Optical probe visualization of air–water flow structure through a sudden area contraction

 Single-fiber optical probes were used to investigate the time-averaged structure of gas–liquid horizontal flow through a sharp-edged sudden area contraction. The probes allowed to measure the local void fraction distribution over several cross sections of a pipe having an inner diameter of 0.08 m upstream and 0.06 m downstream of the sudden contraction. The water mass flow rate was 3 kg/s, while the gas fraction of the volume flow ranged from 0.2 to 0.8. The local void fraction was plotted as a function of its two spatial coordinates, so that a representation of the time-averaged gas distribution over the cross section could be obtained. The contraction was shown to considerably alter the distribution of the phases, so that the correlations for straight pipes appear no longer suitable. Received: 27 August 2001 / Accepted: 19 November 2001