TABLE OF CONTENTS The purpose of this chapter is to state some of the basic ideas and assumptions that underpin vacuum technology.
To familiarise the reader with the scope of vacuum technology, it begins with a summary of the vacuum pressure range and typical applications in the chemical sciences.
The equation of state for a perfect gas is presented and expressions arising from this for pure gases and gas mixtures are given. The kinetic theory of gases, which is a useful model of perfect gases, is introduced and two particularly useful results are emphasised. These are the mean free path ( l) and the mean or thermal velocity ( c). Of particular importance is c/4, which is numerically equal to the volume rate of flow per unit area and which can be used to determine quantities such as area-related pumping speeds, conductances, etc.
The transport properties, particularly viscosity and diffusion, of a perfect gas are discussed and the concepts of gas dynamics are briefly mentioned. Such methods can be applied to flowing gas in, for example, pipework or nozzles and jets.
Typical vacuum processes and plants can be classified according to the pressure regions in which they operate. These regions are shown overleaf.
The term 'vacuum' is applied to pressures below, often considerably below, atmospheric pressure.
The object of vacuum technology is to reduce the number density of gas particles in a given volume of a system. At constant temperature, this always...
