Answer to Question #236220 in Chemical Engineering for AMIT

Question

Velocity profile of a liquid is shown below:

                                                

If the shear stress per unit surface area on the rigid plate over which the liquid flows is measured to be 0.083 N/m².

1.    Calculate the viscosity of the liquid .

2.    What is the maximum velocity at the free surface if the plate is tilted by an angle of 60^o to the horizontal plane and the liquid is allowed to down freely keeping the same film thickness? There is no pressure gradient in the direction of flow. Density of the liquid is 887 kg/m³.

Answer 1

1) The greater the viscosity, the greater the force required. These dependencies are combined into the equation

$F = η v/ A L$

which gives us a working definition of fluid viscosityη. Solving for η gives

$η = F L/ v A$

2.) which defines viscosity in terms of how it is measured. The SI unit of viscosity is $N⋅m/[(m/s)m2] = (N/m2)s$ or Pa⋅s. lists the coefficients of viscosity for various fluids.

Viscosity varies from one fluid to another by several orders of magnitude. As you might expect, the viscosities of gases are much less than those of liquids, and these viscosities are often temperature dependent. The viscosity of blood can be reduced by aspirin consumption, allowing it to flow more easily around the body. (When used over the long term in low doses, aspirin can help prevent heart attacks, and reduce the risk of blood clotting.)