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radiant exhaust pipe heat into back of radiators


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#1 mariner

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Posted 28 November 2017 - 12:16

My, " toy" road car has a Chevy V-8 front mounted but well back from the front axle line. Side radiators are fitted each side of the engine fed from a plenum chamber in the nose.

 

The inside edge of each rad. is at the front of the block and they slope back at 20 degrees to the car's outside edge so the air is discharged out thru the same gap as the exhausts.  They are VW Golf rads.

 

So the exhaust pipes run close to the back of the rads ,about 100-120mm away for the front exhaust on each side. A bit like the 1970's F1 cars with side rads e.g Lotus 72/March 911 etc.

 

The cooling has always been marginal but I have largely fixed it with thicker diesel VW rads and better plenum chamber sealing. Now I have reduced the nose entry size for less drag etc and I am wondering if putting a heat shield  around the exhausts is worth the weight to stop pipe radiant heat soaking into the back of the rads?

 

It is road car with a pull thru fan on part of each radiator matrix.

 

Grateful for any thoughts/knowledge/suggestions.


Edited by mariner, 28 November 2017 - 12:25.


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#2 MatsNorway

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Posted 28 November 2017 - 18:09

Do it. Heat left in the engine bay is also a problem. Hot air in, hotter air out through the exhaust. Thus heating the engine bay ambient air.  If you get serious you should try and log the temps in the bay. you get some very cheap temp loggers with more than enough battery and plenty of resolution options.

 

I do not think the radiant heat is that big compared to the total energy going through the system tho.


Edited by MatsNorway, 28 November 2017 - 18:09.


#3 saudoso

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Posted 28 November 2017 - 22:46

If you're ducting the cooling flow already this might interest you:

http://www.ansys.com...formula-car.pdf

#4 mariner

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Posted 29 November 2017 - 19:19

Saudoso, thanks for the link, it is very interesting. Particularly how REDUCING the rad. duct entry size actually increases flow through the rad - due it seems to it "choking" less.

 

 

For what it is worth my rad layout is not strictly "ducted" as it relies on a large plenum chamber being formed in the nose space to supply high pressure air across the rad. front surfaces. To explain a bit, the intake is at the nose which is  a typical GT/NASCAR vertical apron below the lights, curving away to the sides. A splitter is fitted so, in theory, the intake is at the point of maximum dynamic pressure, and not in a turbulent, post wheel wake like most single seaters.

 

 

That is good but with rads either side of the engine it would need very long ducts to feed the rads. These ducts would be 150 cm long with a 35cm*35cm average cross section. My fear was that the large wetted area and small section would cause so much wall stalling that little effective  air would arrive at the rad face.

 

 

So instead I arranged the whole of the nose area to be a sealed plenum chamber. The roof is the bonnet underside and the sides are the inner wheel arches which slope into  form the outer  edges to the intake duct area .It took  lot of careful sealing  to maintain pressure but it has worked so far , even after I stuck a huge K and N filter  in it to pick up clean , pressurised air for the carb 


Edited by mariner, 30 November 2017 - 09:26.


#5 saudoso

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Posted 30 November 2017 - 19:04

The idea is that as per bernoulli, when you increase the cross section you get lower speed, higher static pressure air crossing the radiator.

Some attention is given to wall shape to avoid flow separation and turbulence.

I'm taking part in an CFD car competition and HX performance is a major factor. There's a lot to be gained with this kind of development.

And about sealing the plenum, the best results I got leaving a gap along the exchanger side like he mentions.

Edited by saudoso, 30 November 2017 - 20:01.