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Heatsink area and welding material

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December 16, 2005 9:08:16 PM

A heatink basically has to be touching the metal top part on the processor, correct? Is this what you are sanding, or the block itself? Is the most area touching the metal area the best? What about attaching copper to copper? Can i just soder this together for the best results?

I was thinking of making something like a cross between this:
http://www.tigerdirect.com/applications/SearchTools/ite...
and this:
http://www.tigerdirect.com/applications/SearchTools/ite...

And what does a heatpipe do and how does it work?
December 16, 2005 9:28:13 PM

i still dont' understand how it works exactly. Does that heatpipe go throughout the base, or just go up to it? What liquid do they put in there or doesn't it really matter?
Related resources
December 16, 2005 9:37:52 PM

Heatpipes simply transfer heat to the heatsink. They're hollow pipes that carry hot air. The advantage is you can have a heatsink quite a distance away from the processor or whatever it is you're cooling. Also, you can disperse heat more efficiently with heatpipes. Another advantage is a passive cooling system (i.e., a system with NO fans). Since heat pipes are great at transfering heat... they can be configured to go all over the place and eventually hook up w/ a heatsink. Heatpipes are commonly found standard in laptops and very very high end video cards.

The disadvantage is they don't work as well as a large heatsink sitting directly on top of the processor. However, a hybrid solution (like the one posted above and the ones you posted) work quite well.

As for soldering stuff, please don't do that. That's what clips are for. Additionally, you need thermal paste between the heatsink and the processor. Metal on metal doesn't transfer heat that well. Using a thermal paste (like arctic silver) does a better job transfering heat.

-mpjesse
December 16, 2005 9:44:39 PM

lol, i wouldn't weld the heatsink to the processor!!! I'd be soldering pieces together for the actual heatsink pieces, like soldering heatpipes to the fins or something.
December 16, 2005 9:46:13 PM

oh, and for the cpu heatpipes, do they use just air, or water, or what?
December 16, 2005 9:52:00 PM

Here is a link on heatpipes for any interested.

http://www.cheresources.com/htpipes.shtml

mpjesse is right about the metal on metal. No matter how smooth it may look and feel, at a microscopic level it looks like a mountain range. Put 2 mountain ranges together and you only have good contact at a couple of the peaks. That's the only place you get good heat transfer between the metals, the gaps slow it way down. Thermal grease fills in all of the gaps with a substance that conducts heat very well, so it's almost like your processor die and the heatsink are one continuous piece.
December 16, 2005 10:11:12 PM

Heat transfer rates depend on the difference between the temperature of the heatsink and the temperature of the air (also the air flow rate, surface area, etc, but those are other topics). To have an efficient heat sink, the entire heat sink should be the same temperature. Normally you have a very hot base (where the processor is). The sink is cooler further away from that heat source, because the fins are shedding heat to the circulating air. For maximum efficiency and heat transfer, you want every part of the heatsink to be the same temperature. Materials like copper and aluminum conduct heat very well, and thus a smaller heatsink made of these material will be close to the same temperature everywhere, making a very efficient sink. Now, as heatsinks get bigger and bigger, the heat transfer within the material just isn't enough, and bigger heatsinks don't give you as much increase in heat transfer anymore because you get more of a temperature difference between the base and the edges. Here's where the heatpipes come in. You'll notice a lot of new heatsinks are big and have heatpipes running from the base to the middle and often the top of a heatsink. The heatpipes transmit heat more efficently than just a big piece of copper. The help to even out the temperature in the sink as a whole by moving the heat to the middle and top of the sink. In itself, it doesn't get rid of much heat at all, but it helps to improve the overall efficiency of the sink by making the middle and top of the fins nearly as hot as the base. It can also be used to move heat around, such as on the new asus board where heatpipes move the heat from the chipset to a common heatsink.

http://www.newegg.com/Product/Product.asp?Item=N82E16813131568
December 18, 2005 12:25:10 PM

Now, wait.... All these premade heat pipe heat sinks only seem to work if your board is sitting horizontal, not vertical. The heat has to rise, correct? Would I be able to bent the heatpipes to make sure that it's in the upright position?
December 18, 2005 5:04:14 PM

Quote:
The heat has to rise, correct?

