Chapter 4
Transient Heat Conduction
436
Large brass plates are heated in an oven. The surface temperature of the plates leaving the oven is to
be determined.
Assumptions
1
Heat conduction in the plate is onedimensional since the plate is large relative to its
thickness and there is thermal symmetry about the center plane.
3
The thermal properties of the plate are
constant.
4
The heat transfer coefficient is constant and uniform over the entire surface.
5
The Fourier
number is
τ
> 0.2 so that the oneterm approximate solutions (or the transient temperature charts) are
applicable (this assumption will be verified).
Properties
The properties of brass at room temperature are given to be
k
= 110 W/m.
°
C,
α
= 33.9
×
10
6
m
2
/s
Analysis
The Biot number for this process is
Bi
hL
k
==
°
°
=
(80
)( .
)
()
.
W/m . C
m
W/m. C
2
0015
110
0 0109
The constants
λ
1
and
A
1
corresponding to this Biot
number are, from Table 41,
11
01039
10018
..
and
A
The Fourier number is
τ
α
××
=>
−
t
L
2
6
339 10
10
90 4
0 2
(.
m / s)(
min
60 s / min)
m)
2
2
Plates
25
°
C
Furnace,
700
°
C
Therefore, the oneterm approximate solution (or the transient temperature charts) is applicable. Then the
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 Fall '10
 Dr.DanielArenas
 Thermodynamics, Mass, Heat, Heat Transfer, Biot, transient heat conduction, oneterm approximate solutions, transient temperature charts

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