# How to set slip velocity and temperature jump

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 April 24, 2012, 23:40 How to set slip velocity and temperature jump #1 New Member   awu Join Date: Mar 2012 Posts: 4 Rep Power: 14 Hey friends: I am dealing with microchannel heat transfer in CFX，but i dont know how to set up slip velocity and temperature jump boundary condition . I choose finite slip wall，but i dont know how to set slip modal and wall velocity.I am new to CFX. Thanks for any possible help.

 April 25, 2012, 07:48 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,819 Rep Power: 144 In CFX you can only have no slip walls or specified shear stress. There is no finite slip built in. You will have to derive it yourself and impose it as an expression (hopefully as CEL) on either a no slip wall (with wall motion presumably) or a shear stress wall.

April 25, 2012, 21:19
slip velocity
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awu
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Quote:
 Originally Posted by ghorrocks In CFX you can only have no slip walls or specified shear stress. There is no finite slip built in. You will have to derive it yourself and impose it as an expression (hopefully as CEL) on either a no slip wall (with wall motion presumably) or a shear stress wall.
Dear ghorrocks:

Thank you for your help. But I still don't fully understand. How can i use CEL to simulate velocity slip?What should i edit in CEL？That would be the best for you give me a example.
Best regard

awuunity
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 April 26, 2012, 06:04 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,819 Rep Power: 144 You have to know the mathematics of what you want to implement before you can implement anything. What is the mathematics of what you want to apply?

April 26, 2012, 08:05
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awu
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Quote:
 Originally Posted by ghorrocks You have to know the mathematics of what you want to implement before you can implement anything. What is the mathematics of what you want to apply?
Dear ghorrocks:

Thank you for your help.I want to simulate water flows through tube and the tube's diameter is 0.01mm, length is 2mm. tube's outer surface temperature is 333.15K.The velocity of inlet set to 0.1m/s,temperature set to 293.15K.Set outlet static pressure to 0Pa.

Best regard

awuunity

 April 26, 2012, 18:39 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,819 Rep Power: 144 This is all routine stuff, the normal boundaries can handle this. Your first post mentioned a finite slip wall - do you really need this?

April 27, 2012, 22:06
3Q
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awu
Join Date: Mar 2012
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Quote:
 Originally Posted by ghorrocks This is all routine stuff, the normal boundaries can handle this. Your first post mentioned a finite slip wall - do you really need this?
Dear ghorrocks:

I learned the help documentation of cfx，I think that maybe i should choose to finite slip wall，but i dont know how to set slip speed according to my model.
Best regard

awuunity

 April 29, 2012, 06:50 #8 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,819 Rep Power: 144 Do you even know what a finite slip wall is?

 June 30, 2018, 15:43 #9 New Member   Jasmina Join Date: Apr 2018 Location: Germany Posts: 11 Rep Power: 8 Hello, Im also dealing with a slip wall condition in Ansys (18.2). i need to calculate a viscous non-newtonian fliud flow through a very small conical needle (0.6 mm diam.), and i read that a slip condition is needed to be set for a non-newtonian fluid. as far as i can say, a "finite slip wall" is appropriate in this case - but for the implementation are some parameters needed, which i never heard before.. in the doc is just the underlying equation listed: pls check out https://www.sharcnet.ca/Software/Ans.../i1301372.html "2.7.1.3 finite slip wall" Has anyone an idea how i could figure out the needed parameters? I couldn't even find the real meaning of them.. thank you very much!

 July 1, 2018, 06:37 #10 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,819 Rep Power: 144 This is not a commonly used part of CFX so I don't think you will get many users who have used it. I have never used it. But it seems to be simple enough to me, it is used to model a shear thinning boundary layer. If you want to work out the value of the parameters to use in it then do a simple analytical boundary flow with your non-newtonian model, and fiddle with the model parameters until the model fits the analytical result closely enough you are happy with it. If you want to get serious you can use a non-linear regression to fit the parameters. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

 July 2, 2018, 08:40 #11 New Member   Jasmina Join Date: Apr 2018 Location: Germany Posts: 11 Rep Power: 8 Thank you for your idea! I will see if I can find some analytical equations which also consider a slip wall... Still, I worry about 3-4 parameters to vary to achieve an appropriate result. Maybe I change the constrains so no "slip-stick" would occur (if that works). Thank you!

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