Preparation And Thermal Performance Study Of Ultra-Thin Flat Heat Pipe

As a phase change cooling form adopting latent heat exchange,flat heat pipe has high heat transfer efficiency,strong thermal conductivity,good temperature uniformity,good stability and long life,and has become an excellent choice to solve the heat dissipation problem in aerospace field.In recent years,the electronic components in aero-engines are gradually developing towards miniaturization,high integration,high performance and thinness.Limited by the size of electronic components and the uniformity of its surface temperature,the flat heat pipe is pushed to develop towards ultra-thin direction and gradually attracted more and more attention.Ultra-thin flat heat pipe,with a large surface area,a flexible and adjustable shape,which is easier to make good contact with the heat transfer plane and to achieve the purpose of effective heat transfer,has received more and more attention and applications in the heat dissipation of electronic components in aero-engines,and become a hotspot of research and development.In practical applications,heat pipes with a thickness less than 2 mm are usually referred to as ultrathin flat heat pipes.In order to verify the feasibility of using this kind of ultra-thin flat heat pipe,this paper attempts to design,process and fabricate an ultra-thin flat heat pipe of red copper material with a thickness of 0.65 mm,and conducts a heat transfer performance study on it.It provides a foundation for the application of ultra-thin plate heat pipe in the electronic components of aero-engine,which has important practical significance.The main contents are as follows:Firstly,ultra-thin flat heat pipe is designed.After determining the selection of shell material,working fluid and internal wicking structure in heat pipe,the internal structure of the heat pipe is designed.Support pillars arranged in a forked arrangement with diameter of 1mm and spacing of 3mm between the centers are etched on one of the heat pipe shells,to support the inner steam space of the flat heat pipe under the action of internal and external pressure difference.Then,a numerical research on the structure design of the heat pipe is carried out to explore whether the structure design can make the heat pipe structure meet the strength requirements,and the influence of the parameter design of the heat pipe structure on its mechanical properties is also explored,so as to provide the basis for the optimal design of the ultra-thin flat heat pipe in the future.Secondly,the ultra-thin flat heat pipe is fabricated and its heat transfer performance is theoretically analyzed.The main production process includes shell processing,pipe fitting cleaning,welding,leak detection,evacuation and charging,and so on.Theoretical analysis of heat transfer performance shows that the minimum heat transfer limit of the heat pipe is the capillary limit,which is used to verify the subsequent experimental results.Finally,the experimental scheme is determined,and an experimental device for testing the heat transfer performance of the ultra-thin flat heat pipe is designed and built,and its heat transfer performance is then studied.The axial temperature distribution on the outer wall of heat pipe in different working conditions is measured.The start-up characteristics of heat pipe with time-varying power are analyzed.The theoretical heat transfer limit is used to verify the experimental heat transfer limit.Taking the thermal resistance of heat pipe as the evaluation parameter of its heat transfer performance,the heat transfer performance of the heat pipe is compared with that of copper sheet of the same size,and the influence of heating power,working inclination and liquid filling rate on heat transfer performance of the heat pipe is analyzed as well.Finally,the radial temperature uniformity performance of the heat pipe is studied.The experimental results show that the start-up characteristics of heat pipe are different under different heating power.The higher the heating power is,the faster the start-up speed of the heat pipe will be,and the start-up time of the condensation of the heat pipe will be delayed compared with that of the evaporation.There is an error between the maximum heat transfer limit of the heat pipe in the actual experiment and the theoretical calculation,which is smaller than the theoretical limit.Compared with copper sheet of the same size,the thermal resistance of the ultra-thin flat heat pipe is reduced by half,and the heat transfer performance is stronger,and the thermal conductivity of the heat pipe is estimated to be about 800 W/m ?K.When the working inclination is 90 degrees,the heat pipe has the best heat transfer performance.The optimal liquid filling rate of the heat pipe is 1.05.The optimal operating power range of the heat pipe is 7.1w-15.876 w,and the maximum heat transfer power is 20.16 w.The radial temperature uniformity performance test shows that the heat pipe presents perfect temperature uniformity at low heating power.With the increase of heating power,the upper surface of the heat pipe still presents good temperature uniformity,while the lower surface gradually becomes worse.