Unit F3

Question 1

Give examples of the bounding surfaces internal flows are confined between

Answer 1

1. stationary passageways
   - pipes,ducts, nozzles, diffusers, orifice plates, Venturi’s, capillary viscometers, parallel plates
2. Moving surfaces
   - parallel plates, hydrodynamic slider bearings, dampers(dash pots), rotary viscometers, heart valves
3. Machinery
   - pumps, hydraulic motors, compressors, turbines

Question 2

Explain laminar flow

Answer 2

Is reynolds number is less that 2100( or 2000)

Question 3

Explain turbulent flow

Answer 3

If Reynolds number is greater than 4000

Question 4

Explain the three stages of development in pipe flows

Answer 4

1. Entrance ,
   - flow is uniform
   - flow is inviscid (no viscous effects)
2. Entrance length,
   - growth of boundary layer
   - velocity profile changes with x
   - maximum velocity at centre line increases
3. Fully developed flow
   - boundary layers on opposite surface join each other
   - velocity profile no longer changes with x
   - shape of the fully developed profile depends on where flow is laminar or turbulent

Question 5

What are some assumptions in the Hagen poiseuille flow (of a horizontal pipe )

Answer 5

-Pipe radius is constant
- steady state conditions
- Newtonian fluid
- no slip condition at the wall
-Flow axial symmetry (Ur = Uθ = 0)
- fluid incompressible
- gravity neglected

Question 6

What is Entrainment

Answer 6

When U is sufficiently large, the max velocity may occur at the moving surface. Entrainment is when the moving surface starts to become the predominant driver of the flow