COUNTERCURRENT FLOODING IN VERTICAL-TO-INCLINED PIPES

Countercurrent flooding data have been obtained using air and water for vertical-to-downwardly inclined pipes containing elbows of varying angles. Experiments were performed with six different test sections, all having an inner diameter of 51 mm and a 1-m-tong vertical tube connected to an inclined or horizontal tube

The flooding data for 112.5° and 135° elbow angles were almost identical and showed that these geometries required the largest gas flow rates for flooding among all the geometries tested. The flooding gas velocities for the 157.5° elbow were slightly less than those of the 112.5° and 135° elbows but greater than those of the vertical pipe without any elbow and vertical-to-horizontal pipes at low to moderate liquid flow rates

In all vertical-to-inclined pipes, flooding was initiated in the inclined section at about 15 to 50 cm downstream of the elbow. Due to the countercurrent flow of gas, the liquid stream just downstream of the elbow became highly agitated and a frothy mixture was carried upstream by gas at flooding. At moderate to high liquid flow rates, the liquid was deflected off at the elbow to form a turbulent, jetlike stream that partially broke up into droplets, These droplets were, at the onset of flooding, 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.