HEAT DISSIPATION?

Anyone know of a fiber material with high thermal conductivity? I need a heat dissipator in a sheet form factor, preferably non-metallic (rules out aluminum and copper). I would be open to suggestions of bonded fibers though. Any help would be appreciated.

When you say fiber, and sheet, do you mean composite(like fiberglass layup), or woven(like wool)?

If it’s woven, then I don’t really know what to tell you. Some fiber materials, like carbon fiber, have good contuctivity, but only in the direction of the fibers, so it would act as a pretty good insulator (bad) if the fibers run parallel to the heat source. And it would be tough to get the fiber to move the way you wanted if it was loose.

But if it’s a composite, you might be in luck. Certain Polymer Matrix Composites (PMCs) using very long strands of carbon fiber, called K1100 carbon fiber, can have conductivities up to 150% of that of copper. Again though, that is only in the direction of the fibers, so the part must be carefully designed to take this into account. According to the following document, these PMCs have replaced heat pipes(a very good mechanical consuctor based on evaporation and capillary flow of liquid) in some applications:

http://www.coolingzone.com/Guest/News/NL_OCT_2001/Carl/Oct_CZ_2001.html

Even non-oriented fiber PMCs can have conductivities comparable to metals, and they can be injection molded. As you can see in the chart at the bottom of the above document, their conductivities range like crazy, which is due to the degree of orientation of the strands in the polymer matrix; the more aligned with heat flow they are, the better the conduction. If you are injection molding, this alignment is due to the mold design, so it’s important to have an expert to consult with on that.

Or, if your application is very high temperature, you might try a Carbon Matrix Composite, which is similar to the PMCs, but uses graphite in place of the polymer. At very high temperatures (like those developed by a super sonic missile nose cone) metals loose their thermal conductivity, and run a risk of overheating and melting. Carbon does not have this problem, so it is used in these applications:

http://www.ms.ornl.gov/researchgroups/cmt/CFCMS/TMS.HTM

As you can imagine, the answer isn’t that easy; All of these materials are pretty expensive – CMCs extremely so – and more difficult than regular plastics to work with.

But the biggest pain might be this: They conduct electricity :frowning: If by non-metallic, you meant non electrically conductive, this is a big bummer.

http://www.zoltek.com/panex_products/milled_overview.pdf

There might be a way around it though: From this data sheet on one brand of carbon fiber polymer additive, it looks like the relationship between percent carbon and thermal conduction is linear, while the relationship between percent carbon and electrical conductivity is very exponential. This could mean that you could find a carbon content which would conduct heat well enough, while also remaining moslty an electrical insulator.

If, on the other hand, you meant that it couldn’t set off metal detectors, or had to be non-magnetic to go in an MRI or microwave or something, then you’re golden.

Also, if you want a little more on more complicated cooling systems, like heat pumps, IDFuel had a Tech Thursday a while back that covered some options:

http://www.idfuel.com/index.php?p=273&more=1&c=1

I hope all this helps. If you end up using any of this stuff, be sure to let us know how it went, I’d really like to know what a part made of PMC looks, feels, or acts like.

i have used this company’s products to increase thermal connectivity. not sure if this what you are trying to accomplish or if you are looking for a non-metallic heat sink but can’t hurt to have a look. the company is called chomerics.

the material i used was in sheet form (.010"/.25mm thk approx.) and had adhesive on both side. i believe the adhesive is optional.