Heat transfer coefficients for melting about a vertical cylinder with or without subcooling and for open or closed containment

Experiments were undertaken to measure heat transfer coefficients for melting about a heated vertical cylinder embedded in a solid phase-change medium whose temperature was either at the melting point or was subcooled below the melting value. In the experiments, the upper surface of the phase-change medium was either closed by a cover which imposes a no-slip velocity boundary condition on the liquid melt or was bounded by an insulated air space which permits unrestrained motion of the liquid. The shape of the melt region was also measured. All the experiments were performed using 99% pure n-eicosane paraffin (melting temperature = 36.4° C) and encompassed both transient and steady-state periods. The cylinder height-to-diameter ratio was ten. It was found that the heat transfer coefficients are identical for the closed-top and open-top configurations. Subcooling tends to delay the onset of natural-convection dominance of the heat transfer process. The natural convection heat transfer coefficients in the presence of subcooling are about 10-15% lower than those for the non-subcooled case. In general, the steady-state natural convection heat transfer coefficients were well correlated in terms of the Nusselt and Rayleigh numbers and, in the absence of subcooling, the functional dependence was shown to be similar to that for natural convection in vertical, parallel walled enclosures without melting.