Experimental investigation on the melting of an organic phase change material subjected to thermocapillary and buoyancy effects at different ambient temperatures

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.