Code Manual for CONTAIN 2.0 - Federation of American Scientists

particles can combine at a time. The agglomeration model used in MAEROS and CONTAIN treats
four processes that lead to agglomeration: particle Brownian diffusion, differential gravitational ~
settling, turbulent shear, and turbulent acceleration in eddies. The agglomeration processes depend
on the physical properties of the gas and particles. Because the particles can be highly irregular, it
is customary to base the agglomeration modeling on the compact spherical-equivalent particle
diameter d, the agglomeration shape factory, and the dynamic shape factor ~. These shape factors
and the three collision efficiencies Col~, Coltl, and Cola used in the model are discussed in more
detail below, after the expressions for the agglomeration kernels are given.
The Brownian or diffusional agglomeration kernel is defined as[Ge182]
where f,~=1 is the sticking coefilcient, ~ and ~ are the spherical-equivalent particle diameters of the
two interacting particles, and ~ is the agglomeration shape factor for the ith particle, and the particle
diffusivity Di is given by
In this expression, K is the Boltzmann constant, p~is the gas viscosity (taken to be that of air), and
~ is the dynamic shape factor. The ~ factor allows for noncontinuum effects of the gas and is called
the Cunningham slip correction factor
Ci=l +Nfii [1.257 + 0.4exp (-l.l/Nti,i)]
where Nhj is the Knudsen number 2~di and k is the mean-free path of the gas (taken to be air). The
factor F is defined as
where
and
di +d. 8(Bi +Dj)
J
F=
di +dj +2gij + ~(di +dj)
gi,j={~