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Thermodynamics 2 > Key terms > Flashcards

Key terms Flashcards

1
Q

What is Absolute Pressure

A

Gauge pressure + Atmospheric Pressure

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2
Q

Adiabatic Boundary

A

A boundary of a system that does not allow heat transfer.

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3
Q

Ambient Pressure, Temperature

A

The pressure, temperature of the surrounding atmosphere.

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4
Q

Boundary

A

The boundary of a system separates it from all other matter.

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5
Q

Carnot Cycle

A

A fully reversible cycle having the maximum possible efficiency.

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6
Q

Coefficient of Performance

A

An expression of efficiency for reversed heat engines- refrigerator or heat pump.

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7
Q

Critical point

A

A point on a property chart beyond which the substance does not experience a transition between liquid and vapour- critical pressure and critical temperature define this point.

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8
Q

Customary Temperature

A

Temperature measured on an arbitrarily chosen scale by a thermometer (usually in degrees C).

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9
Q

Cycle

A

A series of processes by which the substance returns to its original state.

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10
Q

Diathermal Boundary

A

A boundary that allows heat transfer across it.

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11
Q

Displacement Work

A

Work done by virtue of the displacement of the system boundary.

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12
Q

Dryness fraction (x)

A

The proportion of vapour in a liquid-vapour mixture.

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13
Q

Engine

A

A device which produces a work transfer while engaging in heat transfer with the surroundings.

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14
Q

Enthalpy (H)

A

A property derived from:
internal energy + (pressure x volume)
Usually in kJ.

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15
Q

Entropy (S)

A

A property related to the degree of disorder in a substance, usually in kJ/K.

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16
Q

Equilibrium

A

Said to exist when no spontaneous change takes place when a system is isolated from its surroundings.

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17
Q

Extensive Property

A

Any property which depends upon the quantity of substance (i.e. the extent of the system).

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18
Q

Gauge Pressure

A

Pressure above (or below for vacuum gauges) ambient as indicated by a pressure gauge, in kPa or bar.

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19
Q

Heat Pump

A

A device which takes energy from a cold source and transfers it to provide energy to a hotter region using work input.

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20
Q

Heat (Q)

A

Energy transfer under the influence of a temperature difference, usually in kJ.

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21
Q

Heat transfer rate (Q with a dot)

A

Heat transfer in unit time, usually in kW.

22
Q

Intensive Property

A

A property which is independent of the quantity of substance (e.g. pressure, temperature)

23
Q

Internal Energy (U)

A

Energy possessed by a substance by virtue of its phase and temperature, usually in kJ.

24
Q

Isentropic Process

A

A process in which there is no change in the entropy of the substance- usually a reversible adiabetic process.

25
Q

Kinetic Energy (KE)

A

Energy possessed by a body by virtue of its ordered motion, usually in kJ.

26
Q

Perfect Gas

A

A gas for which pv/T, Cp and Cv are taken to be constants.

27
Q

Potential Energy

A

Energy possessed by a substance by virtue of its height above a chosen datum.

28
Q

Power

A

Rate of doing work, usually in kW.

29
Q

Property

A

Identifiable characteristics of a substance such as temperature, pressure, internal energy.

30
Q

Refrigerator

A

A device built to transfer energy from a cold body- it rejects to a higher temperature region, usually the atmosphere.

31
Q

Reversed Engine

A

A refrigerator or heat pump.

32
Q

Reversible Engine

A

An engine which gives the same energy transfers either as a forward or reversed engine- It has the highest possible efficiency.

33
Q

Reversible Process

A

A process which may be reversed such that the process path passes through all the same states in either direction. OR a process that having once taken place can be reversed and in so doing leave no change in either system or surroundings.

34
Q

Saturated Liquid (vapour)

A

A liquid (vapour) at the saturation temperature, i.e. the boiling point for the particular pressure.

35
Q

Specific Gas Constant (R)

A

A constant relating properties for a particular gas; R=pv/T, usually in kJ/kg K.

36
Q

Specific Heat Capacity (Cp, Cv)

A

The energy required to raise the temperature of unit mass through unit temperature rise at constant pressure or constant volume, usually in kJ/kg K.

37
Q

Specific Property

A

The value of an extensive property per unit mass. E.g. Specific enthalpy, h= H/m.

38
Q

Steady flow process

A

Process in which the mass flowrate is constant and the state at any location is constant with respect to time.

39
Q

Superheated Vapour

A

Vapour above the saturation temperature.

40
Q

Surroundings

A

All matter outside a system boundary.

41
Q

System

A

A defined collection of matter.

42
Q

Thermodynamic temperature (T)

A

Temperature defined by the efficiency of reversible engines, absolute temperature measured in Kelvin (K).

43
Q

Triple Point

A

The state in which the solid, liquid and vapour phases exist in equilibrium- for H2O this is used as a datum for properties.

44
Q

Universal gas Constant (R with squiggle)

A

The relationship pV/T, where V is the volume of 1 kmol of any gas, usually in kJ/kmol K.

45
Q

Vapour

A

Part of the gaseous phase at or slightly above the saturation temperature.

46
Q

Work (W)

A

Energy transfer which can be related to the movement of a force, usually in kJ.

47
Q

1st law of thermodynamics and equation

A

Energy is neither created nor destroyed.

Q – W =∆U

48
Q

Thermal Efficiency of a Heat Engine

A

η= (Qh-Qc)/Qh

49
Q

COP of a refrigerator

A

COPref = Qc/(Qh-Qc)

50
Q

COP of a heat pump

A

COPhp= Qh/(Qh-Qc)

51
Q

how to show an engine is reversible (eqn)

A

η= 1/Chp where Chp= Qh/W

Thermodynamics 2 (1 decks)

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