Experimental Study On Sedimentation Phenomena In Boiling Heat Exchange Of Nanofluids And Establishment And Analysis Of Theoretical Models

The contact angles of the nanoparticles affect the morphology and wettability of the nanoparticle deposit during the boiling process.Suspended nanoparticles with a certain contact angle which adsorbed on the bubble interface will inhibit the bubble merger and change the bubble dynamics,and thus affect the heat transfer effect.In this paper,nanoparticles with different contact angles were synthesized to prepare stable dispersed nanofluids.By means of the combination of experimental observation and theoretical analysis,the influence of nanoparticle on the heating surface structure and heat transfer characteristics are investigated.The mechanism of the nanoparticle contact angle on the boiling heat transfer of nanofluids is studied:1 Explore the deposition of nanoparticles with different contact angles and the influence on the boiling heat transfer.According to the different characteristics of nanoparticles with different contact angles,SiO₂ nanofluids with different contact angle were synthesized.The visualization experiment platform was designed to simulate the saturation pool boiling,and the influence of nanoparticles and contact angle on the pool boiling heat transfer coefficient was investigated.The results show that the contact angle of nanoparticles can affect the morphology of the nano-deposited layer on the heating surface and different surface morphologies have different heat transfer effects.The deposition of highly hydrophilic nanoparticles is more uniform,the deposition of partial hydrophilic nanoparticles is irregular and the pool boiling heat transfer is promoted.It can be seen that as the heat flux increases,the nanoparticles deposit more easily.2 Introduce the vapor recoil force to establish a new model of nanoparticle force.Based on the traditional model,this paper introduces the vapor recoil force and establishes a completely new theoretical model.The theoretical analysis shows that the deposition of nanoparticles on the heating surface is mainly related to the heat flux density,the contact angle of the nanoparticles,the receding contact angle of the liquid and the friction coefficient of the heating surface.Under certain circumstances,the higher the heat flux density and the smaller the contact angle of the particles,the easier it is to deposit.The theoretical model is consistent with the experimental results.In this work,a new theoretical model was established to explore the relationship between nanoparticle deposition,heat flux density and contact angle.At the same time,the effect of nanoparticles and contact angle on the heat transfer was explored through experiments.