Vacuum flask
Encyclopedia
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...
storage vessel which keeps its contents hotter or cooler than its surroundings. Invented by Sir James Dewar in 1892, the vacuum flask consists of two flask
Flask
Flask may refer to:* Laboratory flask, laboratory glassware for holding larger volumes than simple test tubes* Vacuum flask a container designed to keep warm drinks warm and refrigerated drinks cold...
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
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
which prevents heat transfer by conduction
Heat conduction
In heat transfer, conduction is a mode of transfer of energy within and between bodies of matter, due to a temperature gradient. Conduction means collisional and diffusive transfer of kinetic energy of particles of ponderable matter . Conduction takes place in all forms of ponderable matter, viz....
or convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
.
Vacuum flasks are used domestically to keep beverages hot or cold for extended periods, and for many purposes in industry.
History
The vacuum flask was invented by Scottish physicistPhysicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
and chemist
Chemist
A chemist is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties such as density and acidity. Chemists carefully describe the properties they study in terms of quantities, with detail on the level of molecules and their component atoms...
Sir James Dewar in 1892 and is sometimes referred to as a Dewar flask or Dewar bottle after its inventor. The first vacuum flasks for commercial use were made in 1904 when a German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
company, Thermos GmbH, was founded. Dewar failed to register a patent for his invention and it was subsequently patented by Thermos, to whom Dewar lost a court case in claiming the rights to the invention.
"Thermos" remains a registered trademark in some countries, but was declared a genericized trademark
Genericized trademark
A genericized trademark is a trademark or brand name that has become the colloquial or generic description for, or synonymous with, a general class of product or service, rather than as an indicator of source or affiliation as intended by the trademark's holder...
in the U.S. in 1963 as it is colloquially synonymous with vacuum flasks in general.
Design
The vacuum flask consists of two flaskFlask
Flask may refer to:* Laboratory flask, laboratory glassware for holding larger volumes than simple test tubes* Vacuum flask a container designed to keep warm drinks warm and refrigerated drinks cold...
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
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
which prevents heat transfer by conduction
Heat conduction
In heat transfer, conduction is a mode of transfer of energy within and between bodies of matter, due to a temperature gradient. Conduction means collisional and diffusive transfer of kinetic energy of particles of ponderable matter . Conduction takes place in all forms of ponderable matter, viz....
or convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
. Heat transfer by thermal radiation
Thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....
may be minimized by silvering
Silvering
Silvering is the chemical process of coating glass with a reflective substance. When glass mirrors first gained widespread usage in Europe during the 16th century, most were made of an amalgam of tin and mercury, but by the 19th century mirrors were commonly made through a process by which silver...
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 water's boiling point. Most heat transfer occurs through the flask's neck and opening, where there is no vacuum. Vacuum flasks are commonly made of metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
, glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
, foam
Foam
-Definition:A foam is a substance that is formed by trapping gas in a liquid or solid in a divided form, i.e. by forming gas regions inside liquid regions, leading to different kinds of dispersed media...
, or plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
, and have their opening stoppered
Bung
A bung is truncated cylindrical or conical closure to seal a container, such as a bottle, tube or barrel. Unlike a lid which encloses a container from the outside without displacing the inner volume, a bung is partially inserted inside the container to act as a seal...
with cork
Cork (material)
Cork is an impermeable, buoyant material, a prime-subset of bark tissue that is harvested for commercial use primarily from Quercus suber , which is endemic to southwest Europe and northwest Africa...
or plastic. Vacuum flasks are commonly used as insulated shipping container
Insulated shipping container
Insulated shipping containers are a type of packaging used to ship temperature sensitive products such as foods, pharmaceuticals, and chemicals. They are used as part of a cold chain to help maintain product freshness and efficacy...
s.
Several applications rely on the use of double vacuum flasks, such as NMR
NMR
NMR may refer to:Applications of Nuclear Magnetic Resonance:* Nuclear magnetic resonance* NMR spectroscopy* Solid-state nuclear magnetic resonance* Protein nuclear magnetic resonance spectroscopy* Proton NMR* Carbon-13 NMR...
and MRI machines. These flasks have two vacuum sections. The flasks contain liquid helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
in the inside flask and liquid nitrogen in the outer flask, with one vacuum section in between. The loss of expensive helium is limited in this way.
Other improvements to the vacuum flask include the vapor-cooled radiation shield and the vapor-cooled neck, which both help to reduce evaporation from the flask.
Domestic use
Vacuum flasks are used to maintain their contents (often but not always liquidLiquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
) at a temperature higher or lower than ambient
Room temperature
-Comfort levels:The American Society of Heating, Refrigerating and Air-Conditioning Engineers has listings for suggested temperatures and air flow rates in different types of buildings and different environmental circumstances. For example, a single office in a building has an occupancy ratio per...
temperature, while retaining the ambient pressure of approximately 1 atmosphere
Atmosphere (unit)
The standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 105 Pa...
(14.7 psi
Pounds per square inch
The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...
). Domestically and in the food industry, they are often used to keep food and drink either cold or hot. A typical domestic vacuum flask will keep liquid cool for about 24 hours, and warm for up to 8.
Some vacuum flasks include a fitted cup or two, for convenience of use with drinks, especially during traveling or family picnics. All designed and combined in one.
Research and industry
In laboratories and industry, vacuum flasks are often used to store liquids which become gaseous at well below ambient temperature, such as oxygenOxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
; 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
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
from building up and shattering the flask. The insulation of the vacuum flask results in a very slow "boil", and thus the contents remain liquid for a long time without the need for expensive refrigeration
Refrigeration
Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...
equipment.
Vacuum flasks have been used to house standard cell
Weston cell
The Weston cell, invented by Edward Weston in 1893, is a wet-chemical cell that produces a highly stable voltage suitable as a laboratory standard for calibration of voltmeters...
s, and ovenized Zener diode
Zener diode
A Zener diode is a special kind of diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "Zener knee voltage" or "Zener...
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 control the output voltage of the Zener standard, due 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, that was encased in foam insulation, and using a large glass vacuum plug, held the saturated cell. The voltage 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 fuels, and NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
used it extensively in the propellant tanks of the Saturn launch vehicles in the 1960s and 1970s.
Security
In December of 2010, airport securityAirport security
Airport security refers to the techniques and methods used in protecting airports and aircraft from crime.Large numbers of people pass through airports. This presents potential targets for terrorism and other forms of crime due to the number of people located in a particular location...
in Canada and the United States began subjecting insulated beverage containers to greater scrutiny, because of the possibility that they could be used to conceal explosives. A U.S. military official said that officials were trying to anticipate possible terror attacks.
Further reading
- Burger, R., , "Double walled vessel with a space for a vacuum between the walls," December 3, 1907.