Properties of Kinematic Waves in Two-Phase Pipe Flows

Abstract

In two-phase pipe flows, the slip velocity or, equivalently, the drift flux is related to the void fraction. This leads to the occurrence of kinematic waves which convey void fraction signals. Kinematic waves have been investigated experimentally in air-water two-phase flows by inducing small void fraction disturbances at the inlet of vertical ducts, the average void fraction varying from 0.01 (bubbly flows) to 0.41 (slug flows). The temporal fluctuations of the void fraction are detected in regularly spaced cross sections by non intrusive impedance probes. The statistical processing of the data reveals the existence of two kinematic modes and provides their velocities and damping or amplification coefficients. The results are presented and discussed. One of the modes, practically absent at low void fractions, is predominant at larger void fractions. As the void fraction increases it changes from damped to amplified and controls the bubble slug transition