variable thermal resistance 2

[HDS]

Is there a component or technique which will allow me to vary the the thermal resistance between two parts?

I want to control the temperature of the first part by changing the amount of heat transferred to the second part. The second part is maintained at a colder temperature than the first.

It can be a mechanical, pneumatic or electrical control.

The only thing I have found in google was a couple of heat pipes used in satellites. They were very expensive.

TIA

 

[IRstuff]

Over what range do you need to control this? Have you considered a TE cooler?

TTFN

FAQ731-376

 

[ivymike]

http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/techbr.pdf

Variable Conductance Insulation
With insulation good enough to keep the converter temperature greater than 300°C for 24 hours after the engine is turned off, what keeps the converter from overheating while the engine is running at high speed? NREL has answered this challenge with a third innovation—variableconductance insulation. Certain compounds of hydrogen and metals release their hydrogen above a particular temperature and then reabsorb hydrogen below that temperature. Because hydrogen gas is a good heat conductor, releasing it into a vacuum "turns off" the insulation provided by the vacuum. The VCI catalytic converter has a small amount of metal hydride within the vacuum envelope. As the converter approaches its maximum safe temperature (about 900°C), the hydride releases its hydrogen, allowing excess heat to escape. As the converter cools back down, it reabsorbs the hydrogen, thus reestablishing the vacuum.

 

[HDS]

IR stuff
The 1st part will be between 80k and 200k.
The 2nd cold part will be at 77k.

The Peltier (TE cooler) I know do not get that cold.

Ivymike
Very interesting but I didn't give enough information to get the right answer.

 

[btrueblood]

The same concept as ivymike showed would work - an insulation within which you can vary the gas pressure, preferrably hydrogen gas.

And, IRstuff's idea is a good one too - I believe BiTe (Bismuth Telluride) thermoelectrics become more efficient at very low temperatures, although the specific alloy(s) used may change; check wikipedia. I know there are thermoelectric arrays used for cooling the optics? or PM tubes for infrared telescopes, a job that was once done with liquid nitrogen...

 

[IRstuff]

I don't think there's anything that prevents operation at cryotemps, it's mostly a matter of how much current can be run and what the efficiency needs to be.

So the question revolves around unsupplied data, i.e., how much heat is to be transferred, and does the hot side stay at its temperature.

TTFN

FAQ731-376

 

[ivymike]

If it's that cold, you could possibly use a CO2 atmosphere between your inner and outer parts, with a little bit of resistive heating available to thaw some CO2 as needed to increase conductivity (like defrosting a windshield). The CO2 would freeze to each surface if not heated, leaving near-vacuum.