NONEQUILIBRIUM PHASE CHANGE—1. Flashing Inception, Critical Flow, and Void Development in Ducts

摘要: Abstract This chapter will introduce the first concepts of nonequilibrium with emphasis on nucleation and flashing in nozzles, subsequent void development. Both number size bubbles must be accurately determined for initial calculation development downstream restrictions. Void upstream a restriction is negligible if inlet subcooled. A new method presented determining nuclei their size, shows this results accurate The activation criterion developed site nucleation, different from that subcooled boiling, one sided due to uniform superheat. priactical utilizing then identified. defined figure-of-merit particular fluid solid combination yields minimum surface energy per site, allows characteristic frequencies, densities sites given sizes obtained data. bubble transport equation used predict density at throat. Throat superheats are calculated standard deviation 1.9K throat up ˜100K expansion rates between 0.2 bar/s over 1 Mbars, extending previous correlations by more than three orders magnitude. fractions all data found literature less 1% confirming earlier assumptions allowing nozzle critical flow an accuracy ˜3%. Accurate correct pressures ˜70 bars below saturation, factor calculating choked flows. quasi-one-dimensional, five-equation model, microcomputer, was calculate behavior flowing, initially subcooled, liquids. Equations mixture vapor mass conservation, momentum liquid were discretized linearized semi-implicitly, solved using successive iteration Newton method. Closure through simple constitutive equations friction spherical growth, model wall small nozzles combined existing bulk large geometries. Good qualitative quantitative agreement experiment confirms adequacy models both nuclei. It shown becomes important as volume-to-surface ratio geometry increased.