REFRIGERATION

Introduction Refrigeration is defined as the process of extracting heat from a lower-temperature heat source, substance, or cooling medium and transferring it to a higher-temperature heat sink. Refrigeration maintains the temperature of the heat source below that of its surroundings while transferring the extracted heat, and any required energy input, to a heat sink, atmospheric air, or surface water. A refrigeration system is a combination of components and equipment connected in a sequential order to produce the refrigeration effect.

Applications of Refrigeration Preservation of perishable food products by storing them at low temperatures: Refrigerators Freezers Cold Stores Providing thermal comfort to human beings by means of air conditioning: Window-type air conditioners Split-type air conditioners Chillers

History Of Refrigeration Natural Refrigeration Using Ice: Transported from colder regions Harvested in winter and stored in ice houses for summer use Made during night by cooling of water by radiation to stratosphere.

History Of Refrigeration Natural Refrigeration Evaporative Cooling: the process of reducing the temperature of a system by evaporation of water. Human beings perspire and dissipate their metabolic heat by evaporative cooling if the ambient temperature is more than skin temperature. Example: earthen pots The water permeates through the pores of earthen vessel to its outer surface where it evaporates to the surrounding, absorbing its latent heat in part from the vessel, which cools the water.

History Of Refrigeration Artificial Refrigeration It is generally agreed that artificial refrigeration began in 1755, when the Scottish professor William Cullen made the first refrigerating machine, which could produce a small quantity of ice in the laboratory. He placed some water in thermal contact with ether under a receiver of a vacuum pump. The evaporation rate of ether increased due to the vacuum pump and water could be frozen.

History Of Refrigeration Artificial Refrigeration The process demonstrated by Cullen was not continuous. The vapors have to be recycled by condensation to the liquid state. The condensation process requires heat rejection to the surroundings. Therefore, the vapor has to be at a higher temperature than the surroundings. To increase the vapor’s temperature, the pressure has to be increased. A compressor is required to increase the pressure.

History Of Refrigeration Artificial Refrigeration Jacob Perkins obtained the first patent for a vapor-compression refrigeration system in 1834. Perkins built a prototype system and it actually worked, although it did not succeed commercially The man responsible for making a practical vapor compression refrigeration system was James Harrison. He was granted a patent in 1856 for a vapor compression system using ether, alcohol or ammonia. The American engineer Alexander Twining received a patent in 1850 for a vapor compression system that uses ether, NH3 and CO2.