Successive solidification and constrained remelting of n-octadecance in a rectangular enclosure: Experimental and numerical study

Abstract

The present research reports experimental and numerical analyses on successive solidification and constrained melting of phase change material (PCM) in a rectangular aluminium enclosure cooled and heated at two vertical and the bottom walls by flowing water. Detailed and quantitative analysis of temperature field, solid front evolution, and shrinkage void formation during successive solidification and remelting of n-octadecane has been studied. After complete solidification, a shrinkage void forms at the top of the cavity. During remelting, liquid PCM formed at the sidewalls flows towards the centre of the enclosure and accumulates in the void. The liquid PCM accumulated in the shrinkage void causes a local temperature rise of 4 °C during the remelting phase, which results in faster melting of PCM from the top. Further, a two-dimensional numerical model is used to predict volumetric shrinkage and expansion during solidification and remelting. The numerically predicted shrinkage void profile is compared with the experiments with the help of real-time images and thermocouple readings and found to be in reasonably good agreement. Moreover, numerical analysis shows oscillations in PCM temperatures at the bottom zone of the enclosure during the remelting process, which indicates the presence of Kelvin–Helmholtz instability formed due to the shear flow between hot liquid close to the bottom wall and cold melting PCM.