Characteristics of interface distribution in air-water two-phase bubbly flow in a vertical pipe was experimentally investigated by using the measurement method of optical fiber probes.The inner diameter of the circular pipe was 100 mm

and superficial gas and liquid velocities ranged from 0 to 0.1 m穝-1 and from 0 to 1.0 m穝-1

respectively.Local distributions of the interfacial area concentration(IAC)

void fraction and bubble diameter were obtained.By analyzing the forces on a bubble

it was found that lift force and turbulent dispersion force determined the radial motion of bubbles

and the former dominated the radial profile of IAC.When the bubble diameter exceeded the critical size of 5.7 mm

the distribution of IAC would change from wall peak to core peak resulting from the lift force pointing to the pipe center due to lift force coefficient changing from positive to negative.