Homework 6 – Due Wednesday, September 29
th
1. Consider the chip we discussed in class. We used a correlation such that
Nu
x
=
0.04
Re
x
0.85
Pr
1/3
.
We were
able to use this local correlation not because the chip was so small (4 mm X 4 mm) but that the object was
not far from the leading edge (120 mm in) , i.e. the L is 120 mm.
a) Find an average coefficient and see if the assumption was valid.
b) Calculate the local and average coefficient if the chip is placed 600 mm from the leading edge. Would
it be safe to assume they can be used interchangeably?
2. A fan can provide air speeds up to 40 m/s is used in a wind tunnel with air at 25
o
C.
a) What is the minimum plate length that can be used to study boundary layer behavior up to Reynolds
numbers of 10
8
?
b)
At what distance will transition occur?
c) Using a spreadsheet, generate lengths between .01 and .2 meters and calculate the Reynolds numbers
for these lengths. Knowing the Re
x,c
and the x
c
, see if there’s a relationship between the two lengths and
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 Fall '10
 DEGRAZIA
 Heat Transfer, heat transfer coefficient, 2 mM, 12 mm, 20 M, 3 m/s

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