# CEL and variable

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 August 2, 2016, 11:55 CEL and variable #1 New Member   Casper Join Date: Nov 2015 Posts: 14 Rep Power: 8 Hi All! How to define density or thermal conductivity variables? When I defined value in CEL expression, it doesn't change like a constant. How Can I define it?

August 2, 2016, 16:27
#2
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Erik
Join Date: Feb 2011
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Quote:
 Originally Posted by Casper_07 It doesn't change like a constant.
....I'm confused, can you explain a little more what you are trying to do exactly?

Are you trying to make it a variable of temperature or something?
You have to make an expression in the format: 0.2 [W/m/K^3]*T^2+ 0.2 [W/m/K^2]*T + 0.5[W/m/K]

Last edited by evcelica; August 3, 2016 at 13:43.

 August 2, 2016, 21:38 #3 New Member   Casper Join Date: Nov 2015 Posts: 14 Rep Power: 8 is it polynomial function? which you described it . I am going to define two points. And then it should be found variables. For instance, T= 300[K] , rho=1.17[kg/m^3], cp=1005.7[J/kg/K], thermal conductivity 0.02624[W/(m/K)] dynamic viscosity 18.46x10^-6 T= 1500[K] , rho=0.235[kg/m^3], cp=1230[J/kg/K], thermal conductivity 0.094[W/(m/K)] dynamic viscosity 54.46x10^-6[Pa/S] How to create like variables?

 August 2, 2016, 22:46 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,140 Rep Power: 134 You can define functions for all these properties (CEL expressions, interpolation functions, user fortran etc) and then you make them define the material properties in the materials tab.

 August 3, 2016, 13:43 #5 Senior Member   Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,095 Rep Power: 21 Be careful using functions for both density and specific heat, it can lead to thermodynamic inconsistencies. Use ideal gas instead to avoid this. (Or Constant Specific Heat, which you probably don't want to do) For your conductivity, if using linear curve fit, it would be: (5.64667*10^-5)[W/m/K^2]*T + 0.0093[W/m/K]