Q: vacuum? A: Below a single atmospheric pressure in a given space. Q: standard environmental conditions? A: temperature is 20 ℃, relative humidity is 65%, atmospheric pressure is 101325Pa. Q: pressure (pressure)? A: The rate of change of momentum of a gas molecule passing through an imaginary plane in the direction of the normal normal to the plane, divided by the plane area, or the normal component of the force exerted by the gas molecule on the surface of its container wall, divided by Surface area. Q: degree of vacuum? A: The levitation of gas under vacuum, usually expressed as the pressure value. Q: vacuum zone division? A: Low vacuum 105 ~ 102Pa Vacuum 102 ~ 10-1Pa High vacuum 10-1 ~ 10-5Pa Ultra-high vacuum Q: Vacuum pump? A: A device to create, improve and maintain a vacuum. Basically include gas transmission pump and gas trap pump two kinds. Q: gas? A: A substance that is free from the constraints of intermolecular forces and can freely occupy any space. Q: The average free path? A: A molecule collides with other gas molecules for two consecutive strides, called the free path. A considerable number of different mean free path, called the average free path. Q: Knud number? A: The mean free path of gas molecules to the diameter of the catheter. Q: viscous flow? A: The mean free path of the gas molecules is much smaller than the minimum interface size of the conduit. The flow at this time depends on the viscosity of the gas, and the viscous flow may be laminar or stagnant. Q: intermediate flow? A: Flow of gas through the conduit between laminar and molecular flow. Q: molecular flow? A: The mean free path of the gas molecules is much larger than the maximum size of the duct section. Q: traffic? A: The volume of gas passing through a section over a given time interval, divided by the time. Q: guide? A: The ratio of the flow of gas to the mean pressure difference across the two specified sections or holes of the conduit when the gas flows through the conduit or the orifice under isothermal conditions