7.13.2.4. Radiative Flux Boundary Condition

Scope

Aria Region, Equation System, Explicit Equation System, Root Finder Equation System

Summary

Radiative heat flux boundary condition. You must specify either a reference temperature or provide a nodal field for irradiation.

Description

This boundary condition models the radiative heat transfer from a specified surface to a surrounding surface. The temperature of the surrounding surface is assumed to have enough thermal mass that its temperature is unaffected by changes in computed temperature, and is therefore known. The heat flux normal to the surface is is given by $q_n = \varepsilon F( \sigma T^4 - G )$ , where the incident radiative flux, or irradiation, $G$ , may either be specified directly as a nodal field, or may be specified through a reference temperature, $G=\sigma T^4_r$ . The Stefan-Boltzmann constant, $\sigma$ , is defined in a Global Constants command block, $\varepsilon$ is the surface emissivity, and $F$ is the form factor.

With the exception of $\sigma$ , each of these parameters may vary in one of several ways, as defined below. The emissivity, if left unspecified, is determined locally from the material associated with the element that underlies each face on the surface. In the case of faces that are created as a result of element death, the emissivity is always determined by the underlying element.

begin Radiative Flux Boundary Condition Name

   Add Surface SurfaceList...

   Emissivity {=} Value [ On SurfaceName  ]

   Emissivity For Bands {=} Emissivity...

   Emissivity Fortran Subroutine {=} Name

   Emissivity Function {=} FunctionName [ On SurfaceName  ]

   Emissivity Subroutine {=} MySub [ On SurfaceName  ]

   Emissivity Time Function {=} FunctionName [ On SurfaceName  ]

   Equation {=} EquationName

   Form Factor Fortran Subroutine {=} Name

   Ignore Flux Coverage

   Integer Data Values...

   Integrated Flux Output VariableName

   Integrated Power Output VariableName

   Irradiation Node Variable {=} Name

   Irradiation Subroutine {=} Name

   Irradiation Time Function {=} Name

   Radiation Form Factor {=} Value

   Radiation Form Factor Subroutine {=} Name

   Radiation Form Factor Temperature Function {=} Name

   Radiation Form Factor Time Function {=} Name

   Real Data Values...

   Reference Temperature {=} Value

   Reference Temperature Fortran Subroutine {=} Name

   Reference Temperature Global Variable {=} GlobalVariableName

   Reference Temperature Subroutine {=} Name

   Reference Temperature Temperature Function {=} FunctionName

   Reference Temperature Time Function {=} FunctionName

   Use Advective Bar Name [ BulkNodes  ]

   Use Banded Wavelength Model ModelName

   Use Bulk Element Name

   Use Data Block Name

   Use Toggle Block ToggleName [ {on} ElementBlockList...  ]

end Radiative Flux Boundary Condition Name

7.13.2.4.1. Line Commands

Add Surface

Syntax: Add Surface SurfaceList…
Summary: Adds surfaces, by name, to a boundary condition’s extent.
Description: This line command is used to add surfaces to the extent of a boundary condition. In Exodus II, surfaces are specified as side sets, that have a global integer identifier. For example, side set 12 would be added by this line command using the surface name surface_12. Note that in SIERRA, each element of an array of strings must be separated by whitespace.

Parameter	Value	Default
SurfaceList	string…	–

Emissivity

Syntax: Emissivity {=} Value [ On SurfaceName ]
Summary: Sets a constant value of emissivity for a defined surface. If the optional parameters are not included, then this is the default emissivity for the enclosure. Otherwise it is only applied to the indicated surface.

Note

If a surface is called out more than once, the emissivity definition is overwritten: last one in wins.

Parameter	Value	Default
{=}	{= \| are \| is}	–
Value	real	–

Emissivity For Bands

Syntax: Emissivity For Bands {=} Emissivity…
Summary: Specify the constant emissivities for each wavelength band.

Parameter	Value	Default
{=}	{= \| are \| is}	–
Emissivity	real…	–

Emissivity Fortran Subroutine

Syntax: Emissivity Fortran Subroutine {=} Name
Summary: Specify the name of a FORTRAN user subroutine that will be used to calculate the convective coefficient for this boundary condition.

Parameter	Value	Default
{=}	{= \| are \| is}	–
Name	string	–

Emissivity Function

Syntax: Emissivity Function {=} FunctionName [ On SurfaceName ]
Summary: Sets a emissivity function for a defined surface. If the optional parameters are not included, then this is the default emissivity for the enclosure. Otherwise it is only applied to the indicated surface.

