In ancient Greece slaves were used to transport snow from the mountains that were stored in straw during the hot summer months. The Egyptians placed pots made of porous material, filled with water outside their homes at night. The cold desert wind chilled the water by the evaporation of moisture.
Currently we have the means to produce refrigeration in any season, but it was from 1923 that the refrigeration took its great impulse with the advent of the mechanical unit ranging from the manufacture of ice cream to the conservation of milk and perishable products.
Refrigeration can be produced in several ways, but the simplest way would be to keep two hot and one cold substances in contact. The heat flowing from the hottest to the coldest will at any given moment provide a thermal equilibrium, that is, it will equal the temperature of both substances. This is what happens when we put a glass of hot milk to cool inside a container with cold water. The milk gives out heat to the water, which in turn will heat up until both reach the same temperature level.
It should also be noted that refrigeration is not a process of adding cold, as one normally thinks, but rather of removing heat. The household refrigerator does not add cold inside the cabinet, but rather, remove the heat from the food stored in it.
