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Mechanics > Thermodynamics > Flashcards

Thermodynamics Flashcards

1
Q

Energy is…(two things)

A
  1. When work is done on or by the system
  2. When heat is added to or removed from the system
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2
Q

Define a system

A

A quantity of matter or a region in space chosen for study

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3
Q

Define Surroundings

A

The mass or region outside the system

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4
Q

Define Boundary

A

The real or imaginary surface that separates the system from its surroundings

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5
Q

Can the boundary of a system be fixed or movable?

A

Yes

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6
Q

Systems may be considered to be…(2 things)

A

Close or open

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7
Q

Define Property

A

Any characteristic of a system

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8
Q

Properties are considered to be…(2 things)

A

Intensive or extensive

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9
Q

Define Intensive properties

A

Those that are independent of the mass of a system, such as temperature, pressure, and density

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10
Q

Define extensive properties

A

Those whose values depend on the size - or extent - of the system.

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11
Q

Define specific properties

A

Extensive properties per unit mass

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12
Q

Define Equilibrium

A

A state of balance. In an equilibrium state there are no unbalanced potentials (or driving forces) within the system.

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13
Q

Define thermal equilibrium

A

If the temperature is the same throughout the entire system

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14
Q

Define Mechanical equilibrium

A

If there is no change in pressure at any point of the system with time.

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15
Q

Define Phase equilibrium

A

If a system involves two phases and when the mass of each phase reaches an equilibrium level and stays there.

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16
Q

Define Chemical equilibrium

A

If the chemical composition of a system does not change with time, that is, no chemical reactions occur

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17
Q

Define State postlude

A

The state of a simple compressible system is completely specified by two Independent, intensive properties

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18
Q

Define Simple compressible system

A

If a system involves no electrical, magnetic, gravitational, motion, and surface tension effects

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19
Q

Define Process

A

Any change that a system undergoes from one equilibrium state to another

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20
Q

Define Path

A

The series of states through which a system passes during a process

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21
Q

How do you describe the process completely?

A

Specify the initial and final states, as well as the path it follows, and the interactions with the surroundings

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22
Q

What is a Quasistatic or quasi-equilibrium process

A

When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times.

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23
Q

Define Isothermal process

A

A process during which the temperature T remains constant

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24
Q

Define Isobaric process

A

A process during which the pressure P remains constant

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25
Q

Define Isochoric process

A

A process during which the specific volume v remains constant

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26
Q

Define a cycle

A

A process during which the initial and final states are identical

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27
Q

What is the Zeroth law of Thermodynamics?

A

If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other

Or…

The zeroth law can be restated as two bodies are in thermal equilibrium if both have the same temperature reading even if they are not in contact.

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28
Q

Temperature Scale

Define Ice point : A mixture of ice and water that is in equilibrium with air saturated with vapor at 1 atm pressure (0°C)

Define Steam point: A mixture of liquid water and water vapor (with no air) in equilibrium at 1 atm pressure (100°C)

A
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29
Q

What is a Thermodynamic temperature scale?

A

A temperature scale that is independent of the properties of any substance

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30
Q

Define Absolute pressure

A

The actual pressure at a given position. It is measured relative to absolute vacuum (i.e., absolute zero pressure)

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31
Q

Define Gage pressure

A

The difference between the absolute pressure and the local atmospheric pressure. Most pressure-measuring devices are calibrated to read zero in the atmosphere, and so they indicate gage pressure

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32
Q

Define Vacuum pressures

A

Pressures below atmospheric pressure

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33
Q

Define Macrosopic forms of energy

A

Those a system possesses as a whole with respect to some outside reference frame, such as kinetic and potential energies

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34
Q

Define Microscopic forms of energy

A

Those related to the molecular structure of a system and the degree of the molecular activity

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35
Q

Define Internal engery, U

A

The sum of all the microscopic forms of energy

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36
Q

Define Kinetic energy, KE

A

The energy that a system possesses as a result of its motion relative to some reference frame

