Linde’s process is known as Adiabatic expansion of compressed gas.
The process is based upon Joule – Thomson Effect, which states,
“When a gas under high pressure is allowed to expand adiabatically through a fine hole into a region of low pressure, it is accompanied by cooling.
The term ‘adiabatically’ means that apparatus is perfectly insulated so that no heat is lost to or gained from the surroundings.
C.T.M (An obvious reason for the cooling is that when the gas expands from a region of high pressure to the region of low pressure, the intermolecular distance increases. Some work is to be done for increasing intermolecular distances. This is done on the cost of Kinetic energy of the gas. Thus, the Kinetic energy of the gas decreases and therefore the temperature falls).
The process based upon the above principle is known as Linde’s Process. The apparatus used is shown in figure on side with names of different parts. This apparatus was used by Linde to liquefy air.
The air is first compressed to about 200 atmospheres in the compressor and then passed through the condensing coils. As a result, the air is cooled and the water vapours present condense to form the water which is removed from receiver. The dry air is then passed through the spiral copper tube which terminates into a jet .The air expands through the jet into the chamber where pressure is about 50 atmospheres. Thus, as a result of Joule-Thomson effect, the air is cooled. As this cooled air moves up, it further cools the incoming air. The cooled air is sent to the compressor again and the process is repeated a number of times till ultimately the air is cooled to such an extent that it liquefies. The liquefied air gets collected at the bottom of the outer chamber and can be drawn off. Any uncondensed air is recirculated.