Turbophoresis is the tendency for
particles
In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass.
They vary greatly in size or quantity, from s ...
to migrate in the direction of decreasing
turbulence
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
level. The principle tends to segregate particles entrained in high velocity
gases
Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma).
A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...
axially toward the wall region.
Caporaloni et al. (1975) first found that because the vertical
gradient
In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gr ...
of
turbulence
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
near a depositing surface is large, turbophoresis is expected to enhance rate of
particle deposition
Particle deposition is the spontaneous attachment of particles to surfaces. The particles in question are normally colloidal particles, while the surfaces involved may be planar, curved, or may represent particles much larger in size than the depos ...
onto the surface. It was also predicted independently by Reeks (1983) who derived it rigorously from the particle
kinetic equation and showed that it arose from a force balance between the net drag force and the gradient of the particle kinetic stresses acting on the particles due to the turbulence. He predicted that this would lead to a buildup of
concentration
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', '' number concentration'', ...
near the wall, a feature which has been observed both experimentally and in
Direct Numerical Simulation
A direct numerical simulation (DNS)Here the origin of the term ''direct numerical simulation'' (see e.g. p. 385 in ) owes to the fact that, at that time, there were considered to be just two principal ways of getting ''theoretical'' results r ...
(DNS). He also independently called it turbophoresis.
Dasgupta et al., (1997)
[Sanjay Dasgupta, R. Jackson and S. Sundaresan: "Developing Flow of Gas-Particle Mixtures in Vertical Ducts", ''Ind. Eng. Chem. Res.'', 1997, 36(8), 3375-3390.] demonstrated that the non-uniform cross-sectional particle distribution observed during high-velocity flow of gas-particle mixtures through a vertical duct is indeed driven by turbophoresis.
References
Turbulence
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