Vacuum is the term that designates the absence of matter in a space. Science admits that it is not yet possible to produce a perfect vacuum. Therefore, vacuum in a closed space, for example, inside a refrigerator, means that that space has gases at a pressure well below atmospheric pressure.
Atmospheric pressure, at sea level, is worth 1.03 kgf / cm2 or 14.7 lbf / in2 or 1atm or 760 mm Hg, at 0ºC of temperature. Thus, a closed space whose pressure is well below 1.03 kgf / cm2 or 760mm Hg will be considered a vacuum. For the refrigeration system, where the vacuum pressure should normally be much lower than
1mm Hg, the millitorr unit (mmTorr) is adopted, equivalent to 0.001mm Hg or 103 Torr.
This value cannot be measured with standard pressure gauges. For pressures below 1 Torr, electronic vacuum meters are used, which indicate pressures below 50 mmTorr.
