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Subhadeep August 21, 2009 14:14

Temperature dependent thermal property in CFX
 
Hi

Trying to define a material in CFX pre with temperature dependent expression

This is what I entered :

2.9544 + 0.02*T [W m^-1 K^-1]

While running gives me error saying :

Error processing expression 'Thermal Conductivity'.
Error at position 17. Units [W m^-1 K^-1] are associated with an expression that is not dimensionless.

What should the correct expression be? Should I take out

[W m^-1 K^-1]

?

Thanks ....

NickFL August 21, 2009 14:56

The problem is that T has a units associated with it. What you need to do is make sure the final result ends with a [W m^-1 K^-1]. So we would have to change it to:

2.9544 [W m^-1 K^-1] + 0.02 [W m^-1 K^-2] * T

Notice the Kelvin unit on T will cancel the one associated with the 0.02 providing the correct units. Let me know if you need further explaination.

Subhadeep August 21, 2009 15:07

Thanks
 
That helped ...

After reading the messages I thought on similar lines but used it like this and that still gave me an error :

2.9544 [W m^-1 K^-1] + 0.02*T [W m^-1 K^-2]

NickFL August 21, 2009 15:29

Needs to be exactly as I have it. Again the units of [W m^-1 K^-2] must be associated with 0.02 and not as you have it where CFX is trying to associate T with [W m^-1 K^-2] when it already has units of [K].

rogbrito August 22, 2009 20:21

Hi Sir,

let me explaining :D! For example, for the heat flux boundary condition, you have to build a variable called Fluxoa, like this (where t is time in [s], and Fluxoa is a heat flux in [W m^-2]:

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]

So, the Fluxoa variable will have the [W m^-2] final heat flux unit !


with kind regards,

Rogerio ;).


Quote:

Originally Posted by Subhadeep (Post 227111)
Hi

Trying to define a material in CFX pre with temperature dependent expression

This is what I entered :

2.9544 + 0.02*T [W m^-1 K^-1]

While running gives me error saying :

Error processing expression 'Thermal Conductivity'.
Error at position 17. Units [W m^-1 K^-1] are associated with an expression that is not dimensionless.

What should the correct expression be? Should I take out

[W m^-1 K^-1]

?

Thanks ....


mactech001 March 22, 2012 02:52

will this be also valid if i were to define a temperature dependent body load please?


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