In vortex casing, the circular chamber is known as:

Explanation:

Free vortex flow:

It is defined as the vortex flow in which no external torque is required to rotate the fluid mass. Thus the liquid in the case of the free vortex is rotating due to the rotation which is imparted to the fluid previously.

Examples of free vortex flow are

1. The flow of liquid through a hole provided at the bottom of a container like in a washbasin
2. The flow of liquid around a circular bend in a pipe
3. A whirlpool in a river
4. The flow of fluid in a centrifugal pump casing and also called whirlpool chamber

Forced Vortex:

It is defined as that type of vortex flow, in which some external torque is required to rotate the fluid mass. The fluid mass in this type of flow rotates at constant angular velocity.

Examples of the forced vortex are

1. A vertical cylinder containing liquid is rotated about its central axis with a constant angular velocity.
2. Flow of liquid inside the impeller of a centrifugal pump
3. Flow of water through the runner of a turbine