Heat Flux
Use this node to add heat flux across boundaries. A positive heat flux adds heat to the domain. This feature is not applicable to inlet boundaries, use the Inflow condition instead.
Material Type
Select an option in the Material type list to specify if the inputs of the Heat Flux section are defined in the material or spatial frame:
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The Solid option specifies that the heat flux q0 is defined in the material frame. Because the heat transfer variables and equations are defined in the spatial frame, the inputs are internally converted to the spatial frame. See Conversion Between Material and Spatial Frames for details.
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The default option for the Heat Flux node is Nonsolid, which defines q0 in the spatial frame. No frame conversion is needed.
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The From material option uses the option selected in the Material type list of the Material Properties section of the material applied on the domain on which the node is active.
This option has no effect when the component does not contain a moving frame because the material and spatial frames are identical in such cases. With a Deformed Geometry or a Moving Mesh interface, the heat transfer features automatically account for deformation effects of the material and spatial frames on heat transfer properties. In particular the effects of volume changes on the density are considered. See Handling Frames in Heat Transfer and Material and Spatial Frames for details.
Heat Flux
Click to select the General inward heat flux (the default), Convective heat flux, or Heat rate button.
General Inward Heat Flux
It adds q0 to the total flux across the selected boundaries. Enter a value for q0 to represent a heat flux that enters the domain. For example, any electric heater is well represented by this condition, and its geometry can be omitted.
Convective Heat Flux
The default option is to enter a User defined value for the Heat transfer coefficient h.
In addition, the following options are also available to control the type of convective heat flux to model: External natural convection, Internal natural convection, External forced convection, or Internal forced convection.
For all options except User defined, select a Fluid: Air (the default), Transformer oil, Water, Moist air, or From material.
When From material is selected, choose a material available on the boundary from the Materials list.
Depending of the selected option, different parameters are needed. You can refer to the Sketch section to get an illustration of the configuration.
External Natural Convection
 
For External natural convection select Vertical wall, Inclined wall, Horizontal plate, upside, Horizontal plate, downside, Long horizontal cylinder, Sphere, or Vertical Thin Cylinder from the list under Heat transfer coefficient. Then enter the applicable information:
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Wall height L.
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Wall height L and the Tilt angle . The tilt angle is the angle between the wall and the vertical direction, for vertical walls.
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Characteristic length (area/perimeter) L. The characteristic length is the ratio between the surface area and its perimeter.
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Cylinder diameter D.
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Sphere diameter D.
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Cylinder height H.
Internal Natural Convection
 
For Internal natural convection select Narrow chimney, parallel plates or Narrow chimney, circular tube from the list under Heat transfer coefficient. Then enter the applicable information:
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Plate distance L and a Chimney height H.
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Tube diameter D and a Chimney height H.
External Forced Convection
 
For External forced convection select Plate, averaged transfer coefficient, Plate, local transfer coefficient, Cylinder in cross flow, or Sphere from the list under Heat transfer coefficient. Then enter the applicable information:
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Plate length L and Velocity, fluid U.
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Position along the plate xpl and Velocity, fluid U.
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Cylinder Diameter D and Velocity, fluid U.
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Sphere Diameter D and Velocity, fluid U.
Internal Forced Convection
 
For Internal forced convection the only option is Isothermal tube. Enter a Tube diameter D and a Velocity, fluid U.
If Velocity, fluid U is User defined, enter a value or expression. Else, select a Wind velocity defined in the Consistent Stabilization section of a Heat Transfer or Heat Transfer in Shells interface.
External conditions
 
First, set the Absolute pressure, pA. For User Defined, enter a value or expression. Else, select an Ambient absolute pressure defined in an Ambient Thermal Properties node under Definitions. The pressure is used to evaluate the Fluid material properties and this setting is not available for the Transformer oil and Water options.
In addition, enter an External temperature, Text. For User defined, enter a value or expression. Else, select an Ambient temperature defined in an Ambient Thermal Properties node under Definitions.
Finally, when the Fluid is Moist air, also set the External relative humidity, , and the Surface relative humidity, , used to evaluate the material properties.
Heat Rate
For Heat rate enter the heat rate P0 across the boundaries where the Heat Flux node is active. In this case q0 = P0 ⁄ A, where A is the total area of the selected boundaries.
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The detailed definition of the predefined heat transfer coefficients is given in The Heat Transfer Coefficients.
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For a thorough introduction about how to calculate heat transfer coefficients, see Incropera and DeWitt in Ref. 18.
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Handling Frames in Heat Transfer
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About the Heat Transfer Interfaces
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Power Transistor: Application Library path Heat_Transfer_Module/Power_Electronics_and_Electronic_Cooling/power_transistor
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Free Convection in a Water Glass: Application Library path Heat_Transfer_Module/Tutorials,_Forced_and_Natural_Convection/cold_water_glass
Location in User Interface
Context menus
 Heat Transfer>Heat Flux
Heat Transfer in Solids>Heat Flux
Heat Transfer in Fluids>Heat Flux
Heat Transfer in Porous Media>Heat Flux
Bioheat Transfer>Heat Flux
Ribbon
Physics Tab with interface as Heat Transfer, Heat Transfer in Solids, Heat Transfer in Fluids, Heat Transfer in Porous Media, Heat Transfer in Building Materials or Bioheat Transfer selected:
Boundaries>interface>Heat Flux