Thermodynamics Flashcards
(146 cards)
1
Q
Energy is…(two things)
A
- When work is done on or by the system
- When heat is added to or removed from the system
2
Q
Define a system
A
A quantity of matter or a region in space chosen for study
3
Q
Define Surroundings
A
The mass or region outside the system
4
Q
Define Boundary
A
The real or imaginary surface that separates the system from its surroundings
5
Q
Can the boundary of a system be fixed or movable?
A
Yes
6
Q
Systems may be considered to be…(2 things)
A
Close or open
7
Q
Define Property
A
Any characteristic of a system
8
Q
Properties are considered to be…(2 things)
A
Intensive or extensive
9
Q
Define Intensive properties
A
Those that are independent of the mass of a system, such as temperature, pressure, and density
10
Q
Define extensive properties
A
Those whose values depend on the size - or extent - of the system.
11
Q
Define specific properties
A
Extensive properties per unit mass
12
Q
Define Equilibrium
A
A state of balance. In an equilibrium state there are no unbalanced potentials (or driving forces) within the system.
13
Q
Define thermal equilibrium
A
If the temperature is the same throughout the entire system
14
Q
Define Mechanical equilibrium
A
If there is no change in pressure at any point of the system with time.
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.
16
Q
Define Chemical equilibrium
A
If the chemical composition of a system does not change with time, that is, no chemical reactions occur
17
Q
Define State postlude
A
The state of a simple compressible system is completely specified by two Independent, intensive properties
18
Q
Define Simple compressible system
A
If a system involves no electrical, magnetic, gravitational, motion, and surface tension effects
19
Q
Define Process
A
Any change that a system undergoes from one equilibrium state to another
20
Q
Define Path
A
The series of states through which a system passes during a process
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
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.
23
Q
Define Isothermal process
A
A process during which the temperature T remains constant
24
Q
Define Isobaric process
A
A process during which the pressure P remains constant
25
Define **Isochoric process**
A process during which the specific volume v remains constant
26
Define a **cycle**
A process during which the initial and final states are identical
27
What is the **Zeroth law of Thermodynamics**?
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.
28
**_Temperature Scale_**
## Footnote
**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)
29
What is a **Thermodynamic temperature scale?**
A temperature scale that is independent of the properties of any substance
30
Define **Absolute pressure**
The actual pressure at a given position. It is measured relative to absolute vacuum (i.e., absolute zero pressure)
31
Define **Gage pressure**
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
32
Define **Vacuum pressures**
Pressures below atmospheric pressure
33
Define **Macrosopic forms of energy**
Those a system possesses as a whole with respect to some outside reference frame, such as kinetic and potential energies
34
Define **Microscopic forms of energy**
Those related to the molecular structure of a system and the degree of the molecular activity
35
Define **Internal engery, U**
The sum of all the microscopic forms of energy
36
Define **Kinetic energy, KE**
The energy that a system possesses as a result of its motion relative to some reference frame
37
Define **Potential energy, PE**
The energy that a system possesses as a result of its elevation in a gravitational field
38
Define **Sensible energy**
The portion of the internal energy of a system associated with the kinetic energies of the molecules
39
Define **Latent energy**
The internal energy associated with the phase of a system
40
Define **chemical energy**
The internal energy associated with the atomic bonds in a molecule
41
Define **Nuclear energy**
The tremendous amount of energy associated with the strong bonds within the nucleus of the atom itself
42
Define **Heat**
The form of energy interaction between two systems or a system and its surroundings due to temperature difference
43
Is this true?
## Footnote
**Energy can cross the boundaries of a closed system in the form of heat and work**
Yes
44
Define **Work**
The energy transfer associated with a force acting through a distance
45
**Heat** transfer **to** a system and **work done by** a system are...
1. Positive?
2. Negative?
1. Positive
46
**Heat** transfer **from** a system and **work done on** a system are
1. Positive?
2. Negative?
2. Negative
47
**Heat** and **work** are associated with a \_\_\_\_, not a \_\_\_\_
**Heat** and **work** are associated with a **_process**_, not a _**state_**
48
**Heat** or **work** has no meaning at a \_\_\_\_?
State
49
**Heat** and **work** are ____ \_\_\_\_ (define this)
**Heat** and **work** are **_path functions_** (their magnitudes depend on the path followed during a process as well as the end states)
50
What are the two requirements for a work interaction between a styem and it's surroundings to exist?
