[Dounia]

Hello everyone,

my study case is transient natural convection in which I'm using boussinisq density in air property, the problem is in the thermal expansion coefficient.

-I search online, and I found a value of 0.0032 (1/k) for air.
-but I found a tutorial video in YouTube that use 0.036 (1/k),
-when I'm using a value of 0.00032(1/k) I found good results.
so my question is! is it logical if I use 0.00032 ?

and how can I know the right value in my case?

I'll be so grateful for any comments or answers.

Best wishes,

Dounia

[LuckyTran]

For ideal gases, you have (see Thermal expansion). You can use more real properties if you like.

[BryceLos]

Originally Posted by LuckyTran

For ideal gases, you have (see Thermal expansion). You can use more real properties if you like.

Hi LuckyTran, I am using NIST real gas model in fluent and I want to know how to access the thermal expansion coefficients via UDF?

Many thanks,
Bryce

[AlexanderZ]

I'm not sure if there is predefined in UDF macro to get thermal coef value

what you can do is:
1. get thermal coef value using scheme, write it to any variable
(to get this variable you may use TUI commands and pick-a-real command.
On the other hand, there should be a scheme name of variable for thermal coef which I don't know)
2. read this variable in UDF

[BryceLos]

Originally Posted by AlexanderZ

I'm not sure if there is predefined in UDF macro to get thermal coef value

what you can do is:
1. get thermal coef value using scheme, write it to any variable
(to get this variable you may use TUI commands and pick-a-real command.
On the other hand, there should be a scheme name of variable for thermal coef which I don't know)
2. read this variable in UDF

Hi Alex,

Thanks for your advice, as I searched there is no macro to access the thermal expansion coefficients. However, I can calculate it using matlab via REFPROP (the values versus temperature). Could you give more details about your approach?

Thanks,
Bryce