On Sat, 18 Aug 2012 22:05:11 -0700, Jeff Liebermann
wrote:

On Sat, 18 Aug 2012 12:59:41 -0700, John Larkin
wrote:

I have this theory that the fins of a heat sink should reduce a fan's
free-flow rate by 50% for optimum heat transfer.

If the input and output temperatures were the same, that might be
true. It might also be true if you consider the reduction in free
flow rate caused by the back pressure due to the head sink obstructing
the air flow.

However, air expands when heated, causing an increase in air flow at
the exhaust end.

Not enough to matter. The expansion goes as absolute temperature.

That's why the exhaust port for a heat removal
system is larger than the intake.

There's no advantage to making an inlet port bigger than the fan that
site there. Disadvantage, if it would let air leak out. But an outlet
port restricts flow, so make it big.



--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

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