Mechanism for the removal of droplets from a liquid surface by a parallel air flow

Abstract

A study has been made of the critical conditions and the mechanism of atomization for the co-current flow of air and a liquid. High speed motion pictures reveal that atomization occurs by the removal of small wavelets which exist on the top of flow surges in the liquid film (called roll waves). The critical conditions are characterized by two limiting behaviors. For thick liquid films the air velocity necessary to initiate atomization is larger than that required to generate roll waves and is insensitive to variations of the flow rate of the liquid. As the liquid film becomes thinner larger gas velocities are needed. For very thin films the critical condition is insensitive to the gas velocity and the liquid mass flow rate needed to initiate atomization is the same as that needed to initiate roll waves. The critical condition for both thick and thin films is not strongly affected by changes in the fluid viscosity. It is suggested that atomization results from a Kelvin—Helmholtz instability whereby the destabilizing force is the pressure variation caused by the compression of the air streamlines at the crests of wavelets.