The structure of thermal field underneath an evaporative water surface

The temperature field beneath an evaporating water surface during natural convection has been investigated using Laser Induced Fluorescence (LIF) technique. Experiments were conducted at two different surface heat flux conditions under thermally unstable stratification. The mean temperature profiles show three distinct regions beneath the water surface where the depth dependency of temperature is different. In the conduction layer, the temperature varied linearly with depth. In the intermediate region, the temperature varied as z−1 whereas, in the bulk region, the temperature varied as z−1/3. These depth dependencies are consistent with the theoretical predictions. The results also show that the relationship between the scales of conduction and convection layers for velocity and temperature defined for wall bounded natural convection are also valid for free surface natural convection however, the length scales ratio showed the opposite trend.