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Chapter 9
Natural Convection
977
A vertical plate in water is considered. The forced motion velocity above which natural convection
heat transfer from the plate is negligible is to be determined.
Assumptions
1
Steady operating conditions exist.
Properties
The properties of water at the film temperature of (
T
s
+
T
∞
)/2
= (60+25)/2 = 42.5
°
C are (Table A15)
υ
β
=×
=
−
065 10
0 00040
6
.
.
m/
s
K
2
1
Analysis
The characteristic length is the height of the plate
L
c
= L =
5
m. The Grashof and Reynolds numbers are
∞
−
∞
∞
−
∞
×
=
×
=
=
×
=
×
−
=
−
=
V
V
L
V
L
T
T
g
Gr
s
6
2
6
13
2
2
6
3
1
2
2
3
10
6
.
4
/s
m
10
65
.
0
)
m
5
(
Re
10
063
.
4
)
/s
m
10
65
.
0
(
)
m
5
)(
K
25
60
)(
K
0004
.
0
)(
m/s
81
.
9
(
)
(
Water
T
∞
= 25
°
C
V
∞
Plate,
T
s
= 60
°
C
L
= 5 m
and the forced motion velocity above which natural convection heat transfer from this plate is negligible is
m/s
2.62
=
⎯→
⎯
=
×
×
⎯→
⎯
=
∞
∞
V
V
Gr
1
.
0
)
10
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This note was uploaded on 01/24/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.
 Fall '10
 Dr.DanielArenas
 Thermodynamics, Convection, Force, Mass, Heat

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