PCM Slurry using Ammonium Alum and Propylene Glycol for Heat Transportation

Abstract

A phase-change material (PCM) slurry for storing and transporting waste heat was studied. The PCM used in this study was ammonium aluminum sulfate dodecahydrate (ammonium alum). Ammonium alum has a melting point of 93.5°C and a latent heat of 259.9 kJ kg−1; however, ammonium alum slurry (prepared by mixing ammonium alum and water) has a lower latent heat of 12.1 kJ kg−1 (at a mass fraction of AlNH4(SO4)2 of 15 wt%) owing to its high solubility. To decrease the solubility of ammonium alum, novel ammonium alum slurry was proposed using propylene glycol (PG) as a poor solvent. In this study, the solubility of ammonium alum in PG and water mixtures was measured. The phase change characteristics were measured using differential scanning calorimetry (DSC). The effects of the mass fraction of ammonium alum and the mass fraction of PG on the melting point and latent heat of the PCM were investigated. It was observed that when the mass fraction of PG increased, the latent heat and melting point increased. In this case, for the same melting point, the volume of particles of ammonium alum can be reduced by adding PG. The viscosity of the saturated ammonium alum solution was measured using a rheometer. The viscosity of the slurry was estimated using Einstein's viscosity equation. The heat-transfer efficiency of the prepared ammonium slurry was analyzed based on these results. It was concluded that the slurry proposed in this study is effective for heat transportation.