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234 Chapter 5

Table 5.11 Continued

Multistage

T| T - T| B - C S - Cp - m - ll! - h 2 - h 2S - h 2LS - Ws - ^2L - h2V - Si - S 2S - S 2LS - S2VS - X
-x s

Degrees of Freedom
Single stage

F=17-17 = 0

Multistage:

F=18-18 = 0____________________________________

Table 5.12 Calculating Procedure for Sizing Steam Turbines_______

1. Obtain the thermodynamic properties (Equations 5.11.14 to 5.11.21) at the inlet
and discharge of the turbine from the steam tables (44).

2. Calculate the mass fraction of water in the turbine exit stream, xs, assuming an
isentropic expansion of the steam from P i to ?2 (Equations 5.11.3 and 5.11.11).

3. Obtain the turbine efficiency, r\ B, for a single-stage turbine from Equation
5.11.5 or Equation 5.11.8 for a multistage turbine.
4. Obtain the correction factor for superheated steam, c s, for a single-stage turbine
from Equation 5.11.6. For a multistage turbine, obtain the correction factors c s and
c p from Equation 5.11.9 and 5.11.10

5. Calculate the exit enthalpy for an isentropic expansion, h 2s, from Equation
5.11.12.
6. Calculate the actual mass fraction of water in the exit steam, x, for a single-stage
turbine from Equation 5.11.2, 5.11.4, and 5.11.13. For a multistage turbine calcu-
late x, from Equation 5.11.2, 5.11.7, and 5.11.13.

7. Calculate the steam flow rate, m, from Equations 5.11.1.

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