Determining the Heat of Fusion and Specific Heat of Microencapsulated Phase Change Material Slurry by Thermal Delay Method

This paper details an experimental study that was performed to investigate the specific heat of microencapsulated phase change material (mPCM) slurry and its heat of fusion at the PCM phase change transition temperature. Six samples (mPCM slurry concentrate with the water solution of propylene glycol used as a main base liquid) were prepared. As the concentrate contains 43.0% mPCM, the actual mass fraction amounts to 8.6, 12.9, 17.2, 21.5, 25.8, and 30.1 wt%, respectively. The thermal delay method was used. Samples were cooled from 50 °C to 10 °C. A higher concentration of microcapsules caused a proportional increase in the specific heat of slurry at the main peak melting temperature. The maximum value of the specific heat changed from 9.2 to 33.7 kJ/kg for 8.6 wt%, and 30.1 wt%, respectively. The specific heat of the mPCM slurry is a constant quantity and depends on the concentration of the microcapsules. The specific heat of the slurry (PCM inside microcapsules in a liquid form) decreased from 4.0 to 3.8 kJ/(kgK) for 8.6 wt%, and 30.1 wt% of mPCM, respectively. The specific heat of the slurry (PCM inside microcapsules in a liquid form) was higher than when the PCM in the microcapsules is in the form of a solid and increased from 4.5 to 5.2 kJ/(kgK) for 8.6 wt% and 30.1 wt% of mPCM, respectively.