|
|
General Liquid/Water Cooling Discussion For discussion about Full Cooling System kits, or general cooling topics. Keep specific cooling items like pumps, radiators, etc... in their specific forums. |
Thread Tools |
05-28-2004, 04:41 AM | #1 |
Cooling Neophyte
Join Date: Apr 2004
Location: Warwickshire, england
Posts: 10
|
Why is pull-pull better than push-pull?
Been reading around and a lot of people cofirmed that pull-pull config is better than a push pull one.
So I've done this: However, I have no idea why it works, can't seem to find any information about it either. You see I don't like doing things without knowing how it works so can someone explain it to me please? |
05-28-2004, 04:46 AM | #2 | |
Cooling Neophyte
Join Date: Nov 2003
Location: Hong Kong
Posts: 81
|
Quote:
BTW. Do I know you? |
|
05-28-2004, 04:55 AM | #3 | |
Cooling Neophyte
Join Date: Apr 2004
Location: Warwickshire, england
Posts: 10
|
Quote:
A few people confrimed pull-pull is better but they didn't explain. From all the threads I read/post, I gathered it's something to do with fans stalling each other in push-pull, better pressure with pull-pull and something to do with dead spot problem when pushing air through the radiator. |
|
05-28-2004, 05:09 AM | #4 |
Cooling Neophyte
Join Date: Oct 2001
Location: maui, hawaii
Posts: 52
|
A few people confrimed pull-pull is better but they didn't explain.(obviously because they got no proof to back it up)
From all the threads I read/post, I gathered it's something to do with fans stalling each other in push-pull,(how would 2 fans blowing the same way stall eachother?, think about that for a minute) better pressure with pull-pull (possible but doubtful) and something to do with dead spot problem when pushing air through the radiator.(dead spots do occur, hence shrouds. push or pull they happen, a push and pull setup helps much more with thick heater cores or getting higher airflow throw rads like bix etc. pull pull in my opinion are 2 fans trying to do the same thing with one spinnen its wheels for no reason
__________________
Cool with the best or burn like the rest. |
05-28-2004, 05:15 AM | #5 | |
Cooling Neophyte
Join Date: Apr 2004
Location: Warwickshire, england
Posts: 10
|
Quote:
They all said better temperature with pull-pull but all unsure why it works |
|
05-28-2004, 08:27 AM | #6 |
Cooling Savant
Join Date: Dec 2002
Location: Sweden
Posts: 336
|
Try moving one or two of Your fans to the pushing side of the rad (lots of work just for checking out, but if You´re *really* curious nothing beats it) and check out how it affects Your CPU temp.
Add a shroud to the pushing fan to decrease the effect of dead spot. Good hunting. I could throw myself into a discussion about how more fans will help eachother overcoming the flow restriction through the rad, but since I don´t know jack shit about it I´ll spare You my BS. regards Mikael S.
__________________
The only constant factor in all Your failures is You. Catapultam habeo. Nisi pecuniam omnen mihi habis, ad caput tuum saxum immane mittam. |
05-28-2004, 09:14 AM | #7 |
Cooling Neophyte
Join Date: Apr 2004
Location: Warwickshire, england
Posts: 10
|
The black fan in the middle is gutted acting as a buffer between the two fans... So I only have 2 fans
|
05-28-2004, 09:34 AM | #8 |
Big PlayerMaking Big Money
Join Date: Aug 2001
Location: irc.lostgeek.com #procooling.com
Posts: 4,782
|
That middle piece isn't doing what you'd hope.
|
05-28-2004, 09:35 AM | #9 |
Cooling Savant
Join Date: Jan 2004
Location: Alberta
Posts: 631
|
A gutted fan is bad. It seems to be fairly restrictive. I think the idea behind pull/pull is to shroud them so they are in parallel, not series, but I could be wrong.
|
05-28-2004, 09:42 PM | #10 |
Cooling Savant
Join Date: Dec 2003
Location: Wales, UK
Posts: 188
|
Try push/pull, push/push and pull/pull and then tell us what temps (well, the differences) ya get That will be more useful!
__________________
Meethoss |
05-29-2004, 12:45 AM | #11 |
Cooling Neophyte
Join Date: Nov 2003
Location: Los Angeles
Posts: 28
|
Hmmm, it makes sense.
