heat sink for video camera in vacuum

Take the case off. Stick it in the vacuum. Point an infrared imager at it. I expect you're gonna find that convection within the case plays a significant role. If the heat can't get from whatever's melting to the case, it doesn't matter what you hook the case to.

Fortunately I am :-p

P = E * A * sigma * T^4

P = power E = emissivity A = area sigma = 5.67 x 10^-8 W m^-2 K^-4 (Stefan-Boltzmann constant)

Note that power transfer is due to the difference in radiated powers, and radiated power depends on absolute temperature (for a small difference in temperature dT, the radiative conductivity of space goes as 4 T^3 dT, so plasma on the Sun is a ridiculously better conductor than radiation at room temperature!).

Of course, A is hard to evaluate. Easy for a sphere, because if the material is lambertian and black (E = 1), all points on the surface are exposed to their surroundings for 2pi stearidans (i.e., if you were very short and stood on the surface, you would get a full hemispheric view). A complicated structure, like a finned heatsink, has a lot of surface area, but little of that surface can "see" the outside. As far as I know, practical /radiators/ (per se) are build with short, widely spaced fins, so there's a lot of surface area without impacting the overall view from any given point. I suppose this is effectively just a "macroscopic matte" finish.

Anyway, supposing your chamber is black (it's not, but the radiation has to bounce around and be absorbed somewhere, and statistically, few of those absorption locations will be the device itself), your 400 cm^2 =

Tim

-- Deep Friar: a very philosophical monk. Website:

Since there is no medium for heat transfer you need to radiate the heat and the case needs to absorb that energy. So you need a heat transmitter and a heat receiver.

Maybe start here to work out the details:

Copper has low emissivity; it's practically a mirror at thermal wavelengths. Paint would help but would probally trash your vacuum. Anodized aluminum would be better, or some chemical treatment of the copper to make it rough and black at IR. Or plaster it with kapton tape, which is almost black in the IR band.

Copperclad FR4, visible:

and with a piece of kapton tape, IR:

The Bergquist stuff may do more harm than good - thick, lousy thermal conductor

- and will also outgass. Epoxy or grease would be a better filler; it would squish to zero thickness where the surfaces contact, and fill the places where they don't.

A machined collar would be a better contact than a bent sheet.

Cooling the cam housing may not be enough, if the internal components heat up.

There are online radiation calculators... somewhere.

What holds the cam in space? Can you beef that up? Conduction to the structure would be better than radiation.

Maybe pack the insides in vacuum grease and mount it on a copper rod?

Best regards, Spehro Pefhany

Thanks! Your calculations confirm what I roughed out with an online calculator. I planned a plate with two "wings" and the camera between. I think this is going to work, assuming the camera has a decent thermal path to its own case.

Thanks,

Jon

Thanks, I will see if I can get them to make it out of aluminum, then.

We already use it in vacuum, it doesn't cause much trouble by outgassing. I did a test some years ago, clamping two flat surfaces with pressure and cooling one, measuring the temperature of the other. It took 20+ minutes to cool the other plate when dry. Put a dot of thermal conductive grease between them, and the other plate cooled in seconds! So, clamping two things together dry conducts heat VERRRRY poorly.

We'd like to be able to open up the chamber and point the camera as needed with a simple mount that won't provide much heat conductivity. A solid path to the chamber wall would obviously be the best for the thermal problem, though. If this doesn't work, then we may have to come up with either a conductive mount system or an extension of the liquid cooling system already in the chamber.

Thanks everybody for the helpful info!

Jon

Perhaps see if the components that get hot could be thermally bonded to the case?

Oh, I found this...

It's an old PowerBasic DOS program from 2002, but works under XP.

Anybody think of leaving the camera outside where it was designed to operate, and pointing it thru a window to see inside? Alternately, do that using a PMT.

structure

I think that apeshit is poor on thermal conductivity.

Isn't this rocket science so to speak? What do they do in space?

Maybe a bath of fluorinert and some phase change scheme to convert the thermal energy to kinetic. Or maybe a vat of the fluorinert and just heat up the mass. This is a problem I never had to solve.

It is the surface finish of the housing that is making it difficult for the object to radiate heat away. Do it with anodized black or any black paint that is acceptable in your vacuum environment and you should get to radiate about 20-40x more heat away than with metallic aluminium.

Anodized to black might be OK (or even dry marker pen for a quick and dirty test provided you don't want ultra hard vacuum).

I once put an early linear regulator into a 6" aluminium cube box and expected it to act as a heatsink. The thing went into foldback mode for overheating within the hour and was far too hot to touch. A coat of black paint and all was well with the world.

One problem may be if there are individual components inside that are getting hot but the first thing to sort out is the fact that your "radiative cooling" is optimised for trapping heat!

Jon Elson schrieb:

Hello,

when the camera case is filled with air at normal pressure, there is a decent thermal path. If you remove all the air, the thermal path is reduced. What about an air tight case filled with helium?

Bye

structure

Sure, but excellent compared to a vacuum, and a dielectric, but the increased capacitance* might cause problems. Since the units are cheap, and most of the high frequency stuff is going to be on-chip anyway, it might be worth a try, at least putting it in contact with ground planes.

• dielectric constant of Apiezon W vacuum wax is around 2.6. Thermal conductivity is 0.189 W/m-K, comparable to unfilled RTV silicone.

Best regards, Spehro Pefhany

Helium is difficult to contain, and will leak out of things that are merely airtight.

The camera case is unlikely to be designed to support any significant pressure differential.

Sylvia.

Very good!

I would wonder if it is a problem at all (not the pressure, the need to remove heat). The camera battery would likely empty before the heat rise would cause a problem. Oh, and what about the battery under a vacuum? Forget the camera.

I mean... unless it is an IR camera. Then, you need one with a chilling chamber and sinking of the imaging element.

You could do a cheap man's version with an aluminum 'tank/sink'and put chilled fluorinert or such in it.

Sylvia Else schrieb:

Hello,

I know, we may use nitrogen or a gas with good thermal conductivity and large molecules.

Small cases are very stable for an internal pressure, for large cases you need much more case wall thickness.

Bye

Don't hold your breath. We had 'low' power amplifier chips UNSOLDER themselves right off their mounting tabs in 10-6 torr.