Why copper?

[MC]

Okay first off I am new to this site so don't shoot me...

I am confused by my data...about a year ago I built two cpu water blocks, one in 6061 alu. and the other in Cu110 and see no difference in water temps.

Both blocks were attached to the same mobo/cpu/rig setup and heatercore/fan setup with a hydor L30. The pump/heatercore were external units in a custom steel enclosure with its own fan/ps etc.

both blocks were cut with same g-code(cnc milled) the only difference was the material Al vs. Cu. I saw absolutely no difference in temp between the two. I put both setups through the same torture test. Both were attached(at diff times obviously) to a P2.4c HT enabled/overclocked 30% 2.4-->3.12Ghz, 2xf@H running and the highest temp I got was 34c, recorded temp via asus probe.

So over the christmas break my nephew comes home with a dead computer...beer&PC's don't mix...some fool spilled a beer sitting on top his case and fried his mobo...me being the nice uncle gave him mine. I want to upgrade to the 875 chipset anyways. As I write this I am using one of my dinosaur pc's an amd 1.0 oc'd to 1100 using scary air cooling. Unfortunately the block I milled was for a P4 and am bored so I figure why not mill a new amd mountable block.

Considering the expense of copper vs. aluminum I am wondering why bother using copper at all? I am also wondering if maybe it was because the block was milled from 1" thick stock with 1/4" channel down to .3 inches. (max z depth was .3 in.) Maybe its the just mass of the block. Has anyone ever tested the similar block designs milled from thicker stocks? Is it possible that there is a plateau I reached in water cooling...the heater core is a one fan 120 mm size and maybe I will see a difference if I hook the blocks to a double-fan-size heater core?

Thanks for any input/insights.
-MC

[jaydee]

http://forums.procooling.com/vbb/sho...r+vrs+aluminum

Also you are not using the mobo's sensor to take temps right?

[MC]

Ah...I think the premise is that since my block design was ideally one for aluminum, using copper isn't gonna benefit my design one iota. well...I guess I will stick to Al

1. It mills cheap & easy...not "sticky" like that redish-metal-stuff
2. I can anodize it pretty colors...I'll post some pics when the weather warms up and I can crank up my anodizing tanks again.
3. I Like the Al top plate cuz I can mill off a few thousandth's and put "pretty pictures" in the anodization, and if I get really "fancy" I can re-anodize the new exposed metal a diff color, as long as I can find electrical connection.
4. My temps were good enuff for me...I'm not interested in "Rocket Surgery"
5. The fact that I never went beyond 200 grit lapping(if you can call 200 grit lapping) should probably get me even lower temps.

anyways thanks for the post, it made good reading, and I never realized Al vs Cu was a big debate here...

-MC

[jaydee]

Originally Posted by MC

Ah...I think the premise is that since my block design was ideally one for aluminum, using copper isn't gonna benefit my design one iota. well...I guess I will stick to Al

1. It mills cheap & easy...not "sticky" like that redish-metal-stuff
2. I can anodize it pretty colors...I'll post some pics when the weather warms up and I can crank up my anodizing tanks again.
3. I Like the Al top plate cuz I can mill off a few thousandth's and put "pretty pictures" in the anodization, and if I get really "fancy" I can re-anodize the new exposed metal a diff color, as long as I can find electrical connection.
4. My temps were good enuff for me...I'm not interested in "Rocket Surgery"
5. The fact that I never went beyond 200 grit lapping(if you can call 200 grit lapping) should probably get me even lower temps.

anyways thanks for the post, it made good reading, and I never realized Al vs Cu was a big debate here...

-MC

I have made several AL blocks on my mill. I agree with all you said above. I love milling AL and made some very good performing blocks from it. I don't use it anymore though. Copper is just superior. Silver is even better.

[bigben2k]

Ah! A new thread that brings up ye ole' Al vs Cu debate!


It may not be obvious with your design, but copper is superior. That aside, please continue using Alu, because you can still make a decent water block with it.

Copper has a better thermal conductivity (do you really want the numbers? I didn't think so! ) but also has a (relatively) high thermal capacity.

