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In the present study, a novel optical technique has been devised for identification of flow patterns during liquid−liquid two-phase upflow through a vertical pipe. It is based on the difference in optical properties of the two phases and estimates the flow patterns on the basis of the proportion of light attenuated and scattered by the two-phase mixture. The nonintrusive measurement system comprises a laser source and a photodiode sensor located on the diametrically opposite position of the test pipe. The light incident on the photodiode is converted to a voltage signal by a processing circuit and recorded in a PC via a data-acquisition system. Two types of statistical analysis, namely, the probability density function analysis and the wavelet resolution technique of the probe signals, have been adopted for a better understanding of the flow phenomena. The distribution has been observed to be bubbly at low flow rates of both the liquids. Core annular flow has been identified at high kerosene velocities. The transition from bubbly to core annular flow occurs through a chaotic distribution of both the liquids where the dominating phase shifts from water to kerosene. This is named as the churn flow pattern. The information thus obtained has been represented as a flow-pattern map. The flow-pattern map has been compared with the existing theoretical and empirical models.

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A non-intrusive optical probe has been developed for the identification of flow patterns during liquid–liquid two-phase flow through a conduit. It is based on the difference in optical properties of the respective phases and works on the basis of the proportion of light attenuated and scattered by the two-phase mixture. The measuring system consists of a laser source, a light-dependent resistance (LDR) and a processing circuit. The source and the detector (LDR) are located on opposite sides of the test pipe to detect light after its passage through the test section containing the two-phase mixture. The LDR generates a variable resistance depending on the intensity of light incident on it. The voltage across the resistance is amplified by a three-stage amplifier circuit. The dc output of the circuit is recorded as time series signal and analysed for flow patterns during liquid–liquid flow through horizontal and vertical tubes. The probe provides similar signals for similar phase distributions in both vertical and horizontal pipes and could be applied successfully to differentiate between dispersed and separated flows in the two tube orientations. It has also been observed that the present method of detection is more effective as compared to a parallel wire conductivity probe in identifying flow patterns at high phase velocities.

The present study has attempted to investigate pressure drop and holdup during simultaneous flow of two liquids through a vertical pipe. The liquids selected were kerosene and water. The measurements were made for phase velocities varying from 0.05-1.2 m/s for both liquids. The pressure drop was measured with a differential pressure transducer while the quick closing valve (QCV) technique was adopted for the measurement of liquid holdup. The measured holdup and pressure drop were analyzed with suitable theoretical models according to the existing flow patterns. The analysis reveals that the homogeneous model is suitable for dispersed bubbly flow whereas bubbly and churn-turbulent flow pattern is better predicted by the drift flux model. On the other hand, the two fluid flow model accurately predicts the pressure drop in core annular flow.