An order from the Guinness Brewery in Dublin in 1892 to develop and install a carbon dioxide liquefaction plant gave von Linde the concrete impulse that started his work with low temperatures. Carl von Linde accepted the project even though his company had never built such a plant. In 1894, von Linde began developing an early air liquefaction machine based on the knowledge gained from carbon dioxide liquefaction. He started from the idea of using the air itself as a refrigerant - using the cold generated when air moves from a higher pressure to a lower one for the additional cooling. This effect had already been described in 1862 by researchers Thomson and Joule.
Sketch of the first air liquefaction plant from 1895.
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| Sketch of the first air liquefaction plant from 1895. |
The process
The more air is compressed, the more cold is generated when it expands. This cooling effect increases exponentially when the air is pre-cooled. However, von Linde could not achieve the temperature Celsius needed to liquefy the air (about minus 190 degrees) from expansion from high to low pressure and precooling alone. That required a cooling cycle in which the cold generated by the expansion is transferred to the compressed, pre-cooled air in the countercurrent. In a continuous process, the cold given off from each cycle was multiplied until the air was liquefied and could be collected in a container.
While proven technology was available for compression and pre-cooling, the challenge for von Linde and his son Friedrich, who worked in the refrigeration testing station after receiving his Doctorate in physics, was to develop a suitable countercurrent apparatus. They decided on a 100-meter long double steel tube, which was wound into a spiral and well insulated, encased in wood.