Investigation On Functional Gradient Porous Wicks For Loop Heat Pipe

Recently,the aerospace industry of our country has developed rapidly,and the aerospace technology has been widely used in thermal control system on the ground.As an effectively two-phase heat transfer device,Loop heat pipe(LHP)has been widely used in thermal control system of space equipment,the thermal industrial and the electronic cooling.The porous wick is an important part of the loop heat pipe,the heat transfer performance of the loop heat pipe will be significantly affected by changing its characteristic parameters.In order to improve the heat transfer performance of loop heat pipe and enable it to work at higher heat load,in this paper,functional gradient porous wick was proposed and related experimental research was carried out.Functional gradient means that a property or a parameter of material changes in steps.And functional gradient porous wicks mean that the thermal conductivity,pore radius and porosity of porous wicks gradually change along the direction of working fluid flow.In order to comprehensively study the effect of change in pore radius on the performance of porous wick and loop heat pipe,reduce the leakage heat from the porous wick to the compensation cavity,and enhance the heat transfer performance of the porous wick,in this paper,functional gradient porous wicks were prepared for flat loop heat pipe,then the characteristic parameters and heat transfer performance of functional gradient porous wicks were studied experimentally.The main work of this research is as follows:1.In this paper,two kinds of functional gradient porous wicks were prepared by Ni and PTFE.The pore radius of porous wicks gradually change along the direction of working fluid flow.During the preparation process,the integrated sintering process was explored.2.The porosities of porous wicks were measured,and pore radius distribution of porous wicks were observed and measured by SEM.Pore radius was controlled about 47.5%.The wicks prepared by powder with small radius have small pore radius.3.An experiment rig for mass transfer of porous wicks was set up.The data indicated that the wicks with the small pore radius showed better capillary force.4.The start-up and operation of the porous wick evaporator were simulated,and the evaporation phenomenon on the surface was visualized.The influence of pore radius variation on the heat transfer performance of functional gradient porous wicks of different materials was comprehensively analyzed.And the differences in heat transfer performance of functional gradient porous wicks were quantitatively indicated when the heat load is 5?20W.The functional gradient porous wicks with large pore size on condenser chamber side and small pore size on evaporator side showed better heat transfer performance at a heat flow density of 25?35 kW/m2.The experimental conclusion in this paper can provide a more precise way to control the pore radius gradient of porous wicks for optimizing the design of pore radius distribution and improving performance of loop heat pipe.