Lateral wetting angle of falling film in dense fluid

Abstract

An investigation of the wetting ability of a liquid-falling film on vertical steel and glass surfaces is performed by measuring the thickness and the width of the water falling film at 313 K up to 27 MPa. An attempt to reconstruct the two-dimensional cross-section of the falling film was made. The cross-section of the falling film is assumed to have the shape of a circular segment. The falling film wetting angle is compared with the sessile drop contact angle. The sessile drop contact angle represents the upper limit of the film wetting angle. A continuous increase in the mass flow at a constant pressure causes the spreading of the film. This happens when the force balance between the interfacial tensions and the dynamic forces, which deform the film geometry, is exceeded. However, if the pressure increases, the wettability goes down. This is partly due to the accumulation of liquid mass, which is caused by a larger buoyancy. The critical mass flow, that is, the minimum mass flow needed to guarantee a wide covering film is reported. The disintegration point of a liquid film is directly affected by its wettability.