- there must be a force acting on the boundary
- the boundary must move
51
**Shaft work** equation
52
**Spring work** equation
53
**Work done on elastic solid bars** equation
54
**Work done to raise or to accelerate a body**
(Main one)
55
Define **Electrial work**
The generalized force is the voltage (the electrical potential) and the generalized displacement is the electrical charge
(Don't worry too much about this)
56
What is the equation for **Electrical work**
(Don't worry too much about this)
57
Define **Magnetic work**
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)
58
Define **Electrical polarization work**
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)
59
What is the **first law of thermodynamics?**
Energy can be neither created nor destroyed during a process; it can only change forms.
60
**The first law:**...
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
Energry balance?
62
**Energy change** of the system:
63
What does **efficiency** indercate?
Indicates how well an energy conversion or transfer process is accomplished.
64
Performance = ?
Performance = Desired output / Required input
65
Combustion efficiency? And what is the symbol?
66
What is the **Mechanical efficiency** of an Nmech and an Nmotor
67
What is a **Pure substance** and example?
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
Define **compresses liquid**
A substance that is not about to vaporize
69
Deinfe **saturated liquid**
A liquid that is about to vaporize
70
Define **saturated vapour**
A vapour that is about to condense
71
Define **Saturated liquid–vapour mixture**
The state at which the liquid and vapour phases coexist in equilibrium
72
Define **Superheated vapour**
A vapour that is not about to condense (i.e., not a saturated vapour)
73
Define **Saturation temperature Tsat**
The temperature at which a pure substance changes phase at a given pressure
74
Define **Saturation pressure Psat **
The pressure at which a pure substance changes phase at a given temperature
75
Define **Latent heat**
The amount of energy absorbed or released during a phase-change process
76
Define **Latent heat of fusion**
The amount of energy absorbed during melting. It is equivalent to the amount of energy released during freezing
77
Define **Latent heat of vaporization**
The amount of energy absorbed during vaporization and it is equivalent to the energy released during condensation
78
Define the **critical point** in a property diagram
The point at which the saturated liquid and saturated vapour states are identical
79
What does a property diagram of a T-v pure substance look like?
80
What is **Quality, x**?
The ratio of the mass of vapor to the total mass of the mixture
81
Quality is between _ and \_, where 0 is ____ \_\_\_\_, 1 is ____ \_\_\_\_
Quality is between **_0_** and **_1_**, where 0 is **_sat. liquid_**, 1 is **_sat. vapour_**
82
What is the equation for Enthalpy?
83
Define the **Equation of state**
Any equation that relates the pressure, temperature, and specific volume of a substance
84
Pv = ZRT what is Z?
85
The farther away Z is from \_\_\_\_, the more the gas deviates from \_\_\_\_-\_\_\_\_ \_\_\_\_
The farther away Z is from **_unity_**, the more the gas deviates from **_ideal-gas behaviour_**
86
Gases behave as an ideal gas at...?
...low densitites (i.e. low pressure, high temperature)
87
Reduced pressure
PR = ?
88
Reduced Temperature
TR = ?
89
What is the equation for the **Pseudo-reduced specific volume**
90
Define **Moving boundary work**
The expansion and compression work in a pistoncylinder device
91
Wb **positive** for...?
Wb is **negative** for...?
...expansion
...compression
92
Wb = ?
Wb = ∫ P dv
93
What is the **Quasi-equilibrium process**?
A process during which the system remains nearly in **equilibrium at all times**
94
What is the **net work done during a cycle**?
**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
Area = A = ∫ ? = ∫ ?
Area = A = ∫ dA = ∫ P dV
96
The area under the process curve on a P-V diagram represents the...?
...boundary work
97
If n = 1 then it's a...?
Isothermal process
98
**Heat input** and **work output** are...?
...**positive**
99
**Heat output** and **work input** are...?
...**negative**
100
∆U = ?
∆U = Q - W
101
What is the E equation for all systems?
E = KE + PE + U
102
Define **Specific heat at constant volume, cv**
The energy required to raise the temperature of the unit mass of a substance by one degree as the volume is maintained constant
103
Define **Specific heat at constant pressure, cp**
The energy required to raise the temperature of the unit mass of a substance by one degree as the pressure is maintained constant
104
cv and cp are _**\_\_\_\_**_.
cv is related to the changes in **_\_\_\_\___\_\_\_\__** and cp
to the changes in _**\_\_\_\_**_
cv and cp are **_properties_**.
cv is related to the changes in **_internal_ _energy_** and cp
to the changes in **_enthalpy_**
105
A common unit for specific heats is...?
