How far can the pinwheel rotor (vanes) be extended into the duct?

Prepare for the IC "A" School Test on Airflow, H2S, and Refrigerants. Utilize flashcards and multiple-choice questions with detailed hints and explanations to ensure success. Get exam-ready today!

Multiple Choice

How far can the pinwheel rotor (vanes) be extended into the duct?

Explanation:
When measuring airflow with a pinwheel rotor, you want the vane to sit deep enough in the duct to be fully in the moving air, but not so far that it collides with the duct or disturbs the flow. Extending the rotor into the duct within a range of about 2.5 to 12 inches hits that balance. Why this range works: it places the vane well inside the core of the airstream, away from the slow-moving boundary layer near the walls, so the reading reflects the true velocity of the passing air. It also avoids protruding so far that the rotor could contact the opposite wall, snag on ducts, or create flow disturbances from being too close to the duct geometry. If you extend less than roughly 2.5 inches, the rotor may sit in near-wall flow where readings are biased low. If you extend more than about 12 inches, practical clearance issues and potential flow distortion become concerns. So the 2.5 to 12 inch range provides reliable, representative measurements.

When measuring airflow with a pinwheel rotor, you want the vane to sit deep enough in the duct to be fully in the moving air, but not so far that it collides with the duct or disturbs the flow. Extending the rotor into the duct within a range of about 2.5 to 12 inches hits that balance.

Why this range works: it places the vane well inside the core of the airstream, away from the slow-moving boundary layer near the walls, so the reading reflects the true velocity of the passing air. It also avoids protruding so far that the rotor could contact the opposite wall, snag on ducts, or create flow disturbances from being too close to the duct geometry. If you extend less than roughly 2.5 inches, the rotor may sit in near-wall flow where readings are biased low. If you extend more than about 12 inches, practical clearance issues and potential flow distortion become concerns. So the 2.5 to 12 inch range provides reliable, representative measurements.

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