# Plastic heat sinks!



## BigRiz (Sep 9, 2010)

I've seen this article on LEDs this morning that got me all excited: http://www.ledsmagazine.com/news/7/9/2

These Japanese scientists actually blended a resin that makes polycarbonate heat conductive! Imagine the posssibilities if this material gets cheap enough... lightweight, cheap LED home bulbs, possibly cheap plastic flashlights that can keep cool and not damage themselves if you leave them on for a few minutes, and so on.. 

Btw I'm "new" here. Actually I've just registered here today but I've been following CPF for the last 3 years or so.


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## Steve K (Sep 9, 2010)

interesting stuff, but it would be nice to see some numbers comparing the material's property to aluminum or copper. 

There's been a press release about some graphite thermal material recently too. It was much more in the developmental stage, though. No details on it either, unfortunately.

It's too early to tell how this will pan out, but it's good to have an option. Molding plastic is much more affordable than milling aluminum (typically). 

I've worked with some carbon filled plastic that was used as a housing for electronics. While the carbon was used for added strength, it was surprising how conductive the carbon made it. I suppose that the same characteristics allow heat to flow more easily too. 

regards,
Steve K.


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## saabluster (Sep 10, 2010)

From the article. "Teijin says that the Raheama-compounded resin can disperse heat on par with aluminum"

I'm sorry but I don't for one second believe that. They give no specs on it either. I know a bit about the various options for using plastic as a heatsink and while some are decent non come close to aluminum.

Welcome to CPF BigRiz! Well...officially anyway


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## qwertyydude (Sep 10, 2010)

Usually when they don't give specs it's already on shaky ground. These things pop up every now and then. Kinda like the water powered car that pops up every time gas prices rise fast.


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## blasterman (Sep 10, 2010)

> *is made from a high-thermal-conductivity resin. *


 
Ok, so it's better than *low *thermal conductivity resin, which basically is an insulator. 

I know that carbon-nano technology has been promising some improved thermal materials that can compete with raw metals, but I still want to see some hard numbers first.


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## alpg88 (Sep 10, 2010)

i can belive it, 
there is a way to grow diamonds in flat shape, i saw a program on tv about it too, it makes aluminium look like plastic next to it, they showed thermal cam of it, they heated up a disc of aluminium and this diamond on the edge with a flame, aluminium only started to get hot, diamond was already completely hot, 
but cost....
http://www.ccl-diamond.com/HTML/Products_Plates.html


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## Dude Dudeson (Sep 10, 2010)

saabluster said:


> From the article. "Teijin says that the Raheama-compounded resin can disperse heat on par with aluminum"
> 
> I'm sorry but I don't for one second believe that. They give no specs on it either. I know a bit about the various options for using plastic as a heatsink and while some are decent non come close to aluminum.
> 
> Welcome to CPF BigRiz! Well...officially anyway


 
Here's a little story of how "the impossible" happened to me with a type of plastic....

In the early 90's I had a set of inline skates with plastic frames. I was a bit skeptical of that choice of material, but at the time anything with metal frames cost way more...

Anyway at some point I decided I wanted to "enlarge" two of the axle holes - being a complete skating noob I hadn't known these particular skates had what's called a "rockered" frame. Front and back wheels elevated maybe a millimeter or two higher than the center wheels. I wanted to make the entire wheelbase flat.

So I took them to a friends house and got ready to drill - with a DRILL PRESS. A full size, freestanding drill press.

Harder, harder, harder I went, until eventually I was nearly hanging my full body weight against the handle, the bit would NOT even go IN the thing!

I think it was only a wood bit, but it was also only like a 16th of an inch larger than the existing hole. The experience really blew me away. The process didn't even create any "filings".

So a plastic that's as thermally conductive as aluminum - sounds pretty impossible to me too, but being this is 2010, and considering some of the crazy stuff being developed with materials in general these days, who knows.....


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## saabluster (Sep 10, 2010)

Dude Dudeson said:


> Here's a little story of how "the impossible" happened to me with a type of plastic....
> 
> In the early 90's I had a set of inline skates with plastic frames. I was a bit skeptical of that choice of material, but at the time anything with metal frames cost way more...
> 
> ...


So it had glass reinforced resin. That's why you had trouble drilling it. Trust me I know all about plastics used as thermal transfer devices. I even have my own special brew that can shed amazing amounts of heat. Still it doesn't come close to aluminum and I am using some pretty extreme measures. These plastics are good for secondary measures but you should always (with current tech) use metal close to the heat source.


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## saabluster (Sep 10, 2010)

alpg88 said:


> i can belive it,
> there is a way to grow diamonds in flat shape, i saw a program on tv about it too, it makes aluminium look like plastic next to it, they showed thermal cam of it, they heated up a disc of aluminium and this diamond on the edge with a flame, aluminium only started to get hot, diamond was already completely hot,
> but cost....
> http://www.ccl-diamond.com/HTML/Products_Plates.html


Plastic is not diamond. Grinding diamond up and using it to improve the thermal characteristics of plastic will only do so in a *very* limited way. Grinding the diamond destroys the entire method that it uses to transfer heat so efficiently.


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## BigRiz (Sep 10, 2010)

Actually, in this article (http://www.teijin.co.jp/english/rd/rd13_11.html) they do give some specifications, and they're pretty good (see image). However, the specifications are just for the filler rather than the mixed resin, which we have yet to see. What's good about this is that it's not something that's just experimental and needs another 10 years for possible commercialisation.... it's already in a commercial product.


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## alpg88 (Sep 10, 2010)

saabluster said:


> Plastic is not diamond. Grinding diamond up and using it to improve the thermal characteristics of plastic will only do so in a *very* limited way. Grinding the diamond destroys the entire method that it uses to transfer heat so efficiently.


 who said anything about grininding diamond????
*grown *diamond and this plastic are not related, what is, is ability for something not metallic to transfer heat as fast as metal, i
see nothing impossible about this plastic, 
hey carbon fiber is stronger than steel and a lot lighter, 50 years ago if i mention anything about carbon fiber, ppl would laugh at me. same about nano tech, and pbly stem cells.
i realize it is very hard for some old school, close minds to even conceive it, but hey, reality is stranger than fiction, and tech progress is way ahead of their imagination.


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## saabluster (Sep 10, 2010)

alpg88 said:


> who said anything about grininding diamond????
> *grown *diamond and this plastic are not related, what is, is ability for something not metallic to transfer heat as fast as metal, i
> see nothing impossible about this plastic,
> hey carbon fiber is stronger than steel and a lot lighter, 50 years ago if i mention anything about carbon fiber, ppl would laugh at me. same about nano tech, and pbly stem cells.
> i realize it is very hard for some old school, close minds to even conceive it, but hey, reality is stranger than fiction, and tech progress is way ahead of their imagination.


