29.2 Fluxes Through Boundaries

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, , over the faces, where is the convective heat transfer rate and 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. For reacting flows, FLUENT reports the total energy flux, which consists of the sensible and formation enthalpies (see Section  13.2.1 for details).

• The radiation heat transfer rate through a boundary is computed by summing the radiation heat transfer rate 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.

Flux Reporting with Particles and Volumetric Sources

Note that the reported mass and heat balances address only flow that enters or leaves the domain through boundaries; they do not include the contributions from user-defined volumetric sources or particle injections. For this reason, a mass or heat imbalance may be reported. To determine if a solution involving a discrete phase is converged, you can compare this imbalance with the change in mass flow or heat content computed in the particle tracking summary report. The net flow rate or heat transfer rate reported in the Flux Reports panel should be nearly equal to the Change in Mass Flow or Heat Content in the summary report generated from the Particle Tracks panel.

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