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.