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Understanding the Fluid Dynamics of Boundary Layers

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William K.
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Re: BOUNDARY LAYER
William K.   3/10/2014 10:12:04 PM
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Joe, actually I did the "books" part of the study quite a few years back. That is when I ran into that irritating "reynolds number" limitation on fluid velocity. But there was enough understanding to allow me to solve our problem. But then we discovered that oher things made the project impossible, and quite expensive as well. On top of that, and best of all, the particulat rule that was driving the development did not get passed. So when the mandate to do the impossible is removed, prudence and wisdom dictate stopping the project.

Of course a general understanding of fluid dynamics is indeed handy in everyday life, I find.

Joe Panfalone
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Re: BOUNDARY LAYER
Joe Panfalone   3/10/2014 9:51:13 AM
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You are spot on. I am glad that someone actually went back to the books on this one.

Joe Panfalone
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Re: useful information
Joe Panfalone   3/10/2014 9:24:22 AM
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I tried to keep it generic without promoting our products but since you asked, it was one of the EXAIR air knives. Also one of my Colleagues had a similar application trying to get under the boundary layer to remove static electricity. If you are interested he did a write up in it http://blog.exair.com/?s=boundary

 

bobjengr
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BOUNDARY LAYER
bobjengr   3/8/2014 2:52:36 PM
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Very good article Joe.  Excellent review.  I had to go back and pull out the book on this one. Pao describes boundary layer as follows: " Since the fluid adheres to the solid boundary, the frictional forces retard the motion of the fluid in a thin boundary layer.  Within the boundary layer the fluid velocity increases from zero at the solid surface to that of the main stream of fluid flow".   He also mentiones the velocity distributio within the boundary layer is influenced by the fluid velocity.  The smaller the viscosity the thinner the boundary layer. Again--great review. 

William K.
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Re: useful information
William K.   3/8/2014 7:44:20 AM
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Joe, this is an interesting tale. BUT what was the final solution? I can immagine a few baffles set close to alter the airflow as being the cheapest appraoch, although an air knife of some sort would possibly be the simplst.

And I know that fluid dynamics, for gasses, at least, is just a mix of inertia, friction, compression, and elasticity, with those last two being opposite sides of the same coin. And someplace in there comes the Reynolds number, which is sometimes a very limiting factor. That is probably why the CFD programs are so very useful. But thanks for an interesting post. I had not considered the possibility of a thermal priner having that type of problem. I wonder how an ink-jet printer would have worked in that instance.

Joe Panfalone
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Re: useful information
Joe Panfalone   3/7/2014 8:20:45 AM
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Thank you. Most applications concerning boundary layer deal with drag so I thought it would be of interest to highlight another less known application. I try to write in layman's terms so the less mathematical inclined can understand.

 

naperlou
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useful information
naperlou   3/6/2014 1:59:35 PM
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Joe, very good article.  This is useful information for people working with moving manufacturing processes.  I basically knew the concept, but it's appearance in these types of applications is new to me.

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