View Full Version : Copper and Aluminum
Hey! I have an idea! I don't know if it would work, if it would make temps better/worse, or anything at all, but it is an idea...
What would happen if you electoplated (or plated in any way) a copper heat sink with aluminum?? I read somewhere that copper has a higher heat transfer rate than aluminum, and aluminum conducts heat into the air better than copper... So what if we took the best of both worlds and coated a low resistance copper heat sink with a high air transfer rate aluminum coating?
Just wondering if this would work. Might there be any chemical reactions between the copper and aluminum that would be bad for the HS, or would the small amount of aluminum not make much of a difference? If so, are there any HS manufactures that make copper heatsinks with aluminum fins? I've been thinking of such a heatsink for a while now, and was wondering...
JigPu
I think you want to go the other way. IE Copper clad Aluminum. We all know that pure copper conducts heat almost 100% better than aluminum, but copper is much more dense than aluminum and consequently does not want to relinquish the heat to air or water as readily as aluminum. I would think that the last thing you want in the core of your thermal radiator is copper, but I could be wrong. I am working on a long term experiment with a Swiftech MC-462A. I have extracted the aluminum pins and found a source for copper clad aluminum pins that I intend to try instead. Staking the pins into the copper baseplate has been quite a challenge since I don't have access to more sophisticated metal working equipment, but I am progressing nevertheless. The summer up here is short and I have been consumed with many seasonal maintenance chores on my house, not to mention recovering from a severe hail storm that levied in excess of $15,000 worth of damage to it and the cars. I still hope to complete it before the end of summer, but one must have their priorities in order. It bugs me not being able to devote the time to this project, but then I'm not sure how many people it would benefit. I mean, who else wants to take the chance of trashing an $80.00 HSF? ;D Stay tuned...
Hoot
It_The_Cow
07-11-01, 11:55 PM
Best wishes Hoot. Your article will be most interesting
Hoot (Jul 11, 2001 11:48 p.m.):
IE Copper clad Aluminum. We all know that pure copper conducts heat almost 100% better than aluminum, but copper is much more dense than aluminum and consequently does not want to relinquish the heat to air or water as readily as aluminum.
Huh? Sorry, but thats just what I wanted... The copper to quckly transfer the heat to the aluminum which will quickly transfer it to the air. The other way around and the heat is more slowly conducted ("pure copper conducts heat almost 100% better than aluminum") and then is more slowly transferred to the air ("but copper is much more dense than aluminum and consequently does not want to relinquish the heat to air or water as readily as aluminum.")
So use the aluminum for the metal -> air transfer and copper for the die -> aluminum transfer. Aluminum coated copper....
Thats how I understand it...
JigPu
Anyone else have anything to say? I am really interested in wether this would work or not, and I would like suggestions, comments, ect.
JigPu
inertia
07-13-01, 12:46 PM
Hoot I know you're a respected member of this board, but I gotta' call ya' out on the copper coated aluminum and say that I think you've got it backwards. But, let us know how it turns out.
Now if ya wanna electroplate a copper heatsink with aluminum, first ya' gotta look at your handy dandy periodic table of the elements. Let's see here, it looks like copper who's symbol is Cu and for which the island of Cypress was named is # 29. Aluminum is # 13. This means something, but I don't remember what. Get an 8 foot piece of wire. Cut it in half. Strip all of the ends. Tie one end of one wire to a copper heatsink. Get some Tums and crush 'em up into a bucket of water. Swish it around. Throw one end of the other wire into the bucket. Hook up the unused ends of the two wires to your DC power supply (could be a battery.) Now, drink a beer. Ok now it should be electroplated with aluminum. Unless you got the polarity wrong. Oh, we determine the polarity with the periodic table. That's what that's for. Um, the copper should be on the hot side. I think. Hook it up like that, if it doesn't work throw away the heatsink and start over, but hook it up the other way this time.
It might be Rolaids. One of 'em is a water-soluble aluminum salt. Use that one. Oh, and hold everything together with Duct Tape. And strip the wires with a Swiss army knife. That's it.
Thanx for the electroplating procedure! I would do it myself, except I don't have a heatsink to mess around with. Both are being used at the moment, and I dont got no backups... Mom would kill me if I messed up her pooter cuz the HS didn't work, and I don't want my pooter conking out...
Would do it if I could...
Anyone else??
JigPu
A few microns of plating will not be enough to realize enhancement. You would probably need something like a mil (.001) or more.
I silver plated my copper baseplate on my MC-462A to approximately 8 microns and it did not result in a measurable improvement in heat transfer from the core to the baseplate.
Hoot
William
07-14-01, 12:42 AM
actually I am with hoot on this as you want the heat to spread, but it has to be dissapated better. Put the metal that gives away heat more easily on the inside. Hmm, how to explain it. Essentially aluminum would be an insulator as it has a lower conductance. By insulating the inside you are forcing the heat outwards and into the air.
