Liquid film thickness of upward air–water annular flow after passing through 90° bend

Abstract

Axial development of the base film thickness of an upward air–water annular flow after passing through a 90° bend was investigated. The pipe diameter D of the channel was 5.0 mm. The ratios, R*, of the radius of curvature of a bend to D were 6.0 and 10. The dimensionless axial distances, z* (=z/D), of measurement positions were 4, 12 and 20, where z is the axial coordinate in the vertical section. The circumferential measurement positions, θ, from the outer side to the inner side of the bend at each z* were 0, 45, 90, 135 and 180°. The liquid film thicknesses on the top and bottom sides in the horizontal section were also measured. At z* = 4, the base film at θ = 0° was thicker than that at the other θ in most of the present experimental conditions. In contrast, the circumferential distribution of the base film thickness was symmetric even at z* = 4 in the cases of high gas volumetric flux and low liquid volumetric flux. The circumferential distributions of the base film thicknesses at z* = 12 and 20 were symmetric in all experimental conditions. At z* = 12 and 20, the circumferential averaged base film thickness after passing through the bend with R* = 10 was larger than that after passing through the bend with R* = 6. The axial velocity in the liquid film was also measured. The circumferential distribution of the axial velocity was nearly symmetric at z* = 12 and 20.