Experimental investigation on the thermal performance of air-cooled multi-port flat heat pipes

Abstract

An experimental investigation is conducted to study the effect of the type of working fluid, liquid filling ratio (FR) and the cooling and heating conditions on the performance of air-cooled multi-port flat heat pipes (AMFHPs) designed for the thermal management of power battery. The results show that, under the same FR of 50%,the ammonia AMFHP owns the highest thermal performance, whose equivalent thermal conductivity is 2.21–3.30 times that of one filled with acetone and 1.05–1.31 times that of one using R134a as working substance. Evaporation thermal resistance of acetone AMFHP is significantly larger than those of the AMFHPs filled with ammonia and R134a, whereas their condensation thermal resistance values are comparative. Secondly, it is found that the equivalent thermal conductivity of the R134a AMFHP with 50% FR is 1.63–2.22 times that of one with 30% FR and 1.14–1.63 times that of one with 70% FR, respectively. Thirdly, result indicates that the effect of cooling air velocity on the equivalent thermal conductivity of AMFHP is insignificant, but the temperature of evaporation section is tightly connected to the cooling air velocity. There exists an economic air velocity for each AMFHP, the appropriate air velocities of the AMFHPs filled with R134a, acetone and ammonia at FR=50% are 3.5 m/s, 2.5 m/s and 3.5 m/s, respectively. In addition, analysis of heat transfer reveals that, the intensity of heat transfer mode of the AMFHPs in liquid pool ranges from R134a, ammonia and acetone, under the same working condition and filling ratio. The most direct conclusion is that the R134a AMFHP with appropriate FR is suitable to meet the thermal management requirements of lithium ion batteries for electric vehicles.