thermal conductivity expression
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hi all.
I would like to add an expression for thermal conductivity k=-0.000837*T^2-0.030641*T+0.147212 But I get the following error: ' Bad expression value '-0.000837*T[K^2]^2-0.030641*T[K]+0.147212' detected in parameter 'Thermal Conductivity' in object '/LIBRARY/MATERIAL:Ice cream/PROPERTIES/THERMAL CONDUCTIVITY'. CEL error: Error at position 12. Units ([K^2]) are associated with a term that is not dimensionless. ' I also tried to write it like this: k=-0.000837*T[K^2]^2-0.030641*T[K]+0.147212 Does anybody know how to use the expressions in cfx? |
Hello Thomas,
You must indicate the units of each constant. So it should be: k=-0.000837 [W m^-1 K^-3]*T^2-0.030641 [W m^-1 K^-2]*T+0.147212 [W m^-1 K^-1] This will give you thermal conductivity in [W m^-1 K^-1] Regards, Possa |
easy :)
thanks! |
Hi Possa.
It worked for me to apply the material with this expression for thermal conductivity, but the solver has problem working with it. I tried to change all the parameters to water one by one, and found out that this expression is the only problem. Do you know if cfx nows that T is temperature? Do I have to define it somewhere? |
The variables and their names is listed in the CFX reference manual, under variables. You should consult it to make sure you use the correct name for variables.
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Hello Thomas,
Yes, you're right. You must change T for Temperature for this to work. Regards, Possa |
I had a look in the reference manual, and it says that the short variable name for temperature is 'T'. But it doesn't work for me.
Do you know where I have to define T in cfx-pre if I want to make my thermal conductivity temperature dependent? |
Hi,
Try putting like this in the expression definition tab: -0.000837 [W m^-1 K^-3]*Temperature^2-0.030641 [W m^-1 K^-2]*Temperature+0.147212 [W m^-1 K^-1] It is Caps sensible (it will recognize Temperature but not temperature). It should work like that. Regards |
Great. This worked for me. Thanks!!
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