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Semester 1 > Thermodyanmics I > Flashcards

Thermodyanmics I Flashcards

1
Q

what is thermodynamics?

A

science of energy

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2
Q

what is energy?

A

ability to change or do work

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3
Q

define entropy

A

measurement of disordeness

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4
Q

name two systems of dimensions

A

english system and metric SI system

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5
Q

name different types of units

A

primary

secondary (can be derived)

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6
Q

define system

A

quantity of matter or region of space defined by a boundary

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7
Q

define boundary

A

anything that separates a system from its surroundings

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8
Q

define stationary system

A

system with constant velocity and elevation

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9
Q

define isolated system

A

neither mass or energy can across the boundary, an example is the universe

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10
Q

define closed system (or fixed mass, control mass or CV)

A

mass cannot cross the boundary but energy can, the boundary can either be fixed or moveable

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11
Q

define open system (or control volume or CV)

A

both energy and mass can cross the boundary

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12
Q

define volume flow rate

A

volume of fluid flowing through cross section per unit time (represented by a V with a dot above it)

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13
Q

define mass flow rate

A

amount of mass flowing through cross section per unit time (represented by m with a dot above it)

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14
Q

define energy flow rate

A

amount of energy flowing through cross section per unit time (represented by E with a dot above it)

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15
Q

define macroscopic energy

A

energy wrt to outside energy frame (what you’re measuring frame)

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16
Q

define microscopic energy

A

energy related to molecular or atomic structure and activity

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17
Q

define internal energy (U)

A

the sum of all microscopic forms of energy of a system

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18
Q

define total energy

A

microscopic energy + macroscopic energy

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19
Q

name the different forms of macroscopic energy

A

kinetic energy + potential energy

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20
Q

equation and definition for kinetic energy

A

associated with a system’s motion

1/2mv^2

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21
Q

equation for potential energy

A

associated with a systems elevation

mgz (z representing elevation/height)

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22
Q

what is mechanical energy?

A

sum of the potential energy and kinetic energy

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23
Q

different types of microscopic energy?

A

sensible, latent, chemical, nuclear

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24
Q

definition of sensible energy?

A

associated with motion of molecules, it is proportional to temperature

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25
Q

definition of latent energy?

A

associated with intermolecular forces and phases of a system

gases have a higher latent energy

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26
Q

equation for total energy

A

E= U +1/2mv^2 +mgz

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27
Q

define heat/heat transfer (Q)

A

energy transferred due to temperature difference

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28
Q

what is heat transfer rate represented as and what are the units?

A

Q with a dot above it

Units: J/s or W

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29
Q

name heat transfer mechanisms

A

conduction, convection, radiation

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30
Q

define adiabatic process

A

a process without heat transfer

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31
Q

define work (W)

A

energy interaction not caused by temperature difference

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32
Q

define power

A

rate of doing work

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33
Q

define mechanical work

A

energy transferred by a force, requires force and displacement

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34
Q

what is boundary work (Wb or PdV work)?

A

one form of mechanical work transferred by a force

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35
Q

name some types of mechanical work

A

shaft work, electrical work, spring work

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36
Q

define dynamic energy and examples

A

energy that crosses the boundary, eg. heat, work

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37
Q

define static energy and examples

A

energy that does not cross the boundary, e.g internal energy (U)

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38
Q

define property

A

any characteristics of a system e.g temperature, volume, pressure and mass

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39
Q

define intensive property and examples

A

NOT dependant on the amount of material in the system e.g temperature, pressure, density

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40
Q

define extensive property and examples

A

IS dependant on amount of material in the system, e.g mass, volume, energy

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41
Q

what is specific property?

