Editing Vacuum flask

{{short description|Double-walled insulated storage vessel}}
{{redirect|Thermos|the company|Thermos LLC|other uses}}
{{About|the vacuum-insulated flask|the flask used in filtration under vacuum|Büchner flask}}
[[File:Thermos.JPG|thumb|upright|The typical design of a [[Thermos L.L.C.|Thermos brand]] vacuum flask, used for maintaining the temperature of fluids such as [[coffee]]]]

A '''vacuum flask''' (also known as a '''Dewar flask''', '''Dewar bottle''' or '''thermos''') is an [[thermal insulation|insulating]] storage vessel that slows the speed at which its contents change in temperature.  It greatly lengthens the time over which its contents remain hotter or cooler than the flask's surroundings by trying to be as [[adiabatic]] as possible. Invented by [[James Dewar]] in 1892, the vacuum flask consists of two [[wiktionary:flask|flask]]s, placed one within the other and joined at the neck. The gap between the two flasks is partially evacuated of air, creating a near-[[vacuum]] which significantly reduces heat transfer by [[heat conduction|conduction]] or [[convection]]. When used to hold cold liquids, this also virtually eliminates condensation on the outside of the flask.

Vacuum flasks are used domestically to keep contents inside hot or cold for extended periods of time. They are also used for [[thermal cooking]]. Vacuum flasks are also used for many purposes in industry.

== History ==
[[File:Vacuum Dewar Flask.svg|thumb|upright|left|Diagram of a vacuum flask]]
[[File:Gustav R. Paalen, Double Welled Vessel 1909.png|thumb|upright|Gustav Robert Paalen, Double Walled Vessel. Patent 27 June 1908, published 13 July 1909]]

The vacuum flask was designed and invented by Scottish scientist [[James Dewar]] in 1892 as a result of his research in the field of [[cryogenics]] and is sometimes called a Dewar flask in his honour. While performing experiments in determining the [[specific heat]] of the element [[palladium]], Dewar made a brass chamber that he enclosed in another chamber to keep the palladium at its desired temperature.<ref name=Soulen>{{cite journal|last=Soulen|first=Robert|title=James Dewar, His Flask and Other Achievements |journal=Physics Today|volume=49|number=3|date=March 1996|pages=32–37|doi=10.1063/1.881490|bibcode = 1996PhT....49c..32S }}</ref> He evacuated the air between the two chambers, creating a partial vacuum to keep the temperature of the contents stable. Dewar refused to patent his invention; this allowed others to develop the flask using new materials such as [[glass]] and [[aluminium]], and it became a significant tool for chemical experiments and also a common household item.<ref name=Soulen/>

Dewar's design was quickly transformed into a commercial item in 1904 as two German [[glassblower]]s, [[Reinhold Burger]] and Albert Aschenbrenner, discovered that it could be used to keep cold drinks cold and warm drinks warm and invented a more robust flask design, which was suited for everyday use.<ref name=Thermos>{{cite web|publisher=Thermos|title=Our History|year=2011|access-date=31 March 2013|url=http://www.thermos.com/history.aspx|archive-date=28 May 2013|archive-url=https://web.archive.org/web/20130528020038/http://www.thermos.com/history.aspx|url-status=dead}}</ref><ref>{{Cite web|title= James Dewar, the man who invented the thermos flask|url= http://www.bbc.co.uk/history/0/21835405|publisher= BBC History|date= 2 April 2013|url-status= dead|archive-url= https://web.archive.org/web/20140504200248/http://www.bbc.co.uk/history/0/21835405|archive-date= 4 May 2014}}</ref> The Dewar flask design had never been patented but the German men who discovered the commercial use for the product named it [[Thermos L.L.C.|''Thermos'']], and subsequently claimed both the rights to the commercial product and the trademark to the name. In his subsequent attempt to claim the rights to the invention, Dewar instead lost a court case to the company.<ref>{{cite web |url=http://www.chemistryexplained.com/Co-Di/Dewar-James.html |title=Dewar, James&nbsp;— BRITISH CHEMIST AND PHYSICIST  |author=Frank A. J. L. James  |publisher= Advameg, Inc. |access-date=30 December 2010}}</ref> The manufacturing and performance of the Thermos bottle was significantly improved and refined by the Viennese inventor and merchant Gustav Robert Paalen, who designed various types for domestic use, which he also patented, and distributed widely, through the Thermos Bottle Companies in the United States, Canada and the UK, which bought licences for respective national markets. The American Thermos Bottle Company built up a mass production in [[Norwich, CT]], which brought prices down and enabled the wide distribution of the product for at-home use.<ref name=Thermos/> Over time, the company expanded the size, shapes and materials of these consumer products, primarily used for carrying [[coffee]] on the go and carrying liquids on camping trips to keep them either hot or cold. Eventually other manufacturers produced similar products for consumer use.

