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Fred wrote:

some snips
In addition to defining the design methodology (which I encoded into an Excel
spread sheet) it has lots of good data for various fin designs.  From this
one can deduce the most efficient fins (that is best heat transfer per unit
horsepower expended) are those that are straight and interrupted every 1/8 of
an inch to provide lots of sharp leading edges to the flow, but no flow
direction changes in the fins. I found an aerospace heat exchanger shop in
Gardena that makes units with the preferred fin design.  Expensive ($800-1000
for a radiator) but on aircraft, what's new.

First cut on Marv's radiator showed optimum at about 16-18 fins per inch. I
plotted drag versus fins spacing and fin height and got some interesting
curves (all based on 15,000 foot cruise).  Speed and altitude have a lot to
do with what the optimum looks like.

I recently completed a test series for Marshall Michaliean who is sponsoring
the development of the Eagle 540 engine (big block V-8, from scratch) for a
Lancair IV.  He had a NASCAR radiator built that used a louvered fin design.
That is, the fins were W shaped, and had lots of little louvers perpendicular
to the flow direction, a dozen or so one way, then a dozen or so the opposite
way.  No data in Kays and London, so we got a little one built, I built a
test rig, pumped hot water through it, varied air flow rates, and plotted the
results in same format as Kays and London (Stanton number versus Reynolds
number for nondimensional data, also plotted friction factor).  Results; good
heat transfer performance, but with pressure drop much higher than straight
fin interrupted designs.  Difference was about 14 pounds drag in cruise as I
recall, worth about 9 knots on Marshall's plane.  So we are changing the
radiator design.

As I do more and more analysis, I am moving towards a "summary" of
recommended guidelines that I plan to publish someday with some curves, rules
of thumb, etc.  The heat exchanger design process is a highly arcane art with
lots of tradeoffs and about 8 key variables all interacting, so it is easy to
get lost.  I will try to simplify through guidelines for frontal area per
horsepower at various speeds, etc.

The key right know is to know what the energy balance is around the Mazda
engine.  With the information you sent, I can make a better pass at it.  I
will forward to you and Marv when done.

Fred

I am very excited to have Fred join our group.  It's only too bad he wasn't
here a couple months ago when we we debating the merits of various HX
configs to death.  Would you share your spreadsheet.  Even if the average
layman can't use it, I hope I can.  I actually forgot most of what I
learned in my ASME HX course but maybe the spreadsheet would help.  I am
most interested in your findings about  commercial/auto cores vs.
straight finned.  I like the idea of lower cooling drag.  Please post
whatever you've got and don't worry about being too technical.  This group
is very thirsty for the heavy duty technical stuff.

Jeff Spitzer

I second that Fred.

Paul Lamar
 
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