Code Manual for CONTAIN 2.0 - Federation of American Scientists

diffusivity being replaced by the particle diffusivity. Details of the treatment for the vapor are given
in Section 12.3.
Thermo~horesiS
E therm=
4Cti(2 + 0.6N~~li2N#3)(T~ - T~)
v~D
(7-45)
Here, N% is the Prandtl number, C is the Cunningham slip correction given in Equation (7-17),
Nti – 21/~ is the Knudsen number, where k is the molecular mean free path, ~ is the dynamic shape
factor, and k~ is the user-specifiable ratio of the gas thermal conductivity to the particle
conductivity. The constants Cmand C~are related to slip and thermal accommodation, respectively
(see Equation (7-19)).
DiffusioDhoresi$
[1
Pg - P,d
‘@h = 4DV2 ( +0.6 N~el’2NScl’3)
(w X
MW1’21n ‘
Pg - P,
~1’2+ X~CM~j’2vdD
)
(7-46)
In Equation (7-46), B, is the boundary layer vapor diffusivity, N%= p~p@, is the Schmidt number;
P~ is the atmosphere pressure; Pv,~is the vapor pressure at the drop surface, P, is the bulk vapor
pressure; ~ is the boundary layer vapor mole fraction; ~ is the molecular weight of waten ~C is
the boundary layer noncondensable gas mole fraction; and WC is the molecular weight of the
noncondensable gas.
The expression given in Equation (7-45) for the thermophoretic collection efficiency is based upon
the expression given in Equation (7-19) for therrnophoretic deposition upon structures together with
the temperature gradients at the drop surface implied by the heat transfer and Nusselt number
relations given for the drop in Section 12.3. Likewise, the diffksiophoresis expression is given by
combining the treatment of diffbsiophoretic deposition on structures given in Equation (7-20) with
the condensation/evaporation rate calculated for the drop as described in Section 12.3. The phoretic
effects can be negative under certain conditions; for example, the diffusiophoretic effect is negative
when the drop is evaporating. Jn such cases, the phoretic effects are still evaluated from Equations
(7-45) and (7-46) and added algebraically to the other collection efficiencies. The total collection
efficiency is constrained to be non-negative, however.
Rev. O 7-35 6/30/97