CFD simulation of melting process of Polyethylene Glycol 1500 (PEG1500) in different geometry enclosures.

This study is fucused on developing computational fluid dynamics (CFD) simulations to model the melting process of a PCM (polyethylene glycol 1500 (PEG 1500)). CFD has been used to investigate the melt percentage profile and optimum aspect ratio. A rectangular enclosure filled with PEG 1500 was isothermally heated from one side and the opposite side was kept at a constant cold temperature. The study was conducted in two phases: i) to keep the volume of the enclosure constant and change the aspect ratio between the height and width (while keeping breadth constant) ii) to keep the heating wall area constant and change the width of the enclosure for same breadth (the volume varies). The thenno-physical properties of PEG 1500 (specific heat capacity, thermal conductivity and viscosity) variation with temperature & time were considered. The Boussinesq approxilllation was applied due to natural convection in place and this ignores density differences in the flow. The change in shape and motion of melting interface with time was established by the melt front contours. The contours of the liquid fraction of PEG 1500 at specific intervals were represented for a total melting time of 375 mins (6.25 hours). The change in melt fraction with time for each case defines the percentage of melted PEG 1500. The melting starts as the enclosure is heated from the vertical wall and progresses to concentrating much at the top part of the enclosure as the heating progresses. The melt rate increases as time progresses. The optimum melting process is observed with the aspect ratio of 2.3 which is a reflection of the highest natural convection happening within the enclosure and the best aspect ratio for energy storage-reuse or energy storage-insulation. The computations were extended to include the experimental temperature conditions involved in the test and the computations agree very well with experimental results.