Diffusion pump: Difference between revisions
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{{Short description|High vacuum pump}} | {{Short description|High vacuum pump}} | ||
[[Image:M6 Diffusion Pump.jpg|right|250 px|thumb|Six inch oil diffusion pump.]] | {{multiple issues| | ||
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<!--[[Image:M6 Diffusion Pump.jpg|right|250 px|thumb|Six inch oil diffusion pump.]]--> | |||
[[File:Ulvac oil diffusion pump ULK-04 cutaway.JPG|thumb|Ulvac oil diffusion pump cutaway]] | [[File:Ulvac oil diffusion pump ULK-04 cutaway.JPG|thumb|Ulvac oil diffusion pump cutaway]] | ||
'''Diffusion pumps''' use a high speed jet of vapor to direct gas [[molecule]]s in the pump throat down into the bottom of the pump and out the exhaust. They were the first type of high [[vacuum pump]]s operating in the regime of [[free molecular flow]], where the movement of the gas molecules can be better understood as [[diffusion]] than by conventional [[fluid dynamics]]. Invented in 1915 by [[Wolfgang Gaede]], he named it a ''diffusion pump'' since his design was based on the finding that gas cannot diffuse against the vapor stream, but will be carried with it to the exhaust.<ref>{{cite journal | author = | '''Diffusion pumps''' use a high speed jet of vapor to direct gas [[molecule]]s in the pump throat down into the bottom of the pump and out the exhaust. They were the first type of high [[vacuum pump]]s operating in the regime of [[free molecular flow]], where the movement of the gas molecules can be better understood as [[diffusion]] than by conventional [[fluid dynamics]]. Invented in 1915 by [[Wolfgang Gaede]], he named it a ''diffusion pump'' since his design was based on the finding that gas cannot diffuse against the vapor stream, but will be carried with it to the exhaust.<ref>{{cite journal | author = Avery DG & Witty, R | year = 1947 | title = Diffusion Pumps: A Critical Discussion of Existing Theories| journal = [[Proc. Phys. Soc.]] | volume = 59 | issue = 6| pages = 1016–1030 | doi = 10.1088/0959-5309/59/6/313 | url = https://iopscience.iop.org/article/10.1088/0959-5309/59/6/313/pdf | url-access = subscription | bibcode = 1947PPS....59.1016A }}</ref>{{better source|date=September 2025}} Some consider the principle of operation to be more precisely described as ''gas-jet pump'',{{says who|date=September 2025}}<!--Do not state in bold font ideas / nomenclature that is not sourced.--> since diffusion also plays a role in other types of high vacuum pumps.{{citation needed lead|date=September 2025}} In modern textbooks, the diffusion pump is categorized as a [[vacuum pump#Momentum transfer|momentum transfer]] pump.{{citation needed lead|date=September 2025}} | ||
The diffusion pump is widely used in both industrial and research applications. Most modern diffusion pumps use [[silicone oil]] or [[polyphenyl ether]]s as the working fluid. | The diffusion pump is widely used in both industrial and research applications.{{citation needed lead|date=September 2025}} Most modern diffusion pumps use [[silicone oil]] or [[polyphenyl ether]]s as the working fluid.{{citation needed lead|date=September 2025}} | ||
==History== | ==History== | ||
In the late 19th century, most vacuums were created using a [[Sprengel pump]], which had the advantage of being very simple to operate, and capable of achieving quite good vacuum given enough time. Compared to later pumps, however, the pumping speed was very slow and the [[vapor pressure]] of the liquid mercury limited the ultimate vacuum. | In the late 19th century, most vacuums were created using a [[Sprengel pump]],{{cn|date=September 2025}} which had the advantage of being very simple to operate, and capable of achieving quite good vacuum given enough time.{{cn|date=September 2025}} Compared to later pumps, however, the pumping speed was very slow and the [[vapor pressure]] of the liquid mercury limited the ultimate vacuum.{{cn|date=September 2025}} | ||
