Fluid flow

Question 1

What is the formula for pressure in a fluid column?

Answer 1

height*density*gravity Mass = kg density = rho gravity = 9.81m/s^2

Note that pressure is the same in all directions and is independent of the size of the object on which pressure is being exerted.

t

Question 2

Explain Bernoulli’s’ equation

Answer 2

Bernoulli’s’ equation is about the conversation of energy in fluid flow. It states that as fluid flows into a narrowing pipe the velocity will increase which means that the pressure will decrease. When a fluid flows in an expanding pipe the opposite happens.

Question 4

What does mu μ symbolise in fluid dynamics

Answer 4

Viscocity

Question 5

What does V symbolise in fluid dynamics

Answer 5

Relative velocity

Question 6

Explain viscocity

Answer 6

Viscocity is a measure of a fluids resistance to deformation. The symbol is μ and it is measured in (kg/ms). This is a result of the friction between the different layers.

Question 7

Explain Stokes law

Answer 7

Stokes law calculates the drag on an object as it travels through a fluid.

F_D = 6πRμV

F_D = Drag force on the sphere

R= radius of the sphere

μ = viscocity of the fluid

V = relative velocity of the sphere

Question 8

What is the relationship between viscocity and the reynolds nubmer

Answer 8

Reynolds number = inertia force/ (viscouse force)

Question 9

Explain terminal velocity in a sphere.

Answer 9

Terminal velocity is the balance between the acceleration of gravity and the countering forces. The primary oppositional force is drag followed by buoyancy.

For a sphere this is

(Sphere Density-Fluid density)*(Sphere Volume)*(Gravity)

6πR*fluid viscosity

((ρ_s-ρ_f)*(4/3πR³)*(9.81))

(6πR_sμ)

Question 11

Explain Pouseuille’s equation for pressure drop in a

Answer 11

Note this applies for laminar flow of viscous fluid in a straight pipe only

Pressure drop = 32*viscocity*length*average velocity

Diameter²

ΔP = (32*μL)*V(Bar)/D²

Question 12

Explain the fanning friction factor

Answer 12

This is a dimensionless number that relates to the fluid flow in a pipe.

In a round pipe it is taken to be 16/Reynolds number.

This can also be calculated as 16μ/ρVD

Question 13

What is the hydrolic dyameter

Answer 13

It is a metric for creating an equivalent round diameter pipes for non round pipes. It is calculated from 4A/P

P is wetted perimeter.

Question 14

Explain the velocity pressure equation.

Answer 14

4*Friction*Length*density*average velocity squared

2 * diameter

4fLρV²/2D

Question 15

Explain the velocity profile in laminar fluid flow

Answer 15

Velocity is slower and the boundary of fluid flow than the centre of fluid flow. The difference is called the boundary profile.