any thoughts on shroud designs??

[mgpaulus]

I asked this in CPU/Processors & Overclocking, but I haven't had any nibbles yet, so I thought I would ask it here:

I recently read an article describing the effectiveness of 60->80mm fan adapters (or rather, the lack thereof). One problem they mentioned was that maybe the act of reducing the hole was increasing the back pressure enough to make the fans ineffective.

So, I was thinking about trying to make a shroud for my Taisol CGK760092 and then setting up an 80mm Panaflo L1A on it, but in suck mode, instead of blow mode. I am hoping this will relieve the back pressure problem. But I have a couple of question in this regard:

Should I have some head room above the Heatsinks fins, and if so, how much?
How far down the sides of the HS should I bring the skirt?

My basic assumption is that the shroud will help bring air in at the bottom of the HS, which will give allow the most air contact with the HS. I also believe that I need to allow enough open space to allow the optimum volume of air into the HS, and not choke it. But, is there a good way to calculate this, or is it a "poke & quiver" problem....?

Any thoughts would be appreciated.

Thanks.

 

[Moohooya]

Erm, not very high tech, but here goes.

Back pressure is relative. If the pressure infront and behind the fan is 10atm it will blow almost was well is it was only 1atm. (OK, the air will weigh a little more, so the fan will have to work a little harder, but you get the idea.) If the pressure behind the fan is 1atm and infront is 2atm, then the fan will have to work harder to push the air. Now turning the fan around you will end up with a pressure behind the fan of 0.5atm while the pressure infront is 1atm, so it will be no better than before you had rotated the fan.

It basically comes down to aerodynamics. Some heatsinks are designed to have air pulled in from between the fins and drawn out of the top, while most x86 heatsinks are designed for air to be forced down from above and out of the fins. You want to maximise three variables.
1) The amount of air pushed through the fan
2) The amount of heatsink in contact with the moving air
3) The circulation in the case so the same air does not go back through the fan.

1 is pretty constant with the fan. As long as you don't overly restrict air movement aroud the fan, it will pump about the same volume of air.
2 is determined by the heatsink design and components you have around the heatsink. If one side of the heatsinkis too close to a cable or a card, air will not be able to exit that side, and you will reduce you cooling by up to 50%
3 is determined by the overall case. Fans, cables, cards etc. Heat rises so blow in cold air at the bottom and exhaust hot air from the top. Make sure there are as few restrictions to air movement as possible.

Next time you see a river, look at the eddies by the bank, logs, rocks etc. An eddie is where the water flows upstream, or swirls around in a spiral. Now imagine this is the air in your case, and the rock is your CPU heatsink. You do not want cold air running around the heatsink while a small eddie of hot air is circulated through the heatsink, again and again and again. Now of course we cannot see the air move, and calculating the movement of air through your case would involve you to measure everything, run a simulation package for several years, and even then you won't be sure. So it is really a best guess kind of thing. If you put heatsink is in the middle of the 'river', less chance it will be caught in an eddie.

If you have a transparent case I guess you could play with dry-ice 🙂 If so, post photos

 

[CTho9305]

<< If you have a transparent case I guess you could play with dry-ice 🙂 If so, post photos >>



i've considered that, but i think its risky. the stuff you see from dry ice is water droplets that condensed. water = bad. you need smoke that isn't attracted to static electricity / won't settle on components.

 

[Howard]

Ever seen an Alpha PEP66? That's an excellent setup (the 'dead' zone of the fan is not directly over the core), plus after the air is 'used up' on the heatsink it doesn't just hit a wall and fly around. If you extend the shroud, up to the very top of the case, you can make a blowhole there and not use a fan on the heatsink. Pretty cool, huh?