The paper describes a theory of particle deposition based formally on
the conservation
equations of particle mass and momentum. These equations are formulated in an
Eulerian coordinate system and are then Reynolds averaged, a procedure which
generates a number of turbulence correlations, two of which are of prime importance.
One represents ‘turbulent diffusion’ and the other
‘turbophoresis’, a convective drift
of particles down gradients of mean-square fluctuating velocity. Turbophoresis is
not a small correction; it dominates the particle dynamic behaviour in the
diffusion-impaction and inertia-moderated regimes.Adopting a simple model for the turbophoretic force, the theory is used to
calculate
deposition from fully developed turbulent pipe flow. Agreement with experimental
measurements is good. It is found that the Saffman lift force plays an important role
in the inertia-moderated regime but that the effect of gravity on deposition from
vertical flows is negligible. The model also predicts an increase in particle
concentration
close to the wall in the diffusion-impaction regime, a result which is partially
corroborated by an independent ‘direct numerical simulation’ study.The new deposition theory represents a considerable advance in physical
understanding over previous free-flight theories. It also offers many avenues
for future
development, particularly in the simultaneous calculation of laminar (pure inertial)
and turbulent particle transport in more complex two- and three-dimensional
geometries.
Langevin PDF simulation of particle deposition in a turbulent pipe flow
