Natural convection in an evaporative air–water system inside a cavity heated by an immersed porous medium

We report on numerical results of natural convection inside a cavity that is partially filled with water and heated by an immersed porous medium. The part of the cavity above the water is occupied by air. The heat provided by the porous medium generates thermal convection in the water and the air. While water evaporation at the free surface generates convection of vapor in the air too. The porous medium is treated as a continuum and the flow inside and outside of it is modeled via the one-domain approach. Herein, we consider two cases at different Rayleigh numbers. In the first case, the flow is laminar in the air and transitional in the water, and in the second one, the flow in both phases is turbulent. Our simulations predict that thermal convection in each phase is organized in a single or dual-roll large scale circulation. Water descends from the free surface along the edges of the cavity and near the bottom it moves mostly around the porous medium. Overall, the presence of the porous medium increases circulation, hence, convective heat transport. On the other hand, the free-surface temperature and evaporation rate are essentially constant and subject only to small-amplitude fluctuations. Furthermore, the convective structures of the two fluids interact with one another at the free surface, and the main roll of the water exerts a low-frequency modulation to those in the gas. These findings can be relevant to industrial applications of water pools.