Aluminum vs. Copper (Tired old debate)

[i_jester]

We all keep seeing different debates as to which material moves, transfers, radiates, absorbs more heat. The real answer of course lies in the facts and the application. There can also be a substantial difference in some of the properties depending upon the finish of the metal surface and any specific alloys used.

1. Thermal conductivity

This is defined as the ability of a substance to MOVE heat from one place to another. If you heat one side, how much of the heat will move (conduct) to the other side and at what rate. If we look at the following chart;

Thermal Conductivity of Common Metals (http://www.engineeringtoolbox.com/36_429.html)

we can see that generally, copper has a much higher thermal conductivity than aluminum. Of course this does not take into account any specific alloys or the finish applied to the surface such as polishing or anodizing but as a whole Aluminum is only 5/8 or .675 % as efficient as copper at moving heat.

So if you are lookin for a metal that will absorb heat on one side and output it on the other, copper is better. But of course that is not the entire answer.

[i_jester]

The next property to examine would be the Specific Heat or heat absortion. This is defined as the amount of energy required to raise the temperature of a substance.

If a particular substance has a higher specific heat, that would mean that you have to apply more energy (heat) to raise its temperature than one with a lower specific heat. Water is a terrific heat absorber as it takes a lot of energy to make it hotter. Therefore it is said to 'Absorb' a lot of heat and has a high specific heat.

By looking at the following chart;

Specific Heat of Common Metals (http://www.engineeringtoolbox.com/24_152.html)

we see that Aluminum has a much higher specific heat than copper, so you would think that Aluminum could absorb a lot more heat than copper without getting as hot. Partially correct. But we must take into account the fact that Aluminum is not nearly as dense as copper so the equivalent weight of aluminum is much larger than the same amount of copper.

In fact, by checking the specific gravity in the following chart:

Specific Gravity of Common Materials (http://www.engineeringtoolbox.com/24_293.html)

we see that the highest listing for Aluminum is 2.8 and the highest listing for Copper is 8.95. What this means is that if you have two blocks of metal, one Al and one Cu, both the same size, the copper one will be 3.2 times as dense as the Aluminum one, whereas if you have two blocks that weigh the same amount, the Aluminum one will be much larger.

So taking into account the specific heat properties where Aluminum can absorb 2.3 times as much heat per pound at the same temperature, but copper is 3.2 times as dense, the
equivalent SIZE of copper will have a higher heat absorbtion capacity while the equivalent WEIGHT of Aluminum will absorb more heat.

Next we will look at Emissivity Coeffecients (Energy Radiation).

[i_jester]

The ability of some common materials to radiate heat is shown in the following chart:

Emissivity Coeffecients (http://www.engineeringtoolbox.com/36_447.html)

As you can see, the rates vary wildly based on the material and finish applied to it. Of course very few CPU or GPU heatsinks rely on passive radiation to remove the heat. This applies mostly to ram chips, northbridge heatsinks, etc.

So we can make an educated guess as to what material to use for these passive heatsinks - Anodized Aluminum. It is a good radiator of heat, is very light(much lighter and cheaper than copper) and quite easy to machine. So bang for the buck is much better with Aluminum than with Copper.

As long as you keep the Aluminum from getting too thick, the inferior ability it has to conduct heat from one side to the other (compared to copper) will not be enough of a factor to keep it from working well.


But when heat conduction becomes more critical, such as when you are trying to keep the CPU supercool by using chilled water or evaporative cooling eg: Phase change, then the superior conductive abilities of copper make it the logical choice.

Also, the fact that for a given size, Copper will have a larger 'Thermal Mass' and will result in less temperature fluctuations is a positive for ultra cool systems.

[dcpusher]

sticky!!! no more of these debates.