Time required for steel rod to come to temperature throughout

[Andrew07]

Hello,

I have to test a component at a low temperature, -40°C. It is essentially a steel rod, with a .74" OD and is 10" long. I am placing it in a cold chamber at -40°C. How do I find the time required for the steel rod to be -40°C all the way through the rod?

Thanks,
Andrew

 

[Compositepro]

Theoretically, forever. The tolerances in your temperature and the design of the chamber (is there a fan?) are required to answer your question.

 

[Andrew07]

If I can assume a heat transfer coefficient, where would I go from there?

I think I may be able to find real-life examples of heat transfer coefficients that would be representative of my test chamber.

 

[IRstuff]

If you know the air velocity inside the chamber, you can calculate a heat transfer coefficient. You do not stipulate temperature the rod starts at. But, since your chamber temperature is the same as the final desired temperature, the cooldown time is mathematically infinite. Nonetheless, there are usually tolerances that allow the rod to be slightly warmer, allowing you to start the testing.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[IRstuff]

Alternately, one can look at miltary-style temperature cycling test procedures which generally have transition times that are adequate for relatively large systems.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[MintJulep]

As noted by others above, the theoretical time is infinite if the target temperature and the chamber temperature are the same.

From a practical point of view, set the chamber temperature a bit lower, then throw the piece in overnight and call it good enough.

 

[willard3]

Is the component homogeneous and isotropic? This is a good place to start.