Two‐phase critical flow of steam‐water mixtures

Abstract

AbstractCritical flow of two‐phase steam‐water mixtures in annuli has been studied, with a cylindrical test section 0.574 in. in diameter with an axially centered rod, 0.137 or 0.375 in. O.D., as a pressure probe. Pressure taps on the wall and the center rod permitted an accurate determination of the pressure profile over the entire length of the section, and, in cases where a movable probe was used, a short distance into the downstream exhaust chamber. Results were correlated by plotting the ratio of the observed critical mass velocity to the theoretical critical mass velocity for homogeneous flow as a function of quality.Exit pressures were found to be lower than most values previously reported. The ratio GO/GTh was found to be independent of the probe diameter, the manner of upstream steam‐water mixing, and, for test sections greater than 9 in. in length, the test section length. Since probe diameter had no observable effect on GO/GTH, the correlation may be applicable to full bore pipes near 1/2 in. in diameter. In the range of qualities from 2 to 15% the critical GO/GTH ratio was depressed with increasing exit (throat) pressure, but at other qualities no pressure dependency was noted. The effect of changing the downstream exhaust chamber pressure was found to influence the exit pressure but to have little effect on the observed critical mass velocity. Addition of surface active agents to the steam‐water mixture did not affect the mass velocity but did result in increased exit pressure.