Definition check — convergent–divergent nozzle A nozzle is termed a convergent–divergent (C–D) nozzle when its cross-section decreases from inlet to throat and then increases from throat to exit. Is this definition correct?

Introduction / Context:
Gas dynamics and steam-nozzle design use specific geometries to accelerate flow. The convergent–divergent (de Laval) nozzle is fundamental for achieving supersonic speeds after sonic choking at the throat. Recognizing the geometric definition is a prerequisite for understanding performance maps and shock behavior.

Given Data / Assumptions:

• Single-phase compressible flow.
• Well-defined minimum-area section (throat).
• Isentropic analysis as a first approximation.

Concept / Approach:
In a C–D nozzle, flow is accelerated subsonically in the convergent section to Mach 1 at the throat under choked conditions, then further accelerated supersonically in the divergent section when back pressure is suitably low. Hence, the geometry necessarily converges to a throat and diverges thereafter. The statement given correctly captures this shape definition.

Step-by-Step Solution:
Identify the convergent entrance: area decreases, velocity rises for subsonic flow.At the throat: Mach = 1 when choked; mass flow is maximized for given upstream state.In the divergent exit: area increases; if properly expanded, velocity becomes supersonic.

Verification / Alternative check:
Rocket nozzles and turbine-stage nozzle blocks use C–D profiles to achieve design Mach numbers and pressure ratios, validating the definition in practice.

Why Other Options Are Wrong:
“False” would deny the standard textbook geometric meaning of a C–D nozzle.

Common Pitfalls:
Confusing “diverging duct” with diffuser; in compressible flow, function depends on Mach regime, not just geometry.

Final Answer:
True