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-   -   Defining non-constant material properties (http://www.cfd-online.com/Forums/cfx/26215-defining-non-constant-material-properties.html)

 Scott August 5, 2008 15:29

Defining non-constant material properties

I have a solid domain defined in my model. The solid material (AlN) has a thermal conductivity that varies significantly within the temperature ranges of my model. Is it possible to define a material in CFX with a lookup table for thermal conductivity? I looked at many material definition examples in the CCL and RGP formats, but I haven't seen anything applicable. Any ideas? Thanks in advance!

 Rogerio Fernandes Brito August 5, 2008 16:19

Re: Defining non-constant material properties

Yes, itīs possible and itīs so easy! Send me your file name.cfx (and name.ccl) and i will help you, Sir.

rogeriobrito2007@hotmail.com

Best,

 Rogerio Fernandes Brito August 5, 2008 16:20

Re: Defining non-constant material properties

donīt forget to send me the expression of your variation of the temperature.

 Scott August 5, 2008 16:53

Re: Defining non-constant material properties

Unfortunately I'm unable to email or post my work. Perhaps you can just point me in the right direction, reference a help file, or paste some CCL code in a reply to this forum thread? Thanks!

 Rogerio Fernandes Brito August 6, 2008 07:14

Re: Defining non-constant material properties

Hi Sir Mr. Scott,

Create a CEL expression like that:

Fluxoa (B*(19453.29701*(t/A)^3.07678)/(4.73947^3.07678+(t/A)^3.07678))

A 1.0 [s] B 1.0 [W m^-2]

where "Fluxoa" is my heat flux in [W m^-2] as my boundary condition. You could create a new material for your fluid with your density in function of the temperature.

Best,

 Josh August 7, 2008 06:18

Re: Defining non-constant material properties

hi, Scott,

I have the same problem in my simulation. currently i am using the functions which are fitted by myself.

this is a compromising approch with certain errors, neverthelessïž it is the only way, as i know, to define your own properties without the table generating software.

 Scott August 8, 2008 14:36

Re: Defining non-constant material properties

Indeed, I took the same approach. I'll document the process I took, for the benefit of others who might have the same question...

First, I created a user function (1D interpolation) for each temperature-dependent material property. I imported the material property data tables (as text files) into the function definitions. Then I made expressions for each function and set the value of the expression equal to the output of the function, with temperature as the function argument. In the material property definition, I set the applicable material properties (e.g. thermal conductivity) to the corresponding expressions. I actually did this for a number of different solid materials that I commonly use, and then exported the materials/user-functions/expressions as a CCL file so I can easily load the detailed material definitions on subsequent models.

 Rogerio Fernandes Brito August 8, 2008 17:35

Re: Defining non-constant material properties

Could you send me your file (.cxf, and .ccl)? I would like to see, because iīm working in a problem like that. Thanks

My e-mail is: rogeriobrito2007@hotmail.com

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