Evaporation rates from fresh and saline water in moving air

Abstract

Measurements of the water evaporation rate in still or moving air date back to the 20th century. Unfortunately, many of these studies have provided a wide variation in the measured data. Also, several of these studies did not consider the effect of water salinity on the evaporation rate. This has motivated the current study, where three methods are used for measuring the evaporation rate. These methods include changes in the water height, water weight, and air humidity. Two evaporation modes are considered: the first is for water at ambient temperature into hot air and the second for heated water into air at ambient temperature. The air and water temperatures are varied over a range of 25-60°C. The air velocity is varied over a range of 2-4 m/s. Also, the water salinity is changed from 26 ppm for freshwater up to 69 000 ppm for rejected brine in desalination processes. The measured data are correlated as a function of the evaporation mode, the pressure difference of the water vapor at the water surface and in the air bulk, and the air velocity. Measured rates compare favorably against a number of literature correlations. Results show a decrease in the evaporation rate upon an increase of the water salinity because of the reduction in the water vapor pressure at the water surface.