Thermofluids

Question 1

What is the second law of thermodynamics?

Answer 1

The total entropy of an isolated system can only increase with time. “You never get out what you put in”

Question 2

What is the first law of thermodynamics?

Answer 2

/\U=Q-W

Where U is the internal energy, Q is the heat supplied to the system and W is the work done BY the system

Question 3

What type of process does a throttle valve represent?

Answer 3

An ISENTHALPIC one.

Question 4

Define isentropic.

Answer 4

No change in entropy. This is ideal.

Question 5

Define viscosity.

Answer 5

Viscosity is a quantity expressing the magnitude of internal friction in a fluid, as measured by the force per unit area resisting uniform flow

Question 6

What is the specific volume of a substance?

Answer 6

It is the ratio of a substances volume to it’s mass. Measured in m^3/kg

Question 7

What is absolute pressure?

Answer 7

Absolute pressure is a comparison between your measured pressure and a vacuum.

Question 8

What is gauge pressure?

Answer 8

Gauge pressure is a comparison between your pressure and a reference pressure (such as that of the atmosphere).

Question 9

Name 3 properties of an ideal gas

Answer 9

• Particles are treated as point-masses
• Particles collide elastically with the walls of the container
• Particles may pass through each other. They contain no attractive potential energy

Question 10

What is the purpose of a U-tub manometer?

Answer 10

To measure the difference between two unknown pressures.

Question 11

What is Bernoulli’s Equation?

Answer 11

P + pgh + (pC*C)/2 = constant(k)

Question 12

When does cavitation occur?

Answer 12

When the pressure of the fluid is below the saturated-vapour pressure, cavitation (vapour bubbles) occurs.

Question 13

What is the critical Reynolds number?

Answer 13

2000

Question 14

What is incompressible flow?

Answer 14

When the density of a fluid remains constant as it goes through fluid flow.

Question 15

Define inviscid flow.

Answer 15

A flow where viscous effects do not significantly influence the flow and are this neglected.

Question 16

What is a Newtonian fluid?

Answer 16

A fluid with a constant viscosity.

Question 17

What does HCP mean? What is the stacking sequence?

Answer 17

Hexagonal closed packed.

Stacking sequence is ABABABAB

Question 18

What is atomic packing fraction?

Answer 18

APF=((Number of particles)*(Particle Volume))/(Unit Cell Volume)

Question 19

How many atoms in a bcc and fcc cubic?

Answer 19

fcc cubic = 4 atoms per unit cell

bcc cubic = 2 atoms per unit cell

Question 20

What is ionic bonding?

Answer 20

Electrostatic attraction arising from an exchange of electrons to form +ve and -ve species

Question 21

What is metallic bonding?

Answer 21

+ve ions in a sea of -ve bonding electrons

Question 22

What is covalent bonding?

Answer 22

Bonding electrons shared between two atoms

Question 23

What is the equation for bond stiffness?

Answer 23

S=Ea.

a. is the interatomic distances

Question 24

What is the equation for Poisson’s Ratio?

Answer 24

v=(transverse strain)/(longitudinal strain)

Question 25

What is the FCC stacking sequence?

Answer 25

ABCABCABC

Question 26

80 Hb 12/1427/30 Explain this

Answer 26

``` 80 is the hardness Hb is the type of test 12 is the ball diameter 1427 is the load in kgfmm^-2 30 is the load duration in seconds ```

Question 27

How many Newtons in 1kgf?

Answer 27

9.81 Newtons =1kgf

Question 28

What is stress intensity factor (k)? | What is the formula?

Answer 28

The stress intensity factor (K) is used in the field of fracture mechanics. It predicts stress intensity near the tip of a crack caused by a remote load or residual stresses. Let ó=stress K=Yó(pi*a)^0.5 a is the crack size Y is the geometry factor (calculated)

Question 29

Name the four processes in the Carnot cycle.

Answer 29

Isothermal Expansion 》Isentropic Expansion 》Isothermal Compression 》Isentropic Compression

Question 30

Define adiabatic.

Answer 30

Relating to or denoting a process or condition in which heat does not enter or leave the system concerned. "the adiabatic expansion of a perfect gas"

Question 31

Define Toughness.

Answer 31

A measure of a materials ability to deform plastically without fracturing, as measured by the energy under the stress strain curve

Question 32

Strength - define it

Answer 32

The measure of a materials resistance to plastic deformation

Question 33

What are the four types of "impurities" that mean a material can never really reach its theoretical strength?

Answer 33

- Vacancy - Interstitial Atom - Interstitial Impurity Atom - Substitutional Impurity Atom

Question 34

What is theoretical strength approximately equal to?

Answer 34

E/3

Question 35

Define stiffness?

Answer 35

The resistance of a material to deformation under an applied force

Question 36

Define stiffness?

Answer 36

The resistance of a material to deformation under an applied force

Question 37

What does the Frenkel Model represent?

Answer 37

The frenkel model predicts the critical shear stress of two closed packed planes sliding over each other.

Question 38

Why is the Frenkel Model too simplistic?

Answer 38

It predicts that the stress can only vary sinusoidally. It doesn't consider a linear defect separating slipped from unslipped regions. No consideration is given to dislocations.

Question 39

What are the three main primary bonds? How do they relate to a material's stiffness?

Answer 39

Covalent - Highest bond stiffness Metallic - Medium bond stiffness Ionic - Lower bond stiffness

Question 40

What is a covalent bond?

Answer 40

Pairs of electrons are shared by two adjacent atoms.

Question 41

What is a metallic bond?

Answer 41

The sharing of free electrons in a lattice of positively charged ions.

Question 42

What is ionic bonding?

Answer 42

The bond formed by electrostatic attraction between positively and negatively charged species. Electrons are shared because sharing is caring.

Question 43

What happens to a shear thinning fluid as a shear stress is applied.

Answer 43

It becomes LESS viscous.

Question 44

What is a saturated liquid?

Answer 44

A liquid that is on the verge of boiling.

Question 45

What is a compressed liquid?

Answer 45

A stable liquid that is either at a lower temperature or a higher pressure than a saturated liquid.

Question 46

What is a saturated vapour?

Answer 46

A vapour that is on the verge of condensing.

Question 47

What is a superheated vapour?

Answer 47

A stable vapour that is either at a lower pressure or higher temperature than a saturated vapour.

Question 48

Why does the Carnot cycle have the maximum possible efficiency?

Answer 48

- The rectangle has the maximum possible area for the given temperatures. - The isentropic processes are impossible to engineer in real life - All of the heat is added at the maximum temperature

Question 49

For the Carnot cycle, what is the compressor/turbine order?

Answer 49

- Isothermal Turbine - Isentropic Turbine - Isothermal Compressor - Isentropic Compressor

Question 50

For an ISENTROPIC feed pump. How do you calculate the change in enthalpy?

Answer 50

dh=v(p2-p1)

Question 51

True or false, for your true stress strain curve. Your true stress strain equals n (your power).

Answer 51

TRUE

Question 52

What is the equation for Bulk Modulus.

Answer 52

B=E/3(1-2v)