PRESSURE WAVE PROPAGATION IN ADIABATIC TWO-PHASE FLOW.
Topical rept. Dec 67-May 68,
MASSACHUSETTS INST OF TECH CAMBRIDGE ENGINEERING PROJECTS LAB
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At present there is a lack of reliable data on the propagation velocity of pressure waves in flowing gas-liquid two-phase systems in the void fraction range from roughly fifty to ninety-five per cent. Classical methods of measuring acoustic velocity such as the acoustic interferometer are shown to be unsuitable for this void fraction range. A technique was developed in which the velocity and strength of shock waves traveling in the mixture was measured. Then by extrapolating the results to a shock wave pressure ratio of unity, the local acoustic velocity is obtained. Measurements of the acoustic velocity were made in a flowing air-water mixture near the inlet and exit of a half-inch diameter vertical pipe fourteen feet in length. These measurements were correlated with the results of void fraction measurements made with quick-closing valves and phase distribution measurements made with an electrical resistance probe. The effect of inlet conditions was investigated by injecting the water along the wall through a porous section, and then repeating the measurements with the water injected at the center with an axial nozzle. Mass velocities used were from 2.57 to 1,310,000 lbhr.sq. ft., void fractions measured were from 0.565 to 0.981, and flow regimes observed were slug, annular, and mist flow. The data indicate that the propagation of acoustic signals is done primarily through the core of the flow. Hence conditions in the core, particularly density inhomogeneities and inlet effects, govern the propagation characteristics. The core propagation model developed offers a logical explanation of the disagreement between existing data and theory. Author
- Fluid Mechanics