Fabrication And Capillary Performance Of Composite Wicks Based On Metal Fiber And Powder Sintering

To meet the demand for high heat flux cooling and improve the efficiency of energy utilization, it is urgent to research and develop high efficient heat transfer technology. Phase change heat transfer components such as heat pipe have been widely applied in the field relating to temperature control. Wick is one of the important factors that determine the heat transfer performance. The conflict between capillary force and permeability restricts the further promotion of the comprehensive capillary performance of single-structural wick. Considering the excellent permeability of fiber porous structure and large capillary pressure of powder porous structure, a novel composite-structure wick based on metal fiber and powder sintering is proposed in this thesis. The fabrication, morphology characterization, mechanical properties and capillary performance of composite-structure wick were symmetrically studied. The main contents in this thesis were as follows:(1) Fabrication of fiber-powder composite porous structurePorous metal fiber sintered structure were fabricated by solid-state sintering of stainless steel fibers produced by cutting method. Fiber-powder composite structure was obtained by filling and sintering stainless steel powder in the porous fiber matrix. Fiber porous matrix can improve the porosity of composite porous structure. The forming mechanism was investigated. Micro-structures on the fiber surface were helpful to the formation of sintering necks between powders and fibers. The influence of sintering parameters on the composition of stainless steel fiber was investigated and the appropriate sintering parameters were obtained in order to prevent the degradation of corrosion resistance and mechanical properties of stainless steel.(2) Mechanical properties of composite porous structuresThe tensile properties of fiber porous matrix and composite porous structure were investigated through uniaxial tensile test. Porosity, sintering temperature, holding time and sintering atmosphere had an influence on the tensile strength of fiber porous matrix. Two tensile fracture mechanisms were proposed including fiber breakage and sintering neck fracture. The mechanical performance of composite porous structure mainly depended on the fiber matrix. Its tensile fracture mechanism was also studied.(3) Wetting characteristics and Liquid permeability of sintered porous structuresThe wetting characteristics of the composite porous structure were examined using the sessile drop method. The influence of powder size, fiber matrix porosity and morphology on the contact angle was analyzed. Permeability test platform was built and forced fluid flow method was used to access their permeability. Composite porous structure showed an order of magnitude of enhancement in the liquid permeability to sintered powder porous structure. Prove that the effect of fiber skeleton to improve the permeability of composite porous structure was significant.(4) Capillary performance of fiber-powder composite wickA novel infrared (IR) thermal imaging method was used to identify and locate the liquid meniscus accurately. Capillary rise curves and capillary performance integrating both capillary pressure and permeability were obtained by data processing. The influence of fiber porous matrix and powder size on the capillary performance of composite-structure wick was investigated. The results showed that composite-structure wick had a better capillary performance to single-structure wicks. The optimal parameters were as follows:fiber porous matrix with 75% porosity, powder with the size of 75-110μm, sintering processes of 1200℃ along with 60 min.