PGS heat sinking question..

[Lifetime17]

Hi D,
Hey its worth a shot at something totally different, why not all the simple properties are there heat absorption and electrical conducting . Have a little time to experiment hopefully something will come of it. Thanks buddy

Rich

 

[Encap]

Hi D,
Hey its worth a shot at something totally different, why not all the simple properties are there heat absorption and electrical conducting . Have a little time to experiment hopefully something will come of it. Thanks buddy

Rich

Good idea --have a go with it.
Just ignore SL's meaningless nonsense, he is just playing a little child's wish it were true don't you wish it was too, mind game.
Doing something that is real is so much better than overtaking the world with imaginary nonsense.
You have the capability, knowledge, and experience of actually making really nice laser hosts that work well, unlike our miracle material daydream world friend.
Be careful of the dust it makes if machining it. It goes everywhere and get into everything--wear a proper mask so you don't inhale the dust---safety first.


Pyrolytic Graphite is nothing new has been extensively studied and used for the last 15+ years --my guess is if it could be used in hand held lasers it would have but it isn't for several real reasons. See page 299 and 300 of 2002 book Spacecraft Thermal Control Handbook: Fundamental technologies by David Gilmore PS:Great book available on Amazon and most books places.

SL can't even comprehend/understand what the published Panasonic PGS information and data sheets say.
Panasonic PGS will never be of any use as a diode heat sink nor as a laser host material. SL doesn't comprehend or understand the nature of the PGS material--how the material behaves in real world applications, only in how it behaves in his imagination.
If he did he would know why it is only made in thicknesses of 1/100th mm to 1/10th mm the thinner it is the better thermal conductivity-wise. The PGS material has a thermal conductivity of 700W for 1/10th mm/100micron thickness and gets higher as it gets thinner to max 1950 in 1/100th mm/10 micron thickness and that is only in the x-y plane not in z. In the z or thickness direction it has a thermal conductivity of 15 regardless of thickness. See: http://www.mouser.com/pdfdocs/thermalgraphitesheets.pdf

Panasonic PGS material that has high thermal conductivity in the z/thickness direction is limited to 3.0mm thick and has a conductivity of 13 see: https://industrial.panasonic.com/cdbs/www-data/pdf/AYA0000/AYA0000C53.pdf
Or as a soft type that has a thermal conductivity og 28 in the z direction see:
https://industrial.panasonic.com/cdbs/www-data/pdf/AYA0000/AYA0000C50.pdf

 

[Lifetime17]

Hi E,
Thanks for the links they are really informative in instituting the material. The Mouser link is awesome i cant stop reading it and their conclusions of the PGS material. Can also be used between the IC and the copper sink. You can even cut a small strip to carry heat away from an object to.

Rich

 

[Astralist]

Hi guys

I'm not a material expert, but i do curious about all these


My question is, what is the use of super high conductivity material is the surface itself is rough and thus minimizing the heat transfer?
This is only my logical thinking, doesn't those graphite very brittle and making it porous after machining? even with some surface polishing?
I always use some CPU thermal compound between the diode module and copper/aluminum heatsink,
regarding about these PGS material, what if the heatsink compound only act as a thermal resistance even if it filled the (porous) gaps??


It would be great if we managed to create pen host made using these PGS tube
8W NUBM44 with 30sec duty is all good (but ofc it's very dangerous, so no, yeah)
Let say 1.5W 520nm in a pen host with 100% duty, running 2x 14500. sweet! :drool:

 

[GSS]

I'm also curious if it's dirty to the touch?

 

[Lifetime17]

Hi Ast,
I will find out about the machining quality of Graphite cylindrical bar. This is only a witch hunt experiment for me nothing solid. I intend to turn down the graphite and if possible press it in an AL sink.I will also use some Arctic Silver compound mixed with 99% copper dust as i do with all my sinks pressed in with a copper core. And if all turns out well i will spray the front of the sink with some duralac for copper that i purchased from a company i deal with for Brass,Copper and Aluminum. This will seal the graphite end of the core, i am testing this spray on a 510 copper module to see if its durable , and left the test piece outdoors since friday. First i polished the sink and focus adapter and only applied the spray to the sink leaving the adapter raw to the elements.
And about a host for 2-14500's i made two in brass and copper , no PSG involved if that what you mean. Here are a few pics of the two hosts in 14500 cell configuration.
Thank you for your inquiry ,,
Rich

 

[Solomon Laser]

Great Lifetime, we are excited to here. But remember, it is pyrolytic graphite that we are after... normal solid graphite has levels half as low as aluminum for heat transfer. The real advantage of graphite will be it's lightness... such as pocket builds. If you find a piece of round pyrolytic graphite I will fund the purchase and you can experiment with it and let us know the results!!! PM me and I will wire you money over paypal

I wonder about a PGS and copper sheet rolled heat sink. They could be rolled on a dowel quite easily, and that will enable those that don't have CNCs or drill presses to make a great homemade heatsink


And

Hi guys

I'm not a material expert, but i do curious about all these


My question is, what is the use of super high conductivity material is the surface itself is rough and thus minimizing the heat transfer?
This is only my logical thinking, doesn't those graphite very brittle and making it porous after machining? even with some surface polishing?
I always use some CPU thermal compound between the diode module and copper/aluminum heatsink,
regarding about these PGS material, what if the heatsink compound only act as a thermal resistance even if it filled the (porous) gaps??


