Thin Film and Annular Flows — Lesson 2

This lesson covers the concepts of velocity distribution, volume flow rate, and shear stress in fluid dynamics. It delves into the derivation of the ordinary differential equation from the Navier Stokes equations using certain assumptions. The lesson also discusses two problems related to thin film flow and angular flow in cylindrical coordinates. The first problem involves a Newtonian liquid flowing down the outer surface of an infinitely long cylinder, while the second problem deals with annular flow in cylindrical coordinates with the outer cylinder moving at a constant velocity. The lesson concludes with special cases where the film thickness is very small compared to the radius of the cylinder and where the inner cylinder radius is almost close to the outer cylinder radius.

Video Highlights

01:01 - Detailed explanation of the thin film problem, including assumptions, derivation of equations, and calculation of velocity distribution and volume flow rate.
13:19 - Discussion of special cases for the thin film problem, including when the film thickness is very small compared to the radius of the cylinder.
23:42 - Introduction and detailed explanation of the annular flow problem, including assumptions, derivation of equations, and calculation of velocity distribution and volume flow rate.
37:25 - Discussion of special cases for the annular flow problem, including when the inner cylinder radius is close to the outer cylinder radius and when the inner cylinder is removed.

Key Takeaways

- The velocity distribution and volume flow rate can be derived from the Navier Stokes equations using certain assumptions.
- In the case of a Newtonian liquid flowing down an infinitely long cylinder, the circumferential direction velocity is zero and the gradient in that direction of any parameter is zero.
- In the case of annular flow in cylindrical coordinates, the flow is purely shear driven with the outer cylinder moving at a constant velocity.
- Special cases reveal that when the film thickness is very small compared to the radius of the cylinder, the volume flow rate is the same as that of a thin film in a vertical flat plate. When the inner cylinder radius is almost close to the outer cylinder radius, the flow becomes a plane Couette flow.