No, not necessarily. If you have a heatpipe with just the working fluid and are using gravity to bring the condensed liquid back to the heat source, then yes. But most heat pipes are lined with a "wicking" material (see the link I posted earlier). The liquid will evaporate where it's hot and condense where it's cooler. The wick makes sure that the fluid gets back to where it needs to be, regardless of the orientation. Inside the pipe, the fluid is basically all the same temperature. The way these heatpipes work is by letting a fliud change phase, between liquid and gas, which takes a lot of energy. The pipe basically reaches a working temperature, then it transfers heat by letting the fluid evaporate at one point and condense at another.
December 18, 2005 5:32:37 PM

i never thought of evening out the heat distribution. according to that, they should design processors for dual heatsinks (one on each side).
December 18, 2005 6:09:04 PM

Ok, so if Gravity is going to bring it back down, instead of this wicking material (which i don't quite get yet, but i keep reading, lol) then i would need something that evaporated at pretty low temperatures, not water, otherwise it wouldn't work on a cpu, which only gets to like 50 C (depending).

WITH a wick, it some how brings the liquid back to the other side, no matter where it is, once it's cooled. I'm guessing this is a paper towel absorption type of idea. But, you still wouldn't be able to use water due to the 100 *C boiling point... or can you? If not, what do they use?

Also, this means that basically the liquid is only on the wick, and the gas is in the center, then cools by the fins, and comes back down, or at least back to the wick. SO, then it can be any shape or form. So i can use the si120 without a problem.

But what if i wanted to build my own heatpipe, just for an experiment? I would get some copper pipe, water, but then how do i coat the inside with a wick of some sort? I could obviosly just put it over the stove to see if it works with gravity, but i'd like to test the theory of having the heat source on top, and if possible, the same temps as a computer. I guess i would just make a jumbo version for fun.
December 18, 2005 9:46:56 PM

Quote:
WITH a wick, it some how brings the liquid back to the other side, no matter where it is, once it's cooled. I'm guessing this is a paper towel absorption type of idea. But, you still wouldn't be able to use water due to the 100 *C boiling point... or can you? If not, what do they use?


You're on the right track. The wick uses capilary action (the same thing that will make water flow up a paper towel) to move the fluid from where it condensed to the heat source, and I know many of them work in one direction. Water could be used as the working fluid, but something like ethanol would probably work better for the temps of a processor. The type of wick used is very important for the overall performance of the heat pipe. I don't know what you would make your own wick out of.

If you decide to make your own, You should definitely read the article I posted earlier, as it goes over the major design points:
http://www.cheresources.com/htpipes.shtml

Also, be aware that your heat pipe must be well sealed. There is danger of an explosion :(  because the pressure will increase as the pipe heats. If you happen to use ethanol and a heat source, you also run the risk of an explosion from pressure and a fire from the ethanol. The bigger the pipe, the bigger the bang if it blows! I would recommend buying a pre-made heat pipe and bending it to suit you. You aren't likely to get very good performance building one yourself anyway.
December 19, 2005 3:12:37 PM

well, i did find a site where a guy built his own out of R134a, but it was gravity fed, not wick.

Where would i buy some of these things? I've got the idea of linking my cpu to the chipset and then have a bend upwards with fins and a fan blowing it right out the side of the case. They would have to be about 10" to a foot and the smaller the better.
December 19, 2005 3:24:15 PM

Soldering the heatsink to the processor is actually an intriguing idea :) 

(not that I would try it!)
December 19, 2005 3:30:07 PM

well, not soldering it, i would still use arctic silver and try to incorperate the board's typical mounting system for both items. But yeah, Why not cool both at the same time? Maybe I could Make a _I_ with the I having the fins and fan. I guess it would be more like __IIII__

I was thinking 3 heatpipes from the cpu and 2 from the chipset and meet in the middle for cooling.
December 19, 2005 5:07:20 PM

Quote:
Soldering the heatsink to the processor is actually an intriguing idea :) 

(not that I would try it!)


Not that I would try it is right! Standard solder melts at around 360 degrees F I think. I don't think you want to take your CPU core to that temperature. You could use a thermal adhesive. That would give you a pretty permanent bond.
As far as making your own heat solution, I don't know where you can buy a heatpipe. You'll probably have to do some searching. It may not be the sort of thing that's easy to get just one of. I don't think there's a huge consumer demand for them. If you can find a company, ask for an engineering sample, sometimes those are free. :wink: You could possibly take something like the Asus A8N32-SLI Deluxe (which I have heard is pretty hard to get ahold of). You might be able to reroute those bad boys or use it as a start for your custom all in one heat solution, since that board is already routing most of the chipset heat to another sink. Are you trying to do something with your processor sink like the Shuttle barebones have?
December 19, 2005 9:33:35 PM

Quote:
You might be able to reroute those bad boys or use it as a start for your custom all in one heat solution, since that board is already routing most of the chipset heat to another sink. Are you trying to do something with your processor sink like the Shuttle barebones have?


Shuttle barebones kits have that? gotta link with a GOOD picture? I can't find one.
December 19, 2005 9:41:47 PM

That's the best explanation of how heat pipes work I've ever seen.

-mpjesse
!