Melting and nucleation temperatures of three salt hydrate phase change materials under static pressures up to 800 MPa

Phase change materials (PCMs) are used for efficient thermal energy storage. When a PCM melts and solidifies, it absorbs and releases a large amount of heat within a small temperature interval. Salt hydrates are interesting PCMs with high storage density, but their solidification is often problematic due to large subcooling. From thermodynamic theory, it should be possible to cause nucleation by applying high pressure to the subcooled melt, and thereby reduce subcooling. However, for the design of a pressure based triggering system there are still many unknown factors. In this context, we investigated the pressure dependence of the melting and nucleation temperatures. We present experimental data of three inorganic PCMs under static pressures up to 800 MPa. For NaOAc 3H2O we observed a shifting of the nucleation temperature from −20°C at ambient pressure to +40°C at 800 MPa. This confirms that within this pressure range, the nucleation temperature of NaOAc 3H2O is shifted above room temperature. For CaCl2 6H2O, a good agreement with reported melting temperature data was observed, and the range of experimental data was extended. For KF 4H2O, the shift of the melting temperature was found to differ considerably from theoretic predictions.