Numerical Investigation Of Phase Change Heat Transfer In A Horizontal Cylinder Including Effects Of Natural Convection

The melting of phase change material (PCM), inside a horizontal cylinder with constant temperature boundary condition is characterized by three main features: (i) irregular, moving solid-liquid interface boundary; (ii) movement of solid phase as a whole as melting occurs; (iii) natural convection in the liquid phase and conduction in the solid phase. Up till now there is no solution that takes into account all three characteristics. A numerical model for this problem which takes into consideration these characteristics has been developed including subcooling effects. Co-ordinate transformation is used to generate fixed regular boundaries, such that body-fitted grid system can be used in the numerical procedures. Using a finite difference formulation, the primitive variable equations of motion are solved simultaneously with the energy equation and moving boundary heat balance equation, for the melt region, and the heat conduction equation for the solid region. Primitive variables are chosen such that the model can be readily extended to three-dimensional geometries. Time dependent natural convection velocities, temperature profiles, melting front locations, heat flux at the cylinder wall, and melt volume are investigated for Rayleigh number from 0.0 to 10(\u276), Stefan number from 0.05 to 0.3 and subcooling degree from 0.0 to 1.5.It has been found that the melting process is strongly influenced by the fluid motion due to natural convection for Rayleigh number higher than 10(\u274), except for a very short period at the beginning, which is dominated by conduction. Also, including the real configuration where the solid drops to the base of the cylinder increases both the heat flux at the cylinder wall and the melt rate by about 8%. In addition, the heat transfer coefficient at the cylinder wall is not uniform, it has a higher value at the bottom and decreases to the top of the cylinder. Moreover, the melting rate is almost controlled by Stefan number, the higher the Stefan number the faster the melting, but the relation is not linear. Finally, subcooling affects both the heat flux and melt rate. The higher the subcooling degree the higher the heat transfer coefficient and lower melt rate, at the beginning of the process, and that effect decreases with time