code_saturne User's Forum

Hello,

I am new to the forum and CS and this is my first post / first question so here goes;

I'm modelling a simple heated pipe (40° uniform wall temp) with water flowing through inlet at 20° and 0.078 kg/s . Pipe is 0.01 m diam x 0.5 m long. I'm getting sensible outlet temperatures of about 25°, which i've verified by hand calcs which get me a theoretical heat flux density at wall of about 47000 W/m2 and a total input of 750 W using Gnielinski method which seem reasonable.

However a colleague of mine has written a script to extract average thermal flux density from the .txt files and this spits out about 4x10^6. Seems right but two orders of magnitude out, we've checked the script and all seems well plus double checked everything is in SI.

On top of that Paravis gives extremely high thermal flux at inlet and outlet, in the order of 10^8 and GMsh gives flux along wall from 81,000 to 189,000.

What am I missing here...??? Does it have anything to do with outlet BC (currently set to thermal flux of 0)? Turbulence model doesn't seem to make a difference, tried both k-eps and k-om SST although mesh is quite coarse at wall.

Thanks in advance!

Please ask if you would like to see files, am not sure of best practices on that.

Hello,

I don't need to see your txt files yet, but I need to know how they are built, as they must be a user-defined, not built-in output of the code... In any case, it is always good mractice to post the listing and setup.log files, which are not too large and provide useful info.

Also, note that the input and output heat flux includes the convective heat flux, so it is normal that it is very high...

Does the wall heat flux seem OK ? What values of y+ do you have at the wall ? mesh might be too coarse.

Regards,

Yvan

Thanks for the quick response.

I was talking about the text outputs from the EnSeight Gold mesh check. Have uploaded the setup log, the listing doesn't want to upload for some reason.

I was aware that it includes convection heat flux but still, it is the wall of the pipe that I am looking at specifically and it should be as high as it is. Not interested in inlet or outlet. Y+ value should be okay too.

Regards,
Nico

Hello,

The results that you mention are obtained with CS (outlet temp=25°C)?. Also you can do an energy balance doing in order to compute the total heat transfer.

Please post the listing file (May be you need to add an extension to the file (e.g. dat, txt)).

Regards,

Luciano