Discussion Forum

Hi Timo. I couldn't open your model because I don't have the heat transer module.

But... I'm going to take a quick *guess* here about what is happening: You are heating up *water*, right? Well, once it gets to 100C, it needs to boil! I'm guessing that you haven't included in the water's material properties the heat of vaporization that is required to boil it. And this is actually a huge amount of heat. So, if I'm right, your model is simply ignoring the reality of how water behaves, and instead simply treating it as a bulk material with a (more-or-less) constant heat capacity, and totally ignoring the phase change (liquid to gas) that would otherwise consume the input microwave energy.

Hi Robert,

thanks for your really quick help.
Ok, I was so in trouble with the permittivity problem that I forgot the phase transfer problem... Really simple thermodynamics..

What do you think is the best way to realize it? I'm relativly new to comsol and I'm about to learn it by doing. So please be patient... :-)

We do have the Chemical Engineering Modul, too. So I should use the Multiphase Flow, Two Phase Flow Modul.
Then I have three different Moduls in my Model. I don't know exactly how to solve the system.

Should I first solve the wave propagation problem as stationary problem (to get the resistive heating) and then the heating and phase transfer problem together (transient)? Is there a better way to solve this problem?

Thanks again for your help

greetz

Timo

Timo:

You have some modules than I do not have, and I'm not an expert on those.

If you have enough memory, you may be able to solve for all the desired outputs at once and self-consistently. Otherwise, you may have to do it sequentially (and carefully). If you actually want to model the phase-changing process, my guess is that you will have to be extremely careful to set it up right. Personally, I doubt any Comsol module can address the physics of boiling water properly. Perhaps someone else who is more knowledgeable about that will comment here?

Hi Robert again,


You're a real help for me. Thank you very much.

In the moment, the memory can be a problem. I use it on my own PC. Our cluster is not yet ready.

Is there a way, not to calculate the boling process "really" but to calculate the vaporization process? I mean, to calculate the same way as I do it now, and subtrate the vaporization energy amount? I know this isn't physically "correct" and isn't a good and elegant way.

It might be good to start with a similar model but without the microwave-process.

Are there some people, who "just" boil water in a beaker (open or better: closed). Then I can use a similar model and "put it" into my microwave.

Thank you all for your help


greetz

Timo

Hi everybody,


I've got an additional question for my microwave oven problem:


I'm about to learn the microwave oven basics, yet, but I was wondering about the port-Boundary-condition in the RF-Modul. I can't find any information about these port stuff when I take a look at the microwave basics.
I know, that the port is the wave-excitation-part in this simulation. Is it the size of the excitating magnetron?
Where can I get to know, what's the size of such a thing in real life? Could I get these informations from CEM?


Thanks for any help


greetz

Timo

The port boundary condition lets you conveniently specify standard configurations of electromagnetic fields that correspond to analytic waveguide modes (TE and TM) and coaxial (TEM) modes. Lumped port and circuit port conditions are also of use, especially with TEM boundary conditions on various kinds of transmission lines. Older versions/predecessors of the RF module didn't have this feature, so the user had to enter the equations for the fields there directly. The port condition is thus a big help. The software also lets you access S parameters directly too, when you use port conditions, and that is also helpful. For a microwave oven, I would guess the physical port driving it would be a rectangular waveguide, fed by the fundamental TE_10 mode. Of course, one could also excite a microwave oven cavity with a small loop. I'm not sure how commercial microwave ovens are built, since if you look inside, the excitation details are hidden behind a frosty plastic window.

The port boundary condition lets you conveniently specify standard configurations of electromagnetic fields that correspond to analytic waveguide modes (TE and TM) and coaxial (TEM) modes. Lumped port and circuit port conditions are also of use, especially with TEM boundary conditions on various kinds of transmission lines. Older versions/predecessors of the RF module didn't have this feature, so the user had to enter the equations for the fields there directly. The port condition is thus a big help. The software also lets you access S parameters directly too, when you use port conditions, and that is also helpful. For a microwave oven, I would guess the physical port driving it would be a rectangular waveguide, fed by the fundamental TE_10 mode. Of course, one could also excite a microwave oven cavity with a small loop. I'm not sure how commercial microwave ovens are built, since if you look inside, the excitation details are hidden behind a frosty plastic window.

