Abstract This study experimentally investigates the melting of the phase change material n-octadecane in a parallelepiped container heated laterally and with a free upper surface. The melting process is influenced by buoyancy and thermocapillary forces. The effect of their relative influence is studied by varying the thickness of the n-octadecane layer from 10\, mm 10 mm (Bo=8. 2 B o = 8. 2, Ma=6 10³ M a = 6 × 10 3) to 30\, mm 30 mm (Bo=74. 2 B o = 74. 2, Ma=1. 8 10⁴ M a = 1. 8 × 10 4), and the effect of the ambient temperature is studied by examining the melting processes at room temperatures above and below n-octadecane’s phase transition temperature. Results demonstrate that seasonal temperature variations, above or below the melting temperature, play a critical role in melting rate and position of the solid/liquid meniscus. The shift from summer (June–July) to fall (October–November) ambient conditions is a leading contributor to the melting rate, especially at small thicknesses. Melting time is reduced by a factor of approximately 2. 5 at ambient temperatures above the melting point for the largest thickness of 30\, mm 30 mm. Despite fluctuations in the ambient temperature and other experimental parameters, these results reveal a tight power law relationship between the Fourier and Bond numbers under below-melting ambient conditions, Fo Bo^-1. 29 Fo ∼ Bo - 1. 29, while a looser correlation is observed for above-melting ambient conditions, Fo Bo^-1. 24 Fo ∼ Bo - 1. 24. The findings offer insights for enhancing the performance of PCM-driven latent heat storage units across diverse climatic conditions.
Roshdy et al. (2026) studied this question.