Refrigeration & Air-Conditioning

Module 2. Refrigerants

Lesson 9
PROPERTIES OF REFRIGERANTS AND COMPARISON

9.1 Ammonia (Refrigerants)

• Boiling point at Atmospheric Condition is - 33 ^oC
• Possible to use for below 0 ^oC application
• It has very large latent heat
• Condenser is almost always of water cooled type.
• Some what inflammable with proper mixture of air.
• Very pungent smell
• Forms dense white fumes in presence of sulphour candle.
• It attacks copper and bronze in presence of moisture but does not corrode iron or steel.
• It is lighter than oil, and is easily separated from it
• It is extremely soluble in water.
• Used with large refrigeration systems, using reciprocating compressions.

9.2 R-22 (CHCl F₂)

• Mono chlorodifluoro methane
• Low evaporating temperature
• At atmospheric pressure B.P - 41oC
• Stable, non-tonic, non- corrosive, non – irritating and non- inflammable
• Water is should be in it - there for driers and desiccants
• Leak detected by Halide Torch or electronic detector
• Phase out by 2020 in developed countries and 2030 in developing countries (Montreal 1987)
• Much faster phase out is being done (EU in 2004

Table 9.1 Properties of refrigerants

9.3 Ozone Layer & UV Rays

· OZONE (O₃) is a bluish gas, harmful to breath.

· 90% of Earth’s Ozone is in stratosphere (15 to 50 km) forming a layer of 2 to 5mm

thick under normal temperature & pressure.

· Its concentration varies with season, hour of day and location.

· Its concentration is greatest at 25 km from Equator & 16 km from poles.

· Ozone comes mostly from photo-disassociation of oxygen by UV Rays of very short wave length.

· Dobson is unit of level of ozone.

UV rays are again classified according their wave lengths.

UV-A 320-400 nm: Not absorbed by ozone

UV-B 280-320 nm ozone protects against most of UVB. Harmful because, it damages DNA, Melanonia and other skin cancer, damages some types of materials, crops and marine organisms.

UV-C <280 nm despite being extremely dangerous, it is completely absorbed by ozone and normal O₂.