Heat Transfer - Latest Discussions - COMSOL Forums

can extract such kind of coordinations to build the model?

Thu, 09 Feb 2012 01:25:20 +0000

Hi, everyone,

I’m building a heat transfer model, so the dependent variable is the temperature T. During the model, I want to obtain the location or coordination (x,y) where the temperature is equal to a specified value, for instance, T=3425[K]. I actually known the contour plot in the result node, and I can extract the data into a .txt file (contain the x,y coordination and the corresponding value of contour). However, as far as I known, the kind of process “postprocessing” can’t be used in the model automatically (am I wrong?).

what I want is
1. obtain the data of the contour (x,y coordination);
2. do some calculation with or without Matlab using the data of the contour;
3. return value(s) after the above-mentioned calculation to the COMSOL to continue the study.
The data of the contour is supervised and extracted at each time-step, and after the specified calculation, the resultant value is imported into the COMSOL though function or something similar.

Is there any accessible way to do this?
Thanks in advance for your advice and guidance.
Best wishes to you and your family.

Using stationary computational results as the initial condition for time-dependant solution

Wed, 08 Feb 2012 17:40:44 +0000

Hi, I'm kind of new to transient analysis in COMSOL and I have a few questions.

Is it possible to use the reults of a stationary study as the initial conditions for transient analysis?

For example, in my current model(using the joule heating and optimization module), I have system heating up to a steady state temperature through a defined current density and boundary heat source. I want to know how long it will take for all parts of the system to cool down to room temperature if the heater and current are turned off.

So far, I've tried introduce a stationary solver as step one, and then a time-dependant solver as step two. However, this just gives me a time dependant solution of the system heating up (not cooling down). I have also tried to use the "Store Solution 2" option in the solver configurations by
- right clicking on the "Store Solution" option and selecting "compute to selected"
- manually changing the heat source and current density to 0
- deleting the optimization solver
- selecting "use store solution 2" under solver configurations--> dependant variables 2 --> Initial values of variables solved for
- and finally right clicking on the "Store Solution" option and selecting "compute from selected"

But, this method just gave me a solution of everything at room temperature.

Can you please help me with this problem?

advantages of comsol??

Wed, 08 Feb 2012 10:10:30 +0000

hi to all,

i am research scholar ... now i am doing research in heat transfer area (laser welding) with moving mesh method... previously i started with ANSYS.. but there is no moving mesh method.so now i have choose comsol..it,s very easy to handle compare to ansys...i have decided work with comsol multiphysics.. but i want to know about advantages of comsol (heat transfer module) compare to ansys or abaqus... please any one tell me about benefits of comsol multiphysics

thanking you
Parma

where can I find the user guide for "Heat transfer module" and "joule heating module"?

Tue, 07 Feb 2012 23:15:53 +0000

Hi guys, just wondering where can I get the user guide of "Heat transfer module" and "joule heating module"? Electronic files will be better.

I do have it for v 3.5, but as the software upgraded to 4.2, I would like to see the explanations corresponding to conditions and equations.

Thanks for letting me know.

Boundary condition of natural convection (heat transfer)

Tue, 07 Feb 2012 23:07:25 +0000

Dear all,

I am having a general question about the boundary condition in natural convection. I am starting with a really simple 2-D model, one rectangular box set as high temperature metal, and outside is another box set as air at room temperature. I would like to see the temperature change when metal is set to 100 C and air is 20 C.

However, I find many ways to set boudary conditions in this case, for example: convective cooling, heat flux, inflow heat flux, and boundary heat source. To me, all the govening equations mentioned above are the same, because they all need to input heat flux amount or heat convection coefficient. It also works if I do not set any boundary condition between the air and metal, I guess the default setting may be heat conduction.

I am not able to set the boundary as "convective cooling" or "heat flux" when I was setting the material as air in the outside box. If I delete the air box, I am able to obtain a reasonable temperature distribution profile by choosing "air" and "external natural convection" in "convective cooling" condition.

Could anybody give me a introduction what is the difference between all these conditions I listed above, and what is the most appropriate one I should choose for a natural convection boundary condition between metal and air? Also, is there any difference between setting the air as "heat transfer in solid" and "heat transfer in liquid" if velocity is not given?

Thanks in advance!!!

How to calculate/record peak value of T variable?

Tue, 07 Feb 2012 18:08:20 +0000

I have a Heat Transfer in Solids model. I would like to know the peak temperature (highest T during the model time) at each (x, y, z) location. Is it possible to add an equation, something like

Tpk = (T>Tpk) * (Tpk-T) + T

?

I tried a few items under Mathematics without any luck. What's the correct method to do it?

beginner_heat transfer

Sat, 04 Feb 2012 16:00:54 +0000

Hello,

I have the honor to join you all the members of COMSOL forum, I am a beginner.

please I am very intersted to discover and use COMSOL. If someone can tell me about some simple problem (examples) with correction and guide or help to do them.

subject: heat transfer

Thank you.

how to couple heat transfer and chemical species transport

Fri, 03 Feb 2012 21:25:23 +0000

I have water vapor + air that are diffusing in a porous media from one side of porous media, and from other side of this porous media I have liquid water entering in. There is also a phase change for water which effects water concentrations (in gas and liquid phases) in porous media.

so my question is if I specify my geometry ( porous media) as a domain for water vapor for example. so how comsol can build a connection between water vapor and water liquid. or how can I determine the temperature of air, when I have only added the water vapor ( steam) as material for geometry? shouldn't be an option for contributing these materials instead of overriding (because when you add another material to same geometry it overrides the previous one) ?

