How to conduct gas migration for dry screw vacuum pump
The movement of molecules on the surface of a dry screw vacuum pump is called migration. In the state of thermal motion, gas molecules move from one part of space to another, and each physical quantity moves from a place of high concentration to a place of low concentration, until each physical quantity reaches a uniform distribution. The diffusion, viscosity and heat conduction of dry screw vacuum pump belong to migration phenomenon.
1, the diffusion
The movement of a gas in another medium due to a concentration gradient is called diffusion. The medium may be another gas (diffusion in this case is called interdiffusion) or a condensable substance.
In dry screw vacuum pumps, helium permeates through glass up to 10-13 l/s. Hydrogen penetrates through iron at 300~400℃, nickel at 450℃, glass at 600℃, and copper at about 640℃. Diffusion coefficient. The ratio of the absolute value of the mass flow rate per unit area to the normal concentration gradient per unit area. Diffusion has been widely used in diffusion pump and surface physics and other practical technology.
2. Viscosity and heat conduction of gas
The transfer of momentum and the exchange of momentum between layers in any medium is called the viscosity of the medium. The ratio of tangential force to velocity gradient on unit area of airflow velocity gradient is viscosity coefficient.
The heat conduction of the dry screw vacuum pump is caused by the different temperatures of the gas parts, plus the heat movement of the gas molecules, and the energy exchange that occurs, so that the cooler part gets heat, the heat conduction of the gas is related to the pressure.