602 | Thermodynamics
10–112 A simple ideal Rankine cycle operates between the
pressure limits of 10 kPa and 3 MPa, with a turbine inlet
temperature of 600°C. Disregarding the pump work, the cycle
efficiency is
(a) 24 percent (b) 37 percent (c) 52 percent
(d) 63 percent (e) 71 percent
10–113 A simple ideal Rankine cycle operates between the
pressure limits of 10 kPa and 5 MPa, with a turbine inlet
temperature of 600°C. The mass fraction of steam that con-
denses at the turbine exit is
(a) 6 percent (b) 9 percent (c) 12 percent
(d) 15 percent (e) 18 percent
10–114 A steam power plant operates on the simple ideal
Rankine cycle between the pressure limits of 10 kPa and 10
MPa, with a turbine inlet temperature of 600°C. The rate of
heat transfer in the boiler is 800 kJ/s. Disregarding the pump
work, the power output of this plant is
(a) 243 kW (b) 284 kW (c) 508 kW
(d) 335 kW (e) 800 kW
10–115 Consider a combined gas-steam power plant. Water
for the steam cycle is heated in a well-insulated heat
exchanger by the exhaust gases that enter at 800 K at a rate
of 60 kg/s and leave at 400 K. Water enters the heat
exchanger at 200°C and 8 MPa and leaves at 350°C and 8
MPa. If the exhaust gases are treated as air with constant spe-
cific heats at room temperature, the mass flow rate of water
through the heat exchanger becomes
(a) 11 kg/s (b) 24 kg/s (c) 46 kg/s
(d) 53 kg/s (e) 60 kg/s
10–116 An ideal reheat Rankine cycle operates between the
pressure limits of 10 kPa and 8 MPa, with reheat occurring at
4 MPa. The temperature of steam at the inlets of both tur-
bines is 500°C, and the enthalpy of steam is 3185 kJ/kg at the
exit of the high-pressure turbine, and 2247 kJ/kg at the exit
of the low-pressure turbine. Disregarding the pump work, the
cycle efficiency is
(a) 29 percent (b) 32 percent (c) 36 percent
(d) 41 percent (e) 49 percent
10–117 Pressurized feedwater in a steam power plant is to
be heated in an ideal open feedwater heater that operates at a
pressure of 0.5 MPa with steam extracted from the turbine. If
the enthalpy of feedwater is 252 kJ/kg and the enthalpy of
extracted steam is 2665 kJ/kg, the mass fraction of steam
extracted from the turbine is
(a) 4 percent (b) 10 percent (c) 16 percent
(d) 27 percent (e) 12 percent
10–118 Consider a steam power plant that operates on the
regenerative Rankine cycle with one open feedwater heater.
The enthalpy of the steam is 3374 kJ/kg at the turbine inlet,
2797 kJ/kg at the location of bleeding, and 2346 kJ/kg at thevaried from 0.5 to 20 MPa. Determine the thermal efficiency
of the cycle and plot it against the boiler pressure, and discuss
the results.
10–106 Using EES (or other) software, investigate the
effect of superheating the steam on the perfor-
mance of a simple ideal Rankine cycle. Steam enters the turbine
at 3 MPa and exits at 10 kPa. The turbine inlet temperature is
varied from 250 to 1100°C. Determine the thermal efficiency
of the cycle and plot it against the turbine inlet temperature,
and discuss the results.
10–107 Using EES (or other) software, investigate the
effect of reheat pressure on the performance
of an ideal Rankine cycle. The maximum and minimum pres-
sures in the cycle are 15 MPa and 10 kPa, respectively, and
steam enters both stages of the turbine at 500°C. The reheat
pressure is varied from 12.5 to 0.5 MPa. Determine the ther-
mal efficiency of the cycle and plot it against the reheat pres-
sure, and discuss the results.
10–108 Using EES (or other) software, investigate the
effect of number of reheat stages on the per-
formance of an ideal Rankine cycle. The maximum and mini-
mum pressures in the cycle are 15 MPa and 10 kPa,
respectively, and steam enters all stages of the turbine at
500°C. For each case, maintain roughly the same pressure
ratio across each turbine stage. Determine the thermal effi-
ciency of the cycle and plot it against the number of reheat
stages 1, 2, 4, and 8, and discuss the results.
10–109 Using EES (or other) software, investigate the
effect of extraction pressure on the perfor-
mance of an ideal regenerative Rankine cycle with one open
feedwater heater. Steam enters the turbine at 15 MPa and
600°C and the condenser at 10 kPa. Determine the thermal
efficiency of the cycle, and plot it against extraction pressures
of 12.5, 10, 7, 5, 2, 1, 0.5, 0.1, and 0.05 MPa, and discuss the
results.
10–110 Using EES (or other) software, investigate the
effect of the number of regeneration stages on
the performance of an ideal regenerative Rankine cycle.
Steam enters the turbine at 15 MPa and 600°C and the con-
denser at 5 kPa. For each case, maintain about the same tem-
perature difference between any two regeneration stages.
Determine the thermal efficiency of the cycle, and plot it
against the number of regeneration stages for 1, 2, 3, 4, 5, 6,
8, and 10 regeneration stages.
Fundamentals of Engineering (FE) Exam Problems
10–111 Consider a steady-flow Carnot cycle with water as
the working fluid executed under the saturation dome
between the pressure limits of 8 MPa and 20 kPa. Water
changes from saturated liquid to saturated vapor during the
heat addition process. The net work output of this cycle is
(a) 494 kJ/kg (b) 975 kJ/kg (c) 596 kJ/kg
(d) 845 kJ/kg (e) 1148 kJ/kg