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Fluids > Thermo Definitions > Flashcards

Thermo Definitions Flashcards

1
Q

Density

A

Mass per unit volume - must have a continuum to be valid

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2
Q

Continuum

A

Make sure fluid etc is uniform

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3
Q

Specific quantities

A

Thermodynamic property per unit mass denoted using lower case letter of the thermodynamic quantity in question

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4
Q

Specific volume

A

Volume per kg - reciprocal of density

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5
Q

Absolute pressure

A

Total pressure

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6
Q

Patm

A

Pressure in the atmosphere

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7
Q

Gauge pressure

A

Diff between absolute and atmospheric pressure

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8
Q

Vacuum

A

Negative guage pressure

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9
Q

1bar

A

10^5 N/m^2

10^5 Pa

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10
Q

Macroscopic energy

A

E a system possesses as a whole with respect to an outside reference phrame

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11
Q

Microscopic

A

E relating to a molecular structure of a system and the degree of molecular activity

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12
Q

Chemical energy

A

The internal energy relating to the atomic bonds in a molecule. Internal energy changes during combustion

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13
Q

Nuclear energy

A

Fission of uranium
Fusion of hydrogen
Good clean energy but need high temp

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14
Q

Intensive properties and egs

A

Not affected by quantity

T, P, density

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15
Q

Extensive properties

A

Depends on how much there is

M,
V

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16
Q

Thermal equilibrium

A

When the system temp is uniform throughout - temp can change, just must be uniform

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17
Q

Mechanical equilibrium

A

When the pressure is uniform and there is no pressure gradients

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18
Q

Chemical equilibrium

A

Where the working substance does not undergo any chemical reactions

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19
Q

Thermodynamic equilibrium

A

When the system is in thermal, mech, and Chem equilibrium

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20
Q

Simple compressible system

A

No electrical, magnetic, gravitational motion or surface tension

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21
Q

Homogenous mixture/ system

A

Uniform and uniformly distributed

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22
Q

Point and path functions

A

Start and end are point functions - they fix the thermodynamic state

Route between is a path function

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23
Q

Process

A

Any state change a system undergoes from one state of equilibrium to another
- the series of states the system passes through during the process is called the path

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24
Q

Quasi equilibrium/ Quadistatic process

A

When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state (eg slow compression of air in a piston cylinder device )

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25
Q

Non- equilibrium process

A

One that occurs very fast and deviates from an equilibrium process path (eg puncturing helium balloon )

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26
Q

Isobaric

A

Constant pressure process- where the system pressure is held constant (eg expansion of gas in a frictionless piston cylinder device)

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27
Q

Isothermal process

A

Temp is constant

Eg phase change process

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28
Q

Isochoric process

A

Volume is help constant- quite common in thermodynamics

Aka isometric process

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29
Q

0th law of thermodynamics

A

If 2 bodies are in equilibrium with a 3rd body, they are also in thermal equilibrium with eachother

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30
Q

Sign of work done BY a system?

A

Positive

31
Q

Work of a rotating shaft equation

A

2pie x n of revs per second x Torque

32
Q

Heat

A

A transfer of energy across a system boundary due to a temp difference between the system and the surroundings

33
Q

Sign of heat received by a system?

A

Positive

34
Q

Adiabatic

A

A process in which there is no energy transfers by the heat transfer mechanism

35
Q

1st law of thermodynamics for closed systems

A

Energy can neither be created or destroyed- can only change forms

36
Q

Qnet?

A

= Qin - Qout

37
Q

Wnet?

A

Wout- Win

38
Q

Delta Esystem?

A

Qnet- Wnet

39
Q

What is saturation temp?

A

The temp at which vaporisation takes place at a given pressure

40
Q

What is saturation pressure?

A

The pressure at which saturation takes place

41
Q

What is a saturated liquid?

A

Totally in liquid phase at sat temp and pressure
Left flat bit
Little f is used to denote Saturday’s properties

42
Q

What is a compressed liquid?

A

Actual temp is lower than saturated temp for the system pressure before sat bit on graph

43
Q

What’s a saturated vapour?

A

Totally vapour- is at sat pressure and temp

Right flat bit
g used to denote properties

44
Q

What’s a superheated vapour?

A

Superheated= when the system temp is greater than the saturated temp for a given pressure
Region to the right of the flat bit

45
Q

What type of vapour are gases?

A

Super-heated vapour

46
Q

What’s quality/dryness?

What’s the equation for it?

A

Used to describe a substance that is in the two phase region and is a measure of the amount of the substance that is in the vapour phase

X= total mass of vapour/ total mass
= mg/(mf+mg)

47
Q

What’s x for saturated liquids?

A

X=0

48
Q

What’s x for saturated vapours?

A

X=1

49
Q

When heating lots of pure fluids at constant pressure what Graph is formed when it’s repeated?

A

A vapour dome- inside it is a mixture

50
Q

When can it be assumed that steam is an ideal gas?

A

At low temps

51
Q

What’s the triple point on a P vs T diagram?

A

Where theres solid, liquid, and gas present

52
Q

Whyre there 2 melting limes in a P vs T diagram?

A

Some substances contract on freezing (like to higher temp- next to vapour)
And some expand on freezing (line to lower temp- next to solid)

53
Q

How can all properties of a pure substance be defined?

A

By knowing 2 independent Properties
Eg, Pv. Tv, Px, Tx

PRESSURE AND TEMP AREN’T INDEPENDENT IN THE TWO PHASE REGION

54
Q

What Substances is the ideal gas equation limited to?

A

Gases and very super heated vapours

55
Q

What’s internal energy?

A

The energy of mass composition - can be one of the 2 independent properties to fully define the state of a pure substance

56
Q

What’s the equation for internal energy in the saturated region?

A

u = uf + x ufg

57
Q

What’s hf?

A

Enthalpy of saturated liquid

58
Q

What’s sf?

A

Entropy of saturated liquid

59
Q

What’s hg?

A

Enthalpy of saturated vapour

60
Q

What’s the equation for enthalpy?

A

H= U + PV

61
Q

What’s the unit for enthalpy?

A

Joule

62
Q

How do you know if smt is super heated?

A

The temp on the table is too high for the pressure given

63
Q

How do you know of smt is sun cooled?

A

If temp is too low for given pressure

64
Q

What’s the equation to get the diff between the sat liquid and vapour properties where the substance is between the two states and is in the 2 phase region?

A

Vfg = Vg - Vf

65
Q

Why should the compressed liquid generally be treated as a saturated liquid at a given temp?

A

Properties of compressed liquids aren’t very pressure sensitive
T-V plot would be pretty much be a vertical line for saturated liquids

66
Q

Which property can yield greater error?

A

Enthalpy

67
Q

Define specific heat capacity

A

Energy required to raise the temp of a substance to one degree

68
Q

What do Cv and Cp stand for?

A

Specific heat capacity at constant volume = cv

Specific heat capacity at constant pressure = cp

These are for gases and vapours

69
Q

Why is cp> cv?

A

Some of the heat being used to produce the work under constant pressure conditions

70
Q

What’s Boyles law?

A

PV = constant

71
Q

What’s charles’ law?

A

V1/T1 = V2/T2

ie V/T = constant

72
Q

When can we assume we have an ideal gas?

A

When temp is greater than 2x critical temp except where pressure is much greater than the critical pressure

When pressure is much lower than 1bar and the substance is in the vapour phase

73
Q

What’re the formulae for reduced pressure and temp?

A

Tr= T/ Tcrit

Pr= P/ Pcrit

Fluids (3 decks)

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