Cooling in vacuum chamber 4

[knowlittle]

I need to slightly cool an aluminum plate sitting in vacuum. I know I can attach copper tubing to the plate and flow chilled water through the tubing. I just wonder if there is a better - less bulky - way.

Plate size: 10" square (250 mm)
Heat input: 10W estimated (from a warmer object nearby)
Temperature to be maintained: 25 deg C

Thanks.

 

[MintJulep]

Prevent it warming in the first place.

Can you simply place a radiation shield between your plate and the heat source?

 

[knowlittle]

The plate's purpose is to absorb the reat radiated from the warmer object at a constant temp (25 plus minus 1 deg C).

 

[IRstuff]

?? OK, vacuum means no useful convection, leaving radiation and conduction.

TTFN
faq731-376

 

[MintJulep]

Is the vacuum chamber transparent to radiation at the relevant frequency? Place your absorber outside.

Can you put something through the wall of the vacuum chamber? Like a chunk of finned heat sink.

Ready-made cold plate?

http://www.lytron.com/Cold-Plates

 

[keefw1956]

A quick hand calc gives a required plate temperature of -14 deg.C (assuming both plate and item have high emittances ~0.9). If you want to use a cooling system you will need a larger Al plate for water or a more exotic coolant. Alternatively you could look at a conductive solution such as attaching the item or Al. plate to the chamber wall (e.g. copper strap or heat pipe) and cooling that.

 

[knowlittle]

1) The vacuum chamber has stainless steel baseplate and stainless steel wall. ID=0.4 m, Height=1m.
2) The subject aluminum plate needs to be lifted out. I cannot permanently attach copper tubing for cooling. The plate is not even and flat on the top.
3) I can place a prefabbed cooling plate (thanks for the link)inside the vacuum chamber and route chilled water to it. Is there a flexible heat conduction path that I can put between the rigid/fixed prefabbed cooling plate and the aluminum plate for 10W max, typically 5-6 W of heat? Copper chains? Gold necklaces? Anything that can be removed out of way so that I can lift the aluminum plate?
Thanks.

 

[IRstuff]

What is the objective of the plate? Are you shielding something else? A better description of the problem beyond your current point design would perhaps provide you with more innovative solutions.

TTFN
faq731-376

 

[knowlittle]

The purpose of the subject plate is to hold multiple witness plates and to keep them at 25 deg C. A witness plate looks like a large (1" dia) thumb tack. The pins are inserted through small holes drilled in the subject plate. Parallel to the subject plate is a hot plate. The hot plate has holes to contain test samples. What outgasses from a sample hits the witness plate, becomes cooled, condensed, and deposited. After the test, the subject plate is removed from the vacuum chamber and individual witness plates are removed/measured for weight gain.

Thanks.

 

[IRstuff]

OK, so that helps a bit. Can these deposits be cleaned from the plate? How long does this process last?

So, front side should be mirror finished, preferrably gold to maximize reflection. All other sides should be black to be as emissive as possible.

Increasing thermal mass and radiation area, i.e., bulk plus radiating fins are enhancements.
Using a phase change material, ala

http://www.saftpak.com/StpPack/ProductDetail.aspx?ID=417

would

http://www.saftpak.com/StpPack/ProductDetail.aspx?ID=417

be another possibility. The idea is that the melting of the PCM absorbs lots of thermal energy, thereby fixing the plate temperature to the melting temperature of the PCM until it's completely melted. The PCD would be sealed within a blister on the back of the plate. The plate would be chilled with sufficiently cool water or refrigeration, and the plate could be used again.

A third, more complicated process would be to directly TE cool the plate. I'm envisioning a dovetail joint on the backside that mates to a dovetail surface with the TEC cold side attached thereon. The TEC hotside would be heat sunk into the base of the chamber.

TTFN
faq731-376

 

[chicopee]

Radiation cooling should do the trick, so keep the temperature of the enclosure lower than that within the vacuum.

 

[knowlittle]

The process lasts 24 hours.
You gave me many options. I need about a day to think through. I will report back tomorrow. Thanks again.

 

[knowlittle]

The process lasts 24 hours.
You gave me many options. I need think over them. I will write back soon. Thanks again.

 

[IRstuff]

The PCM might be a bit challenging for that much heat:

http://www.pcmenergy.com/products.htm

240W*hr/175J/gm = 4.9kg

TTFN
faq731-376

 

[knowlittle]

Thanks. I am focused on thermoelectric cooling right now. The biggest question I have now is if TE will give plus minus 1 deg C control on the cold side. If it does, wattage at the temp? Thanks.

 

[IRstuff]

There are TEC calculators that can do that math. TECs are not particularly power efficient, so that's their downside. Nonetheless, I think that you can make that part of the system a permanent installation with coolant, and something like a SilPad between the plate and the cold side of the TEC to make the plate removable.

http://www.tetech.com/Peltier-Therm...eTemp=65&coldSideTemp=25&potted=1&emailsent=0

TTFN
faq731-376