Study On Manufacturing Method And Heat Transfer Performance Of Ultra-thin Flattened Heat Pipe

With the rapid development towards high performance and miniaturization,the heat dissipation of thin and portable electronics has become more difficult.How to improve the heat dissipation capability has become the key to solving the heating issue.The flattened heat pipe is made of the cylindrical heat pipe,which has the advantages of light weight,fast thermal response and high heat transport capacity.If the flattened heat pipe with appropriate volume and performance can be used for the thermal management of thin and portable electronics,the heat dissipation capacity will be greatly improved to solve the heating problem.However,the conventional flattened heat pipe(thickness greater than 1.2 mm)cannot meet the heat dissipation requirements of thin and portable electronics from the structure volume,the manufacturing method,and the heat transfer performance.In view of this,this thesis focused on the structural design,manufacturing method,heat transfer performance of the ultra-thin flattened heat pipe(UTHP,thickness of 0.4 mm~1.2 mm)with the novel wick structure.The main research contents were as follows:(1)Research on manufacturing method of ultra-thin flattened heat pipeBased on the manufacturing processes of the conventional flattened heat pipe,a new method of manufacturing UTHPs with different sizes by flattening the thin-walled cylindrical heat pipes with different diameters,wall thicknesses and lengths was completely proposed.The finite element analysis of the phase-change flattening process of thin-walled cylindrical heat pipes with different diameters,wall thicknesses and flattening thicknesses was carried out.The effect of the flattening parameter on the dimensional accuracy of the UTHP was studied.The optimum flattening temperature was determined.(2)Heat transfer theoretical analysis and experimental design of ultra-thin flattened heat pipeBased on the heat pipe limits theory,the numerical analysis of the permeability and equivalent diameter and porosity of the spiral woven mesh wick and the capillary limit and carrying limit of the UTHP were carried out.A test system was built to test the capillary performance of the spiral woven mesh by using the infrared thermal imaging method.A heat transfer performance test system for the UTHP samples was designed,and the system error was calculated and analyzed.Simulating the actual usage of smartphones,the heat dissipation performance test system for UTHP cooling modules for smartphone cooling was designed.(3)New wick structure and heat transfer performance of ultra-thin flattened heat pipeTwo novel spiral woven meshes,namely the hybrid spiral woven mesh and band-ship spiral woven mesh,for manufacturing the wick structures of UTHPs with different thicknesses were designed.The effects of the weaving structure parameters of the hybrid spiral woven mesh on the pore shapes of the wick and the heat transfer performance of the UTHP were studied.The contents include: the relationship between the weaving method of the hybrid spiral woven mesh and the pore distribution and size inside the wick was studied;the effect of the weaving method of hybrid spiral woven mesh on the heat transfer performance of UTHP was studied,and the optimum weaving method for the experimental hybrid spiral woven mesh was determined.The effect of the band-shape spiral woven mesh structure on the heat transfer performance of the UTHP were studied.At the same time,combined with the specific heat dissipation requirements of the smartphone,an UTHP cooling module based on UTHP and smartphone bracket was designed,and the heat dissipation performance of the UTHP cooling module under different operating angles were studied.(4)Design and optimization of liquid-vapor passage for ultra-thin flattened heat pipeThe composite orthogonal woven mesh wicks with different widths were designed,and the UTHPs with different widths wicks and different filling ratios were fabricated.The passage area ratio of liquid to vapor of the UTHP was adjusted by changing the width of the wick.The effects of the passage area ratio of liquid to vapor in the tube and the filling ratio parameters on the heat transfer performance of UTHP were studied.The optimum passage area ratio of liquid to vapor for the experimental UTHP was determined.The study results provided a novel idea and useful guidance for the structural design of the UTHP wick.