Which term describes the change in duct size where air moves from a larger area to a smaller area?

Which term describes the change in duct size where air moves from a larger area to a smaller area?

• A. Inlet
• B. Outlet
• C. Air Cleaner
• D. Contractions

Answer: (D)

The change in duct size from a larger area to a smaller area is called a contraction. This occurs because, for steady flow, the product of cross-sectional area and velocity must stay constant (A1 v1 = A2 v2). When the area decreases, the velocity must increase to keep the volume flow rate the same. This speeding up through a narrowed section can also cause a pressure drop and changes in flow characteristics. Inlet and outlet refer to where air enters or leaves the system, and an air cleaner is a device that removes particles, so they don’t describe the actual change in duct size.

The change in duct size from a larger area to a smaller area is called a contraction. This occurs because, for steady flow, the product of cross-sectional area and velocity must stay constant (A1 v1 = A2 v2). When the area decreases, the velocity must increase to keep the volume flow rate the same. This speeding up through a narrowed section can also cause a pressure drop and changes in flow characteristics. Inlet and outlet refer to where air enters or leaves the system, and an air cleaner is a device that removes particles, so they don’t describe the actual change in duct size.