Stripping Model Reference

Stripping Model Properties

Stripping Option

Specifies the stripping models to activate:

Method	Corresponding Method Nodes
Edge Stripping	Edge Stripping See Edge Stripping Model Properties.
Wave Stripping	Wave Stripping See Wave Stripping Model Properties.
Edge and Wave Stripping	Edge Stripping Wave Stripping See Edge Stripping Model Properties and Wave Stripping Model Properties.

Stripping Source Smoothing Sweeps

Applies to Eulerian Multiphase (EMP) simulations only.

If the size of the liquid film is thicker than the size of the cell next to the wall, the mass stripped from the film can completely fill the adjacent cell. This is a potential cause of instability. Stripping Source Smoothing Sweeps are used to spread the source over the neighboring cells to mitigate these instabilities. The value of sweeps is an indicator of the area over which the mass is distributed.

A smoothing sweep of 0 indicates that the total mass from the stripping will be added to the cell where the stripping occurs. A sweep value of n would indicate that the source will be spread over n layers of neighboring cells. The default value for this property is 2, and only positive values are acceptable. The total sum of the smoothed source will be equal to the original mass.

Friction Velocity Scaling Factor

The constant that empirically relates the shear velocity to the free stream velocity ( $K_{\text{*},\infty }$ in Eqn. (2756)). The default setting is 10.0.

This property applies to Eulerian Multiphase (EMP) only. For Lagrangian Multiphase, Mixture Multiphase (MMP), and Dispersed Multiphase (DMP) wave stripping, the Gas Velocity Scaling Factor property is used instead.

Edge Stripping Model Properties

In Dispersed Multiphase edge stripping, the droplet diameter is specified in the dispersed phase rather than being calculated. The properties that relate to droplet size calculations apply to Lagrangian Multiphase edge stripping only.

Minimum Corner Angle

Defines the minimum sharp edge angle to which the edge film stripping model is applied. This angle allows you to define which edges cause stripping, and which edges are due to mesh discretization.

This property applies to Eulerian Multiphase (EMP), Lagrangian Multiphase, Mixture Multiphase (MMP), and Dispersed Multiphase (DMP) edge stripping.

q

A shape factor that is used in the Rosin-Rammler droplet size distribution (see Eqn. (2767)). Reducing the value of q generates statistically smaller droplets.

This property applies to Lagrangian Multiphase edge stripping only.

Critical FR

The force ratio $FR$ that must be exceeded to initiate edge stripping. This value is essentially the ratio of the film momentum flux to the surface tension and gravity force and is used in Eqn. (2757) and Eqn. (2763). Reducing the critical force ratio increases the occurrence of edge stripping.

This property applies to Lagrangian Multiphase, Mixture Multiphase (MMP), and Dispersed Multiphase (DMP) edge stripping.

c1

The droplet diameter scale factor, which is used to scale the parent droplet size (see Eqn. (2764)). Reducing this value reduces the droplet size.

This property applies to Lagrangian Multiphase edge stripping only.

Limit Parent Droplet Diameter

Specifies whether the maximum parent droplet diameter is limited.

This property applies to Lagrangian Multiphase edge stripping only.

Maximum Diameter

Sets the maximum parent droplet diameter. This limit is only applied if the Limit parent droplet diameter property is activated.

This property applies to Lagrangian Multiphase edge stripping only.

Randomized Droplet Diameter

Specifies whether the droplet diameter is calculated or randomized. Randomized droplet diameters use the Rosin-Rammler size distribution (see Eqn. (2767)). Calculated droplet diameters are the average of the size distribution (see Eqn. (2769)).

This property applies to Lagrangian Multiphase edge stripping only.

Wave Stripping Model Properties

The Wave Stripping model assumes that sinusoidal perturbations disturb the flat film surface, and that the most unstable wavelength grows linearly. In some cases, these assumptions are not satisfied: for example, when a film drips from underneath a horizontal surface or ceiling.

Consider the following example: a case with a “hanging film” building up on a ceiling. One would intuitively expect the stripping speed to increase as the film grows thicker, eventually reaching some equilibrium thickness.

To obtain correct results, you can tune the model with a validation study. You can set the following parameters:

• $c_H$ to control the thickness threshold at which stripping occurs
• $c_D$ to control the size of the droplets that result from stripping
• $c_B$ to control the rate at which film mass is stripped

cH

The coefficient ( $c_H$ in Eqn. (2750)) for minimum film thickness to initiate stripping. The default setting is 1.0. Lowering this value makes wave stripping occur at a lower film thickness threshold.

