Experimental Study On Natural Convective Heat Transfer/Thermal Storage Performance Of Microencapsulated Phase Change Material Suspensions

Microencapsulated phase change material suspension (MPCMS) and phase change emulsion are two kinds of novel latent functionally thermal fluids. Compared with the conventional single phase heat transfer fluid such as water, their apparent specific heat in the phase change temperature range is greatly increased. As a result, the heat transfer ability and energy storage ability can be obviously improved. Therefore, they have many potentially important applications in fields such as heating, ventilating, air-conditioning, refrigeration and heat exchangers.In order to obtain stable microencapsulated phase change suspension, two methods for preparing MPCMS are utilized:one method is using1-propanol/water as base fluid and the other method is using water added with promoter as base fluid. Experimental results of both methods are compared and show that the MPCMS prepared with1-propanol/water mixtures is more stable than MPCMS prepared with water added with promoterssince there is no layering after48hours’ standing. Therefore, the1-propanol/water mixtures are chosen for later preparation.10-40wt%MPCMS are prepared using1-propanol/water mixtures of which the density is0.941g/mL as base fluid.In this paper, microscopic morphology, size distribution, viscosity and rheological properties, phase change latent heat, specific heat capacity and thermal conductivity are tested while the influences of temperature and mass concentration on MPCMS are analyzed. In addition, the relationships between thermophysical properties and temperature are fitted. Test and analysis on thermal physical properties of microencapsulated phase change material suspension using1-propanol/water binary liquid mixtures as base fluid show that MPCMS has stable properties, large heat storage and shows the characteristics of the Newtonian fluid and has low viscosity when its mass concentration is as high as40wt%. As for the thermal conductivity of MPCMS, it decreases linearly with the increase of mass concentration.Water,1-propanol/water binary liquid mixtures and10-30wt%MPCMS are used as the heat storage working fluid in an enclosure with a parallel array of five tube bundles with different storage temperature. The effects of phase change material, the mass concentration and temperature of water flowed through the tube bundles are studied, respectively. By comparing the experimental results of MPCMS with mass concentration varied from10wt%to30wt%, it demonstrates that the extent of heat transfer enhancement becomes greater as the mass concentration of MPCM increases from10wt%to30wt%. The experiment of MPCMS with temperature of water flowing through tube bundles varied from50℃to70℃provide a direct proof that the phase change properties of MPCMS is the key factor of the heat transfer enhancement.