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 Post subject: What [do] heatpipes contain[?]
PostPosted: Tue Jun 17, 2008 6:32 am 
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Location: Sweden
What does heatpipes contain? After reading this im confused, or is it simply not as easy as just cuttingthem open?

http://www.phoronix.com/scan.php?page=a ... =892&num=1


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PostPosted: Tue Jun 17, 2008 7:05 am 
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Joined: Fri Jun 13, 2008 12:03 pm
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Location: Pullman, WA, USA
There are a few good posts in the discussion of that article that have some good information. I thought this explained it quite well:

Quote:
The walls are lined with a wicking material that holds the liquid and carries it back to the hot part, where it boils and enters the lumen of the pipe, travels to the cold end, condenses, and repeats the cycle.

But the important thing is that, in a cold state, ALL of the liquid is held in the wick material. Any excess would be pointless. And it's held quite firmly; remember it's the capillary action that sucks the liquid the whole length of the heat pipe back to the hot end.


The methodology of their "investigation" looked to be about as haphazard as their writing, so I'm not surprised that it completely missed the mark.


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PostPosted: Tue Jun 17, 2008 10:22 am 
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Joined: Wed Apr 05, 2006 4:10 am
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Location: Colchester (nuked in 1984)
http://www.aavidthermalloy.com/products/heatpipe/operate.shtml

Quote:
Most pipes use water and methanol/alcohol as the working fluids. Depending on the wick structure, pipes will operate in environments with temperatures as low as -40°C. Upper temperature limits depend on the fluid, but 60°C to 80°C is the average limit.


http://www.aavidthermalloy.com/products/heatpipe/design.shtml

To get water to operate (boil) down at typical CPU temperatures the pressure in the pipe has to be fairly low (not a complete vacuum)

Critical to their function is the internal wick structure, the most efficient being sintered metal.

They're not too difficult to make (http://homepage.ntlworld.com/bill_todd/heatpipe/heatpipe.html) but it is difficult to get to them to work well.

_________________
Bill


Last edited by BillTodd on Mon Sep 29, 2008 2:30 am, edited 1 time in total.

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PostPosted: Tue Jun 17, 2008 3:51 pm 
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Joined: Tue Mar 13, 2007 12:24 pm
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Location: Wiltshire, UK
If you really want to know, and live in the eu, you could order just a heatpipe from german electronics shop conrad. Starting price 8.16 euro's ex delivery: Link that may or may not work (sessions & cookies etc!), if not, go to www.conrad.de and search for 'quick cool heatpipe'.
Someone did a great semi fanless htpc using these... would still like to do something similar. Home built TNN chassis anyone?


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 Post subject:
PostPosted: Wed Aug 20, 2008 11:31 pm 
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Joined: Wed Aug 20, 2008 10:39 pm
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Location: Germany
heatpipes containing ionized water and an internal structure ... sintered metal or grooves

but, when you cut a pipe (I cutted one - an sintered powder) ... you do not see any fluid ... it is only such a little, you can't see ...


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PostPosted: Thu Aug 21, 2008 2:13 am 
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Joined: Sat Aug 20, 2005 3:01 am
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The heatpipes you deal with on computer equipment will contain distilled water, which is cheap and easy, and environmentally safe, amongst other qualities.

The amount is tiny because water converting to steam undergoes a 1-1680 expansion ratio, and if the amount were much greater, no material we have would be able to take the pressure... aka it would burst.... violently.

Hope this helps.

Atomic


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 Post subject:
PostPosted: Wed Sep 10, 2008 5:53 am 
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Joined: Sun Aug 11, 2002 3:26 pm
Posts: 191
A fluid vaporizes more readily as ambient pressure goes down (sometimes AKA "vapor pressure"). So, theoretically, at least, you could use any fluid/pressure combination such that it would vaporize at the temp of the item you want to cool. (even hydrogen under very high pressure)
If you're experimenting and don't have a (or don't have a decent) vacuum pump, look at methyl alcohol. Be careful, though, as the vapor is poisonous. Also look at the freon replacements.
Also, if experimenting, you don't really need a wick/sinter so long as the fluid can flow downwards from the radiator to the heat source.
A HVAC vacuum pump will work just fine for water heat pipes as these drive the pressure low enough that water "boils" out of the AC lines. No need to buy lab gear.
You don't need much fluid, as it's not so much the fluid's thermal capacity, but the fluid's energy of state change.


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 Post subject:
PostPosted: Wed Sep 10, 2008 5:58 am 
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TheAtomicKid wrote:
water converting to steam undergoes a 1-1680 expansion ratio...

I think you might be forgetting that, as water converts, pressure goes up - and vaporization (for a finite heat source) goes down...


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 Post subject:
PostPosted: Tue Sep 23, 2008 2:42 pm 
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Joined: Sat Aug 20, 2005 3:01 am
Posts: 95
Actually, I was simply stating that if there were a significant amount of water in the pipes, as it converted to steam, it would either reach a stable point where the finite amount of heat could no longer convert the remaining water (now under much greater pressure) into steam due to the increased pressure... the only remaining question being whether or not the thin-walled copper heatpipe, could take enough pressure for it to reach a stable point, or whether it would burst.

I'm betting on burst.

Atomic


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