Pipe Friction Flashcards
What is the Hagen-Pouseille and the D’arcy friction theories?
Therefore:
- Hagen-Pouseille - Hf = kV (Laminar Flow)
- D’Arcy - Hf = kv2 (Turbulent Flow)
k = Constant
What are the three types of flow?
- Laminar
- Critical
- Turbulent
What is the ideal type of flow and why?
Turbulent - It causes the water to mix constantly during it’s movement through pipe.
At what velocity does the critical zone in fluid flow usually occur?
Between 0.5 and 1 m/s
What is laminar flow?
- When the fluid remains stationary at pipe walls.
- Usually occurs in smooth pipes, although can occur in rough.
- Viscous forces are prominent
- Inertia forces exist but are not prominent.
What is turbulent flow?
- Usually ‘real’ flow
- The rougher the pipe, the more turbulent the flow
- Inertia forces are prominent
- Chaotic mixing of particles
What is the ideal flow velocity in water pipes and why?
2 m/s as it almost always ensures turbulent flow.
What is the Reynolds Number (Re)?
- A way of classifying flow types
- As flow type is dictated by forces acting on fluid then:
- Re = Inertia Forces / Viscous Forces
What is the equation for the Reynold’s Number of a fluid?
What are the Reynold’s Number zones for laminar, critical and turbulent flow?
- Laminar < 2000
- Critical/ transitional = 2000 - 4000
- Turbulent > 4000
What is head loss due to friction dependent on?
- Proportional to Vn
- Proportional to area of contact
- Dependent on fluid viscosity
- Dependent on pipe roughness
- Independent of pressure
What is the equation for the D’Arcy-Weisbach formula?
How do you find the friction factor (lambda) to calulate head loss due to friction?
- Use a moody diagram.
- You need the pipe roughness, diameter and Reynolds number of the flow.
