Result of Stacking 2 fans 2

[MDGroup]

What happens if you stack 2 cooling fans on the back of an electronic enclosure?

There isn't room to put them side-by-side, so they are piggybacked one on top of the other.

Does it double the amount of airflow? or does it just push the same air twice?

The outlet opening is still the same size, so I assume you don't have to double the size of the intake?

Is the CFM doubled, or does it stay the same?


Ultimate question: Does stacking 2 fans increase the cooling across the electronics inside of the enclosure?

Any thoughts on this are appreciated? Thanks

 

[rb1957]

no, i think you're missing the point that in the doubled set-up, neither fan will work as efficiently as a single fan ('cause they obstruct each other).

 

[telecomguy]

I recommend you read up on 'fans in series' and 'fans in parallel'. You'll find lots of resources to better understand. You're getting a little theory here as well as a little practical input. That's why I hedged my previous statements with 'essentially' and 'ultimate'. Stacked fans do overcome high resistance. And in a sense, you should expect higher CFM, but this is only true because the pressure/flow rate curve becomes steeper. Think of a 100cfm fan that provides 50cfm at your current system resistance. You might see 65cfm flow by putting the fans in series, but you are not doubling the maximum capacity of the fan from 100cfm to 200cfm for the pair. The best you can get is still 100cfm at zero system resistance. But you are also hearing some concerns about the added resistance of the series fan if only one is powered at a time (of if they are running at slightly different speeds, etc).

<tg>

 

[snoopnoon]

physics can not be denied.

Qfan1 = Qfan2*(Dfan1/Dfan2)^3 * (RPMfan1/RPMfan2)

Q=volumetric flow rate
D = hydraulic diameter (same for both fans)
RPM = speed of fan (assume its the same for both??)

thus reducing to:
Qfan1=Qfan2 no flow increase

 

[rb1957]

won't the downstream fan create a lower back pressure on the upstream one (if both are working at the same time) ? I think the two fans working will suck more air than a single fan, and i also expect one fan working alone in this doubled setup will suck less than a single fan (because of the obstruction of the other (non-working) fan).

 

[telecomguy]

snoopnoon, not denying physics. Your calculation is assuming a constant flowrate rather than one dependent on pressure.

See the graph on this page:

http://www.greenheck.com/library/articles/42

At a pressure of 3 (units unknown), a single fan will provide a flow rate of 13 while two fans will produce about 15.

But here's a little info on the real world application of series fans:

http://www.ebmpapst-ad.com/media/content/technical_articles/TA_Using-fans-in-series-and-parallel.pdf

<tg>

 

[flash3780]

You may want to consider using using counter-rotating fans or stator vanes to straighten the flow before it enters the second fan. Compressors in turbine engines are similar to what you're describing. Turbine engine compressors generally result in a pressure rise of 15%-60% per stage.

I found this paper on the web with a bit of information about compressor design:

http://www.tpe.energy.lth.se/fileadmin/tpe/Axial_Flow_Compressor_Mean_Line_Design.pdf

//signed//
Christopher K. Hubley
Mechanical Engineer
Sunpower Incorporated
Athens, Ohio
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http://engineeringliberty.wordpress.com