The son I never had...sigh ;D
Hoot
I have seen a few aluminum heat sinks with "copper cores" but never the other way around. Maby I just don't understand what they mean by "core", but I've never seen a copper heatsink with aluminum core, and so wouldn't the HS manufactures agree with me on aluminum plated copper?
As for the thickness, I was thinking about putting on more than a few microns. I don't know how much, but definatly more than that.
And as for the explination for copper plated aluminum, are you trying to say that since aluminum transfers heat to other substances better, it should be on the inside transferring to the copper? If so, then why even bother with the copper plating? It has lower thermal resistance, but won't transfer the heat to the air as good (the heat would sort of "build up" waiting to get off the copper). My idea was to get the heat through the heat sink as fast as possible (using a low resistance metal) and then get it off the heat sink as fast as possible (using the aluminum which is better at that).
JigPu
Does anyone remember the name of theat heatsink from which the thermoengine is a cheap copy? Its basically the same but the round core piece is solid copper and the fins are Aluminium soldered on. This would seem like a real good idea in the copper/alu tests.
Now where did I see that review??
JigPu (Jul 14, 2001 11:46 a.m.):
I have seen a few aluminum heat sinks with "copper cores" but never the other way around. Maby I just don't understand what they mean by "core", but I've never seen a copper heatsink with aluminum core, and so wouldn't the HS manufactures agree with me on aluminum plated copper?
I think they meant 'base' as the 'core'. You'll need a higher conductivity base for the fins or pins to sit on so that more heat gets distributed to the outer fins rather than just concentrating on the fins just right above the CPU core. A cold heatsink fin doesn't lend much hand in throwing heat to the ambient. Note also that axial fans cannot blow air right smack above the center of the HS, above the CPU core by virtue of their build (anybody wanna try to fix a centrifugal blower to replace the 'normal' fans above a heatsink? The airflow from them blowers are more distributed -ie. uniform mass flow flux). There you have it, two reasons why you need more conductive metals at the base of the fins/heatsink. But of course, these hybrid copper/aluminium heatsinks are either just a gimmick (to sell the aluminium better!) or a economical measure compared to all-copper (or silver!!) heatsinks. Of course, if the CPU core is large enough (old Pentiums, K6s, etc.) so that the entire bottom of the HS is in contact with it, there'll be very little reason to have a copper-cored/based aluminium heatsink.
Oh, BTW, plating an extremely thin layer of highly conductive metal onto a lower conductivity metal would do little to 'spread' heat as it would be quite hard for heat to travel width-wise as the cross-sectional area in the horizontal plane is very small. As all of you know, thermal resistance is inversely proportional to cross-sectional area. What is the optimum thickness? Beats me. 3-dimensional heat transfer is a really tough subject. As for the fins/surface in contact with the air/water, I don't think it really matters whether it's aluminium, copper, gold, silver, or unobtanium, as long as CUMULATIVELY (considering space and cost constraints as well) they appear to be a super-large surface area to your CPU core -but of course, whenever possible, use a highly conductive metal. Take it like this: you can imagine a fin of metal X which is much more a conductive material as metal Y to be of thinner and taller build than a fin made out of metal Y in proportion. Similarly, a heatsink base of copper would appear to the CPU core as a thinner base of aluminium. Of course, the base cannot be infinitesimally thin as the heat transfer in the horizontal plane would be obstructed, as mentioned earlier. Like most things in life, there's an 'optimum curve graph' for it or something like that.
The idea that copper does not transfer heat to the atmosphere as well as aluminium is a complete myth.
Given the same surface area, same surface finish (rougher the better) , same temp difference and air flow, both materials will transfer heat to air the same.
The only possible difference would be due to colour, dark matt colours radiate reat better than light shinny ones, but there's not much in it between copper and aluminium (unless the aluminium is anodised black). Anyway most of the heat is tranfered by convection not radiation so colour is pretty insignificant.
Me did not know that... I read that aluminum transfers to air better than copper, and that is why they made some heat sinks out of aluminum. If that IS true, then this whole idea dosen't work... Still I'd like to see a heat sink like that.
If you know of any numbers proving this, I'd like to know (just to convince the reasoning part of myself about this).
JigPu
Badger (Jul 15, 2001 07:38 a.m.):
The idea that copper does not transfer heat to the atmosphere as well as aluminium is a complete myth.
Given the same surface area, same surface finish (rougher the better) , same temp difference and air flow, both materials will transfer heat to air the same.
The only possible difference would be due to colour, dark matt colours radiate reat better than light shinny ones, but there's not much in it between copper and aluminium (unless the aluminium is anodised black). Anyway most of the heat is tranfered by convection not radiation so colour is pretty insignificant.
Yeah I tough heat transfer by radiation was negligable too....until I got that lemon of a Sunon 120mm AC fan. The hub of that fan gets so hot (has an induction motor there) that it is able to pass on the heat to the aluminium casing (warm to the touch)!! Since there is nearly no direct contact between the hub and the outer casing, the heat must have gotten there by radiation. Beware of using AC fans!!!
