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Specific heat in pcm's

Posted Aug 26, 2010, 1:58 a.m. EDT 4 Replies

Ivette Prado
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Hello,

I have found this forum and it was so useful for me because I had the same problem about how type the apparent specific heat of phase change material in COMSOL.
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"Then you must combine, if you need to smoothen the "(T-Tm')/(Tf-Tm')", a "heaviside" or a "sine step" function. I prefere "sine" step as these are smooth up to to 2-3 derivatives without overshoots, but you must write them out first, a little agebra

PLS CHECK/PLOT this function out carefully, I might well have got the signs or the bolean wrong.

Often I define these expressions as functions in COMSOL as you can then easily check them with the "plot" button"

Read more: apparent specific heat - COMSOL www.comsol.asia/community/forums/general/thread/3014/#ixzz0xglWevdX
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But I've got interest in "sine" step or the function thay you metionated above, i don't know how to use it, but i understood that you can use it for check the function of cp, am I wrong??

I have a material that change phase from 313 to 316 K. The melting cp is 60.5 kJ/kgK and the cp from solid state is 2.5 kJ/kgK, and I type this into the program

Cp= 2500*(T<313)+(60500*(T>313)*(T<316))+2500*(T>316)

It works, but now i would like to plot the function in order to check the latent heat, if the integral of that cp function is the latent heat of my material i could validate the formula. My model is in 2D in COMSOL 3.5a.

I hope I've been clear,
thank you so much.

Ivette.


4 Replies Last Post Aug 9, 2011, 10:45 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Aug 26, 2010, 2:23 a.m. EDT
Hi

in 3.5a I would define a function like this, but then your function is very square, with undefined gradients during the transitions, its better to smoothen these with a heavisde function as discussed in seceral threads on the forum. In V4 zhis is called by the "step" function

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Good luck
Ivar
Hi in 3.5a I would define a function like this, but then your function is very square, with undefined gradients during the transitions, its better to smoothen these with a heavisde function as discussed in seceral threads on the forum. In V4 zhis is called by the "step" function -- Good luck Ivar

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Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Aug 26, 2010, 2:38 a.m. EDT
Hell again
Sorry it was rect() I ment (0 to 1 and back to 0), not step (0 to 1), for some reason, suddenly I can nolonger edit my previous mail

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Good luck
Ivar
Hell again Sorry it was rect() I ment (0 to 1 and back to 0), not step (0 to 1), for some reason, suddenly I can nolonger edit my previous mail -- Good luck Ivar
Ivette Prado
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Posted: 1 decade ago Aug 28, 2010, 1:24 p.m. EDT
Hello,

Thank you so much for your replay... I will try to make my cp's function with the heaviside functions or the rect() function, but what do you mean about not having gradient temperature at transitions? and do you know if i can integrate my cp function in order to obtain my latent heat ??

Thank you so much...

Ivette.
Hello, Thank you so much for your replay... I will try to make my cp's function with the heaviside functions or the rect() function, but what do you mean about not having gradient temperature at transitions? and do you know if i can integrate my cp function in order to obtain my latent heat ?? Thank you so much... Ivette.
Ehsan
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Posted: 1 decade ago Aug 9, 2011, 10:45 a.m. EDT
Hello everyone,

Do you think the following Sin step function is correct? I do not have access to COMSOL now, just wondering is this correct or not! Please Advise on the Sin section!
Cp=2500*(T<313)+(sin(2*T)*(T>313)*(T<316))+2500*(T>316)
Hello everyone, Do you think the following Sin step function is correct? I do not have access to COMSOL now, just wondering is this correct or not! Please Advise on the Sin section! Cp=2500*(T313)*(T316)

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