Multi-phase-fluid discrimination with local fibre-optical probes: II. Gas/liquid flows

We demonstrate fibre-optical sensors (or 'local probes') for gas/liquid dis crimination in multi-phase Rows. These probes distinguish gas bubbles from liquid on the basis of refractive-index contrast. Oblique-tip designs use t otal internal reflection; a simple cleaved-fibre end uses the smaller Fresn el reflectivity of the fibre end. This paper mainly reports data on the dis crimination of gas from liquid in air/water two-phase Flows, but we include also some examples of discrimination in kerosene/air flows and in crude oi l/nitrogen. Quantitative accuracy is again demonstrated by comparison of pr ofiles, across a pipe diameter, of local, time-averaged gas volume fraction s ('void fractions'), with pipe-averaged void fractions determined from a c arefully calibrated gradiomanometer. Companion papers deal with the sensor designs used and results achieved in liquid/liquid flows and three-phase fl ows.