In the case of a fog, the liquid oil phase is dispersed in the form of small particles. These are enclosed by a continuous phase, in this case compressed air. Such systems are referred to as dispersed systems.
An aerosol is defined as a quasi stable and quasi homogenous system, in the sense of physical chemistry, in this case consisting of air and very many insoluble suspended particles. All of these particles form a relatively stable and identifiable system.
Whereas the dispersion medium compressed air is unambiguously specified by the physical parameters pressure, temperature and chemical composition, a complete description of the particles is not normally possible. Such a particle description is determined by
- the surface,
- the characteristics of the individual particles, a difficult matter because of the large number and complex shapes,
- the chemical composition,
- the description of the an aglomerate however, is not possible without knowledge of the individual particles.
Practical reasons, therefore, cause us to limit the description to certain characteristics, so that the selection and definition of parameters is guided by the questions need to characterising the aerosol. In practice, this means establishing the frequency of particle occurrence within the aglomerate. For accurate specification of the dispersed phase, many practical problems and solutions require concentration C1 and relative frequency yf2 . For specifying particle diameter, the geometrical mean of diameter x is used, assuming particles which are by definition spherical.
