Unlock document.
This document is partially blurred.
Unlock all pages and 1 million more documents.
Get Access
9-102
9-128 An ideal reheat Rankine with water as the working fluid is considered. The temperatures at the inlet of both turbines,
and the thermal efficiency of the cycle are to be determined.
Assumptions 1 Steady operating conditions exist. 2 Kinetic and
potential energy changes are negligible.
Analysis From the steam tables (Tables A-4, A-5, and A-6),
kJ/kg 49.256065.542.251
kJ/kg 065.5 mkPa 1
kJ 1
kPa)205000)(/kgm 0010172.0(
/kgm 0010172.0
kJ/kg 42.251
inp,12
3
3
3
kPa 20 @1
kPa 20 @1
whh
hh
f
f
vv
C327.2
3
3
43
3
44
44
4
4
kJ/kg 9.3006
kPa 5000
KkJ/kg 3495.6)3058.4)(96.0(2159.2
kJ/kg 3.2704)4.1985)(96.0(33.798
96.0
kPa 1200
T
h
ss
P
sxss
hxhh
x
P
fgf
fgf
C481.1
5
5
65
5
66
66
6
6
kJ/kg 0.3436
kPa 1200
KkJ/kg 6242.7)0752.7)(96.0(8320.0
kJ/kg 6.2514)5.2357)(96.0(42.251
96.0
kPa 20
T
h
ss
P
sxss
hxhh
x
P
fgf
fgf
Thus,
kJ/kg 2.226342.1516.2514
kJ/kg 0.34823.27040.343649.2569.3006)()(
16out
4523in
hhq
hhhhq
and
35.0% 3500.0
0.3482
2.2263
11
in
out
th q
q
1
5
2
6
s
T
3
4
5 MPa
20 kPa
1200 kPa
9-103
9-129 A steam power plant that operates on an ideal reheat Rankine cycle between the specified pressure limits is
considered. The pressure at which reheating takes place, the total rate of heat input in the boiler, and the thermal efficiency
of the cycle are to be determined.
Assumptions 1 Steady operating conditions exist. 2 Kinetic and potential energy changes are negligible.
Analysis (a) From the steam tables (Tables A-4, A-5, and A-6),
/kgm 00101.0
kJ/kg 81.191
121in,
3
kPa 10 @sat1
kPa 10 @sat1
p
PPw
hh
v
vv
5
T
3
15
9-104
9-130 A steam power plant that operates on a reheat Rankine cycle is considered. The condenser pressure, the net power
3) (Eq. 2.335885.02.3358
2) (Eq.
?
1) (Eq.
95.0
?
KkJ/kg 2815.7
kJ/kg 2.3358
C450
MPa2
kJ/kg 3.3027
1.29485.347685.05.3476
kJ/kg 1.2948
MPa2
KkJ/kg 6317.6
kJ/kg 5.3476
C550
MPa5.12
66556
65
65
6
56
6
6
6
6
5
5
5
5
4334
43
43
4
34
4
3
3
3
3
ssT
s
T
s
sT
s
T
s
s
hhhhh
hh
hh
h
ss
P
h
x
P
s
h
T
P
hhhh
hh
hh
h
ss
P
s
h
T
P
/
/kgm 001010.0
kJ/kg 57.189
121in,
3
kPa 10 @1
kPa 73.9 @1
pp
f
f
PPw
hh
v
vv
1
5
2s
6s
s
T
3
4s
12.5 MPa
P = ?
6
4
2
3
6
1
2
Turbine
Boiler
Condenser
Pump
5
4
9-105
9-131 A steam power plant that operates on a reheat Rankine cycle is considered. The quality (or temperature, if
superheated) of the steam at the turbine exit, the thermal efficiency of the cycle, and the mass flow rate of the steam are to
be determined.
Assumptions 1 Steady operating conditions exist. 2 Kinetic and potential energy changes are negligible.
Analysis (a) From the steam tables (Tables A-4, A-5, and A-6),
/
/kgm 001010.0
kJ/kg 81.191
121in,
3
kPa 10 @1
kPa 10 @1
pp
f
f
PPw
hh
v
vv
5
T
3
9-106
9-132 A steam power plant that operates on the ideal reheat Rankine cycle is considered. The quality (or temperature, if
superheated) of the steam at the turbine exit, the thermal efficiency of the cycle, and the mass flow rate of the steam are to
be determined.
Assumptions 1 Steady operating conditions exist. 2 Kinetic and potential energy changes are negligible.
Analysis (a) From the steam tables (Tables A-4, A-5, and A-6),
/kgm 00101.0
kJ/kg 81.191
121in,
3
kPa 10 @1
kPa 10 @1
p
f
f
PPw
hh
v
vv
5
T
3
PROPRIETARY MATERIAL. © 2017 McGraw-Hill Education. Limited distribution permitted only to teachers and educators for course preparation. If
you are a student using this Manual, you are using it without permission.
