Key terms

Question 1

What is Absolute Pressure

Answer 1

Gauge pressure + Atmospheric Pressure

Question 2

Adiabatic Boundary

Answer 2

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

Question 3

Ambient Pressure, Temperature

Answer 3

The pressure, temperature of the surrounding atmosphere.

Question 4

Boundary

Answer 4

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

Question 5

Carnot Cycle

Answer 5

A fully reversible cycle having the maximum possible efficiency.

Question 6

Coefficient of Performance

Answer 6

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

Question 7

Critical point

Answer 7

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.

Question 8

Customary Temperature

Answer 8

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

Question 9

Cycle

Answer 9

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

Question 10

Diathermal Boundary

Answer 10

A boundary that allows heat transfer across it.

Question 11

Displacement Work

Answer 11

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

Question 12

Dryness fraction (x)

Answer 12

The proportion of vapour in a liquid-vapour mixture.

Question 13

Engine

Answer 13

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

Question 14

Enthalpy (H)

Answer 14

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

Question 15

Entropy (S)

Answer 15

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

Question 16

Equilibrium

Answer 16

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

Question 17

Extensive Property

Answer 17

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

Question 18

Gauge Pressure

Answer 18

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

Question 19

Heat Pump

Answer 19

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

Question 20

Heat (Q)

Answer 20

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

Question 21

Heat transfer rate (Q with a dot)

Answer 21

Heat transfer in unit time, usually in kW.

Question 22

Intensive Property

Answer 22

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

Question 23

Internal Energy (U)

Answer 23

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

Question 24

Isentropic Process

Answer 24

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

Question 25

Kinetic Energy (KE)

Answer 25

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

Question 26

Perfect Gas

Answer 26

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

Question 27

Potential Energy

Answer 27

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

Question 28

Power

Answer 28

Rate of doing work, usually in kW.

Question 29

Property

Answer 29

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

Question 30

Refrigerator

Answer 30

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

Question 31

Reversed Engine

Answer 31

A refrigerator or heat pump.

Question 32

Reversible Engine

Answer 32

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

Question 33

Reversible Process

Answer 33

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.

Question 34

Saturated Liquid (vapour)

Answer 34

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

Question 35

Specific Gas Constant (R)

Answer 35

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

Question 36

Specific Heat Capacity (Cp, Cv)

Answer 36

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.

Question 37

Specific Property

Answer 37

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

Question 38

Steady flow process

Answer 38

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

Question 39

Superheated Vapour

Answer 39

Vapour above the saturation temperature.

Question 40

Surroundings

Answer 40

All matter outside a system boundary.

Question 41

System

Answer 41

A defined collection of matter.

Question 42

Thermodynamic temperature (T)

Answer 42

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

Question 43

Triple Point

Answer 43

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

Question 44

Universal gas Constant (R with squiggle)

Answer 44

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

Question 45

Vapour

Answer 45

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

Question 46

Work (W)

Answer 46

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

Question 47

1st law of thermodynamics and equation

Answer 47

Energy is neither created nor destroyed. | Q – W =∆U

Question 48

Thermal Efficiency of a Heat Engine

Answer 48

η= (Qh-Qc)/Qh

Question 49

COP of a refrigerator

Answer 49

COPref = Qc/(Qh-Qc)

Question 50

COP of a heat pump

Answer 50

COPhp= Qh/(Qh-Qc)

Question 51

how to show an engine is reversible (eqn)

Answer 51

η= 1/Chp where Chp= Qh/W