Study On Heat Transfer Characteristics Of Gradient Pore Wick Vapor Chamber

Vapor chamber(VC)has the advantages of small volume,strong heat transfer ability and good temperature uniformity,so it is the ideal choice for heat dissipation of microelectronic devices.Researching and developing new and efficient VC has become a key technical problem to be solved in high heat flux electronic devices.The wick,as the core component of VC,which play an important role in affecting VC heat transfer performance,is the primary concern in VC research.In order to improve its heat transfer characteristics,this paper designed and developed a radial gradient porous size wick from the internal core member of the VC,and a performance test platform and a visual experimental platform were set up.First,the heat transfer characteristics of VC with different wick structures were tested.The feasibility of the design was verified by comparing and analyzing their heat transfer performance,temperature uniform performance and start-up performance.Secondly,the heat transfer characteristics of gradient pore size wick vapor chamber(VC-G)were further studied.Finally,the vapor-liquid two-phase flow behavior in the gradient pore size wick was carried out,and its phase change heat transfer mechanism was revealed.To sum up,the main work and conclusions of this paper are as follows:(1)Four VCs with different wick structures(VC-G,200-mesh uniform wick,50-mesh uniform wick and no wick)were developed,and a testing platform was built to test their heat transfer performance,temperature uniform performance and start-up performance.The results showed that: Compared with uniform wick(50 mesh and 200 mesh)and no wick VC,the VC-G has the best heat transfer performance,uniform temperature performance and start-up performance.(2)The experimental study on heat transfer characteristics of VC-G was carried out to test the influence of different degree of eccentricity,heat source area and working temperature on its thermal resistance,and its maximum heat transfer capacity was also tested.In addition,its thermal resistance and temperature performance under adverse gravity conditions were tested.The conclusion is that the smaller the degree of eccentricity is,the larger the heat source area is,the lower the working temperature is,the heat transfer performance of VC-G is better.Compared with the adverse gravity condition,VC-G performance is better under the gravity condition.When the heating power of the VC-G exceeds 400 W,the central temperature of the evaporation surface increases sharply,and its temperature uniformity decreases significantly,indicating that VC heat transfer performance deteriorates significantly at this time and can no longer meet the normal heat dissipation requirements.(3)Developed a visual VC-G,and has set up a visualization experiment platform for the VC phase change heat transfer plate,using the high speed CCD(charge coupled device)camera to obtain the formation of droplets in the process of formation,growth,movement and the dripping during condensation process,using infrared thermal imager to obtain the surface temperature distribution during in the process of evaporation condensation changes under the start-up condition.It is concluded that with the increase of heating power,the vapor generation rate and gas-liquid circulation rate increase,which accelerates the process of condensation droplets generation,growth,movement and dropping.The directional flow of vapor in the VC-G makes the vapor converge and form a large bubble,resulting in local high temperature on the condensation surface.In summary,the heat transfer characteristics and the evaporation and condensation process of working medium in the VC-G are systematically revealed in this paper.and the relevant research results will provide theoretical guidance and technical support for the design and further optimization of the VC-G,as well as engineering applications.