Carbon Foam Waterblock

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SUMMARY: Carbon foam has compelling characteristics for electronic cooling.

Another interesting material we ran across that has tantalizing thermal properties is carbon foam. This material is a porous graphite that, similar to copper foam, comes in various densities (pore sizes). The surface area is very large compared to its size and it’s very light.

The material itself looks a bit like lava rock:

C Foam

The sample on the right side is coated with a thin layer of copper – this is done for ease of soldering. One of the nice things about carbon foam is that it is very easy to work – this pin fin array was done with simple hand tools:

C Foam

After some research, we came across a very intriguing study that showed very high thermal conductivities using carbon foam in air cooled heatsinks:

Table

Considering that copper’s W/mK is around 385, values almost triple that of copper is worth investigating. What we decided to do was try building a carbon foam waterblock by modifying an Asetek Antarctica waterblock:

C Foam

The center part was reamed out and carbon foam was fashioned as a replacement:

C Foam

A close look at the replacement shows its “lava rock” look:

C Foam

The Test

The carbon foam waterblock was tested using the CPU Die Simulator and Waterblock Test Rig. The results shown below are at one gpm:

Waterblock

C/W

Pressure Drop – psi

Pressure Drop – inches H2O

Carbon Foam

0.36

0.99

27.4

What a bomb! This particular incarnation is nowhere near competitive to existing CNC machined waterblocks.

One of the saving graces of working with carbon foam is that it’s so easy to shape with hand tools that trying different shapes is not difficult. This was done as a quick trial of a new material – the prototype took about a day to finish. What takes time is to fully understand a new material’s intrinsic properties and exploit them to develop a superior, cost competitive solution – no easy task!

CONCLUSIONS

Carbon foam has compelling characteristics for electronic cooling – someone who has the time to fully exploit this material to develop a cost competitive product might do very well. Go to it!

Carbon Foam Links:

PocoFoam

ORNL

Note: I think one of the most difficult tasks would be to ensure that the foam does not clog – with pores so small, clogging will most likely degrade performance quickly.

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