Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.
Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Fluid Flow in U-loop
Posted 6 mar 2013, 01:41 GMT-5 Fluid & Heat Version 4.2 4 Replies
Please login with a confirmed email address before reporting spam
I have modelled a U-loop with water flowing through inside in 3D, with three different sections (two cylindrical lines and one half of a torus at the bottom). But COMSOL only calculates for the vertical section which ends just before the half-torus at the bottom.
I specified an inlet with a temperature on one end of the loop and would like to see the temperature coming out of the other end.
The physics I use is Non-Isothermal Flow.
Do I need to specify the flow individually for all of those three sections in order for COMSOL to complete the fluid flow calculation throughout the whole U-loop? If so, how can I do it?
Looking forward to your valuable suggestions.
Thanking all of you in advance.
Kind regards,
Gary Yu
Please login with a confirmed email address before reporting spam
the only idea I can come up with is that you have missed something in the definitions of your BC, or the material selections ...
But without the model its just pure guessing ;)
--
Good luck
Ivar
Please login with a confirmed email address before reporting spam
The file was too big to attach, so I took out the very fine meshing and results, made the file much smaller to attach. I also attached some snapshots of the results before I took anything out from the original file.
Thanks again.
Kind regards,
Gary Yu
Attachments:
Please login with a confirmed email address before reporting spam
to upload a file, start by Edit - Clear all solutions, Clear all mesh, File reset model, then save and upload, we can always rerun it ;)
--
Good luck
Ivar
Please login with a confirmed email address before reporting spam
It seems for me that you have some confusions on the type of output / outlet conditions to use.
You have a section with a clear "inlet" of fluid and "outlet" of fluid, this holds for the CFD part (Navier Stokes), but as you have also HT heat transfer, you need BC for the dependent variable T too, these are you input Temperature (inlet) and the "Outflow" Temperature BC for the outlet, saying here fluid is leaving transporting with its heat as stored energy. Check the equations used (equation tab).
The open boundary is a special case combining outflow, inflow for heat and outflow or inflw of fluid. All this WITHOUT defining any pressure condition.
You must remember that for each dependent variable you need to define enough BC to make the solution UNIQUE, so you must think through variable by variable how many BC are needed (as a minimum)
so if you use an inlet and temperature BC on your entrance Boundary (6) and a outflow and outlet (boundary 18 with i.e. p=0) and remove your temperature on the outlet, as well as the open boundary, it should work OK
Then your mesh:
Use the default mesh of COMSOL. You need absolutely a "boundary mesh along the no-slip walls of your tube, else the solution is not converging correctly. This is done in the default mesh set-up. If the mes proposed is too fine for your RAM and computer (or at lest to begin with to get it running) select coarse mesh
Finally the solver: you had obviously played with the solver settings, so I had to delete the solver section and have COMSOL propose a fresh new default solver sequence, then it solved in some 2 min time, it sits though 90 seconds and searching for convergence, because your default starting conditions are quite far from any reasonable initial conditions (all "0")
--
Good luck
Ivar