Particles Sizes and Methods

In order to make clear what this article deals with, the useful and necessary terms, limits and conditions must be defined. Particles, within the frames of this text, is an ensemble of single subjects of disintegrated matter which is dispersed in a continuum fluid or in vacuo. One particle, regardless of its size, is usually not identical with one molecule but with a large number of molecules aggregated by physical forces. In the case of polymeric matter, however, one macro-molecule can be identified with one particle, under certain conditions. The second important attribute which defines one particle is that, physically, it represents a subject delimited in three-dimensional space by a phase discontinuity. The particles, representing one discontinuous phase which can be solid or liquid, are dispersed in a second continuous phase which is gaseous or liquid.

As concerns the sizes of the particles, a strict definition is less easy, because the effective dimen-sion(s) (independently of the physical shape of each individual particle) can vary as a function of the chemical character of the surrounding dispersing fluid but also of the imposed physical conditions: obvious ones, such as, e.g., the temperature, and less obvious as, e.g., the electric charge, etc. Moreover, it has to be taken into account that the results of the measurements of the particle size can strongly depend on the method of its determination. As a result, the questions are not only what the size that we obtain from a particular measuring method means and whether the result corresponds to a true size, but also what kind of effective size we measure by applying any particular method. Not only one but many effective sizes obtained by different measuring methods can correspond to the physical reality (they all can be 'true'). This is due to the fact that the measured data can contain various information on the particle-dispersing fluid and particle-particle interactions, on the size fluctuations in time, on the transport behaviour of the particles in the dispersing fluid, etc. Although all these phenomena can complicate the determination of a definite particle size, they provide much useful information on the whole dispersed par-ticulate system. Having in mind these complications, we can define the range of particle sizes of practical interest as lying within the range from a diameter of few nanometres to thousands of micrometres.

The definition and limitation of the particles and the particle size ranges, as outlined, determine the relevant separation methods. Those methods can be considered relevant that are directly related to the separation according to differences in particle size or concerned indirectly due to the fact that they can provide complementary information necessary to an accurate interpretation of the experimental data obtained from particle size-based separations.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook

Post a comment