Will Placing Fans Almost "back-to-back" Compromise their Performance? 6

[Klogg]

Aerodynamics is not my field, so my apologies if this is an obvious question.

I've got a (relatively) tricky build with an option to place fans about 1cm apart (blowing in opposite directions (i.e. away from each other))

I'm wondering if or how badly they will compromise each others performance at that proximity.

Would it be similar to placing a fan a centimeter away from a solid surface or are there other factors to be taken into consideration?

How much clearance is needed behind a fan for it's performance to remain uncompromised?

If you guys could shed some light on the above for me it'd be very appreciated.

 

[GregLocock]

No, it 'll be like placing them 5mm from a solid surface.

You need to make sure that the slot depth times the perimeter of the fan exceeds the area of the fan.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[rb1957]

that'd be twice the area of the fan, as both fans are blowing out ...

so the area of the inlet (the space between the fans) should be at least equal to the area of the outlet (the two fans).

i think there is going to be some performance drop-off, that the flow into the fan (from two closely spaced fans) isn't going to be as smooth as that on a fan in isolation.

would a barrier between the fans help the performance ? what you may find is that a vibration sets up (as the flow on both sides of the barrier is very unlikely to be in sync.)

maybe the barrier could help deliver air to the core of the fan ... use two barriers to split the inlet area into 1/3rds, and both barriers have a hole in the centre, maybe 1/2 the dia of the fan, so that this middle 1/3 of the inlet air is delivered to the center of the fans ??

good luck

 

[Builditcool]

(It seems my handle might have been updated (was formerly 'Klogg', I think now it may read 'Builditcool'))

"No, it 'll be like placing them 5mm from a solid surface."

Of course (blushing)

Thanks for responding guys. Based on the above it looks like it's not going to work, but you've definitely helped solve a minor mystery for me.

The easiest solution it seems is probably to find a way of increasing the gap between the fans.

Thanks

 

[MikeHalloran]

The proposed placement will work just fine, so long as the fans are no larger than ~1cm diameter.



Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

http://www.greenheck.com/technical/tech_detail.php?display=files/Product_guide/system_eff

Fig 10.

Less than fully developed inlet is generally considered "poor"

 

[amorrison]

Check out various installations empirically.

Put(glue) a sewing thread or tissue on the end of a length of wire.

Check the airflow (viewing the effects of airflow on thread/tissue) of the fan in an open environment and compare airflow with various installation distances.

 

[Heckler]

You might create a backpressure problem but I would set up a test because discounting the design. Is this an enclosure design? What are the oepration conditions?


Here are a couple of articles from the cooling zone website.

http://www.coolingzone.com/Guest/News/NL_JUN_2001/Tony/June_2001_TK.html

http://www.coolingzone.com/Content/Library/Papers/May 1996/Article 01/May 1996_01.html

Best Regards,

Heckler
Sr. Mechanical Engineer
SW2005 SP 5.0 & Pro/E 2001
Dell Precision 370
P4 3.6 GHz, 1GB RAM
XP Pro SP2.0
NVIDIA Quadro FX 1400
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Never argue with an idiot. They'll bring you down to their level and beat you with experience every time.