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Heat transfer through solid cylinder
Posted 2024年6月6日 GMT-4 20:00 Heat Transfer 3 Replies
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I am testing a very simple problem: a 15mm diameter cylinder that is 200mm long with temperature boundaries on each end. One end is 300K, the other end is 5K. No other loads or losses. I am interested in the wattage through each end, which I obtain by doing a surface integration of the heat flux on each end of the cylinder (ht.dfluxz in this case, as the length of the cylinder is along the z-axis).
When using a thermal conductivity that is a function of temperature, I get 153.8 W through the 300K end, but only 0.6 W through the 5K end.
However, if I analytically take the integral of the thermal conductivity from 5-300K, and enter that value as a constant thermal conductivity in Comsol, I get 153.8 W on both ends; they match exactly, as they should. Additionally, this value matches the analytical value.
So this leads me to believe that the problem is setup correctly, but there is something wrong with the temperature dependent material property. It is entered as a Interpolation (k), Local Table, with the correct units specified. The table data goes from 1K to 320K. Plotting it looks correct. In the material, I define thermal conductivity as k(T). The 300K end gets the correct wattage, but the 5K does not. Any suggestions? See attached MPH and tell me what I'm doing wrong here.
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If you integrate the normal conductive heat flux (ht.ndflux) then heat in = heat out, as it should be.
ht.dfluxz does not appear in the list of variables. So I don't know what it is, although apparently Comsol does because it can integrate it. I suggest looking for the definition in documentation or print a report and look there.
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Thanks for the info. Comsol seems to define ht.dfluxz as the "Conductive heat flux, z-component", it is under the "Domain fluxes" category. ( Replace Expression--> Model --> Component1 --> Heat Transfer in Solids --> Domain Fluxes)
However, using your ht.ndflux, which is under the "Boundary fluxes" category, does make the values a lot closer. I now get 153.81 W on the 300K end versus 157.52 W on the 5K end.
Any insight as to why they are not both 153.81W?
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