Steam pressure change across a nozzle As steam flows through a properly designed nozzle (from inlet to exit), the static pressure generally:

Introduction / Context:Nozzles are expansion devices that transform pressure energy (enthalpy) into kinetic energy. Understanding how pressure varies along the nozzle path is fundamental for turbine stage analysis.

Given Data / Assumptions:

• Adiabatic, steady flow through a nozzle.
• Properly matched back pressure to avoid shocks within the nozzle.
• Negligible potential energy changes.

Concept / Approach:From the steady flow energy viewpoint, decreasing static enthalpy appears as increasing kinetic energy. Hence, as the fluid accelerates, static pressure falls. In a CD nozzle, pressure falls through the throat and continues to fall in the divergent part under correctly expanded conditions.

Step-by-Step Solution:Use energy balance: h1 + V1^2/2 ≈ h2 + V2^2/2.As V rises (V2 > V1), h must drop → associated with a drop in p for expansion.Therefore, pressure decreases along the nozzle path.

Verification / Alternative check:Measured pressure profiles and Mach distributions in Laval nozzles show monotonic pressure decrease (absent shocks) from inlet to exit.

Why Other Options Are Wrong:

• (b) Acceleration does not increase static pressure; it reduces it in expansion devices.
• (c) Constant pressure describes throttling valves, not nozzles.
• (d) Oscillation is not characteristic of steady, shock-free flow.
• (e) Pressure does not rise in the convergent section; it falls toward the throat.

Common Pitfalls:Confusing nozzle behavior with diffusers, where velocity decreases and pressure increases.

Final Answer:decreases due to conversion of enthalpy to kinetic energy