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the Analysis of existing techniques of calculations of processes at separation poroshkoobraznyh materials

Grading process poroshkoobraznyh materials, as a rule, is carried out in the gaseous environment, and the disperse structure, a specific surface, concentration in a gas stream, make essential impact on efficiency of separation.

For a choice of an optimum mode of grading

It is necessary to consider the properties of the materials corresponding to set of specified parametres. So, at increase in dispersion of a material more expressed there are the superficial phenomena caused by a surface tension [134]. Superficial energy inherent in such materials can be calculated under the formula [108]:

Where σ - a surface tension;

S' - A surface area.

Superficial energy can turn to other sorts of energy: warmth, chemical energy, mechanical. These transformations lead to change of following properties: dispersion, adhesion and kapilljarnost. Often enough at various stages of grading there are processes of interaction of particles to formation of assembly units. Frequently these formations include a small particles which as a result of grading get to large fraction. In the course of association of particles in assembly units can occur under the influence of capillary pressure. In the assembly unit there is a process of migration of an available liquid phase under the influence of capillary pressure in places of the closest arrangement of particles. Its peak value is defined under the following formula [67]:

Where δ - the size (diameter) of group of particles - the assembly unit.

It is necessary to notice, that character of keeping forces at aggregation can be and an electric origin [33].

The aggregated structures at Ureva N.B. it is characterised rather weak on force of interaction by communications between making particles, and process of aggregation because of reduction of a specific surface as a result of contact is caused by decrease in free superficial energy ∆F which is defined by expression [101, 103]:


The structures formed as a result of interaction remain

For a finding of force of interaction (cohesion) there are also other expressions. For example, as clearance space N between them it is possible to present force of interaction of two convex bodies of any skewness in the form of expression [36]:

Where V (H) - specific energy of interaction of the flat interphase borders parallel each other divided by the same clearance space in width N;

d - the factor of the form depending on radiuses of curvature of surfaces.

For two spheres in radiuses R1и R2выражение (1.7) will assume the following air [36]:


Reduction [96]. Therefore, in practice force of a separation of particles being in contact can make only ¾ from theoretical force of separation Fo [36].

Where φ - value V () at the direct contact, equal to specific energy of adhesion (autogezii).

For the account of a deflexion of the form of a particle from spherical M.D.Barskogo has a concept of the factor of the form is a relation of a surface of an equal sphere on size 5ш to a true surface of a particle \[12]:

The concept of adhesion is general for bonding strengths of two bodies. The concept concerns an adhesion special case autogezii when co-operate (there are in contact) homogeneous bodies, that is applicable to assembly units at separation. The role autogezii in the course of grading of many poroshkoobraznyh should be considered materials [53]. The Theoretical value of specific resistance on rupture Tnчастиц being in interaction is defined by the formula [46]:

Where - specific resistance of particles to shear; - factor of an internal friction.

As to energy dezagregatsii particles in work [44] the example of calculation of this energy for ultradisperse sibunita is resulted at a wet grinding and use expression:

Where і - levigating degree;

σ - a surface tension on border «levigated particles - environment»;

- Specific surface area of the assembly unit before levigating;

V - volume of all processed assembly units.

Authors of this expression use terminology, which not completely

Opens essence of energy dezagregatsii, levigating degree, instead of degree dezagregatsii is used. Also from the practical point of view the question of calculation of energy dezagregatsii, and also scopings of processed assembly units is difficult. Does not reveal, as in practice can be

Degree dezagregatsii, a specific surface of the assembly unit is defined.

Influence on properties of materials is rendered by external factors, such as temperature, pressure, moisture content and others. Therefore for optimisation of process of grading it is necessary to take into consideration set of factors: physical and chemical properties, a production technique, conditions and an operative conditions [73].

At movement of particles in any environment, this environment renders a tractive resistance, therefore at definition of dynamic parametres of a particle it is necessary to consider dynamic viscosity of air [109, 124, 132].

At calculations of movement of a particle in the air environment in attention also the particle form also undertakes, usually the equations of movement of a particle have a condition - the particle is accepted spherical [8, 20, 55, 104]. Thus received equations are similar, but the values received at their decision, can differ considerably because of simplifications, various conditions, assumptions [87].

The equation of movement of a particle for cylindrical system of co-ordinates

Will represent system from three equations [116]:

Where - components of speed of particles; up, u φ, uz - components of speed

Gas stream; r - radius-vector; ∣ - the factor considering

Deflexion of a windage of a particle from the law of resistance,

Defined Stoksom, - Reynolds's [24] made the criterion

For a particle in diameter 5; Stk - dimensionless number Stoksa; Fr - criterion Fruda.

During a particle finding in a grading working area there is a contact to surfaces of structural components, for example, to a wall of the chamber of separation. For impact surface definition on a surface as a result of blow in work [12] following expression is resulted:

Where K1 - restoration factor; - mass of / / fractions; In - device perimetre; m1 - particle mass; υr1 - distance to a wall; φ - proportionality factor; mi - mass of a particle / / krupnosti; F - a cross area of the chamber of separation.

Work of sizing machines in which parting of particles in a gas stream is made, is based on various speed of sedimentation of particles depending on krupnosti. In this connection structurally the separator should provide the parametres necessary for peak efficiency of grading. Therefore for grading process definition of the size of boundary particles, that is what at grading can be carried both to large, and to small [64, 65, 133] is important.

At separation of particles by the size no more 50мкм Shoemakers of M. JA suggests to use the following formula for definition of a boundary particle size at 0

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A source: Trofimchenko Vladimir Nikolaevich. PERFECTION of PROCESS DEZAGREGATSII of PARTICLES of the MATERIAL In the DYNAMIC SEPARATOR With the DEVICE In the form of mnogozahodnyh TAPES. The dissertation on competition of a scientific degree of a Cand.Tech.Sci. Belgorod - 2017. 2017

More on topic the Analysis of existing techniques of calculations of processes at separation poroshkoobraznyh materials:

  1. CHAPTER 1. THE ANALYSIS OF TECHNICS AND TECHNOLOGY OF SEPARATION poroshkoobraznyh OF MATERIALS
  2. Application of the equipment for air separation poroshkoobraznyh materials in technological systems of levigating
  3. 1.2. The analysis of the equipment for parting poroshkoobraznyh materials on krupnosti
  4. 1.2 Analysis of existing domestic approaches and techniques
  5. 2.3. The review and specification of existing dynamic techniques of control by development of the enterprise and complexes of the enterprises.
  6. CHAPTER 2. MATERIALS And RESEARCH TECHNIQUES
  7. the Appendix 1. Techniques of studying of features of informative processes
  8. the Comparative analysis of various approaches of raise of intellectualization of process of the calculations applied in robot scalers
  9. to techniques of the analysis of subgenres
  10. § 1. THE ANALYSIS OF TECHNIQUES OF THE ESTIMATION OF LEASING.
  11. the Analysis of existing apparatus-dependent colour models
  12. 3.2 Techniques of the financial analysis and its private appendices