X-Mozilla-Keys:                                                                                 
Fredmoreno@aol.com wrote:

Paul:

Nope, never saw such a beast, but my knowledge is limited.  Interesting idea.
 As in all things, we face trade offs.  We need limited frontal area, a large
heat exchanger frontal area, thin heat exchanger, good diffuser, and good
flow distribution all packaged within the confines of a small pointy cowl.
Sacrifice one, and get nailed on the other(s).  It sets a mind to pondering.
So far inclined radiators seem to be preferred in many applications, but that
is because one thinks in terms of flat heat exchangers.  Why?  Well, Why NOT?
 Keep the gray matter churning.

Here are some key factors to keep in mind when brainstorming:

1) The area of the heat transfer surface on the air side should be about 5
times that on the coolant side to get the best balance of pressure drop,
power consumption, and heat transfer coefficients.

2) With oval tubes, one needs to support the structure because the oval tubes
try to become round when pressurized and try to blow the core apart.  That is
why oval tube heat exchangers usually have a structural channel on either
side of the radiator, to keep the thing from swelling out as the tubes try to
go round.  Bending loads in the channel are carried into the tanks which
absorb them as tension loads.  Exception is the oval tube heat exchanger made
by punching oval tubes into flat plates which become the fins, and the tubes
are inserted through all the plates.  In this case the flat plates hold the
tubes oval because they extend all around the tube and carry the tension
loads.

3) If you read near the back of Chapter 2 in Compact Heat Exchangers which
includes the figures of the various header designs (figures 2-42 and text on
pages 41-42) the authors write:

"Figure 2-42a describes a folded core concept used to reduce header volume.
However, if the pressure drop across the core is not uniform, as in the case
of the 2-42a configuration [they don't say why, but I suspect it is because
the velocity is high and pressure low at inlet and velocity low and pressure
high at the bottom of the V as you found in your oblique test rig], the flow
distribution over the heat transfer surfaces will not be uniform, and a
penalty in heat exchanger performance is the result.  From this viewpoint,
the design objective is to provide for acceptably uniform flow through the
core with an acceptable header geometry and flow-stream mechanical energy
losses.  Uniformity of flow distribution over the core face is the dominating
function of the headers. ... A poor header configuration may actually result
in a lower overall pressure drop, but the penalty in heat transfer
performance can be very large."

I think our efforts might be best expended in trying to come up with good
diffusers behind oval chin scoops that feed inclined radiators with uniform
flow.  This may require an array of turning vanes mounted on the face of the
radiator to make the final turn into the radiator and provide the necessary
uniformity of flow.

I am crunching numbers for Mike Wills planned 13B installation in a 13 B and
will summarize them on a table I will compile tonight.  I will forward this
to you and Mike and will ask the assembled masses to do sanity check on the
heat flow numbers to make sure I am in the ball park.  Then we will have some
size versus pressure drop figures to play with.

Fred

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