Analysis of field synergy on natural convective heat transfer in porous media

Based on the mathematical model to describe simultaneous heat, moisture and gas migration in porous media, the idea of enhancing convective heat transfer by the synergy between velocity and temperature gradient is applied to derive the expressions about natural convective heat transfer in unsaturated porous media. The final expressions are written as two formulas for the overall and local heat transfer coefficients between the fluid and the wall. For the rectangular porous enclosure with the length-to-width aspect ratio of three, the phenomenon of field synergy on natural convection in unsaturated porous media is observed and verified through numerical calculations, which indicates that the strength of natural convection in porous media is determined not only by temperature difference, fluid velocity and fluid properties, but also by the synergy between fluid velocity and temperature gradient.