What is the rotating set of vanes designed to impart rotation to a mass of fluid?

• A. Diffuser
• B. Casing
• C. Volute
• D. Impeller

Answer: (D)

An impeller is the rotating assembly with blades that transfers energy to the fluid. As it turns, the blades grab fluid at the center and fling it outward, giving the fluid angular (rotational) motion and increased kinetic energy. That rotation is what drives the flow, and the energy can then be converted to higher pressure as the fluid moves through downstream components like a diffuser or volute. The other parts described are stationary: the casing surrounds and directs flow, the diffuser slows the fluid with its stationary vanes to raise pressure, and the volute is a stationary scroll that helps convert velocity into pressure after the impeller. So the device consisting of the rotating vanes designed to impart rotation to the fluid is the impeller.