11 PCM-Metal Foam Composite Systems for Solar Energy Storage
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size of the second system results in faster energy transfer to the PCM. The variation
of liquid fraction with time for the two systems are compared in Fig. 11.16b which
confirms that melting occurs at slightly faster rate if the average pore size is less.
This study is important as it shows that although two systems may have exactly same
material and porosity, variation of pore size leads to different energy absorption rates.
Hence for designing a composite metal foam-PCM system, the pore size of the foam
should also be taken into consideration. Similar results, predicting the increase in
heat transfer with decrease in pore size, has been obtained by pore scale modelling
by Ren et al. (2017).
11.5.6 Effect of Overall System Size
For this study two different cubic domains are considered—with side lengths of
20 and 10 cm, respectively. All the other parameters are same as that specified in
Table 11.1. Figure 11.17 shows the temperature contours for the two systems at time
Fig. 11.17 Temperature contours at the mid-section for domain of side length a 20 cm at t = 500 s;
b 20 cm at t = 2000 s; c 10 cm at t = 500 s; d 10 cm at t = 2000 s