how effective is direct metal-to-metal contact for heat conduction? 6

[knowlittle]

I need to cool a 200 mm square aluminum plate, 10 mm thick to 25 deg C. Test duration is 24 hours. This plate is getting constant radiation heat from underneath, about 20W. What I plan to do is to fabricate a cold plate and place it on the subject plate. The cold plate will have copper tubing embedded on the surface, and water will flow through the copper. I will flip it over and place it on the subject plate. Now the subject plate will directly contact copper tubing with water flowing inside.

Is there an easy way to improve metal to metal contact?
Thanks.

 

[knowlittle]

Thank you for answering all my questions. I am not ready to proceed.

 

[renderu]

What's better. A 20mm cold plate or 10mm? I vote for 10mm.

 

[IRstuff]

According to this calculator, 20mm is slightly, about 10% better than 10mm

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[renderu]

Hello IRstuff. What calculator is that?

 

[IRstuff]

oops:

http://mhtlab.uwaterloo.ca/cgi-bin/strip

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[renderu]

Maybe that can help with the spacing of the tubing But I still think 10mm thickness is better than 20. More material is more resistance.

 

[IRstuff]

For the direct path, yes, but for the points directly in the middle, that might not be incorrect. Just imagine that the copper was paper-thin. The thermal resistance from the middle would be infinitely larger, and the heat would have to flow laterally in the aluminum to get to the coolant tubes. Therefore, there is an optimum thickness that balances the reduction in spreading resistance with the increase in the direct resistance. In either case, this particular example's low power makes it a bit moot. The thermal resistance is very low in any case, and if the calculator is correct, even a 1-mm copper thickness would be adequate.

The link I gave is not right; it should be

http://www.mhtl.uwaterloo.ca/old/onlinetools/strip_source/strip7.html

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[renderu]

I understand your explanation. My resoning is that we already have 10mm of aluminum, which is heated from the underside. Therefore the temperature distribution is already adjusted somewhat on the top surface. Is 10mm enough? I'm not sure but I have a feeling that it is. I'm interested to find out and I may try to solve it on the weekend.

 

[IRstuff]

Dang it, the link keeps getting messed up, let's try Strip

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[25362]

http://en.wikipedia.org/wiki/Thermal_contact_conductance

 

[DRWeig]

knowlittle,

Please don't forget to let us know how it finally works out for you!

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[racookpe1978]

Let's assume he had lots more money, or a LOT more heat to get rid of from his plate-attached-to-a-vacuum chamber-that-needs-cooling.

If he machined his tube holes "inside of" the Al plate so that there were water flow paths inside of a thick AL or Cu plate, rather than on top of the thin plate and only touching at the tangents , then wouldn't he get the best heat transfer rate.

Noe, he'd need a head at each end of the thick heat exchanger plate, and those two head - like any heat exchanger would need to be screwed onto the sides of the thick plate, so he'd have more machining and assembly cost.....

 

[renderu]

Racook, I don't understand what you mean. I don't want to seem mean or anything..... I just don't get it. I'd like further explanation of your point.

Thanks.

 

[IRstuff]

If he machined his tube holes "inside of" the Al plate so that there were water flow paths inside of a thick AL or Cu plate, rather than on top of the thin plate and only touching at the tangents , then wouldn't he get the best heat transfer rate.


Not necessarily. I had assumed that the tubes were brazed to the copper plate, so there's a plausibly solid thermal path from the plate to the coolant.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529