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M.M. Kenisarin, et al. Journal of Energy Storage 27 (2020) 101082 Ghosh and Guha [82] performed numerical and experimental in- vestigations of the effect of container material on the phase change process in a spherical shell. The melting process of the paraffin wax RT27 was studied for different boundary conditions. The shell with diameter of 80 mm was partially filled (85%) with the PCM. The initial PCM material was at the temperature, which was one degree below of the solidus temperature. The study was performed for container mate- rials with three different thermal diffusivities (a): aluminium (aAl = =8.5 × 10−5 m2/s), copper (aCu = =11.3 × 10−5 m2/s) and glass (aglass = =3.42 × 10−7 m2/s). Commercial software Ansys Fluent 16.2 was used for numerical simulations. The simulations were run for three values of Stefan number: 0.13, 0.18, and 0.28. Results were obtained during the experiment with melting of PCM in the spherical cavity of 80 mm in the diameter and the water-bath at the temperature of 47 °C. Density contours from simulation results are shown in Fig. 32. The major findings of that study can be summarized as follows: • The properties of the cavity materials affect the phase change pro- • cess significantly; The ratio of height and breadth (aspect ratio) of the solid phase was higher in the copper cavity (high thermal diffusivity) than in the glass cavity during a transient simulation of the melting process. The higher aspect ratio results in an unstable shape of the solid, which • increases the bouncy effect. Higher Stefan numbers during melting indicate the dominance of the natural convection, as the velocity reaches the maximum values. Recently, Gao et al. [83] conducted the experimental study of the unconstrained melting process of paraffin RT27 addressing the effect of void inside the spherical shall with using a digital camera. The effect of Fig. 33. Generalized results for the liquid fraction [83] (Correlation (7) is corresponds to (22a) of this review). such factors as the diameter of the spherical container (20.05–70.30 mm), filling ratio of PCM (0.8–0.98), heating temperature (32–47 °C) and initial temperature (7–22 °C) have been studied. These experiments showed that there is a new unconstrained melting mode (so-called floating melting), which takes place before the close-contact melting. The existence of voids in the solid PCM causes the floating melting. Generalizing all influencing factors studied in the present study by fitting the experimental data (Fig. 33) allows expressing the correlation of liquid fraction in form: = 0.374Fo0.712Ste0.243Ra0.166Si 0.094 0.192. (24a) Correlation (22a) is applicable for 1.00 × 105 ≤ Ra ≤ 2.70 × 106, 0.050 ≤ Ste ≤ 0.151, 0.85 ≤ ε ≤ 0.95, 0.134 ≤ Si ≤ 0.268, and Fig. 32. Generalized solidification time (t* = =FoSte; β = =1/Bi; γ = =Ste) [82]. 16PDF Image | Journal of Energy Storage 27
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