Four-sensor droplet capable conductivity probe for measurement of churn-turbulent to annular transition flow

Abstract

In churn-turbulent to annular transition two-phase flow, both gas and liquid phase exist in the form of either continuous field (gas core/liquid film) or dispersed field (bubble/droplet). The complexity of the flow structure makes it very difficult to obtain experimental data in the churn-turbulent to annular transition flow. A novel four-sensor conductivity probe has been designed to measure interfacial structures at the churn-turbulent to annular flow regime transition. The new probe incorporates a sensor close to the detection point to serve as a common electrode for the other four sensors. Relatively large droplets can be identified and distinguished from the continuous liquid phase such as a liquid ligament or a film attached to the wall. To satisfy the higher requirements of the probe signal quality for the churn-turbulent and annular transition flow, the probe circuit has been optimized for a faster signal response and less interference. The new probe was tested in a 200 mm × 10 mm channel with an inlet superficial gas velocity up to 19.91 m/s. The measurement results are cross-checked by area-averaging the local superficial liquid and gas velocities and comparing with the measurements from a vortex flow meter and rotameter. The error is less than 10% for the superficial gas velocity and less than 20% for the superficial liquid velocity. The measured droplet size distribution is compared with a previous model, and good agreement is obtained. The effect of superficial gas velocity on droplet and ligament volume fraction as well as interfacial area concentration are investigated using the local measurement results of the three churn-turbulent to annular flow conditions.