Following his invention of the [[Holweck pump|molecular pump]], [[Wolfgang Gaede]] invented the diffusion pump in 1915,<ref>{{cite journal | year = 1915 | journal = [[Annalen der Physik]] | volume = 46 | page = 357 | author = Gaede, W. | doi = 10.1002/andp.19153510304 | title = Die Diffusion der Gase durch Quecksilberdampf bei niederen Drucken und die Diffusionsluftpumpe | issue = 3|bibcode = 1915AnP...351..357G | url = https://zenodo.org/record/1447291 }}</ref> and originally used [[Mercury (element)|elemental mercury]] as the working fluid. After its invention, the design was quickly commercialized by [[Leybold GmbH|Leybold]].<ref>{{cite web | last=Sella | first=Andrea | title=Classic Kit: Gaede's diffusion pump | website=Chemistry World | date=2009-04-28 | url=https://www.chemistryworld.com/opinion/classic-kit-gaedes-diffusion-pump/3004912.article | access-date=2019-08-03}}</ref> It was then improved by [[Irving Langmuir]]<ref>{{cite journal|title=The Condensation Pump: An Improved Form of High Vacuum Pump|first=Irving|last=Langmuir|journal=General Electric Review|year=1916|volume=19|pages=1060–1071|url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015075043383&view=1up&seq=1104}}</ref> and W. Crawford. [[Cecil Reginald Burch]] | Following his invention of the [[Holweck pump|molecular pump]], [[Wolfgang Gaede]] invented the diffusion pump in 1915,<ref>{{cite journal | year = 1915 | journal = [[Annalen der Physik]] | volume = 46 | page = 357 | author = Gaede, W. | doi = 10.1002/andp.19153510304 | title = Die Diffusion der Gase durch Quecksilberdampf bei niederen Drucken und die Diffusionsluftpumpe | issue = 3|bibcode = 1915AnP...351..357G | url = https://zenodo.org/record/1447291 }}</ref> and originally used [[Mercury (element)|elemental mercury]] as the working fluid. After its invention, the design was quickly commercialized by [[Leybold GmbH|Leybold]].<ref>{{cite web | last=Sella | first=Andrea | title=Classic Kit: Gaede's diffusion pump | website=Chemistry World | date=2009-04-28 | url=https://www.chemistryworld.com/opinion/classic-kit-gaedes-diffusion-pump/3004912.article | access-date=2019-08-03}}</ref> It was then improved by [[Irving Langmuir]],<ref>{{cite journal|title=The Condensation Pump: An Improved Form of High Vacuum Pump|first=Irving|last=Langmuir|journal=General Electric Review|year=1916|volume=19|pages=1060–1071|url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015075043383&view=1up&seq=1104}}</ref> and W. Crawford.{{cn|date=September 2025}} [[Cecil Reginald Burch|C.R. Burch]] described the possibility of using [[silicone oil]] in 1928.<ref>{{cite journal | author = Burch, CR | title = Oils, greases and high vacua | journal = [[Nature (journal)|Nature]] | volume = 122 | year = 1928 | page = 729 | doi = 10.1038/122729c0 | issue = 3080|bibcode = 1928Natur.122..729B | s2cid = 4126707 | doi-access = free }} Note, the DOI and URL provided here only allow access to the abstract, not the article as a whole.</ref>{{failed verification|date=September 2025}}<!--Article, to the extent accessible, addresses only oils that are petroleum derivatives. Please provide a quote of the relevant article statements to remove the tag.--> | ||
==Oil diffusion pumps== | ==Oil diffusion pumps== | ||
{{unreferenced section|date=September 2025}} | |||
An oil diffusion pump is used to achieve higher vacuum (lower pressure) than is possible by use of [[Positive displacement vacuum pump|positive displacement]] pumps alone. Although its use has been mainly associated within the high-vacuum range, down to | An oil diffusion pump is used to achieve higher vacuum (lower pressure) than is possible by use of [[Positive displacement vacuum pump|positive displacement]] pumps alone. Although its use has been mainly associated within the high-vacuum range, down to | ||
{{convert|1e-9|mbar|Pa|sigfig=1|abbr=on|lk=on}}, diffusion pumps today can produce pressures approaching | {{convert|1e-9|mbar|Pa|sigfig=1|abbr=on|lk=on}}, diffusion pumps today can produce pressures approaching | ||
