Experimental Study On Heat Transfer Characteristics Of Microencapsulated Phase Change Material Suspensions In Circular Tube

The microencapsulated phase change materials(M EPCM)is a microparticle which is formed by packing core materials into a microcapsule with shell materials.The size of the M EPCM particles is micron scale.In this paper,attempting to improve the heat phase efficiency,we had microcapsulated phase change materials and conducted heat transfer experiments of M EPCM suspensions in circular tube to study the heat transfer characteristics.The MEPCM can absorb or release lots of latent heat when phase change occurs and comparing with water the M EPCM has better heat transfer characteristics.In this paper,microcapsules are prepared by emulsion polymerization with the use of paraffin as the core material and styrene-methyl acrylic polymer as the wall material.And different mass concentration of M EPCM S was also prepared.Because of the high latent heat value of core materials when the phase change occurs,M EPCM S could be the latent functionally thermal fluid to enhance the heat transfer.With the aid of scanning electron microscope(SEM),differential scanning calorimetry(DSC),thermogravimetric analyzer(DTA,TG)and laser particle size analyser,the surface morphology,particle size and distribution,the thermal properties of the M EPCM have been measured and investigated.M eanwhile the thermal performance of different mass concentration of M EPCM suspension were also been measured,including density,stability,DSC,thermal conductivity and dynamic viscosity.In this study,the laminar flow and heat transfer system of water/ M EPCM S was set up.Experiments of heat transfer characteristics of M EPCM S in circular tube were conducted.The effect of Reynolds number,mass flowrate and mass concentration on heat transfer in the tube were analyzed.The results show that the employment of M EPCM particles significantly enchances the heat transfer of fluid,and effectively decreases the wall temperature of the tube,in addition,the wall temperature decreases with the increase of the mass concentration.For the same mass concentration of M EPCM S,the wall temperature of M PCMS with mass concentrations of 2% gradually decreases with the increase of mass flow rate.However,the wall temperature of M PCMS with mass concentrations of 5% is the lowest at a mass flow rate of 23g/s.As the mass flow increases,the wall temperature starts to rise.At the entrance region of the tube,the local Nusselt number of M EPCM suspensions is clearly higher than that of pure water.The mean Nusselt number of M EPCM S is higher than water at low Reynolds number,and firstly increases and then decreases with the increase of Reynolds number.