Hello,

In comsol 3.5, the port boundary can be set to be either Electric field or Magnetic field in user defined tab. But in 4.0a,
The user defined port have no Magnetic Filed choice. And how to set Magnetic filed such as H0z ? Could you give some help ? Thanks in advance.

zhanyh

I have been trying to simulate various microwave port configuration and their effects on the microwave power distribution in the cavity. If you are waveguide is long enough to allow formation of TE or TM mode then, one can use standard mode. In case of the modern domestic microwave oven, the waveguide is very short and also not rectangular. in such case, one may excite the cavity with coaxial feed magnetron. This will leave out the guess work and the simulate right mode propagation in t he waveguide and the cavity.

With best,
Sohan

There are few things one has to take care for simulating microwave heating simulation.

1. Port configuration and magnetron frequency spectrum
2. Position of turntable and load
3. Conducting mesh independent study.. otherwise one would get erroneous results
4. Actual magnetron power feed
5. actual dielectric properties of material. For water it should 78-11*j

Sohan

Hi Sohan,

The dielectric for water i.e. 78-11*j, is it incorporating the fact of change in dielectric constant with the increase in temperature?

In addition do you know about the dielectric constant for crude oil?

I am trying to heat oil with the microwaves heating (RF module) using version 4.0 of COMSOL, but the temperature distribution which I am getting is very huge as compared to the real word and it is also confined to the area adjoining the microwaves port. In real word scenario, temperature should reach a few hundered degree celsius in heating for a day almost and also temperature distribution should be present at a distance say 50% wayay from the source inside the material. Although it will be small but it will be there. In my case I am getting temperature distribution of a few thousand degree Celsius near the port and confined in almost 10 cm distance from the source, which is strange for me.

Can you suggest any potential reason behind this?

Many thanks in advance for any feedback!

Hi Timo,

Have you solved your problem?

I am a new user of COMSOL and getting almost similar errors as you did?

I will appreciate any of your help.

Thanks in advance.

Muhammad:
If the temperature is localized near the source even after a long period of time (1 day as you mentioned) then your thermal diffusivity may be incorrect. Check the thermal conductivity and the specific heat capacity of the crude oil.

Timo:
One simple way to approximately capture the effect of the latent heat of vaporization is to sharply increase the specific heat capacity over a narrow temperature range (around the boiling temperature) such that the additional area under the specific heat-temperature curve equals the latent heat. No multiphase flow required, and no fluid phase change. Again it’s an approximate solution, so it’s not suitable for all problems. However, I found it useful for several applications.

Nagi Elabbasi
Veryst Engineering

Thanks a lot Mr.Nagi (JazakAllah khair)!

Do you mean to say that I have to define thermal conductivity and specific heat capacity as a function temperature as for the time being I am just defining them as constants e.g. thermal conductivity=0.04299(W/m*K) and Heat Capacity at Constant Pressure as 2130(J/Kg*K).

I am also interested in getting the dynamic behavior of oil with the change in temperature, can you please suggest something how can I obtain it?

Many thanks in advance!

You’re welcome.

Yes, you should account for temperature dependence for all relevant properties, since you are talking about significant temperature increases. It may well be that at higher temperatures the thermal conductivity is higher. Evaluating the temperature dependence is another challenge!

Also at high temperatures the viscosity of oil drops and could reach a point where the heat transfer through natural convection becomes significant. In that case, you should setup your model to account for natural convection if you haven’t done so already.

Nagi Elabbasi
Veryst Engineering

Thanks a lot brother for answering!

