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MAE 412
th
Ed)
Cautions:
1.
Always keep in mind the difference between local and average correlations.
2.
The definition of the Reynolds No. varies with different applications, as does
the critical value for the onset of turbulence.
3.
Externalflow convective correlations generally use T
f ,
the film temperature;
internalflow convective correlations use T
m,avg
, the avg mean temp of the
fluid.
4.
Sometimes a problem can’t be started until an initial guess is made about the
temperature to use for fluid properties.
In that case, select an arbitrary
temperature for use in looking up properties, but select one that is reasonable
for the problem.
The results of the ensuing calculations will allow you to
make a better estimate of the fluid properties, and another iteration can then be
made on the problem.
5.
Sometimes it helps to initially assume a wall temperature, make calculations
on that basis, then use the results to refine your heat transfer calculations with
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 Spring '08
 Terry
 Fluid Dynamics, Eqn, Nux Eqn, local correlations Cf,x, Laminar flow NuL, average correlations

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