TITLE.PM5

714 ENGINEERING THERMODYNAMICS

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includes the equipments naming evaporator, compressor, condenser and expansion valve. It

is used for preservation of food, manufacture of ice, solid carbon dioxide and control of air tempera-

ture and humidity in the air-conditioning system.

Important refrigeration applications :

1. Ice making


2. Transportation of foods above and below freezing


3. Industrial air-conditioning


4. Comfort air-conditioning


5. Chemical and related industries


6. Medical and surgical aids


7. Processing food products and beverages


8. Oil refining and synthetic rubber manufacturing


9. Manufacturing and treatment of metals


10. Freezing food products


11. Miscellaneous applications :
    (i) Extremely low temperatures
    (ii) Plumbing
    (iii) Building construction etc.

14.1.2. Elements of refrigeration systems

All refrigeration systems must include atleast four basic units as given below :

(i)A low temperature thermal “sink” to which heat will flow from the space to be cooled.

(ii)Means of extracting energy from the sink, raising the temperature level of this energy,

and delivering it to a heat receiver.

(iii)A receiver to which heat will be transferred from the high temperature high-pressure

refrigerant.

(iv)Means of reducing of pressure and temperature of the refrigerant as it returns from the

receiver to the “sink”.

14.1.3. Refrigeration systems

The various refrigeration systems may be enumerated as below :

1. Ice refrigeration 2. Air refrigeration system


2. Vapour compression refrigeration system


3. Vapour absorption refrigeration system


4. Special refrigeration systems
   (i) Adsorption refrigeration system (ii) Cascade refrigeration system
   (iii) Mixed refrigeration system (iv) Vortex tube refrigeration system
   (v) Thermoelectric refrigeration (vi) Steam jet refrigeration system.

14.1.4. Co-efficient of performance (C.O.P.)

The performance of a refrigeration system is expressed by a term known as the ‘‘co-efficient
of performance’’, which is defined as the ratio of heat absorbed by the refrigerant while passing
through the evaporator to the work input required to compress the refrigerant in the compressor ;
in short it is the ratio between heat extracted and work done (in heat units).
If, Rn = Net refrigerating effect,
W = Work expanded in by the machine during the same interval of time,