I would bet hard money that your waterblock baseplate is about 1/4" thick. If you could make the same comparison, but with a baseplate that's about half as thick as what you have now, you would see a significant difference.

Do you want more info?

BTW, don't post your numbers here! We're on a testing "kick" right now, and we're all about accuracy. That CPU temp has an accuracy of +/- 10 deg C. Report temps when you're at +/- 0.1 deg C, whichever way you get there...

[Butcher]

Originally Posted by bigben2k

Copper has a better thermal conductivity (do you really want the numbers? I didn't think so! ) but also has a (relatively) high thermal capacity.

Aluminium's specific heat capacity is almost 2.5 times greater than copper's actually. Specific heat capacity is largely irrelevant in a steady-state system such as water cooling in any event.

Oh BTW, 6063 is a better alloy for making blocks than 6061 (higher thermal conductivity). If you can get hold of it, 1050 or 1350 is even better.

[pdf27]

Specific heat capacity per unit mass or volume? Per unit volume is the relevant one for waterblocks, but it is usually quoted per unit mass.

[j813]

oh OK from the Feathers issue it's back to Alu & Copper.
so these are the things that make people popular.

[MC]

nooo, please no more numbers...make brain stop hurt now please

hmmm I am confused by the baseplate stuff:

I would bet hard money that your waterblock baseplate is about 1/4" thick. If you could make the same comparison, but with a baseplate that's about half as thick as what you have now, you would see a significant difference.

My block is a 1" thick 3x3.5" Alu. Basic channel design. Channels milled down .7" leaving close to .25" to .3" baseplate, yes. If I were to facemill off say .125 inches I would see better results? If so thats way cool (pun intended).

Oh and by the way I made a trip to the local Hardware store and got 400/600/800/1000 and 1500 grit wet/dry today...happy lappy time. My order from onlinemetals should be here soon...I hope...got four feet of 1/4" copper comming in on this order. can't wait to try some multi-layer copper blocks after reading about some of the copper block posts.

[Butcher]

Originally Posted by pdf27

Specific heat capacity per unit mass or volume? Per unit volume is the relevant one for waterblocks, but it is usually quoted per unit mass.

Good point, I was quoting per unit mass...
Since Al is more than 3 times less dense than Cu, Al is indeed slightly lower per unit volume.

[bigben2k]

Yeah, see? .25 = 1/4" ...

Cut 0.125 and it'll be a whole different ball game. The Alu might actually go up in temp(!) but the copper will come down significantly.

[Cathar]

Originally Posted by Butcher

Good point, I was quoting per unit mass...
Since Al is more than 3 times less dense than Cu, Al is indeed slightly lower per unit volume.

It's all largely irrelevant, except for how it affects the speed of bulk temperature changes when the heat load changes. When a system is in equilibrium only the thermal conductivity matters.

Thermal Capacity per unit volume:

Water: 4.186 J/K-cm³
Aluminium: 2.430 J/K-cm³
Copper: 3.425 J/K-cm³
Silver: 2.435 J/K-cm³

[Cathar]

Originally Posted by bigben2k

Yeah, see? .25 = 1/4" ...

Cut 0.125 and it'll be a whole different ball game. The Alu might actually go up in temp(!) but the copper will come down significantly.

Hmmm, in a basic maze design there's a pretty good chance it'll be the other way 'round.

It all depends on the relative ratio of the material's thermal conductivity vs the rate of thermal convection.

For many waterblock designs, the higher a material's thermal conductivity then thicker you want the base-plate to be.

[jaydee]

Doh nevermind.

[Boli]

I can't quote any numbers mainly because I don't know any offhand (that are suitable) but I don't want to be caught up in a full blown technical discussion about weight vs volume etc. And as such I will use none technical language - but only to demonstrate a point.

That said: I've allways been told that Copper is best at "drawing heat" from a heat source. It will "suck" heat into it better than ALU. But ALU "looses" heat from the same surface area much easier.

So in theory a "badly designed" copper waterblock will perform worse than a similar design of Aluminium, becasue the ALU will "transfer" more heat to the water, due to its properties. BUT if a Cu block is well designed then Coppers "heat sucking" properties work in coppers favour, as it will draw heat away from the core much faster... keep the core at a lower temperature.

