Experimental And Simulation Investigation Of Flat Loop Heat Pipe With Longitudinal Replenishment At A Positive Elevation

With the rapid development of information technology,a higher power and more accurate electronic device puts forward higher requirements on the cooling process.And how to realize the efficient thermal management of electronic equipment has become a research hotspot at home and abroad.In addition to the traditional single-phase convection heat radiation method,Loop Heat Pipe(LHP)has been favored by researchers as a representative of the two-phase heat exchange technology for a far distance.Because it has a strong heat transfer ability,long transmitting distance,low heat transfer resistance,good isothermal properties,and no moving parts,etc.It is widely used in passive heat radiation of high heat flux electronic equipment.To meet the cooling demand,for an electronic equipment with a height of 30mm,an aluminum flat plate evaporator has been developed with a biporous wick and a longitudinal compensation chamber.A water-cooled condenser is located above the evaporator,and the working fluid is ammonia.Comparing with the traditional horizontal structure of LHP,this LHP can not appear the“dry-out and a higher heat transfer capacity has been proved.As the power increases,the gravity can not meet the demand of the heat transfer and flow of fluid.The capillary pressure increases continuously for the pressure balance with the flow pressure drop,eventually the capillary pressure becomes dominant role for a higher heat transfer.This paper focuses on the limit conditions for heat-1(70 W,15.22W/cm~2),heat-2,3(35W,20.71,W/cm~2),the loop heat pipe is operated stably with the condensing temperature of 60°C.The thermal resistance curve of the loop heat pipe tends to decrease with the increase of power.After 20W,it varies around 0.20°C/W.When the power remains the same as before,and the condensation temperature varies between 30°C and 60°C,the temperature of the heat source shows a linear trend,and the heat transfer performance of the loop heat pipe does not change obviously.The relationship between flow and heat transfer in each component of the loop heat pipe has been analyzed,the corresponding experimental process has been simulated by MATLAB.Comparing the simulated values and the experimental results,the error is within the range of±5%.For the pressure drop analysis,When the heat-1 power is less than 30 W,and the heat-2,3 power is less than 15 W,the gravity will balance the flow pressure drop,this is gravity control mode.And conversely,the capillary pressure will provide a driving force for the operation,this is the capillary pressure control mode.This shows that the flat type loop heat pipe of longitudial replenishment assisted by gravity,operation mode will be changed at 30 W.This paper investigates the performance of loop heat pipe under variable power operation.The results show that the heat leak is caused by the different proportion of the gas-liquid phase at an initial conditions and uneven distribution of heaters in the capillary core,which cause a“dry-out”of the LHP at a part of wick,its thermal resistance increases from 0.20°C/W to 0.30°C/W.In summary,according to the analysis of the loop heat pipe stability and variable operation process,the percentage of the two-phase in the compensation chamber should be considered as the main factor.It can be achieved a higher heat transfer capacity by analyzing the relative location and size between the liquid storage chamber,three heaters and wick.