I am trying to find out some relationship of viscosity with temperature and thermal conductivity plus dielectric constant with temperature. But some one suggested me to define the material properties in the way being defined by the built in materials, please find attached the images (water1.jpeg for the properties shown for water defined as built in function, highlighted is the dynamic viscosity, second image is function of temperature.jpeg and shows how dynamic viscosity has been defined as a function of temperature). I am not sure how to incorporate such functions in my model for oil, can you please suggest some thing?

Secondly as you mentioned that at high temperatures, viscosity drops much and the natural convection should also be incorporated. If I find some temperature -viscosity relationship for oil and include it in the model for oil properties, will it not cover this phenomenon of natural convection? Should I have to include it as another parameter or function?

Many thanks for your feedback!

JazakAllah.

Instead of providing linear regression equation in piece-wise function, you can use interpolation as it was done for speed of sound properties of water.

For taking into account of the convention, you need to use solve Navier-Stokes equations. I would recommend you to first set the RF physics right as convection will not change your microwave power distributions in the domain. alter on you can add up more physics.

Sohan

Thanks a lot brother for answering!

I am trying to find out some relationship of viscosity with temperature and thermal conductivity plus dielectric constant with temperature. But some one suggested me to define the material properties in the way being defined by the built in materials, please find attached the images (water1.jpeg for the properties shown for water defined as built in function, highlighted is the dynamic viscosity, second image is function of temperature.jpeg and shows how dynamic viscosity has been defined as a function of temperature). I am not sure how to incorporate such functions in my model for oil, can you please suggest some thing?

Secondly as you mentioned that at high temperatures, viscosity drops much and the natural convection should also be incorporated. If I find some temperature -viscosity relationship for oil and include it in the model for oil properties, will it not cover this phenomenon of natural convection? Should I have to include it as another parameter or function?

Many thanks for your feedback!

JazakAllah.

Thanks a lot Sohan for answering!

Would it work fine if I define all of the properties of oil as interpolation without even one of them as piece wise as I see in the built in functions they use mixture of interpolation and piece wise?

Secondly, would you please elaborate your saying about convection?
What do you mean by saying "Set your Physics Right and After on you can change your Physics"?

Many Thanks in advance for your response!

Yes, it should work.

In developing multi-physics model, first set and solve the most important physics. In your case microwave interaction with oil bearing materials. First set RF wave and solve the EM field using frequency domain solver for your domains. When you obtain the dissipated power density pattern as per your experiences/ intuition, next step to set other physcis such as conduction and convection to take into account of conduction, and convection. Here you will need temperature dependent material properties.
Hope it helps,
Sohan

Thanks Sohan,

After getting the heat dissipation with electromagnetic model, how can I change the properties of material?
As far as I think, the file will be the same and material properties will also remain same. I can change the study but how can I change the properties of material for second study?

In addition, how can I use this heat dissipation (obtained in case of electromagnetic heating) as initial stage for the heat conduction and convection model of second study?

This is the main problem: how to change the properties of material for second study while keeping the results of first study as initial conditions for second study?

I will really appreciate your response.

Many Thanks for your time.

You can change the material properties between studies. What COMSOL will take from the EM study is the heat generation. If your thermal conductivity changes in the second study, there is no problem.

If the dielectric properties of the oil however vary with temperature then you cannot solve for the EM field just once. You can leave out that level of complexity until you have worked out the other issues. Build up the model complexity gradually as Sohan described.

Also, including viscosity by itself in a fluid flow model does not account for natural convection. You need to couple the fluid flow model to the heat transfer one, and account for convection using the Boussinesq approximation or something similar (there are some relevant examples in the COMSOL model gallery).

Nagi Elabbasi
Veryst Engineering

Thanks a lot brother for your answer!

I tried to setup an other study but I have the properties of the materials as the same as you can see in the attached image. I want to run the first study with some settings of the material and then use the result of first study as base point for the second study.