A

extensive property per unit mass

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42
Q

define state

A

condition at an instant time as described/measured by its properties
eg. temperature, pressure, energy

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43
Q

define thermodynamic state

A

a set of physical quantities describing properties of a system

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44
Q

define path function and examples

A

value of the variable depends on transition/path of system to change, e.g work (depends on amount of force applied) and heat, (depends on temperature differences)

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45
Q

define point function and examples

A

value of the variable is not dependant on the transition/path of a system, e.g temperature and pressure

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46
Q

specific weight definition and units

A

weight per unit volume

density * gravitational value measured in Nm-3

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47
Q

specific/relative gravity and units

A

density per density value of water (Nm-3)

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48
Q

define ‘state’

A

condition at an instant time as described/measured by its properties

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49
Q

define ‘thermodynamic state’ and examples

A

a set of physical quantities describing properties of a system
examples: temperature, pressure, energy

50
Q

3 conditions of thermodynamic state properties

A

values of the properties define the state of a system
each property has a single value at each state
all properties are point, not path, functions

51
Q

define ‘path function’ and examples

A

value of the variable depends on transition/path of a system to change, e.g work, heat

52
Q

define ‘point function’ and examples

A

value of variable is not dependant on the transition/path of a system. e.g temperature and pressure

53
Q

define ‘process’

A

a path/passage for a system to change from initial state to final state

54
Q

what properties are being observed in a process?

A

initial and final states

energy and mass interactions during the process

55
Q

define ‘natural process’

A

process where entropy increases, it is a quick irreversible reaction that occurs in nature

56
Q

define ‘unnatural process’

A

total entropy decreases when reaction occurs, it is a logically conceivable reaction

57
Q

define ‘flow process’

A

mass is entering/leaving an open system

58
Q

define ‘non-flow process’

A

closed system, no mass is crossing the boundary

59
Q

define ‘steady flow process’

A

flow remains constant, does not change with time

60
Q

define ‘equlibrium’

A

stable, balanced or unchanging condition with all acting, opposing, competing forces or influences that cancel one another out
change process continues until gradients are nullified/balanced

61
Q

what can occur only under equilibrium?

A

only under equilibrium are system properties fixed, so they can be measured and calculated

62
Q

define ‘thermal equilibrium’

A

same temperature throughout a system

63
Q

define ‘phase equilibrium’

A

no or balanced phase changes

64
Q

define ‘internal thermodynamic equilibrium’ (ITE)

A

equilibrium state within a system, if undistributed no changes occur within the system

65
Q

define ‘global thermodynamic equilibrium’ (GTE)

A

equilibrium within whole system and the intensive parameters remain homogeneous throughout the system

66
Q

define ‘cycle’

A

process or series of processes whose initial and final states are identical

67
Q

what do you need to know in a cycle?

A

initial and final states of a system

energy and mass interactions

68
Q

what is Carnot Engine?

A

a cycle formed from a series of process

69
Q

what occurs during a cycle?

A

system returns to original state. Properties are exactly the same including energy, temperature

70
Q

why is a cycle important?

A

repeating nature allows for continuous operation

71
Q

what is a heat engine?

A

heat from a hot source, converted into work, part disposed into a cold sink

72
Q

what is a heat pump?

A

used to remove heat from cold source to warm sink

73
Q

define ideal cycle

A

for the purpose of analysis and design, used to model real devices by making assumptions
e.g quasi static process + no friction is occurring
allows you to decide the highest efficiency to get from the cycle

74
Q

define entropy

A

measurement of disorder or chaos of energy distribution, the higher level of entropy= the higher amount of wasted energy

75
Q

how to calculate entropy

A

heat change divided by temperature, delta Q/ time

76
Q

is entropy intensive or extensive property

A

extensive property

77
Q

does entropy change in an isolated property?

A

nope, it never decreases

78
Q

define pressure

A

named force exerted by a fluid per unit of contact surface area

79
Q

units of pressure

A

pascal (Pa) or Nm-2 or kgm-1s-2

80
Q

define ‘zero absolute pressure’

A

perfect vacuum where absolute pressure is zero (no single molecules in order to apply pressure)

81
Q

define ‘atmospheric pressure’

A

pressure within the atmosphere, caused by the weight of above the measurement point, it decreases with increasing elevation

82
Q

how to calculate positive gauge pressure

A

absolute pressure- atmospheric pressure

83
Q

how to calculate negative gauge pressure

A

atmospheric pressure- absolute pressure

84
Q

which should you always use, gauge or absolute pressure?

