Critical pressure ratio for initially wet steam Select the correct value of the critical pressure ratio (p₂/p₁ at the throat corresponding to maximum discharge) for initially wet steam. Choose the correct option.

Concept
The critical pressure ratio is the downstream-to-upstream pressure ratio at which flow just becomes sonic at the throat (choked flow), giving maximum mass flow for given inlet conditions. For steam, the critical ratio depends slightly on state:

• Initially wet (near saturation): p_throat/p_inlet ≈ 0.577
• Superheated: p_throat/p_inlet ≈ 0.546

Result
For initially wet steam, the standard value used in turbine/nozzle calculations is about 0.577.

Common pitfall
Do not confuse the superheated value (≈ 0.546) with the wet-steam value.

Final Answer
0.577