I was struggling to see where you were going with that. It is more clear now but still lacks much sense. To say one believes plastic can transfer heat extremely well just because some other completely unrelated material can doesn't make much sense. 

If plastic is to ever rival the better metals the base resin is going to have to improve dramatically. This mess about adding fillers is not going to cut it. There is no evidence at this time to believe plastic will ever be able to do that. Not that it can't or won't happen. I am very open about the possible future development of highly conductive plastics but when I see them talking about a filler I already know what to expect. :fail: Then I see they are focusing all attention on the properties of the filler itself and not how it acts in the plastic itself.:fail: It doesn't matter how good the filler is by itself. 

The shape of the particles and how they link are at least as important as how well the individual particles conduct heat. Looking at the particle shape I highly doubt this stuff will do remarkably well.


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## AnAppleSnail (Sep 10, 2010)

saabluster said:


> I was struggling to see where you were going with that. It is more clear now but still lacks much sense. To say one believes plastic can transfer heat extremely well just because some other completely unrelated material can doesn't make much sense.



Carbon fiber, a common performance polymer, can be structured for low or high thermal conductivity. The only published figures I can find for the fibers themselves are as high as 640 W/m*K. This is a lot better than aluminum, but unfortunately pure carbon fiber isn't very useful - you need a bonding agent. Normally a very strong epoxy is used, and we all know how thermally conductive epoxy is. The epoxy between each fiber reduces the thermal conductivity of the carbon fiber part to what you'd expect from a fiberglass sort of thing.

They already use a form of carbon fiber composites in aircraft brakes because you get a highly heat resistant, very conductive material. I think the base material used with the stuff mentioned in this article is an attempt to make a more-conductive bonding agent for the fibers in the composite. We'll see! But it could work.


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## saabluster (Sep 10, 2010)

AnAppleSnail said:


> Carbon fiber, a common performance polymer, can be structured for low or high thermal conductivity. The only published figures I can find for the fibers themselves are as high as 640 W/m*K. This is a lot better than aluminum, but unfortunately pure carbon fiber isn't very useful - you need a bonding agent. Normally a very strong epoxy is used, and we all know how thermally conductive epoxy is. The epoxy between each fiber reduces the thermal conductivity of the carbon fiber part to what you'd expect from a fiberglass sort of thing.
> 
> They already use a form of carbon fiber composites in aircraft brakes because you get a highly heat resistant, very conductive material. I think the base material used with the stuff mentioned in this article is an attempt to make a more-conductive bonding agent for the fibers in the composite. We'll see! But it could work.



And I will repeat. Until they improve the resin itself all this talk about fillers is much ado about nothing. This product is a filler not an improvement for the resin. I also do not get the sense that this filler is designed so narrowly for improving the characteristics of the composite's resin. Not that it couldn't be used for that but more broadly they mean for it to go into cast plastic parts that could replace metal heatsinks such as the new LED light's heatsink which is based on this filler/plastic combo. I highly doubt they threw a carbon fabric in there as well as it would defeat the whole purpose which is to reduce production complexity/cost. 

BTW I think those brakes are actually carbon/ceramic not carbon/epoxy.


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## AnAppleSnail (Sep 10, 2010)

saabluster said:


> BTW I think those brakes are actually carbon/ceramic not carbon/epoxy.



Ack, they are. I'd hate to think what happens to epoxy at those temperatures.


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## bshanahan14rulz (Sep 10, 2010)

Arctic Silver 5 claims that the silver particles in the suspension are specially shaped so that when the stuff sets, the silver particles align and contact each other much better.

Perhaps this plastic employs a similar method, whereby the mix of resin and special fillers isn't very impressive itself, but when the stuff sets, the fillers arrange themselves in a more useful way.


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## Kestrel (Sep 10, 2010)

With this product being injection molded, the 'setting' is pretty close to instant. And I'd take that Arctic Silver claim with more than a bit of salt. 

*+1* on saabluster's posts btw.


*Edit:*
Yet another issue with this design (and why comparison between aluminum / carbon composites isn't a good one) is that a major issue is the thermal coupling between the matrix material (electrical insulator - conducting heat via phonons i.e. atomic vibration) and the thermally conductive material (probably conducting the majority of heat via electron mobility). The interfaces between these two materials is where the problem is - the thermal coupling is generally poor between materials that conduct heat via two completely different mechanisms.

In college I did some lab research on copper-diamond composites for thermal conduction applications. The thermal conductivity for these composites ended up being rather low, primarily due to poor thermal coupling betwen these two very high _k_ materials.


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## deadrx7conv (Sep 10, 2010)

http://www.greenergylist.com/ThermoComposite/
http://powerelectronics.com/mag/power_graphite_heatsinks_copper/

Carbon fiber and graphite heat sinks were mentioned years ago. Still can't go to my local electronics store and buy one cheaply. 

Hopefully, the plastic ones can be made available soon enough.


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## blasterman (Sep 10, 2010)

We might be overthinking this a bit.

When it comes to heatsinking CPUs, high powered LEDs and other high thermal density devices a heat-sink functions in a couple different ways. This product *might *not have to be good at all of them.

The first requirement of a good heatsink is to rapidly move heat away from the device to keep from damaging it. Next is to radiate the heat via convection; natural or passive. Somewhere in the middle the heatsink acts as a thermal battery which is a function of it's own mass. As I recall, almuminum is better at thermal storage than copper while copper can move heat away faster. The later is where fancy carbon composites come in.

This is why you often see hybrid copper/alu heatsinks on high performance sinks. The middle copper slug moves heat away fast and then passes it off to alu, which at that point has a greater radiating area beause of simple geometery. This why we can often bolt LED stars to junk steel and stuff because the alu star works sufficiently to cool the tiny emitter and then hands it off to the poorer performing steel, but has much greater radiating area.

So, is it possible this resin based sink merely works on the same principle? Is there perhaps a small metal core connected to the emitter array, then the high surface area of the 'conductive resin' gives it sufficient thermal resistance to accomplish what it has to.


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## Kestrel (Sep 10, 2010)

blasterman said:


> As I recall, almuminum is better at thermal storage than copper while copper can move heat away faster.





Kestrel said:


> *Thermal* Specific _Den _*“Thermal*
> *conduct* HeatCap _sity _*volume”*
> (W / mK) (J / gK) (g/cc)_ (J/ccK)​Aluminum *250* __0.85 ___2.7___ *2.3*
> Brass..... *110* __0.38 ___8.6 ___*3.2*
> ...


So for a fixed-size heatsink, aluminum is decent for heatsinking because of its relatively high heat capacity per unit mass. However, it is still not as good as the same volume of copper - definitely less expensive though.