JigPu (Jul 16, 2001 12:03 a.m.):
Me did not know that... I read that aluminum transfers to air better than copper, and that is why they made some heat sinks out of aluminum. If that IS true, then this whole idea dosen't work... Still I'd like to see a heat sink like that.
If you know of any numbers proving this, I'd like to know (just to convince the reasoning part of myself about this).
JigPu
Most theoretical heatsink and radiator analysis is very involved -to extent of using computer simulations (CFD, FEM). The only numbers you'll get easily, of, course, is through experimentation -that's what WE do here. By sifting through all the heatsink and waterblock reviews here you can see that there are aluminium heatsinks/waterblocks that perform better than all-copper heatsinks/waterblocks. But of course, it's usually the other way around -why, copper IS more conductive (one factor out of many), and the geometry, the shape of the copper heatsinks themselves are already refined, no doubt from previous experiences with ALUMINIUM heatsinks. So, it's more a matter of good geometry but without forgetting that materials (and airflow, etc.) also permits heat to be thrown away more easily to the ambient.
Thelemac
07-16-01, 02:24 AM
I'm not really sure if this was implicated or not as I am having difficulty understanding words right now (I'm a tad ti*yawn*red) so here goes:
Even given better conduction to air by AL, coating the CU with it isn't really going to help cause AL conducts the heat within itself much more slowly than the CU...meaning that the CU will be getting the heat to the AL, but the AL won't be taking it that quickly. So you'll have a bottleneck. What you could do to improve CU is get a *really* big fan and stick it on there...CU has a much higher cfm threshold before you get start diminishing returns as it gets heat back to the surface more quickly than AL...so more air would be helpful.
Thelemac (Jul 16, 2001 02:24 a.m.):
I'm not really sure if this was implicated or not as I am having difficulty understanding words right now (I'm a tad ti*yawn*red) so here goes:
Even given better conduction to air by AL, coating the CU with it isn't really going to help cause AL conducts the heat within itself much more slowly than the CU...meaning that the CU will be getting the heat to the AL, but the AL won't be taking it that quickly. So you'll have a bottleneck. What you could do to improve CU is get a *really* big fan and stick it on there...CU has a much higher cfm threshold before you get start diminishing returns as it gets heat back to the surface more quickly than AL...so more air would be helpful.
No, no. Having AL doesn't automatically mean better convection heat transfer to air! Material conductivity is only one aspect of thermal resistance (C/W) of a HSF. It's primarily the way the fins are designed -how tall, how many, how well they let the airflow through. The best possible heat transfer (from a fin) will arise when the ENTIRE fin of a heatsink is at the same temperature as its base (in reality, the temperature at the base of a heatsink is always highest and drops when nearer to the tip since heat has been taken away by airflow or radiation). To have this, you'll need a material with an infinitely high thermal conductivity. The whole fin would have to be made out of that hypothetical material -so why bother with different metals?. To put it in a better way, copper-coated AL fins would be like plastic hot water bottle with a metal outer skin and AL coated copper fins would be like a metal hot water bottle with a plastic outer skin. Why not have an all-metal bottle to cool down the hot water?
Er, have I been beating around the bush?
dozier768
07-16-01, 05:35 AM
Badger (Jul 15, 2001 07:38 a.m.):
The idea that copper does not transfer heat to the atmosphere as well as aluminium is a complete myth.
Given the same surface area, same surface finish (rougher the better) , same temp difference and air flow, both materials will transfer heat to air the same.
The only possible difference would be due to colour, dark matt colours radiate reat better than light shinny ones, but there's not much in it between copper and aluminium (unless the aluminium is anodised black). Anyway most of the heat is tranfered by convection not radiation so colour is pretty insignificant.
well the rougher the more surface area but as far as color goes.... it has nothing to do with radiant heat dissipation it has to do with ultraviolet light radiation absorption and that would not come into play inside your case. or at all for that fact, and the core heat is transferred by conduction to the heatsink and active convection to the air via a fan
Thelemac
07-16-01, 12:28 PM
cjtune (Jul 16, 2001 05:05 a.m.):
No, no. Having AL doesn't automatically mean better convection heat transfer to air! Material conductivity is only one aspect of thermal resistance (C/W) of a HSF. It's primarily the way the fins are designed -how tall, how many, how well they let the airflow through. The best possible heat transfer (from a fin) will arise when the ENTIRE fin of a heatsink is at the same temperature as its base (in reality, the temperature at the base of a heatsink is always highest and drops when nearer to the tip since heat has been taken away by airflow or radiation). To have this, you'll need a material with an infinitely high thermal conductivity. The whole fin would have to be made out of that hypothetical material -so why bother with different metals?. To put it in a better way, copper-coated AL fins would be like plastic hot water bottle with a metal outer skin and AL coated copper fins would be like a metal hot water bottle with a plastic outer skin. Why not have an all-metal bottle to cool down the hot water?
Er, have I been beating around the bush?
