Study On Sintering-dealloying Manufacturing And Heat Transfer Performance Of Multi-scale Composite Porous Structures

With the rapid development of the electronic information manufacturing industry,thermal management technology is becoming increasingly important for the the electronic components.The porous metal structure can transfer heat and mass eff-iciently,because it combines structural property with functional aspect.Hence it has high industrial application value,and it can be used widely in the area of micro-channel heat sink and heat pipe.However,in order to enchance the heat and mass transfer property,the key point is to improve the materals features and surface structure through micromachining technology.Based on the above point,the dissertation forcuses on the subjects of the manufacturing technique for multi-scale composite porous structures.According to the experimental and numerical investigation,the related properties of the heat and quality transferring law were researched and measured in the thesis.In addition,the novel porous structures were applied on the loop heat pipe,and the results were analysised and discussed in detail.The main research contents and conclusions are summarized as follows:(1)Fabrication of multi-scale composite porous structuresMulti-scale composite porous structures were fabracated by the sintering and dealloying method on the step-graded porous structures.Based on requirement of porous structure in different application area,the manufacturing method and influence factors of these novel structures are rescarched as the focus.The forming principle of nano-structure was also studied by combining sintering method and selective corrosion.The surface profile was tested buing 3D microscope with super wide depth of field and SEM.(2)Properties measurement of multi-scale composite porous structuresDuring this chapter,the main influencial factors for physical parameters were investigated and characterized,including thermal conductibility,permeability,capillary performance and wettability.Then the thermal conductivity was measured by steady heat conduction method.The permeability was tested through the forced fluid flow method and accessed.Moreover,the capillary performance was examined with novel infrared(IR)thermal imaging method picture processing technology.The hydrophilic performance was evaluated by droplet penetration experiment.The dynamic process was traced timely and mathmatic model,expecially about the manufactureing method,nano sturcture,etc,were researched in detail.(3)Numerical analysis of loop heat pipe with multi-scale composite porous structuresIn this work,a complete steady state model for anti-gravity loop shaped heat pipe with multi-scale composite porous structures has been presented to investigate in the thermal performance and hydraulic behavior of the AGLSHP.The governing equations for the heat and mass transfer are developed for the loop operation,with specific attention given to the evaporator region.By comparing the numerical simulation with the experimental data,the heat transfer mechanism is revealed.The liquid/vapor velocity and pressure distribution are discussed,and the temperature distribution along the transport line is also analyzed.The numerical results show that with the increase of the heat load,the maximum velocity and pressure value of the liquid and vapor increase as expected.The highest temperature position occurs at the outlet of evaporator.Providing the capillary pressure for the work fluid in the circulation,more attention needs to be paid to the wick in the liquid line.Moreover,the longer condensation length is effective in decreasing the temperature at the outlet of condenser and improving the heat transfer capacity of the AGSLHP.(4)Experimental investigation on heat transfer performance of loop heat pipe with multi-scale composite porous structuresThe anti-gravity loop-shaped heat pipe,which has multi-scale composite porous structures inside,is a novel device used in electronic heat dissipation under the anti-gravity condition on the ground.Two kinds of wick structures with single-powder and continuous step-graded are evaluated for design optimization.The copper powders utilized in the experiment are divided into six kinds of particle size,and three different filling ratios were tested.The thermal performance analysis of the anti-gravity loop-shaped heat pipe used for remote radio unit was also investigated.A series of experiments have been conducted in this work,including the start-up analysis and the maxmium operating power.The results show that the heat transfer performance of the sintered wick samples changes significantly with the variation of the copper powder size.The multi-scale composite sintered wick possesses better overall performance than the single-powder sintered wick,not only in the relatively stable thermal resistance,but also in the low start-up temperature.The effect of the filling ratios of the working fluid is remarkable on the heat transfer performance.Specifically,the low filling ratio sample shows much better start-up characteristic,while the high filling ratio sample is quite outstanding at the high heat load.The experimental observations are validated via ANSYS simulation.The simulation results are found in agreement with the experiment.