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## bshanahan14rulz (Sep 10, 2010)

I think B-man still has a point, though. Just think, this could mean injection-moulded high-performance flashlights for cheap! More people would have more usable light! Illumination for everybody w/o paying for a $30 flashlight! And then it wouldn't be such an inefficient design to have a metal slug inside a plastic flashlight.


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## LotusDarkrose (Sep 10, 2010)

If they got the plastic heatsinking down to be at least on par with aluminum, it would make it a heck of a lot easier to make dive lights. If, if...if.


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## Kandela (Sep 10, 2010)

I say uno ting. PLASTIC is what makes crap.... crap. metal, ANYTHING just stands the test of time, no matter what the fancy schmancy engineer pants say. They work for fancy schmancy fat pants boss man.

+1 for dive lights and anywhere when weight/corrosion is an issue. Plastic heatsinks would be a nice option, but i'd hate to see it becoming mainstream, like our plastic toy cars. :sick2:


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## LiveForNight (Sep 10, 2010)

I have always wondered why they don't make Bakelite handles for high heat flashlights. I have a light that heats my hand up so bad I can't hold it any longer. A thin layer would insulate your hand from all heat and add no weight. I have taken a Bakelite distributor cap off a car that was running for hours and it's almost cold. If they could do this at the turn of the last century what's possible now!

From Wikipedia:

*Bakelite* (pronounced /ˈbeɪkɨlaɪt/), or *polyoxybenzylmethylenglycolanhydride*, is an early plastic. It is a thermosetting phenol formaldehyde resin, formed from an elimination reaction of phenol with formaldehyde, usually with a wood flour filler. It was developed in 1907–1909 by Belgian chemist Dr. Leo Baekeland.
One of the first plastics made from synthetic components (although phenol can be extracted from biological sources), Bakelite was used for its electrically nonconductive and heat-resistant properties in radio and telephone casings and electrical insulators. PAPER REINFORCED PHENOLIC NEMA XX per MIL-I-24768 PBG Normal electrical applications, moderate mechanical strength, continuous operating temperature of 250°F.


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## OldNick (Sep 10, 2010)

But if your torch is getting that hot it may well need your hand to take away the heat. If you mean to actually layer the torch with bakelite, you would have real trouble. As I see it, the whole idea these days is to keep the torch as streamlined as possible. So in may cases a handle would be unwanted.

Sorry I can't think of any more arguments. :devil:

This may be of interest. The biggest thing I can see is no need to have an insulation layer.

6.49 euros.
*CREE XP-G R5 on Ceramic PCB* 
Cree XPGWHT-L1-1T-R5 on Ceramic PCB

http://www.led-tech.de/en/High-Powe...E-XP-G-R5-on-Ceramic-PCB-LT-1713_120_138.html


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## LiveForNight (Sep 10, 2010)

Kestrel said:


> With this product being injection molded, the 'setting' is pretty close to instant. And I'd take that Arctic Silver claim with more than a bit of salt.


 
I agree with you when you say that you don't believe the claims made by the company that manfactures Arctic Silver and even if you are saying that cured heat transfering compounds don't work. The reason I say this is because of a video I once saw where an independent tester replaced the thermal compound under a CPU with toothpaste and Vegemite and mounted a cooler on the CPU. Supposedly the CPU temp only increased a few degrees after the toothpaste and food had time to dry. As I remember the reviewer did say that as long as the compounds were still liquid they were all (even the Vegemite) roughly equal in cooling ability. I believe this is because the contact surface area increases and in turn increases the transfer of thermal energy because the liquid fills microscopic pores in the metal. If the claims in this CPU review were true then that leads to the question, why would you not encapsulate the lights pill in a thin layer of nonconductive heat transfering liquid and then, as discussed earlier, use any old metal or composite material to finish the cooling job? Wouldn't that work?


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## qwertyydude (Sep 10, 2010)

They don't make copper finned cpu coolers because it ends up being really heavy and needing bracing. Plus it's more expensive. But there are all copper versions of heatsinks and they still outperform their copper/aluminum hybrid counterparts. So there's not much credence to the belief that copper can't radiate heat. It can't radiate as much infrared but that's hardly the primary form of heat dissipation in thermally conductive heatsinks.

A perfect examply are these two identical heatsinks. One all copper and one hybrid copper/aluminum fins.

http://www.frostytech.com/articleview.cfm?articleID=2431
http://www.frostytech.com/articleview.cfm?articleID=2430

The all copper one outperforms the hybrid one. 18.1 degrees cooler vs only 18.7 cooler. Lower is better.

So the added expense of all copper generally doesn't yield a vast improvement in performance but you end up paying more and the extra weight is bad for your computer motherboard. This is generally why you don't see all copper heatsinks. It's a myth that all copper heatsinks perform worse than copper/aluminum fins.


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## LiveForNight (Sep 10, 2010)

OldNick said:


> But if your torch is getting that hot it may well need your hand to take away the heat. If you mean to actually layer the torch with bakelite, you would have real trouble. As I see it, the whole idea these days is to keep the torch as streamlined as possible. So in may cases a handle would be unwanted.
> 
> Sorry I can't think of any more arguments. :devil:
> 
> ...


 
Sorry I can't think of any more arguments. *LOL*

I don't mean the whole light only a small area of the handle. I know my little Maratac gets hot and I grip the head tighter to take away the heat. I mean these beast lights ike my Warrior HID. Who cares if it will run 45 minutes I can't hold it after 15 Min without an oven mitt.


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## Steve-at-Springboard (Sep 11, 2010)

A question: In such a composite resin/filler substance, how much resin is there for how much filler? I'm sure it varies depending on what the materials are. Obviously, if you have 95% filler, the resin won't affect things too much. But, I don't know any real-world numbers. 50/50 sounds too low. Perhaps 75% filler? Anybody got some examples?


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## saabluster (Sep 11, 2010)

Steve-at-Springboard said:


> A question: In such a composite resin/filler substance, how much resin is there for how much filler? I'm sure it varies depending on what the materials are. Obviously, if you have 95% filler, the resin won't affect things too much. But, I don't know any real-world numbers. 50/50 sounds too low. Perhaps 75% filler? Anybody got some examples?


It is all over the place. It depends on the material. Generally the higher the loading the better the thermal performance but some additives will cause the mixture to get extremely thick in relatively small amount so the limitation there is the ability to then cast it into a part. Then if you get the loading too high the structural strength will degrade and become to brittle. It's all about finding the happy zone and that varies not just on the filler but the resin.


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## Lynx_Arc (Sep 11, 2010)

I have a strange feeling that we won't see the proper balance of heat transfer, cheaper cost, and durability/usability in thermal plastic such that it will challenge current LED light designs until LED efficiency gets so far up there that you won't have but a fraction of the heat we do now in LEDs. If LEDs drop in voltage down to ~2.4 and efficiency is good, plastic is able to heatsink it imagine cheap 2 cell lights with no drive electronics in the stores costing $2 each again.