Parameter	Value	Default
{=}	{= \| are \| is}	–
FunctionName	string	–

Emissivity Subroutine

Syntax

Emissivity Subroutine {=} MySub [ On SurfaceName ]

Summary

Sets a emissivity user subroutine for a defined surface. If the optional parameters are not included, then this is the default emissivity for the enclosure. Otherwise it is only applied to the indicated surface.

Also, the software supports using locally scoped user data for most user subroutines, but I haven’t figured out a syntax for it here yet. So it is not yet supported. If you need to get data into this subroutine, use the region’s “REAL DATA” and “INTEGER DATA” line commands.

Note

If a surface is called out more than once, the emissivity definition is overwritten: last one in wins.

Parameter	Value	Default
{=}	{= \| are \| is}	–
MySub	string	–

Emissivity Time Function

Syntax: Emissivity Time Function {=} FunctionName [ On SurfaceName ]
Summary: Sets a emissivity function of time for a defined surface. If the optional parameters are not included, then this is the default emissivity for the enclosure. Otherwise it is only applied to the indicated surface.

Parameter	Value	Default
{=}	{= \| are \| is}	–
FunctionName	string	–

Equation

Syntax: Equation {=} EquationName
Summary: This command can be used to apply the Radiative Flux conditions for an equation other than the ENERGY equation.

Parameter	Value	Default
{=}	{= \| are \| is}	–
EquationName	string	–

Form Factor Fortran Subroutine

Syntax: Form Factor Fortran Subroutine {=} Name
Summary: Specify the name of a FORTRAN user subroutine that will be used to calculate the form factor for this boundary condition.

Parameter	Value	Default
{=}	{= \| are \| is}	–
Name	string	–

Ignore Flux Coverage

Syntax: Ignore Flux Coverage
Summary: This command causes the code to ignore the flux coverage Field when contact is present. Thus the flux will be applied even if the BC is being set on a contact surface.

Integer Data

Syntax: Integer Data Values…
Summary: List of integer data values to be used by the FORTRAN user subroutine. Copies of these values are provided to the subroutine hence changes to these values within the subroutine are not saved.

Parameter	Value	Default
Values	integer…	–

Integrated Flux Output

Syntax: Integrated Flux Output VariableName
Summary: Calculate the average flux associated with this flux boundary condition.
Description: This line command specifies that, as a postprocess, the normal flux associated with this boundary condition be integrated over the surface to obtain the total power. This power is then divided by the total area of the surface to obtain the average flux on the surface, and stored in a global variable named “VariableName”. This global variable may then be output to history files, or accessed in user subroutines, etc.

Parameter	Value	Default
VariableName	string	–

Integrated Power Output

Syntax: Integrated Power Output VariableName
Summary: Calculate the total power associated with this flux boundary condition.
Description: This line command specifies that, as a postprocess, the normal flux associated with this boundary condition be integrated over the surface to obtain the total power which is then stored into a global variable named “VariableName”. This global variable may then be output to history files, or accessed in user subroutines, etc.

Parameter	Value	Default
VariableName	string	–

Irradiation Node Variable

Syntax: Irradiation Node Variable {=} Name
Summary: Specifies the name of the node variable in which the incident radiative flux associated with this boundary condition is stored.
Description: The indicated node variable must be a valid user variable. Typically, this variable is defined by the user within the Region scope. The node variable is interpolated to the integration points during the integration of the flux term. Typically, this variable would be calculated in another SIERRA region, e.g., Fuego, and populated by transfer in the appropriate Region.

Parameter	Value	Default
{=}	{= \| are \| is}	–
Name	string	–

Irradiation Subroutine

Syntax: Irradiation Subroutine {=} Name
Summary: Specify the name of a user subroutine used to evaluate the irradiation for this boundary condition.

Parameter	Value	Default
{=}	{= \| are \| is}	–
Name	string	–

Irradiation Time Function

Syntax: Irradiation Time Function {=} Name
Summary: Specifies the name of a time-dependent function that is used to calculate the irradiation associated with this boundary condition.

Parameter	Value	Default
{=}	{= \| are \| is}	–
Name	string	–

Radiation Form Factor

Syntax: Radiation Form Factor {=} Value
Summary: Specifies a constant value for the radiation form factor for this boundary condition.
Description: For two surfaces, the BC surface (1) and far-field surface (2), $\varepsilon$ denoting emissivity, $A$ denoting area, and $F_{12}$ is the view factor.

$F = \begin{cases} 1 & \text{if } A_{2} \gg A_{1} \\ F_{12}/[(1-\varepsilon_{1})F_{12}+\varepsilon_{1}] & \text{for } \varepsilon_{1}=1 \text{ and } A_{2} \text{ not } \gg A_{1} \\ F_{12} & \text{if } \varepsilon_{1} = \varepsilon_{2} = 1 \end{cases}$

Parameter	Value	Default
{=}	{= \| are \| is}	–
Value	real	–

Radiation Form Factor Subroutine

Syntax: Radiation Form Factor Subroutine {=} Name
Summary: Specifies the name of a user subroutine that is used to calculate the radiation form factor associated with this boundary condition.