If I proceed with simulation of first study and then change the settings of material properties manually and carryout the second study, is it the same what I want? I mean is COMSOL using the results of my first study as starting point or initial conditions for the second study, if not then how can I do that?

For the dielectric constant change with temperature, if I define my dielectric constant as interpolation function by inserting a table (different dielectric strength for different temperature) in the input of dielectric properties of oil, and simulate isn't it being considered as dynamic dielectric constant by COMSOL? Will the results of my simulation will incorporate the change in dielectric strength?

Thanks a lot once again for your time and support, JazakAllah!

There is no need to simulate frequency-stationary study. Instead of it, I recommend you to add RF module and perform study with frequency domain solver. This will take material properties at initial temperature. Once you get satisfactory result showing power density, solve the coupled MW heat transfer using transient solver.
Sohan

Thanks a lot brother for your answer!

I tried to setup an other study but I have the properties of the materials as the same as you can see in the attached image. I want to run the first study with some settings of the material and then use the result of first study as base point for the second study.

If I proceed with simulation of first study and then change the settings of material properties manually and carryout the second study, is it the same what I want? I mean is COMSOL using the results of my first study as starting point or initial conditions for the second study, if not then how can I do that?

For the dielectric constant change with temperature, if I define my dielectric constant as interpolation function by inserting a table (different dielectric strength for different temperature) in the input of dielectric properties of oil, and simulate isn't it being considered as dynamic dielectric constant by COMSOL? Will the results of my simulation will incorporate the change in dielectric strength?

Thanks a lot once again for your time and support, JazakAllah!

hi everyone,

I have a question about taking into account boiling of water. After I solved the electromagnetic wave part in Comsol 3.4, I used an if code for Qav_rfw (heat source term for heat transfer) to set it to 0 for a given point after the temperature of that point in food subdomain reaches 102 °C (I assumed that was the boiling point of water in our food stuff). You can do that by going to physics menu > equation systems > subdomain settings. Under subdomain settings you can go to variables tab and just typing an if code for Qav_rfw.

The logic behind why I'm doing this is that we can say the temperature of foods remains somewhat constant when the boiling of water starts due to the heating. If we can set Oav_rfw to 0 for a point when the temperature of that point reaches 102°C, there won't be any available energy to increase the temperature so we can avoid excessive temperature increase. This approach seemed reasonable to me to get a rough idea about temperature distribution during microwave heating. It actually worked and I was able to see Qav_rfw being set to 0 for a point when the temperature went above 102°C. The problem was that the temperature of some points did not stay around 102°C and kept increasing. Sometimes it was just 3-4°C above 102°C sometimes it was 15°C above it. Does this approach makes sense to you and does anyone have any explanation why the temperature kept increasing?

Thank you very much.
nihat

Hi Nihat,

I am also trying to model a phase change behaviour of water in COMSOL 4.0a but do not know how can I accommodate the phase change of water i.e. its conversion to steam after the boiling point of water is reached.

By the way, have you solved your problem? I think maybe the temperature rise at certain points is because of the hot spots which occur in case of heating with microwaves.

Thanks a lot for any help!

Hi Robert,

Can you please let me know, what 'y' stands for in the following expression for E-field of Microwaves?

Ez= cos(pi*y/0.062)[V/m]

This expression is given in the Microwaves Oven Heating of Potato model in COMSOL but in my case it is showing an orange color of expression (it means there is an unknown in the expression). I tried to remove y from the expression and the expression color became black (OK). But now it does not include 'y' which I believe mentions the position of microwaves source w.r.t. y-axis.

By the way, my model is 2-D, is it fine if I apply a 3D Electric field i.e. Ex=0, Ey=0, and Ez=cos(pi*y/0.062)[V/m]?

Thanks for any response!

Hi

Your "y" is the coordinate "y" default name in COMSOL in 2D or in 3D. It is expressed in [m] therefore when you use it in a cos() function that normally accepts dimensionless value it is flagged "organge" formal unit error. This is a warning, not necesarily an error and COMSOL calculates with the values provided, if these have some sense, the results are correct, if these are wrong, you should expect wrong results out, too.

