The desirable properties of refrigerants used in the refrigerant systems on board the ship are as follows:
- Refrigerants should have a low boiling point.
- Vapours of refrigerants should be easily condensable.
- Refrigerants should have high latent heat, otherwise the mass flow rate will be high.
- Critical temperature of refrigerants should be high.
- Refrigerants should have a low specific volume.
- They should be non-corrosive in nature.
- The refrigerants should be stable.
- Refrigerants should be non-toxic.
- They should be easily available.
- Cost should not be too high.
- Should be such that they can be easily stored.
- Refrigerants should be compatible with crank case oil, oil seals, gaskets, metals involved etc.
- They should be environmental friendly.
- They should be non-explosive and non-flammable in nature.
- Refrigerants should be such that leak detection is easily possible.
Some of the Commonly Used Refrigerants are as follows:
- Carbon Dioxide (CO2)
- Methyl Chloride
- Freon (F11, F12, F22)
Out of the above four, Freon is the most commonly used refrigerant on board as it has almost all the desirable properties of refrigerants as mentioned above.
Disadvantages of other three are as follows:
- CO2: It has a disadvantage of low critical temperature thus have difficulty in liquefying. Another disadvantage is that it requires a very high condenser pressure. Hence CO2 is rarely used on board as a refrigerant.
- Methyl Chloride: It is highly explosive in nature and hence is banned for use on board ships.
- Ammonia: It is toxic in nature. It can be used on board but requires special ventilation. It also have corrosive effect on brass, bronze etc in presence of moisture.
Reference: Various notes on Engineering Knowledge.