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-   -   slip flow in microchannel (http://www.cfd-online.com/Forums/main/5186-slip-flow-microchannel.html)

Sander Nagoo September 19, 2002 23:43

slip flow in microchannel
 
Dear sir:

I try to simulate the compressible microchannel flow ( rectangle ). The proposed model assumes the fluid is a continuum but employs a slip velocity boundary condition on the channel wall.

slip wall bc: Uwall=Kn*(dU/dy)wall

My question is, What kind of Kn I should use, mean value of a cross section or not? Thank you for your help.

best regard

Sander Nagoo

Abeer September 20, 2002 18:44

Re: slip flow in microchannel
 
Kn is not it dimensionless number that you calculate from the flow parameters like Re??

Sander Nagoo September 21, 2002 09:16

Re: slip flow in microchannel
 
Dear Abeer:

Thank you for your help. But I still don't fully understand. If I want to calculate the wall velocity, should I use mean value of a corss section.

Best regard

Sander Nagoo

Raju September 24, 2002 13:13

Re: slip flow in microchannel
 
If you are doing this in 2-D then you would not require to take the mean value, it can be calculated by solving for u(gas)-u(wall)= Kn*(du/dy), although i think that this is not the complete equation.

Sander Nagoo September 25, 2002 01:08

Re: slip flow in microchannel
 
Dear Raju:

Thank you for your help. I try to compute slip wall velocity according your way(channel flow,length=3000*10^-6 m,height=1.2*10^-6 m). But I still have two questions about slip velocity.

1)dU/dy is too large, about 10^7.

2)kn=mu*sqrt(pi)/sqrt(2*rho^2*R*T),(mu=1.85*10^-5,rho=1.078,R=296.7,T=314) is too small( knout=0.055).

The slip wall velocity ( kn*dU/dy ) seems too large.What can I do about this problem? Thank you for your help.

Best regard

Sander Nagoo

Raju September 27, 2002 13:45

Re: slip flow in microchannel
 
the slip wall velocity cannot be that large... think this way,when you have a zero velocity when it is no-slip. Then for a small Kn number it should be low. Are you positive that (dU/dy) is so high?


Sander N agoo September 29, 2002 08:06

Re: slip flow in microchannel
 
Dear Raju:

Thank you for your help. Did you ever calculate this problem? Please give me some suggestion. Thank you.

Best Regard

Sander Nagoo


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