Refrigeration Systems: Properties and Designations of Refrigerants

Comprehensive vocabulary flashcards covering the definition, classification, chemical designation, properties, and safety concerns of primary and secondary refrigerants.

Refrigerants

Working substances used in refrigeration systems to absorb and displace heat.

Primary Refrigerants

Substances that produce a refrigeration effect or absorb heat by evaporating at low temperatures and pressures, such as air, water, ammonia, and chlorofluorocarbons.

Secondary Refrigerants

Substances, such as chilled water, brines, and glycols, that are cooled in a refrigeration plant and transported to produce a refrigeration effect at a remote location without undergoing cyclic evaporation and condensation.

Halocarbons

Organic compounds that contain carbon, hydrogen, and elements from the halogen group, including fluorine, chlorine, bromine, iodine, and astatine.

Chlorofluorocarbons (CFC)

Halocarbons containing carbon, hydrogen, chlorine, and fluorine; those containing chlorine and bromine are primary causes of ozone depletion.

Thomas Migley, Jr. and Charles Kettering

Pioneering researchers who synthesized a series of chlorofluorocarbons and introduced the $Rabc$ notation for refrigerant classification.

Isomers

Compounds with the same chemical formula and atomic weight but different chemical structures, distinguished by adding suffixes like a, b, or c (e.g., $R134a$).

Non-azeotropic Mixtures

Refrigerant mixtures denoted by the $R400$ series where the boiling point temperature increases as the mixture evaporates, creating a distinct overlap temperature.

Overlap temperature

The difference between the dew point temperature and the boiling point temperature of a non-azeotropic mixture.

Azeotropic Mixtures

Mixtures of two refrigerants denoted by the $R500$ series that have a unique, constant boiling point at a given concentration until the entire mixture evaporates.

Inorganic Compounds Designation

Refrigerants denoted by the $R700$ series, where the number is obtained by adding the molecular weight of the compound to 700 (e.g., $NH_3$ is $R717$).

Ammonia ($NH_3$)

An eco-friendly, cheap refrigerant with high latent heat of evaporation and high COP, commonly used in large industrial applications despite its toxicity and corrosiveness to cuprous alloys.

Dry Ice

The solid form of $CO_2$ which sublimes at $-78.3\text{ }^\text{o}\text{C}$; it is non-toxic and non-flammable but requires high operating pressures.

Sulfur Dioxide ($SO_2$)

An extremely toxic and irritating refrigerant used in the 1920s that is non-explosive and non-flammable but forms corrosive sulphurous acid in the presence of moisture.

Critical Temperature

The temperature above which a refrigerant cannot be condensed; for an efficient cycle, this should be significantly higher than the normal condenser temperature.

Dielectric Strength

A property required for refrigerants used in hermetically sealed compressors to prevent short circuits when the vapour contacts motor windings.

Time Weighted Average (TWA)

The maximum concentration of a refrigerant to which repeated eight-hour exposures, five days a week, are considered safe.

Short Term Exposure Limit (STEL)

The maximum refrigerant concentration to which workers can be exposed for a duration of up to 15 minutes.

Halide Torch

A leak detection tool for freons involving an alcohol lamp where a blue flame turns green in the presence of chlorofluorocarbons.

Beilstein Test

The chemical principle involving chlorine and copper used as the basis for freon detection by a halide torch.

Oil Logging

The accumulation of lubricating oil in the evaporator caused by insufficient refrigerant velocity, which can block heat transfer or choke the system.

Frothing

A phenomenon in hermetic compressors where liquid refrigerant adsorbed on lubricating oil suddenly boils, creating a vapour-oil mixture that can deprive the crankcase of oil.

Crankcase Heaters

Devices used to prevent frothing in hermetic compressors by ensuring the refrigerant does not condense and mix with the lubricant.