Peculiarity of Evaporating Liquid-Surface with Reference to Turbulent Heat Transfer

Abstract

Experiments have been carried out on a surface of water exposed to the flow of air of the range from 3 to 40m/sec in the velocity and from 30°to 175°C in the temperature. Measured items include not only the heat transfer coefficient, the profiles of velocity and temperature, but also the critical velocity of air for the stability of water surface. Results of heat transfer coefficient measured within the stable region of water surface are nearly in accord with the correlation proposed by Smolsky and Sergeyev, and the heat transfer coefficient becomes greater than that of a solid surface with a rise of the temperature of air. However, the profiles of velocity and temperature measured in the boundary layer are almost in accord with the 1/7 th power law, and it seems likely that they are not affected by evaporation within the range of the present study. Increasing the velocity of air flow, there appears a point at which an abrupt increase in loss of water begins. The velocity of air at the critical point agrees well with the following, wellknown value if the evaporation from the liquid surface is weak. [numerical formula] However, as the temperature of air is raised to cause an increase of evaporation, the deviation of the experimental result from the theoretical value becomes noticeable. It should be concluded, therefore, that the liquid surface subject to evaporation has some peculiarity with respect to the critical velocity for its stability too.