A little lesson on heatsinks

[grainde]

You seem to be missing that the "heatsink" doesn't do any dissipation. Its only a storage and movement conduit for the heat. All dissipation is done by the host. We use the term heatsink but in standard terms they don't actually do any by definition heatsinking. They should be called heat transferrers.

Not missing it, but unfortunately the heat sink with its interface is poorly connected (thermally) to the host. Its great that copper can transfer the heat really quickly away from the sink, but getting rid of that heat is a problem when it hits the 3 Wm-1K-1 grease barrier blocking its heat transfer out of the sink. In both cases with Al and Cu this will be the limiting factor.

If you assume the interface is perfect then you still have the efficacy of the aluminium host as your limiting factor to cooling the sink. If you heat both sinks to the same temp they still are limited by the aluminium host and its intrinsic thermal conductivity and effectiveness at dissipating that heat. :beer:

Edit: If you want to have a play around with some numbers this might be of interest:http://www.roymech.co.uk/Related/Thermos/Thermos_HeatTransfer.html
I havent had the time to read though it all but it looks like it could be useful.

 

[TheDukeAnumber1]

Volumetric Heat Capacity:
2.422/3.45*100-100 = 29.8%

I would like to call this into question.

Isn't this the correct way?
3.45(Cu) / 2.422(Al) * 100 - 100 = 42.4% more

If material X has twice the value of material Y
2(X) / 1(Y) * 100 - 100 = 100% more
vs
1(Y) / 2(X) * 100 - 100 = 50% more

 

[ApexProxy]

You know what, I did swap that. For some reason I didn't catch it... derp. I was getting so technical in my head that I farxed a basic calculation HAHAHA.

 

[Leodahsan]

@Apexproxy
Just for clarifications, I compared my both lasers exactly to say that. A snug fit provides better heat transfer. BUT sometimes we just can't have a snug fit. In my aurora, there are threads before the heatsink, so the heatsink is a little smaller then the ID of the host. The air around the HS, provides thermic insulation.

 

[ApexProxy]

The variances in the same hosts and heatsinks that work in both cause a large amount of error alone. Using different hosts entirely makes it next to impossible to compare them.

You would need to calculate host heat dissipation capabilities, heatsink volume, and heatsink to host heat transfer capabilities, and the volume of material the host uses for heat storage and how efficiently it uses it for both hosts before you can start to compare them bro.

If you have the same host and heatsinks machined to be as similar as possible you can eliminate most of that and just assume a small margin of error for variances in tolerances.

 

[EpicHam]

@EpicHam
Aluminum doesn't corrode as fast as copper. I have many aluminum heatsink lasers and all the heatsinks are just as shiny as day one while the copper ones are all heavily tarnished and corroded. Also. I have full unanodized aluminum hosts that are not tarnishing or corroding at all.

@Leodahsan
You have too many variables with your Aurora SH032 vs Solarforce L2P comparison. Its a simple fact that copper transfers heat faster. The reason your copper heatsink may not work as nicely as your aluminum is that it likely wasn't machined to fit as snugly in its host or that the host itself isn't made to dissipate heat as well. Also, steel's thermal properties SUCK EPIC so the host itself is a ridiculous thermal insulator in comparison to the aluminum host of the Solarforce.

I'm bored so... technicality bomb time.

Thermal Diffusivity is a term we can use which is thermal conductivity divided by density and specific heat capacity at constant pressure. This gives us how far heat can travel down a 1mm by 1mm bar per second in mm²/s. This allows us to see how fast each material transfers heat in a single raw number. Here are our favorite candidates:
Aluminum - 84.18
Copper - 111

Now, here is Volumetric Heat Capacity(J·cm^−3·K^−1):
Aluminum - 2.422
Copper - 3.45

That means copper stores 29.8% more heat energy for the same temperature. Copper is also 24.16% faster at transferring heat based on Thermal Diffusivity.

This means that although Copper takes 37% longer to heat up and once at the same temperature even though it it stored 29.8% more heat it fully cooled down while the Aluminum still retained 1.35% of its heat energy.

