mnick12
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Liquid heat exchangers
So I recently ordered some Peltier chips, and as you may know to run properly they need a good way of disspaiting heat. For small chips a heat sink is
generally enough, but for larger ones you need a massive heat sink or something better. I was thinking of using a liquid heat exchanger also known as
a water block. The problem I have run into is a good water block is generally $60.00 to $90.00. Which is ridiculous considering I can get a 540w chip
for 1/3 the price. I dont even understand why they are so pricey all they are is a machined piece of aluminum or copper with two nozzles.
My idea for the water block was to have it run through a radiator where a fan would cool the coolant back down. But considering how expensive water
blocks are I am forced to go a different route. My question is what would be a good alternative to a water block? Or could a water block be made
without to much trouble?
Here some stuff http://en.wikipedia.org/wiki/Water_block , http://en.wikipedia.org/wiki/Peltier_cooler .
Thanks
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watson.fawkes
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Quote: Originally posted by mnick12  | | My question is what would be a good alternative to a water block? Or could a water block be made without to much trouble? |
If you're handy with a brazing torch, you can make an adequate one without too much trouble. Unlike a water block for a computer,
yours doesn't have to be so compact. Start with a slab of copper about 1/4" thick and the same plan outline as your Peltier device. Now take a length
of refrigeration tubing of convenient diameter, say 1/4". Roll it up into a coil the same height as one of the slab dimensions. Carefully flatten the
coil so that one side is straight for the length of the slab. It may be easier for you to wind it on a former, a block of wood with rounded ends to
avoid pinching the tubing. Braze it all up in a single operation, jeweler's style, where you pre-flux the entire joint, slab and pipe both, lay down
your fusion alloy (hard solder or brazing rod). Heat from the bottom until everything melts.
Add compression fittings if you want to make the block demountable. Or else get a swaging tool for your tubing and just braze the whole thing
together.
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Mr. Wizard
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I agree making one with copper tubing wouldn't be too tough. I would use solder though instead of brazing. Solder will work just as well and can be
done with more commonly available materials and tools. I agree with watson-falkes' suggestion to pre flux and tin everything before you go for the
final bonding. You might even tin the tubing before you form it.
There might be some confusion as to what is soldering and what is brazing. Brazing to me involves a much higher temperature close to red heat, and a
non lead / tin alloy.
[Edited on 11-7-2010 by Mr. Wizard]
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Sedit
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What about just forgoing the solder or brazing and go for epoxy? Make the block itself out of either Plexi glass or metal and for the base tha acts on
the hot surface use a piece of Aluminum pie tin. It will be thin enough for rapid heat exchange yet strong enough to not tear at first sight.
It does not seem like a design that needs overthinking at all. Just glue some tin to a block and run some water thru it as fast as you can.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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ciscosdad
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Soldering/Brazing
I have had considerable experience both soldering and brazing. They are the same thing but with alloys of different temperature ranges.
The keys to success are:
1 clean the base metals (abrasive)
2 apply flux to where you want the braze to go and
3 control the temperature (to avoid oxidizing the substrate or the brazing alloy).
This is why you would choose copper as the plate material. Much easier to braze or solder.
Glue will be a lot less efficient at heat transfer as the epoxy (or whatever) is actually a poor conductor of heat and you will be depending largely
on whatever direct contact points there are between the 2 pieces. Solder or brazing alloy will transfer heat very well for a much better result.
I could go on, but you get the idea.
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Wizzard
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Those 540W modules are a joke. I have one, and if I can get 6V/150W into it without the wires melting, it's a nice day. And I put solid-core copper
wire leads on, about 10AWG. Most peltiers are rated for 12V DC. It's still anice module, but 540W is some rediculous energy output density- Could
likely rival those perfect chips of solicon we pump 200W into 
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watson.fawkes
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I recommended a "brazing torch" to indicate that it takes a lot of heat to get a block of copper and bunch of tubing up to temperature enough to
liquefy your fusion alloy, whatever it is you use. A soldering iron just isn't going to work. Another way of getting it up to heat would be to use an
electric hot plate. Protect the hot plate with a sheet of aluminum, which won't react with ordinary soldering/brazing materials.
I second the recommendation to pre-tin everything. On large pieces like this, it sure helps to get everything to fuse all at once.
