Heat transfer and Rheological behavior of nanoparticle compound microencapsulated phase change material suspensions

Abstract

Addition of microencapsulated phase change materials (MPCM) have been used for enhance the heat transfer of fluids because of the large latent heat during the phase change period of particles. However low thermal conductivity of phase change material diminishes the heat transfer performance of the fluid partially. In the past decade, significant enhancements of nanofluids on the enhancement of thermal conductivity and convective heat transfer were observed in comparison with the base fluids. To improve the thermal conductivity of MPCM suspensions, the additive nanoparticles were used to formulate a novel thermal fluid—nanoparticle compound microencapsulated phase change material suspensions were formulated. The rheology measurements shows that such suspensions are Newtonian fluids at the shear rate of 5–500s−1 and the shear viscosities depend strongly on temperature. Experimental investigations were conducted on the laminar convective heat transfer characteristic of the nanoparticle compound MPCM suspensions in a vertical circular tube with 0.5% TiO2 nanoparticles and various MPCM mass concentrations ranging from 5%–20%. The results exhibit that the convective heat transfer performance of nanoparticle compound MPCM suspensions are significantly improved in comparison of the MPCM suspensions and this enhancement increases with the increasing of the MPCM concentration, the modified Nusselt number can be improved by 27.0% for MPCM concentration of 20 wt%.