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MIcrochannels.

I am simulating microchannels in FLUENT. I have a single channels with rectangular crosssection. Hydrolic diameter is 0.0015, Length is 1 cm.
BC: Inlet> Velocity inlet
Outlet> Outflow
Bottom wall > Heat flux: 100000 w/m2, Th:0.0005m
Upper and side walls: Adiabatic, Th:0.0005m
But What I get in pressure contour is negative pressure inside the channel which does not make any sense.

 thecfduser July 4, 2010 15:19

Hi
the pressure in the N.S equation appears as a gradient. What is important, in an incompressible flow, is the pressure difference and not the pressure.
The pressure will depend on the point in wich u choose the reference pressure (in operating pressure window of Fluent).
Anyway, i think ure simulation is not well posed.
Choose pressure outlet instead of outflow, with pressure=0 on that boundary.
U will get positive pressure inside the microchannel, and ure simulation will be good.

Thank you.
The problem with pressure outlet is that the fluid is not going to atmosphere pressure. It is in a closed circle and I choose outflow to see how much the outlet pressure is. When I choose pressure outlet with 0 Pascal. the outlet pressure is 0 which is not sensible. Even I changed the operation condition but no changed in negative pressure. The gradient is absolutely correct but how can I have the absolute pressure?

 thecfduser July 4, 2010 16:30

With outflow, u assume that ure fluid tempearture dont change anymore at the outlet...(dT/dx=0)....
When u put outlet pressure with 0 Pa, it is the gauge pressure that is 0. To get the absolute pressure, u must know the pressure at least in a point of ure domain (the pressure biggest derivative is 1st order in NS equations).
so in a resume, if u dont know the absolute pressure in a point of ure domain, u cannot get the absolute pressure at ure outlet.
(if u choose a pressure outlet, Fluent will not consider anymore the operating condition. The operating pressure will be calculated from ure outlet).
If u didnt undertsand, write to me again

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