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 Post subject: Thought a peltier cooled air intake - any comments ?
PostPosted: Tue Jan 28, 2003 1:38 pm 
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Hi all,

The Peltier coolers only seems to have real use for overclockers inside a case, because of the backside of the peltier heating up the case; but have anybody tried something similar to the following:

I thought about adding a peltier element OUTSIDE my case, at the air-intake. I would cool down a heatsink(or similar), and let the inbound air pass over it(hopefully cooling the air a LOT).

My idea was to be able to reduce the airflow, and thereby reducing noise. As the peltier is mounted outside of the case, it wouldn't require a fan on the hot side...

Any comments, ideas ?

Rgs
Kenneth

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 Post subject:
PostPosted: Wed Jan 29, 2003 10:10 pm 
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I would create 2 heatsink in front and back of peltier element. The cooler one will go in path of air intake while the hotter one will be vented outside from a fan. (keep in mind as the hot side gets hotter, the temp in cooler side increases as well in peltier element)
However, it might not look quite clean. Maybe you can run a duct inside case that are shielded from heat to back of PC (and put the cooling elements inside PC) from enclosed hot heatsink that will just go from front of case to back of it while the other heatsink gets into the rest of case. It would be rather bulky I would imagine though. (probably will take all my hdd bay to be really effective is my guess)

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 Post subject: you might try...
PostPosted: Sun Feb 09, 2003 12:04 pm 
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...cutting a hole near the top of the case (where hot air accumulates inside). Mount a big heatsink to the inside surface, to cool, and a big heatsink to the outside to carry away the transported heat plus the heat created by the operation of the TEC.
I'm suggesting high on the side rather than on the top so that you might set up the exterior heatshink so that you'd get a convective air loop through it.
Will it work (as in, will it actually get interior temps lower than a passive blowhole - or in with a few inches of "chimney" to provide "stackng pressure" to draw hot air out)? I dunno. You could get the exterior heatsink pretty *hot*, which'd be good as heat tranfer is proportional to the heat differential.
It'd be *quiet*, though, with no moving mechanical parts.
Bob


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 Post subject:
PostPosted: Sun Feb 09, 2003 4:20 pm 
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This post interests me. I think I've found the ideal heatsink for this:

http://www.quicklyshop.com/shop/product ... cts_id/150

you could set it up as a peltier-cooled tunnel for the intake!

bobkoure's idea is well suited to my case, I have a stiff plastic intake duct right over the CPU providing cool air from outside the case to it's fan - I could put a peltier-cooled heatsink right inside that duct maybe.

I've never really had any experiance with peltiers, every site I've seen seems to say they're for harcore overclockers only without really saying why. Is it the case that one side massively cools down at the expense of the other heating up? Is there any net gain?[/b]

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 Post subject: TEC
PostPosted: Sun Feb 09, 2003 5:54 pm 
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Peltiers (AKA TEC) are considered "suitable for overclockers" because
- they generate a lot more heat than they move (and you need to get it *all* out of the case somehow)
- if you reduce the cold-side temp below the "dew point" (actual number depends on the ambient humidity and temp), then, well, dew will form (as in water - which electronic components often don't get along with).
Heat-to-heatsink might actually sidestep both these issues.


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 Post subject:
PostPosted: Sun Feb 09, 2003 6:42 pm 
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Hot metal on top of case isn't great ergononics, so I'd want some kind of cage around it, but a sound idea.

One big improvement with your idea from a silent POV - with the air cooled internally by a TEC why bother with intake/exhaust at all? If it was effective enough you could completely seal off the case. No gaps = quietpc :)

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 Post subject:
PostPosted: Mon Feb 10, 2003 6:21 am 
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Location: Boston, MA
I'm still baffled as to why the side of the case isn't one big heatsink. Sure, that's a lot of costly copper, but considering how expensive cases are these days...

