Flow patterns and pressure gradients of viscous oil–water core–annular flow in a vertical upward pipe

Abstract Using a vertical upward pipe and annular flow generator, the flow pattern, pressure gradient, and drag reduction efficiency of viscous oil–water flow were investigated (superficial oil velocity u o = 0.09 ~ 0.88 m/s, superficial water velocity u w = 0.12 ~ 0.95 m/s) with #500 white oil (20°C, μ o = 1184.7 mPa · s, ρ o = 899.5 kg/m 3 ) and water. Five flow patterns were observed: oil‐in‐water dispersion flow (Do/w), bubble flow (Bo), slug flow (SLo), semi‐annular flow (Semi‐Anw), and annular flow (Anw). Considering the oil contamination on the pipe wall, the friction factor of the Rodriguez model was corrected by introducing the Lockhart–Martinelli parameter X . The pressure reduction factor RF ranged from 10 ~ 120. Water annular flow can increase the viscous oil flow rate by 7 times, and the pressure gradient is reduced to 1/7 that of pure oil.