Experimental investigation of two-phase water–oil flow pressure drop in inclined pipes

• Effect of inclination angle has been considered on the pressure gradient in oil water flow.
• The phase inversion phenomena has been obtained in oil water flow.
• Two-fluid and homogeneous models have been compared with experimental data.
• Obtained two-phase friction factors were compared with single phase friction factors.

In this experimental work the effect of inclination on the pressure gradient in two phase oil–water flow is investigated. The experiments were performed in a 6 m long, 20 mm inner diameter and inclinable acrylic pipe using oil (3 mPa s viscosity and 830 kg/m3 density) and water (1 mPa s viscosity and 990 kg/m3 density) as test fluids. Pressure gradients between inlet and outlet of flow in pipe were measured for inclination angles of 0°, ±5°, ±15°, ±30° and ±45° with respect to the horizontal plane. The experimental results were compared with Homogeneous and Two-Fluid models. It was observed that in high mixture velocities, where dispersed flow prevails, there is a peak pressure gradient which is related to phase inversion. It was also found that, phase inversion appears at higher inlet water cut values in inclinations of −30° and −45° compared with other inclinations. However the two-fluid model and homogeneous model both over-predicted the pressure drop, but two-fluid model predicted the pressure drop with less average deviation. Several correlations for effective mixture viscosity in a homogeneous model were considered and the results were compared with experimental results. Acceptable agreement was seen between the computed and measured data.The experimental two-phase friction factors were compared with the friction factors for single phase flow of oil and water, at the same velocities as the two phase mixture and it was found that the experimental friction factors were less than the predicted friction factors of single phase flow.