negative pressure

sara22 · July 8, 2013, 09:53

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 · July 10, 2013, 03:43

You mean the pressure at the pressure outlet becomes negative?

sara22 · July 10, 2013, 15:28

Quote:

Originally Posted by RodriguezFatz

You mean the pressure at the pressure outlet becomes negative?

yes.pressure @ outlet becomes negative

RodriguezFatz · July 11, 2013, 03:03

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 · July 11, 2013, 04:17

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 · July 11, 2013, 04:19

Quote:

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 · July 12, 2013, 02:14

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 · July 12, 2013, 03:33

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

RodriguezFatz · July 12, 2013, 04:37

Quote:

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...

July 8, 2013, 09:53	negative pressure	#1
sara22 Member Sa.Baraty Join Date: Apr 2013 Location: Iran Posts: 50 Rep Power: 13	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. __________________ thanks

July 10, 2013, 03:43		#2
RodriguezFatz Senior Member Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26	You mean the pressure at the pressure outlet becomes negative? __________________ The skeleton ran out of shampoo in the shower.

July 11, 2013, 03:03		#4
RodriguezFatz Senior Member Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26	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? __________________ The skeleton ran out of shampoo in the shower.

July 12, 2013, 02:14		#7
sara22 Member Sa.Baraty Join Date: Apr 2013 Location: Iran Posts: 50 Rep Power: 13	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. __________________ thanks

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
[blockMesh] non-orthogonal faces and incorrect orientation?	nennbs	OpenFOAM Meshing & Mesh Conversion	7	April 17, 2013 05:42
Raise pressure level in simulation to avoid negative pressures	solimcfd	CFX	3	June 13, 2012 07:28
seeking for help about a room with negative pressure	mengyue1	FLUENT	0	November 26, 2009 06:40
negative pressure in cfx	flar.t	CFX	1	December 18, 2006 23:20
negative pressure	mAx	FLUENT	0	January 25, 2006 14:31

July 11, 2013, 04:17		#5
blackmask Senior Member Join Date: Aug 2011 Posts: 421 Blog Entries: 1 Rep Power: 21	It is possible if there were massive reversed flow at the outlet but then the appropriateness of outlet B.C. might be in question.

July 12, 2013, 03:33		#8
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	Please post images of the velocity and pressure contours and of the residuals.