Manufacture And Thermal Performance Of Sintered-grooved Composite Wick In The Flattened Heat Pipe

With the rapid rising of heat flux and the reduction of dissipating space in the microelectronic field, flattened heat pipe, which has many characteristics, such as high heat conductivity, high reliability, fast thermal response, and without extra electric power, has become an ideal conducting element of universal use in the electronic field. The capillary wick (short for wick) is the key component in the flattened heat pipe. A completely new composite wick named sintered-grooved composite wick is supposed. The sintered-grooved composite wick flattened heat pipe has many advantages, such as simple manufacturing process, low cost, high thermal performance and potential of industrialization. The thesis has taken the sintered-grooved composite wick as research object, the manufacturing process of its flattened heat pipe as the leading clue, and experimental test, numerical simulation and mathematical modeling as the research methods, to study sintered-grooved composite wick forming mechanism and thermal performance of its flattened heat pipe. The mainly research works are summarized as follows:(1) Research on the solid phase sintering process for grooved-sintered wickGrooved-sintered wick is presented and fabricated by solid phase sintering process which could be divided into four phases: reduction phase, sintering starting phase, sintering preservation phase and sintering cooling phase. The effects of the sintering temperature, sintering time and sintering atmosphere on grooved-sintered wick are also discussed. Microstructure of grooved-sintered wick is observed. Tensile and compressive mechanical properties of copper powder sintering materials are tested. The results show that: (?) the increase of sintering temperature can reduce the wick porosity, increase the radial shrinkage, promote the growth rate of sintering neck, however, the sintering time affects little; (?) the oxidation reduction process could manufacture new micro structure—the segmentation cracks structure on the surface of copper powders; (?) grain size grows bigger, number becomes less and the shape of the grain boundary becomes simple after the grooved-sintered wick sintering; and (?) the spherical copper powder size affects greatly on the tensile and compressive strength of powder sintering materials.(2) Study on the phase change flattening process for sintered-grooved composite wick flattened heat pipeA new manufacturing technology named phase change flattening process is presented to fabricate the sintered-grooved composite wick flattened heat pipe. Deformation geometry of flattened heat pipe, vapor pressure mechanism of flattening process, and the elasto-plastic deformation of flattening process are analyzed theoretically and verified by experiments. The results show that: (?) the vapor pressure is determined by the saturated vapor pressure equation; (?) The width, vapor area and grooves of flattened heat pipe change greatly as the flattening proceeds; (?) The maximum equivalent strain distribute on the interface between wick and vapor in the flat section of flattened heat pipe; (?) the buckling phenomenon can be well eliminated when the flattening temperature reaches 480K; and (?) the phase change flattening punch load increases with flattening temperature and displacement.(3) The forming, characterization and performance of the sintered-grooved composite wickThe forming mechanism of crack grooves is established. The sintered-grooved composite wick is characterized theoretically and experimentally. The hydrophilicity, thermal conductivity of copper powder sintering materials is analyzed. Capillary force of sintered-grooved composite wick is discussed theoretically and visualizing tested. The results show that: (?) the crack grooves which mostly appear on the top of tears array periodically and axially and; (?) the copper powder size influents the most greatly on the structure of crack grooves and the sintering temperature and wick sintering thickness also affect greatly; (?) copper powder sintering materials shows hydrophobicity; (?) the thermal conductivity of sintering materials reduces with the increase of porosity; and (?) capillary force of sintered-grooved composite wick decreases with spherical copper powder size.(4) Thermal performance of sintered-grooved composite wick flattened heat pipeThe start-up and isothermal performance of sintered-grooved composite wick flattened heat pipe are tested; Heat transfer limit model and thermal resistance network model of sintered-grooved composite wick flattened heat pipe are set up and tested experimentally. The results show that: (?) the sintered-grooved composite wick flattened heat pipe owns sound start-up and isothermal performance; (?) the wick sintering thickness has the greatest influence on the thermal resistance; (?) the spherical copper powder size affects the most on heat transfer limit and the wick sintering thickness and flattening height also affect greatly; (?) the wick with large copper powder size is sensitive to gravity.