[ebrahem]

what is the equivalent in Fluent of Expert Parameters in CFX-pre

Calculating the Heat Transfer Coefficient in CFX
The Heat Transfer coefficient calculated by CFX will be quite different from standard film coefficients calculated by other means, but it is possible to output values that reflect the standard definition.

In CFX, the Wall Heat Transfer Coefficient = Wall Heat Flux / (Wall Temperature - Wall Adjacent Temperature) Most standard engineering equations we are familiar with use some "bulk temperature" in place of the Wall Adjacent Temperature. Of course CFX has no idea what your "bulk temperature" would be, and must use some other value. When using Wall Adjacent Temperature, which is the fluid temperature of the first fluid node off the wall, the returned value for HTC is going to be completely mesh dependent. Where coarser meshes will give you answers approaching the standard definition using bulk temperature, and a fine mesh would give you very large values, as the denominator of the HTC equation is approaching zero.

If you want the HTC to use a different value for the Reference Temperature instead of Wall Adjacent Temperature, there are a two approaches:

Use the expert parameter "Tbulk for HTC" and set this to your some reference temperature. CFX will now calculate: Wall Heat Transfer Coefficient = Wall Heat Flux / (Wall Temperature - Tbulk for HTC)
Create your own expression for MyBulkTemperature through the geometry, for example, along the pipe length, which may be a function of the length.
Create a new expression for MyHTC = Wall Heat Flux / (Wall Temperature - MyBulkTemperature).
The tricky part is how do you get "Wall Temperature"? Well from the original HTC equation, we can see: Wall Heat Transfer Coefficient = Wall Heat Flux / (Wall Temperature - Wall Adjacent Temperature) Rearrange this equation to: Wall Temperature = (Wall Heat Flux / Wall Heat Transfer Coefficient) + Wall Adjacent Temperature
You can then make a new variable from your "MyHTC" expression, and make a contour, or plot it on a graph with a line running along the wall. Remember this is a boundary only variable.
The same approach can be used for Nusselt numbers as well.