The Moisture Flow, Laminar Flow and Turbulent Flow Multiphysics Interfaces
The Moisture Flow interfaces model moisture transport in air by vapor diffusion and convection.
When a Moisture Flow () multiphysics interface is added from the Chemical Species Transport>Moisture Flow branch  of the Model Wizard or Add Physics windows, one of the Single-Phase Flow interfaces (laminar or turbulent flow) and a Moisture Transport in air interface are added to the Model Builder.
In addition, the Multiphysics node is added, which includes the Moisture Flow multiphysics coupling feature.
The Multiphysics Branch in the COMSOL Multiphysics Reference Manual.
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The Laminar Flow interface () combines a Moisture Transport in Air interface with a Laminar Flow interface.
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The Turbulent Flow, Algebraic yPlus interface () combines a Moisture Transport in Air interface with a Turbulent Flow, Algebraic yPlus interface.
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The Turbulent Flow, L-VEL interface () combines a Moisture Transport in Air interface with a Turbulent Flow, L-VEL interface.
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The Turbulent Flow, k-ε interface () combines a Moisture Transport in Air interface with a Turbulent Flow, k-ε interface.
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The Turbulent Flow, k-ω interface () combines a Moisture Transport in Air interface with a Turbulent Flow, k-ω interface.
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The Turbulent Flow, Low Re k-ε interface () combines a Moisture Transport in Air interface with a Turbulent Flow, Low Re k-ε interface.
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The Turbulent Flow, SST interface () combines a Moisture Transport in Air interface with a Turbulent Flow, SST interface.
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The Turbulent Flow, Spalart-Allmaras interface () combines a Moisture Transport in Air interface with a Turbulent Flow, Spalart-Allmaras interface.
Stationary and time-domain modeling are supported in all space dimensions.
Settings for the Physics Interfaces and Coupling Features
When physics interfaces are added using the predefined couplings, specific settings are included with the physics interfaces and the coupling feature.
Table 8-9: Modified Settings for the Moisture Flow interfaces
Physics or Coupling Interface
Modified Settings (if Any)
Moisture Transport in Air
In the Model Input section of the Moist Air default domain feature, the Absolute pressure, pA, and the Velocity field, u, are automatically set to the variables from the Moisture Flow multiphysics coupling feature.
Laminar Flow / Turbulent Flow
In the Fluid Properties default domain feature, the Density, ρ, and the Dynamic viscosity, μ, are automatically set to the variables from the Moisture Flow multiphysics coupling feature. In addition, the Use pseudo time stepping for stationary equation form check box is automatically selected under the Advanced Settings section.
Moisture Flow
The Fluid flow and Moisture Transport interfaces are preselected
Note that these settings may be overridden if another predefined coupling is added.
On the Constituent Physics Interfaces
The Moisture Transport in Air interface provides features for modeling moisture transfer by vapor convection and diffusion. A Moist Air model is active by default on all domains.
The Laminar Flow interface solves the Navier-Stokes equations for conservation of momentum and the continuity equation for conservation of mass. A Fluid model is active by default on all domains.
The different versions of the Turbulent Flow interface solve the Reynolds averaged Navier-Stokes equations for conservation of momentum and the continuity equation for conservation of mass. A Fluid Properties model is active by default on all domains. Turbulence effects are modeled in different ways:
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The Turbulent Flow, Algebraic yPlus interface uses an enhanced viscosity model based on the local wall distance. The physics interface therefore includes a wall distance equation.
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The Turbulent Flow, L-VEL interface uses an enhanced viscosity model based on the local wall distance. The physics interface therefore includes a wall distance equation.
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The Turbulent Flow, k-ε interface uses the standard two-equation k-ε model with realizability constraints. Flow close to walls is modeled using wall functions.
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The Turbulent Flow, k-ω interface uses the Wilcox revised two-equation k-ω model with realizability constraints. Flow close to walls is modeled using wall functions.
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The Turbulent Flow, Low Re k-ε interface uses the AKN two-equation k-ε model with realizability constraints. The AKN model is a so-called low-Reynolds number model, which means that it resolves the flow all the way down to the wall. The AKN model depends on the distance to the closest wall. The physics interface therefore includes a wall distance equation.
As an add-on Multiphysics Coupling
The Moisture Flow multiphysics coupling is also available when there is at least one of each of the following interfaces with the specified model activated:
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A Laminar Flow or any version of the Turbulent Flow interface, with Fluid model
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Any version of the Moisture Transport interface, with Moist Air model