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## uk_caver (Sep 11, 2010)

Surely, you'll still need some kind of current management (even if just an integrated resistor) as long as there are different-voltage cells that could be put in the device (lithium vs. alkaline vs NiMH).

I'd have thought it tricky for the Vf of a white-producing LED to get down to 2.4V (assuming there isn't any internal voltage boosting), since that seems likely to be getting pretty much towards green light as the shortest possible component wavelength.

Generally speaking, is there any reasonably good rule-of thumb for waste heat production for a given lumens-per-watt [cool] white LED?
(ie 'X lm/W equates to ~Y% of [LED] input power ending up as heat' with a formula relating X and Y)


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## Kestrel (Sep 11, 2010)

Lynx_Arc said:


> I have a strange feeling that we won't see the proper balance of heat transfer, cheaper cost, and durability/usability in thermal plastic such that it will challenge current LED light designs until LED efficiency gets so far up there that you won't have but a fraction of the heat we do now in LEDs.


This. :thumbsup:


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## LiveForNight (Sep 11, 2010)

Just for the hell of it (I'm bored this weekend) I took a cheap Trustfire SSC P7 that I have (I hate this light) and taped the threads of the section between the pill and the battery tube with teflon tape. Before I taped it I painted the spring side of the pill with liquid tape I got from Home Depot leaving a little off the end of the spring for contact with the battery. I then inserted a battery and filled the battery compartment with the rest of my PrimoChill ICE Non-Conductive Liquid Cooling Fluid left over from a computer build. I screwed on the switch cap and turned on the light face down because I didn't seal the tail switch. The results were not what I expected. It lit up so the fluid is truly non electrically conductive but instead of keeping the handle cool the entire light got as hot as the head alone used to get. So instead of transfering the heat away to quickly dissipate it the fluid allowed the heat to transfer quickly to all parts of the flashlight evenly. I left it running for 25 minutes or so before I noticed my seal job was not working at the head and fluid was leaking into the reflector. I then spent about an hour cleaning a mess out of a flashlight I don't like anyway. LOL Ok go ahead and laugh at me now.

BTW: After I do this I find an LED bulb floating in liquid, http://www.engadget.com/2009/07/15/eternaleds-debuts-worlds-first-liquid-cooled-led-light-bulb/


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## jtr1962 (Sep 11, 2010)

uk_caver said:


> Generally speaking, is there any reasonably good rule-of thumb for waste heat production for a given lumens-per-watt [cool] white LED?
> (ie 'X lm/W equates to ~Y% of [LED] input power ending up as heat' with a formula relating X and Y)


A good rule of thumb estimate is to divide the lumens per watt by 350 to get the percentage of power coming out as light. The remainder is heat. For example a Cree XP-G R5 bin is about 135 lm/W at 350 mA. Therefore, the waste heat production is around ( 1 - 135/350 ), or 61%, of the input power.


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## LiveForNight (Sep 11, 2010)

This company has been making thermally conductive plastic heatsinks for computers for a decade. They are just not heat conductive enough to work without the support of copper heatpipes: http://www.coolpolymers.com/overmoldedhp.asp

Here is another write up on a new material from MIT, where it was discovered. It explains the process of aligning polymer molecules well: http://web.mit.edu/press/2010/heat-nanofibers.html This material could easily replace metals for conducting heat.


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## LotusDarkrose (Sep 11, 2010)

Even if this process gets perfected to the point where it's not as good as aluminum, but pretty close, it would be more than suitable for a dive light casing. Given that it can get the heat away enough with the help of the cold water, I see it as a viable option that wouldn't be as hard to waterproof. Again though.."If". Also I stress casing only, since I wouldn't trust an emitter on anything except proven metals (aluminum/copper/brass).


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## AnAppleSnail (Sep 11, 2010)

LotusDarkrose said:


> Even if this process gets perfected to the point where it's not as good as aluminum, but pretty close, it would be more than suitable for a dive light casing. Given that it can get the heat away enough with the help of the cold water, I see it as a viable option that wouldn't be as hard to waterproof. Again though.."If". Also I stress casing only, since I wouldn't trust an emitter on anything except proven metals (aluminum/copper/brass).



I bet you could make a decent reflex dive light like this. LED is on the cylindrical skin of the light, shining onto a mirror that feeds the aspheric optics...or give it one of the weirder recoil-type reflectors with the LED shining into a funny bowl-shaped shiny thing from the side. This would allow the LED to be within 1 cm of the water outside.

Aluminum (in dive lights) is around 250 W/m * K. If you have a mag-size light, the heat has to go about 2 cm to the outside of the light. I think that the LED being so much closer to the outside (after reconfiguring the lens or reflector) you could accept plastic delivering 150 W/m*K without much thermal performance degradation. Now, you'd have to ask the optics folks what the penalties are from the changes in light path...


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## LotusDarkrose (Sep 11, 2010)

And what about those recoil lights if they used stronger leds, or highly driven ones even? Is there glass that would uniform the heat transfer from sides of the head to the led? (Don't know much about recoil design)

Is the recoil type of light that inferior to basic smooth or aspheric types, or is it just that this method has yet to be perfected to that point?

Sorry if my questions seem stupid, lol. Trying to gain some knowledge and get in on some interesting conversations as I go.


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## blasterman (Sep 11, 2010)

> As I remember the reviewer did say that as long as the compounds were still liquid they were all (even the Vegemite) roughly equal in cooling ability.


 
That was over at Dan's Data I believe. I was a pretty interesting conclusion when he found toothpaste worked as well as specialty conductive materials for thermal transfer. Basically, pretty much any liquid type material that forces air out of the bond works fine.

He also tests a huge array of CPU coolers, and by looking at the coolers and using intuition does not have any bearing on the coolers that do a good job. Just like LEDs it seems that having a lot of mass next to the heat source to pull heat away is the first requirement, then things get less critical as convection takes over.


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## AnAppleSnail (Sep 11, 2010)

LotusDarkrose said:


> And what about those recoil lights if they used stronger leds, or highly driven ones even? Is there glass that would uniform the heat transfer from sides of the head to the led? (Don't know much about recoil design)
> 
> Is the recoil type of light that inferior to basic smooth or aspheric types, or is it just that this method has yet to be perfected to that point?
> 
> Sorry if my questions seem stupid, lol. Trying to gain some knowledge and get in on some interesting conversations as I go.



The LED points backwards into a reflector. It can be off to the side, and this design allows ridiculous throw with some useful spill. The main problems are heatsinking - putting an LED in front of a reflector with a bit heatsink on it blocks all the light!

Here's one: Pelican 2020

See how the LED blocks part of the reflector? Some are more like satellite dishes, with the LED shining in from below the reflector, which has a funny shape, to still make the desired beam pattern. A whole lot of LED light can be captured without a hugely deep or massive reflector (the problem with throwy conventional reflector LED lights).


