time needed fto reach thermal equilibrium
time needed fto reach thermal equilibrium
(OP)
How do I calculate the time needed for a metal block to reach its equilibrium in a thermal chamber?
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time needed fto reach thermal equilibrium
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RE: time needed fto reach thermal equilibrium
Remember Newton's law of cooling? The rate of cooling (or heating) is proportional to the temeperature difference.
Do you have the density, thermal conductivity, specific heat and the thermal diffusivity of the metal? Also need to know the dimensions so that you can find the Biot number.
RE: time needed fto reach thermal equilibrium
RE: time needed fto reach thermal equilibrium
But with no more information, I'd make the rash statement that it's doubtful anything would reach equilibrium when the temperature changed by 140° in 15 minutes.
Patricia Lougheed
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RE: time needed fto reach thermal equilibrium
RE: time needed fto reach thermal equilibrium
No, I can't stick anything into the part. I have to calculate the time to prove that it reaches equilibrium in that 15 mins.
RE: time needed fto reach thermal equilibrium
RE: time needed fto reach thermal equilibrium
RE: time needed fto reach thermal equilibrium
We did this way back in an ME lab to ascertain how long a thermocouple needed to remain in the surroundings before it read the "right" temperature. This is not expected to be an accurate method, but a ballpark method, with the uncertainties in the convective heat transfer being the biggest problem.
If you go through this process and it shows you reach equibrium in 10 minutes or in 20 minutes, it may not be too meaningful, as the inaccuracies could be too great. But if it shows that the equilibrum is reached in 30 seconds or takes 4 hours, that would be more meaningful.
RE: time needed fto reach thermal equilibrium
As for calculations, you could assume a worst-case thermal mass located in the center of the component, and the serial thermal resistances to the ambient air. It'll look like an RC-time constant problem from electronics. But, it's something that could be approximated in an Excel spreadsheet.
TTFN
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