[kJ/(kg·°C)] or [kJ/(kg·K)].
106
For ideal gases, u, h, cv, and cp vary with ____ only
**_Temperature_** only
107
At low pressures, all real gases approach...?
...ideal-gas behaviour
108
What are the three ways of calculating ∆u and ∆h?
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
Specific heat ratio for monatomic gases such as helium or argon is....
And for diatomic gases like air is...
Monatomic gases = 1.667
Diatomic gases = 1.4 at room temperature
110
Define the **conversation of mass**
Mass cannot be created or destroyed during a process. Mass is conserved even during chemical reactions
111
Define **Closed systems**
The **mass** of the system remains **constant** during a process
112
Define **control volumes**
**Mass** **can** **cross** the **boundaries**, and so we must keep track of the amount of mass entering and leaving the control volume
113
Mass m and energy E can be converted to each other according to...?
*E = mc2*
114
𝑚̇in = ?
𝑚̇in = 𝑚̇*out*
115
What is **Flow work** or **Flow energy**?
The work (or energy) required to **push** the **mass** **into** or **out** of the **control volume**
116
Wflow = ?
*Wflow* = *Pv*
117
Equation for a **non-flowing fluid**
118
Equation for a **flowing fluid**
119
When the **kinetic** and **potential** **energies** of a **fluid** **stream** are **negligible**...(equation)
Emass = mh
120
Energy balance equation
121
What is a **nozzle**?
A **nozzle** is a device that **increases** the **velocity** of a **fluid** at the **expense** of **pressure**
122
What is a **diffuser**?
A **diffuser** is a device that **increases** the **pressure** of a **fluid** by **slowing** it **down**.
123
The \_\_\_\_-\_\_\_\_ ____ of a nozzle ____ in the flow direction for subsonic flows and ____ for supersonic flows. The reverse is true for \_\_\_\_
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
???
125
What is a **Turbine**?
**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
What is a **compressor**?
**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
What is a **pump**?
**Pumps** work very much like **compressors** except that they handle **liquids** **instead** of **gases**.
128
So...?
129
What is a **Throttling valve**?
**Throttling** **valves** are any kind of **flow**-**restricting** **devices** that cause a **significant** **pressure** **drop** in the **fluid**
130
The **pressure** **drop** in the **fluid** is often accompanied by a **large** **drop** in \_\_\_\_, and for that reason throttling devices are commonly used in ____ \_\_ \_\_-\_\_\_\_ \_\_\_\_
...**_temperature_,** and for that reason throttling devices are commonly used in **_refrigeration and air-conditioning applications_**
131
Internal energy + flow energy = ?
Internal energy + flow energy = constant
132
During a throttling process, the enthalpy of a fluid remains \_\_\_\_. But internal and flow energies may be ____ to each other.
During a throttling process, the enthalpy of a fluid remains **_constant_**. But internal and flow energies may be **_converted_** to each other.
133
The **section** where the **mixing** **process** takes place is commonly referred to as a...?
...**mixing** **chamber**
134
What are **heat exchangers?**
**Heat exchangers** are devices where two moving fluid streams exchange heat without mixing
135
What is the **uniform-flow process**?
**_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
137
What is an **Adiomatic process?**
When there is **no heat transfer**
138
Boundary work can...?
...move up or down
139
In an **Isothermal** **process**, T = ?
T = 0
140
In an **Isobaric process**, P = ?
**P = constant**
141
In an **Isobaric process,** ____ and ____ goes to \_\_\_\_
In an **Isobaric process, _heat**_ and _**work_** goes to **_zero_**
142
∆u = q - w represents an ____ process
∆u = q - w represents an **_audiobatic_** process
143
In a turbine, if V1 = \__ then there's no need for ____ \_\_\_\_
In a turbine, if V1 = **_V2_** then there's no need for **_kinetic**_ _**energy_**
144
In a turbine, if Z = _ then there's no need for ____ \_\_\_\_
In a turbine, if Z = **_0_** then there's no need for **_potential_** **_energy_**
145
m·h1 = Wout + m·h2 represents a...?
...**turbine**
146
m·h2 = Win + m·h1 represents a...?
...**compressor**
