Numerical Simulation And Experimental Study On Convective Heat Transfer Characteristics Of Graphene Oxide Microencapsulated Phase Change Materials Suspension

The reason why microencapsulated phase change materials have broad application prospects in the field of thermal energy transportation is that they have a constant phase change temperature,high energy storage efficiency,and convenient storage and transportation.The thesis mainly studies the convective heat transfer characteristics of microencapsulated phase change materials containing graphene oxide.The research results can provide data support for practical engineering applications.Firstly,the composite microencapsulated phase change materials with lauryl alcohol as core,acrylic resin as shell and graphene oxide as modifier was prepared by suspension polymerization.Compared with the traditional microencapsulated phase change materials(MPCM),a better performance of GO composite microencapsulated phase change materials(GO-MPCM)was obtained.Then,based on the CFD-DPM model,the convective heat transfer process of microencapsulated phase change materials suspension(MPCMS)in a circular tube was studied,and the effects of mass fraction,Reynolds number(Re)and heat flux density on the flow and heat transfer characteristics were analyzed.Finally,an experimental platform for convective heat transfer of latent functional thermal fluid was established,and the convective heat transfer characteristics of MPCMS and GO-MPCMS were studied.The results show that:(1)The prepared microencapsulated phase change materials keep a clear spherical profile,and the core material,shell material and modifier do not react with each other.The average particle size of MPCM is 1?m,the latent heat value of MPCM is 91.83 k J/kg,the packaging efficiency is 43%,and the thermal conductivity is 0.165 W/(m·K),has a mass loss of about 0.4%at 0-100?and 41.6%at 100-200?.Based on the traditional microencapsulated phase change materials,the average particle size of GO-MPCM increased by 35.7%,the latent heat value of GO-MPCM increased by 43%,the packaging efficiency increased by 42.9%,and the thermal conductivity increased by126.7%.The GO-MPCM has no mass loss at 0-100?,and the mass loss is about 8%at 100-200?.(2)The simulation results show that the fluid temperature at three mass fractions(2%,5%,10%)is reduced by 0.75%,5.92%and 47.5%,respectively,and the local Nusselt number(Nu_x)increases by 2.67%,7.89%and 48.85%,respectively,compared with pure water.When the Re increases,the melting zone is longer,the tube wall temperature is lower,the Nu_x is increased,and the convective heat transfer capacity is enhanced.As the heat flux increases,the melting area becomes shorter,and the fluid Nu_x increases.The relationship between Nu_x and Re and Pr of microencapsulated phase change materials suspension with different mass fraction is obtained by fitting.Compared with pure water,the Nu_x enhancement ratio of MPCMS with a mass fraction of 10%is 1.369.(3)Compared with pure water,the Nu of MPCMS increased by 27.6%,and the Nu of GO-MPCMS increased by 28.8%.Compared with MPCMS,the increase of Nu of traditional microencapsulated phase change material suspension mixed with graphene oxide particles is very small.(4)The experimental results show that as the mass flow increases,the length of the melting zone increases,and the wall and outlet temperature of the round tube are lower than pure water under the same conditions.When the mass flow rate and heat flux remain unchanged,the mass fraction increases,and the Nu_x of GO-MPCMS increases.Compared with pure water,the Nu_x of graphene oxide composite microencapsulated phase change material suspension with 10%mass fraction increases by about 28%.(5)Fitting the relationship between Nu_x and Re and Pr of latent functional thermal fluid under different mass fraction,compared with pure water,the Nu_x of latent functional thermal fluid increases.At the same mass fraction,the enhancement ratio of Nu_x of GO-MPCMS is higher than that of MPCMS.Under the same working medium,the higher the mass concentration of graphene oxide composite microencapsulated phase change material suspension,the greater the enhancement ratio of Nu_x.Under the experimental condition,the average Nu increases with the increase of the Re.Under the laminar flow condition,the average Nu of the latent functional thermal fluid is 2-3 times that of the pure water.As Re increases,the pressure drop at the inlet and outlet of the circular tube also increases.