A little lesson on heatsinks

[EpicHam]

If you make use of the full duty cycle yes it would take longer to cool since it can take in more heat. I agree though aluminum has it's place, I have an Al sink for my mag lite build.

Aluminum takes in more heat?

Shouldn't it actually takes in less due to its lower specific heat capacity and density which results in a lower volumetric heat sinking capability and LOWER heat conductivity.

Thus making it worst in every case?

 

[grainde]

^^^Hes talking about copper...

 

[EpicHam]

^^^Hes talking about copper...

 

[jander6442]

OK then fellas, stop talking about and let's see you dump that sorry old aluminum and pony up to copper. No more talk about it and dare not use aluminum in your next 3 builds... oh and no C3 or C6 builds either.

 

[Tonga]

I prefer copper and use it for my builds, but, I do have aluminum sinks just haven't gotten around to using them.

 

[EpicHam]

OK then fellas, stop talking about and let's see you dump that sorry old aluminum and pony up to copper. No more talk about it and dare not use aluminum in your next 3 builds... oh and no C3 or C6 builds either.

I would ,but my nachos budget doesn't allow it

 

[Tonga]

I would ,but my nachos budget doesn't allow it

Ha ha, well I've also gotten into hot water with my wife for doing so!

 

[Trevor]

Copper only appears to dissipate heat slower because it takes more energy per unit of volume to heat copper that aluminum - a function of specific heat and density.

Just because the temperature of copper drops slower as it cools not mean it is shedding less energy.

Trevor

 

[EpicHam]

Copper only appears to dissipate heat slower because it has a higher specific heat - it takes more energy per unit of volume to heat copper that aluminum.

Just because the temperature of copper drops slower as it cools not mean it is shedding less energy.

Trevor

Umm.. You sure you didn't got the data reversed?

 

[Trevor]

Think per unit of volume.

Specific Heat
Aluminum = 0.89 J/g C
Copper = 0.385 J/g C

Density
Aluminum = 2.70 g/cm^3
Copper = 8.96 g/cm^3

So, to raise a cubic centimeter of copper one degree Celsius, you need 3.45 joules. to do the same for aluminum, you need 2.41 joules.

When you store 50 joules in one cubic centimeter of copper, its temperature will rise 14.49 degrees Celsius.

When you store 50 joules in one cubic centimeter of aluminum, its temperature will rise 20.75 degrees Celsius.

Trevor

 

[EpicHam]

Copper only appears to dissipate heat slower because it has a higher specific heat - it takes more energy per unit of volume to heat copper that aluminum.

Trevor

Think per unit of volume.

Specific Heat
Aluminum = 0.89 J/g C
Copper = 0.385 J/g C

Density
Aluminum = 2.70 g/cm^3
Copper = 8.96 g/cm^3

So, to raise a cubic centimeter of copper one degree Celsius, you need 3.45 joules. to do the same for aluminum, you need 2.41 joules.

When you store 50 joules in one cubic centimeter of copper, its temperature will rise 14.49 degrees Celsius.

When you store 50 joules in one cubic centimeter of aluminum, its temperature will rise 20.75 degrees Celsius.

Trevor

 

[Trevor]

When I said "specific heat" in the original post, I was thinking in terms of volume. Whoops!

The point still stands though - it takes more to heat copper than it does aluminum, and just because copper's temperature drops more slowly as it cools does not mean it is dissipating less energy.

I corrected the original post to be less confusing.

Trevor

 

[EpicHam]

When I said "specific heat" in the original post, I was thinking in terms of volume. Whoops!

The point still stands though - it takes more to heat copper than it does aluminum, and just because copper's temperature drops more slowly as it cools does not mean it is dissipating less energy.

I corrected the original post to be less confusing.

Trevor

You know I agree with you.

read my earlier post

 

[Trevor]

Oop, I had, just forgot about it.

...and I got this thread and the other one on heatsinks mixed up; I thought a discussion from over there was happening over here.

I need to stop posting after 8PM or something... this is ridiculous. :crackup:

Trevor

 

[jander6442]

My aluminum bar stock is not feeling your love, as a matter of fact, it officially wants to be dismissed from any laser duty until you all apologize, or order some 2" copper just to machine it down to 20mm heatsink as a token of my appreciation.:na:

 

[Cyparagon]

...netting an over 40% increase in run time.

If your concern is runtime, there are other methods that will net an infinite increase in runtime.

Since I know how much you hate analogies, I'll add one. If you want to get better distance on a tank of gas, you could get a bigger gas tank... or you could get a more efficient car.

Copper: 401 W/(m.K)
Aluminium's : 205 W/(m.K)

People often quote these numbers. But they are a bit misleading.

Take a length of wire, for example. Is 1mΩ/m better than 2mΩ/m? Yes, but only by a small amount. Both will work very well as a conductor. Take the reciprocal, however, and you have CONDUCTIVITY: 1000S/m and 500S/m respectively. Surely 1000 is WAY better than 500, right?