Discussion Forum

You can use temperature dependent functions for permittivity and permeability. This would update the values for every iteration.
Is there any specific reason why you want the change only stepwise after a certain temperature instead of a continuous change?

Hi Martin,

Thanks for answering.
You mean I should define my permittivity and permeability as variables and function of temperature and then do the simulation. If yes, how can I stop my simulation after reaching a specific amount of temperature?

It is not necessary to have a change after a certain temperature, it would be even nice to have a continuous change in the parameters.

Do you have any idea about the equations of permittivity and permeability as function of temperature and their implementation in COMSOL?

I am afraid that if I run the simulation in this way (for example for a heating time of 100 seconds), COMSOL will show me the results after completing the simulation, will it incorporate the changes in permittivity and permeability?

Many thanks for answering again!

Hi Muhammad,

you don't have to change any equations to have e.g. the permittivity dependent on temperature. Just define the respective material properties accordingly. This can be done using a function, it's quite simple: look at the built in material "Air" and properties like "Cp", "rho" or "k" and you will find out yourself.

I don't know if it's possible to set other stop criteria than time in your simulations, may be some more experienced users can help you with that...

But you have to calculate your simulation using a time-dependent study with some reasonable time-steps to understand how temperature and the properties evolve. With the changes in temperature, your properties will change too. To see those changes, you might want to plot emw.epsilonrxx, emw.murxx or the other components like xy, xz,...

Thanks a lot Martin!

When I open the built properties of air defined, I find something like this (please the attached image)
If I define the density of oil as:
rho(pA[1/Pa],T[1/K])[kg/m^3]

which is the way it is defined for built in air density. It is visible that density of air is being changed with change in temperature and pressure but how is it considering the initial density of air?
And how can I define the initial density for the oil and what will be the final value of density after the simulation, can I see it?

Many thanks for feedback!

In addition to my previous question,

Would you please be kind enough to let me know what should I use as the function (for dynamic viscosity of oil)?

As I was checking the basic properties of water for dynamic viscosity and I found the following expressions defined over there (in the intervals section):

Start End Expression
273.15 472.15 1.3799566804-0.021224019151*T^1+1.3604562827E-4*T^2-4.6454090319E-7*T^3+8.9042735735E-10*T^4-9.0790692686E-13*T^5+3.8457331488E-16*T^6

And the function itself was defined as piece-wise. How can I define the properties whether they should piece-wise, interpolation or analytic? In addition, how can I define such an expression for the dynamic viscosity of oil, though you were saying it very easy...

Thanks for any feedback!

Hi Muhammad,

this post should answer both of your posts...

On the picture you uploaded, you defined the property as being a function, not a constant. This is perfect so far, but you still need to define your function (that's why it's colored in orange...).

How to do this?
In the materials node of the model builder, choose the correct material and right click on the respective property group (Basic, Dielectric Losses,...). There you can add the function and define it as it best suits your problem (analytic, piecewise, interpolation).
Again have a look on the properties/functions of air to learn how to properly do it, the usage of the different function types should also be clear after a short look on the built in materials.

Thanks a lot Martin!