The easy way is to replace "y" by "y[1/m]" which transforms "y" from [m] to a number in the dimension of meters, and the orange should dissapear. The better way, in my opinion here, is to add some units on the value 0.062[m] that most probably is a length, then the units cancel out and everything is correct w.r.t the units

--
Good luck
Ivar

Thank you Ivar for your response!

I made all the changes necessary to change the color of orange expressions according to your instructions and the warnings have been removed. I did this because I was thinking that these warnings might be the cause for this error of stiffness matrix. I run the simulation again but still the same error persists. As it is mentioning mod1.E10, mod1.E20,mod1.E21 and Mod1.Ez, I think it is an error for the E-field, is it so? If yes, how can I remove it becasue there is no complexity involved in definition of E-field it is just as simple as Ex=0, Ey=0 and Ez=cos(pi*y/0.062[m])[V/m].

Is it possible that I am getting this error because of the definition of E-field in z component while I am using just a 2D model?

Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
There are 1160 equations giving NaN/Inf in the matrix rows for the variable mod1.E10
at coordinates: (0.0018763,0.00166667), (0.0037526,0.00333333), (0.00382242,0), (0.00757502,0.00333333), (0.00764484,0), ...
There are 290 equations giving NaN/Inf in the matrix rows for the variable mod1.E20
at coordinates: (0.00569872,0.00166667), (0.0018763,0.005), (0.00555907,0.00833333), (0.00938149,0.005), (0.0619473,0.00333333), ...
There are 290 equations giving NaN/Inf in the matrix rows for the variable mod1.E21
at coordinates: (0.00569872,0.00166667), (0.0018763,0.005), (0.00555907,0.00833333), (0.00938149,0.005), (0.0619473,0.00333333), ...
There are 871 equations giving NaN/Inf in the matrix rows for the variable mod1.Ez
at coordinates: (0,0), (0.0114673,0), (0.00573363,0), (0.00281445,0.0025), (0.0056289,0.005), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns


Thanks in advance for any of your response!

Hi

That could be, in 2D normally the "z" is constant, but in electromagnetics, you have the vector product that adds in Z components, even in 2D (x,y) now you shoudl check how your physics is set, what are you solving for, full 3D or in plane out of plane. I do not have acess to my COMSOL worlstation just now so I'm not 100% sure about the naing, and this depends on the physics chosen, take a look, and go over the doc once again

--
Good luck
Ivar

Rehman,

The equation is valid for 3-d model. Instead of using symmetry of oven, use full 2-d model. For your 2-d model just create a rectangular port and add a wave guide piece with width of full wave guide. Assign port on one edge of the piece SE TE10 mode on one edge. I have attached a 2-d MW model simple model ( created in 4.2 a version) herewith for your reference .

Sohan

I made all the changes necessary to change the color of orange expressions according to your instructions and the warnings have been removed. I did this because I was thinking that these warnings might be the cause for this error of stiffness matrix. I run the simulation again but still the same error persists. As it is mentioning mod1.E10, mod1.E20,mod1.E21 and Mod1.Ez, I think it is an error for the E-field, is it so? If yes, how can I remove it becasue there is no complexity involved in definition of E-field it is just as simple as Ex=0, Ey=0 and Ez=cos(pi*y/0.062[m])[V/m].

Is it possible that I am getting this error because of the definition of E-field in z component while I am using just a 2D model?

Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
There are 1160 equations giving NaN/Inf in the matrix rows for the variable mod1.E10
at coordinates: (0.0018763,0.00166667), (0.0037526,0.00333333), (0.00382242,0), (0.00757502,0.00333333), (0.00764484,0), ...
There are 290 equations giving NaN/Inf in the matrix rows for the variable mod1.E20
at coordinates: (0.00569872,0.00166667), (0.0018763,0.005), (0.00555907,0.00833333), (0.00938149,0.005), (0.0619473,0.00333333), ...
There are 290 equations giving NaN/Inf in the matrix rows for the variable mod1.E21
at coordinates: (0.00569872,0.00166667), (0.0018763,0.005), (0.00555907,0.00833333), (0.00938149,0.005), (0.0619473,0.00333333), ...
There are 871 equations giving NaN/Inf in the matrix rows for the variable mod1.Ez
at coordinates: (0,0), (0.0114673,0), (0.00573363,0), (0.00281445,0.0025), (0.0056289,0.005), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns


Thanks in advance for any of your response!

Thanks a lot Sohan,

Unfortunately I am unable to open the file you sent as I think because of the version (I am using version 04a).

I did the same as you suggested. I have a 2D rectangular port and one of its boundaries is excited by using the input Power of 50 KW, Electric field as Ex=0, Ey=0 and Ez=cos(pi*y/0.062[m])[V/m]. Then comes the propagation constant beta which has been defined as: 2*pi/c_const*sqrt(freq^2-c_const^2/(4*0.062^2))

This is just in the same way as it was defined for microwaves oven model. Now when I simulate a layer of oil and a layer of water connected together then I get some temperature distribution but when I define one layer of water as sandwiched between two layers of oil, in that case it gives the error mentioned below. Can you please suggest something, what could be the potential cause of this error and how it can be rectified. By analyzing the error, I have come to know that it is related to E field because it is mentioning mod1.E10,20 etc. and secondly it has something to do with the layer of water as the co-ordinates mentioned are referring to the location where the layer of water is located. But I am not sure what kind of error is it. Can you please elaborate what E-field can be defined reasonably for a 2D wave guide? In addition, what should be the boundary condition between oil and water normally?

Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
There are 1160 equations giving NaN/Inf in the matrix rows for the variable mod1.E10
at coordinates: (0.0018763,0.00166667), (0.0037526,0.00333333), (0.00382242,0), (0.00757502,0.00333333), (0.00764484,0), ...
There are 290 equations giving NaN/Inf in the matrix rows for the variable mod1.E20
at coordinates: (0.00569872,0.00166667), (0.0018763,0.005), (0.00555907,0.00833333), (0.00938149,0.005), (0.0619473,0.00333333), ...
There are 290 equations giving NaN/Inf in the matrix rows for the variable mod1.E21
at coordinates: (0.00569872,0.00166667), (0.0018763,0.005), (0.00555907,0.00833333), (0.00938149,0.005), (0.0619473,0.00333333), ...
There are 871 equations giving NaN/Inf in the matrix rows for the variable mod1.Ez
at coordinates: (0,0), (0.0114673,0), (0.00573363,0), (0.00281445,0.0025), (0.0056289,0.005), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns


Thanks a lot for any help.

Rehman,
It looks like you are stuck with the COMSOL approach which they use for developing MW oven library model. One has to understand why did they took only half model and created those complicated input equations. Only reason of created that model is to reduce the size so that user can run at least that model on laptops.
When you use complete 3-d model or 2-d model you do not necessarily need to provide E-field value and cutoff frequency. You simply select rectangular port type and plug in input microwave power.

I am puzzled why do not get answer when you sandwich water in between oil layer.
To troubleshoot the problem, first assign same properties (oil or water) to all layers and run the model. If it runs for both material properties then it is not the issue with material properties.
How did you create those layers?. Make sure you have activated union instead of assembly in geometry creation.
If problem still persists, send me your model file, I can quickly look in it.

With best wishes,

Sohan

Thanks a lot Sohan for so detailed reply!

I agree with you that by defining a rectangular port, I do not need to define the E-filed and propagation constant but I am using the user defined port in which I will have to take care of the dimensions of rectangular wave guide by providing the propagation constant. Definition of the dimensions will also set the cut off frequency but I am not sure what kind of E-field I can define?