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The oil of a diffusion pump cannot be exposed to the atmosphere when hot. If this occurs, the oil will oxidise and has to be replaced. If a fire occurs, the smoke and residue may contaminate other parts of the system. | The oil of a diffusion pump cannot be exposed to the atmosphere when hot. If this occurs, the oil will oxidise and has to be replaced. If a fire occurs, the smoke and residue may contaminate other parts of the system. | ||
==Oil types== | |||
{{See also|Polyphenyl ether#Ultra-high-vacuum fluids}} | {{See also|Polyphenyl ether#Ultra-high-vacuum fluids}} | ||
===Silicon oils=== | |||
The most common [[silicone oil]]s used in diffusion pumps are [[trisiloxane]]s, which contain the chemical group Si-O-Si-O-Si, to which various [[phenyl group]]s or [[methyl group]]s are attached. These are available as the so-called 702 and 703 blends, which were formerly manufactured by [[Dow Corning]]. These can be further separated into 704 and 705 oils, which are made up of the isomers of tetraphenyl tetramethyl trisiloxane and pentaphenyl trimethyl trisiloxane respectively.<ref>{{cite book | author = O'Hanlon, John F. | date=2003 | title=A User's Guide to Vacuum Technology | chapter=Pump Fluids | location=Hoboken, NJ | publisher=John Wiley & Sons | isbn=9780471467168 | url = https://onlinelibrary.wiley.com/doi/abs/10.1002/0471467162.ch13 | doi=10.1002/0471467162.ch13 | pages=229–246}} Note, there is no available textual content at this weblink.</ref>{{verification needed|date=September 2025}}{{better source|date=September 2025}} | |||
===Hydrocarbon oils=== | |||
{{unreferenced section|date=September 2025}} | |||
The least expensive diffusion pump oils are based on [[hydrocarbon]]s which have been purified by double-distillation. Compared with the other fluids, they have higher vapor pressure, so are usually limited to a pressure of | The least expensive diffusion pump oils are based on [[hydrocarbon]]s which have been purified by double-distillation. Compared with the other fluids, they have higher vapor pressure, so are usually limited to a pressure of | ||
{{convert|1e-6|Torr|Pa|abbr=on|lk=in}}. They are also the most likely to burn or explode if exposed to oxidizers. | {{convert|1e-6|Torr|Pa|abbr=on|lk=in}}. They are also the most likely to burn or explode if exposed to oxidizers. | ||
For pumping reactive species, usually a [[polyphenyl ether]] based oil is used. These oils are the most chemical and heat resistant type of diffusion pump oil. | For pumping reactive species, usually a [[polyphenyl ether]] based oil is used. These oils are the most chemical and heat resistant type of diffusion pump oil. | ||
==Steam ejectors== | ==Steam ejectors== | ||
{{unreferenced section|date=September 2025}} | |||
[[Image:DP_pumping_speed_plot.png|thumb|right|250 px|Plot of pumping speed as a function of pressure for a diffusion pump.]] | [[Image:DP_pumping_speed_plot.png|thumb|right|250 px|Plot of pumping speed as a function of pressure for a diffusion pump.]] | ||
{{main|Vacuum ejector}} | {{main|Vacuum ejector}} | ||
[[Image:Langmuir mercury diffusion pump.jpg|thumb|Early Langmuir mercury diffusion pump ''(vertical column)'' and its backing pump ''(in background)'', about 1920. The diffusion pump was widely used in manufacturing [[vacuum tube]]s, the key technology which dominated the radio and electronics industry for 50 years.]] | [[Image:Langmuir mercury diffusion pump.jpg|thumb|Early Langmuir mercury diffusion pump ''(vertical column)'' and its backing pump ''(in background)'', about 1920.{{cn|date=September 2025}} The diffusion pump was widely used in manufacturing [[vacuum tube]]s, the key technology which dominated the radio and electronics industry for 50 years.{{cn|date=September 2025}}]] | ||