It would explain why Delta makes dual blade fans (basically 2 fans in one) I think it would increase pressure, I'm not sure though. Ask one of the more experienced ones on this forum. I wouldn't say I dont know what I'm talking about, just I'm not as experienced as some others. |
05-29-2004, 01:01 AM | #12 | |
Cooling Neophyte
Join Date: Feb 2004
Location: Da NBH
Posts: 68
|
Quote:
|
|
05-29-2004, 01:34 AM | #13 |
Thermophile
Join Date: Jun 2001
Location: The deserts of Tucson, Az
Posts: 1,264
|
I'd think that putting one fan on each side is better simply because the radiator is in all possible configurations, but only acts to reduce turbulence when its between the two fans. So when you put it in the middle you get a "free" buffer.
However I have nothing to back up my view. |
05-29-2004, 08:46 AM | #14 |
Cooling Neophyte
Join Date: Feb 2004
Location: Boston MA area
Posts: 48
|
So Ph what works better? Pull pull or push pull or is it too close to much worry which you choose?
My 'guess' would be that you don't need the open item between the two fans, that putting two in a pull pull scenario increases pressure, much like multiple compressing fans in a turbojet engine, they don't need a separation between to do that job, but there would be a drop in efficiency, ie the fans won't double the cfm througput. My additional guess is that push pull would work about as well, IF using a shroud on the input fan. But many users who do push pull don't put a shroud on the front in many of the design screenshots I've seen. So to continue this guess (PH your input could be very useful after this), the rad, shroud, pullfan, pullfan design and the pushfan, shroud, rad, shroud, pullfan designs should come very close to each other in efficiency but the thicker the radiator, thinking that would decrease the airflow through it, the more likely the pull pull will work better because the actual pressure increase from two fans working right next to each other would be better to overcome the thick rad pressure drop than push pull. The further benefit is the need for one less shroud in the lineup decreasing size. All guesses, but the scientists are free to confirm or refute |
05-29-2004, 10:05 AM | #15 | |
Cooling Savant
Join Date: Feb 2003
Location: USA - Boston area
Posts: 798
|
Quote:
My only data point is with two undervolted (5V) panaflo L1A fans stacked pulling through a be-cooling core (6x6) in a coolingworks shroud. Adding a gutted 25mm fan as a spacer reduced noise a bit and dropped reported-by-CPU-diode temps by ~.5C (sometimes same as before sometimes 1C lower). To the extent that fan blades are wings and use the coanda effect, you need to not obstruct the top (lifting) surfaces. It's possible that one set of blades (or more likely, one set of struts) was interfering enough that a spacer helped. Might be something else going on, too. With all that said - what is bad about using a hollowed out fan frame as a spacer? |
|
05-29-2004, 11:28 AM | #16 |
Cooling Savant
Join Date: Mar 2003
Location: St. Paul, Minnesota, USA
Posts: 123
|
The basic explanation for a pull configuration being more effective than a push configuration is that when a fan is pushing, more air flows through certain parts of the radiator (mostly in a doughnut-shaped ring corresponding to the blade area of the fan). When the fan is pulling, it does a better job of creating an even partial vacuum, which pulls air through all areas of the heatercore much more evenly. The mroe surface area of the heatercore you take advantage of, the more heat you can transfer.
__________________
Abit NF7-S ... xp1800+ ... Abit GF4ti4200 ... Maxtor 120gb SATA150 Currently gathering parts to water cool everything! (read about the project) |
05-30-2004, 12:07 PM | #17 |
Cooling Savant
Join Date: Jul 2002
Location: Brimingham, UK
Posts: 385
|
Overclex.com did a comparative test on Push, Pull, and Push-Pull configurations (unfortunately not a Pull-Pull), with a BIX. They found that a Push-Pull has negligable advantage over Pull, and that Pull worked better than Push. But we're talking, like, one degree C or so difference between various setups, so I figure efforts to optimise cooling are better invested somewhere else (e.g. ditch the double fan, concentrate on getting good access to cold outside air).
