An experimental investigation of solidification of a Phase Change Material (PCM) in circular enclosures

Abstract

This study involves a detailed characterization of PCM solidification within encapsulations that have a circular cross-section, such as spherical and horizontal cylindrical containers. A quasi-2D cavity was used to emulate the above-mentioned container geometries through symmetry. Rubitherm RT26 was used as the phase change material (PCM). The PCM within the cavity was initially superheated. A constant temperature condition lower than the melting temperature was applied uniformly to the circumferential wall of the cavity via a water jacket. Three experimental measurement techniques were implemented. The first two techniques were used in conjunction to estimate the internal temperature of the PCM and, by extension, the transient temperature fields within the solidifying PCM. These temperature-measuring techniques provided data from a high-resolution grid of thermocouples and a novel technique using an infrared camera. The third technique involved the capture of transient velocity fields within the liquid PCM using particle image velocimetry (PIV). The results suggest that substantial kinetic supercooling effects were present under these conditions, which likely affect the solidification process significantly and should not be neglected in numerical models. Also, the results show that the heat transfer was dominantly convection-driven initially, followed by a period of highly transient velocity behavior before the fluid velocities became nearly stagnant relatively early in the process. It was shown that heat transfer occurred mainly by conduction for the majority of the process.