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Q: Vacuum?

A: Below one atmospheric pressure in a given space.

Q: Standard environmental conditions?

A: The temperature is 20 ℃, the relative humidity is 65%, and the atmospheric pressure is 101325pa.

Q: Pressure (pressure)?

A: The rate of change of momentum along the normal direction of the plane when a gas molecule passes through an imaginary plane, divided by the area of the plane, or the normal component of the force acting on the surface of the vessel wall by the gas molecule, divided by the surface area.

Q: Vacuum degree?

A: The rarefaction of a gas in vacuum is usually expressed by pressure.

Q: Vacuum zone division?

A: Low vacuum 105 ～ 102pa

Medium vacuum 102 ～ 10-1pa

High vacuum 10-1 ～ 10-5pa

Ultra high vacuum < 10-5pa

Q: Vacuum pump?

A: A device used to produce, improve, and maintain a vacuum. It includes gas transfer pump and gas trap pump.

Q: Gas?

A: A substance that is not constrained by intermolecular forces and can freely occupy any space.

Q: Mean free path?

A: The distance traveled by a molecule in two successive collisions with other gas molecules is called free path. The mean value of quite a number of different free paths is called the mean free path.

Fourteen basic knowledge of vacuum pump

Q: Knudsen number?

A: The ratio of the mean free path of the gas molecule to the diameter of the catheter.

Q: Viscous flow?

A: The average free path of gas molecules is much smaller than the minimum interface size of the tube. At this time, the flow depends on the viscosity of the gas, which can be laminar or stagnant.

Q: Intermediate flow?

A: The flow of gas through a duct between laminar flow and molecular flow.

Q: Molecular flow?

A: The average free path of gas molecules is much larger than the maximum size of the duct cross-section.

Q: Flow rate?

A: The volume of gas passing through a section in a given time interval divided by that time.

Q: Flow guide?

A: The ratio of the flow rate to the average pressure difference between the two specified sections of the duct or the two sides of the hole when the gas flows through the duct or orifice at isothermal conditions.