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MW Equations + Phase Change in 4.2
Posted Feb 18, 2012, 6:35 a.m. EST Low-Frequency Electromagnetics, RF & Microwave Engineering Version 4.4, Version 5.0 4 Replies
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Hi,
I am using microwave heating option of the RF module for heating a mixture of oil and water.Can any body let me know which set of equations COMSOL is using to solve the microwave heating problem?
I have consulted the tutorial of microwave heating and it shows only one equation for solution of electric field but I need the other equations too such as how it is calculating the temperature distribution , power density etc. in the model?
Secondly, does any one know whether COMSOL 4.2a is considering the phase change of material with temperature or not such as conversion of water to steam at 1 atm at 100 degree Celsius temperature?
Thanks for any response!
I am using microwave heating option of the RF module for heating a mixture of oil and water.Can any body let me know which set of equations COMSOL is using to solve the microwave heating problem?
I have consulted the tutorial of microwave heating and it shows only one equation for solution of electric field but I need the other equations too such as how it is calculating the temperature distribution , power density etc. in the model?
Secondly, does any one know whether COMSOL 4.2a is considering the phase change of material with temperature or not such as conversion of water to steam at 1 atm at 100 degree Celsius temperature?
Thanks for any response!
4 Replies Last Post Nov 16, 2012, 6:35 a.m. EST
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Posted:
1 decade ago
Hi
you should turn on the equation view (see preferrences) and look into the variables COMSOL uses.
For phase change you must apply them via equations or more advanced features of the materials, making them highly non-linear at the phase transition (but this does not take into account the loss of mass via "evaporation"
--
Good luck
Ivar
you should turn on the equation view (see preferrences) and look into the variables COMSOL uses.
For phase change you must apply them via equations or more advanced features of the materials, making them highly non-linear at the phase transition (but this does not take into account the loss of mass via "evaporation"
--
Good luck
Ivar
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Posted:
1 decade ago
Thanks Ivar for your response!
I tried to look at the variables but they are huge in number and are represented in weak form.Please have a look on the attached image.
Can you please explain some equations from these variables and then I will continue with them?
Many thanks for your help.
I tried to look at the variables but they are huge in number and are represented in weak form.Please have a look on the attached image.
Can you please explain some equations from these variables and then I will continue with them?
Many thanks for your help.
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Posted:
1 decade ago
Hi
indeed there are many and far from obvious to rapidly understand like that. That is also why I'm not even trying to sort them all out myself. I trust COMSOL for the general equation sets, so long the results compare to my model validations. Only if not, then I dig into the equations for specific cases, but that takes quite some time, indeed. And I do not have more doc than you, I'm also a (convinced) COMOSL user, but not linked to any of COMSOL internal developments ;).
What I can say though is that phase change is not included by default. That is anyhow delicate to express as phase change means geometry changes, and even topology changes (hence domain and boundary ID renumbering) and these are difficult to handle. There are a few examples and discussion of the forum on how to change the material properties (Cp(T)) to mimic closely the extra enthalpy change due to phase change, wich is one way to treat the HT issue, apart that when material changes into vapour it will escape from the domain and you need other physics to describe it, than the solid or liquid physics used. But phase change can be considered, check the model library on the boiling water example. the extra work comes when you mix it with e.g. RF heating
By he way forget 4.0, use only the latest versions as the early ones were not fuly ironed out and the stability and possibilities has greatly improved with the latest issues
--
Good luck
Ivar
indeed there are many and far from obvious to rapidly understand like that. That is also why I'm not even trying to sort them all out myself. I trust COMSOL for the general equation sets, so long the results compare to my model validations. Only if not, then I dig into the equations for specific cases, but that takes quite some time, indeed. And I do not have more doc than you, I'm also a (convinced) COMOSL user, but not linked to any of COMSOL internal developments ;).
What I can say though is that phase change is not included by default. That is anyhow delicate to express as phase change means geometry changes, and even topology changes (hence domain and boundary ID renumbering) and these are difficult to handle. There are a few examples and discussion of the forum on how to change the material properties (Cp(T)) to mimic closely the extra enthalpy change due to phase change, wich is one way to treat the HT issue, apart that when material changes into vapour it will escape from the domain and you need other physics to describe it, than the solid or liquid physics used. But phase change can be considered, check the model library on the boiling water example. the extra work comes when you mix it with e.g. RF heating
By he way forget 4.0, use only the latest versions as the early ones were not fuly ironed out and the stability and possibilities has greatly improved with the latest issues
--
Good luck
Ivar
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Posted:
1 decade ago
Hi sir,
i m using COMSOL 4.0a to simulate phase change from water to steam while leakage occurs in a high pressure
and temperature into atmospheric conditions can use this version or latest version is required, and i f i do what
module is to be used. i m new to comsol and doing my MS project plz help me out.
Regards,
khuram saleem