Chapter 7

Question 1

Define a perfect gas.

Answer 1

A gas in which the intermolecular forces are neglected.

Question 2

The energy of a given molecule is the sum of what?

Answer 2

It’s transnational, rotational, vibrational, and electronic energies.

Question 3

The sum of the energies of all the molecules in a given volume of gas is defined as the ____.

Answer 3

Internal energy of the gas.

Question 4

The internal energy per unit mass is defined by what variable?

Answer 4

Entropy – e

Question 5

For a perfect gas, both e and h are functions of ____. only.

Answer 5

Temperature

Question 6

When temperatures are below _____K the specific heats are usually ____.

Answer 6

1000K

constant.

Question 7

What is a “Calorically Perfect” gas?

Answer 7

As gas in which the two specific heats (cp and cv) are constant.

Question 8

Define an Adiabatic Process.

Answer 8

One in which no heat is added to or taken away from the system.

Question 9

Define a Reversible Process.

Answer 9

One in which no dissipative phenomena occur, this is, where the effects of viscosity, thermal conductivity, and mass diffusion are absent.

Question 10

Defin Isentropic process.

Answer 10

One that is both adiabatic and reversible.

Question 11

What are the three main dissipative phenomena?

Answer 11

1. Viscosity
2. Thermal Conductivity
3. Mass diffusion

Question 12

Explain why many practical flows can be modeled as isentropic?

Answer 12

The viscous boundary layer adjacent to the surface is thin compared with the entire flow field, and hence large regions of the flow can be assumed isentropic.

Question 13

Entropy is a function of what two variables?

Answer 13

Temperature and pressure.

Question 14

True or False

Entropy increases with increasing temperature.

Answer 14

True.

Question 15

True or False

Entropy decreases with increasing temperature.

Answer 15

False, it decreases with decreasing temperature.

Question 16

How does pressure affect entropy?

Answer 16

As pressure increases, entropy decreases and VV.

Question 17

Incompressible flows obey ____ laws.

Answer 17

Mechanical Laws

Question 18

What are the primary dependant variables for compressible flow?

Answer 18

p, V, rho, e, and T

Question 19

Is Bernoulli’s equation valid for compressible flow?

Answer 19

No

Question 20

What is static pressure?

Answer 20

The measure of the purely random motion of molecules in a gas.

Question 21

What is stagnation pressure?

Answer 21

The pressure existing at a point (or points) in the flow where V=0.

Question 22

What is the total temperature?

Note: Define it conceptually

Answer 22

If a fluid element is adiabatically slowed to zero velocity the temperature of the fluid element will change. At the point of zero velocity, the temp of the fluid element is the total temperature.

Question 23

What is total enthalpy?

Note: Define it conceptually

Answer 23

If a fluid element is adiabatically slowed to zero velocity the temperature of the fluid element will change. At the point of zero velocity, the temp of the fluid element is the total temperature. The total enthalpy is the total temperature multiplied by cp.

Question 24

True or False

Total enthalpy is constant along a streamline.

Answer 24

True

Question 25

Total pressure and total density are related to what process?

Answer 25

An Isentropic process/flow.

Question 26

Conceptually define specific heat.

Answer 26

The energy required to raise the temperature of a unit mass of a substance by one unit degree. TD Textbook

Question 27

What is the difference between cp and cv?

Answer 27

cv represents the energy required to raise the temperature of the unit mass of a substance by one degree as the volume is maintained constant. The energy required to do the same thing as the pressure is maintained constant is the specific heat at a constant pressure (cp). TD Textbook

Question 28

How are the magnitudes of cp and cv related?

Answer 28

cp > cv

Question 29

True or False The specific heat at a constant volume (cv) is related to the changes in internal energy, and the specific heat at constant pressure (cp) to the changes in enthalpy.

Answer 29

True TD Textbook

Question 30

What is the variable cv named?

Answer 30

Specific heat at a constant volume.

Question 31

What is the variable cp named?

Answer 31

Specific heat at a constant pressure.

Question 32

What is a shockwave?

Answer 32

A shock wave is an extremely thin region, typically on the order of 10^−5 cm, across which the flow properties can change drastically.

Question 33

True or False | Flow across a shockwave is adiabatic.

Answer 33

True

Question 34

The pressure, density, temperature, and entropy_____ across a shockwave.

Answer 34

Increase

Question 35

Mach number and velocity ____ across a shockwave.

Answer 35

Decrease

Question 36

True or False | Subsonic flows have a smoothly varying streamline pattern.

Answer 36

True

Question 37

True or False In subsonic flow, the streamline far ahead of the body is forewarned about the presence of the body and begins to adjust accordingly.

Answer 37

True.

Question 38

True or False In supersonic flows, the flow upstream of the body does not know about the presence of the body until it encounters the leading edge shockwave.

Answer 38

True

Question 39

True or False | Shockwaves are usually at normal angles to the flow.

Answer 39

False, they are usually at oblique angles to the flow.

Question 40

Shockwaves can be considered as an ______ process.

Answer 40

Explosive decompression.

Question 41

True or False | Total entropy is constant across a shockwave.

Answer 41

True

Question 42

Flow ahead of a shockwave (in both the normal and oblique case) must be _____.

Answer 42

Supersonic (M>1).

Question 43

True or False | In some cases behind an oblique shockwave, the flow can be sufficiently decelerated such that the flow is subsonic.

Answer 43

True

Question 44

For normal shockwaves, the downstream flow is always _____.

Answer 44

Subsonic.

Question 45

When a fluid is not flowing, it is at Stagnation State and its thermodynamic properties are _____.

Answer 45

Stagnation Properties.

Question 46

Describe a stagnation reference state.

Answer 46

For a flowing fluid, A "Stagnation State" is defined as a reference estate that would exist if the fluid were decelerated to zero speed and zero potential.

Question 47

To obtain a unique stagnation state, the deceleration process must be ______.

Answer 47

Adiabatic and reversible = "isentropic."

Question 48

What instrument is usually employed to measure total temperature and total pressure?

Answer 48

A pitot-tube.

Question 49

When a fluid is not flowing, its thermodynamic properties are _______.

Answer 49

Stagnation or total properties.

Question 50

What is a stagnation reference state?

Answer 50

A reference state that would exist if the fluid were decelerated to zero speed and zero potential.

Question 51

To obtain a unique stagnation state, the deceleration process must be ____ and _____.

Answer 51

Adiabatic and reversible.

Question 52

True or False | A process does not have to be reversible for Stagnation Enthalpy and Stagnation Temperature.

Answer 52

True

Question 53

True or False

Answer 53

Total Enthalpy and Total temperature are constant for steady and adiabatic flow.

Question 54

For non-adiabatic flow, the temperature and Enthalpy are ____ constant.

Answer 54

Not

Question 55

Irreverstibilites cause entropy to _____ and total pressure to _____.

Answer 55

Increase | Decrease