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Cat B- Mod 2 Physics > 2.3 Thermodynamics > Flashcards

2.3 Thermodynamics Flashcards

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1
Q

What is temperature?

A

Measure of average kinetic energy of the particles in a system.

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2
Q

How is thermal equilibrium reached?

A

When heat flows from a hotter to cooler body and stops when they are the same temp.

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3
Q

What is the difference between heat and temperature?

A

Temperature is the property of a body and heat is the energy that flows too or from a body.

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4
Q

What are the three types of thermometers?

A

Bulb
Bimetallic
Thermistor

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5
Q

What is a thermocouple?

A

They are used to measure high temp, used for applications in the engine.

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6
Q

What is a bulb thermometer?

A

The classic type you find everywhere.

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7
Q

What is a bimetallic thermometer?

A

It shows temp as mechanical displacement. They can be used as a heat switch.

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8
Q

What is a thermistor?

A

A device to measure temp, the electrical resistance changes with temp.

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9
Q

How do you convert Fahrenheit to celsius?

A

F-30/2

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10
Q

How do you convert Celsius to Fahrenheit?

A

C x 1.8 + 32

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11
Q

Which measure of temp is the SI units?

A

Kelvin.

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12
Q

What is absolute zero in degrees celsius?

A

-273.15

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13
Q

What is the key difference between Calorie and calorie?

A

The lower case calorie is 1/1000th of a Calorie.

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14
Q

How does heat flow from a lower to higher object?

A

If work is done.

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15
Q

What is specific heat?

A

The energy required to raise the temp of 1kg object by 1 degree c.

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16
Q

What is the formula for specific heat?

A

Heat energy added divided by mass x change in temp

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17
Q

How do you work out the heat given to an object to heat its mass?

A

mass x specific heat x temp change

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18
Q

What is heat capacity?

A

Ratio of the amount of heat energy transferred to an object to the change in temp.

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19
Q

What are the three methods of heat transfer?

A

Convection, conduction and radiation.

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20
Q

What is conduction?

A

Heat is directly transferred through the material. Only method of heat transfer in solids, sometimes in liquids.

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21
Q

What is convection?

A

Heat transfer in liquids and gasses.

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22
Q

What is radiation?

A

Energy coming from source and travelling through space. It is different to conduction and convection in that the objects do not need to be in contact.

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23
Q

What is the coefficient of linear thermal expansion?

A

The amount that different materials expand/contract when heated or cooled.

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24
Q

What is linear expansion?

A

The change in length proportional to the original length and change in temp.

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25
Q

What is area expansion?

A

The change in dimensions due to application of temps, in 2D bodies.

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26
Q

What is volumetric expansion?

A

The expansion found in 3D bodies.

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27
Q

Because liquids and gasses are free flowing when not in a container the linear coefficient of thermal expansion is not applicable, what is used instead?

A

The coefficient of volumetric thermal expansion.

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28
Q

What is the first law of thermodynamics?

A

Energy can neither be created or destroyed but it can be transformed.

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29
Q

What is the formula for the first law of thermodynamics?

A

Heat energy added= change in internal energy + work done

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30
Q

What is the second law of thermodynamics?

A

The total energy output is equal to the amount of heat supplied.

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31
Q

Second law: Although the energy transferred to the system by heating is equal to the work done by the system, what is key to make this work?

A

The heat supplied must be greater than the work done, therefore some heat must be lost during the work.

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32
Q

What is the heat receiver?

A

The place where heat energy is lost in a machine. Also referred to as heat sink.

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33
Q

What is the formula for thermal efficiency?

A

Work done / heat energy added

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34
Q

Does thermal efficiency have a unit?

A

No

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35
Q

What are examples of heat engines designed to minimise thermal losses?

A

Steam turbines, refrigeration packs and air conditioning units.

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36
Q

Who came up with the carnot engine and what is it?

A

Sadi Carnot, in theory it is a equal input/output engine.

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37
Q

What is entropy?

A

The loss of energy to the environment due to an increase of disorder in the system. Higher chaos gives higher entropy.

38
Q

What is key about entropy?

A

It can remain the same or increase, it cannot go down.

39
Q

What is a thermodynamic cycle?

A

The fluid of a system undergoes a series of processes and finally returns to its initial state.

40
Q

What are the two types of thermodynamic cycles?

A

Open and closed.

41
Q

What are the five basic elements of a thermodynamic cycle?

A

Working substance
Heat Source
Heat receiver
Pump
Engine

42
Q

What is the working substance?

A

A medium that receives, stores and transports the energy.

43
Q

What is the heat source?

A

Supplies thermal energy to the working fluid.

44
Q

What is the heat receiver?

A

Absorbs the heat from the working substance.

