With given information and data from Table A-22E:
The exergy destruction can be evaluated by reducing an exergy rate balance. Rearranging and
expanding the flow exergy terms, Eq. 7.13a becomes:
Introducing Eq. (1) and simpl
8.52 As indicated in Fig. P8.52, a power plant similar to that in Fig. 8.11 operates on a
regenerative vapor power cycle with one closed feedwater heater. Steam enters the first turbine
stage at state 1 where pressure is 12 MPa and temperature is 560oC. S
An insulated turbine operating at steady state receives steam at 300 lbf/in.2, 550F and exhausts
at 3 lbf/in.2 Plot the exergy destruction rate, in Btu per lb of steam flowing, versus turbine
isentropic efficiency ranging from 50 to 100%. The
Figure PHD shows a powergenerating system at steady
state. Saturated liquid water enters at 80 bar with a mass
ow rate of 94 kg/s. Saturated liquid exits at 0.08 bar with
the same mass ow rate. As indicated by arrows, three heat
3. The turbine and pump operate adiabatically.
4. Kinetic and potential energy effects are negligible.
5. Saturated liquid exits the condenser.
First fix each principal state.
State 1: p1 = 12 MPa (120 bar), T1 = 560oC h1 = 3506.2 kJ/kg, s1 = 6.
PROBLEM 7. so
7.80 Steady-state operating data are shown in Fig. P7.80 for an open feedwater heater.
Heat transfer from the feedwater heater to its surroundings occurs at an average outer
surface temperature of 50C at a rate of 100 kW. Ignore the effects
13:20 ELEM 7.5 8
Water vapor at 4.0 MPa and 400C enters an insulated g. H c Mar-n c g NEIL: D7 .
turbine operating at steady state and expands to saturated _._ '
vapor at 0.1 MPa. The effects of motion and gravity can be
neglected. Determine the work dev
cv m1[s6 s5 y(s7 s2 )]
kJ 1 kW
= 74.58 kW/K
[1.7808 0.5677 (0.2024)(2.1387 6.9174)]
kg K 1 kJ/s
(d) The rate of entropy production in the steam trap is determined using the one-inlet, one-exit,
steady-state form of the entropy rate balance
Oxygen (O2) enters a well insulated nozzle operating at steady state at 80 lbf/in.2, 1100R, 90
ft/s. At the nozzle exit, the pressure is 1 lbf/in.2 The isentropic nozzle efficiency is 85%. For the
nozzle, determine the exit velocity, in ft/s,
8.41 Reconsider the cycle of Problem 8.40 as the feedwater heater pressure takes on other
values. Plot the cycle thermal efficiency, cycle work per unit mass entering the turbine, in kJ/kg,
the heat transfer into the cycle per unit mass entering the turbi
Steam at 30 bar and 700C is available at one location in an industrial plant. At another location,
steam at 20 bar and 400C is required for use in a certain process. An engineer suggests that
steam at this condition can be provided by allowin
Steam at 2 MPa and 360C with a mass flow rate of 0.2 kg/s enters an insulated turbine operating
at steady state and exhausts at 300 kPa. Plot the temperature of the exhaust steam, in C, the
power developed by the turbine, in kW, and the rate
'PEgEl EM,7' ? 8
For the water heater of Problem 7.45, devise and evalu-
ate an exergetic efficiency.
So: sad; QWPALEQ 77.21.75; 3:th 'Tkeu/
3 (Ex: r31 Shred) = (34-05: 2 O- O? 5
6 (ti-yam? Cow/fed) 26 $78 :3 ( A)
74. Tux: van: is Mpo
PROBLEM 6.4 (CONTINUED)
(c) air as an ideal gas, T1 = 80oF = 540 oR, p1 = 1 atm; T2 = 340oF = 800 oR, p = 5 atm.
For air as an ideal gas; s = so(T2) so(T1) R ln (p2/p1). With data from Table A-22E
s = (0.69558) (0.60078) (1.986/28.97) ln(5/1) = - 0.01553
Carbon dioxide (CO2) gas undergoes a process in a closed system from T1 = 100oF, p1 = 20
lbf/in.2, to T2 = 400oR, p2 = 50 lbf/in.2 The entropy produced due to internal irreversiblities
during the process is determined to be 0.15 Btu/oR per lb
Air is compressed adiabatically in a piston-cylinder assembly from 1 bar, 300 K to 10 bar, 600
K. The air can be modeled as an ideal gas and kinetic and potential energy effects are negligible.
Determine the amount of entropy produced, in kJ/
PROBLEM 6.73 (CONTINUED)
A thermodynamic power cycle receives energy by heat transfer from an incompressible body of
mass m and specific heat c initially at temperature TH. The cycle discharges energy by heat
transfer to another
Refrigerant 22 is enters a compressor operating at steady state as saturated vapor at 10 bar and
compressed adiabatically in an internally reversible process to 16 bar. Ignoring kinetic and
potential energy effect
Consider the solid rod at steady state shown in Fig. P6.69. The rod is insulated on its lateral
surfaces, but energy transfer occurs at the rate
into the rod at location 1, and energy transfer
occurs at the rate
out of the rod at
Construct a plot, to scale, showing constant-pressure lines of 5.0 and 10 MPa ranging from 100
to 400oC on a T-s diagram for water.
p = 5.0 MPa = 50 bar
W: A colal air- Shndaro one each \uo. known comprrfu'ow
Min No. spzciGA chic 4+ u beginning all wvansuaw. The
hat mama pu- Mxk ms 9+ ciur is 91v.
END.- Dekmxm (a) M Minimum hwwahn +ln. mamum
prawn, (Cd-Kn. Mrm cmcl'eucg, and Ma?-
:5 m: EMEREEE
8.73 Water is the working uid in a reheat-regenerative Rankine cycle with one closed
feedwater heater and one open feedwater heater. Steam enters the turbine at 1400 lbf/in.2 and
1000F and expands to 500 lbf/in.2, where some of the steam is extracted and