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Analysis of Compressors

P M V Subbarao

Professor

Mechanical Engineering Department

Active Devices for Infusion of Life into Fluid.

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Classification of Compressors

Rotodynamic Compressors Positive Displacement

of Compressors vdp pdv

Centrifugal

Compressors

Mixed

Compressors

Axial

Compressors ReciprocatingCompressors

RotoryCompressors

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Centrifugal Vs Axial : Flow Area

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Centrifugal Vs Axial : Level of interaction

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In search of Time scale in Requirement

Primary characteristics of a requirement.

The effect: Dp

The Capacity: Flow Rate Q (m3

/s). Density of fluid: r(kg/m3).

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Machine-Fluid Matching Parameter:

r:, pQf DFor compressible fluid machines

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kji pQ rD

j

i

m

kgsm

kg

sm

3

2

3

.

j

i pQ

D

r

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ji

s

m

s

m

2

23

23

2

23

s

m

s

mi

Takej = -3/2

3

33

s

m

s

m i

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Take i = 1/2&j = -3/4

43

2

22

13

s

m

s

m

4

3

2

1

D

r

pQ

4

3

D

r

p

Q

23

23

21

23

s

m

s

m

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Time Scale of a Machine to Resource

Speed: N (rpm) or n (rps)

ScaleTimeMachine

ScaleTimetRequiremenscaletimeessDimensionl

n1

scaletimeDimension-Non

This is named as Specific Speed, Ns

4

3

D

r

r

p

mnNs

4

3

D

rpQ

4

3

D

r

p

mnNs

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Centrifugal AxialMixed

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Role of specific Speed on Design of A Compressor

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Centrifugal Compressors

The centrifugal compressor consists

essentially of a stationary casing containinga 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.

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Multi Stage Compressors

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ImpellerDiffuser :Rotor-Stator

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Anatomy of A Centrifugal

Compressors

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Vr1

Vw2= Utip

Vf2 =Vr2

Va2

b1

Gas Dynamics of A Perfect Impeller

Vf1=Va1

Ueye

Vw1=0

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Vr1Vf1=Va1

Vw2

Vw2

Vr2

Vr2

Va2

Va2Vf2

b1

Reality of Fluid Mechanicsb2