Meaning
Fluid dynamic state occurring at nozzle throats limits mass flow rate to a maximum value governed by upstream conditions. Achieving a choked flow condition ensures that downstream pressure fluctuations cannot travel upstream to disrupt gas supply regulation during atomization. The condition establishes a stable mass flow rate proportional to upstream pressure and independent of receiver pressure.
Sonic Boundary
Gas velocity reaches local speed of sound when pressure ratios across an orifice exceed a critical threshold. Further drops in downstream pressure cannot increase gas velocity or volume throughput through the throat.
Mass Transfer
Predictable gas delivery requires operating nozzles in choked state to isolate supply lines from chamber dynamics. Upstream stagnation pressure directly governs the mass throughput of argon or nitrogen during melt disintegration. Gas density changes caused by temperature shifts directly alter mass delivery even while velocity remains fixed at Mach one.
Maintaining choked flow condition stabilizes particle size distributions across long production runs.
Pressure Ratio
Critical pressure ratio depends on the specific heat ratio of the atomizing gas. For diatomic nitrogen, sonic velocity occurs when downstream pressure falls below fifty-seven percent of upstream supply pressure. Monoatomic argon reaches choked state at a slightly higher critical ratio of fifty-three percent.
Exceeding this boundary locks gas velocity at the throat, simplifying process control calculations.
