Glossary of Terms

Compression

the reduction in volume of a substance using a mechanical force

Condensation

when a substance changes from a gaseous state to a liquid state

Conduction

A method of heat transfer. Usually through a solid material

Convection

A method of heat transfer. High temperature particles rise above lower temperature particles in a liquid or gas. The higher temperature particles carry the heat energy with them.

Critical point

the temperature above which a gas cannot be condensed by raising its pressure

Energy

the capacity of a physical system to perform work (measured in units called Joules)

Evaporation

when a liquid changes to a gaseous state to form a vapour

Expansion

increasing the volume of a substance, usually a gas

Expansion valve

a valve that regulates the flow of refrigerant fluid causing it to vaporise and expand

Fluid

a liquid, gas or vapour

Freezing

solidification of the water within food by reduction of temperature

Heat

Heat is a form of energy which is transferred through radiation, convection or conduction.

Insulation

Material which has a low heat conductivity and is used to reduce the transfer of heat

Phase change

Substances can change state, usually when they are heated or cooled. For example, liquid water turns into steam when it is heated enough, and it turns into ice when it is cooled enough. State changes are reversible – ice can be melted and then frozen again. No new elements or compounds are formed.

Power

the rate of production or creation of energy, usually measured in units of joules/sec, Watts (Btu/h)

Pressure

the physical force exerted on a substance by a fluid in contact with it, usually measured in units Pascal (bar, psi). A force exerted over a specified area

Pressure, absolute

the physical force exerted on a substance by a fluid in contact with it, usually measured units Pascal (bar abs, psia)

Pressure, gauge

the difference in pressure between that of the substance and standard atmospheric pressure, units bar gauge (psig)

Radiation

Transfer of energy by electromgnetic waves which may tavel through space or a material

Refrigerant

a substance used in a mechanical circuit to create cooling or heating of a product or space

Sublimation

the process of a substance in a solid state changing to a gaseous state without going through a liquid state

Temperature

the degree or intensity of heat present in a substance, measured according to a recognised scale, units °C, (°F)

Temperature, absolute

the degree or intensity of heat present in a substance, measured from absolute zero, units K

Thermometer

Instrument for measuring temperature

Vaporise

when a liquid changes to a gaseous state to form a vapour

Vapour

a substance in the gas phase at a temperature lower than the critical point

Volume

the amount of space that a substance or object occupies, units cubic metres (cubic feet)