Venturimeter design practice: What is the typical included angle of the diffuser (exit cone) in a venturimeter to minimize separation and losses?

Introduction / Context:Venturimeters measure flow rate using a converging section, throat, and a diffuser (exit cone). The diffuser recovers pressure by decelerating the flow. Its angle is critical: too steep causes boundary-layer separation and loss; too shallow makes the device unnecessarily long.

Given Data / Assumptions:

• Subsonic, incompressible flow context typical of industrial metering.
• Well-designed venturimeter uses a modest diffuser angle to balance pressure recovery and length.
• Surface finish is adequate; Reynolds number sufficiently high for diffuser design rules of thumb.

Concept / Approach:Diffuser (exit cone) angles around 7 to 15 degrees (included) are widely adopted to avoid separation while achieving reasonable pressure recovery. Values below ~7 degrees increase length and cost; above ~15 degrees raise the risk of separation and energy loss.

Step-by-Step Solution:Goal: maximize static pressure recovery with minimal length.Constraint: avoid boundary-layer separation in the diffuser.Empirical practice sets included angle near 7–15 degrees, hence Option B.

Verification / Alternative check:Handbooks on flow measurement and standards for venturi meters specify diffuser angles in this common range, confirming the choice.

Why Other Options Are Wrong:

• 2–5 degrees: unnecessarily long device for marginal extra recovery.
• 15–25 or >25 degrees: prone to separation and higher losses.
• 45–60 degrees: would definitely separate; unsuitable for a venturi diffuser.

Common Pitfalls:Confusing half-angle with included angle; if quoting half-angles, the typical values are roughly 3.5–7.5 degrees.

Final Answer:7 to 15 degrees