# Fluids: Shear rate

1. Feb 23, 2010

### JJ21

Hi,

I'm trying to get an expression for the shear rate in a rotating cylinder (as pictured) in terms of the inner cylinder radius, outside cylinder radius and angular velocity. The inside cylinder remains fixed and only the outer cylinder rotates. Assume that the distance x is small.

Any suggestions on how to approach the problem etc would be greatly appreciated.
Thanks

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• ###### rotating cylinder shear sketch.jpg
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2. Feb 28, 2010

### kevjcarvalho

heyy....i think u will have to use newton's law of viscosity

Shear stress(induced in the fluid) = (absolute viscosity of the liquid)*(shear strain rate)
Left hand side =(Torque applied on the outer cylinder to rotate it)/(Curved surface area of the inner cylinder)
=(Force*R2)/(2*pi*R1*L1)

You can get the absolute viscocity of the liquid you are using from the net...but it think u will need the force....just check it out with someone neways