Calculation of shear rate/film thickness
Calculation of shear rate/film thickness
(OP)
I am trying to calculate the shear rate on the surface of a metal coupon being moved at a constant rate in a Newtonian fluid. In order to do this, I need to know the thickness of the boundary film, and I have not been able to find a means of calculating or estimating the boundary film thickness? I would appreciate any help, or references to good reference material that will provide what I need.
Much appreciated
Much appreciated





RE: Calculation of shear rate/film thickness
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Good luck,
Latexman
RE: Calculation of shear rate/film thickness
RE: Calculation of shear rate/film thickness
Good luck,
Latexman
RE: Calculation of shear rate/film thickness
I am tryng to calculate the shear rate on a piece of metal with a given flow moving past it. I am rotating a coupon in an autoclave enviroment, with the large surfaces oriented parallel to rotation so that the flow runs smoothly over the coupon in a high Re laminar flow (Re = 1800 to 2000). It is simple enough to calculate a min/max/ave velocity through the test liquid; however, calculation of shear implies a specific distance over which the velocity gradient occurs. In a pipe or duct this is obvious, but in a my scenario it seems more complicated. I also was considering testing at turbulent conditions (Re > 4000) as well, which would imply a boundary layer, with essentially all of the delta V occuring in the boundary layer.
RE: Calculation of shear rate/film thickness
What is generating this "flow moving past" the rotating coupon in the autoclave?
If this flow is being induced by the rotating coupon, that suggests you should treat the coupon like an agitator. If this is so, does the autoclave have baffles to hinder rotational motion? It'll need them to more closely approximate a mixer. If what you have does closely approximate a mixer, the following post will help:
thread798-185449: Shear Rate Equation
Good luck,
Latexman