45
Q

What is the pump?

A

Moves the working substance from the low pressure side to the high pressure side of the cycle.

46
Q

What is the engine?

A

Converts the thermal energy to work in mechanical energy.

47
Q

What is an open cycle system?

A

Where an opening in the system boundary allows the fluid to be replaced, as the fluid is allowed to leave. I.e. gas turbine engine.

48
Q

What is an example of closed cycle system?

A

Air con unit.

49
Q

What gasses are considered ideal gasses?

A

Hydrogen, oxygen, noble gasses and some heavier gasses like carbon dioxide.

50
Q

What three characteristics are ideal gasses judged on?

A

Temp
Pressure
Density

51
Q

What is boyles law also known as?

A

Isothermal process.

52
Q

What does boyles law describe?

A

The direct relationship between the pressure and the volume of a gas.

53
Q

What is an isothermal process?
Boyles Law

A

At constant temp, the pressure exerted by a gas varies inversely with the volume.

54
Q

Why is an understanding of Boyles law important in aviation?

A

It is essential in calculating the volume and pressure of ICE’s.

55
Q

What is Charles’s law also known as?

A

Isobaric process.

56
Q

What is an isobaric process?
Charles Law

A

At constant pressure the volume increases or decreases by the same amount as the temp.

57
Q

What is Gay-Lussacs law also known as?

A

Isochoric process.

58
Q

What is isochoric process?
Gay-Lussac

A

At constant volume, the pressure varies with the absolute temp.

59
Q

What is the triangle of the three gas laws?

A

PxV over T
P/T= Gay Lussac
V/T= Charles
PxV= Boyle

60
Q

What is key about specific heat at constant volume?

A

No work is done, the only change is in thermal energy.

61
Q

What is key about specific heat at constant pressure?

A

There is change in thermal energy and work done to increase pressure.

62
Q

What is the formula for work?

A

Force x distance moved (s)

63
Q

What is an adiabatic expansion?

A

No heat is transferred to or from the system. It is any process that occurs in a container that is a good insulator.

64
Q

Strictly speaking do adiabatic processes actually exist?

A

No

65
Q

Basic rules: Isochoric

A

Constant volume

66
Q

Basic rules: Isobaric

A

Constant pressure

67
Q

Basic rules: Isothermal

A

Constant temperature

68
Q

Basic rules: Adiabatic

A

No heat transfer

69
Q

What is an engine cycle?

A

Series of thermodynamic processes, heat into work.

70
Q

What are the two types of thermodynamic process?

A

Reversible and irreversible.

71
Q

How can a process be reversible?

A

It has to be in thermodynamic equilibrium with its surroundings. (hypothetical)

72
Q

What is a reciprocating piston engines process?

A

Non flow, heat to mechanical.

73
Q

What is a Gas turbines process?

A

Flow, heat to mechanical.

74
Q

What are the four processes in an Otto cycle (piston engine).

A

Adiabatic Compression
Reversible Isochoric Heating
Adiabatic Expansion
Reversible Isochoric Cooling

75
Q

What is important about the Otto cycle?

A

It is idealistic as it based on a perfect system.

76
Q

What process is used in gas turbine engines?

A

Brayton Cycle

77
Q

What three components are found in a brayton cycle engine?

A

Gas compressor, mixing chamber and expander.

78
Q

What is the constant volume process for a perfect gas?

A

Reversible

79
Q

What is the refrigeration cycle?

A

The opposite of the natural heat cycle, transfers thermal energy from a cold place to a warm place.

80
Q

What three processes can be used to cool gasses?

A

Convection
Conduction
Radiation

81
Q

What is latent heat?

A

The amount of heat that is absorbed or released when a body undergoes a constant-temperature process.

82
Q

What are the two types of curve when considering change of state?

A

Heating or cooling curve.

83
Q

In regards to latent heat what is fusion?

A

The transition from a solid to a liquid via melting.

84
Q

What kind of process is solidifcation?

A

Exothermic.

85
Q

What is the only exception to the solidification rule?

A

Solidification of low temp helium.

86
Q

What is the latent heat of fusion the same as?

A

The latent heat of solidification

87
Q

What is the latent heat of vaporisation the same as?

A

Latent heat of condensation

88
Q

What is temperature?

A

A measure of the average kinetic energy of the particles in a substance.

89
Q

What is Thermal Energy?

A

The total of energy of the particles in a substance.

90
Q

What is heat?

A

The transfer of thermal energy between objects that have different temps.

91
Q

What is the heat of combustion?

A

The energy released as heat when a substance undergoes combustion.

92
Q

What is the key point to understand about latent heat?

A

Heat gained or lost by a body with no corresponding change in temp.

Cat B- Mod 2 Physics (9 decks)

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