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## Justin Case (Sep 11, 2010)

LiveForNight said:


> This company has been making thermally conductive plastic heatsinks for computers for a decade. They are just not heat conductive enough to work without the support of copper heatpipes: http://www.coolpolymers.com/overmoldedhp.asp
> 
> Here is another write up on a new material from MIT, where it was discovered. It explains the process of aligning polymer molecules well: http://web.mit.edu/press/2010/heat-nanofibers.html This material could easily replace metals for conducting heat.



Despite the breathless nature of the MIT press release, I fail to see the big deal. Highly aligned PE, such as Dyneema, is well known to have a higher thermal conductivity vs regular PE. It's all about phonon conduction.

It's also 1D conduction, with a very high anisotropy ratio.

If you simply weave the highly aligned fibers, you have a lot of insulating air in the material. You also don't have perfect fiber alignment anymore, and the thermal conductivity anisotropy gets you.

If you make a fiber composite with the material (while somehow maintaining perfect fiber alignment), then you run into the old interface problem, already described previously in this thread.

It's a long way from component materials to finished product.


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## LiveForNight (Sep 11, 2010)

blasterman said:


> Just like LEDs it seems that having a lot of mass next to the heat source to pull heat away is the first requirement, then things get less critical as convection takes over.


 
Exactly right! CPUs and LEDs are small heat generating monsters with CPUs leading the heat race. Why would you not treat them the same and heat pipe an LED using liquid passive cooling? A fan would be unnecessary because you are not encapsulating the heat generator in a big enclosed metal box like a computer. Run a thin Zalman type ring around the head of a flashlight and then use one of the new heat conducting polymers for the rest of the light and a non heat conductive polymer for the handle. The handle and battery would remain cool and the front of the light would become a true radiator that light manufacturers only attempt to design now out of aluminum. The components would add cost for sure but you are already buying a several hundred dollar flashlight what is another few bucks to cool it properly and extend the life.


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## LiveForNight (Sep 12, 2010)

Justin Case said:


> Despite the breathless nature of the MIT press release, I fail to see the big deal. Highly aligned PE, such as Dyneema, is well known to have a higher thermal conductivity vs regular PE. It's all about phonon conduction.
> 
> It's also 1D conduction, with a very high anisotropy ratio.
> 
> ...


 
Here is my highly technical response: But wouldn't that be cool if it worked! LOL

I don't think it's here now but at some point in the future. I also believe that the light source, LED or whatever, at that future time might not even produce as much heat as they currently do. Perhaps the two will balance out.


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## OldNick (Sep 12, 2010)

LiveForNight said:


> Sorry I can't think of any more arguments. *LOL*
> 
> I don't mean the whole light only a small area of the handle. I know my little Maratac gets hot and I grip the head tighter to take away the heat. I mean these beast lights ike my Warrior HID. Who cares if it will run 45 minutes I can't hold it after 15 Min without an oven mitt.



Glad you took it the right way.

OK, I see what you mean if it's that bad. Trouble is bakelite is used so little these days it would be horrendous $$. I would assume there was something more common and yes I see your point


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## SemiMan (Sep 12, 2010)

I believe the substitute for bakelite these days in all but high temperature applications is of course plastic as most conduct so poorly and have little thermal mass as well.

Mass does not equal heat transfer as one person put it. Graphite heat sinks (yes they do exist) are very light and have the best heat transfer (albeit aligned only in one direction). They can be found in high performance laptops today. You will not find one off the shelf as their properties do not lend themselves well to a general purpose design.

In terms of copper versus copper/aluminum, I did not even realize there was a myth that copper/aluminum hybrids would be better. Copper of course will be superior if used alone in the same equivalent shape. For a specific application, emissivity may come into play in which case black anodized aluminum is better than bare copper but in the described CPU cooler application, this is not going to really come into play with almost all the transfer from forced air conduction.

Thermally enhanced plastics have been around for a long time. Boron Nitride filled plastics have been around decades and are of course better than unfilled plastics but no where near aluminum. That is of course not to say that will never happen.

Semiman


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## qwertyydude (Sep 12, 2010)

I work with a lot of mechanical engineering students at the school I attend and me being a manufacturing engineering student they think they have the upper hand and assume that since the market is saturated with copper/aluminum heatsinks that it must be the best.

I've read several posts here perpetuating this myth over the years and I assume they had to have started with a "patient zero" somewhere who repeated this myth and it gets propagated without being fact checked by anyone. I also see it a lot on computer forums, you'd think the guys building high end computers would know the difference but nope. Computer scientists are not engineers and a lot of mechanical engineers I know assume the same thing even if they should know better. IR emissivity is almost always trumped by convection. The only time IR emissivity matters is in space. Again time to pull the engineer's heads out of the clouds, this time really high stratospheric crowds.


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## AnAppleSnail (Sep 12, 2010)

qwertyydude said:


> The only time IR emissivity matters is in space.



I've seen some reasonably-well-conducted experiments here on CPF testing this - two LEDs driven identically (I think he only matched their Vfs closely, didn't actually swap the LEDs to see if that made a difference), one on a polished aluminum cylinder, the other on an identical cylinder painted with black Krylon. In still air, he found that the black heatsink was rather cooler.

With that said, I think that fans make all the cooling in a computer. Also, the emissivity difference between aluminum and copper isn't as great as polished vs. black metal. Finally, it seems like a fanned heatsink design should be built to make the fans as close to the CPU temperature as possible, without damagingly high weight.


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## jtr1962 (Sep 12, 2010)

SemiMan said:


> In terms of copper versus copper/aluminum, I did not even realize there was a myth that copper/aluminum hybrids would be better. Copper of course will be superior if used alone in the same equivalent shape.


Yes. The only reason you see hybrid copper-aluminum heatsinks in the computer market is cost. I have extensive experience in this area as peltiers are among my hobbies. I can say without a doubt that a pure copper heatsink of the same size and shape will indeed cool better than aluminum. Every thermal simulation software I've used, plus real-world experience, backs this up.

The idea of highly conductive plastics is fascinating. Should we ever develop a plastic which is inexpensive, easy to mold, and has thermal conductivity at least on par with aluminum, it will be revolutionary.


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## LiveForNight (Sep 12, 2010)

qwertyydude said:


> I work with a lot of mechanical engineering students at the school I attend and me being a manufacturing engineering student they think they have the upper hand and assume that since the market is saturated with copper/aluminum heatsinks that it must be the best.
> 
> I've read several posts here perpetuating this myth over the years and I assume they had to have started with a "patient zero" somewhere who repeated this myth and it gets propagated without being fact checked by anyone. I also see it a lot on computer forums, you'd think the guys building high end computers would know the difference but nope. Computer scientists are not engineers and a lot of mechanical engineers I know assume the same thing even if they should know better. IR emissivity is almost always trumped by convection. The only time IR emissivity matters is in space. Again time to pull the engineer's heads out of the clouds, this time really high stratospheric crowds.