9-133C Because the compression process involves the compression of a liquid-vapor mixture which requires a compressor
that will handle two phases, and the expansion process involves the expansion of high-moisture content refrigerant.
9-134C The reversed Carnot cycle serves as a standard against which actual refrigeration cycles can be compared. Also, the
9-135 A steady-flow Carnot refrigeration cycle with refrigerant-134a as the working fluid is considered. The coefficient of
performance, the amount of heat absorbed from the refrigerated space, and the net work input are to be determined.
Assumptions 1 Steady operating conditions exist. 2 Kinetic and potential energy changes are negligible.
Analysis (a) Noting that TH = 60C = 333 K and TL = Tsat @ 140 kPa = −18.77C = 254.2 K, the COP of this Carnot refrigerator
kJ/kg 106.2
kJ/kg 139.1
K 333
K 254.2
H
H
L
L
L
H
L
H
q
T
T
q
T
T
q
q
(c) The net work input is determined from
kJ/kg 32.9 2.1061.139
net LH qqw
s
qL
1
2
9-109
9-142C The minimum temperature that the refrigerant can be cooled to before throttling is the temperature of the sink (the
cooling medium) since heat is transferred from the refrigerant to the cooling medium.
9-143E An ice-making machine operates on the ideal vapor-compression refrigeration cycle, using refrigerant-134a as the
working fluid. The power input to the ice machine is to be determined.
Assumptions 1 Steady operating conditions exist. 2 Kinetic and potential energy changes are negligible.
Analysis In an ideal vapor-compression refrigeration cycle, the compression process is isentropic, the refrigerant enters the
compressor as a saturated vapor at the evaporator pressure, and leaves the condenser as saturated liquid at the condenser
throttlingBtu/lbm 39.33
Btu/lbm 39.33
liquid sat.
psia 80
Btu/lbm 01.115
psia 80
RBtu/lbm 22570.0
Btu/lbm 74.102
vapor sat.
psia 20
34
psia 08 @ 3
3
2
12
2
psia 20 @ 1
psia 20 @ 1
1
hh
hh
P
h
ss
P
ss
hh
P
f
g
g
QH
20 psia
1
2
3
80 psia
T
Win
·
·
9-110
9-144E A refrigerator operating on the ideal vapor-compression refrigeration cycle with refrigerant-134a as the working
fluid is considered. The increase in the COP if the throttling process were replaced by an isentropic expansion is to be
determined.
Assumptions 1 Steady operating conditions exist. 2 Kinetic and potential energy changes are negligible.
Analysis In an ideal vapor-compression refrigeration cycle, the compression process is isentropic, the refrigerant enters the
9-112
9-146 An ideal vapor-compression refrigeration cycle with refrigerant-134a as the working fluid is considered. The quality
of the refrigerant at the end of the throttling process, the COP, and the power input to the compressor are to be determined.
Assumptions 1 Steady operating conditions exist. 2 Kinetic and potential energy changes are negligible.
Analysis (a) In an ideal vapor-compression refrigeration cycle, the compression process is isentropic, the refrigerant enters
9-113
9-147 Problem 9-146 is reconsidered. The effect of evaporator pressure on the COP and the power input is to be
investigated.
Analysis The problem is solved using EES, and the solution is given below.
"Input Data"
{P[1]=140 [kPa]}
h[1]+Wcs=h2s "energy balance on isentropic compressor"
Wc=Wcs/Eta_c"definition of compressor isentropic efficiency"
h[1]+Wc=h[2] "energy balance on real compressor-assumed adiabatic"
s[2]=entropy(Fluid$,h=h[2],P=P[2]) "properties for state 2"
T[2]=temperature(Fluid$,h=h[2],P=P[2])
x[4]=quality(Fluid$,h=h[4],P=P[4]) "properties for state 4"
s[4]=entropy(Fluid$,h=h[4],P=P[4])
T[4]=temperature(Fluid$,h=h[4],P=P[4])
"Evaporator"
P[4]=P[1] "neglect pressure drop across evaporator"
9-114
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-50
-25
0
25
50
75
100
125
s [kJ/kg-K]
T [C]
800 kPa
140 kPa
R134a
T-s diagram for = 1.0
050 100 150 200 250 300
101
102
103
104
h [kJ/kg]
P [kPa]
31.33 C
-18.8 C
R134a
P-h diagram for h = 1.0
-50
-25
0
25
50
75
100
125
T [C]
800 kPa
140 kPa
R134a
T-s diagram for = 0.6
9-119
9-151 A refrigerator with refrigerant-134a as the working fluid is considered. The power input to the compressor, the rate of
heat removal from the refrigerated space, and the pressure drop and the rate of heat gain in the line between the evaporator
and the compressor are to be determined.