Parameter	Value	Default
{=}	{= \| are \| is}	–
Name	string	–

Radiation Form Factor Temperature Function

Syntax: Radiation Form Factor Temperature Function {=} Name
Summary: Specifies the name of a temperature-dependent function that is used to calculate the radiation form factor associated with this boundary condition.

Parameter	Value	Default
{=}	{= \| are \| is}	–
Name	string	–

Radiation Form Factor Time Function

Syntax: Radiation Form Factor Time Function {=} Name
Summary: Specifies the name of a time-dependent function that is used to calculate the form factor associated with this boundary condition.

Parameter	Value	Default
{=}	{= \| are \| is}	–
Name	string	–

Real Data

Syntax: Real Data Values…
Summary: List of real data values to be used by the FORTRAN user subroutine. Copies of these values are provided to the subroutine hence changes to these values within the subroutine are not saved.

Parameter	Value	Default
Values	real…	–

Reference Temperature

Syntax: Reference Temperature {=} Value
Summary: Specify a constant reference temperature for this boundary condition.

Parameter	Value	Default
{=}	{= \| are \| is}	–
Value	real	–

Reference Temperature Fortran Subroutine

Syntax: Reference Temperature Fortran Subroutine {=} Name
Summary: Specifies the name of a FORTRAN user-defined subroutine that will be used to calculate the reference temperature associated with this boundary condition.

Parameter	Value	Default
{=}	{= \| are \| is}	–
Name	string	–

Reference Temperature Global Variable

Syntax: Reference Temperature Global Variable {=} GlobalVariableName
Summary: Specify a global variable to be used for reference temperature.

Parameter	Value	Default
{=}	{= \| are \| is}	–
GlobalVariableName	string	–

Reference Temperature Subroutine

Syntax: Reference Temperature Subroutine {=} Name
Summary: Specifies the name of a user-defined subroutine that is to be used to calculate the reference temperature associated with this boundary condition.

Parameter	Value	Default
{=}	{= \| are \| is}	–
Name	string	–

Reference Temperature Temperature Function

Syntax: Reference Temperature Temperature Function {=} FunctionName
Summary: Specifies the name of the temperature-dependent function that is to be used to calculate the reference temperature associated with this boundary condition.

Parameter	Value	Default
{=}	{= \| are \| is}	–
FunctionName	string	–

Reference Temperature Time Function

Syntax: Reference Temperature Time Function {=} FunctionName
Summary: Specify the name of a time-dependent function for the reference temperature for this boundary condition.

Parameter	Value	Default
{=}	{= \| are \| is}	–
FunctionName	string	–

Use Advective Bar

Syntax: Use Advective Bar Name [ BulkNodes ]
Summary: Use the named advective bar to model the reference temperature.
Description: This line command specifies the name of an advective bar that has been defined using the advective bar command block. The temperature of the advective bar is used as the reference temperature, $T_r$ , for the convective heat transfer and this is computed based on a geometric coupling algorithm. Note that it is illegal to specify both a reference temperature and an advective bar.

Parameter	Value	Default
Name	string	–

Use Banded Wavelength Model

Syntax: Use Banded Wavelength Model ModelName
Summary: Use a specified banded wavelength model for use in enclosure radiation.
Description: Requests that a specific banded wavelength model named ModelName, be associated with an enclosure, where the ModelName is defined outside of the enclosure definition block. Only one BANDED WAVELENGTH MODEL can be used for an enclosure.

Parameter	Value	Default
ModelName	string	–

Use Bulk Element

Syntax: Use Bulk Element Name
Summary: Use the named bulk element to model the reference temperature.
Description: This line command specifies the name of a bulk fluid element that has been defined using the bulk fluid command block. The temperature of the bulk fluid element is used as the reference temperature, $T_r$, for the convective heat transfer.

Note

It is illegal to specify both a reference temperature and a bulk element.

Parameter	Value	Default
Name	string	–

Use Data Block

Syntax: Use Data Block Name
Summary: Reference to predefined data to be used by the user subroutine. These values may be changed by the user subroutine.

Parameter	Value	Default
Name	string	–

Use Toggle Block

Syntax: Use Toggle Block ToggleName [ {on} ElementBlockList… ]
Summary: Specification for toggling entities in the computational model based on Toggle Block parameters. When used at the region level, the list of element blocks to be toggled must be provided. Otherwise a listing of entities is not needed as the Toggle Block will be associated with the command line or the enclosing command block.

Parameter	Value	Default
ToggleName	string	–