20.1 Fluxes Through Boundaries

This section describes the quantities that you can compute for boundaries. For more information about generating flux reports, see this section in the separate User's Guide.

For selected boundary zones, you can compute the following quantities:

• The mass flow rate through a boundary is computed by summing the dot product of the density times the velocity vector and the area projections over the faces of the zone.

• The total heat transfer rate through a boundary is computed by summing the total heat transfer rate, $q = q_{c} + q_{r}$, over the faces, where $q_c$ is the convective heat transfer rate and $q_{r}$ is the radiation heat transfer rate. The computation of the heat transfer through the face depends on the specified boundary condition. For example, the conduction heat transfer on a constant-temperature wall face would be the product of the thermal conductivity with the dot product of the area projection and the temperature gradient. For flow boundaries, the total heat transfer rate is the flow rate of the conserved quantity. Depending on the models that are being used, the total heat transfer rate may include the convective flow of sensible or total enthalpy, diffusive flux of energy, etc. Note that the reference temperature in all enthalpy calculations is always 298.15K

• The radiation heat transfer rate through a boundary is computed by summing the radiation heat transfer rate $q_r$ over the faces. The computation of the radiation heat transfer depends on the radiation model used.

For example, you might use flux reporting to compute the resulting mass flow through a duct with pressure boundaries specified at the inlet and exit.