Study On Phase Change Heat Transfer Of Boiling Condensation In Prismatic Heat Pip

With the rapid development of electronic technology,the degree of integration and miniaturization of electronic components is getting higher and higher,which makes it more difficult to heat the electronic equipment.If the heat cannot be eliminated in time,it will affect the performance and service life of the electronic equipment.The traditional air-cooled heat dissipation method has been difficult to meet the growing demand for heat dissipation of electronic devices,and the high heat flux density in micro-space.The heat dissipation technology of electronic equipment has become one of the important factors restricting the development of information,electronics,national defense and military technology.Based on these problems,flat heat pipe is considered to be a promising heat pipe to solve heat dissipation under high heat flux.It has good heat transfer and uniform temperature performance.It has good prospects in the field of heat dissipation of electronic components.It has the advantages of simple structure,low cost and wide application.This paper designs and builds an experimental platform for visualizing the heat transfer performance of flat heat pipes and studying the phenomenon of boiling condensation phase change heat transfer in tubes,designs a new type of prismatic heat pipes with heated bottom surface and studies their various performances.The temperature uniformity,start-up and heat transfer performance of prismatic heat pipes are tested,and the visualized heat is also captured by a high-speed camera.Various phenomena of bubbles in tubes were observed and studied.Combining heat transfer theory and bubble dynamics theory,these phenomena were analyzed and discussed in order to reveal the mechanism of boiling condensation phase change heat transfer in finite space and how to enhance boiling condensation heat transfer.Based on the theoretical analysis and thermal resistance analysis of heat pipes,a prismatic heating bottom is designed and manufactured,a thermal resistance model is established in the process of heat transfer,and the homogeneity of the new type heat pipes is tested,as well as the start-up and heat transfer performance of the visualized flat heat pipes under different heating power,different liquid filling rate and different heating bottom.The experimental results show that:(1)The heat pipe shows good homogeneity under different heating power,and the prism heating bottom heat pipe has better start-up performance and heat transfer performance than the smooth bottom heat pipe.(2)Under the same conditions,the thermal resistance of prismatic heated bottom heat pipe can be reduced by about 40%when compared with smooth bottom heat pipe at 20*10~4w/m~2,and the temperature difference of prismatic heated bottom surface can be reduced by about 5~C compared with smooth bottom heat pipe.It can be seen that the prismatic bottom heat pipe shows good heat transfer performance.At different filling rates,the thermal resistance of heat pipe decreases with the increase of heat flux density.At the same filling rate,the thermal resistance of heat pipe decreases with the decrease of wall height.(3)When there is an optimum filling rate(50%),the boiling condensation phase change heat transfer effect in the heat pipe is the best.At this time,the distance between the liquid surface and the heating surface and the condensation surface is more appropriate,and the interaction between boiling and condensation is the best,which makes the heat pipe show good heat transfer performance.When the filling rate is 30%,the bubbles and boiling liquid keep high independence with the condensation surface.The interference of condensation surface is very small,which is not conducive to condensation heat transfer.When the filling rate is 70%,the life cycle of bubbles becomes longer,which leads to a lower detachment frequency of bubbles,which is not conducive to the boiling heat transfer on the evaporation surface.The liquid surface is too close to the condensation surface,which makes the condensate film thicker.The liquid bridge generated is not conducive to the condensation heat transfer.The disturbance of bubbles mostly occurs over the liquid and is not conducive to the boiling heat transfer on the evaporation surface.The diameter of bubbles and the number of vaporization cores in prismatic heat pipes are larger than those in smooth heat pipes.