 
I know this is a little off topic but you, as a student, have the knowledge to help me decide. I am in the middle of a new computer build and have never used fans for cooling. If I do use a fan it's attached to a liquid cooler, at the rear of the box and on low. I hate noisy computers - if it's making noise it's broken! I traded away a Nitecore light because it whined like a newborn baby! 

I am trying to decide between the two passive coolers linked below and after reading your post I am now inclined to believe the all copper one would be a better choice. Do you agree?

http://www.newegg.com/Product/Product.aspx?Item=N82E16835887001

http://www.newegg.com/Product/Product.aspx?Item=N82E16835242005


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## uk_caver (Sep 12, 2010)

jtr1962 said:


> I can say without a doubt that a pure copper heatsink of the same size and shape will indeed cool better than aluminum.


True, but I guess in a case where only a given amount of cooling is needed, one person's 'better' could be another person's 'unnecessarily better'.


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## Tally-ho (Sep 12, 2010)

Not so bad:
_Cool Polymers’ CoolPoly line today includes compounds of LCP, nylon 66, PC/ABS, and PPS. They offer thermal conductivities up to 60 W/mK, depending on resin type. Elastomeric TPO compounds are in development. The company offers to custom formulate thermally conductive grades of any engineering or commodity thermoplastic._
http://www.ptonline.com/articles/200106fa1.html

Also:
_Abstract
Epoxy composites based on vapor grown carbon fiber (VGCF) were fabricated and analyzed for room temperature thermophysical properties. An unprecedented high thermal conductivity of 695 W/m K for polymer matrix composites was obtained. The densities of all the composites are lower than 1.5 g/cc. In addition the high value of coefficient of thermal expansion (CTE) of the polymer material was largely reduced by the incorporation of VGCF. Also, unlike metal matrix composite (MMC), the epoxy composite has an electrically insulating surface. Based on the composite thermal conductivities, the room temperature thermal conductivity of VGCF, heat-treated at 2600°C, was estimated to be 1260 W/m K. Furthermore, the longitudinal CTE of the heat-treated VGCF was determined, for the first time, to be −1.5 ppm/K._
http://tiny.cc/5r34g


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## LiveForNight (Sep 12, 2010)

Tally-ho said:


> Not so bad:
> _Cool Polymers’ CoolPoly line today includes compounds of LCP, nylon 66, PC/ABS, and PPS. They offer thermal conductivities up to 60 W/mK, depending on resin type. Elastomeric TPO compounds are in development. The company offers to custom formulate thermally conductive grades of any engineering or commodity thermoplastic._
> http://www.ptonline.com/articles/200106fa1.html


 
Great article! This was in the prose:

"His company (Cool Polymers) has demonstrated the concept in certain applications where thermally conductive plastics provide heat transfer equivalent to aluminum and copper designs. 

....Conductive plastics also weigh 40% less than aluminum; they offer design freedom for molded-in functionality and parts consolidation; and they can eliminate costly post-machining operations."

It would seem plastic heatsinks are closer to reality than I thought. What would this mean for DIY flashlight mods? Anyone with a Dremel and screwdriver could make a flashlight. The rest of us could get in on the fun. I don't have the money to buy a $2k Combo Lathe/Mill for just a fun weekend project! Just buy a blank of plastic and form it to what ever shape, let's say, bike light you want to strap on your helmet!


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## IMSabbel (Sep 12, 2010)

It could also mean _a lot_ for fixed lighting: Aluminium heatsink are one of the largest TCO contributers for such installations. Plastic is always cheaper if you can use it.


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## Justin Case (Sep 12, 2010)

LiveForNight said:


> Great article! This was in the prose:
> 
> "His company (Cool Polymers) has demonstrated the concept in certain applications where thermally conductive plastics provide heat transfer equivalent to aluminum and copper designs.



The article made it reasonably clear that "certain applications" means when you are convection-limited, not conduction-limited. So of course if one selects an application where the higher thermal conductivity of metals doesn't matter, then conductive polymers can look good.


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## saabluster (Sep 12, 2010)

Tally-ho said:


> Not so bad:
> _Cool Polymers’ CoolPoly line today includes compounds of LCP, nylon 66, PC/ABS, and PPS. They offer thermal conductivities up to 60 W/mK, depending on resin type. Elastomeric TPO compounds are in development. The company offers to custom formulate thermally conductive grades of any engineering or commodity thermoplastic._
> http://www.ptonline.com/articles/200106fa1.html
> 
> ...



I already knew about the coolpoly stuff but that second article is news to me. Thanks for digging that up. Those are some truly astounding numbers. I would say that until I see the details I am reservedly excited. Although they were able to reach those numbers was it like the other one mentioned in this thread where it was in one direction. Since I can't read the article it is hard to say. The other caution is that even though they can reach those numbers what was the loading required to do so and how did that affect the structural properties of the plastic. While you can overload a polymer to get higher heat transfer it comes at a price. Generally the plastic becomes very brittle and is not of much use. Wish we could get a copy of that article.


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## CKOD (Sep 13, 2010)

AnAppleSnail said:


> I've seen some reasonably-well-conducted experiments here on CPF testing this - two LEDs driven identically (I think he only matched their Vfs closely, didn't actually swap the LEDs to see if that made a difference), one on a polished aluminum cylinder, the other on an identical cylinder painted with black Krylon. In still air, he found that the black heatsink was rather cooler.
> 
> With that said, I think that fans make all the cooling in a computer. Also, the emissivity difference between aluminum and copper isn't as great as polished vs. black metal. Finally, it seems like a fanned heatsink design should be built to make the fans as close to the CPU temperature as possible, *without damagingly high weight*.


 
We got a winner on the copper/alu mixed heatsinks right there. In addition to aluminum being cheaper then copper, the all copper heatsinks of 4-5 years ago for computers were HEAVY. Heavy enough that they would rip the clips off of the CPU socket mount, and the extreme ones would have to bolt to the motherboard. 

Now, they all bolt/pin to the motherboard anyway, and heatpipes are very, very common, so now they can be 4-8 copper heatpipes assembled in a small aluminum base, with the very high thermal conductivity of the heat pipes taking the heat to the cheap stamped aluminum fins. While they are lighter and use less material, they are even taller then they used to be, adding a nice bending moment, so the heatsinks still need to be bolted to the mobo. It would be awesome to see someone make a mag light double bored for 2x 18650 cells side by side, and have heatpipes bonded to the walls of the body in the gaps provided around the battery. With something like the highly finned bodies fivemega makes, you could move a ton more heat out.


