Correlation-measurements of vertical two-phase flow by means of laser beams

Vertical annular two-phase flow in a transparent tube with an internal diameter of 10 mm was investigated by means of correlation of the signals induced in two photodiodes by a pair of horizontal, parallel laser beams, modulated by the two-phase water-air mixture. It was proved that there are two different perturbations propagating upwards in the glass tube. The two disturbances are effectively additive at the detectors. The two perturbations were identified as: a) The first comes from water-droplets carried by the air-stream of the annular two-phase flow. b) The second is due to the fluctuations of the water-air interface. The propagation of the two disturbances is reproduced by theoretical models. A method for the determination of the most probable wave length, lambdasub(max), of the interface-fluctuations is also presented. The measurements show a linear dependence of lambdasub(max) on the square of the mean relative velocity between the two phases. A hypothesis on the generation mechanism of the entrained droplets is formulated. (Auth.)