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Time and spatially resolved measurements of interfacial waves in vertical annular flow
Authors:RJ Belt  JMC Van’t Westende  HM Prasser  LM Portela
Institution:1. Multi-Scale Physics Department, Delft University of Technology, J.M. Burgerscentrum for Fluid Mechanics, Prins Bernhardlaan 6, 2628 BW Delft, The Netherlands;2. ETH Zürich, Department of Mechanical and Process Engineering, ML K 13, Sonneggstrasse 3, 8092 Zürich, Switzerland
Abstract:Film thickness measurements have been performed in a vertical air/water annular flow in a pipe of 0.05 m diameter. A sensor has been built which allows to measure the film thickness evolution in time at 320 positions, such that the interface of the vertical annular flow can be reconstructed. The large-scale structures moving on the interface are described statistically, with a special attention to the disturbance waves. Probability density functions and mean statistics are given for the height, length, velocity, frequency and spatial distribution of the disturbance waves. In particular, it is shown that the disturbance waves are three-dimensional structures with large height fluctuations in the circumferential and axial direction, giving a meandering path between the maximum height around the circumference. It is also shown that the disturbance waves can flow with a slight inclination with respect to the axial direction. Finally, the disturbance waves are shown to be located randomly in space, within a Gamma distribution whose order only depends on the liquid superficial velocity. Due to the nature of the Gamma distribution, it could indicate that the spatial distribution of the disturbance waves results from a cascade of coalescence processes between the original disturbance waves on the film.
Keywords:Vertical annular flow  Interface reconstruction  Film thickness  Interfacial structures  Disturbance waves
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