Speed up Heat Transfer 1

[durcan]

Hi,
I have a chamber which is in Vacuum, and I have parts that I want to cool down. The problem is the vacuum! The parts are cooling very slow, due to the fact the only heat transfer is radiation. I need to speed up the cooldown? in a controlled mannor. I have to keep the parts in a vacuum until cool.
Any ideas?

 

[quark]

Jacket the chamber and keep the chamber as cool as possible.

Regards,

 

[durcan]

There is a jacket on teh chamber, water cooled and it runs through out the process, the partsare heated up to 480C for a time, and then elements are turned off and cooling begins.
The radiation between the parts and the wall is not good enough to give a quick cool down, there is a quartz heating element between the wall and parts.
Any more ideas?

Thanks

 

[quark]

The rate of heat transfer is proportional to the difference of 4th powers of temperature. So cooling the jacket further does improve the rate of cooling.

Can't you use inert gas inside the chamber?

Regards,

 

[durcan]

Can use it and it does improve, but it is not a "vacuum" cool down. We have to keep it at the same pressure, 1 x 10-6 Torr.
Convection tru the part to its stand might be a way, but the part is sitting on a quartz plate, so won't get much heat flow thru that?

What do you think?

 

[25362]

What are you running through the jacket? Can it be a refrigerant evaporating at cryogenic temperatures or a very cold HT liquid ? Can you insert piping (for example a coil) in the vacuum chamber adding surface to the heat sink? The piping could then run a vaporizing refrigerant or a very cold liquid to enhance the cooling effect.

 

[IRstuff]

Might consider clip-on heat sinks fins to improve thermal loss.

Are thermal straps to the cooling jacket a possibility?

Might also consider using thermal straps to a TEC cold plate. You would only turn this on during cooldown to minimize issues during heat cycle. This might at least transfer the heat elsewhere.

TTFN

 

[pennpoint]

durcan,
ztdep has the concept, we do it all the time. We insert a "shroud" into the vacuum container and circulate the cooling/heating medium through it. Liquid or gasious nitrogen is used mostly. The interior facing walls are painted black (low emissivity).
I am sure you can create your own shroud using copper sheet and attaching copper tubes to the back side (annulus). You have a space simulation chamber if you can hit the -7 scale

Good Luck

pennpoint

 

[JKEngineer]

RE: Pennpoints comments.
What you really want is a high emissivity wall (cold) facing the part to be cooled. This will increase the radiative transfer. If the part can be made highly emissive, even temporarily, this will also help. Any conductive cooling by cooling the supports will also help.

I can offer analysis assistance on the system if it is of interest.

Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

http://www.KleinfeldTechnical.com

 

[pennpoint]

JKEngineer,
Sorry, You are correct. I said "low" ment to say "high" why I don't know. Again you are correct by suggesting the use of a cold plate surface to clamp the component onto. Tube circuits can be attached to the bottom side and fluid circulated through them.

Good Luck

pennpoint

 

[isofilm]

Hi Durcan,

I know you had this problem quite some time ago, but hopefully this will help you and others in the future.

We do a lot of vacuum thermal processing for our active heat spreaders. We need to control the surface chemistry of our devices, which is why we use a vacuum.

Sometimes we need to cool down fairly rapidly, for grain size control. We are able to cool at specific rates by introducing inert gases, such as argon, at predetermined pressures.

We have achieved cool down rates that are orders of magnitude greater than radiation cooling to the water cooled chamber.

Best regards,
Daniel L. Thomas, CTO
Novel Concepts, Inc.

http://www.novelconceptsinc.com