Drift-Flux Model

• Published in: Two-Fluid Model Stability, Simulation and Chaos pp. 163 - 193
• Main Authors: Clausse, Alejandro, Fullmer, William, Ransom, Victor H, Bertodano, Martín López de
• Format: Book Chapter
• Language: English
• Published: Switzerland Springer International Publishing AG 2016; Springer International Publishing
• Subjects: Boiling channel; Bubbly flow; Density wave; Drift-flux; Flow excursion; Kinematic condition; Laplace Transform; Linear stability; Mechanics of fluids; Mixture momentum equation; Non-linear science; Nuclear power & engineering; One-dimensional; Time delay; Transfer function; Two-fluid model; Two-phase flow; Void propagation equation
• ISBN: 9783319449678; 3319449672
• DOI: 10.1007/978-3-319-44968-5_6

This chapter addresses the stable and linearly unstable Drift-Flux Model (DFM). The well-known Drift-Flux wave propagation equation is derived applying the kinematic condition to the FFM of Chap. 10.1007/978-3-319-44968-5_5. This removes the SWT and KH instabilities but preserves the material wave speed and nonlinear evolution of the waves, allowing the analysis of several stable problems of engineering interest, e.g., level swell, drainage, and the propagation of material discontinuities. Then the fixed flux approximation is removed and the DFM mixture momentum equation of Ishii and Hibiki (Thermo-fluid dynamics of two-phase flow, Springer, 2006) that incorporates the drift-flux assumption, i.e., the kinematic equilibrium condition, is introduced. This represents the counterpart to the fixed flux assumption of earlier chapters because it fixes the relative velocity whereas the total flux, j, is now allowed to fluctuate. To illustrate what this difference implies, the DFM is applied to the linear analysis of two global instabilities for boiling channels: the flow excursion and the density wave instability. The DFM is the optimal TFM approximation to analyze global material wave instabilities, if the flow regime is stable, precisely because it precludes the local instabilities specifically addressed by the FFM. Thus, FFM and DFM are natural counterparts that render a broad picture of TFM stability. This wide stability spectrum is one reason why the TFM is so versatile for engineering two-phase flow applications.