Gray Thermal Radiation Model Reference

The Gray Thermal radiation model makes it possible to simulate diffuse radiation independently of wavelength. With this model, radiation properties of the media and surrounding surfaces are considered the same for all wavelengths.

Table 1. Gray Thermal Radiation Model Reference
Theory	See Theory Guide—Radiation Equilibrium.
Provided By	[physics continuum] > Models > Radiation Spectrum
Example Node Path	Continua > Physics 1 > Models > Gray Thermal Radiation
Requires	Space: Three Dimensional Time: any Optional Models: Radiation Radiation: Surface-to-Surface Radiation or Participating Media Radiation (DOM)
Properties	Kirchhoff Enabled When On, enforces Kirchhoff’s law (absorptivity equals emissivity) at surfaces. This property must be activated for radiative heat transfer, and can only be deactivated in the special case of using the Surface-to-Surface model to simulate molecular transport by physical analogy. Kirchhoff’s law is enforced by requiring the sum of the emissivity, reflectivity, and transmissivity to be 1.0 at surfaces. The default is On.
Activates	Model Controls (child nodes)	Thermal Environments > Radiation Temperature. See Setting the Thermal Environment.
	Boundary Inputs	See Boundary Settings.
	Field Functions	Absorption Coefficient, Boundary Emissivity, Boundary Emissivity on External Side, Boundary Reflection Specularity, Boundary Reflection Specularity on External Side, Boundary Reflectivity, Boundary Reflectivity on External Side, Boundary Transmissivity, Direct Directional Incident Radiation, Direct Directional Incident Radiation of <band-name>, Scattering Asymmetry Parameter, Scattering Coefficient, User-specified Diffuse Flux. See Radiation Field Functions Reference.

Boundary Settings

Inflow, Outflow, Free Stream Boundaries, and Wall

Diffuse Radiation Flux: The diffuse radiation flux specified as a scalar profile. Requires the Multiband Thermal Radiation or Gray Thermal Radiation model. See Diffuse Radiation Flux.
Surface Emissivity: The ratio of the power that a body emits to the power it would emit as a black body at the same temperature. See Emissivity.
Surface Reflectivity: The ratio of reflected radiant energy over incident radiant energy at a given surface. See Reflectivity.
Surface Transmissivity: The ratio of transmitted radiant energy over incident radiant energy at a given surface. See Transmissivity.

Setting the Thermal Environment

When the Surface-to-Surface (S2S) Radiation model or the View Factors Calculator model is used, each continuum is required to have a thermal environment. This thermal environment is a simplified representation of the environment surrounding the continuum, from the standpoint of thermal radiation. The Thermal Environment is activated with the Surface-to-Surface (S2S) Radiation model or the View Factors Calculator model. The environment is fully defined by ascribing the desired value to the Radiation Temperature.

The thermal environment is modeled as a black body with unity emissivity, and hence can be characterized solely with the Radiation Temperature. This temperature defines the energy that is effectively radiated from the environment. However, since there has to be only one environment, the value of the Radiation Temperature in every continuum must be the same.

The Radiation Temperature is a scalar quantity which is selected by opening the Thermal Environment node within the Gray Thermal Radiation model. The temperature can then be set in the Properties window.

AMG Linear Solver Defaults

For the Gray Thermal Radiation model, the default value for Cycle Type is V Cycle and the Convergence Tolerance is constant. See AMG Linear Solver Reference.