Flow of a Flashing Mixture of Water and Steam Through Pipes and Valves

Abstract

Abstract A simple method is presented of designing piping and valves, particularly heater drain piping, to carry a flashing mixture of water and steam. Rational design formulas are derived from the energy, continuity, and dynamic equations on the basis of an assumed uniform mixture at any point in the path of flow. Earlier papers have predicted and verified experimentally the existence of a critical pressure, under certain conditions at the end of a pipe carrying a flashing mixture. Results calculated from the derived formulas compare favorably with these published test data. It is noted that if the initial assumption of a uniform mixture is not fulfilled, the limitations imposed on the piping are less severe than for the uniform-mixture case, as the capacity of both valves and pipes will be greater than predicted by formulas. A scheme is suggested for eliminating flashing completely in heater drain systems employing drain coolers.