Performance Experiment And Simulation Study Of The Loop Heat Pipe With Liquid Line Wick

With the continuous development of electronic integration technology,the miniaturization and integration of electronic equipment have become the mainstream trend of today,followed by large electronic equipment heat flux,local heat spots,heat dissipation difficulties and other problems.How to efficiently heat dissipation in limited space has become a new problem.However,traditional fans have a large volume of heat dissipation and low efficiency.Immersion liquid cooling is not suitable for large-scale promotion because of its high cooling cost,complex system and difficult maintenance.Loop heat pipe(LHP)as a passive two phase heat transfer equipment,using the evaporation-condensation phase transformation of working medium to transfer heat,has the advantages of small volume,high heat transfer efficiency,safe and stable operation.LHP is an excellent solution to the problem of electronic chip heat dissipation.A novel type of liquid line wick LHP without compensation chamber is designed and fabricated in this paper.This structure design,on the one hand,effectively reduces the volume of the evaporator,on the other hand,increases the thermal resistance between the evaporator and the liquid line.The optimum filling rate was determined to be 25% by filling rate experiment.The purpose of this paper is to show that the liquid line wick LHP is still feasible and has some advantages over the traditional LHP with compensation chamber.The start-up and heat transfer performance of the novel LHP under horizontal condition were tested by experiments,compared with that of the traditional flat LHP under the same condition.Compared with the traditional LHP,the heat resistance of the liquid line wick LHP is smaller,and it is only 7/10 of that of the traditional loop heat pipe at10 W.Meanwhile,the temperature oscillation phenomenon is effectively eliminated.At high heat loads the heat resistance is larger but the start-up time is greatly reduced.The starting time at 130 W is only 1/2 of that of the traditional loop heat pipe.By testing and analyzing the operation performance of the novel type of LHP under variable working conditions and gravity assisted conditions,it is found that the novel type of LHP can still be started successfully under 10 W load under the most unfavorable working condition when the evaporator and gas line are filled with liquid initially,however,the temperature overshoot of 11.9 ℃ appears.In the horizontal state,it has good variable operating performance,fast response and no temperature oscillation.And the change of inlet temperature of the liquid line wick is little affected by the change of heat load,which can be maintained at a low temperature,which is conducive to the rapid response and stable operation of the system under variable operating conditions.Compared with horizontal operation,the operation performance is greatly improved in gravity assisted operation.The operation performance is significantly improved in 10° or 20° gravity assisted operation,and the ultimate thermal load reaches 230 W and 250 W,respectively.The operation performance improvement effect is attenuated when the gravity inclination continues to increase.Based on the mass conservation equation,energy conservation equation and thermal dynamic equation of the novel LHP,a steady mathematical model of the LHP with liquid line wick is established to predict the evaporation temperature,pressure drop and other operating parameters.The structure and performance of the novel LHP were optimized by simulation calculation of different liquid filling amount and different liquid line wick length.