33.7.2 Exhaust Fan Dialog Box

The Exhaust Fan dialog box sets the boundary conditions for an exhaust fan zone. It is opened from the Boundary Conditions task page. See Section  7.3.13 for details about defining the items below.

Controls

Zone Name   sets the name of the zone.

Phase   displays the name of the phase. It appears only for multiphase flows.

Momentum   contains the momentum parameters.

Gauge Pressure   sets the gauge pressure at the outlet boundary.

Backflow Direction Specification Method   sets the direction of the inflow stream should the flow reverse direction. You can choose Direction Vector, Normal to Boundary, or From Neighboring Cell.

Coordinate System   contains a drop-down list for selecting the coordinate system. You can choose Cartesian, Cylindrical, or Local Cylindrical. This option is available only for Direction Vector.

X, Y, Z-Component of Flow Direction   allows you to specify the velocity components in x, y, and z directions respectively. This option is available for cartesian coordinate system.

Radial Equilibrium Pressure Distribution   enables the radial equilibrium pressure distribution. See Section  7.3.8 for details.

This item appears only for 3D and axisymmetric swirl solvers.

Pressure Jump   specifies the rise in pressure across the fan. See Section  7.3.13 for details.

Target Mass Flow Rate   allows you to set mass flow rate as a boundary condition at the outlet.

Turbulence   displays the turbulence parameters.

Specification Method   specifies which method will be used to input the turbulence parameters. You can choose K and Epsilon ( $k$- $\epsilon$ models and RSM only), K and Omega ( $k$- $\omega$ models only), Intensity and Length Scale, Intensity and Viscosity Ratio, Intensity and Hydraulic Diameter, or Turbulent Viscosity Ratio (Spalart-Allmaras model only). See Section  7.3.2 for information about the inputs for each of these methods. (This item will appear only for turbulent flow calculations.)

Backflow Turbulent Kinetic Energy, Backflow Turbulent Dissipation Rate   set values for the turbulence kinetic energy $k$ and its dissipation rate $\epsilon$. These items will appear if you choose K and Epsilon as the Specification Method.

Backflow Turbulent Kinetic Energy, Backflow Specification Dissipation Rate   set values for the turbulence kinetic energy $k$ and its specific dissipation rate $\omega$. These items will appear if you choose K and Omega as the Specification Method.

Backflow Turbulent Intensity, Backflow Turbulent Length Scale   set values for turbulence intensity $I$ and turbulence length scale $\ell$. These items will appear if you choose Intensity and Length Scale as the Specification Method.

Backflow Turbulent Intensity, Backflow Turbulent Viscosity Ratio   set values for turbulence intensity $I$ and turbulent viscosity ratio $\mu_t/\mu$. These items will appear if you choose Intensity and Viscosity Ratio as the Specification Method.

Backflow Turbulent Intensity, Backflow Hydraulic Diameter   set values for turbulence intensity $I$ and hydraulic diameter $L$. These items will appear if you choose Intensity and Hydraulic Diameter as the Specification Method.

Backflow Turbulent Viscosity Ratio   sets the value of the backflow turbulent viscosity ratio $\mu_t/\mu$. This item will appear if you choose Turbulent Viscosity Ratio as the Specification Method.

Reynolds-Stress Specification Method   specifies which method will be used to determine the backflow Reynolds stress boundary conditions when the Reynolds stress turbulence model is used. You can choose either K or Turbulence Intensity or Reynolds-Stress Components. If you choose the former, ANSYS FLUENT will compute the Reynolds stresses for you. If you choose the latter, you will explicitly specify the Reynolds stresses yourself. See Section  12.14.3 for details. (This item will appear only for RSM turbulent flow calculations.)

Backflow UU,VV,WW,UV,VW,UW Reynolds Stresses   specify the backflow Reynolds stress components when Reynolds-Stress Components is chosen as the Reynolds-Stress Specification Method.

Thermal   contains the thermal parameters. This parameter is available only when the energy equation is turned on.

Backflow Total Temperature   sets the total temperature of the inflow stream should the flow reverse direction.

Radiation   contains the boundary conditions for the radiation model at the exhaust fan.

Participates in S2S Radiation   specifies whether or not fan participate in S2S radiation. This parameter is available only if you select Surface to Surface radiation model.

Participates in Solar Ray Tracing   specifies whether or not fan participate in solar ray tracing.

External Black Body Temperature Method, Internal Emissivity   set the radiation boundary conditions when you are using the P-1 model, the DTRM, the discrete ordinates model, or the S2S model for radiation heat transfer. See Section  13.3.6 for details.

Species   contains the species parameters.

Specify Species in Mole Fractions   allows you to specify the species in mole fractions rather than mass fractions.

Mean Mixture Fraction, Mixture Fraction Variance   set inlet values for the PDF mixture fraction and its variance. (These items will appear only if you are using the non-premixed or partially premixed combustion model.)

Secondary Mean Mixture Fraction, Secondary Mixture Fraction Variance   set inlet values for the secondary mixture fraction and its variance. (These items will appear only if you are using the non-premixed or partially premixed combustion model with two mixture fractions.)

Species Mass Fractions   contains inputs for the mass fractions of defined species. See Section  15.1.5 for details about these inputs. These items will appear only if you are modeling non-reacting multi-species flow or you are using the finite-rate reaction formulation.

Backflow Progress Variable   sets the value of the progress variable for premixed turbulent combustion. See Section  17.3.3 for details.

This item will appear only if the premixed or partially premixed combustion model is used.

DPM   contains the discrete phase parameters. This tab is available only if you have defined at least one injection.

Discrete Phase BC Type   sets the way that the discrete phase behaves with respect to the boundary. This item appears when one or more injections have been defined.

reflect   rebounds the particle off the boundary with a change in its momentum as defined by the coefficient of restitution. (See Figure  23.4.1.)

trap   terminates the trajectory calculations and records the fate of the particle as "trapped''. In the case of evaporating droplets, their entire mass instantaneously passes into the vapor phase and enters the cell adjacent to the boundary. See Figure  23.4.2.

escape   reports the particle as having "escaped'' when it encounters the boundary. Trajectory calculations are terminated. See Figure  23.4.3.

wall-jet   indicates that the direction and velocity of the droplet particles are given by the resulting momentum flux, which is a function of the impingement angle. See Figure  15.6.1TH-dpm-disp-bound-walljet in the separate Theory Guide.

wall-film   consists of four regimes: stick, rebound, spread, and splash, which are based on the impact energy and wall temperature. Detailed information on the wall-film model can be found in this section in the separate Theory Guide. The Number Of Splashed Drops must be specified.

user-defined   specifies a user-defined function to define the discrete phase boundary condition type.

Discrete Phase BC Function   sets the user-defined function from the drop-down list.

Multiphase   contains the multiphase parameters.

Backflow Granular Temperature   specifies temperature for the solids phase and is proportional to the kinetic energy of the random motion of the particles.

Backflow Volume Fraction   specifies the volume fraction of the secondary phase selected in the Boundary Conditions task page. This section of the dialog box will appear when one of the multiphase models is being used. See Section  24.2.9 for details.

UDS   contains the UDS parameters.

User-Defined Scalar Boundary Condition   appears only if user defines scalars are specified.

User Scalar-n   specifies the whether the scalar is a specified flux or a specified value.

User-Defined Scalar Boundary Value   appears only if user defines scalars are specified.

User Scalar-n   specifies the value of the scalar.