Steam nozzles and flow: identify the correct statement Options describe expansion, frictional effect on dryness fraction, and the definition of critical pressure at the throat. Choose the single correct statement.

Concept/Approach

• Ideal nozzle expansion is treated as steady-flow, adiabatic, and approximately isentropic, not a complete Rankine cycle (which is a closed power cycle of boiler–turbine/expander–condenser–pump).
• With wet steam and friction, entropy rises; moisture generally increases (dryness fraction tends to decrease), not increase.
• Critical pressure is the pressure at the throat when the mass flow is choked (maximum), so the statement about the throat pressure being called critical pressure is correct.

Final Answer
The pressure of steam at the throat is called the critical pressure.