Engine cooling Fan ... Blowing or Sucking

[not2fast]

Hi,
I have a small Heat bench that I put together to test a few small M/C Radiators, at the moment its set up to suck air through the Radiator. I'm measuring the Depression with a water manometer between the Fan and the Rad for each test... e.g. lets say its 20mm H2O @ 8m/sec

Now if I change the setup so the fan is Blowing with the same given positive pressure @ 20mm will the velocity and Air Flow be the same or slightly different ?

any thoughts...

Regards
not2fast

 

[FoMoCoMoFo]

I'm thinking it will push slightly more than it pulls

 

[evelrod]

I'll take the other tack. My reasoning (always in question) is the rad will tend to straighten out the airflow to the fan blades...given the fan is properly ducted/shrouded.

In my limited use of electric fans for both primary and secondary installations, street and race, "suck" has always proven superior.

Rod

 

[FoMoCoMoFo]

I too right or wrong have always preferred "suck" mode in real world applications. my thinking was that putting the fan & shroud in front hindered ram air flow and created turbulence ahead of the rad. again could be wrong. I understood not2fast to be talking about a test stand, don't know how close his fan/rad are, didn't consider any air straightening effect. just looked at pressure and figured higher=more "slightly" happy motoring and/or sucking & blowing

 

[not2fast]

Thanks for the reply, could you elaborate why that would be, sounds like there would not be a big difference between the 2 setups.

not2fast

 

[not2fast]

Ooops new bowser.. need to refresh the page to show the new replies.

I've built a Box thats around 300mm Sq, opposite the Rad is the Fan approx 300mm from the Rad.

 

[FoMoCoMoFo]

no one said there would be a "big difference". slightly is the word you used first, and i used in my replies. if you were just turning the fan around and pushing air through this restriction (radiator) rather than pulling i think the difference in pressure and flow would be greater.but your talking about regulating the pressure. so I'm thinking it may only amount to a small difference in air density ? probably effect amp. draw on the fan, (electric?) more than air flow. or temperature drop, or what is it exactly that your looking at ?

 

[Landmark]

Not2fast...
It's rare to see someone try to push air through a radiator.
When you push air, it tend to find every other way out of the setup, exept through the radiator.
When you "suck" air, you actually ask mother nature to help you push air into the radiator. Atmosferic pressure distribution on the radiator surface is even, there is no way around the problem, air has to go through the radiator.
cheers, Chr

 

[not2fast]

Thanks Landmark,
Good old Mother nature, that makes sense well said.
I'll explain this setup ... the actual intended application is using a Centrifugal Plastic Fan this is ducted (Blowing) towards the Radiator, I hear what your saying about the leaks and the Fan Housing (Shroud) and ducting will be Molded from Fiberglass in one piece.

After Molding I was intending to cut the inside Fan Housing on a Milling machine so as I can reduce leakage where ever possible and make this a nice close fit to the OD of the Fan, so all going well the leaks will be minimal if not zero.

not2fast

 

[not2fast]

Thanks Landmark,
Good old Mother nature, that makes sense well said.
I'll explain this setup ... the actual intended application is using a Centrifugal Plastic Fan this is ducted (Blowing) towards the Radiator, I hear what your saying about the leaks and the Fan Housing (Shroud) and ducting will be Molded from Fiberglass in one piece.

After Molding I was intending to cut the inside Fan Housing on a Milling machine so as I can reduce leakage where ever possible and make this a nice close fit to the OD of the Fan, so all going well the leaks will be minimal if not zero.

not2fast

 

[kilrbee]

are you the same n2f that I have seen with extensive forced induction publishing?

 

[IceStationZebra]

In my experience with off-road equipment we usually get more air flow when we pull instead of push. Realize that the benefits/differences will depend on the installation specifics including shroud design, distance between fan and radiator. For axial fans add in shroud opening design (sharp edge, flange, etc.), fan tip clearance, fan design, etc.
I agree with Landmark that when using a pusher fan the air tries to get out where ever it can. Many of the axial pusher fans now have a very large disc in the center to prevent the high pressure air from "leaking" around the center hub.

It is somewhat unfair to use the same fan in both push and pull configurations. A properly engineered fan will generally have been optimized for one or the other.

ISZ