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Neil K wrote:

Paul,

        You are correct in saying the second rad would have a 15%
less temperature drop from the first however, in the big
picture this equates to only a 2.25 degree difference.

        Given your example of 100 degree delta T and that this
delta T doesn't change over time (the engine is producing
heat at a constant rate and the ambient air remains at the
same temp, and all flow rates remain the same) the
percentage of heat removed will remain the same.  Your
example shows a 15% heat change (15deg drop of 100deg delta
coolant) through the first rad.

        The second rad starts with coolant at 85deg delta.  15% of
85 is 12.75, or , the second rad drops the water temp
another 12.75deg.  If the 2 rads were in parallel the total
drop would be 30deg.  In series the total drop is 27.75
degrees or 2.25 % less than parallel.

        To me, this is an acceptable trade-off considering
installation issues of not requiring Y pipes. Less hose,
Less clamps. Less water. Less weight.  And the entire
installation requires less space.

        Another issue is there are no flow balancing problems to
worry about with a series configuration since all the
coolant must go through both rads.  On Jim's installation we
found the right rad was always favored (ran hotter) over the
left.  We added a control valve to the right rad which
helped but without very accurate temp probes places all
over, we couldn't guarantee a good balance.  Also, the valve
added even more weight and more clamps.  We switched the
rads to series and the overall cooling improved
considerably.

        We could have added thermostatically controlled valves to
better maintain equal flows but again... that would be a lot
of complexity for very little gain.  It would be simpler to
make the rads 3% larger in size.

        As far as the air inlet bell shape is concerned, the left
and right are identical.  The camera angle probably makes
them look different.  If cooling the water is still a
problem for me, I can change the shapes.  As it turned out,
building those ducts was a fairly simple task.

Neil

Well the proof is in the pudding. I hope your analysis is correct
and we will finally see you at Sun & Fun if not Copper State.
A rotary powered Lancair 240/320 should have no problem averaging 200 MPH
in the cross country races to win the Everett Hatch Memorial $500 (U.S.)
prize. Heaven knows you have earned it for perseverance alone.

BTW what are the origin of those new rads we are looking at in your
pictures?

Paul Lamar
 
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