Centrifugal compressors work by using centrifugal force to increase the pressure of a gas. They have several main parts: an impeller, diffuser, and volute casing. Gas enters the impeller eye axially and is accelerated radially by the spinning impeller blades. This converts the gas' kinetic energy into pressure energy. The gas exits the impeller and enters the diffuser, where more of its kinetic energy is converted to increased static pressure. Slip occurs because the gas does not perfectly follow the spinning impeller blades and exits at a slightly different angle than designed, reducing the compressor's efficiency.

1. CENTRIFUGAL COMPRESSOR

2. DEFINITION AND PARTS OF CENTRIFUGAL COMPRESSOR
• Centrifugal compressor is a Turbo machine in which the Kinetic energy of
compressible fluid is converted into pressure energy by the means of
centrifugal force generated by the rotation of impeller.
The main parts of a Centrifugal Compressor are:
• Accelerating Nozzle
• Inlet Guide Vanes (IGV)
• Hub (Impeller Disc)
• Impeller Blade
• Impeller Eye
• Diffuser
• Volute casing

3. WORKING OF CENTRIFUGAL COMPRESSOR
• The air enters the impeller eye of a centrifugal compressor in an axial direction
with absolute velocity V1. The gas then flows radially through the impeller
passage due to centrifugal force.
• The impeller rotates at a very high speed. Energy is imparted to the gas by the
rotating blades where it is converted into kinetic energy as it moves from
radius r1 to r2, along with the small pressure rise during its radial flow in the
impeller.
• The impeller vanes at the eye are bent to provide shock-less entry. The gas
leaving from the impeller blades is turned through an angle β2, and leaves
with an absolute velocity V2 at angle α2.
• The gas then enters the diffuser. The diffuser surrounding the impeller
converts the KE to pressure energy .Hence, there is rise in static pressure of
the gas.
• Gas then enters the casing and the outlet pipe, where some more KE is
converted into pressure energy.

4. CENTRIFUGAL COMPRESSOR ASSEMBLY

5. CENTRIFUGAL COMPRESSOR ASSEMBLY

6. CENTRIFUGAL COMPRESSOR WITH IGV AND VANED DIFFUSER

14. SLIP IN CENTRIFUGAL COMPRESSOR
• The fluid leaves the impeller at an angle β’2 other than the actual blade angle
β2 . This is due to ‘slip of fluid'.
• Angle β’2 is less than angle β2 .
• In centrifugal compressors, the air trapped between the impeller vanes is
reluctant to move round with the impeller and this results in a higher static
pressure on the lending face of the vane than on the trailing face of the vane.
• This problem is due to the inertia of the air. Then the air tends to flow round
the edges of the vanes in the clearance space between impeller and casing.
One explanation for this is that of the relative eddy hypothesis.
• Slip can be reduced by increasing the number of impeller vanes and reducing
the clearance space.
• Thus Vw2 is reduced to Vw2’ and the difference Vw2 - Vw2’ defined as the slip.
•

15. SLIP IN CENTRIFUGAL COMPRESSOR