TITLE.PM5

158 ENGINEERING THERMODYNAMICS

dharm

/M-therm/Th4-4.pm5

Air

out

Centrifugal

Electric motor compressor

Q

W

Air in

Fig. 4.35. Centrifugal compressor.

Applying energy equation to the system (Fig. 4.35)

∆ Z = 0 (generally taken)

h 1 C^1

2

+ 2

F

HG

I

KJ – Q =

h 2 C^1

2

+ 2

F

HG

I
KJ – W
The Q is taken as negative as heat is lost from the system and W is taken as negative as
work is supplied to the system.

or h

C

1 1

2

+ 2

F

HG

I

KJ – Q =

h 2 C^2

2

2

+

F

HG

I

KJ

• W ...(4.57)

4.12.5. Reciprocating compressor

Refer Fig. 4.36. The reciprocating compressor draws in air from atmosphere and supplies at
a considerable higher pressure in small quantities (compared with centrifugal compressor). The
reciprocating compressor can be considered as steady flow system provided the control volume
includes the receiver which reduces the fluctuations of flow considerably.

Receiver

Compressor

Q W

(^21) Air
in
Fig. 4.36. Reciprocating compressor.