Unit 4: Pressure Flow

Question 1

What is the difference between distributed losses and local losses?

Answer 1

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

Question 2

What are the variables in the Darcy-Weisbach equation?

Answer 2

λ = friction factor
v = avarage velocity
D = pipe diameter

J = λv^2/2gD

Question 3

How do you estimate the friction factor, λ?

Answer 3

The friction factor is determined differently depending if the flow is laminar, transitional or turbulent

Question 4

How do you assess the flow regime?

Answer 4

You calculate the reynolds number (Re)
Laminar Re ≤ 2000
Transitional 2000 ≤ Re ≤ 4000
Turbulent Re ≥ 4000

Question 5

When do you use Prandtl-von Karman?

3rd equation in the support sheet

Answer 5

Transitional flow in smooth pipes

10^5 < Re ≤ 10^7

Since the relative roughness term is not included in Prandtl-von Karman we know we are dealing with smooth pipes

Question 6

When do you use von Karman?

4th equation in the support sheet

Answer 6

Wholly turbulent flow in Rough pipes

Since (1/Reynalds number) is not included in von-Karman we know that the term is equal to 0. This means that Re is enormous i.e wholly turbulent

Question 7

When do you use Colebrook?

5th equation in the support sheet

Answer 7

Turbulent flow in Rough pipes

Since both reynolds number and relative roughness are present in this equation we know that the flow is turbulent (but not wholly) and that it flows in rough pipes

Question 8

What is relative roughness?

Answer 8

Roughness over the charecteristic length of the geometry

ε/D

Question 9

What is pressure drop?

Answer 9

∆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)

Question 10

What is the moody chart?

Answer 10

It is a way to estimate the friction factor, relative roughness or reynolds number by having information about the other variables.

Question 11

What is the local losses proportional to?

Answer 11

the velocity squared

n V^2/2g

Question 12

What function has a pump?

Answer 12

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

Question 13

Write an expression for the energy that the pump needs to provide to counteract the head loss

Answer 13

∆H = Y + vB^2/2g + J1L1+J2L2

Y is the difference of hight between the free surfaces

Question 14

Write an expression for the power given by the pump to overcome the hydrulic losses

Answer 14

PW = γQ∆H [Watt]

Q = VA is the discharge

Question 15

Write an expression for the power given to the pump to overcome the hydrulic and mechanic losses

Answer 15

PW = γQ∆H/η [Watt]

η = 0,75-0,85 is the efficiency of the pump

Question 16

What function has a turbine?

Answer 16

A turbine turns Flow into energy by taking advantage of head losses

Question 17

Write an expression for the energy that the unit weight of fluid provides to the turbine.

Answer 17

∆H = Y - vB^2/2g - J1L1 - J2L2

Y is the difference of hight between the free surfaces

Question 18

Write an expression for the power given by the flow to the turbine

Answer 18

PT = γQ∆H [Watt]

Q = VA is the discharge

Question 19

Write an expression for the actual usefull power converted.

Answer 19

Pe = ηγQ∆H [Watt]

η ≤ 0,9 is the efficiency of the turbine