External Radiation Source
Use this node in 2D and 3D components to define an external radiation source as a point or directional radiation source with view factors calculation. Only the external view factors (Fext) are recomputed when the radiation source moves, not the complete view factors. When specular radiation is involved (with Opaque Surface or Semitransparent Surface), the cost of computation of these external view factors can be important. Each External Radiation Source node contributes to the incident radiative heat flux on all spectral bands, GBi on all the boundaries where a Diffuse Surface, Diffuse Mirror, Opaque Surface, or Semitransparent Surface boundary condition is active. The source contribution, GextDir, i, is equal to the product of the view factor of the source by the source radiosity. For radiation sources located on a point, GextDir, i=Fext, i Ps, i. For directional radiative source, GextDir, i = Fext, i q0, s.
Only direct irradiation from the source is accounted for. Diffuse irradiation inclusion is controlled through the Include diffuse radiation check box in Ambient section of Diffuse Surface (Surface-to-Surface Radiation Interface) and Diffuse Mirror (Surface-to-Surface Radiation Interface) features.
The external radiation sources are ignored on the boundaries when neither Diffuse Surface, Diffuse Mirror, Opaque Surface, nor Semitransparent Surface is active.
External Radiation Source
Select a Source position: Point coordinate (default) or Infinite distance. In 3D, Solar position is also available.
Point Coordinate
For Point coordinate define the Source location xs. The source radiates uniformly in all directions.
xs should not belong to any surface where a Diffuse Surface, Diffuse Mirror, Opaque Surface, or Semitransparent Surface boundary condition is active.
Infinite Distance
For Infinite distance define the Incident radiation direction is.
Solar Position
Solar position is available for 3D components. When this option is selected, use it to estimate the external radiative heat source due to the direct striking of the Sun rays.
North, west, and the up directions correspond to the x, y, and z directions, respectively. Azimuth angle is measured from true north, hence x direction corresponds to true north as well.
Depending on the presence of an Ambient Properties node under Definitions and on the type of Ambient data selected in this node, further parameters should be set for the definition of the location on Earth.
If the type of Ambient data is Meteorological data (ASHRAE 2013), Meteorological data (ASHRAE 2017) or Meteorological data (ASHRAE 2021) in the Ambient Properties node under Definitions, it is available in the Ambient data list of the External Radiation Source node. When selected from this list, the location is set to the Weather station selected in the Ambient Properties node under Definitions. Click to select the Include daylight saving time (Time zone + 1) check box to add one hour to the default setting for the station selected.
Else, when Ambient data is User defined in the Ambient Properties node under Definitions, None is the only option in the Ambient data list of the External Radiation Source node, and the following parameters should be set.
Select an option from the Location defined by list: Coordinates (default) or City.
For City select a predefined city and country combination from the list. Click to select the Include daylight saving time (Time zone + 1) check box to add one hour to the default setting for the city selected. For example, if New York City, USA is selected and the default standard time zone is UTC–5 hours, when the check box is selected, the daylight saving time is used instead (UTC–4 hours).
If Coordinates is selected, or your city is not listed in the Location defined by table, define the following parameters:
•
Latitude, a decimal value, positive in the northern hemisphere (the default is Greenwich UK latitude, 51.477). Enter a value without a unit to avoid double conversion. This is because the latitude value is expected to represent degrees but the model’s unit for angles may be different (for example, the SI unit for the angle is radians).
•
Longitude, a decimal value, positive at the east of the Prime Meridian (the default is Greenwich UK longitude, −0.0005). Enter a value without a unit to avoid double conversion. This is because the latitude value is expected to represent degrees but the model’s unit for angles may be different (for example, the SI unit for the angle is radians).
•
Time zone, the number of hours to add to UTC to get local time (the default is Greenwich UK time zone, 0). For example in New York City, USA the time zone is UTC–5 hours (standard time zone) or UTC–4 hours (with daylight saving time).
For either selection (City or Coordinates), in the Date table enter the:
•
Day, the default is 01. Enter a value without a unit to avoid double conversion. This is because the value is expected to represent days but the model’s unit for time may be different (for example, the SI unit for time is seconds).
•
Month, the default is 6 (June). Enter a value without a unit to avoid double conversion. This is because the value is expected to represent months but the model’s unit for time may be different (for example, the SI unit for time is seconds).
•
Year, the default is 2012. Enter a value without a unit to avoid double conversion. This is because the value is expected to represent years but the model’s unit for time may be different (for example, the SI unit for time is seconds). The solar position is accurate for a date between 2000 and 2199.
