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August 16, 1999, 20:14 
Nonslip Boundary condition

#1 
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Hi everybody,
Can anybody explain why nonslip boundary condition from the physical (maybe atom) point of view please? Say, we want to calculate the flow field of the mercury through a tube made of glass, can we still use this nonslip boundary condition? thanks. 

August 17, 1999, 00:35 
Re: Nonslip Boundary condition

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(1). try to look up the properties of mercury in a handbook first. (2). If it says the viscosity is zero, then you can use slip boundary condition at the wall. (3). Otherwise, if it has a viscosity value, then use the nonslip boundary condition. (4). If you can't find it, then run two cases with slip and nonslip conditions. And compare the results with the test data.


August 17, 1999, 13:00 
Re:Nonslip Boundary condition

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Hi. Could anyone tell me what the slip boundary condition is? Thank you.


August 17, 1999, 14:11 
Re: Nonslip Boundary condition

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For mercury the surface tension is extremely high and this has also to be taken into account. For example if you try to 'inject' mecury into a medium using a syringe, this one might just break. Also, a little amount of mercury in a tube would rather 'roll' rather than flow. So if you're talking about a small glass tube, you will certainly need a nonslip boundary condition (viscosity, friction) and some treatment for the surface tension. Check the viscosity of mercury, the velocity of its flow and find out (using simple books about the theory of the boundary layer) whether the boundary layer will be much smaller than the size of the glass tube (slip BC) or of the same scale (nonslip BC).
As to your question related to the microscopic scale of the friction, it is a whole field of Physics! 

August 17, 1999, 20:38 
Re:Nonslip Boundary condition

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(1).For a stationary wall ( or ground ), a nonslip condition is that the fluid velocity at the wall point is zero.(because of the existence of the viscosity) (2). In some analyses, the fluid viscosity is removed from the governing equations, and the resultant equation is INVISCID. (that is nonviscous). (3). For inviscid flows, we can not apply the nonslip boundary condition at the wall because there is not viscosity by assumption. (4). In the inviscid flow case, the fluid velocity at the wall is allowed to slip along the contour of the surface (move on the surface and tangent to the surface). This condition is called "slip condition".


August 18, 1999, 16:05 
Re:Nonslip Boundary condition

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Thank you for your answering. I'd like to make sure that I understand well. For inviscid flows, the normal component of the velocity is zero at the boundary  this is what your saying, isn't it?
Then can the tangental velocity be any? Is there any condition such as the derivative in tangential direction is zero? Thank you again. 

November 28, 2012, 00:26 

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regards, prishor 

November 28, 2012, 03:19 

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