So my group and I are working on a college project for a well known company and trying to understand a particular concept regarding an engine cooling fan.

lets say:

-front- refers to position in front of the fan blades
-back- refers to position in back of the fan blades
-the fan pulls air in from front to back (radiator mounted in front of fan)
-disk- refers to the circular plate holding the fan blades together in the typical array fashion.
-the vehicle is STATIONARY


Fluid mechanics says there is a higher pressure in back of the fan when compared to the front (when rotating). There is also an engine block in back of the fan, in close proximity, possibly increasing pressure furthur.

So....here is the question/inquery:

This higher pressure in back of the fan will want to flow to the lower pressure in the front of the fan, right? So what if you give it a chance to. If you had holes in the disk of the fan would you have a flow path in reverse here (back to front)? We want to know if this 'backflow' is happening in this case.

Thanks guys and gals.

-Scott.

 

Just what are you trying to accomplish? I initially assumed it was engine cooling (heat transfer rom the rad to the ambient air), but I'm not sure.

Generally the cooling fan is mounted in close proximity to the radiator, and/or it has a shroud around it in order to draw air thru the rad and not from elsewhere, like from the area between the fan and the rad. or from behind th fan. Air takes the path of least resistance doesn't it? If your fan isn't shrouded, it's pulling air from wherever it can get it easiest. That may not be thru the rad. Most (all?) OEM fans are shrouded. Many "home-brewed" ones aren't, even in race cars. It doesn't surprise me that many racers have overheating problems. It also doesn't surprise me that OEMs throw good money at installing shrouds, seals, etc. That's not done just to spend money or make the car heavier.

If the downstream air effectively has no place to go it will find a way out if there is one or back up to the fan. Plug the hose of a shop vac into the "blow" rather than "suck" port and block off the end of the hose. Pressure in the hose increases until an equilibrium is reached. Motor speed changes. (faster or slower? why?). Perhaps it gets to the point where flow stops and you just have a pressure differential across the fan. If the engine cooling got to that point you'd have a problem.

When the vehicle is moving, you can create low pressure areas downstream of the fan to help move the air thru the rad/fan system. With no vehicle motion, sealing, shrouding, ducting, etc. is more critical to keep the air moving across the rad. It that where you are?

How about some specifics. Is this basic airflow research or is there a specific problem you are trying to solve?

 

OldSStroker:

First let me thank you for your help a while back concerning Rubber Isostatic Pressing (RIP). You had some good ideas and I don't think I actually said 'thankyou'. BTW, our process did not work all that great.....well, great enough to impress the Prof. and get a 4.0 but not quite enough to employ in actual manufacturing.


This is a specific problem we are working on. We are counting on the 'backflow' to convectively cool the fan drive mechanism. I'm not allowed to be too descriptive as confidentiality is a concern . So we are looking to maximize the 'backflow' in order cool this drive mechanism.

If you would like some clarification please send a Private Message.

Thanks again for the help and concern.

-Scott.

 

anyone care to comment on the the initial simplified version of the post?

Thanks, Scott.

 

How about switching the pitch of the blades nearest the clutch to create flow in the direction you want? Put a divider ring between the outer portion of the fan which draws air thru the rad, and the inner portion which cools the clutch? The divider might be a little wider than the fan and act like an endplate.

Just kidding.... or maybe not.