Film Thickness and Wave Velocity Measurements in a Vertical Duct

Abstract

This paper describes the experimental investigation of an upward annular air-water flow in a duct with a 6.35 mm by 63.5 mm rectangular cross section. The test section was instrumented to measure the film thickness and the interfacial wave velocity. Flush-wire electrical conductivity probes were used to obtain local film thickness measurement with a spatial resolution of 200 μm or better and a temporal resolution greater than 2 kHz. Measurements of the base films range from 50 μm to ∼325 μm (2% to 10% of half-channel thickness). Statistical analysis shows that the standard deviation of the film thickness is a good measure of the film roughness. The relative roughness and the nondimensional film thickness are correlated as functions of the phasic Reynolds number ratio, R=Rel0.15/Reg0.3. It is found that at R=0.15, the relative roughness is a maximum. A simple model developed by matching the interfacial shear in the two fluids, predicts the wave velocity data very well.