Assis et al. [1] gave a numerical model for solidification in spheres considering curvilinear geometry, shrinkage of phase change material (pcm) and air gap variation for the material RT27. Their numerical results of melt fraction (MF) and the product of Fourier and Stefan numbers (Fig. 5(b)) were correlated by Eq. (3) [1]. This correlation is valid for the pcm RT27 which has a melting range (28–30 °C) and for Stefan number (Ste) ≤ 0.4.

From Fig. 5(a) and their statement (3.2 [1]) total freezing times are

The corresponding values of the product of Fourier and Stefan numbers ( = Fo Ste) calculated taking the thermo physical properties given in their paper are 0.173 (for case(A)) and 0.1845 (case(B)). Both the calculated values of Fo Ste are much beyond the scale of 0.05 given in Fig. 5(b).

It may be noted from Fig....

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