Learning Forum

[Mahra Abdulla]

Hello,

I'm doing a heat transfer project where we need to model flow inside a pipe and was given the following information: D = 5cm, L/D = 50, fluid is water, Re = 1000, constant heat flux q = 100 W/m2, and Tin = 20C. 

I modeled the pipe flow as laminar in a 2D axisymmetric pipe and was able to get the velocity and temperature contours and plots along x without an issue. However when I tried to plot the heat transfer coefficient the average value was way below the expected. It's giving me an average of 16.67 when it should be around 96. I even calculated it using a surface integral of an area weighted average along the wall and its the same. I'm not sure what's wrong? Or what to even check... I was following tutorials online but none showed how to plot the convection heat transfer coefficient so I just did a normal plot after making a line along the wall length to use as a reference for the plot. And then x axis is just the position along the length of the pipe. Any help would be much appreciated... thanks!

[DrAmine]

 

You said that the temperature field is looking fine. If yes then I expect that it is a post-processing issue. Did you change the reference temperature value under Reference Values and set it to your inle temperature or the reference value you have in mind?  Generally the value be like q (100 W/m²) / (Twall-Tinlet( 20°C)))

[Mahra Abdulla]

Hello,

Thank you for responding! I changed the reference values to be taken from the inlet and the graph looks much more reasonable now, however now the heat transfer coefficient is too high... The theoretical value is 98.186 and now I'm getting 123.02 which gives a high error percentage. I've attached some images of the boundary conditions and reference values I used... Please let me know if you see anything wrong. Appreciate all the help, thank you.

[DrAmine]

Please provide details on your mesh resolution? The expected value is based on which formula?

[DrAmine]

Also you need to account for the entrance region when comparing with any "correlation" / "formula": You are flowing as plug here.