Paul,

  Thanks for your book it's an interesting read.
  I have put together a quick layout of how I would like to do my belly
  mounted radiator.  The attached pictures I hope explain what I am
trying to  accomplish.  You mention a separation of about 2" from
the belly for boundary layer  separation, does this have to extent
the entire length of the radiator or is  the way I show it ok?  I
didn't see anything that gave me a frontal opening size relationship
to  the area of the radiator, is there a percentage rule of thumb
for this?  Any other suggestions on what I'm showing to improve
would be appreciated.

  Randy

  Excellent illustrations Randy. Reduces the frontal area over the
  splitter plate idea and is far more cosmetic. A Canard P51.

  Is that Solid Works or Rhino 3D?

  You will still need the Kays & London wedge inlet diffuser page 36.
  Also you will need to take the bottom panel off as it will
  retard the hot air flow out from the front back side of the
  rad page 46. If you just lower the panel it will add frontal
  area. Not good. Just do away with it and let the hot air
  dump into that air stream.

  I would use Venetian blind cowl flaps page 51.

  I found the dims on the Neon rads I have. Here they are.

  The rule of thumb is 20% of the frontal area of the rad.
  With the P51 style scoop you are committed :) I dislike
  commitments all my old girlfriends used to tell me :)

  Paul Lamar

  Randy,

  I see you have shown two radiators.  Are you going to use
  both of them somehow?

  Doug in Japan.

  Yes. I was going to build a cross counter flow  rad (book  page 25
)  for testing but that is now far down on the priority list as
Perry Mick  has already tested it and it works well. If you are
pressed for  space it is worth it.

  Paul Lamar

  --

Paul

For years I was excited about that cross counter flow design you
introduced and actually did drawing to incorporate it under my
engine. That is until I read a comment last year on Stewart
Component websites claiming the such setup increase the back
pressure  and therefore flow significantly.

http://www.stewartcomponents.com/tech_tips/Tech_Tips_5.htm

I don't believe the longer effective water passages it will increase
pressure 16 times but it will be significantly more than double.
 This got me thinking about some to the water flow challenges I have
had in my line of work.  In essence, when the  water channels
lengthen or  restrictions are increased,  the effect of back
pressure on flow will rise in a  non linear fashion.

In a water heat exchanger, high velocity enhances turbulence, thus
wall contact time.  Velocity is upper limited by restriction and
internal pump fluid slippage.   Engine pumps are centrifugal
 devices hence produce highest flow when the system has the  least
restriction.  Said another way, maintain as high as water flow as
possible through the engine.  To get  300hp out of the 13B engine
I'll need,  according to Jim at Racing Beat, the man who's been
there, at least  40 gals a minute water flow. Choke the flow
anywhere in the system and pumping rate falls off as water pressure
goes up. Knowingly increasing the water pressure may not be a good
thing for thin wall items tending to corrode over time.

For comparison purposes oil heat exchangers have positive
displacement pumps, have to squirt  a viscous liquid through
inherently small openings  and thus have a slower flowing, robust
heat exchanger in need of built-in turbulators and must be able to
withstand high pressures..  Many oil heat exchangers are designed to
be cross flow because the characteristics of wall contact time are
enhanced by the slower flow. Oil  by nature as you know is less
thermal conductive than water.

This discussion basically boils down to whether it is more prudent
to have a single thick core thick radiator or two thinner ones in a
reverse crossed mode RCM like you have shown.   Actually I have
found that when the air gap between the two radiators in the reverse
cross flow is taken into account, the total installed package is
thicker than a single thicker unit.

Paul your thoughts that  proper air flow through heat exchanger is
 paramount and on that I wholeheartedly agree.  I'm not so sure the
old rule of the first 1/4 of the radiator does 50% of the cooling is
correct anymore however.  That would depend on fin count air
resistance, tube design, number of  rows and how well the unit is
maintained.  A clogged heat exchanger is as good as the dirt it
catches.    Dave Garber showed me a very compact  design unit he had
made that used two rows of  the newer  overside elongated tubes.
 These are about 1.5 in" in length but  essentially the same
standard width. The Dave Garber design installed package thickness
came out to about 2.5 inches.  compared to close to 4 inch thick for
a similar RCM design.  That is assuming a one inch air gap between
the heat exchanges  helps isolate infrared heat transmission.

In Dave's design, air flow had to traverse about three inches to get
through it though.  The tubes were angled as was the heat exchanger
so air flow was actually parallel to the fins and that might be a
deciding factor in the high performance he experienced.   So high
that he had to cover up the first few inches of it as you can see by
the photo. His  heat exchanger wetted area is about 12 inches tall
by 28 inches long.  .  Thats my 8cm x 11cm (3.1/8" x  4 3/8") wallet
in the foreground for scale purposes.

I will try an identical system but lay it on its side under the
engine and make it 16" wide (max 20" with the side tanks included)
by 19" or 20"  in depth.  I 'm not sure how to angle or curved the
side tanks to help insure even flow distribution though.  Logic
dictates at center inlet and outlets with the tanks sides curving
out toward the ends. Understanding how fluids  flow is hard to
predict other than it takes the path of least resistance.

Doug in Japan

Well apparently Stewart did not read Kays & London's bible Compact
Heat Exchangers  :)

==========================================================================
   "The design of a heat exchanger involves a consideration of both
the heat transfer rates between the fluids and the mechanical
pumping power expended to overcome fluid friction and move the
fluids through the heat exchanger. For a heat exchanger operating
with high-density fluids, the friction-power expenditure is
generally small relative to the heat transfer rate, with the result
that the friction-power expenditure is seldom of controlling influence."

[What they are saying here is the HP consumed by the water pump is
of minor importance. In fact the Mazda pump only consumes about 3 HP.]

"However, for low-density fluids, such as gases, it is very easy to
expend as much mechanical energy in overcoming friction power as is
transferred as heat."

[What is being said here is HP is consumed by cooling drag. Since
cooling drag can be as high as 30% of over all drag the HP could be
as much as 30% of 200 HP or 60 HP. As you can see cooling drag
becomes a very important issue.]

"And it should be remembered that in most thermal power systems
mechanical energy is worth 4 to 10 times as much as its equivalent
in heat."

[Here they are referring to the heat balance of most internal
combustion engines that only derive about 25% to 10% of the heat
energy in a gallon of fuel as mechanical HP.]

==========================================================================

Builders have done some really dumb things like use electric water pumps
with 1/10 the HP and got away with it. The early Mazda pumps, many people
still use, have a restricter in them. Mazda woke up with the RX8 pump.

You need my book or Kays & London's book Doug :)

Paul Lamar

Doug,
As you stated, water will flow the path of least resistance. If you put both
inlet and outlet in the middle of the respective tanks, the flow will want to
pass through the center few tubes. The correction would be to put a difuser in
one (inlet) tank to force some flow to the edges. More weight and restriction.

It would be better to put connections on opposite sides and the flow will even
out on it's own. Geothermal installs do this by hooking up the loops so the
closest to the supply is connected the farthest from the return on the
respective headers.

Years ago, Caterpillar radiators had the tubes angled slightly so that the air
passinng between two tubes in one row was directed at the side of a tube in
the row behind. The tubes were only angled something like 10 degrees. The
problem they had is with traping dirt and debris. In that application it is
hard to design to shed the dirt. AC applications should not have a big problem
with that.

Dale Davies