Experimental Study On Boiling Heat Transfer Performance Of Nanofluids On Different Heating Surface

Aiming at the problem of boiling surface heat transfer enhancement of condensed reflux liquid in engineering,this paper designed a closed loop boiling heat transfer experimental device to study the boiling heat transfer test of different nano fluids on the surface of foamed copper.Type,concentration,base fluid on different PPI numbers,thickness,material,porosity,foam metal heat transfer enhancement effect.On the basis of verifying the reliability of the boiling heat transfer experimental device built by deionized water,the following research work was carried out and several achievements were made:Firstly,the closed loop saturation boiling experimental device with condensate reflux designed in this paper is different from the saturated pool boiling device of deionized water large container.The test shows that the device has a maximum boiling heat transfer coefficient with no condensate reflux due to reflux with condensate.The large container saturated pool boiling maximum heat transfer coefficient increased by 15%.Secondly,the boiling heat transfer performance of graphene/alumina nanoparticle mixture fluid in glycol water mixed liquid solution under normal pressure was studied experimentally.The volume ratio of ethylene glycol to deionized water is 20:80,50:50,100:0,the mass concentration of the nanoparticles is 0.01%,and the mass ratio of graphene to alumina in the mixture is 1:1.The experimental results show that the enhanced boiling heat transfer effect of graphene and alumina/graphene in ethylene glycol is better than that of adding alumina;the collision frequency and sedimentation of different nanoparticles during boiling process due to the difference in density between the two nanoparticles The speed changes,so that the nanoparticles are deposited less on the heating surface,and the morphology is favorable to increase the number of gasification cores on the heating surface,so that the boiling heat transfer performance of the mixed particle nano-fluid is more remarkable than that of the single graphene or alumina nano-particle nano-fluid.The addition of graphene/alumina nanoparticles to different ethylene glycol water mixtures can improve the boiling heat transfer performance of the base liquid;the interaction between the two-component solution and the reflux liquid in the boiling process exacerbates the disturbance and separation of the bubbles.The mixture of liquid-based alumina/graphene nanoparticle mixture with a mass concentration of 0.01%and a deionized water volume ratio of 50:50 has the best effect on the boiling heat transfer performance of the base liquid,and the critical heat flux density.And the maximum boiling heat transfer coefficient increased by 82.72%and 94.15%,respectively.Thirdly,the boiling heat transfer performance of different thickness of foamed copper surface was tested under different atmospheric pressures of different Al2O3 nanofluids with a mean particle size of 50 nm.The test results show that:based on the experimental device in this test,?1?the best matching foam copper parameters of deionized water are thickness4mm,porosity 0.9,pore density 60PPI,and its boiling heat transfer performance is better than water in smooth copper.The surface is increased by 100%;?2?the water-based Al₂O₃nanofluid with a mass concentration of 0.05%,the best matching foam copper parameters are thickness 4mm,porosity 0.9,pore density 30PPI,and the boiling heat transfer performance is the same as that of deionized water.The boiling heat transfer performance of the copper foam surface is increased by 7%-16%;?3?as the nanoparticle mass concentration increases and the foam copper pore density and foam copper thickness increase,it can play a certain role in the low heat flux density range.The heat transfer enhancement effect is enhanced,but the heat transfer enhancement effect is significantly reduced in the high heat flux density range.The increase of the foamed copper pore density and the thickness of the foamed copper is more obvious than the increase of the nanoparticle mass concentration;?4?The concentration of 0.05%ethylene glycol water mixture?40EG:60DW?based Al₂O₃nanofluids has the best boiling heat transfer on the surface of foamed copper with a pore density of 30 PPI,a thickness of 4 mm and a porosity of 0.9,compared with based liquid.Glycol water The boiling heat transfer performance of the mixed liquid on the surface of the foamed copper is increased by 2%-10%;?5?The condensed reflux liquid in the test device with closed loop in gravity reflux and the capillary pumping of the copper foam facilitates the disturbance of the bubble and The detachment can effectively enhance the boiling heat transfer effect of the foamed copper surface.Finally,in this paper,water-based graphene nanofluids with a mass concentration of0.001%,0.01%,and 0.05%under normal pressure have foam densities of 5PPI,15PPI,30PPI,porosity 0.88,0.98,and thickness of 6mm.The boiling heat transfer of nickel on two low-porosity foam metal heating surfaces was studied experimentally.The dispersant was sodium hexametaphosphate.The results in the experimental range show that the boiling heat transfer performance of the foamed copper with a porosity of 0.98 decreases with the increase of the mass concentration of graphene nanoparticles.As the heat flux density increases,the foamed copper with a porosity of 0.98 has a higher boiling heat transfer performance than the foam with a porosity of 0.88.At high pore density,the boiling heat transfer performance of graphene nanofluids on the foam surface with a porosity of 0.98 is worse than that of the foam with a porosity of 0.88.The heat exchange of the low concentration graphene nanofluid on the surface of the foamed copper is good;the heat exchange of the high concentration graphene nanofluid on the surface of the foamed nickel is good.The water-based nanofluid with a graphene mass concentration of 0.05%has the best boiling heat transfer performance on the foamed copper surface with a pore density of15 PPI,a thickness of 6 mm and a porosity of 0.88.