# negative pressure

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 July 8, 2013, 09:53 negative pressure #1 Member   Sa.Baraty Join Date: Apr 2013 Location: Iran Posts: 50 Rep Power: 6 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 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 20 You mean the pressure at the pressure outlet becomes negative? __________________ The skeleton ran out of shampoo in the shower.

July 10, 2013, 15:28
#3
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Sa.Baraty
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Quote:
 Originally Posted by RodriguezFatz You mean the pressure at the pressure outlet becomes negative?
yes.pressure @ outlet becomes negative
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thanks

 July 11, 2013, 03:03 #4 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 20 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 11, 2013, 04:17 #5 Senior Member   Join Date: Aug 2011 Posts: 315 Rep Power: 14 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 11, 2013, 04:19
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Philipp
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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.
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The skeleton ran out of shampoo in the shower.

 July 12, 2013, 02:14 #7 Member   Sa.Baraty Join Date: Apr 2013 Location: Iran Posts: 50 Rep Power: 6 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

 July 12, 2013, 03:33 #8 Senior Member     Alex Join Date: Jun 2012 Location: Germany Posts: 1,534 Rep Power: 25 Please post images of the velocity and pressure contours and of the residuals.

July 12, 2013, 04:37
#9
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Philipp
Join Date: Jun 2011
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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...
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The skeleton ran out of shampoo in the shower.

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