S2: Fluids

Question 1

What’s the first law of thermodynamics?

Answer 1

Change in energy of a system is equal to the difference between energy input and energy output

Delta Esys= Wnet in + Qnet in

Question 2

What is the net work done in terms of energy?

Answer 2

Mech energy transfers in/out is net work done

Question 3

What’s net heat added in terms of energy transfers

Answer 3

Thermal energy in/our is net heat added

Question 4

What are the 3 forms of fluid energy?

Answer 4

Internal, kinetic, potential

Question 5

Define specific energy

Answer 5

Fluid energy per unit mass

Question 6

What are the 4 forms of work?

Answer 6

Shaft work, pressure work, viscous work, other work

Question 7

What’s shaft power and it’s equation?

Answer 7

•
Wshaft = wTshaft = 2pie
•
x n x Tshaft

Question 8

What’s the equation for work done by pressure forces

Answer 8

SWpressure = Pd9 = PAds

Question 9

What’s the equation for rate of pressure work

Answer 9

•

Wpressure = PA ds/dt = PAV

Question 10

For steady flow what’s the equation for mass flow rate?

Answer 10

•

m= row1A1V1 = row2A2V2

Question 11

Where is the kinetic energy correction factor used?

What’re the values for laminar and turbulent flow?

Answer 11

When there’s incompressible flow with none uniform velocity at 1 and 2

L= 2
T= 1.04-1.10

Question 12

How does fluid flow in an open channel?

Answer 12

Fluid flows under gravity

Question 13

How does fluid flow in a closed pipe?

Answer 13

Pressure difference drives flow

Question 14

What shaped pipes withstand highest internal pressure?

Answer 14

Circular

Question 15

What are the 2 types of viscous flow?

Answer 15

Turbulent and laminar

Question 16

Which type of flow (turbulent / laminar) has the sharpest nose?

Answer 16

Laminar

Turbulent is almost flat

Question 17

For steady state flow, what is shear force proportional to?

Answer 17

Shear rate

Mue u/y

Shear force = Mue dux/dy

Question 18

When does Newton’s law of viscosity (shear force proportional to shear rate) not apply and apply?

Answer 18

Applies- Newtonian fluids (gas, water, petrol)

Doesn’t- non Newtonian fluids (toothpaste, painting, marmalade, polymers)

Question 19

What’s the diff between laminar and turbulent flow?

Answer 19

Laminar- flows in layers

Turbulent- layers mix at macroscopic level

Question 20

What are the 4 factors that affect the type of fluid flow?

Answer 20

Velocity
Density
Kinematic viscosity
Diameter (geometry)

Question 21

What values should be given to Reynolds number for each flow type?

Answer 21

<2000 laminar

2000-4000 transition flow

> 4000 turbulent flow

Question 22

What equation describes how long a fluid will take to reach full flow?

Answer 22

Le/D = 0.06 Re laminar

Le/D = 4.4 Re ^1/6 turbulent

Question 23

In pipes, what does the friction force depend on?

Answer 23

Solid characteristics

• geometry, size : D
• particle toughness : K (increases as pipe ages)

Fluid characteristics

• density
• viscosity

Relative velocity
-solid vs liquid v

Question 24

What’s the equation for relative toughness?

Answer 24

K/D