Code Manual for CONTAIN 2.0 - Federation of American Scientists

This constraint thus reduces the number of sectional agglomeration coefficients. If this geometric
constraint is not satisfied by the input parameters specified by the user, the code will abort.
The calculation of the coefficients is time consuming. Therefore, the coefficients are either read in
from a file or calculated on the fwstcall to the aerosol model for use throughout the entire problem.
Using a constant set of coefficients imposes some modeling constraints, however. These arise
because parameters embedded in the coefficients are also effectively held fixed, despite the fact that
they should vary with changing conditions during the problem. A simple multiplier in a coefficient
should not be considered embedded because the coefficient can be calculated for a unit multiplier
and resealed when used. In fact, the deposition coefficients, except that for settling, are calculated
for a unit forcing factor. The coefficient set employed in CONTAIN uses 8(’’nsectn”)2+ 8(’’nsectn”)
storage locations, not counting the condensation coefficients, which are not used when the moving
grid method is employed. (For an aerosol with 20 sections this corresponds to 3360 storage
locations.)
The following constraints pertain to the current coefficient set:
● The aerosol material density is assumed to be the same for all components.
● The aerosol shape, as modeled by the dynamic and agglomeration shape factors, is
independent of aerosol composition.
● The medium in which the aerosol processes are assumed to occur has fixed
composition and is taken to be air. In addition, gas properties appearing in <
expressions for deposition rates are evaluated for bulk conditions, not boundary layer
conditions, unless otherwise specified.
● The degree of turbulent agglomeration is fixed throughout the problem. This is
controlled by the turbulent dissipation coefficient, “turbds” specified in the global
AEROSOL input block.
● Other parameters that control deposition rates do not depend on particle composition.
For example, the ratio of the thermal conductivity of air to that of the aerosol
material, “tkgop,” also in the global AEROSOL input block, is fixed.
The pressure and temperature of the atmosphere are embedded in these coefficients and are fixed for
a single set of coefllcients. However, the aerosol module actually calculates four sets of coefficients
at points given by combinations of two temperatures (Tfi~ and T_) and two pressures (Pti~ and
P_). These temperatures and pressures are specified in the AEROSOL input block as “tgas1,“
“tgas2,” “pgasl,” and “pgas2,” respectively. Changing thermal-hydraulic conditions during the
problem are accommodated by interpolating between these sets of coefilcients. The Tti~, T~u, Ptin,
and P- parameters are chosen to bound the temperatures and pressures expected. At the expense
of larger sets of coefficients, some of the constraints above can be removed by interpolating to
accommodate other changing parameters or by separating the coefficients so that a relevant
parameter is not embedded.
Rev O 6/30/97