[Shomaz ul Haq]

Dear all,

Hi. Hope all are well. I am trying to make the expression "MyHTC = Wall Heat Flux / (Wall Temperature - MyBulkTemperature)" as guided in the FAQs. For this the required "Wall Temperature = (Wall Heat Flux / Wall Heat Transfer Coefficient) + Wall Adjacent Temperature". I made the following expression in CFD-Post for Wall Temperature i.e. "(Qwall/htc)+tnw" but I am getting no values but <variable> [K]. Why is that? Also where do I get "MyBulkTemperature"? Any help would be appreciated. Can somebody please help? Would be grateful. Thank you.

[Shomaz ul Haq]

Any help would be appreciated.

[urosgrivc]

Do you want your HTC walues to be based on the farfield temperatures?
if so
You can set an expert parameter T-bulk in (pre) and it will calculate walues based not on near wall (bulk) temperature but from your fixed (T-bulk) value.

If you dont set the (T-bulk) value, temperatures near wall are -> average temperatures in the first element near wall, and are very grid dependant.
smaler the element higher the htc, to some extent of corse and not for all cases.

[Shomaz ul Haq]

Thanks urosgrivic. Yes one can use the expert parameter "Tbulk for HTC", but I am using the second approach. I am trying to create my own own expression for "MyHTC". So I need help regarding my CFD-Post expression for Wall Temperature i.e. "(Qwall/htc)+tnw" but I am getting no values but <variable> [K]. Would be grateful for help. Thank you.

[Shomaz ul Haq]

Would be grateful for any help. Thank you.

[ghorrocks]

What are you trying to do? I think you are asking how you get the HTC based on a defined bulk temperature from a simulation you have already completed, so you want to do it in post processing.

If this is the case, isn't the equation you want MyHTC = Wall Heat Flux / (Wall Temperature - MyBulkTemperature)? Then Wall Heat Flux and Wall Temperature are solution variables and MyBulkTemperature is a value you define. Now MyHTC is defined and the function should work.

[Shomaz ul Haq]

Thanks a lot Glenn. Yes I am doing all this in CFD-Post. I need help regarding my CFD-Post expression for Wall Temperature i.e. "(Qwall/htc)+tnw". This is the expression I used but I am getting no values but <variable> [K]. Also what value or expression of "MyBulkTemperature" should I use and how? Would be grateful. Thank you.

[ghorrocks]

Can you get wall temperature directly with "Wall Temperature" or "Twall"?

[evcelica]

You get no value for your expression because it is dependent on position. You can make a variable, and then plot it on a surface. Or draw a line along the wall, and make a chart for it on that line.

For MyBulkTemperature, you would use whatever temperature or expression you want which defines the bulk temperature of the fluid. For example, in a pipe, I use the mass flow average of the temperature in each cross section along the pipe. so it is a function which changes along the length of the pipe. Your case for MyBulkTemperature may be different.