Effect of length-to-diameter ratio on axial velocity and hydrodynamic entrance length in air-water twophase flow in vertical pipes

The effect of pipe length-to-diameter ratio (L/D) on air-water two phase slug flow regime development is hereby investigated. Axial velocity along the leading Taylor bubble and hydrodynamic entrance length required to establish a fully developed parabolic profile were critically assessed. The eccentricity distribution of axial velocity on leading Taylor bubble stream and on its nose is observed in all the L/D geometry ratios. The radial component of the axial velocity profile in the liquid film ahead of the leading Taylor bubble is represented by a power law function; with exponent n=6.1 for L/D=833.3 and n=5.7 for L/D=1666.7. Despite a decrease in the exponent as L/D ratio increases, the full parabolic profile could not be reached. This suggests that further investigation on L/D ratio incorporating other inherent variables which are likely to affect the development of the full parabolic profile may be required.