The Siemens cycle is a technique used to cool or
liquefy gases. A
gas
Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma).
A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...
is compressed, leading to an increase in its
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
due to the directly proportional relationship between temperature and pressure (as stated by
Gay-Lussac's law
Gay-Lussac's law usually refers to Joseph-Louis Gay-Lussac's law of combining volumes of gases, discovered in 1808 and published in 1809. It sometimes refers to the proportionality of the volume of a gas to its absolute temperature at constant pr ...
). The compressed gas is then cooled by a
heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
and decompressed, resulting in a (possibly condensed) gas that is colder than the original at the same pressure.
Carl Wilhelm Siemens
Sir Carl Wilhelm Siemens (4 April 1823 – 19 November 1883), anglicised to Charles William Siemens, was a German-British electrical engineer and businessman.
Biography
Siemens was born in the village of Lenthe, today part of Gehrden, near Han ...
patented the Siemens cycle in 1857.
In the Siemens cycle the gas is:
:1. Heated – by compressing the gas – adding external energy into the gas, to give it what is needed for running through the cycle
:2. Cooled – by immersing the gas in a cooler environment, losing some of its heat (and energy)
:3. Cooled through heat exchanger with returning gas from next (and last stage)
:4. Cooled further by expanding the gas and doing work, removing heat (and energy)
The gas which is now at its coolest in the current cycle, is recycled and sent back to be –
:5. Heated – when participating as the coolant for stage 3, and then
:6. Resent to stage one, to start the next cycle, and be slightly reheated by compression.
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.
See also
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Adiabatic process
In thermodynamics, an adiabatic process (Greek: ''adiábatos'', "impassable") is a type of thermodynamic process that occurs without transferring heat or mass between the thermodynamic system and its environment. Unlike an isothermal process, ...
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Gas compressor
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Compressors are similar to pumps: both increase the pressure on a fluid and both can transp ...
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Hampson–Linde cycle
The Hampson–Linde cycle is a process for the liquefaction of gases, especially for air separation. William Hampson and Carl von Linde independently filed for patents of the cycle in 1895: Hampson on 23 May 1895 and Linde on 5 June 1895.
The Ha ...
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Regenerative cooling
Regenerative cooling is a method of cooling gases in which compressed gas is cooled by allowing it to expand and thereby take heat from the surroundings. The cooled expanded gas then passes through a heat exchanger where it cools the incoming comp ...
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Timeline of low-temperature technology
The following is a timeline of low-temperature technology and cryogenic technology (refrigeration down to –273.15 °C, –459.67 °F or 0 K). It also lists important milestones in thermometry, thermodynamics, statistical physics and ca ...
References
Thermodynamic cycles
1857 in science
1857 in Germany
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