Fire hose nozzles are generally designed with which outlet shape to achieve a high-velocity jet at subsonic conditions for water?

Introduction / Context:
Firefighting requires long-reach, coherent water jets to deliver momentum to targets. Nozzle geometry controls pressure-to-velocity conversion and jet quality. The appropriate shape depends on whether the working fluid is compressible and on the speed regime.

Given Data / Assumptions:

• Fluid: water (essentially incompressible at these conditions).
• Subsonic speeds; no compressible-flow choking phenomena.
• Objective: maximize jet velocity and coherence.

Concept / Approach:

For incompressible subsonic flows, a convergent nozzle reduces cross-sectional area to convert pressure energy into kinetic energy (Bernoulli principle). Convergent–divergent designs are used for compressible gases to achieve supersonic speeds across a throat; this is unnecessary and detrimental for liquid water jets. A purely divergent section would decelerate the flow and degrade the jet.

Step-by-Step Solution:

Verification / Alternative check:

Practical firefighting nozzles and hydraulic texts recommend smooth convergent contours with slight straightening sections to preserve jet coherence and minimize turbulence at the exit.

Why Other Options Are Wrong:

Divergent (a) causes diffusion (velocity drop). Convergent–divergent (c) is for compressible supersonic gases. Cylindrical (d) offers less acceleration and may produce a weaker jet. A mere “Venturi throat only” (e) is not how water jets are produced at hose tips.

Common Pitfalls:

Confusing gas nozzle design with liquid jet production; liquids do not require a divergent section to accelerate.

Final Answer:

Convergent