Boiling Heat Transfer Performance And Visualization Of Porous Structure

There are many factors that affect the boiling heat transfer performance of the surface:surface material,surface roughness and surface structure.Improving the surface structure is the main method to enhance the boiling heat transfer performance.The new porous composite structure has a larger contact area,which makes the number of vaporization cores.Increase,reduce the degree of superheat,strengthen the heat transfer effect,and increase the critical heat flux density of the surface.First,this paper designs and sinters three kinds of porous structures:uniform porous layer structure,porous composite 16-core structure and porous composite 32-core structure,and analyzes the enhanced heat transfer mechanism of the porous composite structure.The porous composite structure not only increases the total contact area during boiling,but also effectively separates the gas-liquid flow,making the gas-liquid convection on the entire porous surface more violent,and can also provide liquid supplement channels during boiling to speed up the liquid return.The manufacturing process of sintered porous structure including mold manufacturing and sintering process is analyzed.The micro morphology,bonding strength and porosity of the sample are also studied.An experimental test device for boiling heat transfer was designed and built,and the process of experimental testing,data collection and visual image shooting was carried out,and the error analysis of the experimental results was carried out.Finally,the test results of different samples were compared.In this paper,the difference in boiling heat transfer performance of different porous structures is studied by building a pool boiling experiment platform.The porous structure has different properties within the measured heat flux density range.In the low heat flux density stage,the heat transfer performance of the uniform porous layer structure is stronger than that of the porous composite structure,which is 1.5 times that of the light surface.With the increase of heat flow density,the excellent liquid supply capacity of the porous composite structure greatly enhances the heat transfer effect,and the heat transfer effect of the porous composite 32-core structure is better than that of the 16-core structure.The experiment also shows that the heat transfer effect of the porous composite structure is related to the particle size and the height of the composite layer.The best particle size in the test range is 60μm;the critical heat flow of the porous composite 32-core structure with the composite layer height of1mm reaches 386 W/cm~2,The heat transfer coefficient is up to 9.5 W/(cm~2 K).Finally,a visual study of the bubble motion trajectory during boiling heat transfer between the light surface and the three porous structures under different heat fluxes was carried out.High-speed photography showed that there are three continuous regions:isolated bubble nucleate boiling zone,fully developed nucleate boiling zone and Bubbles gather nodules in boiling area.The study found that the changes in the heat transfer performance of the structure can be reasonably explained based on the bubble behavior.