Fabrication And Performance Of High Power Ultra-thin Flat Heat Pipe With Composite Mesh Wick

As a high thermal conductive and high reliability heat transfer element,ultra-thin flat heat pipe(UTFHP)is widely used in portable intellectual devices,such as smartphone and tablets.There are two forming technology of UTFHPs,including flattening by conventional cylindrical heat pipes and welding technology,by which two sheets with wick structure are bonded.Limited by the size of cylindrical heat pipes,the UTFHPs formed by flattening have smaller size and lower heat load.Therefore,this paper designed a kind of UTFHP with three-layer composite mesh wick structure which improves the capillary by strengthening treatment for adapting the heat dissipation requirement of the electronic equipment with high power.The influence of filling ratio and the structure of supporting column on the star-up performance of UTFHPs is studied,and the influence of the composite mesh wick structure,the structure of supporting column,filling ratio,gravity,and cooling power of the UTFHPs is also studied.The main contents of this paper are as follows:(1)the study on structural design and manufacturing of UTFHPBy comparing the physical parameters of different materials,the suitable material was selected as the sheet of the UTFHP,on which the manufacturing technology was studied.In this paper,the welding technology was used to manufacture UTFHP.To ensure the size of finished UTFHP,the sheet was designed with special injection structure,which can be completely removed by resistance welding after vacuuming and filling process.(2)fabrication and capillary strengthening treatment of three-layer composite mesh wickThree-layer composite mesh wicks with different pores were treated by strengthening at different time after being fabricated by solid-state sintering technology.Scanning electron microscope and high-speed camera were used to observe and characterize the surface morphology of the composite wick with different parameters and test the capillary performance.The optimal mesh parameters and capillary strengthening treatment time of the composite were obtained.The results show that the three-layer 330 mesh composite wick has the best capillary performance,and the climbing height is 44.2 mm.When the time of capillary strengthening treatment is 30 minutes,the capillary performance of composite wick can be improved by30.3%.(3)study on the heat transfer performance of UTFHPThe heat transfer performance test device was set up to study the influence of filling ratio and the structure of supporting column on the start-up performance.And the influence of composite wick、filling ratio,the structure of supporting column,gravity and cooling power on the heat transfer performance of UTFHP was also compared with the evaluation parameters of limiting working power,thermal resistance,temperature difference between evaporation and condensation and equivalent thermal conductivity.The results show that the limited working power of UTFHP can be as high as 26 W under the level test state,and the maximum equivalent thermal conductivity can reach 13110 W/(m·K),which is 32.7 times higher than that of pure copper.Compared with the UTFHP without capillary strengthening,the maximum equivalent thermal conductivity of UTFHP can be increased by 30.9%.