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:
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.
The default option for the Heat Flux node is Nonsolid, which defines q0 in the spatial frame. No frame conversion is needed.
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.
Heat Flux
Select the Flux type from the list: General inward heat flux (default), Convective heat flux, Heat rate, or Nucleate boiling heat flux.
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 (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:
Wall height L and the Tilt angle ϕ. The tilt angle is the angle between the wall and the vertical direction, ϕ = 0 for vertical walls.
Characteristic length (area/perimeter) L. The characteristic length is the ratio between the surface area and its perimeter.
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:
Plate distance L and a Chimney height H.
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:
Plate length L and Velocity, fluid U.
Position along the plate xpl and Velocity, fluid U.
Cylinder Diameter D and Velocity, fluid U.
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 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 Properties node under Definitions.
Finally, when the Fluid is Moist air, also set the External relative humidity, ϕw,ext, and the Surface relative humidity, ϕw,s, 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.
Nucleate Boiling Heat Flux
This option computes q0 with the Rohsenow’s correlation, that evaluates the heat flux due to nucleate boiling on a surface immersed in a liquid pool. See Nucleate Pool Boiling Correlation for details about the correlation.
The correlation applies to clean surfaces, and is insensitive to the shape and orientation of the surface. It relies on empirical constants Csf and s that are predefined for several combinations of fluid and surface materials, and on the boiling fluid properties at saturation temperature, also predefined for some fluids.
Select an option in the Fluid list:
When Water, Benzene, n-Pentane, or Ethanol is selected, the material properties of the liquid and vapor phases required in the correlation are predefined (at saturation temperature and pA=1 atm). Depending on the selected fluid, different materials and finishings are available in the Surface list. For each option, the empirical constants Csf and s are predefined.
When From material is selected in the Fluid list, first choose materials available on the boundary from the Liquid materials and Vapor materials lists, to define ρl, Cp,l, kl, μl, and ρv. Then set the Ambient pressure, pA, the Saturation temperature, Tsat, the Latent heat of evaporation, Lv, and the Liquid-vapor surface tension, σ. Finally, enter values or expressions for the Rohsenow’s correlation parameters: the Prandtl number exponent, s, and the Liquid-surface combination factor, Csf, which accounts for surface roughness, that tends to increase the number of active nucleation sites for boiling.
This boundary condition will give incorrect results if T < Tsat and should only be used in a limited interval of validity Tsat + T1 < T < Tsat + T2. Typically, for water T1=10 K and T2=30 K.
Power Transistor: Application Library path Heat_Transfer_Module/Power_Electronics_and_Electronic_Cooling/power_transistor
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
Ribbon
Physics tab with interface as Heat Transfer in Solids and Fluids, or any version of the Heat Transfer interface selected:
Physics tab with Porous Medium>Fluid or Porous Medium>Porous Matrix selected in the model tree: