A study of the speed of propagation of small amplitude pressure pulses in a two-phase, two-component mixture with an annular flow pattern

Abstract

In a single-phase fluid the critical flow rate is determined by the speed of sound in the fluid, i.e., the speed at which a pressure wave of infinitesimal amplitude is propagated through the single-phase system. Since this fact has been experimentally verified for single-phase gases, a logical approach is to assume that a similar situation exists in two-phase systems. This approach has led to a comparison of measured critical flow rates to pulse propagation speeds in two-phase systems. Although trend-wise agreement has been found for bubbly two-phase systems, significant differences in the magnitude exist. To obtain a better understanding of the relationship between critical flow rates and pulse propagation speeds in two-phase systems, an experimental study was performed on the propagation of pressure pulses in a water-air system with an annular flow pattern. In order to maintain an annular flow pattern, the range of the void fraction was limited to values between 0.88 and 0.97. In this range of void fractions the pulse propagation speed was determined experimentally to be essentially the same as the sonic speed in the air. This result is consistent with theoretical predictions for pulse propagation in a stratified medium, but is considerably different from the pulse propagation speed in bubbly two-phase mixtures where the propagation speed is substantially lower than the sonic speed in either the liquid or gas phase.