In a cyclone separator used for removing dust from a gas stream, how does the gas enter and move within the vessel?

Introduction / Context:
Cyclone separators use swirling gas flow to generate centrifugal forces that drive particles to the wall, where they fall into a dust hopper while cleaned gas exits via a vortex finder.

Concept / Approach:
The gas typically enters tangentially at high velocity, establishing a strong vortex. Inside, the flow follows a double helical path: a downward outer spiral near the wall and an inner upward spiral exiting through the central outlet. This swirl produces radial acceleration that separates particles by inertia.

Final Answer:
Both (b) and (c)