Evaporation of water from a partially filled, cylindrical container to a forced convection air flow

Experiments were performed to investigate the evaporation of liquid water from a partially filled, open-topped cylindrical container situated in the lower wall of a flat, rectangular duct. During the course of the experiments, parametric variations were made of the air flow in the duct (giving rise to a seven-fold variation of the Reynolds number, Re) and of the distance H between the evaporating surface and the top of the container (ranging from 0.1 to 3 container diameters, D). Supplementary experiments were conducted with toluene as the evaporating liquid. It was found that the evaporation rate did not decrease monotonically with increasing H. Rather, a local maximum in the evaporation rate occurred at H D ~ 0.5 for all of the Reynolds numbers investigated. The enhancement of the evaporative mass transfer due to the presence of the maximum ranged from 15 to 35%, depending on the Reynolds number. At all Reynolds numbers except the lowest, vigorous sloshing of the liquid surface occurred at the same H D at which the evaporation rate displayed a maximum. However, the sloshing is not a prerequisite for the evaporation maximum because such a maximum still occurred when there was no sloshing (i.e. at the lowest Reynolds number). The toluene experiments also indicated the presence of a local maximum in the distribution of the evaporation rate.