Code Manual for CONTAIN 2.0 - Federation of American Scientists

The flight time and average velocity to the first structure in Case 1 of the TOF/KU model are the
same as they are for the TFI trapping model. Note, however, that the TOF/KU Case 1 trapping rate
differs from the TFI rate. The TFI model takes the sum of the gravitational fall time and the first
impact flight time as the time of fIight, while the TOF/KU model takes the shorter of the two as the
time of flight. The rates are different because if the debris reaches the first structure under Case 1
of the TOF/KU model, it is assumed to be trapped there. The main input parameter that affects this
case of the TOF/KU model is the first trapping length, L1. If a direct line of travel from a primary
entrance flow path to a structure can be clearly identified, then this distance should be given as LI.
Otherwise, it is recommended that LI be set equal to 6 times the cell gas volume divided by the
surface area of all surfaces in the cell.
An alternate trapping behavior corresponding only to the time of flight to the first structure can be
obtained by intentionally speci~ing an artificially large N~U,~,l value. If this is done, the & criterion
for re-entrainment will never be met and debris will always stick on the frostimpact. This technique
may be useful for performing sensitivity studies. In most predictive calculations, however, the
default Nfi cutoff values should be used.
If the N~ucriterion for re-entrainment on the first impact is met, sticking on the first impact is not
assumed and subsequent impacts on nonhorizontal surfaces will be considered as described below.
6.3.6.2 TOF/KU Case 2: Tratminp On Structures Bevond The First Inmact. The velocity v~,zused
for evaluating Nfi for impacts after the fmt is the second Wucture convective velocity, V2,if defined.
This velocity is more specifically the convective velocity for the inner face of the second structure
defined in the structure input block and can be controlled by changing the default hydraulic area and
coefficients in that input block. Note that none of the parameters specified in the DCH-CELL input
block have an effect on V2. It is recommended that at least two structures be defined in
subcompartments so that either a forced or natural convection velocity is calculated in the heat
transfer module and stored in Vzfor use in the TOF/KU model. If fewer than two structures are
defined, then the model will use the average gas velocity through the cell, v~,,v~, for v~,z.
Under the default RHODG = GAS option, N~ufor the second trapping criterion is given by
N Ku,s,2 =
If RHODG = MIX is specified, the second trapping NKUnumber is given by
N Ku,s,2 =
~
P~,i‘:2 (6-108)
2 2
pg,i ‘g,2 + pd,i ‘d,avg
d,~t - pg,i - pd,i go
(6-109)