I have checked for every boundary and domain and it seems good to me but still I am not able to get the heat distribution. I have also activated the union. Layers have been defined just as rectangles with different dimensions.

Please have a look on the attached model and rectify me where I am wrong.

Thanks for the feedback once again!

I am not able to open your module as you used heat transfer module which is not subscribed by us. Send me module with RF module.

Hi Timo,

I have also a similar problem. Have you solved it?

Thanks.

Assalam o alaykum brother,

I am also trying to convert water into steam at a specific temperature (say 100 degree Celsius). I could not find any latent heat of vaporization in COMSOL and was wondering how can I define it.I have just a block of water and I am heating it with microwaves. It should absorb the heat and water should be converted to steam.

I also tried to change the specific heat capacity of water as suggested by you to Timo last time but on checking its specific heat capacity I found it defined as piece wise format:

Start 273.15 , End: 553.75 and Function: 12010.1471-80.4072879*T^1+0.309866854*T^2-5.38186884E-4*T^3+3.62536437E-7*T^4


How can I change this expression for it to include specific heat capacity very high near the boiling point of water?

Can you please suggest some thing?

Thanks.

Hei

What I remember from my training (but I havent tried it out yet) is that one can replace the linear Cp curve by an "S" with a steep increase around the boiling temperature, but o stay continuous (no sharp angles on the interpolation curve) and typically spread the extra latent heat capacity over 0.5-2degC width.
With a varning such rapid changes in slope often are overlooked y the sovler stepping, in automatic mode, so careful time stepping is often required

--
Good luck
Ivar

There are several ways to do that. One way is to add to Cp a built-in “Rectangle” COMSOL function that acts around 100 Celsius (say from 98 to 102). The function value should be zero below 98 and above 102, and equal to the latent heat divided by 4 between 98 and 102. Make sure as Ivar mentioned to select a smooth function and make sure also that the time stepping is small enough to not skip over that narrow temperature range.

Nagi Elabbasi
Veryst Engineering

Thanks brother!

I have tried to define the rectangle function but I was only able to define it in "Global Definitions" or "Definitions" section. I could not find a way to apply this function to Cp. In addition it was automatically taking the highest value as 1 inside the duration. How can I change this value from 1 to "Cp/4" inside the interval?

Can you please suggest some thing by having a look on the attached file?

Thanks.

Hi

Hi there are two ways, once the function has been defined:

Either in the physics node ou define a UserDefined Cp with the expression referring to the different functions or parameters or typing you need, ...


or directly in the related material node in the Cp variable field

--
Good luck
Ivar

Thanks Ivar,

Still I am not getting it how to include the function value inside my Cp calculation? As you would have seen in the file I sent you last time, the built in Cp is being defined as a function of T as

12010.1471-80.4072879*T^1+0.309866854*T^2-5.38186884E-4*T^3+3.62536437E-7*T^4

with temperature ranging from 273 to 575 Kelvin.
Do you mean that I should define Cp as this function ranging from 273 to 371 Kelvin and 375 to 575 Kelvin while rectangular function will be defined as Cp/4 in between 371 and 375 Kelvin?
If so, it can also be defined as an interpolation function without caring for definition of rectangular function, am I right?

Please clarify...

Thanks.

Hi

if you want to refer to a function, only reated to a material property, you can create/add a new material, then right click the "Basic" node and add local fuctions therein, and refer to them in your material property expressions. Check how it's don ein the "complex" materials inthe built-in material library, (i.e. "air"),

with the interpolation function you can use higher order interpolation polynomial to make it rather "smooth", following the values as Nagi explained

--
Good luck
Ivar

You might want to check out these models for bulk vaporization:

Boiling Water (CFD Module) : www.comsol.com/showroom/gallery/3972/

Chicken Patties (Heat Transfer Module) : www.comsol.com/showroom/gallery/448/

Simpler models are also available for surface film vaporization (from technical support only).