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

ACRE NL web site. http://www.rotaryeng.net