Which of the following best describes the diffuser's effect on the airflow?

• A. It speeds up the flow without changing pressure.
• B. It converts pressure into velocity.
• C. It filters the air.
• D. It slows the flow and converts velocity into pressure.

Answer: (D)

The diffuser slows the airflow and converts velocity into pressure. When air enters a diffuser, the duct expands, causing the flow to decelerate. As velocity drops, the dynamic (motion) energy is transformed into static pressure energy, raising the air pressure at the diffuser outlet. This is why diffusers are used to recover pressure and prepare the air for further stages in a system. The other ideas—speeding up the flow, filtering the air, or converting pressure into velocity—don’t match how a diffuser operates.