Effect of inclination on circumferential film thickness variation in annular gas/liquid flow

Time-varying, circumferentially local liquid film thickness data have been collected on a 38 mm internal diameter pipe at inclinations of 0∘0∘, 30∘30∘, 45∘45∘, 60∘60∘ and 85∘85∘ from the horizontal using flush-mounted and parallel wire conductance probes. Analysis of these data permits time-averaged thicknesses, probability density functions, and power spectral densities to be determined. Results show that the distribution of the liquid film is not symmetrical with thicker films on the lower part of the pipe, which are dominated by large disturbance waves. Moreover, as the inclination angle deviates from horizontal, the film thickness distribution becomes systematically less asymmetric. The probability density functions show a strong narrow peak where the liquid film is less disturbed by the presence of waves. The power spectra show that a large portion of wave energy at the bottom is carried by waves of frequency ⩽12Hz. There is no influence of liquid velocity on the shape of the spectra. However, the dominant frequency appears to decrease with increasing liquid flow rate. The frequency of the disturbance waves at the bottom decreases with increasing inclination. Moreover, the spectra tend to flatten out with increasing inclination, due to the more uniform distribution of energy among waves of a broad frequency range.