Mahmoud Roshdy

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 $$10\,\text {mm}$$ 10 mm ( $$Bo=8.2$$ B o = 8.2 , $$Ma=6 \times 10^3$$ M a = 6 × 10 3 ) to $$30\,\text {mm}$$ 30 mm ( $$Bo=74.2$$ B o = 74.2 , $$Ma=1.8 \times 10^4$$ 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 $$30\, \text {mm}$$ 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, $$\text {Fo} \sim \text {Bo}^{-1.29}$$ Fo ∼ Bo - 1.29 , while a looser correlation is observed for above-melting ambient conditions, $$\text {Fo} \sim \text {Bo}^{-1.24}$$ Fo ∼ Bo - 1.24 . The findings offer insights for enhancing the performance of PCM-driven latent heat storage units across diverse climatic conditions.