Analysis of Countercurrent Flooding Data Obtained in Vertical-to-Inclined Pipes Containing Elbows of Varying Angle

Abstract

Countercurrent flooding data obtained using air and water in vertical-to-downwardly inclined pipes containing elbows of varying angle have been analysed to determine the flooding mechanisms involved, Experiments were performed with six different test sections, all having an inner diameter of 51 mm and a 1 m long vertical tube connected to an inclined or horizontal tube with elbows of varying angle. In all vertical-to-inclined pipes, the flooding was initiated in the inclined section at about 15 to 50 cm downstream of the elbow. The hydraulic jump was not observed at all in the inclined sections. Due to the countercurrent flow of gas, the liquid stream just downstream of the elbow became highly agitated and a frothy mixture formed, which was carried upstream at sufficiently high gas flow rates at flooding. At moderate to high liquid flow rates, water was deflected off at the elbow to form a turbulent, jet-like stream that partially broke up into droplets that were entrained and carried over by the gas stream. Comparison of the data with the slugging correlation at low liquid flow rates and with the liquid entrainment/carryover model at high liquid flow rates suggested that these mechanisms are likely responsible for flooding in vertical-to-inclined pipes.