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