I think I didn't make myself clear on that. By "Even given better conduction" I meant "Even if there were better conduction"
dozier768 (Jul 16, 2001 05:35 a.m.):
Badger (Jul 15, 2001 07:38 a.m.):
The idea that copper does not transfer heat to the atmosphere as well as aluminium is a complete myth.
Given the same surface area, same surface finish (rougher the better) , same temp difference and air flow, both materials will transfer heat to air the same.
The only possible difference would be due to colour, dark matt colours radiate reat better than light shinny ones, but there's not much in it between copper and aluminium (unless the aluminium is anodised black). Anyway most of the heat is tranfered by convection not radiation so colour is pretty insignificant.
well the rougher the more surface area but as far as color goes.... it has nothing to do with radiant heat dissipation it has to do with ultraviolet light radiation absorption and that would not come into play inside your case. or at all for that fact, and the core heat is transferred by conduction to the heatsink and active convection to the air via a fan
Oh yes it does !, that's why manufacturers often anodize aluminium heatsinks black, and the same reason why most car radiators are black.
Badger (Jul 17, 2001 12:42 a.m.):
dozier768 (Jul 16, 2001 05:35 a.m.):
Badger (Jul 15, 2001 07:38 a.m.):
The idea that copper does not transfer heat to the atmosphere as well as aluminium is a complete myth.
Given the same surface area, same surface finish (rougher the better) , same temp difference and air flow, both materials will transfer heat to air the same.
The only possible difference would be due to colour, dark matt colours radiate reat better than light shinny ones, but there's not much in it between copper and aluminium (unless the aluminium is anodised black). Anyway most of the heat is tranfered by convection not radiation so colour is pretty insignificant.
well the rougher the more surface area but as far as color goes.... it has nothing to do with radiant heat dissipation it has to do with ultraviolet light radiation absorption and that would not come into play inside your case. or at all for that fact, and the core heat is transferred by conduction to the heatsink and active convection to the air via a fan
Oh yes it does !, that's why manufacturers often anodize aluminium heatsinks black, and the same reason why most car radiators are black.
Yes, I agree. It's to approach the emissivity of a 'blackbody' (which is a hypothetical body incapable of reflecting back any light). Not just black, I think there are other colours as well that do the trick but I can't remember... red?
dozier768
07-17-01, 01:34 AM
Badger (Jul 17, 2001 12:42 a.m.):
dozier768 (Jul 16, 2001 05:35 a.m.):
Badger (Jul 15, 2001 07:38 a.m.):
The idea that copper does not transfer heat to the atmosphere as well as aluminium is a complete myth.
Given the same surface area, same surface finish (rougher the better) , same temp difference and air flow, both materials will transfer heat to air the same.
The only possible difference would be due to colour, dark matt colours radiate reat better than light shinny ones, but there's not much in it between copper and aluminium (unless the aluminium is anodised black). Anyway most of the heat is tranfered by convection not radiation so colour is pretty insignificant.
well the rougher the more surface area but as far as color goes.... it has nothing to do with radiant heat dissipation it has to do with ultraviolet light radiation absorption and that would not come into play inside your case. or at all for that fact, and the core heat is transferred by conduction to the heatsink and active convection to the air via a fan
Oh yes it does !, that's why manufacturers often anodize aluminium heatsinks black, and the same reason why most car radiators are black.
what light radiation would infiltrate your case? and the amount of heat produced would be to miniscule to warrant any action and the reason they anodize things it to resist corrosion and the reason for painting a radiator is the same
Crazy Jayhawk
07-17-01, 01:47 AM
The best color/texture for a heatsink would be rough black. Roughness increases surface area and black is the best color for heat radiation. A shiny heatsink may look good but its heat transfer is going to be hindered.
Anodization inhibits corrosion, but it also increases heat transfer.
dozier768
07-17-01, 01:51 AM
that's it. anybody out there want to paint there heatsink black? Goahead and do it and tell me what the delta is ill bet its the same, or worse due to insulation. it would be a good experiment anyhow maybe HOOT would take it upon himself to end this argument. I'm running a watercooler. perhaps I should put black dye in my water? of course that makes sense.
dozier768 (Jul 17, 2001 01:54 a.m.):
that's it. anybody out there want to paint there heatsink black? Goahead and do it and tell me what the delta is ill bet its the same, or worse due to insulation. it would be a good experiment anyhow maybe HOOT would take it upon himself to end this argument. I'm running a watercooler. perhaps I should put black dye in my water? of course that makes sense.
Whoa, whoa, don't go overboard there! Anodizing only add microns of tough, black metal oxide to heatsinks. It's mostly for corrosion protection or cosmetic purposes as heat transfer due to radiation is practically negligable compared to convection from airflow -don't see many anodized HSFs nowadays do you? Besides, a fin can only 'see'...other fins (mostly). But still, heat does transfer through radiation and rest assured for you, dozier768, the above discussions were more 'academic' than practical.
Be warned lest someone should actually go ahead and actually PAINT a heatsink or radiator black -it'll definitely increase the C/W (thermal resistance) of the heatsink as most paints are polymer based, dries thick, and does not adhere as well as anondization to the metal surface.
