optimum fan/radiator clearance 1

[krue0101]

hello,

Can anyone tell me the theory behind the optimum location for a pusher fan in relationship to a radiator on a gas engine.

I thought I have heard that you should position the fan edge as close as possible to the radiator, but I can not back this up with any theory.

Can anyone give me a hint.

thanks,

joe

 

[imok2]

Joe, If your an engineer you should understand what this site says. Good luck :>)

http://www.tifac.org.in/news/axialfans.htm

 

[ko99]

Nice reference, imok, but I didn't notice anything in there to answer krue's question. I'm not an automotive engineer, but I'll take a crack at it:

High-velocity air exits the fan blades in the shape of a ring with a dead spot at the hub. Unless your radiator has the same ring shape (unlikely) it's better to space the fan further away from the radiator so the air spreads to the dead spots (center and corners) before entering the radiator. This space is called a plenum.

The ideal plenum depth is a function of fan speed, blade angle, target size, etc, but I suspect you don't have room for the perfect plenum. Also, be careful not to restrict the fan inlet.

The plenum should be ducted -- walls around the periphery to prevent leakage -- this forces all the air to enter the radiator.

Of course, if you have a fan assembly that already includes a built-in plenum and duct, ignore what I just said and butt it up against the radiator.

ko (

http://www.ecooling.biz)

 

[JimCasey]

Another significant factor is that the fan should be ducted or much of the pressurized air will spill off the tips of the (low aspect ratio) blades. The ducting forces very much more of the flow to enter the radiator in an axial path than it would if the blade were in free air.

 

[krue0101]

Thank you for sharing your expertise, it is much appreciated.

Joe K.

 

[CowtownBallin]

ko99,
I'm making a Formula-1 style go-cart, with a radiator and fan assembly mounted in the side pod between the front and rear wheel on the right side. I have about four feet of room in which to play with the ideal plenum depth. Do you have an actual function that I can apply in this case? I've heard people throw around numbers like "depth should be 40% of fan diameter" but I can't justify that on paper. Thanks

Miran

 

[ko99]

I've heard similar rules of thumb. I'm sorry I don't have a formula, I generally build a CFD model to design plenums. You might want to try a fan manufacturer. I've found these three to be pretty helpful:

http://www.comairrotron.com/

http://www.ebmpapst.us/

http://nmbtech.com/index_f.html

ko (

http://www.ecooling.biz)