It would be great if we managed to create pen host made using these PGS tube
8W NUBM44 with 30sec duty is all good (but ofc it's very dangerous, so no, yeah)
Let say 1.5W 520nm in a pen host with 100% duty, running 2x 14500. sweet!

The trouble with PGS is it is not too durable on the outside... it will eventually wear when put in the pocket with keys, knives, flashlights and other things we love. Also, it just transfers the heat (super super fast) from the diode... so we still need to get it in the air somehow, oh and not burn our hands too! I think it could be done, but we would need a very dense fin design and the end of the pen would have to be at least 2cm wide...:thinking:

 

[Astralist]

The trouble with PGS is it is not too durable on the outside... it will eventually wear when put in the pocket with keys, knives, flashlights and other things we love. Also, it just transfers the heat (super super fast) from the diode... so we still need to get it in the air somehow, oh and not burn our hands too! I think it could be done, but we would need a very dense fin design and the end of the pen would have to be at least 2cm wide...:thinking:

Then i could say that it's good for making laser module right?
just like those 12mm module, or whatever the size is, and then it will be inserted to external host with fins made of copper/aluminum
Sweet!

 

[Rivem]

While the graphite bar stock might not be as good for thermal conducticity at contacts, its going to be much more EMISSIVE, so the radiative heat transfer is going to be much better than other materials. Convection off of a graphite surface should also be better due to actual surface properties. The contact between module and heatsink will be difficult, but I think your method is on point Rich. Might want to try for a tighter than usual tolerance though since the graphite will yield.

I wasn't aware that the "secret" material was PGS though. That being able to make a good host seems like nonsense to me. The only way I could see that working is if it was radially aligned around a tube with very high quality graphite. Maybe for some types of thermal contacts, but not for a whole host. Anybody that's taken thermal design courses should be able to elaborate more on that.

Ultimately, I think it's something worth taking a shot at. I think I might have made the suggestion of making things as black as possible to EP when he asked for host finish advice and I dumped a ton of thermodynamics on him.:crackup:

 

[Lifetime17]

Hi Riven,
The graphite core i will use is a high density type at 1-1/2" diameter , And has a great heat transfer ratio and has a high electrical conductivity. I will bore out a Copper or Aluminum sink and press in the graphite core with arctic silver mixed with 99% pure copper powder that i use in all my core pressed sinks. I will cut it down on a band saw and drill out for the 12mm module, then drill and tap it for a set screw. Just hoping it take the threads of the tap. Or i might just have to drill a hole press in a copper sleeve and use the same method with the arctic silver to keep it snug. This should work out ok. Being that the graphite is 1-1/2" i will keep it at that without turning it down and assemble it in a mag light host with a NUBM44 at 4.5A. The driver will then be sinked in the battery tube on a copper sink also .

Rich

 

[Rivem]

Hi Riven,
The graphite core i will use is a high density type at 1-1/2" diameter , And has a great heat transfer ratio and has a high electrical conductivity. I will bore out a Copper or Aluminum sink and press in the graphite core with arctic silver mixed with 99% pure copper powder that i use in all my core pressed sinks. I will cut it down on a band saw and drill out for the 12mm module, then drill and tap it for a set screw. Just hoping it take the threads of the tap. Or i might just have to drill a hole press in a copper sleeve and use the same method with the arctic silver to keep it snug. This should work out ok. Being that the graphite is 1-1/2" i will keep it at that without turning it down and assemble it in a mag light host with a NUBM44 at 4.5A. The driver will then be sinked in the battery tube on a copper sink also .

Rich

Yeah Rich. That should work pretty well, but I think that exposing the graphite will probably be a better bet thermally than using it as a sink or contact material between the module and something else. Maybe not as good visually or for durability though.:thinking:

I'll do some math if I get the time tonight.

 

[Lifetime17]

Hi Riv,
Thanks buddy always looking for some positive input on options. ill hold off til you have some more input.

RicH

 

[ArcticDude]

I'm willing to do / try to make thermodynamic simulation with Autodesk Fusion360, but I will need material properties for that graphite bar and also number how much heat diode is generating. We could compare simulation results of 12mm moudule pressed on graphite bar versus 25mm Cu module in same size host.



--------
EDIT

Rich can you PM me Graphite Bar host dimensions?
Would love to see and compare results of simulation & how it will perform in reality.

