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Gas Dynamics > CH1: Thermodynamics Review > Flashcards

CH1: Thermodynamics Review Flashcards

1
Q

Define a thermodynamic system.

A

A quantity of matter separated from the surroundings by a closed boundary.

Elements of Gas Dynamics, Roshko, Pg. 2

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2
Q

Define thermodynamic “variables of state.”

A

Variables that only depend on the current state of the system. They are independent of the path taken from one state to another.

Elements of Gas Dynamics, Roshko, Pg. 3

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3
Q

State the zeroth law of thermodynamics.

A

Two systems that are in thermal contact (separated by an enclosure that transmits heat) are in equilibrium only if the temperature is the same in both.

Elements of Gas Dynamics, Roshko, Pg. 3

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4
Q

The internal energy of a system (E) is associated with what law of thermodynamics?

A

The first law.

Elements of Gas Dynamics, Roshko, Pg. 3

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5
Q

What is the difference between intensive and extensive properties?

A

Extensive is mass dependent, while intensive is mass independent (or mass normalized).

Elements of Gas Dynamics, Roshko, Pg. 4

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6
Q

By conservation of energy, the difference in the internal energy E for a given state between states A and B must be equal to ______.

A

The sum of the work and the heat.

EB - EA = sum(W + Q)

Elements of Gas Dynamics, Roshko, Pg. 5

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7
Q

How are the signs of Q and W determined?

A

With respect to the surroundings.

Note: Heat Transfer to a system and work done by a system are positive (Cengel, Intro to thermodynamics and HT, Pg 69)

Elements of Gas Dynamics, Roshko, Pg. 5

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8
Q

From the first law of TD, the difference in the internal energy (E) from state 1 to state 2 is the sum of what two variables?

A

The heat (Q) and work (W).

Elements of Gas Dynamics, Roshko, Pg. 5

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9
Q

All natural or spontaneous processes are _____.

A

Irreversible.

Elements of Gas Dynamics, Roshko, Pg. 6

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10
Q

Define the term “current.”

A

The term current refers to the flux of a quantity like heat, mass, momentum, etc.

Elements of Gas Dynamics, Roshko, Pg. 6

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11
Q

A system is in stable equilibrium if it is free of ______.

A

Currents.

Elements of Gas Dynamics, Roshko, Pg. 6

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12
Q

How is equilibrium related to reversible processes?

A

A process leading from one state to another is reversible if the system remains in equilibrium for the entire process.

Note: This requires the work (W) and the heat (Q) to be added in such a way that there are no currents.

Elements of Gas Dynamics, Roshko, Pg. 6

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13
Q

The general definition of a thermally perfect gas is _________.

A

A gas that ignores or neglects the effects of intermolecular forces.

Modern Compressible Flow, Anderson, Pg. 20

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14
Q

The internal energy of a “thermally perfect” gas is a function of what variable(s)?

A

Temperature only. E = f(T).

Note: This is not the same as a calorically perfect gas in which E = cv*T.

Elements of Gas Dynamics, Roshko, Pg. 9

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15
Q

What is the critical temperature?

A

The highest temperature at which a real gas can be liquified.

Elements of Gas Dynamics, Roshko, Pg. 9

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16
Q

True or False
If we know the specific heat (c) for two different processes, we know c for all processes.

A

True.

Elements of Gas Dynamics, Roshko, Pg. 10

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17
Q

What is a calorically perfect gas?

A

A gas that has constant specific heats.

Note: As a consequence, the internal energy per unit mass (e) is a function of temperature multiplied by cv.

Elements of Gas Dynamics, Roshko, Pg. 9

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18
Q

Enthalpy (H) is defined as ________.
Note: Give the actual equation.

A

H = E + pV

where, E = internal energy, p = pressure, and V = volume. Units are Joules.

Elements of Gas Dynamics, Roshko, Pg. 11

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19
Q

What is an adiabatic, reversible process with respect to the system?

A

A process in which no heat is transferred to or from the system and in which the work is done reversibly.

Elements of Gas Dynamics, Roshko, Pg. 13

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20
Q

An adiabatic, reversible process that remains in equilibrium (no currents) for the entire process is often called an _____ process.

A

Isentropic.

Elements of Gas Dynamics, Roshko, Pg. 14

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21
Q

For an isentropic process, entropy (S) remains ______.

A

Constant.

Elements of Gas Dynamics, Roshko, Pg. 14

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22
Q

True or False
Initial and final states have the same temperature in the adiabatic, irreversible expansion of a perfect gas.

A

True

Extra Notes: Read the explanation of the shocktube setup at the start of section 1.8 in the reference and this will make much more sense.

Elements of Gas Dynamics, Roshko, Pg. 15

23
Q

True or False
In adiabatic flow through a resistance, the enthalpy per unit mass (h) upstream is not the same as downstream.

A

False. They are the same for adiabatic flow, the resistance does not matter in this case.

Elements of Gas Dynamics, Roshko, Pg. 16

24
Q

True or False
For any natural, irreversible process, dS < dQ/T.

A

False. dS>dQ/T holds for any natural, irreversible process.

Elements of Gas Dynamics, Roshko, Pg. 20

25
Q

How is the Gibbs free energy (G) defined (give the actual equation)?

A

G = H - TS

Where the units are:
H = Enthalpy := J
T = Absolute Temperature :=K
S = Entropy := J/K

Elements of Gas Dynamics, Roshko, Pg. 21

26
Q

True or False
A system has reached a state of stable equilibrium if no further spontaneous processes are possible.

A

True

Elements of Gas Dynamics, Roshko, Pg. 24

27
Q

In equilibrium, G is at a ________.

A

Minimum.

Elements of Gas Dynamics, Roshko, Pg. 27

28
Q

Which of the following are NOT state variable(s):
1. Volume
2. Temperature
3. Pressure
4. Mass
5. Enthalpy (H)
6. Internal Energy (E)
7. Entropy (S)
8. Work (W)
9. Heat (Q)

A

Work (W) and Heat (Q).

Handout 1

29
Q

What are the SI units for the following state variables:
1. Internal Energy (E)
2. Enthalpy (H)
3. Entropy (S)

A
  1. Joules (J)
  2. Joules( J)
  3. Joules/Kelvin (J/K)
30
Q

In low-speed flows, only the ____ and ________ equations are important.

A

mass (continuity)
momentum

Lecture 1 PP, Slide 3

31
Q

True or False
In low-speed flow, the energy equation is decoupled.

A

True.

Lecture 1 PP, Slide 3

32
Q

In low-speed flows, the enthalpy of the fluid is ________ than the kinetic energy.

A

much greater

Lecture 1 PP, Slide 3

33
Q

In a thermodynamic system, a boundary must be a ____________.

A

Closed surface.

Lecture 1 PP, Slide 3

34
Q

In a thermodynamic system, can heat and work cross a boundary?

A

Yes.

Lecture 1 PP, Slide 3

35
Q

Give the thermodynamic conditions for isentropic flow.

A
  1. Reversible
  2. Adiabatic
  3. In equilibrium (no currents, e.g., no friction, no mass diffusion, etc)

Lecture 1 PP, Slide 3

36
Q

Which law of thermodynamics does the following statement correspond to?

“The heat flowing into a system equals the sum of the change in internal energy plus the work done by the system.”

A

The first law of TD.

Lecture 1 PP, Slide 4

37
Q

Which law of thermodynamics does the following statement correspond to?

“The sum of the heat flowing into a system and the work done by the system is zero.”

A

The first law of TD.

Lecture 1 PP, Slide 4

38
Q

Which law of thermodynamics does the following statement correspond to?

“A system operating in contract with a thermal reservoir cannot produce positive work in its surroundings.”

A

The second law of TD.

Lecture 1 PP, Slide 4

39
Q

Which law of thermodynamics does the following statement correspond to?

“As the temperature goes to zero, the entropy of a system approaches a constant value.”

A

The third law of TD.

Lecture 1 PP, Slide 4

40
Q

With respect to the zeroth, first, and second laws of thermodynamics, what are the state variables that describe the laws?

A

Zeroth: Temperature
1st: Energy
2nd: Entropy

Lecture 1 PP, Slide 9

41
Q

Properties that do not depend on mass are referred to as ____________.

A

Intensive properties.

Lecture 1 PP, Slide 10

42
Q

The energy of a system can only be changed from one equilibrium state to another via the addition/subtraction of _____ & _________.

A

Work and heat.

Lecture 1 PP, Slide 14

43
Q

True or False
Departure from equilibrium results in irreversibility.

A

True.

Lecture 1 PP, Slide 15

44
Q

The specific heats for a __________ are constant.

A

Calorically perfect gas

Lecture 1 PP, Slide 20

45
Q

True or False
For a real gas, the specific heat is process-independent.

A

False. It is process dependant because it depends on temperature at any given state.

Lecture 1 PP, Slide 21

46
Q

What thermodynamic state variable is a qualitative measure of irreversibility?

A

Entropy.

Lecture 1 PP, Slide 25

47
Q

Entropy production depends upon ____________ gradients.

A

Transport

Lecture 1 PP, Slide 32

48
Q

True or False
A system has reached a state of “stable” equilibrium if no further spontaneous processes are possible.

A

True

Lecture 1 PP, Slide 33

49
Q

What phenomena (or “processes”) are not present when a fluid flow is in equilibrium?

A

Diffusion processes (e.g., currents):
> Viscosity
> Thermal conduction
> Mass Diffusion

CH1_more PDF, Slide 6

50
Q

True or False
Enthalpy has meaning only when there is a single molecule under study.

A

False. Enthalpy only has meaning for a group of molecules such as a mole.

CH1_more PDF Slide 7

51
Q

True or False
A single molecule can have internal energy and enthalpy.

A

False. A single molecule can have internal energy but NOT enthalpy.

CH1_more PDF Slide 7

52
Q

Describe the basic idea of the “Law of Mass Action.”

A

The rate of the chemical reaction is directly proportional to the product of the activities or concentrations of the reactants.

CH1_more PDF Slide 9

53
Q

What is the critical point on a PV diagram?

A

It is the point where the liquid, vapor, and supercritical fluid points meet.

CH1_more PDF Slide 10

54
Q

For a simple system, the energy e and the pressure p depend only upon _________ and _________.

A

1/rho, T

Elements of Gas Dynamics, Roshko, Pg. 10

Gas Dynamics (9 decks)

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