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Negative Pressure at microchannel outlet.

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Old   August 25, 2015, 08:43
Default Negative Pressure at microchannel outlet.
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vikas yadav
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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!!
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Old   August 25, 2015, 15:12
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Lucky Tran
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Negative absolute pressure is obviously non-physical but a negative gauge pressure is okay. You just have a sub-atmospheric pressure at the outlet.
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Old   August 26, 2015, 08:54
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Quote:
Originally Posted by LuckyTran View Post
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.
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Old   August 27, 2015, 01:16
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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.
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