Question about Chimneys for cooling

[SavantGuarde]

Hi all new poster here and hopefully there is someone who can help me with a problem.

I race superkarts (http://spearmotorsports.com/superkart.aspx contians some nice pictures if you have no idea what one is) and I have a minor problem which I wonder if an f1 style chimney could fix.

The real problem is all my aerodynamic books do not contain information regarding chimneys and the web seems to lack an in-depth explanation to what actually is going on and how they achieve the desired effect.

If anyone could point me to a resource or provide a simple diagram showing rough principles (shapes angles etc ) that would be really benificial.

The possible application of the chimney is to help the airflow through the radiator. At the moment there is no ducting on the other side of the radiator at all which isnt really condusive to efficient flow. There is no room to fully duct the radiator but as an experiment I want to seal it off and use a vertical chimney to see if it improves flow. before doing anything I need to know how these things work

Thanks for any help in advance

[West]

I left my aero book at work, but here are a few basic concepts.

If you look at the kart from overhead, a chimney may be shaped like a teardrop to provide less sensitivity to side winds. A few years ago F1 teams would also position chimneys such that the low-pressure area of winglets help extract the hot air.

[aeronut]

Welcome to the forum. There is a large association of people here with an amazing collective memory for F1 information. You might want to check out what Craig Scarborough has written here:

http://scarbsf1.com/cooling.html

[Jersey Tom]

The first step would be to figure out specifically what the problem is, before throwing things at it to fix it.

Hard to tell.. but it doesn't look like there's good ducting of any sort to that rear radiator and its in a position for bad airflow. Its massive though, bigger than a 600cc sportbike rad.

[SavantGuarde]

Sorry I should have been a little more specific as there are a lot of photos on that site and actually that kart has two radiators instead of one!

The radiator behind the seat is typically used for twin-cylinder variants of the superkarts that require extra cooling. I agree these radiators are in a bad position and not even coming close to the full cooling potential. There are a lot of aerodynamic problems with these machines (most notably the large lump in the seat with the crash helmet on) but we only have very limited testing opportunities and little in the way of fabrication and protoyping. For the single cylinder karts (which I race) we only use the sidepod radiator.

The radiator we are thinking about the chimney for, is the one in the left (from the drivers perspective) side-pod. This rad is ducted into the radiator surface(quite a large rad too as i'm sure you can see in these two images: )

But there is no actual ducting OUT of the radiator. Any air that passes through it just passes into the kart and the seat / chassis etc. No flow whatsoever. What we are proposing to test is a simple box on the other side of the radiator and an experimental f1 style "chimney" to see if this arrangement improves airflow and the engine temperature overall.

Thanks for the sources and comments thus far I think I have a good idea of what arrangement to use. It will be very simple and interesting to see if it works.

[Jersey Tom]

To take advantage of a chimney you need a nice low pressure air zone to give some pressure differential and suck the air out. Could get the same effect with some louvres (sp?) or naca ducts. The latter would probably be more cost effective and package nicely.

But like I said, rather than just taking a stab at the dark in fixing a problem, first find out what specifically your problem is. Get some thermocouples. Check inlet and outlet CLT temp to each radiator. Check inlet and outlet air temps. Measure your water pump flowrate even. Mo flow = mo betta.

Again.. to solve a problem you first gotta know specifically what the problem is. Is it a water pump issue, a problem with the side radiator, a problem with the rear radiator, or what.

You could probably eliminate your problem just by putting inlet ducting on that rear radiator that I'd imagine is doing very little right now. Thing might even be overcooled at that point.

[Conceptual]

Did anything ever come of this?

[SavantGuarde]

not yet! We are planning to have something working on this front this year in the summer.

The problem is that the needs for cooling these engines varies greatly with the ambient temperature, so its not quite the season for it yet! We have already had cooling problems this year but quite the opposite effect!

The problem is that if we make the cooling too efficient then the engine does not get up to temp correctly and can also cold seize! therefor when (if) we make this system we are going to try a sliding apature so that I can control the amount of cooling as I watch the temp.

Bloody two strokes!