James, I certainly wasn't singling you out, just want to be clear on that.
Those numbers were just some average coefficients for stock materials that I
grabbed real quick. The numbers themselves aren't all that meaningful,
and it appears that they were miss represented. Based on looking again,
they are conduction coefficients not convection. As you know, conduction is
a material property; the overall heat transfer of a radiator would be
dependant on the system as a whole not just a material.
In terms of materials we are talking about, conduction coefficients are
Aluminum 237W/m^2*K
Brass 120
Air .025
Copper 401
Lead 35.3
Nickel 90.7
Tin 66.6
Steel 45-65
>From http://hypertextbook.com/physics/thermal/conduction/
Of course the efficiency of the entire radiator is based on the individual
properties, thicknesses, and contact resistances. Without turning this into
homework the greatest contact resistance is between the surface and the air,
and it becomes very important to maximize that. That was my only point.
As a few people have mentioned, successive cores in a radiator get less
efficient because by the time the air gets to the rear cores the temp has
gone up too much and drives the heat transfer down. Other ways to improve
heat transfer are:
Add surface area exposed to ambient temp air with fins, tubes, whatever.
Increase airflow, as we've already discussed.
Use more efficient materials.
Unfortunately I have to get to a meeting, but I loved your comments about
the 90deg fan drive on a FWD car. I'm sure that somewhere in automotive
history that got tried with some very interesting results.
James Nazarian
71 MGBGT V8
71 MGB Tourer
87 BMW 325es
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