Learning Forum

[hwang289]

Hi, I am currently running a simulation of the flow distribution of microchannel heat exchanger header. I figured out that if I give pressure outlet with at all channels in fixed 0 gauge pressure, it shows severe backflow and the solution is totally wrong.

On the other hand, I figured out that if I use the pressure outlet- from neighboring cells (pressure specifcation method, not backflow), I was able to get reasonable solutions.

To justify using this boundary condition, I was looking through the ansys manual, but there was no detailed description of this method. Can anyone help me how this boundary condition setting works? Is there any difference between outlet(outflow) boundary condition?

Thank you

[Rob]

What backflow phase have you set? Is gravity on? Why are you using VOF, or are you also boiling the liquid?

Do NOT use the outflow boundary. It's an older option, and really should have been removed in about Fluent 5! 

[hwang289]

It's an adiabatic case but we are injecting R454B liq-vap mixture into the header and try to check the distribution of each phase in the outlet channels. I set the backflow only has vapor phase. As I mentioned in the question, do you know the difference between setting a fixed pressure value and setting as from neighboring cells in the pressure specification method?

[Rob]

If you check the Help on the panel it gives some information, but it looks to take adjacent cell velocity into account. 

Note, with VOF you can't add a mixture on a boundary, you can only add one or other (or another other) so check what the inlet condition is too.