Modern Engineering Thermodynamics

528 CHAPTER 13: Vapor and Gas Power Cycles
heat input rate of this engine. Ignore the boiler feed pump
power requirement.
6. In 1790 John Curr of Sheffield, England, made an atmospheric
steam engine with a 61.0-inch diameter piston and an 9.50 ft
stroke. The engine operated with a mean effective piston
pressure of 7.00 lbf/in 2 and ran at 12.0 strokes per minute. It
produced a duty of 9.38 million. Determine (a) the thermal
efficiency, (b) the horsepower output, and (c) the boiler heat
input rate of this engine. Ignore the boiler feed pump power
requirement.
7.* An engine operating on a Carnot cycle extracts 10.0 kJ of heat per
cycle from a thermal reservoir at 1000.°C and rejects a smaller
amount of heat to a low-temperature thermal reservoir at 10.0°C.
Determine the net work produced per cycle of operation.
8.* We need to get 1.00 kW of power from a heat engine operating
on a Carnot cycle. 3.00 kW of heat is supplied to the engine
from a thermal reservoir at 600. K. What is the required
temperature of the low-temperature reservoir, and how much
heat must be rejected to it?
9. For the thermal reservoir temperatures shown in Table 13.4,
determine (a) the Carnot cycle heat engine thermal efficiency
and (b) which is the more effective method of increasing this
efficiency, increasing T H by an amount ΔT or lowering T L by an
amount ΔT, and why.
Table 13.4 Problem 9
No. T H (°F) T L (°F)
1 4000. 500.
2 4000. 100.
3 2000. 500.
4 2000. 100.
10. Steam enters the turbine of a power plant at 200. psia, 500.°F.
How much will the Carnot cycle thermal efficiency increase if
the condenser pressure is lowered from 14.7 to 1.00 psia?
11. Steam enters the piston cylinder of a Newcomen cycle steam
engine at 14.7 psia, 212°F and condenses at 6.00 psia. Plot the
thermal efficiency of the reversible cycle vs. the average cylinder
wall temperature over the range 170.°F ≤ (T b ) avg ≤ 212°F.
Neglect the power used by the boiler feed pump.
12. Determine the maximum possible thermal efficiency of an
atmospheric steam engine with a boiler temperature of 212°F
and a condensation temperature of 70.0°F if it operates on
a. A Carnot cycle.
b. A Newcomen cycle assuming an average cylinder wall
temperature of 141°F.
c. A Rankine cycle.
13. Steam with a quality of 1.00 enters the turbine of a Rankine
cycle power plant at 400. psia and exits at 1.00 psia. Neglecting
pumping power, determine the Rankine cycle isentropic thermal
efficiency.
14. Determine the decrease in Carnot and isentropic Rankine cycle
thermal efficiencies if the condenser is removed from the engine
discussed in text Example 13.5 and the steam is allowed to
exhaust directly into the atmosphere at 14.7 psia. Assume the
cycles are still closed loop.
15. Show that the Carnot and isentropic Rankine cycle thermal
efficiencies for an engine whose boiler produces dry saturated
steam at 100. psia and whose condenser operates at 1.00 psia
are 29.7% and 26.1%, respectively. Draw the appropriate T–s
and p–v diagrams for these cycles.
16. Rework Problem 15 for an engine without a condenser, with the
steam exhausting directly into the atmosphere at 14.7 psia.
Determine the Carnot and isentropic Rankine cycle thermal
efficiencies and their percent decrease due to the removal of the
condenser. Assume the cycles are still closed loop.
17. Steam enters the turbine of a Rankine cycle power plant at
200. psia and 500.°F. How much will the isentropic Rankine
cycle thermal efficiency increase if the condenser pressure is
lowered from 14.7 psia to 1.00 psia? Neglect the pump work.
18. A small portable nuclear-powered Rankine cycle steam power
plant has a turbine inlet state of 200. psia, 600.°F, and a
condenser temperature of 80.0°F. The steam mass flow rate is
0.500 lbm/s. Assuming that the condenser exit state is a
saturated liquid, that the pump and turbine isentropic
efficiencies are 55.0% and 75.0%, respectively, and that there are
no pressure losses across the boiler or condenser, determine
a. The actual power required to drive the pump.
b. The actual power output of the plant.
c. The actual thermal efficiency of the plant.
19. A Rankine cycle power plant is to be used as a stationary power
source for a polar research station. The working fluid is
Refrigerant-22 at a flow rate of 9.00 lbm/s, and the turbine inlet
state is saturated vapor at 200.°F. The condenser is air cooled
and has an internal temperature of 0.00°F. Assuming a turbine
and pump isentropic efficiency of 85.0% and that the refrigerant
leaves the condenser as a saturated liquid, determine the overall
thermodynamic efficiency and the net power output of the
system.
20.* A solar-powered Rankine cycle power plant uses 18.5 × 10 3 m 2
of solar collectors. Refrigerant-22 is used as the working fluid at
a flow rate of 1.00 kg/s and is transformed to a saturated vapor
in the solar collectors (which function as the boiler) at a
temperature of 40.0°C. The condenser for the system operates
at 20.0°C and has a quality of 0.00 at the exit. The pump
and prime mover isentropic efficiencies are 65.0% and 75.0%,
respectively. Determine the prime mover power output
and system thermal efficiency when the incident solar flux
is 8.00 W/m 2 .
21.* Saltwater oceans have subsurface stratification layers called
thermoclines across which large temperature differences can exist.
A 1.00 MW Rankine cycle power plant using ammonia as the
working fluid is being designed to operate on a thermocline
temperature difference. The ammonia exits the boiler as a
saturated vapor at 28.0°C and exits the condenser as a saturated
liquid at 10.0°C. For an isentropic system, determine
a. The thermal efficiency of the power plant.
b. The pump to turbine power ratio.
c. The required mass flow rate of ammonia.
22. The condensation that can occur in the low-pressure end of a
steam turbine is undesirable because it can cause corrosion and
blade erosion, thus reducing the turbine’s isentropic efficiency.
This can be avoided by superheating the steam before it enters
the turbine. What degree of superheat would be required if the
steam entered an isentropic turbine at 300. psia and exited as a
saturated vapor at 1.00 psia?
23.* Steam enters the turbine of a Rankine cycle power plant at
12.0 MPa and 400.°C. How much does the isentropic thermal