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Question about crossflow fans

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July 16, 2011 5:02:09 PM

Hello,
I am designing a compact mid tower case with a 90 degree rotated motherboard. I want to place the PSU behind the MOBO tray, but in order to keep the width of the tower down I would have to swith my design from a 140 or 120mm fan for the psu exhaust to either a couple of 80mm fans or 90mm fans. I am using sketchup and its tells me the space available for fan placement would be about 98mm width by 168mm in lenth in this configuration. I am curious if I could use a tangential(crossflow) fan for exhaust and the effectivness of doing so.
a b B Homebuilt system
a b V Motherboard
July 16, 2011 5:51:54 PM

Why not just compartmentalise the psu into the bottom of the case?
As a gamer/modder, I wont use less than 120mm's on a build,
too many small fans is too noisy, and on the psu? crazy talk hehe
I like the idea of the psu mounting there tho, maybe worth investimigating :) 
i'll try getting a pic done but bewarned, I'm creative, not artistic :) 
Moto
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July 16, 2011 6:23:57 PM

lol. I meant to say CPU exhaust fan..not PSU..THAT IS crazy talk.lmao..thanx for catching that. I too prefer nothing less than a 120mm fan.
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a b B Homebuilt system
a b V Motherboard
July 16, 2011 6:32:57 PM

Right, I'm kind of with you now, psu behind the mobo in a normalwidth case, means the cpu fan is closer to the near side window,
necessitating a lower profile cpu fan,
my first though there would be a grilled and filtered intake 120mm mounted on the side window with a shroud that fits over the heatsink,
you would need a cable extension for the line going to the cpu fan socket on the mobo tho, for when you needed to remove the side panel
plus if its that close to the side, what provision are you drawing in for the graphics card/s?
maybe post the sketchup if you feel comfortable doing that?
Moto
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July 16, 2011 7:55:50 PM

tried posting but cant. anyways the chassis is aprx 10" wide has 2 220mm intake fans on bottom, 1 220mm front intake fan and currently has 1 140mm cpu exhaust fan on top(rotated mobo like raven series). In this format I have the PSU on backside of 5.25" drives near front of case turned so the back of the PSU would be facing up. chassis is about 14" hight and 20" length. looks odd with 5.25" bays near side of case recessed aprx.5-7mm from side. In order to mount PSU behind Mobo tray I would have to shave aprx. 48mm towards the mobo leaving the cards recessed aprx 38mm from side panel. from the base where cards would mount to mobo I have aprx.317mm clearance to face of bottom intake fans.
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July 16, 2011 8:00:03 PM

the chassis top to bottom from the outside measures 353mm. and front to back measure 533mm, I guess thats nearly 21" long.
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a b B Homebuilt system
a b V Motherboard
July 16, 2011 8:19:27 PM

Really need pics to get a grip on this one lol
try photobucket then posting the img links, works for me :) 
I can kind of see what your building but certain orientations aren't too clear for me,
you say the back of the psu, I asssume that to be where the switch and plug are mounted?
if thats at the top, which way is the fan on the psu facing, towards mobo or towards the front of case?
Moto
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July 16, 2011 8:42:58 PM

It seems that the most I could get the case width down to would be 235mm aprx. 9.25" but still stuck with the cpu exhaust dilemma and size of fan. I would almost wonder(with that much airflow going into the case from the bottom) If I could go without the cpu exhaust fan and just have open venting. or of course trying to go with the option of a crossflow fan, being that they are smaller in width, and supposedly have decent cfm( thinking maybe 100cfm) but if that where the case I might run into noise issues as I don't know about the dcb. ratings and whether or not the manufacture ratings on a fan like that would be real world cfm or just figures they got from testing as it seems there are discrepancies between owners of such fans vs. manufacturer specs.
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July 16, 2011 8:55:23 PM

Hope this works.


