An annular flow for an incompressible Newtonian fluid occurs in the co-axial cylindrical annulus region between two coaxial cylinders of radius r1 and r2. The inner pipe is pulled to the right side with a linear velocity (V). Pressure drop (P) in the pipe is negligible. Considering the cylindrical coordinates given in the figure;

a.Show differential volume element on the figure, write down a differential momentum balance equation and the necessary boundary conditions for the solution.

b. Obtain the expressions for the momentum flux and the velocity distribution.