CalCoolage
07-17-01, 11:10 AM
If it is a myth that aluminum transfers heat to the air better than copper, it is a myth originated and spread by engineers and physicists. It is counter-intuitive and I've never hear anyone attempt an explanation. There are products which embody this, done by apparently very competent engineers, as from Alpha.
Provided the property is not a myth, a few microns of aluminum plating should improve the heat transfer to air of a copper heat sink, and being so thin would not impede thermal conduction at all (.001% ?) perpendicular to the surface. Conduction along the thin cross section would of course be negligible.
Not all materials can be plated to others and stay on. Sometimes you have to plate several layers of different things to get to the final layer, like for chrome plating steel.
Possibly there is a simpler way of treating the surface of copper to impove its properties, or there may be a sufficiently good alloy, and manufactures are already using it. Surface treatments have gotten to be very sophisticated. Computer chips in themselves are a sort of surface treatment of silicon.
CalCoolage (Jul 17, 2001 11:10 a.m.):
If it is a myth that aluminum transfers heat to the air better than copper, it is a myth originated and spread by engineers and physicists. It is counter-intuitive and I've never hear anyone attempt an explanation. There are products which embody this, done by apparently very competent engineers, as from Alpha.
Provided the property is not a myth, a few microns of aluminum plating should improve the heat transfer to air of a copper heat sink, and being so thin would not impede thermal conduction at all (.001% ?) perpendicular to the surface. Conduction along the thin cross section would of course be negligible.
Not all materials can be plated to others and stay on. Sometimes you have to plate several layers of different things to get to the final layer, like for chrome plating steel.
Possibly there is a simpler way of treating the surface of copper to impove its properties, or there may be a sufficiently good alloy, and manufactures are already using it. Surface treatments have gotten to be very sophisticated. Computer chips in themselves are a sort of surface treatment of silicon.
I still maintain it is a myth. If you can show me just one article accredited to a suitably qualified engineer or physicists I'll reconsider, but I know no such artical exists because it ain't so.
Alpha heatsinks do use copper and aluminium granted, but the copper is just used next to the cpu where the heat flux is greatest as a heat distributor, the aluminium is used for the rest of the HS to because it is lighter, easier to manufacture and cheaper.
Aluminium coating by thermal spray is a well established and simple process.If an aluminium coating really would increase the performance of a heatink dont you think the 'competent engineers' who design heatsinks and radiators would have tried it by now?
dozier768 (Jul 17, 2001 01:54 a.m.):
it would be a good experiment anyhow maybe HOOT would take it upon himself to end this argument.
Leave me out of this one. I've said all I care to say about the subject. ;D
Hoot
dozier768
07-17-01, 06:49 PM
Hoot (Jul 17, 2001 03:02 p.m.):
dozier768 (Jul 17, 2001 01:54 a.m.):
it would be a good experiment anyhow maybe HOOT would take it upon himself to end this argument.
Leave me out of this one. I've said all I care to say about the subject. ;D
Hoot
Sorry Hoot, I was at the boiling point and you were the first person I thought of that would actually wager an opinion based on personal experience and common sense. I was merely trying to explain that the color factor wouldn't play in to the equation and someone had to get all huffy about it. If someone doesn't like my opinion fine ignore it, if I'm wrong fine prove it and correct me in an adult manner, and leave out the exclamation points.
No, it's really a myth that aluminium transfers heat better to air (compared to copper?).
A fin, from base to tip, will have a temperature gradient. At the base, the fin is the hottest, and at the tip, the coolest. Material property such as thermal conductivity will determine 'how hard' it is for heat to flow through the fin from its base to the extremities (tip and sides). Less conductive a metal is, a larger temperature difference will be set-up between the base and the surfaces. Conversely, a highly conductive metal will permit heat transfer with lesser temperature differences throughout the length and cross-section of the fin. Given equal (mean) surface temperatures (and dimensions), heat transfer to air is the same, but with the lower conductivity metal, the base will be hotter than the higher conductivity metal.
For heat transfer to air, I can tell you (at my level, B.Mech) that there are no equations that require any material properties from the hot surfaces. Just the boundary condition, that is, the surface temperature distribution. If your CPU emits 100W of waste heat, and if its temperature isn't going any higher, you can be sure that the surface temperature distribution of the aluminium HSF on it will be in such a way that the same 100W of heat will be transferred out if it were using a copper HSF (of same dimensions, airflow, bla bla), but with the base of the aluminium HSF hotter than the copper HSF. Period.
I know that there would be a larger temp difference between the base and the tips on a heatsink with low thermal conductivity, and less a difference with a high conductivity. However, thank you for being someone who actually messes with the formulas. If the equation is not matieral dependant, then I believe you...
