The PCM-water emulsion with low supercooling

This study aims to develop paraffin waxes based phase change material (PCM) emulsion with low supercooling degree, which can be applied in a thermal energy storage (TES) systems to maximize the use of natural heating and cooling sources via solar thermal collectors or evaporative coolers, and to raise the energy efficiency of the chillers operating at off-peak period. Paraffin waxes are cheap with moderate thermal storage densities and a suited range of melting temperatures as PCM. But they generally tend to become supercooled in phase change process, and they have low thermal conductivity. PCM emulsions are superior in their heat transfer rates compared to the original materials but the supercooling degree is expected to increase along with the droplets decline. In this study, a kind of hexadecane-water emulsion with small droplet size was prepared and analysed. The modified multi-wall carbon nano-tube (MWCNT) particles were dispersed in emulsion as the nucleating agent to reduce the supercooling degree. The MWCNT particles were modified with carboxyl groups to increase the compatibility with the organic liquid. Thermal analysis of the hexadecane-water emulsions with well dispersed MWCNT particles by differential scanning calorimeter (DSC) indicated that the supercooling degree of emulsion was significantly decreased. The effective ranges of nucleating agent concentration were summarized which provided a promising way of improving the performance of the energy efficiency in TES systems.