On density-wave oscillations in two-phase flows

Abstract

Density-wave oscillations in two-phase boiling flow systems have been studied numerically using a robust model based on two non-linear, functional, integro-differential equations. Results of several numerical simulations are used to gain insight into the physical mechanism behind density-wave oscillations. For a wide range of parameter values we find that: (1) traveling density-waves do not play an important role during the oscillations, and that oscillations may persist with very weak traveling density waves; (2) the oscillation period is between three and four times the channel transit time rather than twice as commonly reported; and (3) the variation in mixture velocity, in general, plays a more important role than the variation in mixture density in determining the channel pressure drop characteristics. A physical mechanism for these non-linear oscillations applicable to a large region of parameter space, as suggested by—and consistent with—the results of the numerical experiments, is proposed.