The term "thermos" became a household name for vacuum flasks in general. {{As of|2023}}, ''Thermos'' and ''THERMOS'' remains a [[registered trademark]] in some countries, including the United States,<ref name="USPTO_67002">{{Cite web |url=https://tsdr.uspto.gov/#caseNumber=67002&caseSearchType=US_APPLICATION&caseType=SERIAL_NO&searchType=statusSearch |title=US Registration Number: 67002 |access-date=2023-04-24 |website=Trademark Search, [[United States Patent and Trademark Office]] |language=en |quote="Thermos" LIVE For:DOUBLE-WALLED GLASS VESSELS WITH VACUUM BETWEEN THE WALLS}}</ref><ref name="USPTO_176064">{{Cite web |url=https://tsdr.uspto.gov/#caseNumber=176064&caseSearchType=US_APPLICATION&caseType=SERIAL_NO&searchType=statusSearch |title=US Registration Number: 176064|access-date=2023-04-24 |website=Trademark Search, [[United States Patent and Trademark Office]] |language=en |quote="THERMOS" LIVE For:Temperature-Retaining Vessels}}</ref><ref name="USPTO_229816">{{Cite web |url=https://tsdr.uspto.gov/#caseNumber=229816&caseSearchType=US_APPLICATION&caseType=SERIAL_NO&searchType=statusSearch |title=US Registration Number: 229816|access-date=2023-04-24 |website=Trademark Search, [[United States Patent and Trademark Office]] |language=en |quote="THERMOS" LIVE For:BOTTLES, JARS, DECANTERS, CARAFES, [ HIP FLASKS,] COFFEEPOTS, TEAPOTS, JUGS, LUNCH KITS, LUNCH BOXES, CARRYING CASES FOR BOTTLES [, AND DOUBLE-WALLED VACUUM FILLERS OF GLASS USED IN BOTTLES, JARS, CARAFES, JUGS, DECANTERS, COFFEEPOTS, AND TEA-POTS] }}</ref> but the lowercase "thermos" was declared a [[generic trademark|genericized trademark]] by court action in the United States in 1963.<ref name="Folsom1980">{{Cite journal |title=Trademarked generic words |journal=The Yale Law Journal |url=https://openyls.law.yale.edu/handle/20.500.13051/15969 |last1=Folsom |first1=Ralph |volume=89 |last2=Teply |first2=Larry |hdl=20.500.13051/15969 |year=1980 |issue=7 |page=1324 |doi=10.2307/795968 |jstor=795968 |language=en |hdl-access=free}}</ref><ref name="Thermos_v_Alladin_1963">{{Cite court|litigants=King-Seeley Thermos Co. v. Aladdin Industries, Incorporated|court=United States Court of Appeals Second Circuit|vol=321|reporter=F.2nd|opinion=577 |url=https://scholar.google.com/scholar_case?case=326773422967317335|date=1963-07-11}}</ref><ref name="Thermos_v_Alladin_1970">{{Cite court|litigants=King-Seeley Thermos Co. v. Aladdin Industries, Incorporated|court=United States Court of Appeals Second Circuit|vol=320|reporter=F.Supp|opinion=1156 |url=https://scholar.google.com/scholar_case?case=17095472866185626824|date=1970-12-30}}</ref>

== Design ==
[[File:Termos, Thermofix original - Nordiska museet - NMA.0097258.jpg|thumb|upright|1930s "Thermofix" vacuum flask]]
[[file:Thermal dosirak case.jpg|thumb|A low, wide opening design]]

The vacuum flask consists of two vessels, one placed within the other and joined at the neck. The gap between the two vessels is partially evacuated of air, creating a partial-[[vacuum]] which reduces heat [[heat conduction|conduction]] or [[convection]]. Heat transfer by [[thermal radiation]] may be minimized by [[silvering]] flask surfaces facing the gap but can become problematic if the flask's contents or surroundings are very hot; hence vacuum flasks usually hold contents below the boiling point of water. Most heat transfer occurs through the neck and opening of the flask, where there is no vacuum. Vacuum flasks are usually made of [[metal]], [[borosilicate glass]], [[foam]] or [[plastic]] and have their opening [[bung|stoppered]] with [[cork (material)|cork]] or polyethylene plastic. Vacuum flasks are often used as [[insulated shipping container]]s.

Extremely large or long vacuum flasks sometimes cannot fully support the inner flask from the neck alone, so additional support is provided by ''spacers'' between the interior and exterior shell. These spacers act as a thermal bridge and partially reduce the insulating properties of the flask around the area where the spacer contacts the interior surface.

