Choked flow in nozzles — terminology When a nozzle operates at the condition of maximum mass flow rate (for fixed upstream total state), the nozzle is said to be:

Introduction / Context:
Designers of turbines, ejectors, and propulsion systems rely on the concept of choked flow. At a particular back pressure ratio, the sonic condition is reached at the throat and the mass flow rate stops increasing even if the downstream pressure is reduced further.

Given Data / Assumptions:

• Steady, adiabatic nozzle without shaft work.
• Negligible potential-energy changes; kinetic energy rise dominates.
• Ideal gas/steam behavior for defining the critical pressure ratio.

Concept / Approach:
Choking occurs when Mach number at the minimum area section equals 1. At this point, the mass flux ṁ/A depends only on upstream stagnation temperature and pressure and on gas properties. Further reducing back pressure changes the downstream expansion pattern but does not increase ṁ for the given upstream state.

Step-by-Step Solution:
Decrease back pressure from near-stagnation; ṁ rises until the sonic condition is met.At the critical pressure ratio, throat reaches Mach 1 ⇒ ṁ is maximum.Beyond this point, ṁ remains fixed; only downstream shock/expansion structure is altered.

Verification / Alternative check:
For perfect gases, the critical pressure ratio p*/p0 is a function of γ. Measurements of ṁ vs. back pressure show a plateau beyond the critical point—classic evidence of choking.

Why Other Options Are Wrong:
“Underdamping/Overdamping” are vibration terms, unrelated to nozzle flow; “None of these” is incorrect because the proper term is “Choked.”

Common Pitfalls:
Assuming temperature must always drop in throttling; here we discuss nozzles (expansion with kinetic energy rise), not throttling valves.

Final Answer:
Choked