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The article on the vacuum cleaner is located elsewhere.
In physics, a vacuum is the absence of matter in a volume of space. A partial vacuum is expressed in units of pressure. The SI unit of pressure is the pascal (abbreviated to Pa in usage). It can also be expressed using the torr, using the barometer scale, or as a percentage of atmospheric pressure using the bar. The antithesis of a vacuum, which is technically unachievable, is called a plenum. A perfect vacuum is not in the least obtainable in a laboratory; much of outer space is supposed to consist of an almost perfect vacuum, with a small number of molecules per cubic metre.
1 Degrees of vacuum
- Atmospheric pressure = 100 kPa
- Vacuum cleaner = approximately 80 kPa
- Mechanical vacuum pumpA vacuum pump is a pump that generates vacuum or further reduces the pressure of an existing vacuum. A vacuum pump can be a positive displacement pump that transports a gas load from an inlet port to an outlet, or exhaust, port. Vacuum pumps can also work = approximately 100 Pa to 100 μPa
- Near earth outer space = approximately 130 μPa
- Pressure on the MoonFor other moons in the solar system see natural satellite. For other uses see Moon (disambiguation). The Moon is the only natural satellite of Earth. It has no formal name other than "The Moon" although it is occasionally called Luna ( Latin for moon to d = approximately 1.3 μPa
- Interstellar space = approximately 13 nPa
- CryopumpA vacuum cryopump typically consists of a vacuum-tight vessel with a valved inlet, containing a highly absorbent material such as a synthetic zeolite microporous on the scale of 0. 1 to 1 nanometers, and an enclosing cryogenic vessel. In industrial cryopued MBEMolecular beam epitaxy also called MBE, is the deposition of one or more pure materials onto a single crystal wafer, one layer of atoms at a time, under ultra-high vacuum, forming a perfect crystal. In solid-source MBE, ultra-pure elements such as gallium chamber = 133 nPa to 1.3 nPa
2 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 dynamicsFluid dynamics is the study of fluids ( liquids and gases) in motion, and the effect of the fluid motion on fluid boundaries, such as solid containers or other fluids. Fluid dynamics is a branch of fluid mechanics, and has a number of subdisciplines, incl. 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.
