Liquid‐liquid flows in an inclined pipe

Experimental measurements are reported of oil‐water flows in a 20 cm ID pipe at mean velocities between 2.7 and 35 cm/s, at deviation angles θ from vertical between 0 and 65°, and at water flow rate fractions between 30 and 100%. The distribution of the water volume fraction αw across a pipe section is obtained using local high‐frequency probes. The mean water volume fraction in the section and the slip velocity Vs between oil and water are also determined. High Vs values (up to 50 cm/s) are measured at large deviation angles; they are associated with oil droplet swarms or continuous oil phase zones. Both αw profiles and Vs values depend only on the mean water volume fraction and not on the total flow rate Qt in the range investigated. At low oil volume fractions αo, all droplets are concentrated close to the upper side of the pipe. At larger αo values, a slower linear variation of αw with the distance y from the axis is measured. A model is suggested relating the slope ∂αw/∂y in a vertical plane to the existence of internal density waves in the stratified mixture.