Critical (throat) pressure in steam nozzles – terminology The static pressure of steam at the throat of a steam nozzle (where the flow first reaches sonic velocity) is commonly termed the:

Introduction / Context:
In nozzle flow, the term “critical” refers to the sonic condition at the minimum area (throat). Recognizing the associated pressure is essential for sizing and for understanding choking and discharge behavior.

Given Data / Assumptions:

• Convergent–divergent steam nozzle.
• Isentropic idealization for terminology.
• Critical condition corresponds to Mach number = 1 at the throat.

Concept / Approach:
When the pressure ratio across the nozzle exceeds the critical value, the flow chokes at the throat and the static pressure there takes a specific value called the critical pressure. Downstream pressure reductions do not alter throat pressure under choked conditions.

Step-by-Step Solution:
Identify the throat as the minimum area where choking occurs.Associate the sonic condition with a unique pressure level for given inlet state.Name this pressure: critical pressure.

Verification / Alternative check:
T–s and p–v diagrams for nozzle flow show the state at the throat marked by the critical condition; empirical discharge curves confirm a plateau beyond the critical pressure ratio.

Why Other Options Are Wrong:

• Stagnation pressure refers to the total pressure at zero velocity (inlet total state).
• Exit/back pressure is downstream of the nozzle.
• Condenser pressure pertains to the steam cycle sink, not the nozzle throat.
• Impulse pressure is not a standard term here.

Common Pitfalls:
Confusing stagnation (total) properties with static throat properties. Critical pressure is a static property at M = 1.

Final Answer:
critical pressure