Page 105 - Handbook of Energy Engineering Calculations

FIGURE 27 Mollier chart of turbine condition lines.

For 0 percent engine efficiency, the other extreme in the efficiency range,
h = h and the condition line is a horizontal line, Draw this line as shown in
2
1
Fig. 27.
Between 0 and 100 percent efficiency, the condition lines become more

nearly vertical as the engine efficiency approaches 100 percent, or an
isentropic expansion. Draw the condition lines for 25, 50, and 75 percent
efficiency, as shown in Fig. 27.
For the isentropic expansion, the available energy = h − h , Btu/lb of
2x
1
steam. This is the energy that an ideal turbine would make available.
For actual turbines, the enthalpy at the exhaust pressure h = h −
2
1
(available energy) (engine efficiency)/100, where available energy = h – h 2x
1
for an ideal turbine working between the same initial and exhaust pressures.

Thus, the available energy converted to useful work for any engine efficiency
= (ideal available energy, Btu/lb)(engine efficiency, percent)/100. Using this
relation, the available energy at each of the given engine efficiencies is found

by substituting the ideal available energy and the actual engine efficiency.

2. Sketch the condition lines for various throttle pressures
Draw the throttle- and exhaust-pressure lines on the Mollier chart, Fig. 28.