Investigation of Choking Phenomena of Supersonic Micro-nozzle Flow with Flashing Evaporation

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1. When intitially subcooled high temperature and high pressure liquid is accelerated through a converging-diverging nozzle and is expanded beyond its asturation condition, flash evaporation occurs in the converging section or at the throat of the nozzle. The choking of such a flow with flash evaporation is classified into three patterns.2. The choking condition depends on the initial pressure and the subcooling of the compressible liquid. A flow model for calculating the critical massflux through the nozzle is presented assuming an isentropic, homogeneous, equilibrium two-phase flow. The mass flowrate calculated by the present model agrees well with the experimental results.3. When the flow choked at the nozzle throat, a pressure wave is generated and propagated upstream so as to adjust the upstream flow conditions. The propagation velocity of a pressure wave through a compressible gas-liquid two phase flow depends on the void fraction and the relation between them is established.4. The characteristics of supersonic micro-nozzle depends not only on the Mach number but also the Reynolds number based on the flow condition at the nozzle exit. The range of overexpansion, correct-expansion, and underexpansion of a such a nozzle is clarified, and the data of the critical flow rate through the supersonic micro-nozzle was obtained.