Page 82 - Handbook of Energy Engineering Calculations

the proposed binary cycle. Find the cycle efficiency without mercury.

Calculation Procedure:

1. Tabulate the key enthalpies and entropies for the cycle
Set up two columns, thus:

2. Compute the quality of the exhaust for each vapor
Since expansion in each turbine is at constant entropy, Fig. 14b, the quality
for the mercury exhaust, x is: 0.1194 = 0.0299 + x (0.1l21); x = 0.798.
m
m
m
For the steam cycle, the quality, x is: 1.6293 = 0.1326 + x (1.8456); x =
s
s
s
0.81.
3. Find the exhaust enthalpy for each vapor
Using the properties of mercury from a set of tables, the enthalpy of the
mercury exhaust, H = 22.6 + 0.798(123) = 120.7 Btu/lb (281.2 kJ/kg). The
me
enthalpy of the condensed mercury, H = 22.6 Btu/lb (52.7 kJ/kg).
mf
For the exhaust steam, the enthalpy H = 69.7 + 0.81(1036.3) = 909.1
se
Btu/lb (2118 kJ/kg), using steam-table data. The enthalpy of the condensed
steam, H = 69.7 Btu/lb (162.4 kJ/kg).
sf
Assuming 98 percent quality steam leaving the mercury condenser, then
the enthalpy of the wet steam leaving the mercury condenser, H = 571.7 +
sw
0.98(611.7) = 1171.2 Btu/lb (2728 kJ/kg).