Physical principles used for the separation

Principles of basic importance during the separation are based on the effect of inertial and electric forces, gravity, and the resistance of a fluid medium. Besides this, the diffusion, the interception principle and other effects find application. In particular types of industrial separators, a combination of these principles is usually used and, in addition, the particle motion may be affected by further transport phenomena, such as thermophoresis, diffusion and coagulation. The separation process is naturally affected by characteristics of the particles to be separated, by the technical operating parameters of the gas to be purified, and also by certain characteristics of the separator itself. Thus, the separation process can hardly be exactly described mathematically, and most separators are designed on the basis of experimental data rather than pure theoretical principles. 

The gravitational principle can be applied during horizontal flow of a mixture of gas and particles, where the gas velocity is almost zero in a limiting layer of the gas at the boundary surface, so that the motion of particles induced by gravity can occur. The motion of particles in a stationary medium reaches a steady state and the velocity of fall results from an equilibrium between gravitational and aerodynamic effects. The quantity of particles separated on the given areas is determined by the particle concentration in the limit layer and by the velocity of fall. 

The effect of external forces on the motion of bodies, which tend to remain in the original dynamic condition, is the basis of the inertial principle. In the presence of a force, the motion of a body is changed in direction of action of the force. When polluted gas flows around a curved separating area, then it is possible to observe different curvatures of the paths of particles and the carrying gas trajectory, with a retention of the particle on a given area. This principle may be used in different types of dry mechanical separators. 

Particle motion in a real gas is affected by the molecular structure of the gas and by turbulence. These two characteristics are considered as diffusion phenomena. During the separation of particles from a pure gas, molecular as well as turbulent diffusion may occur. Molecular diffusion is the motion induced by action of molecular phenomena due to the characteristic random motion of molecules. The action of molecular forces is clearly manifested for particles smaller than 1 /xm. The diffusion phenomenon connected with 

The screen effect (interception) may be used for the separation of particles from a gas when there are other bodies in the flow comparable with the size of particles driven by the gas. 

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