FIGURE 8. Temperature variation at outer (1,3) and inner (2,4) surface of capsule with PCM (1,2) and the capsule fabricated from stainless steel (3,4) These data revealed insignificant differences between temperature fields from the externally heating surface and the inner side of the capsule with the PCM as well as the presence of such a difference on the opposite side. The uniformity of the temperature field in the capsule with PCM was approximately the same as the uniformity of the capsule made entirely of steel. When the PCM was freezing, the difference in capsule with PCM was more than in the one made of steel. When PCM was melting this difference was smaller. These data certify that radiant heat transfer plays an important part in the heat transfer processing in the medium of semitransparent materials. Twenty melting cycles were performed in capsules with PCM. The maximal temperature was 1175 K on the outer surface and 1160 K on the inner one. For the experiment without shields, the temperature difference was 5 to 10 K less. In both cases these differences were less than in case with capsule made of stainless steel only. Judging by a darker color in the top part of the capsule during its cooling, we have made the conclusion that liquid PCM is collected in the lower part of the capsule. The hollow volume is connected to pipes for filling. The analyses of temperature curves showed that during 90 percent of freezing time, the surface temperature change was in the 1175 to 1125 K range. The duration of this process was 3.5 minutes for every capsule. The heat flow range in this case was 25000 to 36000 Wt/m.
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