10–61
10–71 Saturated ammonia vapor condenses on a vertical ASTM A240 410S stainless steel plate at 190 kPa. The highest
rate of condensation that can be produced by the plate, without cooling the plate below the minimum suitable temperature set
by the ASME Code for Process Piping, is to be determined.
Assumptions 1 Steady state conditions. 2 The plate is isothermal. 3 The condensate flow is wavy-laminar over the plate. 4
The vapor density is much smaller than the liquid density.
(2.492×10−4)(1359500)(9.81
(3.711×10−7)2)1 3
The Reynolds number is 30 < Re < 1800, so the assumption for wavy-laminar flow is verified. The condensation heat
1.08 Re1.22 −5.2(𝑔
𝜈𝑙2)1 3
1.08(1151)1.22−5.2(9.81
(3.711×10−7)2)1 3
The rate of heat transfer on the plate during the condensation process is
0.107 kg/s. If the condensation rate is above 0.107 kg/s, it would increase the heat transfer rate on the plate. This would
10–62
10–63
10–73 Prob. 10-72 is reconsidered. The effects of plate temperature and the angle of the plate from the vertical on the
average heat transfer coefficient and the rate at which the condensate drips off are to be investigated.
Analysis The problem is solved using EES, and the solution is given below.
“GIVEN”
T_sat=100 [C]
g=9.81 [m/s^2]
“ANALYSIS”
“(a)”
Ts
[C]
h
[W/m2.C]
cond
m
[kg/s]
40
42.5
45
47.5
50
52.5
55
57.5
65
67.5
85
87.5
90
4212
4272
4334
4398
4464
4533
4605
4680
4929
5023
5984
6213
6500
0.4165
0.406
0.3951
0.3839
0.3722
0.3601
0.3476
0.3346
0.2929
0.2779
0.1561
0.1355
0.1138
4500
5000
5500
6000
6500
0.15
0.25
0.3
0.35
0.4
0.45
10–64
10–65
10–66
10-75 The rate of condensation and the heat transfer rate for a vertical pipe, with specified surface temperature, are to be
determined.
Assumptions 1 Steady operating condition exists. 2 The surface has uniform temperature. 3 The pipe can be treated as a
vertical plate. 4 The condensate flow is wavy-laminar over the entire tube (this assumption will be verified). 5 Nusselt’s
7.729
)10326.0(
81.9
)102314)(10315.0(
)80100)(675.0)(1(70.3
81.4
)(70.3
81.4Re
820.0
3/1
2633
820.0
3/1
2
sat
wavyvert,
=
−
+=
−
+=
−−
lfgl
sl g
h
TTLk
K W/m6633
)/sm 10326.0(
2.5)7.729(08.1
2.5Re08.1
2
=
−
−
l
Then the rate of heat transfer during this condensation process becomes
−=
)(
2
sat
s
TTDLhQ
10–67
10-76 Saturated steam at a saturation temperature of Tsat = 55C condenses on the outer surface of a vertical tube which is
maintained at 45C. The required tube length to condense steam at a rate of 10 kg/h is to be determined.
C W/m644.0
CJ/kg 4181
/sm10554.0/
skg/m10547.0
kg/m 1.988
26
3
3
=
=
==
=
=
−
−
l
pl
lll
l
l
k
c
1/3
vertical,w avy 1.22 2
1/3
2
2
1.22 6 2 2
Re
1.08Re 5.2
215.5 (0.644 W /m C) 9.81 m /s 5644 W /m C
1.08(215.5) 5.2 (0.554 10 m /s)
l
l
kg
hh
n
–
æö
÷
ç÷
ç
== ÷
ç÷
ç÷
ç
–èø
æö
´ ×° ÷
ç÷
ç
= = ×°
÷
ç÷
ç÷
-´
èø
The rate of heat transfer during this condensation process is
W664,6)J/kg 10kg/s)(2399 3600/10(3* === fg
hmQ
Steam
55C
Condensate
Ltube = ?
D = 3 cm
10–68
10–69
10-78 Saturated vapor condenses on the outer surface of a 1.5-m-long vertical tube at 60°C that is maintained with a surface
temperature of 40°C. The rate of heat transfer to the tube and the required tube diameter to condense 12 kg/h of steam are to
be determined.
10–70
10–71
10-80 Saturated ammonia vapor at a saturation temperature of Tsat = 10C condenses on the outer surface of a horizontal tube
which is maintained at –10C. The rate of heat transfer from the ammonia and the rate of condensation of ammonia are to be
determined.
10–72
10–81 Saturated R-134a vapor condenses on a horizontal ASTM A268 TP443 stainless steel tube at 133 kPa. Determine
whether the tube would comply with the ASME Code for Process Piping if the condensation rate of R-134a on the tube
hfg= 213.0 kJ/kg, ρv = 6.787 kg/m3.
At the film temperature, Tf = (−20 − 30)°C/2 = −25°C,
cpl = 1283 J/kg∙K, kl = 0.1047 W/m∙K, ρl = 1374 kg/m3, μl = 3.882 × 10−4 kg/m∙s
Analysis The modified latent heat of vaporization is
ℎ𝑓𝑔
10–73
10–74
10-83 There is film condensation on the outer surfaces of N horizontal tubes arranged in a vertical tier. The value of N for
which the average heat transfer coefficient for the entire tier be equal to half of the value for a single horizontal tube is to be
determined.
Assumptions Steady operating conditions exist.
N
h
2
4/1
tube1 ,horizontal
10–75
10–76
10–85 Saturated steam at a pressure of 4.25 kPa and thus at a saturation temperature of Tsat = 30C (Table A-9) condenses on
the outer surfaces of 144 horizontal tubes arranged in a 1212 square array maintained at 20C by circulating cooling water.
The rate of heat transfer to the cooling water and the rate of condensation of steam on the tubes are to be determined.
Assumptions 1 Steady operating conditions exist. 2 The tubes are
10–77
10–78
10–79
10–80