Heat Transfer Performance Study Of The Micro-flat Plate Heat Pipe

With the rapid development of the semiconductor industry,the heat flux density of electronic components is increasing.The problem of heat dissipation has become an important reason to limit the progress of electronic technology.In order to solve the heat dissipation problem of high heat flux density and improve the thermal performance of micro-flat plate heat pipe(MFPHP),it is necessary to study the heat transfer characteristics and mechanism of the MFPHP by testing and theoretical analysis.Therefore,this paper on the MFPHP numerical simulation and experimental study lay the foundation for practical applications.The main work is as follows:First,a two-dimensional physical model of the MFPHP is established,and the numerical simulation is carried out by using VOF multiphase flow model and evaporative condensation model.The effects of liquid filling rate and heat source power on flow heat transfer were studied.The results show that the heat transfer performance of the heat pipe is affected by the difference of the filling rate.When the liquid filling rate is 30%,the overall temperature of the heat pipe increases with the increase of heat source power.Then,the MFPHP was fabricated and the experimental test platform of the MFPHP was set up.Experiments were carried out with acetone as the working fluid of the MFPHP.The effects of liquid filling rate,vacuum degree and heat flux on heat transfer performance were studied.The results show that the different liquid filling rate will affect the heat transfer performance of the heat pipe,filling rate of 30%,then the best performance of the heat pipe.When the filling rate is 30%,with the increase of the heat source power,the temperature of the evaporation section increases and the thermal resistance becomes smaller.When the heat transfer limit is reached,the heat pipe is dry and the thermal resistance becomes large.In the heat transfer limit,the heat pipe maximum heat transfer to 120 W,the minimum thermal resistance of 0.44 K/W.In addition,the heat transfer performance of the MFPHP and the heat transfer performance of the MFPHP with poor sealing were studied.The comparison between the experimental results and the simulation results shows that the trend of the simulation thermal resistance and the experimental thermal resistance are consistent.Finally,the heat resistance model of the heat pipe is established,and the thermal resistance model shows that the working fluid has a great influence on the heat transfer performance.M1(multi-walled carbon nanotubes with an aspect ratio of 666)-acetone nanofluid and M2(multi-walled carbon nanotubes with an aspect ratio of 200)of 0.002wt%,0.005wt%,0.01wt% and 0.015wt%,respectively,were prepared by two-step method.The multi-walled carbon nanotubes(MWCNTs)-acetone nanofluid were used to optimize the MFPHP instead of acetone.Using the above-mentioned nanofluid as the working fluid,the heat pipe wall temperature was obtained by experiment to study the heat transfer performance of the heat pipe.The results show that the different mass concentration affects the heat transfer performance of the heat pipe,and the best mass concentration(0.005wt%)is existed.The thermal resistance of M1-acetone nanofluid(0.005wt%)and M2-acetone nanofluid(0.005wt%)was reduced by 40% and 16%,respectively,compared with acetone heat pipe.In addition,the results also show that the same mass concentration,MWCNTs with different aspect ratio will affect the heat pipe heat transfer.Based on the above experimental phenomena,the reason of changing the heat transfer performance of MWCNTs-acetone nanofluid with different mass concentration was analyzed.One part of the nanoparticles was deposited on the inner surface of the heat pipe and the other part of the nanoparticles was suspended in the base liquid.Distribution affects the heat transfer performance of the MFPHP.