Barsky Critical Regimes of Two-Phase Flows with a Polydisperse Solid Phase

1. Auflage 2010
ISBN: 978-90-481-8838-3
Verlag: Springer Netherland
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, Band 93, 348 Seiten, eBook

Reihe: Fluid Mechanics and Its Applications

Critical regimes of two-phase flows with a polydisperse solid phase form the basis of such widespread industrial processes as separation of various powdery materials and minerals dressing. It is impossible to describe such complicated flows analytically. Therefore, this study concentrates on invariants experimentally revealed and theoretically grounded for such flows. This approach can be compared with the situation in gases, where in order to determine principal parameters of their state, one does not need to measure the kinetic energy and velocity of each molecule and find its contribution to the temperature and pressure. These parameters are determined in a simple way for the system on the whole. A novel conception of two-phase flows allowing the formulation of their statistical parameters is physically substantiated. On the basis of the invariants and these parameters, a comprehensive method of estimating and predicting mass transfer in such flows is developed. It is noteworthy that the presented results are mostly phenomenological. Such an approach can be successfully extended to the separation of liquids, gases and isotopes. The book is intended for students and specialists engaged in chemical technology, mineral dressing, ceramics, microelectronics, pharmacology, power generation, thermal engineering and other fields in which flows carrying solid particles are used in the technological process.

Zielgruppe

Research

Autoren/Hrsg.

Barsky, Eugene

Inhaltsverzeichnis

General Ideas of Mass Transfer Processes in Critical Regimes.- Principles of Modeling Processes in Moving Media.- System of Particles of the Same Size Class in a Critical Flow.- System of Particles of Several Size Classes.- Principal Statistical Relations of Mass Transfer in Critical Flow.- Correlation Between the Apparatus and the Cell.- Structural Model of Mass Transfer in Critical Regimes of Two-Phase Flows.- Correlation Between Statistical and Empirical Results.- Entropy of Composition: Optimization Criterion.- Stability and Kinetic Aspects of Mass Distribution in Critical Regimes.- Critical Regimes of Two-Phase Flows in Complicated Systems.- Stochastic Model of Critical Regimes of Two-Phase Flows.- Mass Transfer in Critical Regimes of Two-Phase Flows.- Universal Curves Criteria.

Leseproben

"Chapter 1 General Ideas of Mass Transfer Processes in Critical Regimes (p. 1-2)

Abstract Experimental studies have shown that despite a visual chaos in critical regimes of two-phase flows, there is a definite, almost deterministic order in the polyfractional solid phase distribution along the flow and counter the flow. The affinity of separation curves as a function of principal parameters of the flow in a turbulent regime is substantiated. Criteria of the affinization of separation curves are empirically established and experimentally substantiated.

Keywords Regularity - Granulometric composition - Size - Density - Concentration - Velocity - Process stability - Fractional extraction -Affinity -Separation curve -Productivity -Separation

1.1 Granulometric Characteristics of Bulk Material

First of all, we examine characteristics of a solid phase constituting a two-phase flow, because in critical regimes the process of particles separation according to their size grade or density can be organized most easily. Processing of ground materials is among the most widespread processes in today’s industry.

Many millions of tons of various materials are ground daily in mining, in various branches of chemical industry, in metallurgy, at the production of cement, ceramics, glass and other building materials, as well as in most novel branches of industry. Various natural and artificial materials become pourable when ground, and in this state they pass all the stages of technological processes, namely, extraction of useful components, production of powders with a specified particle size, compounding of necessary mixtures and compositions, treatment of particle surface and addition of various elements, drying, baking, etc. In this state it is convenient to granulate materials from particles of any composition or press products of any shape. As a rule, a solid phase is introduced into moving flows in this state only. At present, more and more low-quality raw materials are being processed because of growing production volumes.At the same time, the requirements for the quality of the final products constantly grow.

To meet these requirements, separation processes are becoming more and more important. Most often, the separation is performed by particle size or density, and more rarely – by shape, color or other parameters. While formerly, with a rather rough technology, it was sufficient to use various sieves for the separation by size, presentday operations with fine powders require separation carried out using moving media – air or water. As for separation by other parameters (density, particle shape), it can be realized only in moving media.

Before determining separation parameters, we examine principal characteristics of a bulk material. Such a material can be characterized by its specific density of particles, bulk density, humidity, porosity, etc. Usually a ground material contains, depending on its size grade, many millions of particles. These particles can differ in size, shape, surface state, etc. However, the material’s principal characteristic is connected with dispersity."