Why not cut a hole, and mount a peltier junction in the case, near the top? Mount a large heatsinks on both sides of the case to absorb / radiate heat, and insulate the hot side from touching the case. Since there are no electronics on the hot side, you can run it as high as you like without risking any components (until the aluminum melts / the heat feeds back into the case). The dew side would be inside the case wall, and would allow water to run out the bottom of the case into a pan of some sorts. This may not be a pleasant option in Austin, Texas, but it would be perfect for here in Boston, MA, at least during the winter...

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 Post subject:
PostPosted: Mon Feb 10, 2003 6:37 am 
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Wonder if the top could keep coffee warm.

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 Post subject:
PostPosted: Mon Feb 10, 2003 6:51 am 
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jhh wrote:
Wonder if the top could keep coffee warm.


Yeah, it would probably encourage cats to sleep on it too. :)

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 Post subject: why a hole?
PostPosted: Mon Feb 10, 2003 7:17 am 
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Y'know, you could just use the case itself as the "inner" heatsink (assuming it was metal - probably would work best on an aluminum case
Just clear the paint off the case where the TEC is going to go alongside it, bond the TEC on one way or another (thermal epoxy, screw+clamp, whatever), then just run the thing.
Use your hand to feel the limits of the area of there the case wall is getting cold/cool and insulate the outer side of this area so the heat exchange would all be on the inside.
You'd still need some sort of heat sink on the outside - although I kind of like the idea that you could mount this in the top of the case and set it up as a coffee-cup-warmer :-) I suspect that you'd get better cooling with a heatsink to the side with fins aligned vertically so that air could rise up between them (thermosyphon).
IMHO, something like a Zalman "flower" mounted sideways might look kind'a cool. Without a cage, you'd be limited in how much heat you could move in that you'd want the heatsink hot - but not so hot that it could burn.
Oh - and you're almost certainly going to need a separate power supply to run the TEC - computer power supplies don't typically provide the kind of current you're going to want at 12V - and 14V (unavailable from your PS) would actually work better, anyway...


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 Post subject:
PostPosted: Mon Feb 10, 2003 7:28 am 
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how much power do TECs use? I've got a 300w Zalman PSU, although I imagine the typical draw is <150w

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 Post subject: here's a BIG pelletier
PostPosted: Mon Feb 10, 2003 8:53 am 
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After this conversation, I couldn't resist browsing ebay to see what might be there that might work. Here's a take-out TEC that's 12x18x12 with a "buy it now" of $150
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3310811863&category=26261
It's got a heatsink already on it - and *fans*. The heatsink might work without fans if you didn't crank the colling power up much.
I'd think about buying an aluminum case just to bolt this TEC onto...


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 Post subject:
PostPosted: Mon Feb 10, 2003 9:02 am 
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not sure somthing with 2 162mm fans belongs in a silent pc forum ;)

I have seen small peltier elements for ~ £8/$12, I think they're abt 4cm square with just a small-ish passive heatsink on the other side. I think they'd at least cool the heatsink I mentioned earlier for an icy tunnel effect.

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 Post subject:
PostPosted: Mon Feb 10, 2003 10:22 am 
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jhh wrote:
I have seen small peltier elements for ~ £8/$12.

Hang with me for a sec while I run a physics experiment by (it'll be germane, I promise)
Take two cups of tea (same qty and same temp - and hot)
Take two small containers of milk/cream/whatever (same qty and both room temp)
Pour one milk into one tea.
Wait 5 or 10 min.
Pour the second milk into the other tea.
Which one is hotter?
If you said "The one I poured into first", you're right - and you understand that the greater the temperature differential the faster the heat transfer (first cup started out cooler, so slower transfer).

OK - so back to case cooling: If you're going to run a TEC, you want the cool side as temperature-different as possible (for heat transfer efficiency).
This is why I was proposing the cool side be somewhere high in the case.
Your TEC will be much less efficient cooling room-temp air.

