STATIC FLOW INSTABILITY ONSET IN TUBES, CHANNELS, ANNULI, AND ROD BUNDLES

A theoretical model is developed for the onset of flow instability for vertical upflow and downflow of a boiling fluid in a constant pressure drop flow channel. The model is based on momentum and energy balance equations with an algebraic modeling of two-phase velocity-slip effects. Predictions of the theory are tested against experimental data for pressure, heat flux, length, inlet subcooling, and exit fluid quality effects. The predictions of the dependency of the minimum mass flux on these variables are in complete agreement with the trends of the data. The experimental data have been taken from round tube, rectangular channel, annuli, and rod bundle geometries, with vertical upflow and downflow, under both non-bulk boiling and net vapor generation conditions. The data collection given here appears to be among the most complete available in the literature. The theoretical results suggest a method for correlating about limited ranges of operating state parameters for a fixed geometry. The method is given in the paper along with specific correlating lines.