Designation of various Refrigerant selection

Designation of Refrigerant for educational purpose

1. Refrigerant A working fluid in a compression refrigeration system must satisfy a number of requirements that can be divided into two groups: The refrigerant should not cause any risk of injuries, fire or property damage in case of leakage. The chemical, physical and thermodynamic properties of the refrigerant must suit the system and the working conditions at a reasonable cost.

2. The criteria can be specified more precisely as follows: It is not possible to fulfill all the requirements above at the same time.

3. The most important criterion is chemical stability within the refrigeration system. All the other criteria are meaningless if the refrigerant decomposes or reacts with the materials used in the system. However, the chemical criterion can also be a problem. When a refrigerant is emitted to the atmosphere, it should not be so stable that it can exist indefinitely. The ideal refrigerant would be totally stable in use within the system, but would decompose easily in the atmosphere without the formation of any harmful substances.

4. The thermodynamic and transport properties determine the performance of the refrigeration system. The pressure should be neither too high nor too low. A pressure below atmospheric is undesirable, because air can then be sucked into the system, resulting in problems such as inert gases in the condenser or ice plugs in the expansion valve. The latent heat multiplied by the vapor density gives an estimate of the capacity of a refrigeration system. A refrigerant with a high pressure gives a higher capacity, but a refrigerant with a low critical pressure compared with the pressure in the system leads to a low coefficient of performance (COP). This tradeoff between high capacity and high efficiency must be considered when choosing the refrigerant. Another desired criterion is that the specific heat should be small compared to the latent heat of vaporization, in order to achieve small losses in the expansion device. Oil is normally present in a refrigeration system, and the interaction between the oil and the refrigerant must be considered. High oil solubility is used in hermetic compressors, but immiscible oils are normally used when the working fluid is ammonia.

5. According to an international agreement, refrigerants are represented by the letter R (as in Refrigerants) followed by a two- or three-digit number and, in some cases, one or two letters. The designation Rxyz is determined by the chemical composition of the molecule, as described below.

6. THE METHANE, ETHANE AND PROPANE SERIES: Here, (x) gives the number of carbon atoms in the chemical formula , minus one.​ (x) = 0 is the methane series , but the 0 is ignored for these compounds. Examples are R12 and R22. (x) = 1 is the members of the ethane series , such as R114, R124 and R134a. (x) = 2 is the propane series , e.g. R290 (propane). For these groups, (y) describes the number of hydrogen atoms plus one and (z) describes the number of fluorine atoms.

7. ZEOTROPIC AND AZEOTROPIC MIXTURES (x) = 4 refers to zeotropic mixtures . The components in the mixture have different boiling points, and thus the refrigerant mixture has a temperature glide. R407A and R407C are examples of such refrigerants (see section 5.7). (x) = 5 refers to azeotropic mixtures. These act like homogeneous substances with one specific boiling point, and therefore they have no glide. R502 and R507 are examples of azeotropic mixtures (see section 5.7). Here, (y) and (z) are ordinal numbers.

8. HIGH ORGANIC COMPOUNDS (x) = 6 means that the composition is organic, e.g. butane, R600, and isobutene, R600a. This group has several subgroups, for example hydrocarbons, oxygen compounds, sulfuric compounds and nitrogen compounds. The subgroups have been assigned different number series within the main group, so (y) and (z) describe the subgroup and order within the subgroup.

9. INORGANIC COMPOUNDS (x) = 7 refers to inorganic compounds, such as ammonia, R717, water, R718, and carbon dioxide, R744. In this group, (y) and (z) are the molar mass.

10. UNSATURATED ORGANIC COMPOUNDS (x) = 11 stands for unsaturated ethane compounds, such as R1150 (ethylene). (x) = 12 stands for unsaturated propane compounds, such as R1270(propylene). The (y) and (z) are the same as for the ethane and propane series.

11. LETTERS AT THE END The last letter, if any, in the designation number means different things: Lower-case letters describe the structure of the molecule. For example, R600 is butane and R600a is isobutane . These two compounds have the same chemical formula, but different spatial arrangements, and they therefore have slightly different properties. Capital letters describe specific mixing proportions of different components. For example , R407 A-E are mixtures of the refrigerants R32, R125 and R134a. R407A has the following mixing proportions: 20% R32, 40% R125 and 40% R134a, while R407C consists of 23% R32, 25% R125 and 52% R134a.