Investigation Of Thermo-physicals And Laminar Flow And Phase Change Heat Transfer Charteristics In Mini-tubes Of PCE

With the development of global society and economics,the problems such as energy shortage,environment pollution and imbalance of energy supply and demand are becoming more and more serious.Recent years,the thermal energy storage(TES)system has attracted more and more attentions.Phase change material(PCM)which can absorb or release a large amount of heat at a constant temperature when undergoing a change in phase is a commonly used material in TES.As a newly phase change fluid,phase change emulsion(PCE)which has good fluidity,can be used both as energy transfer and energy storage medium and has large energy storage capacity is a promising PCM.The present study is focus on the(1)the preparation of PCE;(2)the thermo-physicals of PCE and pumping power when used as energy transfer medium;(3)the flow and heat transfer characteristics of PCE in the test tube with 2.0mm and 4.0mm inner diameter,respectively.In the present study,the PCE is prepared by D-phase method.The results of the measurement of thermo-physicals shows,the stability of PCE is related to the kind of surfactants and the stirring intensity.The size distribution of PCE with different mass fraction is similarity,the average particle size of n-hexadecane PCE is 290 nm and the n-octodecane PCE is 320 nm.The rheological behavior is measured by a rheometer,the rheological behavior of PCE is related to the mass fraction,the viscosity is increased with the increase of mass fraction and decreased with increase of temperature.The phase change behavior of PCE is measured by DSC,the latent heat is proportional to the mass fraction of PCM and exist a large supercooling.The thermal conductivity of PCE is measured by hot-wire method,the thermal conductivity is decreased with the mass fraction of PCM and increased with temperature.The pumping power of PCE is larger than water under the same heat storage capacity.The Nusselt number of PCE is much larger than water under the same condition.The deviation of flow friction coefficient of PCE based on experiment date and theoretical calculation results is within ±18.0%.The larger heating power,the local heat transfer coefficient is smaller at the same position and the heat transfer coefficient will reach the minimum value earlier,what is more,the heat transfer coefficient is larger at the later section.The local heat transfer coefficient increase with the increase of flow velocity and mass fraction of PCM.The heat transfer coefficient is much larger in the smaller test tube under the same Re.The heat transfer correlations were developed based on experiment data and the deviation between experimental data and developed correlations is within ±20%.