BTW, if you're just trying to get your CPU down to reasonable temp with as little fan noise as possible, I'd suggest water cooling without TEC.
There's no condensation to deal with and very little noise. If you use something like a "slantfin" baseboard heater unit as a passive radiator, you might be able to do without a fan at all. I'm using a BlackIce radiator mounted so that my 120mm case exhaust fan blows through it. I've got the fan throttled back to about 950~1000RPM and it doesn't make much noise (under ambient where I am - so effectively silent/unmeasureable). My case temps run about 28C and my processor (Ath 2100+) at 38C at idle or as hot as 42C when running SciSoft Sandra CPU-test continuously (AKA "burn in") for a couple of hours. I'd run it overnight, but I'm running a web server (family/community photos, mostly) and IIS gets um... unresponsive when I'm running these tests...

Oh - I'd also suggest that those $12 TECs won't actually move enough heat to matter much anyway (but they also don't draw enough power that you need a dedicated power supply, so they'd at least be cheap to play with. BTW (and !WARNING!) read up on TEC before you get tempted to sandwich this between your heat sink and your CPU (just to see...). If the TEC isn't rated for the heat output of your CPU, it's actually worse than no TEC. You can fry your CPU fast. I would guess the $12 TEC is about a 20W one - and you'd need about 75~100W.

And you're totally right about 2 160mm fans not belonging here - (unless they're turning under 1000RPM, I guess... :-) )


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 Post subject:
PostPosted: Mon Feb 10, 2003 11:05 am 
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good, clear example there! I should have seen it - for just about any natural quantity a greater differential = faster transfer. Air blowing over a cooled heatsink very slowly still might be cooled down by a few degrees.

you're right - I checked up and it seems the little TEC can only handle 17 watts - pretty pathetic really. And to think I have a Palomino! Don't know how they can them as suitable for putting straight onto CPU die. I still might get one just to play around with and see what I can make, seems an interesting project at least :)

I take it since TECs seem to have a max temp difference the more efficient the heat dissipation on the hot side the cooler the cold side will get?
Problem is that even if I have these at the top of the case, it's likely more than 17wats of heat could be removed via 2 7v Panaflo 80L

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 Post subject: worth it?
PostPosted: Mon Feb 10, 2003 11:48 am 
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A 17W TEC is most definitely not suitable for your Pal. That's why I did the "warning" thing :-).
Yes, the cooler the hot side of a TEC gets, the cooler the cold side gets (it's not one-for-one, ran into a formula for this somewhere but don't remember / can't find it). Further, with a TEC, there is no passive heat transfer from cold to hot, so you'd be moving 17W out (probably less than that, but call it 17) and have, ummm Palominos are about 65~70W, so best case is you'd have 48W building up.
Oh - right, there's no guarantee that this'd cool any better than a couple of fans exhausting air - or even, if you have room above the case and don't drag it off to LAN parties, a "blowhole" with a couple-foot chimney to cause "stacking pressure" to passively draw air out of the case. BTW, I'm in New England, where there are still old barns with cupolas on 'em - which were designed to do the same thing (get hot in the sun and use stacking pressure to vent the barn). Of course now they're painted white (to be cutesy), but I'd guess the original ones were painted with something darker (like maybe "oxblood" or maybe even soot from fireplace chimneys - both available to early farmers). Talk about a digression. Sorry :-)


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 Post subject:
PostPosted: Mon Feb 10, 2003 1:47 pm 
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I have room for maybe six inches above the case, how does stacking pressure work - I'm guessing becasue the greater the volume of hot air rising the more pressure it creates? Or maybe becasue the air at the end of a chimney is cooller then that just over a case, and therefore there's a higher air-mass differential?

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 Post subject: How chimneys work
PostPosted: Thu Feb 13, 2003 8:46 pm 
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Y'know, I need to go back to my physics books on this one.
It's definitely a matter of the mass of air rising, but the relationship between chimney width and height.
Once there's hot air rising, more (not so hot) air can get pulled along through a process called "air entrainment" (same process that pulls the plastic shower curtain in when you run a shower).
Anyway, will 6" make a difference? I dunno. It won't hurt, though.
Oh - and I'd bet a quart-sized yogurt container with the bottom cut off would make a dandy chimney (or you could try linking a chimney with something acoustic-absorptive).


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