X-Mozilla-Keys:                                                                                 
Russell Kent wrote:

Rotating the tubes slightly will probably help both heat transfer and
reduce air pressure loss.

Paul Lamar

You'd want the tubes to face into the relative wind in order to minimize the
airstream turning.  Presumably the relative wind within the duct is pretty
darn close to the axis of the duct.

Russell Kent

Yes I agree. You also want turbulent air contact with both sides
of the tube. If one side is laminar and the other is stalled
it might be less efficient in terms of heat transfer.
We need to study this on a micro level. The fins could
also be saw tooth shaped. To optimise this thing might require
a lot of experiments. 

I  just thought of another use
and that is in the air conditioning industry. I think they would
apreciate a low air pressure loss compact heat exchanger with 
this form factor (shape). It would be a waste of time and money for
car engine cooling but might be useful in the car air conditioning
system.
 
Paul Lamar
 
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