[sara22]

Hi all.
I simulated one heat sink that has some microchannels. and boundary conditions:
1 velocity inlet for fluid inlet
2 pressure outlet for fluid outlet.
and two thermal boundary for heat sink.
when converge my RUN pressure @ out let become negative.!????
please help me.

[RodriguezFatz]

You mean the pressure at the pressure outlet becomes negative?

[sara22]

Originally Posted by RodriguezFatz

You mean the pressure at the pressure outlet becomes negative?

yes.pressure @ outlet becomes negative

[RodriguezFatz]

But this doesn't make any sense to me. If you set the outlet pressure to some value (as a BC), how can this value change during your simulation?

[blackmask]

It is possible if there were massive reversed flow at the outlet but then the appropriateness of outlet B.C. might be in question.

[RodriguezFatz]

Originally Posted by blackmask

It is possible if there were massive reversed flow at the outlet but then the appropriateness of outlet B.C. might be in question.

Yes, but he says "converge" in his initial post. I doubt he will get convergence in such a case.

[sara22]

yes my RUN become converge. But pressure value @ outlet is negative.for example pressure @ inlet B.C be 5687 Pa. and @ Outlet B.C be -879 Pa.

[flotus1]

Please post images of the velocity and pressure contours and of the residuals.

[RodriguezFatz]

Originally Posted by sara22

yes my RUN become converge. But pressure value @ outlet is negative.for example pressure @ inlet B.C be 5687 Pa. and @ Outlet B.C be -879 Pa.

Generally, negative pressures are no problem, since your pressures are gauge pressures. There is a large positive offset of 1e5 Pa to them...