REFRIGERATION CYCLE

Properties of a good refrigerant:-

1.      It should have lower B.P.

2.      It should have high heat of latent.

3.      It should have higher freezing point.

4.      It should be non-inflammable, non-explosive & non-poisonous.

5.      It should have high dielectric strength & high heat conductivity.

6.      It should be soluble in oil lubricating.

7.      Viscosity should be minimum in both liquid and vapour state.

8.      It should be cheap and easily available.

The Refrigerant Freon:-

               Freon is the trade name of group related refrigerants. They are known individually by the name of Freon 12, Freon 13, Freon 14, Freon 21, Freon 22 etc or R-12, R-13, R-14, R-21, R-22 etc. according to their chemical composition.

Properties of R-12:-

Chemical formula of r-12 is CCl₂F₂ (dichlorodifluoromethane)

Ø  It is colorless liquid, non-inflammable, non-poisonous, odorless, and non-explosive.

Ø  Boiling point at atmosphere pressure- (-)29.8C

Ø  Freezing point at atmosphere pressure- (-)158C

Ø  Specific gravity of liquid at (-)15C – 1.44kg/1

Ø  Specific gravity of liquid at (+)30C ^__ 1.29kg/1

Ø  Specific gravity at atmospheric pressure -4.26kg/m³

Ø  Specific heat at (+)30C – C_p= 0.147

Ø  Specific heat at (+)30C – C_v = 0.130

Ø  Critical temperature – 112C

Ø  Critical pressure – 40.1kg/cm²

                Chemical formula of Freon-22 is CHCIF₂ (monochloro diflouromethane). Since it is less harmful for ozone layer as compared to first one so it is mostly used in ac coaches. Another reason of preference of Freon-22 is that it has higher latent heat (69btu/pound) than Freon-12 (96btu/pound) i.e. one pound of Freon-22 transfers 69 Btu heat & Freon-12 transfer 96 Btu heat.

Type of ac coaches:-

     There are two types of ac coaches-

1.      Under slung ac coaches

2.      RMPU (roof mounted packing unit) ac coaches.

1. Under slung ac coaches:   In this type of ac coaches whole system is beneath the coach so there is higher probability of accident. Compressor that is used here is also huge in size.

2. RMPU ac coaches: Now days these type of ac coaches are manufactured because it is small, compact and more reliable than the first one. In this type of coaches the whole system is at the roof of coach which is clear from its name in one ac coach two unit are place. If by chance one is failed then other can cool the coach.

Characteristics of RMPU:

1.      Cheap: It is light in weight (1100kg) & amount of fuel required is also reduced.

2.      Refrigerant leak: Due to use of brushless alternator less maintenance is required.

3.      Controlling of capacity: In this type of ac coaches four compressors are used from which we can control capacity from 25%-100% due to which there is saving of electricity each compressor starts one by one.

Different component of coaches:-

VRLA battery

Alternator (18kW & 25kW)

Rectifier/regulator

Compressor (shielded & unshielded type)

Condenser

Evaporator

DC compressor & condenser &evaporator motor

Control panel

Power panel

WRA

Inverter

Converter