There are two refrigeration systems: 1. Vapour Compression Refrigeration System 2. Vapour Absorption Refrigeration System.
1. Vapour Compression Refrigeration System:
This is the most important system for commercial and domestic utility. The working fluid, known as refrigerant. It can be used over a large range of temperatures.
Working:
The working substance (refrigerant) is such that it readily evaporates and condenses.
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The following are the main components of the vapour compression system:
1. Compressor:
Compressor is considered as the heart of the vapour compression system. It pumps the refrigerant through the system in the same way as the heart pumps the blood through the human body.
The evaporator being on the suction side of the compressor, the pressure in the evaporator is lowered by the compressor and this low pressure causes the refrigerant to evaporate at reduced temperature and pressure.
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2. Condenser:
Condenser is that part of the refrigerating system in which the refrigerant condenses and gives off heat due to its condensation. The heat given off by the refrigerant is absorbed by a medium which can move it to the final disposal point. In other words, it may be said that condenser is the door through which the unwanted heat flows out of the refrigeration system.
3. Expansion Valve or Capillary Tube:
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It regarded as one the basic components of the refrigeration system.
It performs the following two functions:
(i) It regulates the flow of the refrigerant depending upon the load on the evaporator.
(ii) It reduces the pressure and temperature of the refrigerant coming from the condenser as per requirement of the system.
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Capillary tube is 40 cm long and 0.75 mm to 1.0 mm in diameter is used in domestic refrigerator.
4. Evaporator:
Evaporator is that part of the refrigeration system in which the refrigerant boils (Evaporates) and absorbs heat. The absorbed heat is transferred to the condenser where it is dissipated to atmosphere.
The main advantages of this system of refrigeration over the other systems are the smaller size for a given refrigerating capacity, higher coefficient of performance. It can be used over a large range of temperatures.
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The main disadvantages like toxity, inflammability and leakage of vapours have been eliminated by development of non-toxic, non-flammable vapours to be used as refrigerants.
Merits of Vapour Compression System:
Merits:
1. For the same refrigeration effect the size of the evaporator is small.
2. Coefficient of performance (C.O.P.) is high.
Demerits:
1. These are having inflammability, toxicity.
2. More chances of leakage of vapour.
2. Vapour Absorption Refrigeration System:
It is one of the oldest methods of producing refrigerating effect. The refrigerant, commonly used in this system is ammonia.
In the vapour absorption refrigeration system, the compressor is replaced by an absorber, a pump, a generator and a pressure reducing valve. In addition to condenser, receiver, expansion valve and evaporator as in the vapour compression refrigeration system. In this system the vapour refrigerant from the evaporator is drawn into an absorber where it is absorbed by the weak solution of the refrigerant forming a strong solution.
This strong solution is pumped to the generator where it is heated by some external source. During the heating process, the vapour refrigerant, is driven off by the solution and enter into the condenser where it is liquified. The liquified refrigerant then flow into evaporator and thus cycle is completed.
Coefficient of Performance (C.O.P.):
The coefficient of performance may be defined as the ratio of the refrigeration effect to the work done during the cycle.
