### 16.2.10. Variables Relevant for Radiation Calculations

The following table contains a list of variables (with both long and short variable names) that can be used when working with radiation calculations. For an explanation of the column headings, see List of Field Variables.

A B in the Type column indicates that the variable contains only non-zero values on the boundary of the model.

Long Variable Name | Short Variable Name | Units | Availability | Definition
--- | --- | --- | --- | ---
Wall Radiative Heat Flux | Qrad | [W m^-2] | 2,B DT, R, TS | Wall Radiative Heat Flux represents the net radiative energy flux leaving the boundary. It is computed as the difference between the radiative emission and the incoming radiative flux (Wall Irradiation Flux).
Wall Heat Flux | Qwall | [W m^-2] | 2,B C, DT, R, TS | Wall Heat Flux is sum of the Wall Radiative Heat Flux and the Wall Convective Heat Flux. For an adiabatic wall, the sum should be zero.
Wall Irradiation Flux | irrad | [W m^-2] | 2,B C, DT, R, TS | Wall Irradiation Flux represents the incoming radiative flux. It is computed as the solid angle integral of the incoming Radiative Intensity over a hemisphere on the boundary. For simulations using the multiband model, the Wall Irradiation Flux for each spectral band is also available for postprocessing.

Radiation Intensity

radint

[W m^-2 sr^-1]

RA, R, A, M, C, P, TS

Radiation Intensity represents the radiative energy flow (in units of energy per time) per unit solid angle (solid angle of the outgoing or incoming radiation, measured in steradians) and per unit area (area of a surface that is normal to the ray direction).

Note: This quantity should not be used for quantitative calculations when computed using surface-to-surface models, since it has been agglomerated and it represents an average value over the whole domain.

Wall Absorbed Radiation Flux | sabsor | [W m^-2] | 2,B DT, R, TS | Wall Absorbed Radiation Flux represents the absorbed heat flux due to radiation, and is computed as Wall Radiative Heat Flux minus reflection and emission.
Incident Radiation | radinc | [kg s^-3] | 1 C, DT, M, R, TS | The integral of `Radiation Intensity` over a full sphere of unit radius. For isotropic radiation, it is a factor of greater than the `Radiation Intensity`.
Absorption Coefficient | absorp | [m^-1] | 1 C, M, R, TS | For details, see Table 16.2: Common CEL Field Variables and Predefined Expressions
Scattering Coefficient | scatter | [m^-1] | 1 C, M, R, TS
Refractive Index | refrac | [ ] | 1 C, R, TS
Radiative Emission | rademis | [kg s^-3] | 1 RA
Extinction Coefficient | extinct | [m^-1] | 1 C
Emissivity | emis | [ ] | 1 C

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