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Originally Posted by JoeKamel
Why is the hollowed out fan a restriction though? From the description of a Venture Tube, a VT is a place in the path of the flow of a liquid where there is a constriction or other type of decrease in diameter of available flow. A hollowed out fan, isn't going to provide anything in tha respect as it is going to have the same diameter opening (80mm to another 80mm, 120mm to another 120 mm) with nothing in its path because the an itself has been hollowed out leaving nothieng but a hollow ring.
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That's exactly what I thought originally.
I also came across
this :
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There's not a simple answer and we do not have 'one size fits all' situation here I am affraid.
Basically it all depends on your hardware d00de. If you happen to be a happy owner of high performance small and very restrictive radiator (some car heater cores) your best bet is going to be push/pull config. It holds for low pressure fans (25mm generally, oh I am talking 120m fans here since smaller are jst waste of time in performance cooling)
with high pressure fans (35mm thick and up) you may get better results with all pull config. All the above assumes well designed and sealed shroud in action.
The theory behind it is the same as with pumps in WC loop.
Right, lets put things in order here, shall we?
1. Case One - restrictive rad and low pressure fans.
What we need here is more pressure to be able to push air through in respectale volumes. there are two ways of doing so, you either stack fans and have pull-only/push-only situation or you go for a fan on each side (push-pull). I found through experiments (aoerodynamics is too complicated to entertain here and I cannot say I have it mastered sufficiently to write about it) that stacking two fans is optimal and stacking four fans produces no air flow at all . Stacking two fans gives better results than push pull config due to almost double pressure produced by such an assy. Another possible config is mounting two 25mm fans in pull only config side by side with tapering shroud. With restrictive rads it does not work since all you gonna get is air blown out instead of being sucked (push config) and not much coming out in pull config. I works wonders with low restriction rad since CFMs almost double but ressure stays the same (with low-res rads we do not need pressure)
Let's proceede to next case
2. Case Two - Restrictive rad and high pressure fans (35+mm thick fans rated 130CFM and more)
The best config here is for two fans side by side in pull config mounted on a tapering shroud. We do not need increase in pressure, we already got it but more CFM would be nice so we mount fans in parallel. Pull config and shroud ensures no dead spots as gav2000uk very righly observed.
Reasoning behind is that with high pressure fans can push close to rated max CFMs (which number describes CFM with 0PSI back pressure and conversly max back pressure is obtained with 0CFM - same as with pumps and water) so increase in presure wouldn't yield almost any increase in performance (stacking/push-pll config)
3. Case Three - Low restriction Rad and low pressure fans
What is worth remebering is that the less restrictive the rad is the poorer performer it going to be assuming no limits on fan power. In other words low-res rads have a point of diminishing returns where increase air flow does not produce any more cooling. With PC water cooling such conditions are not attainable .
This case offers very quiet radiator subsystem (low pressure fans are, and shoudl be low noise designs) but needs to be of decent size to offer needed performance (at least 240x240 if not 240x360mm of finned area)
4. Case Four - Low restriction Rad and high pressure fans
same as case four but fans are usually ran at 7volts to limit noise levels but are able to be set to fuul steam for benching/gaming periods
The choice of a system config. is dependant on ones brief. Performance?, low noise? size?, for each combination of requirements there is the best combination of hardware. There isn't anything like The Best config for everybody
I hope it helps, if I slipped anywhere feel free to correct me and if anything is mud-clear ask
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As comestic is quite a important part of my system so I think I'll pass with the carboard and duct tape idea.... However, I might go as far as cutting aluminum and a bit of silicone sealant.
I'm the pround owner of 2X 130CFM Y-S tech fan so I think a tapering shroud is what I should be making in my next upgrade.