When a water droplet impacts a free surface with sufficient velocity, the momentum transfer results in the formation of a hemispherical cavity expanding radially from the point of impact.
This article is only meant to provide a very cursory overview of vacuum fundamentals, how to produce a vacuum and and some of the more common applications of vacuum technology. A number of resources for further information are referenced at the conclusion.
Compiled from material originally presented in Volume 1 of the Bell Jar with various updates and additions. Introduction A vacuum system typically consists of one or more pumps which are connected to a chamber.
The former produces the vacuum, the latter contains whatever apparatus requires the use of the vacuum.
In between the two may be various combinations of tubing, fittings and valves. These are required for the system to operate but each introduces other complications such as leaks, additional surface area for outgassing and added resistance to the flow of gas from the chamber to the pumps.
Additionally, one or more vacuum gauges are usually connected to the system to monitor pressure. The More Common Units of Pressure Measurement Traditionally, the pressure in a system is stated in terms of the height of a column of mercury that may be supported by the pressure in the system.
At one standard atmosphere the force is 1.
This pressure will support a mercury column millimeter high as in a barometer. One millimeter of mercury is the equivalent of 1 Torr. A thousandth of a millimeter is referred to as a micron of mercury or, in more current terminology, 1 milliTorr mTorr. To be proper in the modern scientific world, the SI system of units is used.
To convert Torr to Pascal, divide by 0. Measurement of pressure in a vacuum system is done with any of a variety of gauges which, for the most part, work through somewhat indirect means e. The former are typically used at higher pressures 1 to mTorrthe latter in lower ranges.
Such gauges are sensitive to the type of gas in the system, requiring that corrections be made.
Accidents have occured when this was not taken into account. For example, the presence of argon in a system will result in a pressure reading on a thermal conductivity gauge thermocouple or Pirani, for example that is much lower than the true pressure.
It is possible to significantly overpressure a system while the gauge is still indicating vacuum. The only gauges that are gas-type independent are those which directly measure pressure as force per unit area.
Barometers, McLeod gauges and other liquid manometers are examples of direct gauges. Direct gauges also include instruments where the pressure causes a tube to distort the principle of the common dial, or Bourdon, gauge or where the displacement of a metal diaphragm is measured by electrical means the principle of the capacitance manometer.
Means of Producing Vacuum Low grade vacuum may be reached using a variety of means. In the range to several 10s of Torr, sealed reciprocating piston compressors as are commonly found in refrigerators may be used.
Piston compressors have the disadvantage of the dead space which exists above the piston.
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This, plus leakage past the piston, limits the degree of vacuum that can be achieved.Find your vacuum generator easily amongst the 1, products from the leading brands (VUOTOTECNICA, VACUUBRAND, EXAIR, ) on DirectIndustry, the industry specialist for your professional purchases.
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