A

absolute pressure

85
Q

define temperature

A

a thermal state to distinguish a hot body from a cold body

it is proportional to the average kinetic energy (sensible energy) of the molecules

86
Q

name the two types of temperature scales

A

freezing/ice point- e.g. ice and water mixture in equilibrium at 1 atm pressure
boiling/steam point- e.g water, liquid and vapour mixture in equilibrium at 1 atm

87
Q

temperature value in degree F from degree C equation

A

T(F)+ 1.8(C) +32

88
Q

temperature difference in degree F from degree C equation

A

d(F) = 1.8 dt’(C)

89
Q

what is the Kelvin scale?

A

temperature measured with absolute zero as basis in degrees Centigrade

90
Q

temperature value of Kelvin equation

A

T(K)= t(C) +273.15

91
Q

temperature difference of Kelvin equation

A

dT(K)=dt(C)

92
Q

what is the Rankine scale?

A

absolute temperature scale in English system, Units R

93
Q

temperature value of Rankine equation

A 
T(R)= T(F) + 459.17
T(R)= 1.8t(K)
94
Q

temperature difference of Rankine equation

A 
dT(R)= dT(F)
dT(R)= 1.8dT(K)
95
Q

what is the zeroth law of thermodynamics?

A

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

96
Q

define ‘pure substance’

A

element/compound of only one component with definite, chemical properties and composition

97
Q

define ‘latent heat’

A

energy absorbed or released during phase changes

98
Q

what are the three principle gases?

A

solid, liquid and gas

99
Q

describe ‘gas phase’ (2 principles)

A

the molecules are at a higher energy level than liquid and solid phases
gases releases large amount of energy when condensed and frozen

100
Q

describe ‘solid phase’

A

large amount of energy needed to melt/vaporise

101
Q

define ‘compressed liquid’/’sub-cooled liquid’

A

at 1 atm pressure, temperatures above freezing point and below point
the liquid is compressed if it is not about to vaporise

102
Q

define ‘saturated liquid’

A

liquid that is about to vaporise

Q=> U (sensible energy) +PdV

103
Q

define ‘saturated liquid and vapour’

A

a mixture of saturated liquid and vapour and they exist in equilibrium

104
Q

define ‘superheated vapour’ and the heat transfer equation

A

vapour not about to condense

Q=>U (sensible energy) +PdV

105
Q

define ‘enthalpy’

A

internal energy + pressure*volume

106
Q

define ‘saturated vapour’

A

vapour about to condense

Q= U (latent energy) + PdV

107
Q

define ‘saturation pressure’

A

at a given temperature, the boiling pressure is saturation pressure.
this is because boiling temperature depends on pressure

108
Q

define ‘saturation temperature’

A

at a given pressure, the boiling temperature is called saturation pressure

109
Q

What is quality (x)?

A

Ratio of the vapour mass to the mass of the mixture

X= m(vapour)/ m (mix)

110
Q

Define quality

A

One of the independent variables to describe the state of a system

111
Q

Define ideal gas

A

Theoretical gas with randomly moving point particles not interacting except colliding elastically

112
Q

Examples of gases treated as ideal gases

A

Air, nitrogen, oxygen, helium, argon, neon, krypton

113
Q

Example of dense gases

A

Water vapour

114
Q

Define specific heat (C) and what is it related to

A

Energy required to raise temperature of unit mass by 1 degree
It is related to internal energy, U( sensible energy)

115
Q

What is Cp and Cv and what are they related to

A

Cv is specific heat at constant volume (sensible energy)

Cp is specific heat at constant pressure (sensible energy + boundary work)

116
Q

Which out of Cp and Cv is greater and why

A

Cp is always greater than CV because h= u + Pv

117
Q

Total internal energy change in the system ( delta e of system)

A 
delta e (in) - delta e(out) = du
Delta e(in) - delta (out) = CvdT
118
Q

Equation for change in internal energy with temperature at a constant volume

A

Cv = (du/dT) v

119
Q

Equation for change in enthalpy with temperature at a constant pressure

A

Cp= (dh/dT)p as h=u + Pv

120
Q

What is different about C values for monoatomic gas?

A

Specific heat (C) of monoatomic gases (eg argon, helium) remain constant over the temperature range

121
Q

specific heat relations for ideal gases and how to derive

A 
differentiate enthalpy equation to get dh=du +rdT
dh/dt= du/dT + R
replace dh by CpdT and du by CvdT
Cp= Cv +R
k= Cp/Cv

Semester 1 (5 decks)

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