MELTING OF A PHASE CHANGE MATERIAL WITH NATURAL CONVECTION AND RADIATION: A SIMPLIFIED MODEL FOR ENGINEERING APPLICATIONS
A simplified model for combined natural convection and radiation during melting process of a phase change material (PCM) is presented. Enthalpy method is adopted to solve the phase change problem, the natural convection occurring in the liquid PCM is accounted for using the enhanced thermal conductivity approach coupled with the scaling theory, and the absorbed shortwave radiation is added into the energy equation as a source term using a simplified solution algorithm. First, the simplified model for natural convection during melting is validated using a CFD model, in addition to experimental and numerical benchmark solutions for a test case. Then, the simplified model for both natural convection and radiation is applied to the melting of a fatty acid eutectic filled in glass bricks and validated against lattice Boltzmann-discrete ordinate method (LBM-DOM). Finally, the complete model is applied to study the thermal behavior of a translucent wall; then validated experimentally using a full-scale building located in southern France. It was shown that (1) the proposed simplified model is simple to implement and its simulations run significantly faster than those of CFD models and LBM-DOM model. Consequently, it can be easily integrated into an energy simulation tool for yearly performance evaluation, (2) during PCM melting process, natural convection has a noteworthy role as it enhances the average fraction of liquid and the position of the melting front, (3) shortwave radiation enhances the average liquid fraction, (4) to be closer to reality, natural convection and radiation during melting must be considered.