Several technological applications, such as [[NMR]] and [[MRI]] machines, rely on the use of double vacuum flasks. These flasks have two vacuum sections. The inner flask contains liquid [[helium]] and the outer flask contains liquid nitrogen, with one vacuum section in between. The loss of precious helium is limited in this way.

Other improvements to the vacuum flask include the ''vapour-cooled radiation shield'' and the ''vapour-cooled neck'',<ref>{{cite web |url=http://www.cryogenicsociety.org/resources/cryo_central/history_of_cryogenics/ |title=History of Cryogenics: A Cryo Central resource from the CSA |publisher=Cryogenicsociety.org |date=2008-04-18 |access-date=2012-11-29 |archive-date=2018-03-27 |archive-url=https://web.archive.org/web/20180327202832/https://www.cryogenicsociety.org/resources/cryo_central/history_of_cryogenics/ |url-status=dead }}</ref> both of which help to reduce evaporation from the flask.

== Research and industry ==
{{see also|Cryogenic storage dewar}}
[[File:Dewargefäß Deutsches Museum.jpg|thumb|upright|Laboratory Dewar flask, [[Deutsches Museum]], Munich]]
[[File:Liquid nitrogen tank.JPG|thumb|upright|left|A [[cryogenic storage dewar]] of [[liquid nitrogen]], used to supply a [[Cryopreservation|cryogenic freezer]]]]

In laboratories and industry, vacuum flasks are often used to hold liquefied gases (commonly liquid nitrogen with a boiling point of 77 K) for flash freezing, sample preparation and other processes where creating or maintaining an extreme low temperature is desired.  Larger vacuum flasks store liquids that become gaseous at well below ambient temperature, such as [[oxygen]] and [[nitrogen]]; in this case the leakage of heat into the extremely cold interior of the bottle results in a slow boiling-off of the liquid so that a narrow unstoppered opening, or a stoppered opening protected by a [[pressure relief valve]], is necessary to prevent [[pressure]] from building up and eventually shattering the flask. The insulation of the vacuum flask results in a very slow "boil" and thus the contents remain liquid for long periods without [[refrigeration]] equipment.

Vacuum flasks have been used to house [[Weston cell|standard cell]]s and ovenized [[Zener diode]]s, along with their printed circuit board, in precision voltage-regulating devices used as electrical standards. The flask helped with controlling the Zener temperature over a long time span and was used to reduce variations of the output voltage of the Zener standard owing to temperature fluctuation to within a few parts per million.

One notable use was by Guildline Instruments, of Canada, in their Transvolt, model 9154B, saturated standard cell, which is an electrical voltage standard. Here a silvered vacuum flask was encased in foam insulation and, using a large glass vacuum plug, held the saturated cell. The output of the device was 1.018 volts and was held to within a few parts per million.

The principle of the vacuum flask makes it ideal for storing certain types of rocket fuel, and [[NASA]] used it extensively in the propellant tanks of the Saturn launch vehicles in the 1960s and 1970s.<ref>Cortright, Edgar. "Apollo Expeditions to the Moon." Official NASA publications. 1975.</ref>

The design and shape of the Dewar flask was used as a model for [[optical]] experiments based on the idea that the shape of the two compartments with the space in between is similar to the way the light hits the eye.<ref>{{cite journal | last1 = Haynes | first1 = John | last2 = Scott | first2 = Jesse | year = 1948 | title = A Method for Silvering a Dewar Flask for Optical Experiments | journal = Science | volume = 107 | issue = 2777| page = 301 | doi=10.1126/science.107.2777.301| pmid = 17791184 | bibcode = 1948Sci...107..301H }}</ref> The vacuum flask has also been part of experiments using it as the capacitor of different chemicals in order to keep them at a consistent temperature.<ref>{{cite journal | last1 = Elliot | first1 = Willard | year = 1970 | title = A Spectrophotometric Dewar Flask with Integral Light Shield | journal = Public Health Reports | volume = 85 | issue = 3| pages = 276–279 | doi=10.2307/4593845| pmc = 2031665 | pmid=4984895| jstor = 4593845 }}</ref>

