Negative Pressure at microchannel outlet.

vikasy123 · August 25, 2015, 09:43

Dear all,

I am modelling flow through microchannel with velocity inlet and outflow boundary conditions at inlet and outlet respectively.
I am getting negative pressure at outlet, Is it possible to have negative pressure at outlet ? My Operating pressure is 101325 Pa.

Thanks!!

LuckyTran · August 25, 2015, 16:12

Negative absolute pressure is obviously non-physical but a negative gauge pressure is okay. You just have a sub-atmospheric pressure at the outlet.

vikasy123 · August 26, 2015, 09:54

Quote:

Originally Posted by LuckyTran

Negative absolute pressure is obviously non-physical but a negative gauge pressure is okay. You just have a sub-atmospheric pressure at the outlet.

Thanks LuckyTran for your comment.
But i am not able to understand how flow will be possible if pressure at outlet is sub-atmospheric.
Please help me to understand.

Steffen595 · August 27, 2015, 02:16

the calculation does not care. If the outlet velocity is higher than at the inlet, then you change the static term to the velocity term in Bernoulli equation. And then, if the inlet pressure is 0 gauge, outlet pressure has to be lower.
Ansys would not do negative absolute, it would throw a warning. I managed to get a few MPa minus in Autodesk fluid sim.

August 25, 2015, 09:43	Negative Pressure at microchannel outlet.	#1
vikasy123 New Member vikas yadav Join Date: Jul 2015 Posts: 9 Rep Power: 11	Dear all, I am modelling flow through microchannel with velocity inlet and outflow boundary conditions at inlet and outlet respectively. I am getting negative pressure at outlet, Is it possible to have negative pressure at outlet ? My Operating pressure is 101325 Pa. Thanks!!

August 27, 2015, 02:16		#4
Steffen595 Senior Member Join Date: May 2012 Location: Melbourne Posts: 161 Rep Power: 14	the calculation does not care. If the outlet velocity is higher than at the inlet, then you change the static term to the velocity term in Bernoulli equation. And then, if the inlet pressure is 0 gauge, outlet pressure has to be lower. Ansys would not do negative absolute, it would throw a warning. I managed to get a few MPa minus in Autodesk fluid sim. vikasy123 likes this.

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August 25, 2015, 16:12		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,747 Rep Power: 66	Negative absolute pressure is obviously non-physical but a negative gauge pressure is okay. You just have a sub-atmospheric pressure at the outlet.