# cooling, copper or aluminum

Sometimes the question comes up, whether to use copper or aluminum for cooling purposes. Two figures are generally important, the heat conductivity and the heat capacity.
## Copper

Copper has
- an atomic weight of 63.5g / mol
- a density of 8920kg / m^3
- a molar volume of 7.11 cm^3
- a thermal conductivity of 400W / m*K
- an expansion coefficient of 16.5 *10^-6 / K
- a heat capacity of 24 J / K*mol

## Aluminum

Aluminum has
- an atomic weight of 27.0g /mol
- a density of 2700kg / m^3
- a molar volume of 10.0 cm^3
- a thermal conductivity of 235W / m*K
- an expansion coefficient of 23.1 *10^-6 / K
- a heat capacity of 24 J / K*mol

## Calculated conclusions

From the above values follows for the weight
- copper has a heat capacity of 0.378 J / K*g
- aluminum has a heat capacity of 0.888 J / K*g
- copper has only 42% of the capacity per weight { 0.426 }
- aluminum has
**2.35 fold** the capacity per weight { 2.35 }

for the volume
- copper has a heat capacity of 3.37 J / K*cm^3
- aluminum has a heat capacity of 2.40 J / K*cm^3
- copper has
**40% more** capacity per volume { 1.40 }
- aluminum has 29% less capacity per volume { 0.712 }

## Compensate the conductivity

Now let us increase the crossection for aluminum to

compensate the lesser conductivity.
- copper has a conductivity that is 70% better { 1.70 }
- aluminum has a conductivity that is 59% of the copper one {0.587 }

Thus we take 70% more aluminum and get the
- weight advantage on capacity of aluminum is down to
**38% better** than copper { 1.38 }
- volume advantage on capacity of copper is increased to
**2.38 fold** against aluminum { 2.38 }

for a unit length of equally good conduction

So when heat has to be dumped, the more the better, the quicker

the better, the results are :

If weight or cost is a concern, aluminum is favoured,

if volume is a concern, copper is better.

## The system should be fast

The application may require a good head conduction with lowest heat

capacity, for example when a dynamic systems should behave as fast

as possible. Thus let us now get the conduction to capacity ratio.

Related to weight we get for
- aluminum 267 W*g / m*J
- copper 1058 W*g / m*J

Related to volume we get for
- aluminum 80 W*cm^3 / m*J
- copper 119 W*cm^3 / m*J

Here, in both cases copper is better suited for a fast system.

To be continued...

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last updated: 5.april.2005

Copyright (99,2005) Ing.Büro R.Tschaggelar