An experimental assessment of the evaporation correlations for natural,forced and combined convection regimes

Abstract

In the present study, the applicability of widely used evaporation models (Dalton approach-based correlations) is experimentally investigated for natural, forced, and combined convection regimes. A series of experimental measurements are carried out over a wide range of water temperatures and air velocities for 0.01 ≤ Gr/Re² ≤ 100 in a heated rectangular pool. The investigations show that the evaporation rate strongly depends on the convection regime's Gr/Re² value. The results show that the evaporation rate increases with the difference in vapour pressures over both forced convection (0.01 ≤ Gr/Re² ≤ 0.1) and turbulent mixed convection regimes (0.15 ≤ Gr/Re² ≤ 25). However, the escalation rate of evaporation decreases with Gr/Re² in the forced convection regime whereas in the turbulent mixed convection it increases. In addition, over the range of the free convection regime (Gr/Re² ≥ 25), the evaporation rate is affected not only by the vapour pressure difference but also by the density variation. A dimensionless correlation using the experimental data of all convection regimes (0.01 ≤ Gr/Re² ≤ 100) is proposed to cover different water surface geometries and airflow conditions.