Reform of the drift-flux model of multiphase flow in pipes, wellbores, and reactor vessels

Abstract

To aid the understanding of multiphase flows and development of associated computational simulations, we reappraise the drift-flux model to improve accuracy and physical understanding. New insights are supported by careful re-derivation, literature review, and empirical verification. We directly calculate C0 and C1 using simultaneous measurements of instantaneous gas fraction and gas-liquid velocities, all obtained from a microscopic measurement volume (∼1 mm3) inside a macroscopic gas-liquid pipe flow (∼5000 cm3) containing bubbles of ~250 μm diameter. A reformulated drift-flux plot is created for this macroscopic flow by using γ-beam densitometry and total flow measurements. The microscopic and macroscopic data both confirm that significant error exists in common methods and assumptions regarding the drift-flux model, namely in the common assumption that the drift-flux parameters C0 and C1 are invariant with respect to changes of flow. Our reformulated drift-flux model finds greatly different values of C0 and C1 from those predicted by standard drift flux methods, and finds values of C0 and C1 to undergo a regime transition due to changing bubble dynamics in the multiphase flow, wherein at low gas flow the bubbles seldom interact, as if they are at infinite dilution, while above a critical gas flow the hydrodynamics change due to bubbles interacting significantly with each other. These insights are uncovered only by reformulation of the practices of the drift-flux model.