Because comsol only allows us to add one material for porous media, but I need to apply heat transfer on all of these materials in porous media. so what should I do ?

I am new to comsol, and I am testing comsol's abilities. so please tell me whether you can have a geometry with few materials applied to all of that geometry and not parts of it ( like multi-component flow inside a pipe) ?

Thank you very much

Distributed Heat Source and model coupling

Fri, 03 Feb 2012 18:27:06 +0000

Hello everybody,

I have to convert a model for a simulation of SLM-process from Comsol 3.5a to version 4.2. The whole simulation consists of two models. One model for the material, which will be molten and one modell for the heat source, which calculates the intensity distribution of the laser. The dependet variable for the intensity is I. The 3.5a version model uses a extrusion variable from the powder domain to the laser heat source model domain, which is named T. In the material domain, T is the temperature of the model. The intensity I and the temperature in the material model are linked via a weak form PDE in the heat source model, but this did not work for me in the version 4.2.

So I tried to couple both models the other way round. The transmitted heat in W/m³ is a function of the intensity I. I defined a general extrusion operator named 'laser_extru' from the heat source model to the powder domain. I added a heat source node to the heat transfer module. For Q in W/m³ I added my function 'some_coefficents*mod2.laser_extru(Intens)' with Intens=mod2.I. When I try to solve the problem, I get an error, that the interpolation of the extrusion operator did not work, because no origin could be found and the operator Jacobian could not be computed. I am new to Comsol so I'm not familiar with the extrusion operator concept. Does anybody have a hint for me?

I also had a look at this model (http://www.comsol.com/showroom/gallery/699/). They used almost exactly the same weak PDE as it is used in the version 3.5a model, but my port to the version 4.2 just does not work.

Handover of temperature between Heat Transfer Physics Modules

Fri, 03 Feb 2012 13:30:11 +0000

Hello everybody,

I have a problem with a Comsol model. I have two heat transfer Modules. The first module is used, to compute the heating phase of a to be simulated SLM-process. There shall be a displacement due to the heat during the heating phase, but the there shall be no stress at the start of the cooling phase in the area of the powder and the molten material. Therefor the second heat transfer module ist used with a different starting temperatur. The starting temperature shall be the end temperature of the first heat transfer module. Therefor I set the starting temperature of module 2 to T2 = T. The problem is solved in two study steps, one for the heating phase and one for the cooling phase with segregated solvers. The study steps contain different time intervalls for the heating an cooling phase. The heating phase seems to be calculated correctly. When the cooling phase starts to compute, the temperature of the heating phase does not get handed over to the second module. Instead a start value of 0 K seems to be used.

I started using Comsol just a few weeks ago, so I'm relatively new to the software. I'd be thankful for every hint or advice.

Manipulating heat-transfer coefficient

Fri, 03 Feb 2012 09:56:06 +0000

Hi All,

I have 3 domains, from bottom to top iron, air and glas. Iron and Glas are defined as heat transfer in solid, Air as heat transfer in fluids. Iron being heated, the heat flow to air and glas.

i want to increase the heat flux from iron to air by manipulating the heat-transfer coefficient.

the convective cooling doesnt work here, it works only at outer boundary.

thanks. happy weekend

akmal

is viscosity controlling for convection problems ?

Fri, 03 Feb 2012 09:49:20 +0000

i tried solving simple 2 D problems .. which did not converge in transient condition .
By Simple i mean , a rectangle (2D) with a simple inflow and & outflow on each end.
So i tried inputting a parameter called viscosity as mu and then made it very high value (towards solid) and then decreased the parameter to that of water .. surprisingly answer converged ?

and my friend too told me a similar aspect stating that "solve it at higher viscosity and sweep it for lower viscosity so that answer will converge" .

is this really so ?

How to couple T variables in bluk and thin film

Thu, 02 Feb 2012 14:36:02 +0000

We are modeling heat transfer in solids that contain a thin film within the bulk. So we have "Heat Transfer in Solids" for the bulk, and "Thin Conductive Shell" for the thin film. The default variable for the former is T and the latter T2. We haven't found a way to specify "T=T2" (it is the same temperature we are trying to solve), except just change T2 to T, i.e. setting the dependent variable in both Physics to T. That seems to work, except we would get Reset History error, see this thread:

http://www.comsol.com/community/forums/general/thread/25804/

What is the correct way to tell COMSOL that T and T2 are the same temperature variable?

laser material removal simulation

Tue, 24 Jan 2012 16:14:52 +0000

hi , i am trying to simulate material removal (steel) by a laser by changing the density and other properties of steel to that of air once the temperature goes above the vaporization temperature but the problem is that as soon as the material cools, the density goes back to that of steel . i want to make a permanent change in the material property .
the expression which i am using is
rho = rho_steel*(T<T_vap) + rho_air*(T>=T_vap)
here T_vap is the vaporization temp.
Can anyone help me with this ?
Thanks
Hirendra

Thermal Resonators

Sun, 22 Jan 2012 22:40:41 +0000

Hi,

I'm looking to model thermal resonators using COMSOL. The structure basically needs to do the following couplings: Run a current through it, account for joule heating and therefore displacement. The stress due to the displacement leads to change in the conductivity and therefore the current, via piezoresistance.

