density(1.67 k W/m2,3.35 k W/m2,5.02 k W/m2,6.69 k W/m2,8.36 k W/m2),five kinds of filling ratio(30%,40%,50%,60%,70%),different proportion of methanol-based mixed working fluid(water and methanol are mixed with a ratio of 1:19,1:4,1:1,4:1,19:1,ethanol and methanol are mixed with a ratio of 1:19,1:4,1:1,4:1,19:1)on its heat transfer performance.In addition,based on the thermal characteristics of power battery,the heat dissipation device of hybrid working fluid thermosyphon was designed,the heat dissipation test platform was built.and the basic research on the application of mixed working fluid thermosyphon was carried out.The results show that:(1)Under the same filling ratio and the same working fluid,with the increase of heat flux density,the outer wall temperature and the heat transfer coefficient of the mixed working fluid thermosyphon increase.Under the same heat flux density,the wall temperature of the mixed working fluid thermosyphon from the evaporation section to the adiabatic section and then to the condensing section decreases continuously(Te>Ta>Tc)and the axial temperature has the same changing trend.(2)Under the same heat flux density and the same working fluid,the thermal resistance and the maximum temperature difference of the methanol-based mixed working fluid thermosyphon decrease with the decrease of filling ratio in the range of30%~70%.The optimal filling ratio of methanol-based mixed working fluid thermosyphon is within 30%~40%.(3)Under the condition of filling ratio of 30% and heat flux density of5.02 k W/m2,the starting mode of different methanol-based mixed working fluid thermosyphon is temperature gradient type,and the starting time has little difference between 200 s and 300 s.Among them,the fastest starting is the water/methanol mixed working fluid thermosyphon with methanol ratio of 95%.(4)Under the condition of filling ratio of 30% and heat flux density of5.02 k W/m2,the maximum temperature difference of the water/methanol mixed working fluid thermosyphon with a methanol ratio of 95% is 7.3℃ smaller than that of the pure methanol thermosyphon,and the maximum temperature difference of the thermosyphon of the ethanol/methanol mixed working fluid thermosyphon with a methanol ratio of 95% is 5.4℃ smaller than that of the pure methanol thermosyphon.In contrast,the temperature distribution of the methanol-based thermosyphon with a methanol ratio of 95% is more uniform.(5)Under the condition of filling ratio of 30% and heat flux density of5.02 k W/m2,with the increase of the proportion of methanol in the mixed working fluid,the heat transfer performance of the methanol-based thermosyphon was enhanced.The thermal resistance of the water/methanol mixed working fluid and ethanol/methanol mixed working fluid thermosyphon with methanol ratio of 95% is55.0% and 46.3% lower than that of methanol ratio of 5%,respectively.The equivalent thermal conductivity of the thermosyphon of water/methanol mixed working fluid and ethanol/methanol mixed working fluid with methanol ratio of 95%is 2.27 times and 1.84 times that of methanol ratio of 5%,respectively.Among the ten methanol-based mixed working fluid thermosyphon studied,the water/methanol mixed working fluid thermosyphon with methanol ratio of 95% has the best heat transfer effect.(6)Among the three cooling methods(heat pipe cooling system,fan cooling and natural cooling),the simulated battery temperature under the heat pipe cooling system is the lowest.The mixed working fluid thermosyphon heat dissipation device can control the temperature at the best working temperature of power battery,so it is feasible to apply mixed working fluid thermosyphon in the thermal management of power battery.