1. Analysis of Compressors
P M V Subbarao
Professor
Mechanical Engineering Department
Active Devices for Infusion of Life into Fluid….

2. Classification of Compressors
Rotodynamic Compressors
− ∫ vdp
Centrifugal
Compressors
Axial
Compressors
Mixed
Compressors
Positive Displacement
of Compressors
∫pdv
Reciprocating
Compressors
Rotory
Compressors

3. Centrifugal Vs Axial : Flow Area

4. Centrifugal Vs Axial : Level of interaction

5. In search of Time scale in Requirement
•
•
•
•
Primary characteristics of a requirement.
The effect: ∆p
The Capacity: Flow Rate Q (m3/s).
Density of fluid: ρ(kg/m3).

6. Machine-Fluid Matching Parameter:
Π = f ( Q, ∆p : ρ )
For compressible fluid machines

7. Π = Q × ( ∆p ) × ρ
j
i
 ∆p 

Π = Q ×
 ρ 


j
i
 m3 
Π =
 s 



i
 kg



2
×  m.s

kg 

3
m 

j
k

8. m
Π=
 s

3
i
 m 
 × 2 
 s 
 

2
j
Take j = -3/2
i
 m3   m 2 
 × 2 
Π=
 s  s 

 

m
Π =
 s

3
i
−3
  m −3 
 ×  −3 
 s 
 

2

9. Take i = 1/2 & j = -3/4
m
Π=
 s

3
1
2
 m 
 × 2 
 s 
 

2
−3
4
Π=
 ∆p 
Π = ( Q) × 
 ρ 



1
2
−3
Q
Π=
4
 ∆p 
 ρ


3
4
m
s
3
1
2
2
×
m
s
−3
−3
2
2

10. Time Scale of a Machine to Resource
Speed: N (rpm) or n (rps)
Dimensionless time scale =
Requirement Time Scale
Machine Time Scale
Π
Non - Dimension time scale =
1
n
This is named as Specific Speed, Ns

n m
Ns =
 ∆p 

ρ


3
4
Q
Π=
4
 ∆p 
 ρ



n m
Ns =
4
3
ρ
 ∆p 
 ρ


3

11. Centrifugal
Mixed
Axial

12. Role of specific Speed on Design of A Compressor

13. Centrifugal Compressors
•
•
•
•
•
The centrifugal compressor consists
essentially of a stationary casing containing
a rotating impeller which imparts a high
velocity to the air, and
A number of diverging passages (Diffuser)
in which the air is decelerated with a
consequent rise in static pressure.
Air is sucked into the impeller eye and
whirled round at high speed by the vanes on
the impeller disc.
Centripetal acceleration leads to increase in
rise of some amount of static pressure.
The remaining increase in rise of pressure
occurs in diffuser.

14. Multi Stage Compressors

15. Impeller–Diffuser :Rotor-Stator

16. Anatomy of A Centrifugal
Compressors

17. Gas Dynamics of A Perfect Impeller
Va2
Vf2 =Vr2
Vw2= Utip
Ueye
b1
Vr1
Vw1=0
Vf1=Va1

18. Va2
Vr2
b2
Reality of Fluid Mechanics
Vw2
Va2
Vf2
Vr2
Vw2
b1
Vr1
Vf1=Va1