SPECIFIC REFRIGERANTS CLASS NOTES FOR MECHANICAL ENGINEERING

 

SPECIFIC REFRIGERANTS CLASS

NOTES FOR MECHANICAL

 ENGINEERING

Different refrigerants have different

properties. Different applications require

different refrigerants. Their selection is a

compromise of properties for an

application. Ammonia suits best for

large scale cooling requirements.

There is a prohibition on the

manufacture and use of R-11 and R-12. These have high Ozone

depletion & Global warning.

Fig. Refrigerants

Specific refrigerants

  1. CFC (Chloro- Fluoro- Carbon) refrigerants.
 CFC (Fully Chloro-fluoro Hydrocarbon)
These came into existence were in 1928. Their came into existence in 1960.  These are non-toxic and non-inflammable. Started using these in air conditioners, refrigerators, automobiles. Common use of these is as foaming agents in insulators, cleaning agents for semi-conductors and propellants for aerosols sprays. Their trade name Freon from Du Pont company of USA. These were first generation refrigerants.
Refrigerants like R-11 & R-115.
  1. Have longer life.
  2. Not flammable or non-explosive
  3. Low toxicity, noncorrosive, and compatible with other materials
  4.  High temperatures break down into their elements. These are harmful to humans-respiratory system.
  5. Harmful to environment . These cause high ozone depletion and global warming.
  6. Complete ban on production R-11, R-12 & R-115 because of negative impact on environment. Montreal Act of 1987 put a ban to save the atmosphere. Chlorine from these compounds in the atmosphere reacted with the Ozone layer and started destroying it. One atom of chlorine destroys 100000 molecules of ozone. Chlorine stays in atmosphere for 100 years. Ozone layer is in the stratosphere from 10 km to 50 km above the earth. Ozone depletion allows ultra-violet radiations reaching the earth. It causes cataract, skin problems & damage to crops
      . These CFC act as green house gases and trap heat causing global warming.
 2.  HCFC (Partly halogenated, Hydro chloro Fluoro Carbon) refrigerants
HCFC
Hydro chloro fluoro Carbon Refrigerants like R-22, R-123. It is the second generation of refrigerants. Presence of a hydrogen atom makes these unstable.
  1. Have shorter life
  2. Cause less ozone depletion and less global warming
  3.  Allowed use as replacement.
  4. EPA requires phase out by 2030
3. HFC Refrigerants (partly Fluorinated, Hydro-Fluoro-Carbon) Refrigerants-Are Alternative refrigerants
(a)  HFC (Hydro fluoro carbon) Refrigerants
These are first generation alternative refrigerants to CFC.
  1. Contain one or more hydrogen atoms & no chlorine atoms
  2. Have no ozone depletion potential and affect global warming
  3. These have long life and act as green house gases.
  4. Typically used in new systems specially designed for their use
  5. Used in synthetic lubricating oils
  6. Change old systems to use these refrigerants.
  7.  Kigali Amendment 2016 to Montreal protocol 1987 requires their replacement. All HFC and HFC blend refrigerants like R-404A, R-410A, R-407 C replaced R-22 face early phase out as per EPA. EPA started working for alternatives under SNAM (Significant New Alternatives Program) as per Clean Air Act of 1990. Under this, delete a refrigerant alternative if found unsuitable for environment.
(b)FC Refrigerants (Fully Fluorinated) Refrigerants—Alternatives
(c) PFC Refrigerants (Per Fluoro carbons) Refrigerants—Alternatives with high GWP
4.  Commonly Used refrigerants
Ammonia (NH3,R-717)
It is cheap. Has pungent smell and irritating to eyes make its leakage easy detection. It is inflammable only in high concentrations. Ammonia does not ignite. It does not support combustion. Ammonia has very high affinity for water. Ammonia occurs naturally from livestock animals and soil surfaces. It comes from man made reactive processes like fuel combustion process and sewage treatment plants.. Its latent heat is large (8.7 times of F-12 and 6 times of R-134a). There is no global warming and ozone depletion. Commonly use is in commercial, industrial, indirect space cooling applications. It has environmental and economic benefits .
Commonly used in ice plants, cold storage and industrial plants
FREON-22 (HCFC, CHclF2
It is a colorless green house gas. Its global warming potential is high. Make it from chloroform:
HCCl3 + 2 HF = HCF2Cl + 2 HCl
Used in domestic, Commercial and industrial air conditioning.
High global warming potential makes a way for its phase out. Some tried substitutes are like R-404A, R-410A, R-407C.  All these face phase out.
WATER (R-718)
It is a wonderful naturally available substance. Latent heat of water is extremely high as 2501 kJ/kg at 00C. It posses zero ODP & GWP. Available in abundance with no cost. Evaporation causes cooling is the principle behind its use. It reduces power input. Vapor compression system use water in large quantities. Limitation is its non suitability for temperatures below 00C. Easily useable in air conditioning applications.
(i) Used in stem-jet water vapor refrigeration where low pressure steam is available.
(ii) Used in water chilling units of vapor absorption units.
5.   HFC-134a (CF3CH2F)
Used as a replacement refrigerant for CFC-12.  
Design engineers conducted research. Conducted tests regarding
(i)   Potential health effects,
(ii) Toxicity,
(iii)  Flammability,
(iv) Corrosion
(v)  Evaluated the effect on the life of plants
(vi) Effect on the performance of the refrigeration plant
(vii) Effect on the system’s cooling capacity.
(i) HFC-134a does not pose a cancer risk.
(ii) HFC-134a does not pose a birth defects risk.
(iii)  HFC-134-a is more safe.
(iv) Like CFC-12, HFC-134a is non inflammable, non-toxic and non-inflammable under normal temperatures and pressures.
Concluded that HFC-134 is the most suitable alternative for R-12.  Used in automobile air conditioning, plastic foam blowing and as a propellant. It has global warming potential.

 

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