Growth of dry patches in an evaporating film flowing around a horizontal circular tube

Abstract

The falling film flows over solid surfaces have been exploited extensively, but the modeling of film dry-out and the dry patches' formation poses a considerable challenge. Here, we presented a simple mathematical model that accounts for the evaporation to predict the evolution of dry patches in a falling film. Besides, we also analyzed the effect of flow rate, spray temperature, and tube diameter on the growth of dry patches. The distribution of liquid film thickness is asymmetrical, and the film thickness decreases firstly and then increases after a central angle of 90°. The liquid film covered the tube initially under the action of gravity, then evaporation thinned liquid film and induced small dry patches. With the increasing flow rate, decreasing spray temperature, or decreasing tube diameter, the dry-out time increases, and the dry patche area decreases. It is more effective to suppress dry patches' appearance by controlling both flow rate and spray temperature rather than tube diameter.