Experimental Study Of Loop Heat Pipe Enhanced By Pressure Head Of Evaporation

Heat dissipation becomes the primary consideration with the wide application of high heat flux components.Loop heat pipe is a two-phase heat sink that relies on wick to provide capillary pumping.It has high efficiency,long transmission distance and strong heat transfer capability.It is widely used in electronic component devices for cooling.This paper first introduces the research status of loop heat pipes at home and abroad.It is found that the capillary force is not the only driving force for the operation of the loop heat pipe.The driving force generated by the phase change of the working fluid is not negligible during the operation of the loop heat pipe.Based on this,this paper proposes and builds a loop heat pipe with prominent vapor phase indenter,and analyzes the loop heat pipe and the capillary pump driven loop heat pipe from the thermodynamic angle,pressure drop angle and energy angle.Similarities and differences.In this type of loop heat pipe,a porous medium with high permeability,high porosity and low thermal conductivity is selected as the wick,and the wick is separated from the evaporator heating plate to form a phase change space(evaporation chamber).),this structural design causes the phase change of the working fluid to occur outside the wick,thereby increasing the vapor phase head and the cyclic driving force.At the same time,due to the "discharge and vapor barrier" effect of the wick,the gas generated by the phase change can flow in one direction,thereby reducing the occurrence of "leakage".In the experimental system,the condenser was a cannulated water cooling method.In this paper,the effects of different charging ratios,different heat sink temperatures,different working fluids and different vacuum degrees on system operation are studied experimentally.The main conclusions are as follows:(1)The loop heat pipe can start normally and maintain stable operation within the range of 20%-80% of charging ratios,and when the heat load is 75 W and the charging ratio is 35%,the loop heat pipe shows the best work.Characteristics,at this time,the operating temperature of the evaporator bottom plate is at least 65.1 ° C,the starting time is as short as 1350 s,and the operating thermal resistance is at least 0.18 K / W.At the same time,the loop heat pipe failed to start when the charging ratio was too low(15%)or too high(85%).(2)Loop heat pipe emphasized by pressure head of evaporation has an optimum heat sink temperature of 18°C.At the same time,as the heat sink temperature increases,the start time of the loop heat pipe and the operating temperature of the evaporator bottom plate are subject to certain effects,and excessive heat sink temperatures can cause loop heat pipe start-up failure.Secondly,loop heat pipe emphasized by pressure head of evaporation with methanol as the working fluid shows better heat transfer performance,and the basis of selecting the working fluid is considered from the perspective of value factor.(3)Different vacuum degrees,that is,non-condensable gases affect the start of the loop heat pipe.When the vacuum is drawn to 190Pa(vacuum degree 101135Pa),the evaporator bottom plate temperature is at least 55.7°C,the start-up time is at least 550 s,and the thermal resistance is at least 0.14K/W.At the same time,the operating heat resistance of loop heat pipe emphasized by pressure head of evaporation is lower when the operating temperatures of the evaporator wall are similar compared to the loop heat pipes driven by different capillary pumping forces.(4)The temperature fluctuation of the loop heat pipe emphasized by pressure head of evaporation is different from that of the loop heat pipe driven by the capillary pumping force.During the all operation of the loop heat pipe,there is almost no significant temperature fluctuation in the heated base plate.In addition,as the charging ratios increases or as the heat sink temperature increases,the all temperature of the loop heat pipe fluctuates sharply.