air flow diagram for Radeon GPU?

[cvicisso]

I am already pushing the cooling limit of my rig with 3 x 6950 OC'd.  There's an air gap between each card, a big-ass fan blowing directly on them, yada yada, yada...

I want more hashing power.  The wife isn't going to let me start a new rig until this one starts producing, so...

I ordered some flexible PCIe 'risers' in order to add another card (or two), but I need to get the heat under control before I do anything.  Here's my question:

HOW DOES THE AIR FLOW THROUGH THESE CARDS?  Does the fan pull IN from all the slots in the plastic shroud, and push OUT the opening in the back where the video connectors are?  If so, why does 'blocking' the fan by putting the GPUs closer together have such a drastic impact on heat?  Does the fan pull in air from it's 'hole' too?    A picture would be awesome!

Here's my plan: I have an old hot tub air blower (the thing that makes the bubbles) that I'd like to take advantage of.  I tried using it to blow on the tops of the cards (instead of the big-ass room fan that's doing it now - side panel is removed), but temperatures went all over the place.  Some up, some down... it was a mess.  I shut it off and put the room fan back. 

What I would like to do instead is rig up a shroud to place around the EXHAUSTS of the cards and use the blower to SUCK from there.  And believe me - this thing'll suck a golf ball through a garden hose faster than a Thai hooker.     I'm willing to give it a shot (the bitminer - not the hooker), but need to verify where the exhausts really are.  It seems like I can feel air coming out of some of the plastic vents on the GPU inside the case with my hand, but it's hard to tell with all those other fans blowing around. 

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[sniper_sniperson]

Usually the air flows are researched in empiric way - on black background with artifical light pointed upwards some guy creates smoke and the other guy records it with proper camera for the goal.

Particularly on your problem - when two cards are too close one to each other the fan of the first starts sucking the heat from the PCB surface of the second.

[cvicisso]

That's my whole question.  Is the card drawing air from the fan (like - from the hole that the fan sits in?), or is it drawing it from the vents in the plastic shroud?  Surely someone here knows the answer to this...

[fascistmuffin]

That's my whole question.  Is the card drawing air from the fan (like - from the hole that the fan sits in?), or is it drawing it from the vents in the plastic shroud?  Surely someone here knows the answer to this...

The fan of the cards are intake fans, drawing the air in the plastic cover and out the back where the DVI plugs are.

For your blower idea, you might want to include the cases' rear exhaust fan located above the PCI slots, since that will cause a lot of air suction through the case, pulling heat off the top of the cards and reducing the heat of the air the card's intake fans will suck in.

[computerparts]

You completely failed to mention which 6950's you have. Are they reference (fan at the far right), or non reference (more than one fan or fan in the middle)? Without knowing this it is impossible to tell you the airflow of your card.

[AtlasONo]

Yes it sucks it in from the center. Grab some string, incense stick or a dust bunny to visualize it and see for yourself

[cvicisso]

You completely failed to mention which 6950's you have. Are they reference (fan at the far right), or non reference (more than one fan or fan in the middle)? Without knowing this it is impossible to tell you the airflow of your card.

Wow - it seems strange (or retarded) that a 'reference' card would/wouldn't draw air directly from the fan (the 'hole') as compared to a non-reference card simply due to the fan placement on the card.  Methinks it doesn't matter (which is why I didn't mention it). 

But ok - I'm you're huckleberry...  I have a non-reference HIS card.  The fan is in the middle.  Now, please tell me the difference (in airflow) between my card and a reference card with the fan at the end.  BTW, this is rhetorical - the question has already been answered (thank you). 

[cvicisso]

That's my whole question.  Is the card drawing air from the fan (like - from the hole that the fan sits in?), or is it drawing it from the vents in the plastic shroud?  Surely someone here knows the answer to this...

The fan of the cards are intake fans, drawing the air in the plastic cover and out the back where the DVI plugs are.

For your blower idea, you might want to include the cases' rear exhaust fan located above the PCI slots, since that will cause a lot of air suction through the case, pulling heat off the top of the cards and reducing the heat of the air the card's intake fans will suck in.

Thanks for the simple, non-sarcastic answer and the great idea about the rear exhaust fan. I'll let you know how it turns out.