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10-1
Solutions Manual for
Heat and Mass Transfer: Fundamentals & Applications
6th Edition
Yunus A. Çengel, Afshin J. Ghajar
McGraw-Hill Education, 2020
Chapter 10
BOILING AND CONDENSATION
PROPRIETARY AND CONFIDENTIAL
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10-2
10-3
10-4
10-5
10-6
10-13 Water is boiled at a saturation (or boiling) temperature of Tsat = 120C by a brass heating element whose temperature is
not to exceed Ts = 125C. The highest rate of steam production is to be determined.
10-7
10-8
10-9
10-10
10-17 A polished copper tube is used to generate 1.5 kg/s of steam at 270 kPa. The surface temperature of the tube, with the
interest to minimize the excess temperature, is to be determined.
33.1Pr
=
l
KJ/kg 4263
=
pl
l
c
Also, Csf = 0.013 and n = 1 for the boiling of water on a mechanically polished copper surface (Table 10-3).
Analysis The heat flux can be determined from the rate of vaporization to be
26
3
vaporvapor
)J/kg 102174)(kg/s 5.1( =
hm
hm
fg
10-11
10-18 Water is boiled at 3344 kPa by a heating element sheathed in an ASTM B725 nickel-copper alloy tube. The tube
is immersed in the water horizontally. Determine whether the tube complies with the ASME Code for Process Piping if it is
used to boil the water at an evaporation rate of 1 kg/s. If not, the highest evaporation rate of water that can be achieved by the
heater is to be determined.
Assumptions 1 Steady state conditions. 2 Heat losses from the boiler are negligible. 3 Boiling regime is nucleate.
0.0284 ]1 2
(0.0060)(1767000)(0.836)1.0]3
Solving for the surface temperature yields,
0.0284 ]1 2
(0.0060)(1767000)(0.836)1.0]3
𝑞̇nucleate =1.2752×108W/m2
Note: The nucleate boiling assumption is appropriate. With Ts = 260°C, the excess temperature is ΔT = Ts – Tsat = 260 – 240
272.8°C. This is above the maximum use temperature set by the ASME Code for Process Piping. To comply with the code,
the evaporation rate of water will need to be reduced to 0.2267 kg/s or lower.
10-12
10-13
10-14
10-21 Water is boiled at sea level (1 atm pressure) and thus at a saturation (or boiling) temperature of Tsat = 100C by a
stainless steel heating element. The surface temperature of the heating element and its power rating are to be determined.
75.1Pr
N/m 0589.0
kg/m 60.0
kg/m 9.957
3
3
=
=
=
=
l
v
l
CJ/kg 4217
m/skg 10282.0
J/kg 102257
3
3
=
=
=
−
pl
l
fg
c
h
Also,
=
sf
C
0.0130 and n = 1.0 for the boiling of water on a stainless steel surface (Table 10-3 ). Note that we expressed the
properties in units specified under Eq. 10-2 connection with their definitions in order to avoid unit manipulations.
Analysis The density of water at room temperature is very nearly 1 kg/L, and thus the mass of 1 L water at 18C is nearly 1
kg. The rate of energy transfer needed to evaporate half of this water in 32 min and the heat flux are
2
kW 5878.0
s) 60(32
kJ/kg) kg)(2257 5.0(
=
=
=→==
fg
fg
t
mh
QmhtQQ
P = 1 atm
1 L
Water, 100C
Coffee
maker
10-15
10-22 Water is boiled at sea level (1 atm pressure) and thus at a saturation (or boiling) temperature of Tsat = 100C by a
copper heating element. The surface temperature of the heating element and its power rating are to be determined.
75.1Pr
N/m 0589.0
kg/m 60.0
kg/m 9.957
3
3
=
=
=
=
l
v
l
CJ/kg 4217
m/skg 10282.0
J/kg 102257
3
3
=
=
=
−
pl
l
fg
c
h
Also,
=
sf
C
0.0130 and n = 1.0 for the boiling of water on a copper surface (Table 10-3 ). Note that we expressed the
properties in units specified under Eq. 10-2 connection with their definitions in order to avoid unit manipulations.
Analysis The density of water at room temperature is very nearly 1 kg/L, and thus the mass of 1 L water at 18C is nearly 1
kg. The rate of energy transfer needed to evaporate half of this water in 32 min and the heat flux are
2
kW 5878.0
s) 60(32
kJ/kg) kg)(2257 5.0(
=
=
=→==
fg
fg
t
mh
QmhtQQ
P = 1 atm
1 L
Water, 100C
Coffee
maker
10-16
10-23 Water is boiled at sea level (1 atm pressure) and thus at a saturation (or boiling) temperature of Tsat = 100C in a teflon-
pitted stainless steel pan placed on an electric burner. The water level drops by 10 cm in 30 min during boiling. The inner
75.1Pr
N/m 0589.0
kg/m 60.0
kg/m 9.957
3
3
=
=
=
=
l
v
l
CJ/kg 4217
m/skg 10282.0
J/kg 102257
3
3
=
=
=
−
pl
l
fg
c
h
Also,
=
sf
C
0.0058 and n = 1.0 for the boiling of water on a teflon-pitted stainless steel surface (Table 10-3). Note that we
expressed the properties in units specified under Eq. 10-2 connection with their definitions in order to avoid unit
manipulations.
22
222
evap
23
evap
evap
W/m240,200=)m 42 W)/(0.0317547(/
m 03142.04/m) 20.0(4/
kW 547.7kJ/kg) kg/s)(2257 03344.0(
kg/s 003344.0
s 6015
m) 0.10 /4m) 0.2()(kg/m 9.957(
==
===
===
=
=
=
=
s
s
fg
AQq
DA
hmQ
t
V
t
m
m
Heating
P = 1 atm
Ts
100C
Water
10-17
10-18
10-25 Water is boiled at Tsat = 120C in a mechanically polished stainless steel pressure cooker whose inner surface
temperature is maintained at Ts = 128C. The boiling heat transfer coefficient is to be determined.
Assumptions 1 Steady operating conditions exist. 2 Heat losses from the heater and the boiler are negligible.
44.1Pr
CJ/kg 4244N/m 0550.0
=
==
l
pl
c
Also,
=
sf
C
0.0130 and n = 1.0 for the boiling of water on a mechanically
polished stainless steel surface (Table 10-3). Note that we expressed the
properties in units specified under Eq. 10-2 in connection with their
2
3
W/m900,116
44.1)102203(0130.0
0550.0
=
The boiling heat transfer coefficient is
CkW/m 14.6 2==
−
=
−
=⎯→⎯−= C W/m610,14
C)120128(
W/m900,116
)( 2
2
sat
nucleate
satnucleate TT
q
hTThq
s
s
Heating
128C
Water
10-19
10-20