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## Kandela (Sep 13, 2010)

Originally Posted by OldNick 
But if your torch is getting that hot it may well need your hand to take away the heat. If you mean to actually layer the torch with bakelite, you would have real trouble. As I see it, the whole idea these days is to keep the torch as streamlined as possible. So in may cases a handle would be unwanted.

Sorry I can't think of any more arguments. 

This may be of interest. The biggest thing I can see is no need to have an insulation layer.

6.49 euros.
CREE XP-G R5 on Ceramic PCB 
Cree XPGWHT-L1-1T-R5 on Ceramic PCB

http://www.led-tech.de/en/High-Power...3_120_138.html
Sorry I can't think of any more arguments. LOL

I don't mean the whole light only a small area of the handle. I know my little Maratac gets hot and I grip the head tighter to take away the heat. I mean these beast lights ike my Warrior HID. Who cares if it will run 45 minutes I can't hold it after 15 Min without an oven mitt. 


^^^^^^^^^^^^^^^^^^^^^^^^^^

Heatsinking via hand?! LOL you guys are crazy. Hilarious.

Never have I had a flashlight where I actually had to even CONSIDER using portions of my body to radiate heat away! It was never an issue, or even a thought! On ANY electronic!

I can see it now, *2215, epiderimically mounted muscular heatsinks complete with fiber heat transfer veins!

haaaaaa cps nerds RULE

lovecpf


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## blasterman (Sep 13, 2010)

> I did not even realize there was a myth that copper/aluminum hybrids would be better.


 
I didn't realize there was a myth or that anybody stated that in this thread.

I did notice for several years that most of the heat-sinks I encountered in high end servers were copper/alu hybrids, and the price difference between copper an alu sinks in a $50,000-$1,000,000 piece of hardware is trivial. So, I have to believe there was some engineering justification for this other than IBM engineers not being as smart as the ones in this thread.


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## AnAppleSnail (Sep 13, 2010)

CKOD said:


> It would be awesome to see someone make a mag light double bored for 2x 18650 cells side by side, and have heatpipes bonded to the walls of the body in the gaps provided around the battery. With something like the highly finned bodies fivemega makes, you could move a ton more heat out.



Sure you could get the heat off the LED, but then what? The high thermal mass of those lights is a feature. Just because the outside wall of the flashlight is only a few degrees cooler than the LED doesn't make a good cooling system - then you need to hold the flashlight. That's just good heat distribution, then you have to export the heat.

Unless you have enough fins for steady-state cooling, the decreased thermal mass of heat pipes instead of a metal slug is a penalty to general use (putting the light down for a few minutes to work on things).



blasterman said:


> I didn't realize there was a myth or that anybody stated that in this thread.
> 
> I did notice for several years that most of the heat-sinks I encountered in high end servers were copper/alu hybrids, and the price difference between copper an alu sinks in a $50,000-$1,000,000 piece of hardware is trivial. So, I have to believe there was some engineering justification for this other than IBM engineers not being as smart as the ones in this thread.



Surely the only real gain in Copper/Aluminum heatsinks is in decreased weight? These days heatpipes replace the old copper cores, but as mentioned above it makes the heatsinks taller.


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## SemiMan (Sep 13, 2010)

blasterman said:


> I didn't realize there was a myth or that anybody stated that in this thread.
> 
> I did notice for several years that most of the heat-sinks I encountered in high end servers were copper/alu hybrids, and the price difference between copper an alu sinks in a $50,000-$1,000,000 piece of hardware is trivial. So, I have to believe there was some engineering justification for this other than IBM engineers not being as smart as the ones in this thread.



Weight is one issues.

Profit is another. Ever dollar saved is another dollar of profit and even in $50-$100K unit, profit still matters.

Semiman


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## Justin Case (Sep 13, 2010)

saabluster said:


> I already knew about the coolpoly stuff but that second article is news to me. Thanks for digging that up. Those are some truly astounding numbers. I would say that until I see the details I am reservedly excited. Although they were able to reach those numbers was it like the other one mentioned in this thread where it was in one direction. Since I can't read the article it is hard to say. The other caution is that even though they can reach those numbers what was the loading required to do so and how did that affect the structural properties of the plastic. While you can overload a polymer to get higher heat transfer it comes at a price. Generally the plastic becomes very brittle and is not of much use. Wish we could get a copy of that article.



The manuscript was submitted in 2001. Anything commercialized off it in the intervening 9 years with those published properties? I doubt it, since you don't see any VGCF epoxy composites with thermal conductivity anywhere near ~700W/m-K.


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## Th232 (Sep 13, 2010)

Kandela said:


> Heatsinking via hand?! LOL you guys are crazy. Hilarious.
> 
> Never have I had a flashlight where I actually had to even CONSIDER using portions of my body to radiate heat away! It was never an issue, or even a thought! On ANY electronic!
> 
> ...



The reason you've never had to think about it is because you're already doing it when you hold a torch in your hand. Heat gets transferred to your blood, which promptly gets pulled away by circulation.


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## saabluster (Sep 13, 2010)

Justin Case said:


> The manuscript was submitted in 2001. Anything commercialized off it in the intervening 9 years with those published properties? I doubt it, since you don't see any VGCF epoxy composites with thermal conductivity anywhere near ~700W/m-K.



Certainly there has not been any commercialization of it that I know but I do think this may have potential. But like I say until I can actually read the article there is little in the way of conclusions to be drawn one way or the other. Anyone found that article available for free?


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## Th232 (Sep 14, 2010)

Email inbound.:thumbsup:


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## LiveForNight (Sep 14, 2010)

"since you don't see any VGCF epoxy composites with thermal conductivity anywhere near ~700W/m-K."


The conclusion in the below listed article claims that high production costs, "hinders the extensive applications of the carboned based composites."

http://etd.ohiolink.edu/send-pdf.cgi/Hsieh FengHsu.pdf?acc_num=ohiou1146149557

It's not that it isn't available now but too expensive to be practical.


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## Tally-ho (Sep 14, 2010)

Carbon nano-tube:
http://en.wikipedia.org/wiki/Carbon_nanotube

_*Thermal*
Main article: Thermal properties of nanostructures
All nanotubes are expected to be very good thermal conductors along the tube, exhibiting a property known as "ballistic conduction", but good insulators laterally to the tube axis. Measurements show that a SWNT has a room-temperature thermal conductivity along its axis of about 3500 W·m−1·K−1;[36] compare this to copper, a metal well-known for its good thermal conductivity, which transmits 385 W·m−1·K−1. A SWNT has a room-temperature thermal conductivity across its axis of about 1.52 W·m−1·K−1,[37] which is about as thermally conductive as soil. The temperature stability of carbon nanotubes is estimated to be up to 2800 °C in vacuum and about 750 °C in air.[38]_

I don't get used with thermal conductivity "measurement standards" so i hope you will understand this better than me and drop me a line to explain it briefly (in english (in french prefered )).
BTW: I heard some years ago of a CPU's heatsink with a base made of carbon nano-tubes sticked together in the same axis. It was supposed to beat copper. It was discussed a lot but i forgot about it before it was (probably never) manufactured.

