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Refrigerant R12 or Freon 12
Refrigerant R-11 is another refrigerant used commonly in the refrigeration and air conditioning systems. The chemical name of R11 is trichloromonofluoromethane (it is methane series compound) and its chemical formula is CCl3F. The molecular weight of R11 refrigerant is 137.4 and its boiling point is 74.7 degree F.
Refrigerant R-11 is considered to be safe refrigerant as it is nonflammable and non-explosive. It is used in the applications like air conditioning of small buildings, factories, departmental stores, theaters etc. It can be used in the applications where the refrigeration load ranges from 150 to 2000 tons along with the centrifugal compressor. R-11 refrigerant is also used as the solvent and the secondary refrigerant.
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Problems Associated with R-11
Here are some of the problems associated with R-11 that have restricted the use of this refrigerant:
1) Low operating pressures: Under the normal atmospheric conditions the operating pressures for refrigerant R-11 are 0.3 bar in the evaporator and 1.25 bar in the condenser, which are on very lower side. Further, the compressor displacement required per ton of refrigeration is also very high for R-11 due to which the compressor has to handle large volumes of refrigerant. Only centrifugal compressor can handle large volume of the refrigerant and work at lower pressures, due to which only this compressor is used with refrigerant R11.
2) High potential to deplete ozone layer: Refrigerant R11 is chlorofluorocarbon (CFC). Among all the refrigerants commonly used for the refrigeration and air conditioning applications, R11 has the highest potential to cause the depletion of the ozone layer from the upper layers of the atmosphere and the greenhouse effect. This is mainly because three atoms of chlorine present in the R11 compound. The atoms of chlorine, released in the atmosphere have very long life, and they tend to reach the upper layers of atmosphere where they break the molecules of the ozone and destroy the ozone layer.
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Replacements for R11
Since R11 has highest potential to cause the depletion of ozone layer, as per the Montreal Protocol, its use and production has to be stopped completely in the phase manner. R-11 is now being replaced by other environment friendly refrigerants, of which the most common is R-123.
If the R-11 refrigeration equipment that were manufactured before 1990 are being replaced by R-123 (dichlorotrifluoroethane) refrigerant then some alteration would be required in the chiller. It is required to replace the seals, gaskets, bushings and diaphragm of the chillers. In case of the hermetic compressors, it is also important to change the motor, and improvement in the efficiency of the other compressors may be required. For retrofitting the R-11 equipment improvement in the efficiency of the heat exchangers, replacement of the expansion valve and the improvement of the controls are also required.
But one should remember that refrigerant R-123 is hydrochlorofluorocarbon (HCFC) and even it has ozone depletion potential though small. By January 1, 2020, the production and use of even this refrigerant has to be stopped completely.
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1) Book: Principles of Refrigeration by Roy J Dossat, fourth edition, Prentice Hall