Subject: [FlyRotary] Re: Thick vs Thin


> Posted for <daveleonard@cox.net>:
>
> Good point bill, there are lots of other important factors.  But this
> disussion is about thick vs thin.  Metal, coolant, air , and fin qualities
> have to be judged separately.  I am assuming these qualities are the same
> thick and thin.
>
> As far as delta T being smaller for thin rads, you miss one of the main
points
> in the example above.  Slow down the air in the thin rad and it collects
the
> same amount of heat that the thick rad delivers.  No matter how thin, slow
> down the air enough and the delta T is the same.  All factors can be set
to
> the same - coolant heat loss, delta Tair, mass of intake air, weight of
the
> radiator etc.  The only major differences are speed of the air and thus
the
> drag of the air through the rad.
>
> Dave Leonard

Didn't introduce this earlier because the discussion is complicated enough
without adding more factors.  But, this is a major factor and its time has
come.

The 'drag through the radiator' is caused by a very necessary factor -
turbulance.  Turbulance is a huge factor in how much heat will be transfered
to the air from the fins.  Low velocity will result in low heat transfer.

Another way of putting it is that generating turbulance through the rad is
the very best use of the energy in the high speed air we snagged.  The
energy not used by moving the air slowly through a thin rad helps in
re-accelerating air at the outlet but the disadvantage of requiring a higher
volume of air more than offset this small advantage.

I'm sure this debate will not be settled until we can have a side by side
comparison of the two approaches with all other factors being the same.  You
guys with the thin rads hurry up and finish your planes so we can have a
"fly-off"!

Tracy Crook