Refrigerants

Introduction

The refrigerant is a heat carrying medium which during their cycle (i.e. compression. condensation. expansion and evaporation) in the refrigeration system absorbs heat from a low temperature system and discards the heat so absorbed to a higher temperature system. The natural ice and a mixture of ice and salt were the first refrigerants. In 1834. ether. ammonia. sulphur dioxide. methyl chloride and carbon dioxide came into use as refrigerants in compression cycle refrigeration machines. Most of the early refrigerant materials have been discarded for safety reasons or for lack of chemical or thermal stability. In the present days. many new

refrigerants including halo-carbon compounds. hydro-carbon compounds are used for air-conditioning and refrigeration applications. The suitability of a refrigerant for a certain application is determined by its physical. thermodynamic. chemical properties and by various practical factors. There is no one refrigerant which can be used for all types of applications i.e. there is no ideal refrigerant. If one refrigerant has certain good advantages. it will have some disadvantages also. Hence. a refrigerant is chosen which has greater advantages and less disadvantages.

 

Desirable Properties of an Ideal Refrigerant

We have discussed above that there is no ideal refrigerant. A refrigerant is said to be ideal if it has all of the following properties :

1.Low boiling and freezing point.

2.High critical pressure and temperature.

3.High latent heat of vaporisation.

4.Low specific heat of liquid. and high specific heat of vapour.

5.Low specific volume Of vapour.

6.High thermal conductivity.

7.Non-corrosive to metal.

8.Non-flammable and non-explosive.

9.Non-toxic,

10.Low cost.

11.Easily and regularly available.

12. Easy to liquify at moderate pressure and temperature—

13. Easy of locating leaks by odour or suitable indicator

14. Mixes well with oil.

15. High coefficient performance.

16. Ozone friendly

 

 Classification of Refrigerants

The refrigerants may. broadly. be classified into the following two groups :

l. Primary refrigerants. and 2. Secondary refrigerants.

The refrigerants which directly take part in the refrigeration system are called primary whereas the refrigerants which are first cooled by primary refrigerants and then used for cooling purposes are known as secondary refrigerants.

The primary refrigerants are further classified into the following four groups .

l. Halo-carbon or organic refrigerants.

2. Azeotrope refrigerants.

3. Inorganic refrigerants. and

4. Hydro-carbon refrigerants.

Book: 

Rs Khurmi 

Modern Refrigeration and Air Conditioning 

This article was taken by Rs Khurmi