Since I know people will not believe me here are the calculations:
Thermal Diffusivity:
84.18/111*100-100 = 24.16%

Volumetric Heat Capacity:
2.422/3.45*100-100 = 29.8%

This next one warrants an explanation because its much more complicated. This calculation shows how much longer copper takes to reach the same temperature taking into account that both it and the aluminum are gaining temperature(the laser is on) but at the same time they are also transferring some away into the air and host simultaneously. Copper is losing heat 24.16% faster than aluminum while requiring 29.8% more heat to reach the same temperature which means it loses 7.2% of its heat while increasing the 29.8% more energy required to reach the same temperature. The calculation:
29.8+24.16% = 37%

The next part is after knowing the copper now has 129.8% of the heat energy that aluminum has at the same temperature you now take into account that it will lose all its heat energy 24% faster. This means it will lose all its heat energy while Aluminum will still have 1.35% of its heat energy remaining.
129.8-24%-100 = 1.35%

In total, if you turned on two identical lasers, one with an Aluminum heatsink and one with a Copper heatsink, at the same exact time and turned them both off when they reached a set temperature the copper would have taken 37% longer to do so. Then, assuming you had the two lasers with their heatsinks at the same exact temperature the copper heatsink would cool down 1.35% quicker even tough it contained 29.8% more heat energy. Therefore, copper takes longer to warm up and then cools off in a tiny bit less time.

To me the gain of 37% more ON time and reducing OFF time by 1.35% is well worth it when I am limited on heatsink size.

MIGHTY BRILLIANT!!
I learned something today !
But Aluminium DOES corrode faster , just not the same way as copper . As aluminium oxides adheres to the solid untarnished layer while the copper oxide flakes off and creates a channel for oxygen to attack the layers below.
If you don't believe the electronegativity series ,there's always Google.

 

[ApexProxy]

MIGHTY BRILLIANT!!
I learned something today !
But Aluminium DOES corrode faster , just not the same way as copper . As aluminium oxides adheres to the solid untarnished layer while the copper oxide flakes off and creates a channel for oxygen to attack the layers below.
If you don't believe the electronegativity series ,there's always Google.

Here is the thing, saying it "corrodes faster" is massively subjective. It depends drastically how you define "faster". Aluminum will quickly form a thin oxidized layer on the very surface that is barely visible. That layer acts as a sort of barrier preventing further corrosion. The layer tends to be thin enough so that you don't really even see it. The layer is also stronger than the unoxidized aluminum underneath so it acts as a protective layer. This is a very similar effect to what happens when we anodize aluminum. On the other hand copper corrodes heavily in the environments seen in our pockets. The very surface molecules of the heatsink may not oxidize quite as quickly but given a week or two of pocket time and use and it looks pretty crappy. The oxidization also tends to penetrate into the copper causing it to lose its desirable looks even faster.

A copper heatsink and an aluminum heatsink after 6 months of roughly equal use are going to have drastically different levels of corrosion and oxidization.

Sorry bro, but I couldn't disagree more with the statement that aluminum heatsinks corrode faster than copper.

 

[EpicHam]

Here is the thing, saying it "corrodes faster" is massively subjective. It depends drastically how you define "faster". Aluminum will quickly form a thin oxidized layer on the very surface that is barely visible. That layer acts as a sort of barrier preventing further corrosion. The layer tends to be thin enough so that you don't really even see it. The layer is also stronger than the unoxidized aluminum underneath so it acts as a protective layer. This is a very similar effect to what happens when we anodize aluminum. On the other hand copper corrodes heavily in the environments seen in our pockets. The very surface molecules of the heatsink may not oxidize quite as quickly but given a week or two of pocket time and use and it looks pretty crappy. The oxidization also tends to penetrate into the copper causing it to lose its desirable looks even faster.

Sorry bro, but I couldn't disagree more with the statement that aluminum heatsinks corrode faster than copper.

psssst , that's what I just said .
I have always been referring to the material itself.
Look at my earlier post about aluminium-copper alloy which provides the best of both worlds

 

[ApexProxy]

OI! Then you are saying your whole statement (said several times) that our aluminum heatsinks corrode faster is irrelevant? Who cares about corrosion you cannot see when it comes to talking about a positive of aluminum being that it doesn't look bad as quickly.

Ur giving me a headache :/

Sadly, aluminum bronze's thermal conductivity completely blows at less than 1/4 of that of pure copper btw.

