Page 222 - Fluid Mechanics and Thermodynamics of Turbomachinery

Centrifugal Pumps, Fans and Compressors 203

FIG. 7.3. Mollier diagram for the complete centrifugal compressor stage.

Inlet casing

The fluid is accelerated from velocity c 0 to velocity c 1 and the static pressure falls
from p 0 to p 1 as indicated in Figure 7.3. Since the stagnation enthalpy is constant
in steady, adiabatic flow without shaft work then h 00 D h 01 or,

1 2
1 2
h 0 C c D h 1 C c .
2 0 2 1
Some efficiency definitions appropriate to this process are stated in Chapter 2.

Impeller

The general three-dimensional motion has components of velocity c r ,c , and c x
2
2
2
2
respectively in the radial, tangential and axial directions and c D c C c C c .
r x
Thus, from eqn. (2.12e), the rothalpy is
1
2
2
I D h C .c C c C c 2 2Uc /.
2 r x
2
1
Adding and subtracting U this becomes
2
1
2
2
2
I D h C f.U c / C c C c 2 U g. (7.1)
2 r x