Analysis of the physical stability of PCM slurries

Microencapsulated phase change material slurry (mPCM slurry) is a latent heat storage fluid in which the PCM microparticles have been dispersed in water. One of the main issues to be tackled is its lack of physical stability, since stratification problems tend to occur. Generally, an unstabilization process in PCM slurries can take weeks or even months. To predict the physical stability of PCM slurries without having to wait so long, a methodology well known in the food and pharmaceutical fields has been applied. This methodology basically consists of measuring samples with a rheometer in oscillatory mode. These measurements can be related to visually obtained measurements of the unstabilization process of creaming, specifically with the creaming percentage over time. From the frequency sweeps accomplished, an exponential relationship between the creaming percentage and the elastic module of the PCM slurries have been obtained. From the strain sweeps, the cohesive energies of the PCM slurries have been calculated and related to the creaming percentage, observing a linear relationship. In this way, the dominant parameters in the unstabilization process have been obtained which manufacturers can modify in order to improve the physical stability of PCM slurries.