In a centrifugal compressor, what does the diffuser do?

• A. It slows the air and increases pressure
• B. It increases pressure by heating the air
• C. It accelerates the air toward the combustor
• D. It cools the air

Answer: (A)

In a centrifugal compressor, the diffuser’s job is to recover pressure by slowing the high-velocity air leaving the impeller. The impeller adds kinetic energy, giving the air a high velocity but only moderate static pressure. The diffuser provides a gradually expanding path that decelerates the flow, converting that velocity (dynamic) energy into static pressure energy. This increases the air pressure before it moves to the next stage without adding heat. It does not heat or cool the air, nor does it accelerate it toward the combustor.