Experimental Investigation of the Viscosity and Density of Microencapsulated Phase Change Material Slurries for Enhanced Heat Capacity and Transfer

Working fluids that incorporate solid microencapsulated phase change materials (MPCMs) can benefit from properties such as density and viscosity, which are crucial for improving heat capacity and transfer. However, limited data are available on these parameters for specific slurry and mass ratios. In this study, we present a comparative analysis of the experimental results on the viscosity of three different MPCM aqueous dispersions, namely MPCM 31-S50, MPCM 25-S50, and Micronal 5428X. Varying MPCM mass ratios of distilled water were used to obtain different mass concentrations of the phase change material (PCM), and the resulting slurries were analysed at temperatures ranging from 15 to 40 degrees C. Our findings showed that all slurries exhibited non-Newtonian characteristics at low shear rates, with viscosity stabilising at higher shear rates, resulting in the characteristics of a Newtonian fluid. The viscosity results were highly dependent on the type of MPCM base dispersion, particularly at high mass ratios, with the slurries having viscosities higher than those of water. Furthermore, we conducted density experiments as a function of temperature, using a flow test setup and a Coriolis flowmeter (Endress+Hauser, Reinach, Switzerland) to determine the density of two MPCMs, namely MPCM 25-S50 and Micronal 5428X. The test samples were prepared at mass concentrations of 10%, 15%, and 20% of the phase change material. We found significant differences in density and viscosity for different MPCM slurries as a result of both the PCM concentration and the material studied. Our results also revealed an apparent PCM phase change process, in which the slurry density significantly decreased in the temperature range of the phase transition from solid to liquid.