Natural convection dominated melting inside uniformly and discretely heated rectangular cavities

A numerical study has been conducted for natural convection dominated melting inside uniformly and discretely heated rectangular cavities. A computational methodology based on the enthalpy method for the phase change is first outlined and validated with experimental data. The model is next employed to determine the effect of the sources dimension beta and span eta, of the aspect ratio of the cavity A and of the wall-PCM thermal diffusivity ratio <(alpha)over bar> on the melting process. Results show that for a uniformly heated wall, the melting time reach a maximum for A approximate to 10. For A less than or similar to 10, convection dominated melting is enhanced and the melting time is reduced. For A greater than or similar to 10, the larger heated surface area promotes conduction dominated melting and the resulting melting times are also reduced. For discretely heated cavities of aspect ratio A less than or similar to 4.0 with a low wall thermal diffusivity ratio (<(alpha)over bar> approximate to 1.5), the source span eta is the most influential parameter. For 0.625 less than or equal to A less than or equal to 2.5 and eta greater than or similar to 0.45, the melting times are larger and the top sources quickly overheat. If eta less than or similar to 0.45, the melting times are shorter and the temperatures of the sources remain equal and moderate during the melting process. Threshold values <(alpha)over bar>(min) above which melting becomes independent of the source distribution were determined for cavities of aspect ratios ranging from 0.625 to 10.