__________________
"There is a thin line between magic and madness" |
05-30-2004, 04:56 PM | #18 | |
Cooling Savant
Join Date: Feb 2003
Location: USA - Boston area
Posts: 798
|
Quote:
I've since ordered a couple of surplus cage fans and will checking out the same noise / static-air-pressure trade-off with these. I suspect it'll be better than stacking axial fans (it is based on the fan/blower curves I've been looking at - but I may be overlooking something important) Bob |
|
05-30-2004, 07:04 PM | #19 |
Big PlayerMaking Big Money
Join Date: Aug 2001
Location: irc.lostgeek.com #procooling.com
Posts: 4,782
|
Your hollowed out fan case is a venturi tube
You'd be better off to use long screws and duct tape or similar in between fans. |
05-30-2004, 09:14 PM | #20 |
Cooling Savant
Join Date: Feb 2003
Location: USA - Boston area
Posts: 798
|
Hmmm... I only have two data points
I started out with a simple "wrap of tape around screws" and was concerned with vortexes coming off sharp edges and so "hollowed out" a fan frame, radiusing everything. As measured incredibly crudely by looking at the temp shown on my CPU diode - I saw no difference. I'd expected to see a drop, but would certainly have noticed a rise. And... I'd also been concerned about the inside lip of the coolingworks shroud that I used (inner hole is 105mm or so - standard 120mm fan blade swept area diameter). The panaflos I used faired out in an oblong way to 130mm across the corners (less across the flats, of course - no "meat" there). So I carved the shroud to match. Again, no difference in CPU diode temps. I suspect that the fact that I'm using these fans way undervolted makes a lot of this not matter - or my measurement technique is so crude that I'm not seeing the difference that's actually there. (The diode temp on this CPU does go up and down in lockstep with my room temp so I think I'd see a delta - but maybe not - hardly near your standards...) Anyway, the next time I take this setup out, a squirrel cage is going in (whole new set of issues to learn about) |
05-31-2004, 04:35 AM | #21 | |
Cooling Neophyte
Join Date: Feb 2004
Location: Da NBH
Posts: 68
|
Quote:
|
|
06-02-2004, 10:09 AM | #22 | ||
Cooling Neophyte
Join Date: Apr 2004
Location: Warwickshire, england
Posts: 10
|
Quote:
I also came across this : Quote:
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. |
||
06-02-2004, 02:32 PM | #23 |
Cooling Savant
Join Date: Feb 2003
Location: USA - Boston area
Posts: 798
|
I'd love so see some radiator air pressure resistance curves.
The only online one I've been able to find is from BillA. Radiator Heat Dissipation Testing (pg4) - scroll down to the chart labeled "Static Backpressure vs. Air Flow". This is now very outdated in the sense that there are only two radiators listed that you can still get: - The "big momma" radiator is a 6x6x2 heater core (with restrictive barbs, but we don't care about that for air resistance). - I think the "original" Black Ice is the same as the current Black Ice Pro (only the BIP now comes with 1/2" beaded inlet/outlet). I'd love to see more info about other radiators/cores if someone had the equipment and felt so motivated (read: "doesn't have a life" ) Did cpl1234 have some data elsewhere? IMHO, the comments are all common-sensical, but I'd love to see which radiators/fans he's basing that on. Oh - then there's the whole issue that axial fans, thick bodied or not, are really not appropriate for pushing/pulling air through a heater core - unless maybe those $100 for-Toyota cores that are 1" thick or so have dramatically less air resistance. I'm guessing that they're aluminum anyway (aluminum block engines and radiators, why introduce copper/brass even if you do have anti-corrosion additives in your antifreeze?). The engines probably do have bronze in 'em - but probably not where water touches. |
06-02-2004, 02:42 PM | #24 | |
Cooling Savant
Join Date: Jul 2002
Location: Brimingham, UK
Posts: 385
|
Quote:
__________________
"There is a thin line between magic and madness" |
|
06-02-2004, 03:16 PM | #25 |
Cooling Savant
Join Date: May 2004
Location: San Diego, CA
Posts: 202
|
Pull-Pull works better because of pressure
Its pretty basic why pull pull works better though I hadn't thought about it 'till I started reading this thread.
Basically, so much air has so much cooling capacity. More air the better, and we fool ourselves into thinking more CFM=more air. But really a 50CFM fan at sea level will beat a 60CFM fan in Mexico City, because there's just less air per cubic foot up there around 7000 feet. The pull-pull config probably moves a smaller volume of air (no data on that, just a thought experiment) than the push-pull, but at a higher presser per CF. Basically as far as cooling goes, the more air molecules blowing over my rad the better. If I have a higher pressure, that means I have more of those molecules in a given volume, so my radiative system can do more work. Each turn of the second stage fan gets to scoop more molecules of air than if it was just sitting there open-faced. Its kinda like a supercharger intercooler, makes the air denser before it goes into it, hence there is more oxygen to burn in the fixed volume of the engine. |
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests) | |
|
|