How Designated of a Refrigerants?

Designation of refrigerants

Since a large number of refrigerants have been developed over the years for a wide variety of applications, a numbering system has been adopted to designate various refrigerants. From the number one can get some useful information about the type of refrigerant, its chemical composition, molecular weight etc. All the refrigerants are designated by R followed by a unique number.

i) Fully saturated, halogenated compounds: These refrigerants are derivatives of alkanes (CnH2n+2) such as methane (CH4), ethane (C2H6).

These refrigerants are designated by R XYZ, where

• X+1 indicates the number of Carbon (C) atoms
• Y-1 indicates number of Hydrogen (H) atoms, and
• Z indicates number of Fluorine (F) atoms

The balance indicates the number of Chlorine atoms. Only 2 digits indicates that the value of X is zero.

Ex: R 22

• X = 0 ⇒ No. of Carbon atoms = 0+1 = 1 ⇒ derivative of methane (CH4)
• Y = 2 ⇒ No. of Hydrogen atoms = 2-1 = 1
• Z = 2 ⇒ No. of Fluorine atoms = 2

The balance = 4 – no. of (H+F) atoms = 4-1-2 = 1 ⇒ No. of Chlorine atoms = 1

∴The chemical formula of R 22 = CHClF2

Similarly it can be shown that the chemical formula of:

• R12 = CCl2F2
• R134a = C2H2F4 (derivative of ethane)

(letter a stands for isomer, e.g. molecules having same chemical composition but different atomic arrangement, e.g. R134 and R134a)

ii) Inorganic refrigerants: These are designated by number 7 followed by the molecular weight of the refrigerant (rounded-off).

Ex.:

Ammonia:                      Molecular weight is 17,             ∴ the designation is R 717

Carbon dioxide:             Molecular weight is 44,            ∴ the designation is R 744

Water:                              Molecular weight is 18,             ∴ the designation is R 718

iii) Mixtures: Azeotropic mixtures are designated by 500 series, where as zeotropic refrigerants (e.g. non-azeotropic mixtures) are designated by 400 series.

Azeotropic mixtures:

• R 500: Mixture of R 12 (73.8 %) and R 152a (26.2%)
• R 502: Mixture of R 22 (48.8 %) and R 115 (51.2%)
• R503: Mixture of R 23 (40.1 %) and R 13 (59.9%)
• R507A: Mixture of R 125 (50%) and R 143a (50%)

Zeotropic mixtures:

• R404A : Mixture of R 125 (44%), R 143a (52%) and R 134a (4%)
• R407A : Mixture of R 32 (20%), R 125 (40%) and R 134a (40%)
• R407B : Mixture of R 32 (10%), R 125 (70%) and R 134a (20%)
• R410A : Mixture of R 32 (50%) and R 125 (50%)

iv) Hydrocarbons:

• Propane (C3H8) : R 290
• n-butane (C4H10) : R 600
• iso-butane (C4H10) : R 600a

Unsaturated Hydrocarbons:

•  R1150 (C2H4)
• R1270 (C3H6)

Types of Refrigerants

Refrigerant selection criteria

Refrigerant selection criteria:

Selection of refrigerant for a particular application is based on the following requirements:

• Thermodynamic and thermo-physical properties
• Environmental and safety properties
• Economics

Primary and Secondary Refrigerants

Primary Refrigerants:

Primary refrigerants are those fluids, which are used directly as working fluids, for example in vapour compression and vapour absorption refrigeration systems. When used in compression or absorption systems, these fluids provide refrigeration by undergoing a phase change process in the evaporator. As the name implies, secondary refrigerants are those liquids, which are used for transporting thermal energy from one location to other.

Secondary Refrigerants:

Secondary refrigerants are also known under the name brine’s or antifreeze’s. Of course, if the operating temperatures are above 0°C, then pure water can also be used as secondary refrigerant, for example in large air conditioning systems. Antifreeze’s or brine’s are used when refrigeration is required at sub-zero temperatures.

Unlike primary refrigerants, the secondary refrigerants do not undergo phase change as they transport energy from one location to other. An important property of a secondary refrigerant is its freezing point. Generally, the freezing point of a brine will be lower than the freezing point of its constituents. The temperature at which freezing of a brine takes place its depends on its concentration. The concentration at which a lowest temperature can be reached without solidification is called as eutectic point. The commonly used secondary refrigerants are the solutions of water and ethylene glycol, propylene glycol or calcium chloride. These solutions are known under the general name of brine’s.

Properties of a good Refrigerants

Refrigerants:

The thermodynamic efficiency of a refrigeration system depends mainly on its operating temperatures. However, important practical issues such as the system design, size, initial and operating costs, safety, reliability, and serviceability etc. depend very much on the type of refrigerant selected for a given application. Due to several environmental issues such as ozone layer depletion and global warming and their relation to the various refrigerants used, the selection of suitable refrigerant has become one of the most important issues in recent times. Replacement of an existing refrigerant by a completely new refrigerant, for whatever reason, is an expensive proposition as it may call for several changes in the design and manufacturing of refrigeration systems. Hence it is very important to understand the issues related to the selection and use of refrigerants. In principle, any fluid can be used as a refrigerant. Air used in an air cycle refrigeration system can also be considered as a refrigerant. However, in this lecture the attention is mainly focused on those fluids that can be used as refrigerants in vapour compression refrigeration systems only.

The refrigerant is a heat carrying medium which during their cycles (i.e. compression, condensation, expansion, evaporation) in the refrigeration system absorb heat from a low temperature system and discard the heat so absorbed to a higher temperature system.

Properties of a good refrigerants:

• Low boiling Point
• High Critical Temperature
• High latent heat of vaporisation
• Low  specific heat of liquid
• Low specific volume of vapour
• Non-corrosive to metal
• Non-flammable
• Non-explosive
• Non-toxic
• Low cost
• Easy to liquify at moderate pressure and temperature
• Easy to locating leaks by odour or suitable indicator
• Mixes well with oil.