590 | Thermodynamics
*Problems designated by a “C” are concept questions, and students
are encouraged to answer them all. Problems designated by an “E”
are in English units, and the SI users can ignore them. Problems
with a CD-EES icon are solved using EES, and complete solutions
together with parametric studies are included on the enclosed DVD.
Problems with a computer-EES icon are comprehensive in nature,
and are intended to be solved with a computer, preferably using the
EES software that accompanies this text.
PROBLEMS*Carnot Vapor Cycle
10–1C Why is excessive moisture in steam undesirable in
steam turbines? What is the highest moisture content
allowed?
10–2C Why is the Carnot cycle not a realistic model for
steam power plants?
10–3E Water enters the boiler of a steady-flow Carnot
engine as a saturated liquid at 180 psia and leaves with a
quality of 0.90. Steam leaves the turbine at a pressure of 14.7
psia. Show the cycle on a T-sdiagram relative to the satura-
tion lines, and determine (a) the thermal efficiency, (b) the
quality at the end of the isothermal heat-rejection process,
and (c) the net work output. Answers: (a) 19.3 percent,
(b) 0.153, (c) 148 Btu/lbm
10–4 A steady-flow Carnot cycle uses water as the working
fluid. Water changes from saturated liquid to saturated vapor
as heat is transferred to it from a source at 250°C. Heat rejec-
tion takes place at a pressure of 20 kPa. Show the cycle on
aT-sdiagram relative to the saturation lines, and determine
(a) the thermal efficiency, (b) the amount of heat rejected, in
kJ/kg, and (c) the net work output.
10–5 Repeat Prob. 10–4 for a heat rejection pressure of
10 kPa.
10–6 Consider a steady-flow Carnot cycle with water as the
working fluid. The maximum and minimum temperatures in
the cycle are 350 and 60°C. The quality of water is 0.891 at
the beginning of the heat-rejection process and 0.1 at the end.
Show the cycle on a T-sdiagram relative to the saturation
lines, and determine (a) the thermal efficiency, (b) the pres-
sure at the turbine inlet, and (c) the net work output.
Answers:(a) 0.465, (b) 1.40 MPa, (c) 1623 kJ/kg
The Simple Rankine Cycle
10–7C What four processes make up the simple ideal Rank-
ine cycle?
10–8C Consider a simple ideal Rankine cycle with fixed
turbine inlet conditions. What is the effect of lowering the
condenser pressure on
Pump work input: (a) increases, (b) decreases,
(c) remains the same
Turbine work (a) increases, (b) decreases,
output: (c) remains the same
Heat supplied: (a) increases, (b) decreases,
(c) remains the same
Heat rejected: (a) increases, (b) decreases,
(c) remains the same
Cycle efficiency: (a) increases, (b) decreases,
(c) remains the same
Moisture content (a) increases, (b) decreases,
at turbine exit: (c) remains the same10–9C Consider a simple ideal Rankine cycle with fixed
turbine inlet temperature and condenser pressure. What is the
effect of increasing the boiler pressure onPump work input: (a) increases, (b) decreases,
(c) remains the same
Turbine work (a) increases, (b) decreases,
output: (c) remains the same
Heat supplied: (a) increases, (b) decreases,
(c) remains the same
Heat rejected: (a) increases, (b) decreases,
(c) remains the same
Cycle efficiency: (a) increases, (b) decreases,
(c) remains the same
Moisture content (a) increases, (b) decreases,
at turbine exit: (c) remains the same10–10C Consider a simple ideal Rankine cycle with fixed
boiler and condenser pressures. What is the effect of super-
heating the steam to a higher temperature onPump work input: (a) increases, (b) decreases,
(c) remains the same
Turbine work (a) increases, (b) decreases,
output: (c) remains the same
Heat supplied: (a) increases, (b) decreases,
(c) remains the same
Heat rejected: (a) increases, (b) decreases,
(c) remains the same
Cycle efficiency: (a) increases, (b) decreases,
(c) remains the same
Moisture content (a) increases, (b) decreases,
at turbine exit: (c) remains the same10–11C How do actual vapor power cycles differ from ide-
alized ones?