Modern Engineering Thermodynamics

Problems 357
flow rate of 15.0 lbm/min. The inlet steam is at 400.0°F,
100. psia and it exits at 14.7 psia, 90.0% quality. Determine
a. The rate of heat loss from the engine.
b. Its entropy production rate.
c. Its entrance and exit specific flow availabilities. Use
saturated liquid water at 80.0°F as the local environment
(ground state).
55.* A design for a turbine has been proposed involving the
adiabatic, steady flow of steam through the turbine. Saturated
vapor at 300.°C enters the turbine and the steam leaves at
0.200 MPa with a quality of 95.0%.
a. Draw a T-s diagram for the turbine.
b. Determine the work and entropy production per kilogram
of steam flowing through the turbine.
c. If the atmospheric temperature is 25.0°C, determine the
entrance and exit specific flow availabilities.
Neglect any kinetic and potential energy effects and take the
local environment (ground state) to be saturated liquid water
at 80.0°F.
56.* Steam enters a turbine at 2.00 MPa and 700.°C and exits the
turbine at 0.200 MPa and 400.°C. The process is steady flow,
steady state, and adiabatic. Using saturated liquid water at
20.0°C as the local environment (ground state), determine the
following items on the basis of a steam flow rate of 6.30 kg/s:
a. The irreversibility rate of the turbine.
b. The turbine’s entrance and exit specific flow availabilities.
c. The turbine’s actual output power.
57. Saturated liquid water enters a badly worn boiler feed pump
at 1.00 psia and exits the pump as a saturated liquid at 600
psia in a steady flow, steady state, adiabatic process. Using
saturated liquid water at 70.0°F as the local environment
(ground state), determine the following items on the basis of
a steam flow rate of 75.0 lbm/s:
a. The irreversibility rate of the pump.
b. The pump’s entrance and exit specific flow availabilities.
c. The pump’s actual input power.
58.* Saturated liquid ammonia enters a boiler in a refrigeration
system at −20.0°C and exits the boiler as a superheated vapor
at 100. kPa and 10.0°C in a steady flow, steady state, process.
Using saturated liquid ammonia at 0.00°C as the local
environment (ground state), determine the following items on
the basis of an ammonia flow rate of 12.0 kg/s:
a. The irreversibility rate of the boiler.
b. The boiler’s entrance and exit specific flow availabilities.
c. The boiler’s heat input rate.
59. Saturated Refrigerant-22 vapor enters the condenser of a large
refrigeration system at 80.0°F and exits as a saturated liquid at
80.0°F in a steady flow, steady state process. Using saturated
liquid Refrigerant-22 at 0.00°F as the local environment
(ground state), determine the following items on the basis of
an ammonia flow rate of 80.0 lbm/s:
a. The irreversibility rate of the condenser.
b. The condenser’s entrance and exit specific flow
availabilities.
c. The condenser’s heat rejection rate.
60. Air (an ideal gas) enters a throttle at 70.0°F and 150. psia and
exits at 14.7 psia in a steady flow, steady state, adiabatic,
aergonic process. Determine the irreversibility rate per unit
mass of air flowing through the throttle. The local
environment (ground state) is 14.7 psia and 70.0°F.
61.* Superheated steam at 1.30 kg/s, 0.0100 MPa, and 400.°C
enters a horizontal, stationary, insulated diffuser with a
velocity of 100. m/s. The friction and other irreversibilities
within the nozzle cause the exit pressure to be 115% of that
produced by an isentropic expansion. Taking the local
environment (ground state) to be that of saturated liquid
water at 20.0°C, determine
a. The inlet specific flow availability.
b. The exit specific flow availability.
c. The irreversibility rate inside the diffuser.
62.* A new solar collection system has a net input availability rate
of 600. kJ/s and an availability destruction rate of 80.0 kJ/s.
Determine the second law availability efficiency of this system
if it loses availability at a rate of 345 kJ/s to the surroundings.
63. A closed domestic gas hot water heater contains 415 lbm of
water at 45.0°F. Determine the first and second law efficiencies
as this water is heated to 130.°F using 39,589 Btu from a gas
burner. The temperature of the local environment (ground
state) is 55.0°F.
64.* A large, closed, industrial electrical hot water heater contains
2000. kg of water at 15.0°C. Determine the first and second
law efficiencies as this water is heated to 75.0°C using
0.550 MJ of electrical energy. The temperature of the local
environment (ground state) is 20.0°C.
65. In Example 10.10, the following equation was developed for
the second law availability efficiency ε of heating a liquid in a
closed uninsulated tank:
2
ΔT − T 0 ln 1 + ΔT 3
6
ε = mc4
T 7
5
Is there a value of ΔT that maximizes ε? Hint: Set dε/d(ΔT) = 0
and solve for ΔT.
66.* An electric heater is used to increase the temperature of liquid
water in an open tank from 10.0 to 80.0°C in a steady state,
steady flow process. The mass flow rate of the water through the
tank is 3.70 kg/s, and the electric heater adds 1500. kW to the
water. Determine the first and second law efficiencies of this
system. The temperature of the local environment (ground
state) is 10.0°C.
67.* A solar water heater is used to increase the temperature of
liquid water in an open cattle watering tank from 3.00°C to
18.0°C in a steady state, steady flow process. The mass flow rate
of the water through the tank is 1.50 kg/s, and the solar heater
adds 100. kW to the water. Determine the first and second law
efficiencies of this system. The temperature of the local
environment (ground state) is 0.00°C.
68. In Example 10.11, the following equation was developed for
the second law availability efficiency ε of heating a liquid in
an open, uninsulated tank:
2
ΔT − T 0 ln 1 + ΔT 3
6
ε = _mc4
T 7
5
Is there a value of ΔT that maximizes ε? Hint: Set dε/d(ΔT) =
0 and solve for ΔT.
69. An automobile engine has a Carnot thermal efficiency of 56.0%
and an actual thermal efficiency of 21.0%. Determine the second
law availability efficiency of this engine.
Q in
_Q in