The industrial Dewar flask is the base for a device used to passively insulate medical shipments.<ref>{{cite magazine|url=https://www.wired.com/2013/06/how-to-design-a-life-saving-device|title=This Revolutionary Cooler Could Save Millions of Lives|date=18 June 2013|magazine=WIRED|last1=Stinson|first1=Liz}}</ref><ref>{{cite web|url=http://www.fiercevaccines.com/story/gates-backed-device-extends-cold-chain-rural-areas/2013-07-18|archive-url=https://web.archive.org/web/20130721200830/http://www.fiercevaccines.com/story/gates-backed-device-extends-cold-chain-rural-areas/2013-07-18|url-status=usurped|archive-date=July 21, 2013|title=Gates-backed device extends cold chain to rural areas|work=FierceVaccines}}</ref> Most vaccines are sensitive to heat<ref>{{cite journal|title=Frequent exposure to suboptimal temperatures in vaccine cold-chain system in India: results of temperature monitoring in 10 states| pmc=3845272 | pmid=24347729|doi=10.2471/BLT.13.119974|volume=91| issue=12 |year=2013|pages=906–13|vauthors= Murhekar MV, Dutta S, Kapoor AN, Bitragunta S, Dodum R, Ghosh P, Swamy KK, Mukhopadhyay K, Ningombam S, Parmar K, Ravishankar D, Singh B, Singh V, Sisodiya R, Subramanian R, Takum T|journal=Bulletin of the World Health Organization}}</ref><ref>{{cite journal|title=Evaluation of the Cold-Chain for Oral Polio Vaccine in a Rural District of India|pmc=1802111| pmid=17236617|volume=122|issue=1|year=2007|pages=112–21|vauthors= Samant Y, Lanjewar H, Parker D, Block L, Tomar GS, Stein B|doi=10.1177/003335490712200116|journal=Public Health Reports}}</ref> and require a [[cold chain]] system to keep them at stable, near freezing temperatures. The Arktek device uses eight one-litre ice blocks to hold vaccines at under 10 [[Celsius|°C]].<ref>{{cite press release|url=http://arktek.org/news-detail.html|title=Arktek Awarded Prequalified PQS Status by WHO|date=2015-04-26|publisher=ARKTEK|access-date=2016-02-25|archive-date=2016-03-11|archive-url=https://web.archive.org/web/20160311052133/http://arktek.org/news-detail.html|url-status=dead}}</ref>

In the oil and gas industry, Dewar flasks are used to insulate the electronic components in [[Wireline Logging|wireline logging]] tools.<ref>{{Cite web|title=Thermal Management of Downhole Oil and Gas Logging Sensors for HTHP Applications Using Nanoporous Materials|url=https://www.researchgate.net/publication/267492247|access-date=2021-02-11|website=ResearchGate|language=en}}</ref> Conventional logging tools (rated to 350&nbsp;°F) are upgraded to high-temperature specifications by installing all sensitive electronic components in a Dewar flask.<ref>Baird, Tom, et al. "High-pressure, high-temperature well logging, perforating and testing." ''Oilfield Review'' 5.2/3 (1993): 15-32.</ref>

== Safety ==
Vacuum flasks are at risk of  [[Implosion (mechanical process)|implosion]] hazard, and glass vessels under vacuum, in particular, may shatter unexpectedly.  Chips, scratches or cracks can be a starting point for dangerous vessel failure, especially when the vessel temperature changes rapidly (when hot or cold liquid is added). Proper preparation of the Dewar vacuum flask by tempering prior to use is advised to maintain and optimize the functioning of the unit. Glass vacuum flasks are usually fitted into a metal base with the cylinder contained in or coated with mesh, aluminum or plastic to aid in handling, protect it from physical damage, and contain fragments should they break.{{Citation needed|date=November 2018}}

In addition, cryogenic storage dewars are usually pressurized, and they may explode if [[pressure relief valve]]s are not used.

[[Thermal expansion]] has to be taken into account when engineering a vacuum flask. The outer and inner walls are exposed to different temperatures and will expand at different rates. The vacuum flask can rupture due to the differential in thermal expansion between the outer and inner walls. [[Expansion joint]]s are commonly used in tubular vacuum flasks to avoid rupture and maintain vacuum integrity.

== See also ==
* {{anl|Hermetic seal}}
* {{anl|James Webb Space Telescope sunshield}}
* {{anl|Tervis Tumbler}}
* {{anl|Thermal cooking}}
* {{anl|Yeti Holdings}}

== References ==

{{reflist}}

== Further reading ==

* Burger, R., {{US patent|872795}}, ''"Double walled vessel with a space for a vacuum between the walls,"'' December 3, 1907.
* {{cite journal | author = Sella, Andrea | title = Dewar's Flask | journal = [[Chemistry World]] |date=August 2008 | page = 75 | url = http://www.rsc.org/chemistryworld/Issues/2008/August/DewarsFlask.asp | access-date = 2008-08-30 }}

== External links ==
*{{Commons category-inline|Vacuum flasks}}

{{Laboratory equipment}}
{{Authority control}}

[[Category:Vacuum flasks| ]]
[[Category:1892 introductions]]
[[Category:Cryogenics]]
[[Category:Scottish inventions]]
[[Category:19th-century inventions]]
[[Category:Containers]]
[[Category:Bottles]]