Purpose of volute casing
It collects the compressed air and delivers it to the outlet.
Some additional pressure rise occurs here
Centrifugal compressor is ____ discharge & _____ pressure
High discharge and low pressure
Pressure ratio
3 to 4
Stalling
It is temporary Boundary flow separation that occurs due to positive pressure gradient in dir of flow
Surging
It is permanent flow separation & causes unsteady reversible flow
Choking
Choking is the condition when flow velocity reaches sonic speed (Mach 1), and mass flow rate becomes maximum and constant.
Main components of centrifugal compressor
Impeller
Diffuser
Volute Casing
Pressure ratio with single stage compressor
5:1
Pressure ratio with multi stage compressor
12:1
Inlet casing
the fn is to deliver air to impeller eye with minimum loss and to provide uniform velocity profile at eye
Slip factor
Actual whirl component at exit/ideal whirl component at exit
Degree of reaction
Temp rise in rotor(impeller)
Temperature rise in stage
Frictional losses in centrifugal compressor is proportional to
Velocity^2 mass^2
Axial flow compressor application
Aircrafts(open gas turbine)
Pressure ratio of axial compressor
Very less 1.2 to 1.4
Axial flow is reverse of
Reaction turbine
Axial flow compressor consists of
Moving blade(rotor)
Fixed blade(casing)
Degree of reaction in axial compressor
Enthalpy or pressure rise in moving blade / that in stage
Purpose of fixed blade
Convert part of KE to PE by diffusion process
Pr ratio
Axial compressor
Centrifugal
Reciprocating
1.1 to 1.4
4 to 6
5 to 8
