Author:
READE WALTER C.,COLLINS LANCE R.
Abstract
Coagulation and growth of aerosol particles subject to isotropic turbulence has been
explored using direct numerical simulations. The computations follow the trajectories
of 262 144 initial particles as they are convected by the turbulent flow field. Collision
between two parent particles leads to the formation of a new daughter particle with
the mass and momentum (but not necessarily the energy) of the parent particles. The
initially monodisperse population of particles will develop a size distribution over
time that is controlled by the collision dynamics. In an earlier study, Sundaram &
Collins (1997) showed that collision rates in isotropic turbulence are controlled by
two statistics: (i) the radial distribution of the particles and (ii) the relative velocity
probability density function. Their study considered particles that rebound elastically;
however, we find that the formula that they derived is equally valid in a coagulating
system. However, coagulation alters the numerical values of these statistics from the
values they attain for the elastic rebound case. This difference is substantial and must
be taken into consideration to properly predict the evolution of the size distribution
of a population of particles. The DNS results also show surprising trends in the
relative breadth of the particle size distribution. First, in all cases, the standard
deviation of the particle size distribution of particles with finite Stokes numbers is
much larger than the standard deviation for either the zero-Stokes-number or infinite-Stokes-number limits. Secondly, for particles with small initial Stokes numbers, the
standard deviation of the final particle size distribution decreases with increasing
initial particle size; however, the opposite trend is observed for particles with slightly
larger initial Stokes numbers. An explanation for these phenomena can be found by
carefully examining the functional dependence of the radial distribution function on
the particle size and Stokes number.
Publisher
Cambridge University Press (CUP)
Subject
Mechanical Engineering,Mechanics of Materials,Condensed Matter Physics
Cited by
68 articles.
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