Research On Heat Transfer Performance Of High Power Micro-channel Plate Heat Pipe

With the development of micromachining technology and electronic technology,high-power electronic devices are more and more widely applied to all aspects of production and life.However,with the improvement of the power of electronic appliances and other equipment,the heat dissipation problem has become a bottleneck that restricts its development.As an efficient heat transfer device using phase transition for heat transfer,flat-plate heat pipe is widely used to solve the heat dissipation problem of high power equipment.In this paper,based on the different application backgrounds of flat-plate heat pipe radiators,the heat transfer performance and visualization of the unslotted and nine slotted flat-plate heat pipe with 40 rectangular channels and different aspect ratios were studied by means of visual experimental study.First of all,the effects of different heating power inputs(80-180W)and different fluid filling ratios(25%,48%,55%)on start-up temperature,start-up time,the Z-axis temperature difference,the relative thermal resistance and the equivalent thermal conductivity of the unslotted flat-plate heat pipe were studied.Furthermore,the gas-liquid two-phase behavior of the interior working fluid of the unslotted flat-plate heat pipe,and the coupling heat transfer behavior of the boiling liquid and the condensate were observed through a visualizable window under different experimental conditions.It is found that the start-up time of the unslotted flat-plate heat pipe decreases with the increase of heating power input and increases with the increase of the fluid filling ratio.Simultaneously,the start-up temperature of the unslotted flat-plate heat pipe increases with the increase of heating power input.The relative thermal resistance on Z-axis of the unslotted flat-plate heat pipe increases with the increase of heating time and then decreases to reach a stable value.Through the experimental study of visualization,it is found that,with the increase of heating power input,the disturbance of the working fluid in the unslotted flat-plate heat pipe increases and the number of bubbles increases.With the increase of heating power input,the condensate on the condensing surface of the unslotted flat-plate heat pipe will be more obvious.It can be seen that the condensate flows down under the action of gravity.In addition,the coupling phenomenon between the boiling liquid and the condensed liquid is observed through a visual window.Then,nine slotted flat-plate heat pipes with different aspect ratios(1:1-3:1)were divided into three groups.All experiments were both studied under the vacuum degree of 1×10~-33 Pa,the liquid filling ratio of 48%and the heating power inputs of 80-200W.The effects of different slot depth,width and aspect ratio on start-up time,Z-axis temperature difference,relative thermal resistance and equivalent thermal conductivity of the semi visualized slotted flat-plate heat pipe were studied.When the experimental conditions are the same,with the increase of slot depth,the start-up time,axial temperature difference,relative thermal resistance of three groups of slotted flat-plate heat pipes decrease,but the equivalent thermal conductivity increases.By comparison,it is found that the heat transfer performance of three slotted flat-plate heat pipes with aspect ratios of 3:1,3:2 and 1:1 is better in three groups of slotted flat-plate heat pipes.Further experiments on the three slotted flat-plate heat pipes were studied,and it is found that the heat transfer performance of the slotted plate heat pipe with aspect ratio of 3:1 is obviously better than that of the other two flat-plate heat pipe units.Finally,a comparative study on the slotted flat-plate heat pipe with 40 rectangular micro channels with the size of 200mm×0.4mm×1.2mm and unslotted flat-plate heat pipe was conducted.Two kinds of flat-plate heat pipes were using acetone as the working fluid under the vacuum degreed of 1×10~-33 Pa,and the start-up characteristics,isothermal performance and heat transfer performance of the two kinds of flat-plate heat pipes were compared and analyzed.The results show that the start-up time of the slotted flat-plate heat pipe with aspect ratio of 3:1 is shortened by 33%and the start-up temperature increases by 12.5%on average compared with that of unslotted flat-plate heat pipe.The relative thermal resistance of the slotted flat-plate heat pipe with aspect ratio of 3:1 is reduced by 52.9%compared with that of unslotted flat-plate heat pipe.At the same time,it is found that the equivalent thermal conductivity of the slotted flat-plate heat pipe with aspect ratio of 3:1 is twice as much as that of the unslotted flat-plate heat pipe.At the same heating power input,bubbles are easier to produce in the slotted flat-plate heat pipe with aspect ratio of 3:1,and the disturbance of the internal working fluid of the slotted flat-plate heat pipe with aspect ratio of 3:1 is more severe.Meanwhile,the number of bubbles in the slotted flat-plate heat pipe with aspect ratio of 3:1is relatively more.According to the comprehensive analysis,the heat transfer performance of the slotted flat-plate heat pipe with aspect ratio of 3:1 is the best.