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# Vacuum freeze drying machine concept and measuring unit ( A)

2020/10/19
Vacuum freeze drying machine concept and measuring units

vacuum concept of vacuum freezing dryer

absolute vacuum refers to the space without gas state, but in fact this kind of space is not there.

we usually say the vacuum of vacuum freeze drier refers to a certain space, the atmospheric pressure is lower than gas state, also said that the number of molecules of gas inside the space density is lower than the atmospheric pressure in the region of number density of gas molecules.

different vacuum state, is the space with different number density of molecules, such as in the standard state ( STP: 0 degrees, 101325 pa) The number of molecules of the gas density of 2. 6870 * 10/25m / - 3, and in a vacuum, density of 1 * 10 / - 4 pa, the number of molecules of the gas density is only 2. 65 * 10/16m / - 3

（ 2) Vacuum freeze drying machine vacuum unit of measure

in vacuum is commonly used in vacuum freezing dryer technology to measure vacuum degree of thin gas space. Usually vacuum degree by the pressure value of the gas, the lower the pressure value, the higher vacuum degree; The lower the pressure value, the higher the vacuum degree.

common pressure units have

( 1) PASCAL: pressure unit in international units, legal pressure units in China. Pa pressure is 1 square meter area 1 n the action of force that is

1 pa = 1 n/m2

barye: 1 barye pressure is 1 cm2 area role dyn force that is 1 barye = 1 dyn/cm2

standard atmosphere: in 1927, the seventh international conference on measurement, to defined, under normal atmospheric pressure in gravity acceleration for 980. Temperature of 0 degrees 665 cm/s2, mercury, mercury density to 13. Under the condition of 5915 g/cm3, 760 mm high hg produce called 1 ATM pressure 1 ATM = 760 MMHG = 1013250 dyn/cm2

the measuring accuracy of this standard atmosphere depends on the density of mercury, is strict enough. So in 1954 the tenth international conference on measurement and redefines the standard atmospheric pressure, which is 1 ATM = 1013250 dyn/cm2 = 101325 pa

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