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37
Q

Define Potential energy, PE

A

The energy that a system possesses as a result of its elevation in a gravitational field

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38
Q

Define Sensible energy

A

The portion of the internal energy of a system associated with the kinetic energies of the molecules

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39
Q

Define Latent energy

A

The internal energy associated with the phase of a system

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40
Q

Define chemical energy

A

The internal energy associated with the atomic bonds in a molecule

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41
Q

Define Nuclear energy

A

The tremendous amount of energy associated with the strong bonds within the nucleus of the atom itself

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42
Q

Define Heat

A

The form of energy interaction between two systems or a system and its surroundings due to temperature difference

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43
Q

Is this true?

Energy can cross the boundaries of a closed system in the form of heat and work

A

Yes

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44
Q

Define Work

A

The energy transfer associated with a force acting through a distance

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45
Q

Heat transfer to a system and work done by a system are…

  1. Positive?
  2. Negative?
A
  1. Positive
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46
Q

Heat transfer from a system and work done on a system are

  1. Positive?
  2. Negative?
A
  1. Negative
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47
Q

Heat and work are associated with a ____, not a ____

A

Heat and work are associated with a process**, not a **state

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48
Q

Heat or work has no meaning at a ____?

A

State

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49
Q

Heat and work are ____ ____ (define this)

A

Heat and work are path functions (their magnitudes depend on the path followed during a process as well as the end states)

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50
Q

What are the two requirements for a work interaction between a styem and it’s surroundings to exist?

A
  • there must be a force acting on the boundary
  • the boundary must move
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51
Q

Shaft work equation

A
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52
Q

Spring work equation

A
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53
Q

Work done on elastic solid bars equation

A
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54
Q

Work done to raise or to accelerate a body

A

(Main one)

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55
Q

Define Electrial work

A

The generalized force is the voltage (the electrical potential) and the generalized displacement is the electrical charge

(Don’t worry too much about this)

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56
Q

What is the equation for Electrical work

A

(Don’t worry too much about this)

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57
Q

Define Magnetic work

A

The generalized force is the magnetic field strength and the generalized displacement is the total magnetic dipole moment

(Don’t worry too much about this)

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58
Q

Define Electrical polarization work

A

The generalized force is the electric field strength and the generalized displacement is the polarization of the medium

(Don’t worry too much about this)

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59
Q

What is the first law of thermodynamics?

A

Energy can be neither created nor destroyed during a process; it can only change forms.

60
Q

The first law:…

A

For all adiabatic processes between two specified states of a closed system, the net work done is the same regardless of the nature of the closed system and the details of the process.

61
Q

Energry balance?

A
62
Q

Energy change of the system:

A
63
Q

What does efficiency indercate?

A

Indicates how well an energy conversion or transfer process is accomplished.

64
Q

Performance = ?

A

Performance = Desired output / Required input

65
Q

Combustion efficiency? And what is the symbol?

A
66
Q

What is the Mechanical efficiency of an Nmech and an Nmotor

A
67
Q

What is a Pure substance and example?

A

A substance that has a fixed chemical composition throughout

Air is a mixture of several gases, but it is considered to be a pure substance.

68
Q

Define compresses liquid

A

A substance that is not about to vaporize

69
Q

Deinfe saturated liquid

A

A liquid that is about to vaporize

70
Q

Define saturated vapour

A

A vapour that is about to condense

71
Q

Define Saturated liquid–vapour mixture

A

The state at which the liquid and vapour phases coexist in equilibrium

72
Q

Define Superheated vapour

A

A vapour that is not about to condense (i.e., not a saturated vapour)

73
Q

Define Saturation temperature Tsat

A

The temperature at which a pure substance changes phase at a given pressure

74
Q

Define Saturation pressure Psat

A

The pressure at which a pure substance changes phase at a given temperature

75
Q

Define Latent heat

A

The amount of energy absorbed or released during a phase-change process

76
Q

Define Latent heat of fusion

A

The amount of energy absorbed during melting. It is equivalent to the amount of energy released during freezing

77
Q

Define Latent heat of vaporization

A

The amount of energy absorbed during vaporization and it is equivalent to the energy released during condensation

78
Q

Define the critical point in a property diagram

A

The point at which the saturated liquid and saturated vapour states are identical

79
Q

What does a property diagram of a T-v pure substance look like?