For either selection (City or Coordinates), in the Local time table enter the:
•
Hour, the default is 12. Enter a value without a unit to avoid double conversion. This is because the value is expected to represent hours but the model’s unit for time may be different (for example, the SI unit for time is seconds).
•
Minute, the default is 0. Enter a value without a unit to avoid double conversion. This is because the value is expected to represent minutes but the model’s unit for time may be different (for example, the SI unit for time is seconds).
•
Second, the default is 0.
For temporal studies, these inputs define the start time of the simulation. By default, the Update time from solver check box is selected, and the time is then automatically updated with the time from the solver. Clear this check box to manually set the time update.
For either selection of Ambient data type in an Ambient Properties node under Definitions, define the Solar irradiance field Is as the incident radiative intensity coming directly from the Sun. Is represents the heat flux received from the Sun by a surface perpendicular to the Sun rays. When surfaces are not perpendicular to the Sun rays the heat flux received from the Sun depends on the incident angle.
For User defined, enter a value or expression for the Solar irradiance Is. Else, select a Clear sky noon beam normal irradiance defined in an Ambient Properties node under Definitions.
If Wavelength dependence of radiative properties is Solar and ambient or Multiple spectral bands, the solar irradiance is divided among all spectral bands Bi as qs, i = q0,sFEPi(Tsun) where FEPi(Tsun) is the fractional blackbody emissive power over Bi interval at Tsun = 5780 K.
Radiative Intensity
This section is available when Source position is set either to Point coordinate or Infinite distance.
Point Coordinate
If Wavelength dependence of radiative properties is Constant, enter a value or expression to define the Source heat rate Ps.
If Wavelength dependence of radiative properties is Solar and ambient or Multiple spectral bands, set the Radiative intensity to Blackbody, User defined for each band, or User defined.
When Radiative intensity is set to User defined, enter a value or expression for the Source heat rate distribution Ps,λ. The wavelength may be accessed through the rad.lambda variable. This distribution is integrated on each spectral band to obtain the source heat rate Ps,i for each spectral band.
When Radiative intensity is set to Blackbody, enter a value for the Source temperature Ts and the Source heat rate Ps, to define the source power on the spectral band Bi as Ps, i = FEPi(Ts)Ps where FEPi(Ts) is the fractional blackbody emissive power over Bi interval at Ts.
When Radiative intensity is set to User defined for each band, enter a value for the Source heat rate Ps,i for each spectral band. Within a spectral band, each value is assumed to be independent of wavelength.
Infinite Distance
If Wavelength dependence of radiative properties is Constant, enter a value or expression to define the Source heat flux q0,s. Alternatively, select a Clear sky noon beam normal irradiance defined in an Ambient Properties node under Definitions.
If Wavelength dependence of radiative properties is Solar and ambient or Multiple spectral bands, set the Radiative intensity to Blackbody, User defined for each band, or User defined.
When Radiative intensity is set to User defined, enter a value or expression for the Source heat flux distribution q0,s,λ. The wavelength may be accessed through the rad.lambda variable. This distribution is integrated on each spectral band to obtain the source heat flux q0,s,i for each spectral band.
When Radiative intensity is set to Blackbody, enter a value for the Source temperature Ts and the Source heat flux q0,s, to define the source heat flux on the spectral band Bi as qs, i = FEPi(Ts)q0,s where FEPi(Ts) is the fractional blackbody emissive power over Bi interval at Ts.
When Radiative intensity is set to User defined for each band, enter a value for the Source heat flux q0,s,i for each spectral band. Within a spectral band, each value is assumed to be independent of wavelength.
The Wavelength dependence of radiative properties is defined in the physics interface settings, in the Radiation Settings section. When only one spectral band is defined, the i subscript in variable names is removed.
The Sun position is updated if the location, date, or local time changes during a simulation. In particular for transient analysis, if the unit system for the time is in seconds (default), the time change can be taken into account by adding t to the Second field in the Local time table. Note that no validity range is prescribed on the time inputs. It is possible to enter values that exceed the expected boundary. For example, entering 5h 2min 81s is equivalent to 5h 3min 21s. This makes it possible to enter t in the second field, even if the solution is calculated for more than 60s.
The Surface-to-Surface Radiation Interface
Theory for Surface-to-Surface Radiation
Sun’s Radiation Effect on Two Coolers Placed Under a Parasol: Application Library path Heat_Transfer_Module/Thermal_Radiation/parasol
Location in User Interface
Context Menus
 Surface-to-Surface Radiation>External Radiation Source
Ribbon
Physics tab with Surface-to-Surface Radiation selected:
Global>External Radiation Source