Abstract:
A study on high-viscosity oil-water flow in horizontal pipes has been conducted
applying experimental, mechanism analysis and empirical modelling, and CFD
simulation approaches.
A horizontal 1 inch flow loop was modified by adding a designed sampling
section to achieve water holdup measurement. Experiments on high-viscosity
oil-water flow were conducted. Apart from the data obtained in the present
experiments, raw data from previous experiments conducted in the same
research group was collated. From the experimental investigation, it is found
that that the relationship between the water holdup of water-lubricated flow and
input water volume fraction is closely related to the oil core concentricity and oil
fouling on the pipe wall. The water holdup is higher than the input water volume
fraction only when the oil core is about concentric. The pressure gradient of
water-lubricated flow can be one to two orders of magnitude higher than that of
single water flow. This increased frictional loss is closely related to oil fouling on
the pipe wall.
Mechanism analysis and empirical modelling of oil-water flow were conducted.
The ratio of the gravitational force to viscous force was proposed to
characterise liquid-liquid flows in horizontal pipes into gravitational force
dominant, viscous force dominant and gravitational force and viscous force
comparable flow featured with different basic flow regimes. For viscous force
dominant flow, an empirical criterion on the formation of stable water-lubricated
flow was proposed. Existing empirical and mechanistic models for the prediction
of water holdup and/or pressure gradient were evaluated with the experimental
data; the applicability of different models is demonstrated.
Three-dimensional CFD modelling of oil-water flow was performed using the
commercial CFD code Fluent. The phase configurations calculated from the
CFD model show a fair agreement with those from experiments and mechanism
analysis. The velocity distribution of core annular flow is characterised with
nearly constant velocity across the oil core when the oil viscosity is significantly higher than the water viscosity, indicating that the high-viscosity oil core flows
inside the water as a solid body. The velocity profile becomes similar to that of
single phase flow as the oil viscosity becomes close to the water viscosity.
