Code Manual for CONTAIN 2.0 - Federation of American Scientists

Because the heat and mass transfer analogy is used to determine the condensation mass transfer
coefficient, this multiplier will also affect condensation mass transfer rates (see Section 10.2.1.3). ~
10.2 Mass Transfer Processe$
This section discusses a number of topics related to individual mass transfer processes at the
interface between the gaseous bulk fluid and a surface. Note that a discussion of the effects of the
coupling between the various heat and mass transfer processes at such an interface, through the
interface temperature calculation is given in Section 10.6.
Section 10.2.1 is an extension of the discussion in Section 10.1.1 on the evaluation of the boundary
layer properties and nondimensional numbers. Whereas the latter discusses quantities related to heat
transfer, the former extends the discussion to quantities related to condensation mass transfer. The
vapor diffisivity, the Schmidt number, and Sherwood number are discussed in this section.
Section 10.2.2 discusses the modeling of condensate films on heat transfer structures. The default
film model, which uses a fixed fti depth parameter, is discussed, as well as a film tracking model
implemented in CONTAIN 1.2. The latter model allows films to be treated according to film flow
correlations. It also allows films to be modeled on a generalized surface represented by a number
of structure surfaces.
Section 10.2.3 derives the standard expression for condensation (and evaporation) mass transfer
under quasi-steady conditions. For most reactor accident scenarios, the containment thermal
hydraulic conditions will be such that the condensation mass transfer process will dominate much ~
of the time. Thus, this process plays a key role in the discussion given in Section 10.6 on the
coupling between various heat and mass transfer processes.
10.2.1 Boundary Layer Properties and Nondimensional Numbers for Mass Transfer
This section discusses a number of quantities appearing in expressions for condensation mass
transfer. One quantity is the diffusivity, B,, of steam in the mixture of noncondensable gases
present. In code versions prior to CONTAIN 1.2, the diffusivity of steam in air is used regardless
of the noncondensable gas composition present. A more general model for the diffusivity has been
implemented in CONTAIN 1.2 and is described in Section 10.2.1.1. The evaluation of the Schmidt
and Sherwood numbers appearing in expressions for mass transfer are discussed in Section 10.2.1.2.
Methods for changing the default modeling of condensation mass transfer rates are discussed in
Section 10.2.1.3.
10.2.1.1 Diffimivitv of Steam. In code versions prior to CONTAIN 1.2, the diffusivity assumed for
steam is not a function of the gas composition. The value used is based upon a formulation given
in Reference Bir60 which, when evaluated specifically for water vapor in air, reduces to
Rev. O 10-22
(lo-33)
6/30/97