Investigation of the characteristics and mechanisms of contact melting and float melting phenomena inside a sphere

Abstract

In recent decades, unconstrained melting processes with high heat-transfer rates have attracted significant interest. This study provides an in-depth investigation of the characteristics and mechanisms of two unconstrained melting phenomena (contact melting and float melting modes) of n-eicosane inside a sphere subjected to a non-isothermal wall temperature. The effects of the heating time, initial temperature, and heating temperature are studied using an improved image processing method. Quantitative and qualitative comparisons with the two melting modes demonstrate that contact melting within the sphere occurs at a higher rate (up to 2.97%) than float melting. This is because of the long-term contact state of the solid phase change material (PCM) and low thermal resistance across the bottom thin liquid PCM layer. A float melting phenomenon occurs during the melting process is a random event depending on whether the solid PCM can reach the state of force equilibrium during the initial unconstrained melting process. Due to the free motion of the solid PCM and random movement of the floating bubbles, the probability of occurrence of the contact melting mode is greater than that of the float melting mode with a maximum probability of only 46.66%. Finally, dimensional analysis of the experimental data was performed and presented with an overall uncertainty below 15%. The findings can contribute to a better understanding of the float melting and spark the interest of more researchers to further explore the unconstrained melting process.