Related articles
Edit |
Discuss Article
VacuumThe article on the vacuum cleaner is located elsewhere.
In physics, a vacuum is the absence of matter (molecules, atoms...) in a volume of space. A partial vacuum is expressed in pressure units. The SI unit of pressure is pascal (Pa). It can also be expressed as a percentage of atmospheric pressure using the bar or barometer scale.
Degrees of vacuum
Creating a vacuum
When creating a partial vacuum, the matter in the volume being evacuated flows differently at different pressures based on the laws of fluid dynamics. Initially a vacuum pump can be used to remove the material, as the molecules are interacting with each other and will push on their neighboring molecules in what is known as viscous flow. When the distance between the molecules increases, the molecules interact with the walls of the chamber more often than the other molecules, and compression pumping is no longer effective.
At this stage, the system has entered a state called molecular flow, where the velocity of each molecule is approximately random. Methods to remove the remaining gas include:
- Converting the molecules of gas to their solid phase by freezing them, called cryopumping or cryotrapping
- Converting them to solids by electrically combining them with other materials, called ion pumping
- Use of another specialized pump. Examples are turbomolecular pump or diffusion pump.
At extremely low pressures, outgassing of the vacuum vessel occurs over time. Even if a high vacuum is generated in a hermetically
sealed container, there is no guarantee that an adequately low pressure will
continue unless outgassing has been accounted for. Outgassing is generally worse at higher temperatures. Even materials which are not naively
considered absorbent will outgas. Water vapor is a primary outgas component,
even in hard metal vessels (such as stainless steel or titanium).
Outgassing can be reduced by desiccation prior to vacuum pumping. Vessels
lined with a highly gas-permeable material such as palladium (which is
a high-capacity hydrogen sponge) create special outgassing problems.
The quantum-mechanical vacuum
Quantum physics reveals that even an ideal vacuum, with an measured pressure of zero torr, isn't really empty. One reason is that the walls of the vacuum chamber emit light in the form of black-body radiation: visible light if they are at a temperature of thousands of degrees, infrared light if they are cooler. This soup of photons will be in thermodynamic equilibrium with the walls, and the vacuum can consequently be said to have a particular temperature. More fundamentally, there are quantum-mechanical fluctuations in the vacuum. This may be responsible for the observed value of the cosmological constant.
See also
External links
Source | Copyright
|
 |
 |
|
Webmasters: Add your website here:
Readers: Edit |
Discuss Listings
Vacuum Terminology and Technology
Vacuum history; biographies of famous physicists, and mathematicians.
http://www.mcallister.com/vacuum.html
Vacuum Technology and Vacuum Coating Forum
Discuss subjects about vacuum physics, vacuum and coating systems, evaporation coating and sputtering technology.
http://www.industrycommunity.com/myforum/alex_yuan/index.html
Vacuum Technology Guide
Links to buyers guides, organizations, research, eZines and journals world-wide.
http://www.sansalone.de/engl/links.htm
Graphic Symbols for Vacuum Components
A handy indexed reference for examples of graphic symbols for components used in vacuum technology. Useful when constructing vacuum system schematics.
http://vacuumfeedthru.com/tech_libr/symbols/default.htm
American Vacuum Society
Includes descriptions of the society's aims, online access to publications, administrative information, related news and information on conferences.
http://www.avs.org/
The Bell Jar
Site of vacuum technology and techniques for students and amateur scientists. Articles; links; experiments.
http://www.belljar.net/
International Union for Vacuum Science, Technique, and Applications
International meetings, conferences and workshops, educational opportunities, international awards and prizes.
http://www.iuvsta.org
The Society of Vacuum Coaters
Education and information about vacuum coating. Technical conferences, educational programs, publications.
http://www.svc.org/
Introduction to Vacuum Technology
Some basic principles for beginners.
http://www.phys.uwosh.edu/rioux/texts/vacuum.pdf
Thermo Vacuum Generators
One of the worlds leading manufacturers of UHV components. On this web-site you will also find a lot of reference data on vacuum components (e.g. pumps, gauges, valves, flanges etc.) including their principles of operation.
http://www.vacgen.com
How Thermoses (Vacuum Flasks) Work
For inquisitive people howstuffworks.com tells about how thermoses work. You can find there other vacuum-based devices as vacuum cleaner and television.
http://home.howstuffworks.com/thermos.htm
Mc Nally Institute
An excellent resource with enormous amount of information for advanced vacuum users about pumps and seals (troubleshooting, specifications etc.)
http://www.mcnallyinstitute.com
Building your own Vacuum pump
How to build your own Vacuum pump
http://www.dream-models.com/eco/vacuumpump.html
The AVS Education Website
Promotes communication, dissemination of knowledge, recommended practices, research, and education in the use of vacuum and other controlled environments to develop new materials, process technology, devices, and related understanding of material properties.
http://www.avseducation.org/
Vacuum pumps
Contains descriptions of several types of vacuum pumps and general information about productions of low pressures. Good for students.
http://www.studhelp.net/vacuum/index.htm
What is vacuum?
Nice web-site for beginners who want to know "what vacuum is"...
http://www.inter-uni.com/wanttoknow/index.html
Pumps - The Engineering ToolBox
Different information on pumps and piping systems.
http://www.engineeringtoolbox.com/34.html
Pressure, Mean Free Path, Units Converter
Background information about gas pressure and gas molecule mean free path and helpful pressure units converter.
http://www.greatbond.net/index.htm
British Vacuum Council
The representative for Great Britain on the International Union for Vacuum Science, Technique and Application. As such it has a role to stimulate international collaboration in the fields of vacuum science, techniques and applications and related multi-disciplinary topics including solid-vacuum and other interfaces.
http://www.astec.ac.uk/vacsci/British-Vacuum-Council/
Vacuum Technology Lessons
Lessons and practical exercises on Vacuum Technology.
http://acept.la.asu.edu/PiN/rdg/vacuum/
Ultra High Vacuum
Describes what ultra high vacuum (UHV) is, why we need in it, how to get UHV.
http://www.getphysics.net/index.htm
Pulsed Laser Deposition
Thin film vacuum deposition technique using short laser pulses to produce flux of deposited particles from a target. This technique provides an excellent quality of the film.
http://www.physandtech.net/index.htm
Gas Flow Regimes and Pumping Speed
Theory on gas flows, pipe conductances, throughput and pumping speed.
http://www.newequation.net
Vacuum Physics
Introduction to vacuum technology, leak detection, vacuum measurements, working principles of vacuum pumps and seals.
http://homelaboratory.net/
|
