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thermal properties depandent of T°

Posted 4 apr 2011, 11:26 GMT-4 Results & Visualization Version 3.5a 3 Replies

Issam Bendaoud
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hi,
i work on COMSOL 3.5a and 3.5 to make a model with heat transfer and i need to introduce thermal properties of material which change with temperature (exp: K(T)), in scalar expression i should enter the equation of K(T) :
K(T)=(6.158*T+4803.6)*(T>=293&T<873)+(-0.306*T^2+624.19*T-300709)*(T>=873&T<1173)+(-1e-4*T^3+0.654*T^2-950.08*T+463551)*(T>=1173&T<1673)

i specify that K takes different values for 293<T<873 , 873<T<1173 , 1173<T<1673
i need your help to check if my expression of K is correct or not


thank's all
3 Replies Last Post 6 apr 2011, 09:33 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 5 apr 2011, 01:43 GMT-4
Hi

you have a simple way to check your equation: enter it into a "new function" and plot it out.
When I try I get an error message, remains how to debug it, I would chop it up in segments, check each one by one and then add next segment, you will rapidly find out ;)

I would anyhow propose that you define it as a function of interpolation or piecewise analytical type.

--
Good luck
Ivar
Hi you have a simple way to check your equation: enter it into a "new function" and plot it out. When I try I get an error message, remains how to debug it, I would chop it up in segments, check each one by one and then add next segment, you will rapidly find out ;) I would anyhow propose that you define it as a function of interpolation or piecewise analytical type. -- Good luck Ivar
Issam Bendaoud
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Posted: 1 decade ago 5 apr 2011, 05:09 GMT-4
hi,
thank's for your help, i tried what told me but no way it diverge. When i put equation (+) another equation and put the temperature condition , Comsol add the equations or it separate them according to temperature ?????
hi, thank's for your help, i tried what told me but no way it diverge. When i put equation (+) another equation and put the temperature condition , Comsol add the equations or it separate them according to temperature ?????
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 6 apr 2011, 09:33 GMT-4
Hi

I believe its because you need to write && and not &

I get the following for:

(6.158*T+4803.6)*(T>=293&&T<873)+(-0.306*T^2+624.19*T-300709)*(T>=873&&T<1173)+(-1e-4*T^3+0.654*T^2-950.08*T+463551)*(T>=1173&&T<1673)



--
Good luck
Ivar
Hi I believe its because you need to write && and not & I get the following for: (6.158*T+4803.6)*(T>=293&&T=873&&T=1173&&T

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