I finally need to do eigenfrequency analysis on the structural resonance and also do transient analysis of the displacement.

Can anyone suggest which are the suitable physics' to add? I tried "Joule Heating and Thermal Expansion" but I'm unable to do the mechanical eigenfrequency analysis of my structure.

natural convection

Tue, 20 Dec 2011 09:04:22 +0000

hi all.

this is problem about natural convection.

first, the file I attached, free_convection.mph, is from model gallery. so it works very well. this model has low and high temperature in right and left sides of square.

second, free_convection_modified.mph has low and high temperature in top and bottom of square.
almost are same with "free_convection.mph".
but the result is very strange, the result should be like this " http://www.youtube.com/watch?v=nveHV29gD-E "

do you guys know what problem is?

ByungDal

how to model ALE (solid-liquid interface) & moving boundary (topography change)? -thx

Mon, 10 Oct 2011 13:11:26 +0000

Questions

I’m a working on the modeling the laser-material interaction, which is typically a thermal one and involves phase change of melting and evaporation, recoil pressure induced by the evaporation and movement of the liquid (melting material) using Navier-Stoke. After severel weeks study and research, a lot of questions puzzle me all time. Could anyone here do me a favor to give me some suggestion and tips, thanks for your help sincerely in advance.

1. ALE

From the papers and materials in literature I have read already, ALE is a comman method to track the solid-liquid interface and liquid-gas interface. But this need to specify the displacement or velocity.
In my model, the interface is physically correlative to the temperature (melting point or evaporation temperature). The liquid-gas interface can be traced using the velocity of the liquid, but there is no velocity at the solid-liquid interface (is there any chance to use the velocity of liquid again, just like the liquid-gas interface?). In this kind of situation where there is no obvious velocity term in domain, just like the solid-liquid interface here, how to built the moving of the mesh is the most difficult problem which puzzle me a lot? Could you give me some idea? Thanks.

2. liquid volume fraction

The method of liquid volume fraction fl can distinguish the liquid and the solid, of which the value are 1 and 0 respectively. but how to plot and visualize the function puzzle me to see the different zone, though I think it is a very basic question. Could you give some idea? Thanks.

3. Moving boundary

As the laser-material interaction time go on, the bulk material will remove and a new boundary of laser-material interaction is created, ie.the laser-matterial interaction is a moving boundary. How to deal the moving boundary or the geometry change? As far as I known, the common method to change the topography or geometry is to change the matterial properties or build the geophagy with t (time). But the geography changes according to the temperature (evaporation temperature ), how and what can I do to deal with this?

Thans for you suggestion and tips very much.
Best regards to you and your family.

FM Huang

Modeling Laser ablation of Aluminum

Fri, 19 Aug 2011 10:55:00 +0000

Hi everyone :)
I use comsol 3.5 to model laser ablation of Aluminum in the following stack - Aluminum/Silicon nitride/Silicon. How to couple the heat transfer equations to the ablation and melting of Aluminum? I would also need to model the recoil of molten Aluminum material. From the previous comsol conference papers, I got the all equations in hand.

But I have a doubt whether the coupling should be done by incorporating heat transfer module and Fluid mechanics module and substitute appropriate sub domain boundary conditions for each of the material or use ALE to model the moving liquid once aluminum has reached melting point? (I need to see how solid aluminum changes to liquid phase and moves due to laser ablation)
If I use two separate modules and use appropriate sub domain boundary conditions, would melting and molten aluminum flow be visualizable in post processing?

My another doubt is, the laser beam has Guassian power distribution and Aluminum would have specific reflectivity for the beam. how to account for these effects in the model? In the weak form? If so kindly explain.

Thanks in advance :)

How to simulate the process of laser overlapping deposition

Tue, 15 Mar 2011 09:18:48 +0000

Hi, everyone.
I am a new user of COMSOL. Now, I want to simulate the temperature field of laser overlapping deposition. This is a additive process in which material is added continously. I don't know how to model the additive process.
I wish to get help here.

Modelling laser ablation in COMSOL

Tue, 01 Mar 2011 14:29:59 +0000

Hi,

I have a fairly simple question about COMSOL.

I have made a model in which a block is heated by a pulsing laser heat source.
I am using an iterative approach to solve it by solving for each pulse and then resolving with this solution as the intial conditions.

My question is would it be possilbe to actually 'remove' some of the material from the block, at each iteration, that has a temperature greater than a certain value?
e.g remove individual mesh elements if their temperature is greater than the vaporization temperature of the material.

I would really appreciate some help!
I have 2 weeks left to submit this project and would really like to get this working.

Thanks.
-Adam