### 10.8.8. Radiometers

A radiometer is a user-defined point in space that monitors the irradiation heat flux at the required location. For a description of the radiometer settings, see Radiometer: Frame Overview in the CFX-Pre User's Guide.

A radiometer reports the irradiation heat flux at the specified location using a hemisphere based on the direction provided. The irradiation heat flux is relative to the radiometer temperature (that is, the incoming radiation minus the emission from the radiometer based on its specified temperature). By default, radiometers are ideal and the efficiency factor is 1.

Refer to Variables Relevant for Radiation Calculations in the CFX Reference Guide for definitions of radiation variables such as `Irradiation Heat Flux` and `Incident Radiation`.

For each radiometer, the following parameters must be specified:

- Location

  The physical location of the radiometer in the domain, in Cartesian or cylindrical coordinates.

- Temperature

  The temperature of the radiometer.

- Quadrature points

  The number of rays used for tracing from the radiometer location.

- Viewing direction

  The direction in which the radiometer points, specified as direction vector components.

The following parameter may be optionally specified:

Diagnostic Output Level

The CFX-Solver will write the radiometer ray traces to a series of polylines in a .csv file that can be visualized in CFD-Post. This can be used to determine if the number of quadrature points is optimal. The output is controlled as follows:

- `0` - Quiet. No .csv file is written. This is the default.

- `1` - Minimal. At the last radiation iteration, a .csv file is written, named pflux.<radiometer name>.csv.

- `2` - Verbose. At each radiation iteration, a .csv file is written at named <timestep>_pflux.<radiometer name>.csv.

Note: The ray traces out of a radiometer are distributed slightly differently from those out of a boundary. Consequently, for a small number of rays, the value of `Irradiation Heat Flux` at a boundary node may be different than that at a radiometer that is at the same location. However, it will converge to the same value for a sufficient number of rays.

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