The production of cold is accomplished by two well-known mechanisms,such as
- Cooling by evaporation
- Cooling by heat transfer
1. Cooling by evaporation
Whenever a liquid evaporates, it absorbs heat from its surroundings, which cools the liquid.
Example: cooling of the water in earthen pots for drinking purposes.
2. Cooling by heat transfer
It is known that heat always travels from a hot space to a cold space, during this process hot space
cools down and cold space heats up. This is cooling by heat transfer.
It the reversible flow of heat transfer is required (transfer of heat from cold space to hot space)
an external energy is required as per the second law of thermodynamics.
Unit of refrigeration
Due to the fact that refigeration was first produced by ice, the refrigeration effect of refrigerating system was compared with the refrigeration produced by ice. The rate of cooling was expressed in terms of
“Tons of ice required per unit time”.
One ton of refrigeration is defined as the amount of cooling produced by melting one ton of ice from
and at O*C in 24 hours.
One american ton of ice x Latent heat of condensation of ice
One Ton of Refrigeration = ————————————————————————-
24 hours (duration)
(1 x 907 x 336)
= ——————— 1 amerian ton = 907kg
= 12700 KJ/hr
One Ton of Refrigeration (1 TR) = 12700 KJ/hr.
= 210 KJ/min.
3.516 KJ/sec. or KW