The steam ejector is a popular form of pump for vacuum [[distillation]] and [[freeze-drying]]. A jet of steam entrains the vapour that must be removed from the vacuum chamber. Steam ejectors can have single or multiple stages, with and without [[Condenser (steam turbine)|condensers]] in between the stages. While both steam ejectors and diffusion pumps use jets of vapor to entrain gas, they work on fundamentally different principles - steam ejectors rely on viscous flow and mixing to pump gas, whereas diffusion pumps use molecular diffusion. This has several consequences. In diffusion pumps, the inlet pressure can be much lower than the static pressure of jet, whereas in steam ejectors the two pressures are about the same. Also, diffusion pumps are capable of much higher compression ratios, and cannot discharge directly to atmosphere. | The steam ejector is a popular form of pump for vacuum [[distillation]] and [[freeze-drying]]. A jet of steam entrains the vapour that must be removed from the vacuum chamber. Steam ejectors can have single or multiple stages, with and without [[Condenser (steam turbine)|condensers]] in between the stages. While both steam ejectors and diffusion pumps use jets of vapor to entrain gas, they work on fundamentally different principles - steam ejectors rely on viscous flow and mixing to pump gas, whereas diffusion pumps use molecular diffusion. This has several consequences. In diffusion pumps, the inlet pressure can be much lower than the static pressure of jet, whereas in steam ejectors the two pressures are about the same. Also, diffusion pumps are capable of much higher compression ratios, and cannot discharge directly to atmosphere. | ||
Latest revision as of 21:27, 1 October 2025
Template:Short description Template:Multiple issues
Diffusion pumps use a high speed jet of vapor to direct gas molecules in the pump throat down into the bottom of the pump and out the exhaust. They were the first type of high vacuum pumps operating in the regime of free molecular flow, where the movement of the gas molecules can be better understood as diffusion than by conventional fluid dynamics. Invented in 1915 by Wolfgang Gaede, he named it a diffusion pump since his design was based on the finding that gas cannot diffuse against the vapor stream, but will be carried with it to the exhaust.[1]Template:Better source Some consider the principle of operation to be more precisely described as gas-jet pump,Template:Says who since diffusion also plays a role in other types of high vacuum pumps.Template:Citation needed lead In modern textbooks, the diffusion pump is categorized as a momentum transfer pump.Template:Citation needed lead
The diffusion pump is widely used in both industrial and research applications.Template:Citation needed lead Most modern diffusion pumps use silicone oil or polyphenyl ethers as the working fluid.Template:Citation needed lead
History
In the late 19th century, most vacuums were created using a Sprengel pump,Script error: No such module "Unsubst". which had the advantage of being very simple to operate, and capable of achieving quite good vacuum given enough time.Script error: No such module "Unsubst". Compared to later pumps, however, the pumping speed was very slow and the vapor pressure of the liquid mercury limited the ultimate vacuum.Script error: No such module "Unsubst".
Following his invention of the molecular pump, Wolfgang Gaede invented the diffusion pump in 1915,[2] and originally used elemental mercury as the working fluid. After its invention, the design was quickly commercialized by Leybold.[3] It was then improved by Irving Langmuir,[4] and W. Crawford.Script error: No such module "Unsubst". C.R. Burch described the possibility of using silicone oil in 1928.[5]Script error: No such module "Unsubst".
Oil diffusion pumps
Script error: No such module "Unsubst". An oil diffusion pump is used to achieve higher vacuum (lower pressure) than is possible by use of positive displacement pumps alone. Although its use has been mainly associated within the high-vacuum range, down to Template:Convert, diffusion pumps today can produce pressures approaching Template:Convert when properly used with modern fluids and accessories. The features that make the diffusion pump attractive for high and ultra-high vacuum use are its high pumping speed for all gases and low cost per unit pumping speed when compared with other types of pump used in the same vacuum range. Diffusion pumps cannot discharge directly into the atmosphere, so a mechanical forepump is typically used to maintain an outlet pressure around Template:Convert.
