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Phase change, melting ice example

Posted Mar 22, 2011, 10:20 a.m. EDT Heat Transfer & Phase Change 2 Replies

Janne Hirvonen
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Hi. I'm trying to learn how to model phase change and I've been following this 1D example about melting ice:
www.comsol.com/showroom/gallery/474/

I have it mostly working, but in my results even half of the ice hasn't melted by 1200s, unlike in the example figures where it seems to be completely melted by 60s. I think I've understood everything about it except for the phase change pulse D. In pages 2-3 it says that the integral of D must equal unity to satisfy a condition.

Currently I have just declared the expression D = diff(H,T), which I understand is the derivative of H with respect to T. H is defined by the Heaviside function H = flc2hs(T - T_fusion, dT). I've tried changing the dT from 0.1 to 2, but it doesn't seem to have an effect.

The D is supposed to be normalized, but if it doesn't come like that automatically, I don't know how to do it. I tried checking the value of the integral through Subdomain Integration, but I don't even know what variable it is integrating it about. Just telling it to integrate at 1200s (the final moment) gives the value 5,25e-5 which doesn't really tell me much, other than not being 1 as the integral over the whole T range should be. Could this be the cause of the slow melting?
2 Replies Last Post Oct 11, 2011, 7:36 a.m. EDT
COMSOL Moderator

Hello Janne Hirvonen

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JiYoung Park
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Posted: 1 decade ago Oct 6, 2011, 7:19 a.m. EDT
Hi,

You mean D=0 for all the time ?

That may because the time dependent solver passed out the melting temperature.

Therefore, you should decrease the time step to figure out the time when fl is set 0 to 1.

I think BDF solver is best for this problem.

regards.
Hi, You mean D=0 for all the time ? That may because the time dependent solver passed out the melting temperature. Therefore, you should decrease the time step to figure out the time when fl is set 0 to 1. I think BDF solver is best for this problem. regards.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Oct 11, 2011, 7:36 a.m. EDT
Hi

the default solver is using an "automatc step" identification, it skip easily over some rapid changes, or even sinus oscillations. To avoid this use a strict or intermediate stepping scheme (find the right tab to set) and give enough manual steps around the phase change point

--
Good luck
Ivar
Hi the default solver is using an "automatc step" identification, it skip easily over some rapid changes, or even sinus oscillations. To avoid this use a strict or intermediate stepping scheme (find the right tab to set) and give enough manual steps around the phase change point -- Good luck Ivar

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