In parts 1 and 2 we talked about the Kinetic Theory of Gases and in particular, we showed how the movement of atoms affects principles such as molecular density, mean free path, and molecular velocity and how they are used to analyze the macroscopic properties of gases such as pressure, temperature, and flow in a vacuum environment. Here we will discuss the related topic of gas flow, gas speed, conductance, diffusion, and effusion once again focusing on the fundamental concepts.
Speed of Gas Flow – When designing and using vacuum systems, it is critical to be able predict the time required to draw the pressure down to a desired level. Since this time is directly related to the speed of the gas flowing through the system, it is therefore important to understand what influences the speed of gas flow. Of practical importance is the influence of pipe diameter, pipe bends, and devices such as filters and condensers. Flow phenomena are not easily understood unless the differing properties of gas in the so-called continuum and molecular flow ranges are taken into account.