Handbook of Turbomachinery Second Edition Revised - Ventech!

Theoretically this efficiency is:
or
Where
compressor efficiency ¼
compressor adiabatic efficiency ¼ T1CY
isentropic enthalpy rise across compressor stage
through compressor pressure ratio
actual enthalpy rise across compressor stage
T2C T1C
T2C ¼ compressor outlet air total temperature (degrees R).
Y ¼ðP2C=P1CÞ 0:283
1.
There are three main areas on the centrifugal compressor map. The central
area is the stable operating zone. The surge line in the low flow rate area at
the left of Fig. 18(a) defines an area of pressure and flow rate where
compressor operation is unstable. Surging occurs when the mass flow rate
through the compressor is reduced while maintaining a constant pressure
ratio until a point is reached where local flow reversal occurs in the
boundary layers. If the flow rate is further reduced, complete reversal
occurs. This will relieve the adverse pressure gradient until a new flow
regime is established at a lower pressure ratio. The flow rate will again build
up to the initial condition, and this flow instability will continue at a fixed
frequency and in some cases can become quite violent.
The compressor map shows a tradeoff in compressor design. The
narrower the operating range of the compressor, the sharper the surge.
However, the broader the range, the lower the peak efficiency.
Turbine Performance Map
The performance map for the turbine shows the lines of constant corrected
speed, corrected exhaust gas flow, and overall turbine efficiency plotted
against turbine pressure ratio (Fig. 19). The total-to-static pressure ratio is
used here since the actual exit conditions cannot be predicted for a
particular installation.
Where
pressure ratio ðexpansion ratioÞ ¼ P1T
P2T
P1T ¼ inlet gas total absolute pressure (in. Hg).
Copyright © 2003 Marcel Dekker, Inc.