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VISCOSITY

VISCOSITY. Matt Matt Amine Nassim. 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. How to measure viscosity.

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VISCOSITY

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  1. VISCOSITY Matt Matt Amine Nassim

  2. 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

  3. How to measureviscosity • There are many ways to measure viscosity • The falling-sphere method is a simple way to study viscosity fluids at varying temperatures

  4. 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 

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. THEORY • velocity can now be described as vc = v (1 + 2.4x) (1 + 1.65y).

  11. 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].

  12. 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

  13. Thank you Don’t forget to vote!

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