This property applies to Lagrangian Multiphase, Mixture Multiphase (MMP), and Dispersed Multiphase (DMP) wave stripping only.

cD

The droplet diameter coefficient ( $c_D$ in Eqn. (2752)). The default setting is 3.78. Increasing this number leads to bigger particles (but the total amount of mass that is stripped remains the same).

This property applies to Eulerian Multiphase (EMP) and Lagrangian Multiphase wave stripping only. In Dispersed Multiphase (DMP) wave stripping, the droplet diameter is specified in the dispersed phase rather than being calculated.

cB

The breakup rate scaling coefficient ( $c_B$ in Eqn. (2754)). The default setting is 1.0. Increasing this number increases the rate of wave stripping (more particles per time-step).

This property applies to Eulerian Multiphase (EMP), Lagrangian Multiphase, Mixture Multiphase (MMP), and Dispersed Multiphase (DMP) wave stripping.

Gas Velocity Scaling Factor

The constant that empirically relates the shear velocity to the free stream velocity ( $K_{\text{*},\infty }$ in Eqn. (2756)). The default setting is 10.0.

This property applies to Lagrangian Multiphase, Mixture Multiphase (MMP), and Dispersed Multiphase (DMP) wave stripping only. For Eulerian Multiphase (EMP) wave stripping, the Friction Velocity Scaling Factor reference value is used instead.

Minimum Particle Diameter

Sets the minimum allowed particle diameter for wave stripping in simulations with Film-Lagrangian phase interactions. The minimum particle diameter $D_{\min }$ is used to compute the resonance wavelength as ${\lambda }_{\min }=\frac{D_{\min }}{c_D\frac{3}{4}{\left(\frac{1}{1.89}\right)}^3}$ .

Particles with a smaller diameter than $D_{\min }$ are prevented from stripping away from the fluid film phase and wave stripping will be deactivated for those particles.

You can define the Minimum Particle Diameter through a constant scalar profile (default value of 1E-8m) or by using a scalar field function.

Film Stripping Field Functions

Available when edge stripping is activated in a Film-EMP phase interaction:

Film-EMP Edge Stripping Continuity Source of [Phase Interaction]

The rate that mass is extracted from the film, in kg/s.

Film-EMP Edge Stripping Momentum Source of [Phase Interaction]

The force, in Newtons, corresponding to the mass extraction rate (above) that is calculated by the Edge Stripping model.

Available when wave stripping is activated in a Film-EMP phase interaction.

Film-EMP Wave Stripping Continuity Source of [Phase Interaction]

The rate that mass is extracted from the film, in kg/s.

Film-EMP Wave Stripping Momentum Source of [Phase Interaction]

The force, in Newtons, corresponding to the mass extraction rate (above) that is calculated by the Wave Stripping model.

Available when edge stripping is activated in a Film-MMP phase interaction:

Film-MMP Edge Stripping Continuity Source of [Phase Interaction]

The rate that mass is extracted from the film, in kg/s.

Available when wave stripping is activated in a Film-MMP phase interaction:

Film-MMP Wave Stripping Continuity Source of [Phase Interaction]

The rate that mass is extracted from the film, in kg/s.

The following field functions are made available when the Temporary Storage Retained expert property of the Fluid Film Segregated Flow solver is activated. They allow you to see whether any stripping occurs and how fast.

Film Wave Stripping Minimum Thickness

The minimum thickness that allows stripping, $h_{\text{min}}$ in Eqn. (2750).

Film Wave Stripping Time Scale

The time scale ( $t_b$ in Eqn. (2753)) of wave stripping, where the film thickness exceeds $h_{\text{min}}$ .

Available when the Temporary Storage Retained expert property of the Segregated Energy solver is activated for Film-MMP or Film-EMP phase interactions. These field functions allow you to see stripping energy transfer rates.

Film Edge Stripping Energy Transfer Rate of [Phase Interaction]

The power transferred between the film and the dispersed liquid, in kg W, corresponding to the mass extraction rate that is calculated by multiplying the edge stripping continuity source with the fluid film enthalpy.

Film Wave Stripping Energy Transfer Rate of [Phase Interaction]

The power transferred between the film and the dispersed liquid, in kg W, corresponding to the mass extraction rate that is calculated by multiplying the wave stripping continuity source with the fluid film enthalpy.