Melting Process:
The simulation of the melting process was carried out over a period of 3600 seconds for all three models, allowing for a comparative analysis. The results are presented in Figure (3):
The diagram under discussion Figure (4), which chronicles the changes in liquid fraction over the course of the melting process, is commonly known as a ”Liquid Fraction Time-Lapse Diagram.” This visual representation delineates the evolving behavior of the phase change material (PCM) as it undergoes the melting process through distinct phases.
In the initial stage, the PCM adjacent to the fin walls gradually transforms into a liquid state, primarily facilitated by conduction. As time elapses, the thickness of the liquefied layer steadily increases. Once this layer attains a sufficient thickness, the onset of natural convection currents marks the commencement of the second stage.
Throughout the second stage, four discrete regions of melted PCM manifest themselves. Region (1) originates from fin (1), while region (2) results from the melted PCM arising from fin (2) and the upper surface of fin (4). Region (3) is generated from the melted PCM originating from fin (3) and the upper surface of fin (5), and region (4) emerges from the lower surface of fin (4) and fin (5). Natural convection becomes increasingly influential during this phase, driven by the broadening expanse of the melted PCM region and the expanding interface between the melted and solid PCM.
In the ultimate stage, regions (1), (2), and (3) amalgamate to create a unified melted PCM domain in the upper half of the cylinder. In this phase, the pace of the melting process decelerates as the influence of natural convection diminishes. This decline is attributable to the diminishing boundary between the melted and solid PCM, which results in a flatter, semi-horizontal line. Over time, this line contracts until complete melting is achieved.
This ”Liquid Fraction Time-Lapse Diagram” offers a comprehensive visual narrative of the melting process and the evolving role of natural convection across different phases.
Figure (4) presents the evolution of the liquid PCM fraction over time. The results demonstrate a consistent increase in the liquid fraction. In the first and second stages, as discussed earlier, the liquid fraction exhibits a linear increase over time. However, as we enter stage (3), this increase becomes slightly less pronounced compared to the initial stages. Notably, the deceleration effect is more prominent in the A-1 model, attributable to the greater distance of the lower fins from the bottom of the heat exchanger (H.E.). Across the first two stages, the liquid fraction in model A-1 surpasses that of the other two models. Yet, in the third stage, the liquid fraction in A-1 lags the other two models. Models A-2 and A-3 exhibit nearly identical liquid fractions, with A-2 displaying a marginally higher liquid fraction during the third stage for the same time frame. In summary, the liquid fraction graph indicates that, overall, models A-2 and A-3 outperform A-1.