### 7.19.1. Algebraic Slip Model Specification

The ASM model is not set up in the same way as other multiphase problems. Only one fluid for a variable composition mixture is used in the Domains tab on CFX-Pre. When setting up a problem to run with the Algebraic Slip Model, you should first create a material for the variable composition mixture. For details, see Material Details View: Variable Composition Mixture in the CFX-Pre User's Guide. When setting the thermodynamic state of the mixture, the choice of liquid or gas is not important. When specifying the domain options, define the fluid in Fluids and Particle Definitions... and select the fluid Material.

#### 7.19.1.1. Fluid Models

The continuous phase should be set to `Constraint` on the Component Details tab. The remaining phases can be set to either `Algebraic Slip` or `Transport Equation`. `Transport Equations` and `Algebraic Slip` components can be combined, meaning that a mixture of components may be present in the continuous phase. At least one component must be set to `Constraint`. For any dispersed phases, choose the `Algebraic Slip` option.

The Algebraic Slip option can be set to `Drag Force Balance` or `Slip Velocity`. Drag Force Balance uses the closed relationship for the slip velocity. For details, see Derivation of the Algebraic Slip Equation in the CFX-Solver Theory Guide.

| (7–25)

where the subscript refers to bulk quantities and refers to dispersed phase quantities. The drag coefficient can be directly specified or the Schiller Naumann model can be used. In both cases, the mean diameter must be specified.

The slip velocity may also be directly specified.

#### 7.19.1.2. Wall Deposition

For wall boundaries, there is the option of specifying wall deposition for a dispersed phase. When deposition is selected for a phase that contacts a wall boundary, the mass of the particular phase is removed from the calculation and replaced with the mass of the ballast phase (the component that was selected as `Constraint` on the Fluid Models tab). The deposition rate is determined from the slip velocity of the algebraic slip component.

#### 7.19.1.3. Limitations

As the model makes a number of assumptions, the model will not produce the best results when:

- Non-drag forces are significant.

- The dispersed phase does not reach terminal velocity quickly (that is, particles with significant mass are present).

  For details, see Derivation of the Algebraic Slip Equation in the CFX-Solver Theory Guide.

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