CFD simulation of horizontal oil-water flow with matched density and medium viscosity ratio in different flow regimes

Abstract

Simulation of horizontal oil-water flow with matched density and medium viscosity ratio ( ⁄ =18.8) in several different flow regimes (core annular flow, oil plugs/bubbles in water and dispersed flow) was performed with the CFD package FLUENT in this study. The volume of fluid (VOF) multiphase flow modeling method in conjunction with the SST k-ω scheme was applied to simulate the oil-water flow. The influences of the turbulence schemes and wall contact angles on the simulation results were investigated for a core annular flow (CAF) case.The SST k-ω turbulence scheme with turbulence damping at the interface gives better predictions than the standard k-ε and RNG k-ε models for the case under consideration. The flow regime of density-matched oil-water flow with medium viscosity ratio, or more generally speaking, the flow regime of fluids where the surface tension is playing a prevailing role is sensitive to the wall contact angle. Simulation results were compared with experimental counterparts. Satisfactory agreement in the prediction of flow patterns were obtained for CAF and oil plugs/bubbles in water. The simulation results also demonstrated some detailed flow characteristics of CAF with relatively low-viscosity oil (oil viscosity one order higher than the water viscosity in the present study compared to the extensively studied CAF with oil viscosity being two to three orders higher than the water viscosity). Different from the velocity profiles of high-viscosity oil CAF where there is sharp change in the velocity gradient at the phase interface with velocity across the oil core being roughly flat, there is no sharp change in the velocity gradient at the phase interface for CAF with relatively low-viscosity oil.

A new approach to model friction losses in the water‐assisted pipeline transportation of heavy oil and bitumen

“…The present study is focused on the lubricated pipe flow (LPF) of heavy oils and bitumen, where a water annulus separates the viscous oil from the pipe wall. The benefit of LPF over other pipe flow technologies is that the annular water layer is found in the high shear region near the pipe wall, and thus much lower pumping energy input is required than if the viscous oil were transported alone at comparable process conditions …”

“…In the industrial application of LPF, some oil tends to permanently adhere to the pipe wall leading to the formation of an oil‐film, an effect called wall‐fouling . Frictional pressure losses in a fouled pipe are higher than those in an unfouled pipe under otherwise identical conditions . Unfortunately, the wall‐fouling layer cannot be avoided during pipeline operation in most industrial situations .…”

“…Frictional pressure losses in a fouled pipe are higher than those in an unfouled pipe under otherwise identical conditions . Unfortunately, the wall‐fouling layer cannot be avoided during pipeline operation in most industrial situations . Different degrees of wall‐fouling are experienced in various applications of LPF, and therefore this pipe flow technology can be divided into two major categories: core‐annular flow (CAF); and continuous water‐assisted flow (CWAF).…”

“…A technical challenge to the application of lubricated pipe flow is the unavailability of a reliable model to predict pressure losses on the basis of flow conditions . The issue is that although a number of empirical, semi‐mechanistic, and numerical models have been proposed, these models are only appropriate for idealized core‐annular flow or are highly system‐specific.…”

“…Single‐fluid models generally take an empirical approach to predict pressure gradients for lubricated pipe flow. The flow is modelled as a hypothetical single‐phase fluid . In many cases, the hypothetical fluid is taken to have the properties of water as it is the fluid that usually contacts the pipe wall under fully developed flow conditions.…”