Chapter 10
Boiling and Condensation
1027E
Water is boiled at a temperature of
T
sat
= 250
°
F by a nickelplated heating element whose surface
temperature is maintained at
T
s
= 280
°
F. The boiling heat transfer coefficient, the electric power consumed,
and the rate of evaporation of water are to be determined.
Assumptions
1
Steady operating conditions exist.
2
Heat losses from the boiler are negligible.
3
The
boiling regime is nucleate boiling since
Δ
TTT
s
=
−
=
−
=
°
sat
F
280 250
30
which is in the nucleate boiling
range of 9 to 55
°
F for water.
Properties
The properties of water at the saturation temperature of 250
°
F are
(Tables 101 and A9E)
ρ
σ
l
v
l
=
=
==
=
5882
0 0723
0 003755
01208
143
.
.
..
.
lbm / ft
lbm / ft
lbf / ft
lbm / s
Pr
3
3
2
h
fg
l
pl
=
=⋅
°
lbm
/ h ft
t
u
/
l
b
m
F
T
s
=280
°
F
Water
250
°
F
946
0556
1015
Btu /
lbm
C
B
μ
.
.
Heating element
Also,
g
= 32.2 ft/s
2
and
0.0060 and
n
= 1.0 for the boiling of water on a nickel plated surface (Table
103). Note that we expressed the properties in units that will cancel each other in boiling heat transfer
relations.
C
sf
=
Analysis
(
a
)
Assuming nucleate boiling, the heat flux can be determined from Rohsenow relation to be
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 Fall '10
 Dr.DanielArenas
 Thermodynamics, Mass, Power, Heat, Heat Transfer, Nucleate Boiling

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