I thought it would work better (with more than a few microns)
JigPu
*spazzed*
07-18-01, 01:28 AM
Now if i were at school and had a shop to work on some of these theories, we'd have some of this sorted out (some of it) I'm working on some of them right now, with what I have handy, which is not much :)
CalCoolage
07-18-01, 10:34 AM
[quote]Badger (Jul 17, 2001 02:50 p.m.):
I still maintain it is a myth. If you can show me just one article accredited to a suitably qualified engineer or physicists I'll reconsider, but I know no such article exists because it ain't so.
/quote]
I have never seen a design sheet that did not assume the sink would be made of aluminum.
If such an article exists, I probably could not recognize it for what it was, and IAC would probably not understand it. Nonetheless, the fact that some people don't know of this particular theory (if there is one) does not show to me that others do not..
FWIW, which may be nothing, I'll say where I personally picked up the myth, and why I give it credence. Several years ago I used to read a non-Internet forum that had a guy who made his own heat sinks. He had been an SAE automotive engineer most of his life and his former hobby was building performance cars. He would saw blocks of aluminum, cut sheet material, knew where to obtain adhesive with excellent thermal conductivity (way before AS epoxy), would press fit or bond fins into cut slots, etc., all by his own hand. After reading incredulously about one of these, considering the amount of physical work and design time, I asked him if copper or silver would not be better. He said copper conducts better, but aluminum gives up its heat better, so it was close. Being the agnostic that I am, but also having awesome respect for the guy, I asked as politely as I could manage, would he explain how that could possibly be. He said some material properties just have to be accepted as what they are.
Not very convincing, I know, but he did not appear to be simply getting the info from someone else, and was the type of guy who could quote obscure coefficients out the whazoo.
Note that he was saying all copper and all aluminum sinks are approximately equivalent. The question still arises what happens when you combine the two.
He also clued me into the fact that silver is not really very expensive. (Everyone knows the cost of copper is trivial, I hope.) He worked out the cost of substituting silver, on the spot, He considered it practical for heat sinks, but did not know whether it would really accomplish anything.
>Aluminium coating by thermal spray is a well established and simple process
Interesting. Why DO they coat copper with aluminum this way, if I may ask?
>.If an aluminium coating really would increase the performance of a heatink dont you think >the 'competent engineers' who design heatsinks and radiators would have tried it by now
Too expensive? But I don't know that they haven't.
Possibly there is a simpler and cheaper way of treating copper to improve its properties.
I'm told that copper radiators with aluminum fins are in use, again indicating that aluminum is better for fins.
>the copper is just used next to the cpu where the heat flux is greatest as a heat distributor,
>the aluminium is used for the rest of the HS to because it is lighter, easier to manufacture
>and cheaper
But the fact that Apha used a complex, and expensive, dual material sink really shows that there is theory to back it as a better heat sink, not that they wanted to make a cheap heat sink. It seems to me an all copper sink of the same shape would be cheaper.
Aluminum is cheaper but copper is still dirt cheap, not expensive. The material cost is probably under a dollar. Copper things are not difficult to manufacture, they are easy. Check out the Gadiator clone. The reason copper sinks are more expensive to contract for is that aluminum fabricators are commonplace but copper fabricators are specialized and rare. (because of aluminum storm doors and such.) Supply and demand, coupled with competition. In addition, most of the copper sinks are an elaborate design, not simple like 99% of aluminum sinks. Probably the elaborate design is also the major contributor to their efficiency.
*spazzed* (Jul 18, 2001 01:28 a.m.):
Now if i were at school and had a shop to work on some of these theories, we'd have some of this sorted out (some of it) I'm working on some of them right now, with what I have handy, which is not much :)
Yeah, I'll be great if you could help to put up some figures from any experimentation. It'll probably convert the remaining hard-core believers of that 'aluminium-transfers-heat-to-air-better' myth. Don't forget the consequence of the first law of thermodynamics:
Energy_stored = Energy_in - Energy_out
where thermal energy is a function of temperature. Then you'll understand why a CPU core melts or just sits at a higher temperature.
Bad Maniac
07-18-01, 11:01 AM
People people, please! think about this for a while.
It is impossible to have a metal transfering heat better to another material compared to another metal. what descides how well copper or aluminum transfers heat to air is descided by the delta heat transfering capability of air and the metal in question (sorry cant think of the right word.), nothing else. So copper transfers to air just as well as it transfers to anything else, water for example. and the same goes for aluminum. and Plating a copper heatsink in aluminum would not yield any measurable improvement in my opinion.
Thanks for the lots and lots of info CalCoolage, it is likely that copper-aluminium hybrid heatsinks are manufactured as a compromise between cost and performance. Afterall, there are more facilities for the fabrication of aluminium parts than copper parts so although the material is cheap, the molds and machine setups in a factory may not be economically feasible to manufacture any more than a flat plate of copper (could also be outsourced...) to use as a HS base compared to the more complicated fins which need more complicated equipment (which they already have or are familiar with). If HSFs are mass-produced this way, capital costs really does matter but the end product will be cheaper than say, a machine shop whose costs for machining a block of aluminium or copper is of not much difference (both are soft metals -and cheap too).
