Nozzle efficiency — correct definition Select the correct definition of nozzle efficiency for a steam or gas nozzle operating between a given inlet state and a specified outlet pressure.

Introduction / Context:
Nozzles convert enthalpy into directed kinetic energy. The nozzle efficiency indicates how effectively the available isentropic enthalpy drop is transformed into jet kinetic energy, a crucial metric for turbine stage matching and thrust devices.

Given Data / Assumptions:

• Specified nozzle inlet state and outlet pressure.
• Adiabatic device with no shaft work.
• Negligible changes in potential energy.

Concept / Approach:
The ideal kinetic energy per kilogram obtainable from a given pressure drop equals the isentropic enthalpy drop h_in − h_out,s. The actual kinetic energy equals V_actual^2 / 2. Their ratio defines nozzle efficiency: η_nozzle = (V_actual^2 / 2) / (h_in − h_out,s). This measure excludes blade work and stage aggregation; those are covered by diagram and stage efficiencies.

Step-by-Step Solution:
Establish ideal reference using isentropic outlet: Δh_s = h_in − h_out,s.Measure actual outlet velocity V_actual; compute KE_actual = V_actual^2 / 2.Form η_nozzle = KE_actual / Δh_s.Interpret: η_nozzle < 1 due to friction, shock, and boundary-layer losses.

Verification / Alternative check:
The velocity coefficient φ_v = V_actual / V_ideal relates as η_nozzle = φ_v^2, providing an alternative way to determine nozzle efficiency from measured velocities.

Why Other Options Are Wrong:
Option A is the diagram (blading) efficiency. Option B is the stage efficiency. Option D is false because option C states the standard definition correctly.

Common Pitfalls:
Confusing nozzle efficiency with discharge coefficient (area flow losses) or with stage/overall efficiencies that include rotor effects.

Final Answer:
Nozzle efficiency = (actual kinetic energy at nozzle exit per kg) / (ideal isentropic heat drop across the nozzle per kg)