Investigation On Flow And Heat Transfer Characteristics Of Solid Particle Suspension In A Circular Tube

With the rapid development of modern industry,the traditional heat transfer medium（water,oil,alcohol,etc.）has been unable to meet the increasing heat transfer load in heat utilization sites.Nanoparticles with high thermal conductivity and phase change microcapsu les with high specific heat are combined with traditional working medium to enhance heat transfer.In this paper,a flow heat transfer experimental device is built,Taking three kinds of solid particle suspensions:nanoparticles suspension,microencapsulated phase change material suspension and hybrid suspension as the research object,the heat transfer characteristics,flow characteristics and comprehensive enhanced heat transfer characteristics of solid particle suspension in circular tube are analyzed through experiments.The main work is as follows:（1）Effects of surfactant and nanoparticle mass fraction on the heat transfer characteristics,flow characteristics and comprehensive enhanced heat transfer characteristics of nanoparticle suspension in circular tube were experimentally studied.The results indicated that the average Nusselt number,friction resistance coefficient and comprehensive evaluation factor of nano particle suspension increase with the increase of nanoparticle mass fraction.When sodium dodecylbenzene sulfonate（PVP）is selected as surfactant and the ratio of surfactant to nanoparticle mass fraction is 1:1,the comprehensive enhanced heat transfer performance of Si O₂-H₂O nanoparticle suspension with 6%mass fraction is the best,which is 46%higher than that of water.（2）Three kinds of microencapsulated phase change material with different particle sizes were prepared.,the core phase change material is n-octadecane and the shell material is melamine formaldehyde resin.The heat transfer characteristics,flow characteristics and comprehensive enhanced heat transfer characteristics of microencapsulated phase change material suspensions with different particle sizes and mass fractions in a circular tube were studied.The results indicated that the average Nusselt number,friction coefficient and comprehensive evaluation factor of microencapsulated phase change material suspension were positively correlated with the mass fraction of particles.At low Reynolds number,the overall heat transfer enhancement performance of the 1μm particle diameter microencapsulated phase change material suspension is slightly higher than that of the 3μm particle diameter microencapsulated phase change material suspension,while at high Reynolds number,it is roughly the opposite.（3）The hybrid suspension was prepared by mixing nanoparticles with microencapsulat ed phase change material.The effects of the ratio of nanoparticles to microencapsulated phase change material and the mass fraction of mixed particles on the heat transfer characteristics,flow characteristics and comprehensive enhanced heat transfer characteristics of hybrid suspension in a circular tube were experimentally analyzed.The results indicated that when the ratio of nanoparticles to hybrid suspension is 1:3 and the mass fraction of mixed particles is 6%,the comprehensive heat transfer enhancement performance of hybrid suspension is the best,which is 55.5%-78.7%higher than that of water.（4）The heat transfer characteristics,flow characteristics and comprehensive enhanced heat transfer characteristics of nanoparticle suspension,microencapsulated phase change material suspension and hybrid suspension were compared and analyzed,and the differences of enhanced heat transfer of three solid particle suspensions were obtained.The results indicated that the comprehensive heat transfer enhancement performance of hybrid suspension and microencapsulated phase change material suspension is stronger than that of nanoparticle suspension.When Si O₂/MEPCM ratio changes from 2:1 to 1:2,the comprehensive heat transfer enhancement performance of microencapsulated phase change material is slightly stronger than that of mixed particle suspension,while Si O₂/MEPCM ratio is 1:3,The comprehensive heat transfer enhancement performance of microencapsulated phase change material suspension is lower than that of hybrid suspension.