In the ventilation duct scenario, what assumption is made about the ends of the duct?

• A. Open-ended
• B. Closed at both ends
• C. One end closed
• D. Both ends closed

Answer: (A)

In this kind of ventilation flow problem, the ends of the duct are treated as open to the surrounding space. That means the pressure at the duct ends is essentially atmospheric, so the ends don’t introduce an extra end-cap resistance. This boundary condition reflects the real situation where air freely enters or leaves the duct into rooms or outdoors, and the flow is driven mainly by the pressure difference along the duct and by friction inside it. If the ends were closed (one or both), you’d have a very different situation with built-up pressure and no steady external mass exchange, which isn’t typical for a ventilation supply/exhaust scenario.