Pipe Flow

Question 1

True or False
Mass conservation applies only to laminar flows and uniform velocity profiles.

Answer 1

False (Mass conservation is true for all flows and all velocity profiles)

Question 2

What does the energy grade line represent in a fluid flow system?
A) The velocity of the fluid along a streamline
B) The total energy per unit weight of the fluid along a streamline
C) The pressure energy per unit weight of the fluid

Answer 2

B) The total energy per unit weight of the fluid along a streamline

Question 2

How is the head loss due to friction represented in Bernoulli’s equation for real fluids?

Answer 2

The head loss due to friction is parameterised based on force balance and is typically given by h_f = 4𝜏_0L/ρgD, where 𝜏_0 is the shear stress at the pipe wall.

Question 3

True or False
The hydraulic grade line is always above the energy grade line in a flowing fluid.

Answer 3

False (The hydraulic grade line is below the energy grade line because it does not include the velocity head)

Question 4

Which factors influence the friction factor in the context of fluid flow through a pipe?
A) The velocity and pipe diameter only
B) The Reynolds number and the relative roughness
k_s/D
C) The flow rate and the hydraulic grade line

Answer 4

B) The Reynolds number and the relative roughness
k_s/D

Question 5

True or False
In a steady flow analysis, the force balance equation down a pipe includes terms for gravitational forces, pressure forces, and frictional losses.

Answer 5

True

Question 6

How do calculate wetted perimeter?

Answer 6

πD

Question 7

What role does kinematic viscosity play in determining the shear stress at the pipe wall?

Answer 7

Kinematic viscosity, along with fluid speed, pipe diameter, and wall roughness, affects the Reynolds number, which in turn influences the friction factor and thus the shear stress at the pipe wall.

Question 8

True or False
In Nikuradse’s experiments, the friction factor for laminar flow is inversely proportional to the Reynolds number.

Answer 8

True

Question 9

In the context of pipe flow, the equation
f = 64/R_e is applicable for Reynolds numbers less than _______.

Answer 9

2300

Question 10

What does the Moody Diagram represent?
A) The relationship between flow rate and pipe diameter
B) The plot of friction factors for different flow regimes and pipe roughness
C) The calculation method for energy losses in bends and fittings

Answer 10

B) The plot of friction factors for different flow regimes and pipe roughness

Question 11

How does pipe roughness affect the friction factor in turbulent flow according to Nikuradse’s findings?

Answer 11

In turbulent flow, as Reynolds number increases, the friction factor becomes less dependent on it and more influenced by the relative roughness of the pipe, which affects the friction factor significantly at high Reynolds numbers.

Question 12

True or False
The friction factor in turbulent flow is independent of the roughness of the pipe walls.

Answer 12

False (It depends on both the Reynolds number and the relative roughness of the pipe walls)

Question 13

Which method is not typically used to solve for the friction factor f in turbulent flow regimes?
A) Trial and error
B) Newton-Raphson
C) Analytical solutions

Answer 13

C) Analytical solutions (as the equation is implicit in f and generally requires numerical or graphical solutions)

Question 14

True or False
The Colebrook-White equation can directly calculate the friction factor without any iterations or graphical methods.

Answer 14

False (It often requires iterative methods like Newton-Raphson or graphical methods to solve due to its implicit nature)

Question 15

Highly turbulent pipe flows lose energy primarily due to
_________, which is a characteristic of these flow types.

Answer 15

turbulent mixing

Question 16

What does the term ‘viscous forces dominate’ imply in the context of laminar flow?

Answer 16

It implies that in laminar flow conditions, the fluid’s viscosity is the primary resistance against flow movement, leading to a linear relationship between the friction factor and the inverse of the Reynolds number.

Question 17

How do you calculate h_f for pipes?

Answer 17

h_f = fLU^2/D2g

Question 18

What happens when R_e -> ∞?

Answer 18

Value on right of equation becomes 0 leaving relative roughness.

Question 19

What happens to curve when Re is large?

Answer 19

For very large Reynolds numbers each curve flattens out and f is hence independent of Re.