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There are different ranges of those small radiators. No, I won't be using those radiators specifically, they dont have sufficient pressure capability. just an example of what is out there .

 

But there are a range of like things for cooling electronics in harsh vibration environments.

but The motorcycle motoX radiators are the most likely - although it really requires a custom job because inevitably the inlets and exits are in the wrong place, and we want crossflow and most of the the motoX  are top to bottom, (some are X flow) . Still, brazing or tigging ally pipes into the aluminium is not difficult.

 

I dont have any practical feel for how the shapes of the tanks on a crossflow influence distribution of the coolant. Does anyone know ?

You see tapers on the tanks at the sides in some of the higher performance crossflows.

 

The radiator supplied with the LCH kit is a crossflow from a CBR1300 I think.

 

One can go deep core radiators, stacked but any of that is lower in efficiency than just more surface area as of course the air heats up as it passes the first cores. But better than nothign once you are out of available surface area and cant forget there is plenty of static pressure to push through multi cores. This is not thermo fan territory.

Temperature difference is king.

 

ANyway Skip, the 4 and 5" dia  lines up to a meter long are suitable for piping airflow with little pressure loss in our application and speed. Cant go below 4" ID. You could pipe the air directly to the radiator if you have trouble. I reckon getting that seal on core cowling will take a bit of work.

The seal has to be good (stable and rigid ) under a couple of inches of water pressure, which really is not many psi fractions.

But, let's see how your bird goes.  I think I calculated 18 liters of coolant was enough to start up, do a circuit and taxi and shutdown without exceeding 100 deg C. (in case of having no coolant cooling- just energy to heat up the coolant).

 

 

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Radiator cowling design is an extremely difficult subject and most of the work in this space was done in WW2. If you can find someone with a moderately good solutions it's probably the right one unles

Hi SKip That's all fine but the math doesnt lie.   AND the temperature difference between the inlet air to the radiator and the coolant temperature is a critical. If you heat the air hi

Geez Fella's, It's not a moon rocket or a race car. There are plenty of 912's around running too cold that need foam over a part of the radiator in winter.. Nev

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52 minutes ago, RFguy said:

--------------------------we want crossflow and most of the the motoX  are top to bottom, (some are X flow) . --------------------------

 

I

Why??

 

Please explained/expand.

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In my case I have generally, lots of space  in the horizontal plane, and little in the vertical plan, so cross flow will give me the most useful geometry from a number of cores perspective .

 

From what I read, getting even flow distribution  is more difficult the more pipes you have/longer the tanks. in the wide aspect cross flow, the tanks are short in length (height), and the number of pipes is less. 

I'm sure there is a expert here that can pipe up on this. 

 

If the resistance of the flow in each tube is low compared to the input pressure than the system should self balance.
IE long tubes in a cross flow will have higher individual pressure drop than short tubes. and thus they'll distribute more evenly.

 

But its not quite so simple- since there is variation in density, volume as the fluid goes from  hot to cold ! more reading required.

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I found a good paper to read

"Effect of non-uniform airflow on the performance of a parallel-flow heat exchanger considering internal fluid distribution"
document source : https://doi.org/10.1016/j.applthermaleng.2020.115685

 

Now, interesting  for this crossflow radiator (aspect = 1.38) square uniform side tanks, no special shapes) as the mass flow rate goes up, so does the variation in distribution of flow. and that the tubes in the middle suffer . 

A number of different aspect ratios was tested (width/height ratio), and non uniformity of flow distribution increases with reducing aspect ratio- so square is crap. and because of the pressure drops in the tubes becomign greater compared ot the in/out tank presssures as I'd expected (very similar to electricity and laws of current sharing) .

 

and when you take into account the effects of  non uniform airflow , then the radiator performance will decrease more quickly (and we are talking 4x difference for aspect = 0.7 to aspect = 1.4 ) This is significant. so use wide aspect ratios. 2:1 or better.

 

 

image.thumb.png.b2336b0c4a4c133160ef9e8e884c44aa.png

image.thumb.png.58d389d1ef981c0629ce60ed8b695985.png

 

 

 

 

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Ah! BUT orientation of the tank/tubes (ref your statement & my Q) should have very little difference on performance. You can pretty much put a Rotax radiator in any position and get the same efficiency SUBJECT TO GOOD AIR FLOW.

 

This holds good for all radiators - I have converted a Ford Falcon cross flow radiator (tank on each side horizontal tubes) to vertical (tank top/bottom tubes vertical - did the same job as when in in its previous orientation.

 

Radiator orientation has more to do with space availably than physics.

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Geez Fella's, It's not a moon rocket or a race car. There are plenty of 912's around running too cold that need foam over a part of the radiator in winter.. Nev

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6 minutes ago, onetrack said:

There's some useful cooling information (car-based) in the link below. A couple of the major factors in efficient cooling appears to be in fin design and tube shape. 

 

https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.824.1312&rep=rep1&type=pdf

Makes sense to me.

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You can acquire double or triple pass crossflow radiators, where the tanks have restrictions that divert the coolant flow to keep criss-crossing the core. These double or triple pass radiators are more efficient because they keep the coolant in the airflow for longer.

In too many radiators, the coolant flow is too fast to permit maximum coolant heat transfer. That's why removing a thermostat usually doesn't cure overheating problems, it usually only worsens them.

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15 minutes ago, onetrack said:


You can acquire double or triple pass crossflow radiators, where the tanks have restrictions that divert the coolant flow to keep criss-crossing the core. These double or triple pass radiators are more efficient because they keep the coolant in the airflow for longer.

In too many radiators, the coolant flow is too fast to permit maximum coolant heat transfer. That's why removing a thermostat usually doesn't cure overheating problems, it usually only worsens them.

Seem to me that most overheating problems, relate to lack of air flow, rather than coolant "speed".

 

Experimental set ups aside - got a cooling problem -  First check air flow restrictions then  external "core" blockage which  could be anything from damaged fins, insect or dirt build up.

 

Air flow restrictions - body damage/ accessories that partially block air flow - fix/remove. Paper/plastic/straw/etc - manually remove

 

Damaged/flattened fins  can sometimes be partially rehabilitated using a thin flat blade screw driver or even a bit flat metal out of a windscreen wiper GENTLY& PROGRESSIVLY  return the flatted fins to something like their original position.

 

Drive through a swarm of bees/grass hoppers/ blowing chaff/etc and your radiator leading surface is likely to become blocked in whole or part - best to reverse blow with compressed air (access can be a problem requiring removal of radiator).

 

Dust/chaff/insects can slowly build up over time progressively reducing radiator efficacy use above treatment. Sometimes using a brush with air to disturbed the material works best. Worst cases may require "rodding" with a flat wire such as found in some windscreen wiper refills.

 

Be careful about using high pressure water instead of air- very easy to damage radiator fins and sometimes the water will cause the material to swell preventing wash out.

 

After that consider a radiator flush to remove internal coolant flow restriction - the habitual use of tap /dam or contaminated water will eventually block internal cores.

 

Personally - when I have a fully functional radiator, on a ground vehicle/engine, I cover the inlet side with fiberglass fly screen material. The minimal air flow restriction that the fly screen imposes is nothing compared with the above scenarios - Leave the bottom of the fly screen loose, the continually movement in the air flow will tend to "shed" insect bodies & the like. I have not had an overheating problem, due to a contaminated radiator in 45 + years of driving & maintaining.

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