EDIT: Don't bother with an explanation, the french version of the wikipedia article is shorter but way more comprehensible for me:
_Dureté [modifier]
Certains nanotubes sont plus durs que le diamant11.
Conductivité thermique [modifier]
Les nanotubes de carbone ont une conductivité thermique plus grande que celle du diamant (de 6 à 20 W.cm-1.K-1)._
:wow:


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## Justin Case (Sep 14, 2010)

LiveForNight said:


> "since you don't see any VGCF epoxy composites with thermal conductivity anywhere near ~700W/m-K."
> 
> 
> The conclusion in the below listed article claims that high production costs, "hinders the extensive applications of the carboned based composites."
> ...



The paragraph with that conclusion talks about standard carbon fiber composites, not vapor grown carbon fibers.


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## LiveForNight (Sep 14, 2010)

Justin Case said:


> The paragraph with that conclusion talks about standard carbon fiber composites, not vapor grown carbon fibers.


 
Right, readily available standard carbon fiber composites have a thermal conductivity greater than ~700W/m-K and could be used but are cost prohibitive. So what is the great advance with vapor grown? That would be even more costly in production when fully developed. So essentially this technology will not be available for use for anyone here for a very long time. I'm agreeing with you. There is no big deal to this. You knew right away because you understand it through study or work in the field. I had to research first. 
Cheers
.


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## AnAppleSnail (Sep 14, 2010)

Justin Case said:


> The paragraph with that conclusion talks about standard carbon fiber composites, not vapor grown carbon fibers.



Vapor-grown ones are more expensive, aren't they? Something like nickel sputter-coated on a silicon substrate, with horribly toxic complex gases with lots of carbon added in small amounts to a vacuum and heated, and they grow like grass? And the length is limited because of pesky things like gravity.


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## Justin Case (Sep 16, 2010)

Tally-ho said:


> _Epoxy composites based on vapor grown carbon fiber (VGCF) were fabricated and analyzed for room temperature thermophysical properties. An unprecedented high thermal conductivity of 695 W/m K for polymer matrix composites was obtained. The densities of all the composites are lower than 1.5 g/cc. In addition the high value of coefficient of thermal expansion (CTE) of the polymer material was largely reduced by the incorporation of VGCF. Also, unlike metal matrix composite (MMC), the epoxy composite has an electrically insulating surface. Based on the composite thermal conductivities, the room temperature thermal conductivity of VGCF, heat-treated at 2600°C, was estimated to be 1260 W/m K. Furthermore, the longitudinal CTE of the heat-treated VGCF was determined, for the first time, to be −1.5 ppm/K._
> http://tiny.cc/5r34g


 
This paper has a lot of problems IMO.

For example:

1. The authors make no statement in the paper that they conducted a calibration run of their thermal conductivity measuring equipment. This is basic experimental procedure.

2. Their 4-point probe measurement is claimed to show insulating properties for surface electrical conductivity, yet the very high thermal conductivity certainly indicates VGCF loading well into the percolation regime. Thus, one would expect non-trivial electrical conductivity, which is what most every other researcher finds. Most likely, the reason is because they measured surface resistivity on a face perpendicular to the long fiber direction. On that face, there is probably no percolation -- each fiber is still surrounded by epoxy. So of course, in the "cross direction", resistivity will be high. But in the long fiber direction, I bet resistivity is low.

3. In fact, it appears to me that the authors grew a continuous mat of carbon fibers and made an epoxy composite from that. Thus, of course you are going to get "percolation" since the continuous fibers are going to go from end to end of the composite in the long fiber direction. So it looks to me that the thermal conductivity measurement is really just measuring some biased, weighted fraction of the carbon fibers exposed at the face of the composite block.

4. The thermal conductivity was less than that given by the rule of mixtures, which is a typical result. However, the explanation was that the assumed value for the thermal conductivity of the VGCF must be less than the usual book value of ~1900W/K. They extrapolate their thermal conductivity data out to a VGCF loading of 100% to give an estimate of the thermal conductivity of pure VGCF of about 1260W/K. Hogwash. There is no actual thermal conductivity measurement data for their VGCF to support such a claim.

5. The porosity measured increased with fiber loading (over 10% at 46% loading). Yet, thermal conductivity also increased dramatically. This indicates to me, as discussed in #3 above, that the dimensions of the sample are the same as the dimensions of the continuous fiber mat. Thus, you have exposed ends of the VGCFs at the faces of the sample normal to the long fiber direction, and the thermal conductivity measurements are basically sampling the fibers themselves. If the composite dimensions were larger than the length of an fiber (or particle, which is the typical case when using fillers such as alumina), then you'd think that porosity would affect the degree of percolation and hence the conductivity. I bet that if the authors had made an epoxy composite with dimensions much longer than the length of their fibers, they would have basically measured the thermal conductivity of epoxy since the faces would be pure epoxy and insulating.


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## JetPilot (Oct 11, 2010)

Dude Dudeson said:


> Here's a little story of how "the impossible" happened to me with a type of plastic....
> 
> In the early 90's I had a set of inline skates with plastic frames. I was a bit skeptical of that choice of material, but at the time anything with metal frames cost way more...
> 
> ...


 
This one I just do not beleive. If what you wrote is true, you must have been using a drillbit that had NO sharp edge to it, and I do not mean Dull, I mean totally rounded, or you put the Drill bit in backwards.... Or even more likely is that you forgot to turn the drill press on !! What I see as most likely in the above story is that this is just total BS, yes people do just totally post fabricated stories on the internet sometimes, welcome to reality. I have worked with strong, advanced plastics, and even glass reinforced composites, and they can be easily drilled.

Mike


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## SemiMan (Oct 13, 2010)

JetPilot said:


> This one I just do not beleive. If what you wrote is true, you must have been using a drillbit that had NO sharp edge to it, and I do not mean Dull, I mean totally rounded, or you put the Drill bit in backwards.... Or even more likely is that you forgot to turn the drill press on !! What I see as most likely in the above story is that this is just total BS, yes people do just totally post fabricated stories on the internet sometimes, welcome to reality. I have worked with strong, advanced plastics, and even glass reinforced composites, and they can be easily drilled.
> 
> Mike



Mike, thank you for posting what I was thinking... 

I did have another theory though. Perhaps the stop on the drill press was set such that the bit would make it to the skate, but no further. If one was unfamiliar with a press, that could happen. Of course, given the nature of molded frames, even supporting a frame flat for drilling would be very difficult.

Semiman


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