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July 16, 2011 9:03:04 PM

might have to search for "brainrazer" and click the "see this users profile".
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a b B Homebuilt system
a b V Motherboard
July 16, 2011 9:39:43 PM

Managed to see some of those links, I think see the plan now,
you're going to have to balance how much of the psu is sticking out of the right hand side of the case (left from the back view) with the room needed for gfx cards I think, and that should give you enough for something like http://www.xoxide.com/noctua-nhc12p-hp-cooler.html with the sidemount style?
Moto
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July 17, 2011 4:37:14 AM

I see what your saying and like the info, but if you go to photobucket and look up "brainrazer" and see my profile(I have posted a couple more pics) you'll see that I have a full size atx mobo tray and PSU all within chassis limits at this point. The depth from the grafx card mount is about 12.25" to 12.45" to the face of the intake fans at the chassis bottom giving enough room for nearly every card available with the exception of a radeon 5970? and a few others. The width of the chassis even cut down to 9.25" should give enough clearance for the mounting of a CPU cooler as you suggested(which I was looking up around the time of your posting.lol) My biggest difficulty with the current design( I forgot to save my work before shutting down) is the current placement of the psu placed 1-2mm away from the 5.25" bay and the distance to the wall plug in for the power cord to reach(its just abnormally long). Also if I could cut the width of the chassis down to that length( I originally was around 12" in width before current revisions) what would be the best size fan available to use as cpu exhaust? I'm thinking I might be able to squeeze a 90mm fan, or 2 80mm's, but as the both of us have stated we don't like anything under 120mm. I don't believe it to be a matter of preference but more a matter of cooling efficiency(and noise :)  ). That is where I come into the thought of a "crossflow" fan(don't think it's been done, but there might be a reason aside from noone ever thinking of it) or (because of the size and position of the other fans coupled with the vortex fan grills) possibly to not even have an exhaust fan at all and leave an open grill area. The thought of that( no fan at all) does worry me and leave me skeptic of my design(not to say it wouldn't work, just a matter of efficiency). Any thoughts on this?

p.s. my pics at photobucket show the case with a 140mm exhaust fan.
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a b B Homebuilt system
a b V Motherboard
July 17, 2011 11:15:05 AM

I dont mean length of the gfx card, I mean the width, from the mobo to the sidepanel, thats the clearance I'm concerned about :) 
and turbulence can be harnessed to create vortices, although its a bit beyond my technological understanding to create or design a stable vortex hehe :) ,
it would involve lots of tiny tweaks to fan postitions, measurement and above all, the fans muxt never move from your placement, or the vortex is lost
Moto
Moto
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July 17, 2011 3:03:47 PM

yeah I got ya. I will need space for the plugs on the cards, especially with a card like my 6970 where the plugs face the side panel(with a quick eyeball measurement I think I'll need 2-2.25"'s of clearance), very good observation :)  . Interesting about the Vortex idea, I too don't know much about them.I might have to do some research about those. Thank you for the info and the help.
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a b B Homebuilt system
a b V Motherboard
July 17, 2011 4:47:21 PM

Well if you crossflow two fan streams, it will affect both of them and create vortices, which you could use to benefit cooling, if you could influence or control them with accuracy. but as I said, thats far too geeky for me to consider approaching as a project lol
Moto
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July 27, 2011 1:32:14 AM

Well I have decided to go with a slight variation for the design with the case being about 10" wide to be able to keep the large fans and with hdd's facing toward front of case. The PSU will be mounted next to the 5.25" bays to keep the cords behind the mobo tray (after testing PSu cord length I find it will work) but this forces the 5.25" bays to be some form of toolless design. With a 14cm fan for exhaust it should still keep the width proper for cable connections to the grafx cards. I have stayed with the 90 degree rotation of the mobo so the typical back would be on top, I have flipped the board around so the graphics cards would be by the 5.25" bays and the cpu in the rear of the case.( easier cable management) but still have no idea about the effectiveness of tangential fans. If anyone has had experience with tangential fans please let me know what you have experienced with them and if they might be effective, I am still interested about those.
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July 31, 2011 11:59:12 AM

brainrazer said:
If anyone has had experience with tangential fans please let me know what you have experienced with them and if they might be effective, I am still interested about those.

I recently purchased a cross flow fan from Newegg. http://www.newegg.com/Product/Product.aspx?Item=N82E168...

I'm severely disappointed by it because it promised such great volume but failed to deliver. It flings the air from the center to the outside in all directions, much like a centrifuge. If ducted correctly, a cross flow fan can be very effective. This, however, is not ducted correctly. It's as though the engineers just thought it looked cool and went with it before giving it any thought or testing. This fan tends to suck air in from itself, merely recirculating the hot air instead of drawing in cool, fresh air. I really wish I could get my hands on some fabricating equipment so I could redesign this thing.

If you can, compartmentalize your case (isolate the CPU from the video card, PSU and drives,) then provide smaller, more efficient cooling solutions for each compartment. Apple did this to great effect with some of their old G4/G5 towers.

Good luck with your case design.
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