Thermal Performance Analysis Of Three Shaped Microchannel Loop Heat Pipes

With the rapid development of industrial technologies such as power electronics,new energy vehicle batteries and high-power LED,space miniaturization and high heat flux density are gradually becoming the characteristics of heat sources.Because of the limited heat dissipation performance of conventional cooling devices,research on new high heat dissipation heat pipes is becoming increasingly important.In this paper,three kinds of shaped microchannel loop heat pipe samples are designed in combination with the advantages of easy start of loop heat pipe and thin thickness of pulsating heat pipe.The heat pipe replaces the capillary wick of the conventional loop heat pipe as a vaporizer by microchannel structure,which are the tree-like bionic microchannel loop heat pipe,the parallel microchannel loop heat pipe,and the self-similar fractal microchannel loop heat pipe.The author carried out the analysis of heat transfer performance of three heat pipes by means of experimental research and numerical simulation research,exploring the operating characteristics,starting characteristics and thermal resistance characteristics of heat pipes under different filling rates and different tilt angles.Firstly,four phenomena were found in the tree-like bionic microchannel loop heat pipe and the parallel microchannel loop heat pipe: the wave stability phenomenon,the maintaining stability phenomenon,the platform-type instability phenomenon and the rising instability phenomenon,while only two phenomena were found in self-similar fractal micro channel: the maintaining stability phenomenon and the rising instability phenomenon.Secondly,the starting temperatures of the three heat pipes increase with the increase of the liquid filling rate.The tree-like bionic microchannel loop heat pipe has the lowest starting temperature at the inclination angle of 60°,while the other two heat pipes is 90°.Finally,the optimal thermal resistance of the wave stability phenomenon in the tree-like bionic microchannel heat pipe is 30%(The charging ratio,CR)and 60°,the maintaining stability phenomenon is 45% and 60°.The optimal thermal resistance of the wave stability phenomenon in parallel microchannel loop heat pipe is 30% and 90°.the maintaining stability phenomenon is 60% and 90°.The optimal thermal resistance in the self-similar fractal microchannel loop heat pipe occurs at 45%,60% or 75% and 90°.The operating characteristic at this time is the maintaining stability phenomenon.Comparing the three heat pipes,the heat performance of the tree-like bionic microchannel loop heat pipe is the best,followed by the parallel microchannel loop heat pipe,and the heat performance of the self-similar fractal microchannel loop heat pipe is the lowest.However,due to the influence of turbulent fluctuation caused by steam backflow,the average temperature fluctuation range of the evaporator in the treelike bionic microchannel loop heat pipe is also the largest.