Siemens cycle

The Siemens cycle is a technique used to cool or liquefy gases. A gas is compressed, leading to an increase in its temperature (by Gay-Lussac's law relating pressure and temperature). The compressed gas is then cooled by a heat exchanger, then the cool, compressed gas is allowed to decompress, further cooling it (again by Gay-Lussac's law). This results in a gas (or liquefied gas) that is colder than the original and at the same pressure.

Carl Wilhelm Siemens patented the Siemens cycle in 1857.

In the Siemens cycle the gas is:

The gas which is now at its coolest in the current cycle, is recycled and sent back to be -

In each cycle the net cooling is more than the heat added at the beginning of the cycle. As the gas passes more cycles and becomes cooler, reaching lower temperatures at the expanding cylinder (stage 4 of the Siemens cycle) becomes more difficult.

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