1. Vacuum: In vacuum science, the meaning of vacuum refers to the state of gas below an atmospheric pressure in a given space. People usually refer to this thin gas state as a vacuum condition.

2, vacuum degree: vacuum degree as the name implies is the degree of vacuum. The degree of gas dilution in a vacuum state is usually expressed by "high vacuum" and "low vacuum. High vacuum degree means "good" vacuum degree, and low vacuum degree means "poor" vacuum degree. The so-called "vacuum" refers to the gas state in a given space, the pressure is lower than 101325 Pa SCA (that is, a standard atmospheric pressure of about 1013hPa). In the vacuum state, the degree of rarefaction of the gas is usually expressed by the pressure value of the gas. Obviously, the smaller the pressure value, the thinner the gas.

Vacuum pump limit pressure: the lowest pressure that the vacuum pump can reach.

4. Ultimate vacuum: After the vacuum container is fully pumped, it is stable at a certain degree of vacuum, which is called the ultimate vacuum. Generally, the vacuum container shall be subjected to 12 hours of gas refining and then 12 hours of vacuuming. The last hour shall be measured every 10 minutes, and the average value of 10 times shall be taken as the ultimate vacuum value.

5. Atmospheric pressure: The pressure caused by a thick layer of atmosphere surrounding the earth's surface or surface objects is called atmospheric pressure.

Standard atmospheric pressure: refers to the air pressure at sea level under standard atmospheric conditions. 1 standard atmospheric pressure = 760mmHg = 101325 Pa

Absolute pressure and relative pressure: the pressure directly acting on the surface of the container or object is called absolute pressure, and the absolute pressure value is based on absolute vacuum. The pressure measured by pressure gauge, vacuum gauge, U-shaped tube and other instruments is called gauge pressure and relative pressure.

8. Standard condition: usually refers to the condition with a temperature of 0 ℃ and a pressure of 101325Pa(1 standard atmospheric pressure, 760 mmHg). So that there is a uniform standard in comparing gas volumes. The density of a gas, unless otherwise specified, is said under standard conditions.

9. Pumping rate: Under certain pressure and temperature, the volume of gas drawn from the pump inlet per unit time is called the pumping rate. Short for pumping speed.

10, the main pump: in the vacuum system, used to obtain the required vacuum degree to meet the specific process requirements of the vacuum pump.

11. Pre-pump: a vacuum pump used to maintain the pre-stage pressure of a vacuum pump below its critical pre-stage pressure. Such as roots vacuum unit roots vacuum pump before the configuration of the rotary vane or liquid ring pump is the front pump.

12. Vacuum gauge: an instrument used to measure vacuum.

13. Vacuum system: it is a vacuum pump, vacuum gauge, pumped container and other components such as vacuum valves, cold traps, etc., with the help of vacuum pipes, combined according to certain requirements, and has the required pumping function. Its function is to obtain a vacuum within a specified time and space, maintain a vacuum, and confirm the implementation of a process or physical process within the system.

14. Saturated steam: When the liquid evaporates in a limited confined space, the liquid molecules enter the upper space through the liquid surface and become vapor molecules. Because the steam molecules are in the disorder of thermal motion, they collide with each other and collide with the container wall and the liquid surface. When colliding with the liquid surface, some molecules are attracted by the liquid molecules and return to the liquid to become liquid molecules. At the beginning of evaporation, the number of molecules entering the space is greater than the number of molecules in the return liquid. As the evaporation continues, the density of the space vapor molecules increases, and therefore the number of molecules in the return liquid also increases. When the number of molecules entering the space per unit time is equal to the number of molecules in the return liquid, the evaporation and condensation are in a state of dynamic balance. At this time, although the evaporation and condensation are still going on, the density of vapor molecules in the space no longer increases. At this time, the state is called the saturated state. The liquid in the saturated state is called saturated liquid, and its corresponding steam is saturated steam, but it is only wet saturated steam at first, and it is dry saturated steam after all the water in the steam evaporates. The process temperature of steam from unsaturated to wet saturation to dry saturation does not increase. If heating continues after dry saturation, the temperature will rise and become superheated steam.

15. Saturated vapor pressure: vapor pressure refers to the vapor of the substance on the surface of a liquid (or solid), and the pressure generated by these vapors on the surface of the liquid is the vapor pressure of the liquid. For example, the surface of water has a water vapor pressure, and when the vapor pressure of water reaches the total pressure of the gas on the surface of the water, the water boils. We usually see water boiling, that is, at 100 degrees Celsius, the vapor pressure of water is equal to one atmosphere. The vapor pressure changes with temperature, the higher the temperature, the greater the vapor pressure, of course, and the type of liquid. At a certain temperature, the pressure generated by the vapor in equilibrium with the liquid (or solid) of the same substance is called saturated vapor pressure, which increases with the increase of temperature.

◆Gas law

1, Boyle-Malott's law: a certain mass of gas, at constant temperature, the product of the pressure of the gas and its volume is constant. Namely: P V = C
In the vacuum system, along with the pumping process, the gas quality is changing, can only keep the temperature constant, so the gas pressure and the volume of the product and the quality of the gas is proportional to. Namely: P V = C M

2, Gay Lussac's law: a certain mass of gas, under constant pressure, the volume of the gas is proportional to its absolute temperature. Namely: V = C T

3, Charlie's law: a certain mass of gas, in a constant volume, the pressure of the gas is proportional to its absolute temperature. Namely: P = C T

4. Avogadro's law: Different kinds of gases have the same temperature and pressure, and the number of molecules contained in the same volume is equal.

If P1 = P2 T1 = T2 then n1 = n2

5. Dalton's law: The total pressure of a gas mixture that does not chemically interact with each other is equal to the sum of the sub-pressures of various gases.

If there are I kinds of gases mixed, the total pressure is: P = P1 P2 P3 …… Pi

6. equation of state of ideal gas: P V = M R T / u

P -- gas pressure Pa V -- gas volume m3 T -- gas absolute temperature K

M -- gas mass Kg u -- molar mass of gas Kg/mol

R-universal gas constant, suitable for any gas, independent of gas quality, R = 8.31 J / mol.K

◆ Pressure unit conversion

◆ Saturated vapor pressure of water (kPa)