I don't think it matters a huge amount here between brazing and soldering. I wouldn't use a lead-based solder, though, out of concern for both the
environment (your own) and bond strength. I would specifically recommend a silver-bearing fusion alloy, though, because they have much lower surface
tension when liquid. There's a lot of surface contact area in a cooling block, which is the whole point, after all, and it all needs fusion with your
alloy so that it's actually, not apparently, in thermal contact. There are tin/antimony/silver solders available as lead-free plumbers solder
available at home stores. I already have a supply of 2% silver brazing alloy, though, which is what I'd use if I were doing it today.
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mnick12
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Thanks for the ideas.My chips are 40mmX40mm , but they are still in the mail.
I am thinking about using aluminum blocks instead of copper since they are quite a bit cheaper. My idea is to order some of that thin copper tubing
you see on refrigeration units wind it into tightly packed zigzags and then bond to the block with a thermally conductive epoxy or braze it. My torch
is a plumbers propane torch so I hope that will work.
Thanks.
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unionised
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| Quote: Originally posted by Wizzard | | Those 540W modules are a joke. I have one, and if I can get 6V/150W into it without the wires melting, it's a nice day. And I put solid-core copper
wire leads on, about 10AWG. Most peltiers are rated for 12V DC. It's still anice module, but 540W is some rediculous energy output density- Could
likely rival those perfect chips of solicon we pump 200W into
|
Are they rated for the power that you feed them, or the power they pump?
In any event, good luck trying to solder aluminium. It's not impossible, but it's tricky. Thermal epoxy might be a better bet.
Also, why not cut out the middle man and glue the coiled tubing straight to the Peltier?
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densest
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@unionised - the Peltier units have extremely thin alumina plates for top and bottom - strong, but very brittle. The metal in contact with them must
be level to an extraordinary degree or they'll shatter. Also, the heat is dumped in in an array of point sources and the lateral heat conductivity is
very low so a metal heat spreader is very useful when trying to couple such a unit to anything else.
[Edited on 13-7-2010 by densest]
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franklyn
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| Quote: Originally posted by densest | | Peltier units have extremely thin alumina plates for top and bottom - strong, but very brittle. The metal in contact with them must be level to an
extraordinary degree or they'll shatter. Also, the heat is dumped in in an array of point sources and the lateral heat conductivity is very low so a
metal heat spreader is very useful when trying to couple such a unit to anything else. |
Lapping offers no
particular advantage.
Products like this are what are used to mate Heat sinks to CPU processors.
http://www.google.com/search?hl=en&source=hp&q=arcti...
@ mnick12
Water cooling is quiet but heat sinking capacity depends on the
capability of a particular system employed not the method used.
The computer case is the major obstacle to cooling adequacy.
Simply leaving the case door off will improve the ability of any
chip heat sink fan. A work around is to channel air directly from
outside the case with a PVC pipe duct attached to a hole cut
into the case door directly over the heat sink fan .
There are commercially available units employing a flexible duct.
- Fan duct kits
http://2cionline.com/nova/Products/computers/cpu_vent.htm
http://www.directron.com/badongs60.html
http://www.highspeedpc.com/Merchant2/merchant.mv?Screen=CTGY...
- Fan adpters and ducts
http://www.jab-tech.com/Fan-adpters-and-ducts-c-171.html
3 inch flexible duct
http://www.grainger.com/Grainger/items/3C590?Pid=search
4 inch inch flexible duct
- http://www.grainger.com/Grainger/items/3C591?Pid=search
.
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JohnWW
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Here are a few PDFs on the subject of Peltier (effect) coolers:
http://www.designer-iii.com/cco/Peltier.pdf
http://www.solstice-analyse.com/docs/produits/prelevement_co...
http://ankersmidsampling.com/cooler%20APC%203xx%20m&c.pd...
http://www.freepatentsonline.com/5960142.html
http://saaubi.people.wm.edu/TeachingWebPages/Physics252_Spri...
http://www.micropelt.com/down/datasheet_mpc_d403_d404.pdf
http://www.bradford-space.com/pdf/be_paper_peltier_glovebox....
http://web.mit.edu/nanoengineering/publications/PDFs/NPO3055...
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Texium
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