Mixing of solid particles

A reactor model based on solid particles in BMF may be used for situations in which there is deliberate mixing of the reacting system. An example is that of a fluid-solid system in a well-stirred tank (i.e., a CSTR)-usually referred to as a slurry reactor, since the fluid is normally a liquid (but may also include a gas phase) the system may be semibatch with respect to the solid phase, or may be continuous with respect to all phases (as considered here). Another example involves mixing of solid particles by virtue of the flow of fluid through them an important case is that of a fluidized bed, in which upward flow of fluid through the particles brings about a particular type of behavior. The treatment here is a crude approximation to this case the actual flow pattern and resulting performance in a fluidized bed are more complicated, and are dealt with further in Chapter 23. 

In the mixing of solid particles, the following three mechanisms may be involved ... 

Brothman et al 24 have given an alternative theory for the process of mixing of solid particles, which has been described as a shuffling process. It is proposed that, as mixing takes place, there will be an increasing chance that a sample of a given size intercepts more than one part of the interface, and hence the number of mixed samples will increase... 

Roseman B, Donald MB. Mixing and de-mixing of solid particles part 2 effect of varying the operating conditions of a horizontal drum mixer. Br Chem Eng 1962 7(1) 823. 

The mass transfer coefficient increases with gas velocity because the gas-liquid interfacial area and the mixing of solid particles increase with gas velocity. However, skewed bubble-size distribution occurs when gas velocity is increased beyond a certain value, and the interfacial area does not increase further. The solid mixing also approaches a constant level. The transfer coefficient has been reported to be proportional to gas velocity to an exponent in the range of 0.44-0.98. ... 

Flow rates of solutions or suspensions are measured with tracers such as Br and Na. For gas flows, radioactive rare gases, Ar, Rr, and Xe are commonly used. Mixing processes are followed by measuring the tracer concentration. In mixing of solid particles, the best tracer is a fraction of the material itself made radioactive by neutron irradiation. 

D. K. Singh. A Fundamental Study of the Mixing of Solid Particles. Ph.D. Dissertation, University of Rochester, New York, 1978. 

The mixing of solid particles in a three-phase fluidized bed was analyzed by Evstrop eva et al. [73] taking cine-camera films of the particle motion in bidlmensional beds of 2.5 mm and 3.9 mm glass beads. Two types of tracer particles were employed ... 

P.M.C. Lacey. The Mixing of Solid Particles, Paper Read before the Graduates and Students of the Institution of Chemical Engineers, 21, pp. 53-59, February 26, 1943. 

S.J. Chen, L.T. Fan and C.A. Watson, Mixing of Solid Particles in Motionless Mixer—Axial Dispersed Plug Flow Model, I EC Process Design and Development 12, pp. 42-47.1973. 

J.Gyenis, J. Nemeth and J. Arva, Gravity Mixing of Solid Particle Systems in Steady-State Static Mixer Tubes, Sm ws CAc/w. 13(5), pp. 51-55,1991. 

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