Lecture 4 - Pressure flow Flashcards
Describe bernoulli equation
The total head of a perfect incompressible fluid in steady flow conditions is constant along its paths.
Se bilder
Describe the different terms in the bernoulli equation
What is the difference between distributed losses and local losses?
**Distributed head losses **are due to friction and are effected by the length of the pipe.
Local head losses are due to unsteady flow conditions and are effected by connections and changes in the pipes
What are the variables in the Darcy-Weisbach equation?
λ = friction factor
v = avarage velocity
D = pipe diameter
J = λv^2/2gD
How do you estimate the friction factor, λ?
The friction factor is determined differently depending if the flow is laminar, transitional or turbulent
How do you assess the flow regime?
You calculate the reynolds number (Re)
Laminar Re ≤ 2000
Transitional 2000 ≤ Re ≤ 4000
Turbulent Re ≥ 4000
What is relative roughness?
Roughness over the charecteristic length of the geometry
ε/D
What is pressure drop?
∆P/γ = ∆H
Happens in a horizontal pipe with steady velocity. The only thing that can change is the pressure head wich would drop in real fluids. (bernoullis equation)
What is the moody chart?
It is a way to estimate the friction factor, relative roughness or reynolds number by having information about the other variables.
What is the local losses proportional to?
the velocity squared
n V^2/2g
What function has a pump?
A pump controls the flow by working on the flowing fluid by discharging the fluid to a higher head at its discharge flange than is found at the pump inlet
pumps energy to the flow
Write an expression for the energy that the pump needs to provide to counteract the head loss
∆H = Y + vB^2/2g + J1L1+J2L2
Y is the difference of hight between the free surfaces
Write an expression for the power given by the pump to overcome the hydrulic losses
PW = γQ∆H [Watt]
Q = VA is the discharge
Write an expression for the power given to the pump to overcome the hydrulic and mechanic losses
PW = γQ∆H/η [Watt]
η = 0,75-0,85 is the efficiency of the pump
What function has a turbine?
A turbine turns Flow into energy by taking advantage of head losses
