Positive v's Negative AirFlow Test...

Soldato
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Only for one case obviously however, interesting article... on the temps resulting from running different configs. Might be good for newbies

https://www.kitguru.net/components/...irflow-testing-with-be-quiet-pure-base-500dx/

Thermals-1-1024x1024.png
 
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Did I miss something, or did the negative get the best results, at which point they pulled "dust trap" out of their rear orifice and declared positive the winner? But I agree that pretty much any config with some in and some out will give similar results. Axial fans are good at pushing, poor at sucking, so the limiting factor is usually the amount of air being blown in, as long as it get some help out.

Oh, is there a link to proving that hot air rising makes no difference, since the effect is negligible at computer temps?
 
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Oh, is there a link to proving that hot air rising makes no difference, since the effect is negligible at computer temps?

I think there's two things there from my experience to answer that.

1. If there's sufficient airflow vs temperature generated, then hot air rising doesn't matter. It'll get removed from the pressure and airflow before it can stick around to be a problem anyway. So there's no difference at all in this case.
2. If there isn't, then hot air rising does become important because if the case isn't designed for it (and in some cases even ones designed for it), then you could end up with a heat trap that just runs away (normally in the rear top corner, after heat soak and unable to dissipate any more before more is added). So there's a difference in this situation.

Which then begs the question of whats a "normal" computer temp inside the case to look out for? Or what pressure and air do we need to avoid this? We don't all use the same components after all, or even at the same speeds (fans, pumps, etc).
 
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I appreciate your point, but surely 2) will only happen if there are no fans at all? Even a couple of fans will completely overwhelm the effect. Back in the days of completely passive cooling then yes, I'd want a big vent on the top. But even one 80mm probably wipes that updraught out.
 
Soldato
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Thanks for the link, will have a watch.

I was always under the impression that hot air rises only applies to "static" environments and that as soon as you introduce even just one fan then the theory is no longer relevant to the environment.

It would be interesting if there was thermal imaging too (though haven't watched the video yet to see if it actually has or not!)
 
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I was always under the impression that hot air rises only applies to "static" environments and that as soon as you introduce even just one fan then the theory is no longer relevant to the environment.


That was kinda my point. But I still see people saying that top mounted rads must extract from the case "because hot air rises". And it bugs me. But OT.
 
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That was kinda my point. But I still see people saying that top mounted rads must extract from the case "because hot air rises". And it bugs me. But OT.

Agreed, top mounted rads in exhaust "because hot air rises" only applies if the airflow and pressure is insufficient to alter dynamic of the movement from hotter air inside the case. Or, if you have fans running at a really low rpm where it barely has much pressure or airflow. But this is essentially a variant of 1) that I posted about (and what I was posting about regarding 2), but that's going a bit OT so stopped there too. :) )

But, the point is, there's quite a few variances involved in such a test that might make testing only show one subset of scenarios, and can't cover them all.
 
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My case has negative pressure and cools superbly. I have 4 x 120mm intakes and 5 x 120mm exhaust. But 3 of those exhaust fans are in the roof, I get the feeling they do very little and that the 2 on the back shift far more air out of the rear of the case. So maybe actually slightly positive pressure.
 
Soldato
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That testing is of little if any use.

The difference in pressure on intake vs exhaust side of a fan with 1.5mm H2O pressure rating is the same as the difference in air pressure on our feet vs on our waist standing at sea level.
Barometric pressure at sea level is 10.3323mm H2O
Barometric pressure at 1m above sea level is 10.3308m H2O .. a difference of 1.5mm H2O​

Key is not how many fans are used or how many are intake vs exhaust. It's all about how air is flowing through case. Most decent tower cases perform best with all PCIe back slot covers removed to increase rear vent area around GPU for better front to back airflow and lower temp air entering both CPU and GPU coolers. Generally a couple good pressure rated 140mm front intakes with all openigs in front have of case not covered by intake fans blocked of so airflow from intake fans has to flow through case and out, not leak around intake fans going in circles, and have case fan speeds cycle with component cooler fans so case airflow increases as component air use increase.
 
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Another obvious point is that positive pressure allows you to control where the air is entering from, most importantly, through filters. Negative pressure can have it entering from any opening, and potentially letting in a lot more dust.
 
Soldato
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Another obvious point is that positive pressure allows you to control where the air is entering from, most importantly, through filters. Negative pressure can have it entering from any opening, and potentially letting in a lot more dust.
Good point!

Dust getting into USB, headphone and mic sockets can (and does) cause problems. Was also a problem with disc units, but we don't see them much anymore.
 
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Another obvious point is that positive pressure allows you to control where the air is entering from, most importantly, through filters. Negative pressure can have it entering from any opening, and potentially letting in a lot more dust.

this, i always go for positive pressure which can be hard with dust filters and i always try and vent out the top and back
gpus and psu can be dumping heat out the back and i dont want to pull that heat back in
heat rises is another reason i dump out the top but i admit i dont think it has an impact as such but same situation, i know im not pulling that heat back in if i pull from the bottom and the front
atm i have 10 in and 7 out, 7 in are on rads, one is a 240 in push pull at the bottom, 6 out are on 2x360 rads in the top out ofc have no filters, rest all have filters which i try and clean as often as i can, but its a heavy case lol
 
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