Example 61
Stainless steel parts (AISI 304) are heated in a furnace to
a temperature of 850°C. Each part is brickshaped with a
height of 1 cm, a width of 1.5 cm and a length of 2 cm.
The parts leave on a conveyor belt traveling at 3 cm/s and
are cooled by air at 20°C. The convective heat transfer
coefficient between the parts and the air is 138 W/m
2
·°C.
How far must a part travel from the furnace exit before it
reaches 100°C? Assume the side of the part resting on
the belt is perfectly insulated and the other five sides are
exposed to the convective cooling.
Solution:
Check to see if the lumped system approximation is valid.
Calculate characteristic length as
( )( )( )
()
() ()
2
1.5cm
1.0cm
2.0cm
1.5
2.0
2 1.5
1.0
2 2.0
1.0
cm
char
V
L
A
==
++
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 Spring '08
 BORCATASCIUC
 Heat, Heat Transfer, 1 cm, 2 cm, 1m, 2.0 cm

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