Silver has a really good thermal conductivity but a weak volumetric heat capacity. Diamond is similar but much more drastic with a badass wicked thermal conductivity and a totally fail volumetric heat capacity. If you look at tables you will find that copper has basically one of the best balances between the two properties of any standard material.

 

[EpicHam]

OI! Then you are saying your whole statement (said several times) that our aluminum heatsinks corrode faster is irrelevant? Who cares about corrosion you cannot see when it comes to talking about a positive of aluminum being that it doesn't look bad as quickly.

Ur giving me a headache :/

Sadly, aluminum bronze's thermal conductivity completely blows at less than 1/4 of that of pure copper btw.

I never said "aluminium heatsink" corrodes faster.
I said aluminium corrodes faster , but as the oxide layer forms a hard crust protecting the layers below , it appears that it doesn't corrode as fast.

Gonna add in my quotes later


Here's the guide into anodizing copper
http://www.ehow.com/how_7629581_anodize-copper.html

No.
Copper module matched to be a copper heatsink would be ideal.
Aluminum modules DOES NOT hold more heat and copper does not radiate heat slower (aka, it does not have better heat retention)
Maybe I'm wrong , but if that is the case, I WOULD LOVE to read on the source


As for the corrosion problem.
Scientifically, aluminum corrodes a LOT faster due to being lower electronegativity in the series.

(Pardon the BIG CHART, if its any smaller, it might get hard to read)
Its the oxide layer that rapidly forms as its exposed to air which protects aluminum from further corrosion.

As copper is a LOT less likely to corrode, it also mean that its oxide layer is a LOT easier to remove the corroded layer.
7 Ways to Clean Copper - wikiHow
Regular copper cleaner fluid would do the trick , as for the copper module , cleaning would be a bit tougher ,since the diode is in it so you'll have to remove the diode first.

HOWEVER, copper's cleaning cycle is in the once a few years . So that shouldn't be too much hassle.

 

[hwang21]

Wait it takes two weeks for copper to discolor? :thinking:

 

[EpicHam]

Wait it takes two weeks for copper to discolor? :thinking:

It takes about 20 years for Copper to oxidize beyond operational condition in normal circumstances.

As long as you're not sprinkling your heatsinks with Muriatic Acid or salting it up for the oxygen monsters.
It should be fine .

 

[ApexProxy]

They do discolor pretty damn fast. I actually notice discoloration even faster than that the more often the surface is touched. The salts and everything else on your hands wreak havoc on the copper.

Again Ham, we are talking about the visual side of corrosion... copper looks like crap quick, aluminum does not.

 

[EpicHam]

He said discolor not oxidize down to nothing.

They do discolor pretty damn fast. I actually notice discoloration even faster than that the more often the surface is touched. The salts on your hands wreak havoc on the copper.

That is true , but its still operational tho.
Copper pipes for example last anywhere up to 20-50 years under the Atlantis Plumbing Installation practices.
And we are talking about even in high pH condition.
They do tarnish , but they still work and as they can be easily maintained. It shouldn't be much of a problem.

Hmmm... maybe I should make a copper laser


EDIT: They do look crap quick , but its also easily fixed .
As always.
Performance
Appearance
Convenience

Your call.
I tend to go for performance.

 

[ApexProxy]

That is true , but its still operational tho.
Copper pipes for example last anywhere up to 20-50 years under the Atlantis Plumbing Installation practices.
And we are talking about even in high pH condition.
They do tarnish , but they still work and as they can be easily maintained. It shouldn't be much of a problem.

Hmmm... maybe I should make a copper laser


EDIT: They do look crap quick , but its also easily fixed .
As always.
Performance
Appearance
Convenience

Your call.
I tend to go for performance.

I go for performance when its needed mostly. Like, I will not build a 9mm 445nm laser without copper unless it has a freaking MONSTER heatsink. I do however build aluminum heatsink M140s and still attain some respectable duty cycles. The more you lean towards appearance the more carefully you have to build to make sure you get every last bit of performance out of your materials.

 

[jander6442]

Well, I'm looking at breaking into the Smithsonian and getting me a piece of the shuttles belly tiles... then 3-D print one of Jays stubby mags with/direct diode pressed in.

Copper is better, but more expensive so I'll be happy we have copper modules for now and to be using aluminum as a sink. Wonder how the copper is holding up at the interface of the aluminum sink... Copper chloride w/aluminum poof.