At least that is my way of thinking it... I have prob. got it all wrong, but it keeps it nice and simple for my brain (it being 06:51 now)

[Cathar]

Boli, copper and aluminium transfer heat into the water at exactly the same rate. The rate of thermal convection is not based on the physical properties of the solid.

[Boli]

*shrugs* I was just told somewhere along the line that ALU disapates heat better (air or water), and taken it as truth as no-one argued against it.

[Cathar]

Originally Posted by Boli

*shrugs* I was just told somewhere along the line that ALU disapates heat better (air or water), and taken it as truth as no-one argued against it.

The physical formula that describes thermal convection has no units/elements in it that are based upon the properties of the solid, except for the amount of surface area that is exposed to the fluid/gas.

Whomever originated and subsequently propogated the "Al dissipates heat better" arguments knew nothing at all of what they were talking about.

There are legitimate reasons, primarily based around weight restrictions, for why aluminium may be a better material to use in certain very strictly defined scenarios, but this has absolutely nothing at all to do with aluminium giving up heat better than copper.

[SysCrusher]

I believe the idea of alu dissipates heat better than cu came from the heat capacity of the two. The reason why cu will stay warmer longer is because it's heat capacity is more than Alu. Doesnt make Alu dissipate heat better Cu.

[Cathar]

Originally Posted by SysCrusher

I believe the idea of alu dissipates heat better than cu came from the heat capacity of the two. The reason why cu will stay warmer longer is because it's heat capacity is more than Alu. Doesnt make Alu dissipate heat better Cu.

Hmmm, maybe, but one would really have to not understand the nature of thermal transfer to come to that conclusion (based on heat capacity).

Assuming the exact same design for a copper and an aluminium heatsink/block.

The thermal gradient through the copper (for equivalent volume) is lower. The rate of thermal convection means that the surface of the copper and the aluminium that is in contact with the liquid/air must be, on average, equal.

So we're left with what's going on between the heat source and the point of convection, and how quickly the heat moves. The thermal conductivity tells us that it's harder to move heat through the aluminium, meaning that the heat source will be hotter than the copper over the gap to where the thermal convection is going on.

I think what may fool many people is thinking that heat energy (joules) equates to temperature (K). Yes, the two are related inside some material, but they are not interchangeable (without first applying per-material specific modifiers), and this is where the confusion arises.

[myv65]

I have my own theory on the "gives up heat" thing. One aspect is the misperception that thermal capacity has an effect on steady state heat transfer. In reality, all this means is that a block with lower thermal capacity will cool more quickly when you turn off your PC. Whoopey!

More importantly, this is a true statement for air-cooled heat sinks, but not for the reason most people think. A heat sink needs to "handle" three heat transfers. It needs to receive thermal energy from the chip, transfer through its own material, then convect it to air. Convection by nature is much less efficient than conduction through most metals. This means that surface area tends to matter a lot more than anything else.

By virtue of its lower density, you can create a lot more surface area with a given mass of aluminum than copper. That's pretty simple to understand. What's not obvious, and what takes a little thinking to understand, is that on a fixed weight basis the conduction of aluminum is better than copper. Just as an approximation, say copper beats aluminum by 2:1 on conductivity. In contrast, aluminum beats copper by over 3:1 in density. For the same weight, you can have more than three times the cross sectional area for conduction. Since delta_T is a function of both conductivity and section area, a given weight of aluminum will have a lower delta_T in conduction than the same weight in copper.

If you understand all that, you'll realize that aluminum really does "get rid of heat better than copper" for air-cooled heat sinks.

If you're extra-special smart, you'll further realize that the die represents a fixed area for heat transfer. This means that you can't take advantage of additional section area when touching the die. This is why early high performance air heat sinks migrated toward copper bases with aluminum fins or pins and why as a general rule all copper tends to beat all aluminum.

When it comes to water, convection gets much more efficient than air. The benefit of low density largely evaporates (pun intended) and all copper offers better performance than all aluminum.