Setting the Gas Boundary Conditions

Define the boundary conditions and specify the appropriate property values.

The gas enters the domain at 1.0 m/s with a temperature of 293.15 K, and a composition of 99% dry air and 1% H2O.

To set the gas boundary conditions:

Set up the inlet.

  1. Edit the Regions > Fluid > Boundaries > Top > Physics Values node and set the following properties:
    Node Property Setting
    Species Mass Fraction Value [0.01, 0.0, 0.99]
    Static Temperature Value 293.15 K


    Leave the default velocity magnitude to 1.0 m/s.

Set up an outlet for the gas to leave at the bottom of the domain. The outlet gas composition is unknown and cannot be specified. The outlet gas composition is therefore matched to the composition inside the domain. Create user field functions to specify the mass fraction of each species. Set the outlet temperature to 293.15 K.

  1. Right-click the Automation > Field Functions node and select New > Scalar from the pop-up menu.
  2. Rename the User Field Function 1 to MassFractionH2OCell.
  3. Select the MassFractionH2OCell node and set the following properties:
    Property Setting
    Function Name MassFractionH2OCell
    Definition ${MassFractionH2O}
    Ignore Boundary Values Activated


  4. In the same way, create field functions for the mass fraction of C2H6O2 and the mass fraction of air.
    Property Setting
    Function Name MassFractionC2H6O2Cell
    Definition ${MassFractionC2H6O2}
    Ignore Boundary Values Activated
    Property Setting
    Function Name MassFractionAirCell
    Definition ${MassFractionAir}
    Ignore Boundary Values Activated
  5. Edit the Regions > Fluid > Boundaries > Bottom node and set the following properties:
    Node Property Setting
    Bottom Type Pressure Outlet
    Physics Values > Species Mass Fraction Method Composite
    Composite > H2O Method Field Function
    Scalar Function MassFractionH2OCell
    Composite > C2H6O2 Method Field Function
    Scalar Function MassFractionC2H6O2Cell
    Composite > Air Method Field Function
    Scalar Function MassFractionAirCell
    Physics Values > Static Temperature Value 293.15 K