viscosity matt amine nassim. viscosity viscosity is an internal property of a fluid that offers...
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VISCOSITY
MattMattAmine Nassim
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Viscosity
Viscosity is an internal property of a fluid that offers resistance to flow
If the fluid has a high viscosity it strongly resists flow,
If the fluid has a low viscosity, it offers less resistance to flow
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How to measure viscosity
There are many ways to measure viscosity
The falling-sphere method is a simple way to study viscosity fluids at varying temperatures
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Falling-sphere method A cylinder is filled with fluid and two marks
placed at the ends of the distance
You drop a sphere into a liquid and measure the time required for the sphere to travel a calibrated distance
Layers of fluid molecules sliding over other layers with type of frictional forces depending on the viscosity. Fluid stationary at wall moves with increasing velocity away from wall
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THEORY The force needed to separate molecules of
the fluid according to Stokes is : F = 6(pi)Rnvc R: radius of the sphere n: viscosity of the fluid vc: velocity of the sphere This force can be set equal to the
gravitational force modified to account for the buoyant effect as follows
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THEORY
6 (pi) R n vc = 4/3 (pi) R3 (pS-pL) g
pS : the density of the sphere
pL : the density of the liquid
g : acceleration due to gravity
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THEORY
velocity can be set equal to L/t (distance/time) and the equation solved for n as
n = [2 g R2 (pS-pL) t] / 9L
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THEORY
The velocity must be modified for the compression of the fluid by the cylinder walls
vc = v (1 + 2.4x) x is the ratio of sphere diameter to
cylinder diameter
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THEORY
The velocity must also be modified for the finite falling distance by
vc = v (1 + 1.65y ) y is the ratio of sphere diameter to
total liquid height
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THEORY
velocity can now be described as
vc = v (1 + 2.4x) (1 + 1.65y).
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THEORY The new values for vc can now be
substituted into equation
n = [2 g R2 (pS-pL) t] / [9L (1 + 2.4x) (1 + 1.65y)].
Different size particles yield dramatically different settling velocities.
all variables necessary to calculate n can be measured directly except for density, which can be easily calculated from measurements [1].
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Estimated Cost
2m Glass Tube: $10 Plastic Sphere: $0.5(we might use more than one sphere
with different densities depends on the estimated viscosity of the fluid)
Stop Watch: $0
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