 

[Rivem]

I'm willing to do / try to make thermodynamic simulation with Autodesk Fusion360, but I will need material properties for that graphite bar and also number how much heat diode is generating. We could compare simulation results of 12mm moudule pressed on graphite bar versus 25mm Cu module in same size host.



--------
EDIT

Rich can you PM me Graphite Bar host dimensions?
Would love to see and compare results of simulation & how it will perform in reality.

(ROOM TEMP)
Graphite:
K= 168 W/(mK)
Cp= 717 J/(kgC)
ε≈0.98
ρ=2.3 - 2.7 10^3 kg/m^3

That's at least what I could look up in my engineering reference.

Here's copper for comparison:
K=401
Cp=385
ε≈0.78 (best case rough oxide, negligible raw)
ρ=8.79

Aluminum:
K=205
Cp=897
ε≈0.77 (best case black anodized, negligible raw)
ρ=2.7

Just by these numbers, the typical graphite would be inferior to aluminum except in suface emissivity. Probably a bit better in convective heat transfer due to surface, but even the estimation for that is really nasty math relying on geometry.

Edit:

For the uninitiated:

• k-thermal conductivity
• Cp-specific heat capacity, related to duty cycle in typical laser cases
• epsilon is emissivity for radiative heat transfer.
• rho is density for combination with Cp

Also, there is another major factor I can't really calculate or look up. Contact conditions have dramatically decreased thermal conductivity, so you should generally avoid using multiple materials. That's also why direct press hosts and heatsinks can generally perform a lot better and why TIMs are so important.

PGS is pretty much a TIM and structurally more uniform and ordered than typical graphite stock, so it has a really high thermal conductivity. Maybe as an indium alternative, but nobody is going to make a miracle host out of it since it's really only like that in sheet form.

Edit2: Just to be clear, the super high thermal performance can be had by pyrolytic "graphite"/carbon stock, but it's really hard to find in big pieces affordably. Specs are for normal graphite stock (used for electrodes). Solomon is correct on that matter.

The process used to make it involves heating a polymer and pressurizing it in a very controlled process, so it's way more common in thin sheets and plate.

 

[Lifetime17]

Hi,
Long day i sent the reply to Riv in a PM ok the bar is 1-1/2 x 6" length , I will be cutting 1" in length for a press fit in CU or AL sink.the sink will be in a 2" dia outer sink.

 

[Encap]

Keep in mind graphite conducts thermally in a very different manner than metals do.

It is generally accepted that graphite--any/every type of graphite-- is a phonon conductor and that >99% of heat is transported by phonons or quantized lattice vibrations. The thermal conductivity in layer planes in more than 200 times the conductivity out of plane. This makes graphite a very good conductor in two directions "a" and "b" and virtually an insulator in the third direction"c". The thermal conductivity of any graphite assembly is critically dependent on the orientation of the layer planes.

Here is a more detailed explanation comparing diamond to graphite:
" Diamond is one of the best thermal conductors known, in fact diamond is a better thermal conductor than metals (thermal conductivity (W/m-K): aluminum=237, copper=401, diamond=2200). The carbon atoms in diamond are sp3 hybridized and every carbon is bonded to 4 other carbon atoms located at the vertices of a tetrahedron. Hence the bonding in diamond is a uniform, continuous 3-dimensional network of C−C single (sigma) bonds. Graphite on the other hand is formed from sp2 hybridized carbon atoms that form a continuous 2-dimensional sigma and pi bonding network. This 2-dimensional network forms sheets of graphite, but there is little connection between the sheets, in fact, the sheet-sheet separation is a whopping ~3.4 angstroms. This might lead us to suspect that heat conduction in the 2-dimensional sheet of graphite would be superior to diamond, but that heat conduction between graphite sheets would be very low. This is, in fact, an accurate description of thermal conduction in graphite. Thermal conductivity parallel to the graphite sheets high, but thermal conduction perpendicular very low. Therefore, when we consider thermal conduction over all possible directions (anisotropic) diamond would be superior to graphite.

I'd just like to touch on the mechanisms behind thermal conductivity.
There are two ways in which heat is transmitted through solids: phonons and electronic conductivity. The latter occurs in electrically conductive solids, where conduction band electrons are free to move throughout the structure, carrying thermal energy along with them. This is a significant component to the thermal conductivity of metals and explains some of the in-plane conductivity of graphite. Electrically conductive solids tend to also be good thermal conductors for this reason, but this mode of conduction is not accessible to diamond.
Phonons and electrons travel very well along graphite's graphene sheets, but poorly between them, due to weak inter-layer interactions and the large distance between layers, explaining the anisotropy of its thermal and electronic conductivity.

Metals exhibit both modes of thermal conduction in varying degrees of importance and conduct isotropically since they lack the layered structure of graphite."
From: https://chemistry.stackexchange.com/questions/12404/why-does-diamond-conduct-heat-better-than-graphite