A
80
Q

What is Quality, x?

A

The ratio of the mass of vapor to the total mass of the mixture

81
Q

Quality is between _ and _, where 0 is ____ ____, 1 is ____ ____

A

Quality is between 0 and 1, where 0 is sat. liquid, 1 is sat. vapour

82
Q

What is the equation for Enthalpy?

A
83
Q

Define the Equation of state

A

Any equation that relates the pressure, temperature, and specific volume of a substance

84
Q

Pv = ZRT what is Z?

A
85
Q

The farther away Z is from ____, the more the gas deviates from ____-____ ____

A

The farther away Z is from unity, the more the gas deviates from ideal-gas behaviour

86
Q

Gases behave as an ideal gas at…?

A

…low densitites (i.e. low pressure, high temperature)

87
Q

Reduced pressure

PR = ?

A
88
Q

Reduced Temperature

TR = ?

A
89
Q

What is the equation for the ​Pseudo-reduced specific volume

A
90
Q

Define Moving boundary work

A

The expansion and compression work in a pistoncylinder device

91
Q

Wb positive for…?

Wb is negative for…?

A

…expansion

…compression

92
Q

Wb = ?

A

Wb = ∫ P dv

93
Q

What is the Quasi-equilibrium process?

A

A process during which the system remains nearly in equilibrium at all times

94
Q

What is the net work done during a cycle?

A

The net work done during a cycle is the difference between the work done by the system and the work done on the system

95
Q

Area = A = ∫ ? = ∫ ?

A

Area = A = ∫ dA = ∫ P dV

96
Q

The area under the process curve on a P-V diagram represents the…?

A

…boundary work

97
Q

If n = 1 then it’s a…?

A

Isothermal process

98
Q

Heat input and work output are…?

A

…positive

99
Q

Heat output and work input are…?

A

…negative

100
Q

∆U = ?

A

∆U = Q - W

101
Q

What is the E equation for all systems?

A

E = KE + PE + U

102
Q

Define Specific heat at constant volume, cv

A

The energy required to raise the temperature of the unit mass of a substance by one degree as the volume is maintained constant

103
Q

Define Specific heat at constant pressure, cp

A

The energy required to raise the temperature of the unit mass of a substance by one degree as the pressure is maintained constant

104
Q

cv and cp are ______.

cv is related to the changes in ___\_____\__ and cp

to the changes in ______

A

cv and cp are properties.

cv is related to the changes in internal energy and cp

to the changes in enthalpy

105
Q

A common unit for specific heats is…?

A

[kJ/(kg·°C)] or [kJ/(kg·K)].

106
Q

For ideal gases, u, h, cv, and cp vary with ____ only

A

Temperature only

107
Q

At low pressures, all real gases approach…?

A

…ideal-gas behaviour

108
Q

What are the three ways of calculating ∆u and ∆h?

A
  1. By using tabulated u and h data
  2. By using cv or cp relations (from tables) as a functoin of temperature and performing the intergations
  3. By using average specific heats
109
Q

Specific heat ratio for monatomic gases such as helium or argon is….

And for diatomic gases like air is…

A

Monatomic gases = 1.667

Diatomic gases = 1.4 at room temperature

110
Q

Define the conversation of mass

A

Mass cannot be created or destroyed during a process. Mass is conserved even during chemical reactions

111
Q

Define Closed systems

A

The mass of the system remains constant during a process

112
Q

Define control volumes

A

Mass can cross the boundaries, and so we must keep track of the amount of mass entering and leaving the control volume

113
Q

Mass m and energy E can be converted to each other according to…?

