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 factor calculation. 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 or Diffuse Mirror boundary condition is active. The source contribution, GextDir, Bi, is equal to the product of the view factor of the source by the source radiosity. For radiation sources located on a point, GextDir, Bi=Fext, Bi Ps, Bi. For directional radiative source, GextDir, Bi = Fext, Bi 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 and Diffuse Mirror features.
•
The external radiation sources are ignored on the boundaries when neither Diffuse Surface nor Diffuse Mirror is active.
•
If this feature is combined with heat transfer in 2D and 1D, the thickness is assumed to be infinite for the view factor computation. The user-defined value for d is still used in the heat transfer equation.
Direct Irradiation Source
Select a Source position: Point coordinate (the default) or Infinite distance. In 3D, Solar position is also available.
Point Coordinate
For Point coordinate define the Source location xs and the Source power Ps. The source radiates uniformly in all directions.
If Wavelength dependence of emissivity is Solar and ambient or Multiple spectral bands, set the Source power definition to Blackbody or User defined. When Blackbody is selected, enter the Source temperature, Ts, to define the source power on the spectral band Bi as Ps, Bi = FEPBi(Ts)Ps where FEPBi(Ts) is the fractional blackbody emissive power over Bi interval at Ts. When User defined is selected, enter an expression to define the source power on each spectral band Bi, Ps, Bi.
xs should not belong to any surface where a Diffuse Surface or Diffuse Mirror boundary condition is active.
Infinite Distance
For Infinite distance define the Incident radiation direction is and the Source heat flux q0,s.
If Wavelength dependence of emissivity is Solar and ambient or Multiple spectral bands, set the Source heat flux definition to Blackbody or User defined.
•
When Blackbody is selected, enter the Source temperature, Ts, to define the source heat flux on the spectral band Bi as q0, s, Bi = q0, sFEPBi(Ts)q0, s where FEPBi(Ts) is the fractional blackbody emissive power over Bi interval at Ts.
•
When User defined is selected, enter an expression to define the source heat flux on each spectral band Bi, q0, s, Bi.
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 type of Ambient data selected in the Ambient Settings section of the parent physics interface, further parameters should be set for the definition of the location on earth.
If the type of Ambient data is Meteorological data (ASHRAE 2013), the location is set to the Weather station selected in the Ambient Settings section. 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, the following parameters should be set.
Select an option from the Location defined by list: Coordinates (the 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 starting 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. Unselect this check box to manually set the time update.
For either selection of Ambient data type in the Ambient Settings section, 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 the Ambient Settings section of a Heat Transfer or Heat Transfer in Shells interface.
If Wavelength dependence of emissivity is Solar and ambient or Multiple spectral bands, the solar irradiance is divided among all spectral bands Bi as q0, s, Bi = q0,sFEPBi(Tsun)q0, s where FEPBi(Tsun) is the fractional blackbody emissive power over Bi interval at Tsun = 5780 K.
The Wavelength dependence of emissivity is defined in the physics interface settings, in the Radiation Settings section. When only one spectral band is defined, the Bi 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 (the 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 computed for more than 60s.
The Heat Transfer with 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
 Heat Transfer with Surface-to-Surface Radiation>Global>External Radiation Source
 Surface-to-Surface Radiation>Global>External Radiation Source
More locations are available if the Surface-to-surface radiation check box is selected under the Physical Model section. For example:
Heat Transfer in Solids>Global>External Radiation Source
Ribbon
Physics Tab with Heat Transfer in Solids, Heat Transfer in Fluids, Heat Transfer in Porous Media, Heat Transfer in Building Materials, Bioheat Transfer, Heat Transfer with Surface-to-Surface Radiation, Surface-to-Surface Radiation or Heat Transfer with Radiation in Participating Media selected:
Global>External Radiation Source