As for you ex-SAE automotive engineer friend, it really beats the heck out of me why he says that aluminium 'gives up its heat better'. Even in a transient process (eg. heat to constant temperature and then remove heating), copper would cool down the fastest given equal temperatures and cooling as the specific heat capacity of aluminium is 3x that of copper (900J/(kg.K) vs. 300J/(kg.K)) -ie. aluminium holds 3x more thermal energy per mass of it at any given temperature than copper. For heavens sake, the thermal conductivity of aluminium can be taken to be the same as that to copper (200-300 W/(k.m)) if compared to steel (10-20 W/(k.m) only), so why so much fuss?
JigPu (Jul 17, 2001 08:59 p.m.):
I know that there would be a larger temp difference between the base and the tips on a heatsink with low thermal conductivity, and less a difference with a high conductivity. However, thank you for being someone who actually messes with the formulas. If the equation is not matieral dependant, then I believe you...
I thought it would work better (with more than a few microns)
JigPu
How heat transfer to air via convection is not material dependant (except for the properties of the air itself and maybe some surface roughness factor), but how well a heatsink transfers heat from the CPU core to the air IS material dependent but is balanced with the geometry of the heatsink and the airflow provided -so it's not just by virtue of material alone. IF you even want to consider radiative heat transfer, you'll need to take in account of the emmisivity, temperature, and positioning of the surrounding objects within a casing. Don't you be buying a 1-ft tall lead heatsink.
CalCoolage
07-19-01, 07:26 AM
>How heat transfer to air via convection is not material dependant (except for the
>properties of the air itself...
OK, lets suppose that we have a given volume of flow for both water and air. Is it not the thermal properties of water versus air which determines that water will cool better than air? ( rather than something like viscosity.) Why then is it irrelevant to the heat transfer what the thermal properties of the sink are? Sure the heat is carried away by convection, but the transfer of heat from the sink to the fluid is by conduction. A unit volume of water takes up more heat than air, and that seems to be the relavent property. If aluminum gives up more heat per volume unit then copper, that would seem to be the relavent property.
I did find a design sheet for heat sinks that had some formulas. Unfortunately, the design procedure works in a logical circle and involves using a "nomograph" look up, so I couldn't guess much about what the thermal resistance does to the effectiveness of a heat sink. Except for emissivity, no other property of the material enters into the figuring. Emissivity enters into heat radiation part, but not the heat conduction part. Whether the properties of copper are slipped in via the "fin effectiveness factor" I couldn't guess. But the temperature difference enters into the thermal resistance calculation as the fourth root. No wonder copper sinks perform so closely to aluminum sinks, even though copper is twice the conductor aluminum is. Still, the forth root of 2 is 1.19 so one might expect copper sinks to be 20% better than identical aluminum sinks, which does not seem to be the case.
BTW, the myth is alive and well. At
http://www.amdmb.com/article-display.php?ArticleID=101&PageID=4
They review a silver plated copper sink, and say the silver plating "gives it a higher heat dispersal rate than Copper ."
They also have this copper-aluminum babe. I don't think they were trying to save money or weight on this one:
The Swiftech MC-462A Rev1... the heatsink itself is comprised over a copper bottom and aluminum pins. Weighing in at 760 grams its attachment method alleviates any concerns you might have because of the weight.
*spazzed*
07-19-01, 02:47 PM
I'm working on a heatsink that has a copper core with aluminum fins, all held together by silver solder (the jewlers stuff).........copper in the middle, because it absorbs heat better from a heat source, and aluminum fins, since aluminum dissipates heat into the air better than copper. The silver solder is to hold everything together with as little loss of heat transfer as possible :)
Hope it works
Spaz, I didn't know you could silver solder aluminum, but whatever the process to get there, it sounds like an excellent idea. Can't wait to see it and hear how it performs.
Hoot
*spazzed* (Jul 19, 2001 02:47 p.m.):
I'm working on a heatsink that has a copper core with aluminum fins, all held together by silver solder (the jewlers stuff).........copper in the middle, because it absorbs heat better from a heat source, and aluminum fins, since aluminum dissipates heat into the air better than copper. The silver solder is to hold everything together with as little loss of heat transfer as possible :)
Hope it works
You cant silver solder aluminium, plus if you read this thread you will see the message coming accross that the idea that aluminium conducts heat to air better than copper is a fallacy.
Good luck anyway, but dont wast your time trying to silver solder alu and copper together!
CalCoolage (Jul 19, 2001 07:26 a.m.):
>How heat transfer to air via convection is not material dependant (except for the
>properties of the air itself...
OK, lets suppose that we have a given volume of flow for both water and air. Is it not the thermal properties of water versus air which determines that water will cool better than air? ( rather than something like viscosity.) Why then is it irrelevant to the heat transfer what the thermal properties of the sink are?....
How heat transfers through fluid depends on the property of the fluid -yes, by conduction and advection, the movement of the fluid itself. Only the surface temperatures of the heatsink is needed -the surface of any material.
