Boundary Conditions
The boundary condition parameters for the Heat module apply to Boundaries in the Flow Analysis Tree. The options also apply to interfaces for which the Flow module is blanked on one side of the interface, creating a Boundary.
The boundary conditions appear in the Properties panel when you select a boundary in the Flow Analysis Tree under General Boundaries.
Adiabatic
Adiabatic is a thermal boundary condition in which the heat flux is set to 0 (as if insulated).
Adiabatic is the default condition for the
Heat module when you select a
Wall,
Rotating Wall, or
Symmetry boundary condition for the
Flow module.
Specified Temperature
Specified Temperature is a thermal boundary condition when you know the
temperature at a boundary. The
Specified Temperature boundary condition is the default condition when you select
Specified Velocity,
Specified Volumetric Flux,
Specified Total Pressure, or
Specified Pressure Inlet for the
Flow module. The temperature of a fluid exiting the domain is based on the internal (upwind) temperature. The temperature of a fluid entering the domain is based on the
Specified Temperature. In addition to convective effects, the
Specified Temperature influences the internal temperature by conduction.
Specify Total Temperature
Specify Total Temperature is a thermal boundary condition when you know the
total temperature at a boundary.
The
temperature of a fluid exiting the domain is based on the internal (upwind) temperature. The temperature of a fluid entering the domain is based on
Specify Total Temperature. In addition to convective effects,
Specify Total Temperature influences the internal temperature by conduction.
Outlet
Outlet is a thermal boundary condition at an opening where the flow is expected to exit the domain. For back flow, the Temperature of the incoming fluid is specified by User Specified or Fully Developed.
• Fully Developed—Temperature of any fluid reentering the domain is based on the cell center temperature of the cells processing faces which form the Outlet boundary.
• User Specified—Temperature of any fluid re-entering the domain is based on the specified temperature.
The heat equation
Outlet boundary condition is the default condition when you select a
Specified Pressure Outlet or
Resistor Capacitor boundary condition for the
Flow module. The
temperature of the fluid exiting the outlet is based on the internal (upwind) temperature. The
temperature of a fluid reentering the domain is based on the
Specified Temperature. The
Specified Temperature at the
Outlet influences the internal temperature by conduction. Typically this effect is insignificant unless the outflow is very small or the
conductivity is very high (low Péclet number).
Symmetry
Symmetry for the
Heat module implies that there is no heat flux or
temperature gradient normal to the boundary.
Symmetry for the
Heat module is the same as the
Adiabatic boundary conditions.
Adiabatic is the default boundary condition for the
Heat module when you select a
Symmetry boundary condition for the
Flow module.
Symmetry boundary condition for the
Heat module usually correspond to a physical symmetry in the model. However, it does not have to correspond, if the effects of the boundary condition are logical.
Specified Heat Flux
Specified Heat Flux is a set of thermal boundaries that you use when you know the average value of heat flux (
flux per area) or total heat (
total flux). You can specify the
Specified Heat Flux boundary condition for a selected
Boundary.
Heat flux is driven by the temperature gradient always flowing from high temperature regions to lower temperature regions.
The direction of the heat flow is determined using these options:
• Inflow—Imposes a positive temperature gradient in the direction into the domain.
• Outflow—Imposes a positive temperature gradient in the direction out of the domain.
• Both—Heat flows both into and out of the domain.
Specified Total Heat Flux
Specified Total Heat Flux is a set of thermal boundaries you can use when you know the average value of heat flux (
flux per area) or total heat (
total flux).
Heat flux is driven by temperature gradient and is always flowing from high temperature regions to lower temperature regions.
The direction of the heat flow is determined using these options:
• Inflow
• Outflow
• Both
Convection/Radiation
Convection/Radiation is a collection of thermal boundary conditions in which heat flux is a function of the external
convection,
radiation, or both. The different options are listed below:
• Convection—From
Options, select
Convection. Under the expanded list of
Options, specify the values for
Exchange Coefficent and
Convection Ambient Temperature.
• Convection/Radiation—Use boundary conditions to specify
Radiation and
Convection processes. From
Options, select
Convection/Radiation. Under the expanded list of
Options, specify the values for
Exchange Coefficient,
Convection Ambient Temperature,
Emissivity, and
Radiation Ambient Temperature.
Output
The
integrated quantities available as output from the
Heat module for the boundaries are shown in
output variables.