A

E = mc2

114
Q

𝑚̇<em>in</em> = ?

A

𝑚̇<em>in </em>= 𝑚̇out

115
Q

What is Flow work or Flow energy?

A

The work (or energy) required to push the mass into or out of the control volume

116
Q

Wflow = ?

A

Wflow​ = Pv

117
Q

Equation for a non-flowing fluid

A
118
Q

Equation for a flowing fluid

A
119
Q

When the kinetic and potential energies of a fluid stream are negligible…(equation)

A

Emass = mh

120
Q

Energy balance equation

A
121
Q

What is a nozzle?

A

A nozzle is a device that increases the velocity of a fluid at the expense of pressure

122
Q

What is a diffuser?

A

A diffuser is a device that increases the pressure of a fluid by slowing it down.

123
Q

The ____-____ ____ of a nozzle ____ in the flow direction for subsonic flows and ____ for supersonic flows. The reverse is true for ____

A

The cross-sectional area of a nozzle decreases in the flow direction for subsonic flows and increases for supersonic flows. The reverse is true for diffusers

124
Q

???

A
125
Q

What is a Turbine?

A

Turbine drives the electric generator in steam, gas, or hydroelectric power plants. As the fluid passes through the turbine, work is done against the blades, which are attached to the shaft. As a result, the shaft rotates, and the turbine produces work.

126
Q

What is a compressor?

A

Compressors, as well as pumps and fans, are devices used to increase the pressure of a fluid. Work is supplied to these devices from an external source through a rotating shaft.

127
Q

What is a pump?

A

Pumps work very much like compressors except that they handle liquids instead of gases.

128
Q

So…?

A
129
Q

What is a Throttling valve?

A

Throttling valves are any kind of flow-restricting devices that cause a significant pressure drop in the fluid

130
Q

The pressure drop in the fluid is often accompanied by a large drop in ____, and for that reason throttling devices are commonly used in ____ __ __-____ ____

A

…temperature, and for that reason throttling devices are commonly used in refrigeration and air-conditioning applications

131
Q

Internal energy + flow energy = ?

A

Internal energy + flow energy = constant

132
Q

During a throttling process, the enthalpy of a fluid remains ____. But internal and flow energies may be ____ to each other.

A

During a throttling process, the enthalpy of a fluid remains constant. But internal and flow energies may be converted to each other.

133
Q

The section where the mixing process takes place is commonly referred to as a…?

A

…mixing chamber

134
Q

What are heat exchangers?

A

Heat exchangers are devices where two moving fluid streams exchange heat without mixing

135
Q

What is the uniform-flow process?

A

Uniform-flow process:

The fluid flow at any inlet or exit is uniform and steady, and thus the fluid properties do not change with time or position over the cross section of an inlet or exit.

If they do, they are averaged and treated as constants for the entire process.

136
Q
A
137
Q

What is an Adiomatic process?

A

When there is no heat transfer

138
Q

Boundary work can…?

A

…move up or down

139
Q

In an Isothermal process, T = ?

A

T = 0

140
Q

In an Isobaric process, P = ?

A

P = constant

141
Q

In an Isobaric process, ____ and ____ goes to ____

A

In an Isobaric process, heat** and **work goes to zero

142
Q

∆u = q - w represents an ____ process

A

∆u = q - w represents an audiobatic process

143
Q

In a turbine, if V1 = __ then there’s no need for ____ ____

A

In a turbine, if V1 = V2 then there’s no need for kinetic** **energy

144
Q

In a turbine, if Z = _ then there’s no need for ____ ____

A

In a turbine, if Z = 0 then there’s no need for potential energy

145
Q

m·h1 = Wout + m·h2 represents a…?

A

…turbine

146
Q

m·h2 = Win + m·h1 represents a…?

A

…compressor

Mechanics (4 decks)

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