Experimental characterization of interfacial wave structure of a falling liquid film in a vertical large pipe diameter

There is considerable literature on the thicknesses of falling liquid films, much of which is focussed on either flat plates or small diameter pipes. Many studies provide time series data of the film thickness at one or two points on the pipe wall. This paper reports on an investigation of the interfacial structure of falling liquid films (liquid Reynolds numbers, ReL=618-1670) in a large diameter pipe (127 mm) using a Multiple Pin Film Sensor (MPFS) which is capable of providing measurements of film thickness and interfacial waves with excellent resolution in time and in the circumferential and axial directions. Parameters, such as film thicknesses, wave velocities and frequencies were extracted. 3D interfacial wave structures were reconstructed from the film thickness data. The waves seen were much localized unlike those in smaller diameter pipes which are characterised as coherent rings. The mean film thicknesses are generally in good agreement with published models. The mean film thickness obtained from MPFS was also compared with the output of two other sensors, Ultrasound and conductance ring pairs. There is good agreement between the three methods particularly when the fact that the ring pair technique provides a circumferentially averaged value