How heat transfer through a heatsink depends on the material of the heatsink, among others. Only the temperature of the interfaces in needed (did I say it was watercooled or TEC cooled? It doesn't matter, as long as a temperature gradient exists)
But when one says air removes heat BETTER from aluminium, we are looking at the heat transfer process from the view point of the working fluid (be it air, water, or flourinert). But if we say, aluminium transfers heat (conducts) better than copper, we are looking at the latter condition, which requires values of thermal conductivity.
As for specific heat capacity, yes, it is of NO CONCERN because as time progresses (esp. on the hours/days a PC might be on) as once it is saturated, they'll ALL reach a constant temperature. In other words, the heat capacity only delays heat from being transferred form the heatsink to the air (but of course the CPU is being cooled as the waste heat is still being removed form it and is being stored in the heatsink) -for the first few minutes after powering up. In a water cooler setup, if your radiator or bong is inept at throwing heat to the ambient, however large the heat capacity of the water in your rig after adding additives or whatever will not help your CPU except for the first hour or so.
I did find a design sheet for heat sinks that had some formulas...
This is sheet for the design of the geometry of a heatsink to determine its effectiveness in throwing away heat via the combined effects of convection and radiation (how's this, dozier768? Looks like the engineers gave a damn about it). Look for a variable 'k' anywhere in the equations. If you find it, try and substitute different values and see what you come up with. But then it may have been taken as one lump sum when determining the (expermental) correlations between fin performance/effectiveness/thermal resistance with respect to length, thickness, and the convection (ie. airflow) heat transfer coefficient -which also has to be determined expermentally. BTW, the fourth root (ie. deltaT0.25) is from natural convection, that is, the movement of air without the assistance of fans -it seems either that the engineers where very thorough in including this (which is usually neglegable with forced convection), or this heatsink was meant for passive cooling (no fans). Together, the heat transferred will vary to deltaT to the power of 1.25 (deltaT0.25*deltaT) for natural convection. Even then, it is NOT always to the power of 0.25 -this depends on the temperature range and fluid type. Between lower temperature ranges, the (additional) deltaT may be to the power of 0.2 or 0.18.
BTW, the myth is alive and well. At
http://www.amdmb.com/article-display.php?ArticleID=101&PageID=4 ....
Did they test the SAME make of heatsink but without the silver coating? Nope, didn't see any 'plain' Akasa there... Anyhow, read my prevous posts above again.
They also have this copper-aluminum babe. I don't think they were trying to save money or weight on this one:
The Swiftech MC-462A Rev1... the heatsink itself is comprised over a copper bottom and aluminum pins....
I think we have discussed copper-based HSFs previously too...
Ergh, just found out there's a 4098 char limit on posts... :(
*spazzed* (Jul 19, 2001 02:47 p.m.):
I'm working on a heatsink that has a copper core with aluminum fins, all held together by silver solder.....
Hybrid copper-aluminium heatsinks are implemented as a 'cost-effective' measure when the design engineers are at a lost at designing better HSF geometry (very complex, you know). If $$$ permits, you might as well go for an all-copper HSF with the same build. But try and build one anyway -we'd like to see the results and take care to solder the Al-Cu interface properly. BTW, I don't think aluminium can be soldered. AS2 epoxy as alternative, maybe? Mating surfaces obviouslty must be super flat and reasonably smooth.
*spazzed*
07-20-01, 01:08 PM
Well the solder did stick........ for a while. When heat was applied again, the bond broke and everything fell apart :-( Gonna try AS epoxy, if I can get my dad to let me borrow his credit card. :'(
*spazzed* (Jul 20, 2001 01:09 p.m.):
Well the solder did stick........ for a while. When heat was applied again, the bond broke and everything fell apart :-( Gonna try AS epoxy, if I can get my dad to let me borrow his credit card. :'(
Nope, looks like aluminium really cannot be soldered upon.
I'm afraid to ask. How many Durons or Tbirds do you have for it to be tested on once you're finished?
Reminder: Apply only a thiiiiiin layer of AS2 and SQUASH to halves real hard till it cures (using a clamp?).
*spazzed*
07-21-01, 11:08 AM
cjtune (Jul 21, 2001 11:01 a.m.):
*spazzed* (Jul 20, 2001 01:09 p.m.):
Well the solder did stick........ for a while. When heat was applied again, the bond broke and everything fell apart :-( Gonna try AS epoxy, if I can get my dad to let me borrow his credit card. :'(
Nope, looks like aluminium really cannot be soldered upon.
I'm afraid to ask. How many Durons or Tbirds do you have for it to be tested on once you're finished?
Reminder: Apply only a thiiiiiin layer of AS2 and SQUASH to halves real hard till it cures (using a clamp?).
No durons or t-birds, I had a Plll, but then sold it to get a t-bird. Don;'t have enough cash right now. I have a celeron 533@825(that doesn;t make that much heat). I might try a different type of heat source, to simulate something of a higher heat range. Or just use that crappy celeron
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