摘要
We investigate the free evaporation of water into air from a small-scale (≈0.1 m) circular pool for low Grashof (Gr) number values under dominant downward flow motion. Repeatable experiments performed at atmospheric pressure for air temperatures at 290 K, 300 K and 310 K and relative humidity values ranging from 30% to 60%, are described and compared to detailed Finite Element Method (FEM) numerical simulations. For the free evaporation regimes considered here, a downward thermally-induced flow originated at the rim of the pool overcomes the concentration-induced buoyancy, consequently forcing the far-stream warm dry air to descend into the lower temperature air-water interface. Experimental results show that a steady-state recirculation zone near the air-water interface develops for Gr numbers greater than or equal to 50. The Sherwood number (Sh) for this geometry appropriately scales with Gr1/4 for drier free-stream boundary conditions, while it approaches a constant value for smaller mass transfer potentials (i.e., more humid environments). A stable Sherwood number (Sh correlation as a function of Gr values is proposed, covering Gr values from 10 to 105."