The oil diffusion pump is operated with an oil of low vapor pressure. The high speed jet is generated by boiling the fluid and directing the vapor through a jet assembly. Note that the oil is gaseous when entering the nozzles. Within the nozzles, the flow changes from laminar to supersonic and molecular. Often, several jets are used in series to enhance the pumping action. The outside of the diffusion pump is cooled using either air flow, water lines or a water-filled jacket. As the vapor jet hits the outer cooled shell of the diffusion pump, the working fluid condenses and is recovered and directed back to the boiler. The pumped gases continue flowing to the base of the pump at increased pressure, flowing out through the diffusion pump outlet, where they are compressed to ambient pressure by the secondary mechanical forepump and exhausted.
Unlike turbomolecular pumps and cryopumps, diffusion pumps have no moving parts and as a result are quite durable and reliable. They can function over pressure ranges of Template:Convert. They are driven only by convection and thus have a very low energy efficiency.
One major disadvantage of diffusion pumps is the tendency to backstream oil into the vacuum chamber. This oil can contaminate surfaces inside the chamber or upon contact with hot filaments or electrical discharges may result in carbonaceous or siliceous deposits. Due to backstreaming, oil diffusion pumps are not suitable for use with highly sensitive analytical equipment or other applications which require an extremely clean vacuum environment, but mercury diffusion pumps may be in the case of ultra high vacuum chambers used for metal deposition. Often cold traps and baffles are used to minimize backstreaming, although this results in some loss of pumping speed.
The oil of a diffusion pump cannot be exposed to the atmosphere when hot. If this occurs, the oil will oxidise and has to be replaced. If a fire occurs, the smoke and residue may contaminate other parts of the system.
Oil types
Script error: No such module "Labelled list hatnote".
Silicon oils
The most common silicone oils used in diffusion pumps are trisiloxanes, which contain the chemical group Si-O-Si-O-Si, to which various phenyl groups or methyl groups are attached. These are available as the so-called 702 and 703 blends, which were formerly manufactured by Dow Corning. These can be further separated into 704 and 705 oils, which are made up of the isomers of tetraphenyl tetramethyl trisiloxane and pentaphenyl trimethyl trisiloxane respectively.[6]Script error: No such module "Unsubst".Template:Better source
Hydrocarbon oils
Script error: No such module "Unsubst". The least expensive diffusion pump oils are based on hydrocarbons which have been purified by double-distillation. Compared with the other fluids, they have higher vapor pressure, so are usually limited to a pressure of Template:Convert. They are also the most likely to burn or explode if exposed to oxidizers.
For pumping reactive species, usually a polyphenyl ether based oil is used. These oils are the most chemical and heat resistant type of diffusion pump oil.
Steam ejectors
Script error: No such module "Unsubst".
Script error: No such module "Labelled list hatnote".
The steam ejector is a popular form of pump for vacuum distillation and freeze-drying. A jet of steam entrains the vapour that must be removed from the vacuum chamber. Steam ejectors can have single or multiple stages, with and without condensers in between the stages. While both steam ejectors and diffusion pumps use jets of vapor to entrain gas, they work on fundamentally different principles - steam ejectors rely on viscous flow and mixing to pump gas, whereas diffusion pumps use molecular diffusion. This has several consequences. In diffusion pumps, the inlet pressure can be much lower than the static pressure of jet, whereas in steam ejectors the two pressures are about the same. Also, diffusion pumps are capable of much higher compression ratios, and cannot discharge directly to atmosphere.
See also
References
External links
Further reading
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- ↑ Script error: No such module "Citation/CS1". Note, the DOI and URL provided here only allow access to the abstract, not the article as a whole.
- ↑ Script error: No such module "citation/CS1". Note, there is no available textual content at this weblink.