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.

• Radiation—From Options, select Radiation. Under the expanded list of Options, specify the values for Emissivity and Radiation 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.