Heat and Moisture
Use this multiphysics coupling () to model coupled heat and moisture transfer in two kinds of media:
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In building materials, by taking into account heat and moisture storage, latent heat effects, and liquid and convective transport of moisture. This coupling is available when a Building Material feature of the Heat Transfer interface and a Building Material feature of the Moisture Transport interface are active on the same domain. It can be applied to the computation of different moisture variations phenomena in building components, such as drying of initial construction moisture, condensation due to migration of moisture from outside to inside in summer, and moisture accumulation by interstitial condensation due to diffusion in the winter. The thermodynamics properties of the building material depend both on the dry solid properties and on the moisture content, and the evaporation of liquid water adds a latent heat source in the diffusion equation for temperature. Reversely, the variations of moisture content due to liquid transport (capillary flow) and vapor diffusion are temperature dependent.
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In moist air, by modeling moisture transport by vapor diffusion and convection, and heat transfer by conduction and convection. The thermodynamics properties of moist air depend on the moisture content, whereas the temperature is used to define the saturation conditions for vapor concentration. This coupling is available when a Fluid or Moist Air feature of the Heat Transfer interface and a Moist Air feature of the Moisture Transport interface are active on the same domain. The Fluid type should be set to Moist air if the Fluid feature is used, to take fully advantage of the coupling.
The Heat and Moisture coupling synchronizes the features from the Heat Transfer and Moisture Transport interfaces:
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It defines the relative humidity (with corresponding reference temperature and pressure) in order to set the corresponding inputs in the Moist Air feature of the Heat Transfer interface.
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It defines the moisture storage function w and the vapor permeability δp (or vapor resistance factor μ) in order to set the corresponding inputs in the Building Material feature of the Heat Transfer interface.
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It defines the temperature T in order to set the model inputs in the features of the Moisture Transport interface.
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It computes the latent heat source due to evaporation and condensation fluxes on surfaces, and adds it in the heat transfer equation.
Settings
The Label is the default multiphysics coupling feature name.
The Name is used primarily as a scope prefix for variables defined by the coupling node. Refer to such variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different coupling nodes or physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first multiphysics coupling feature in the model) is ham1.
Domain Selection
When nodes are added from the context menu, you can select Manual (the default) from the Selection list to choose specific domains to define the domains with heat and moisture transport, or select All domains as needed.
Coupled Interfaces
This section defines the physics involved in the multiphysics coupling.
Select the Heat transfer interface associated to the temperature dependent variable and the Moisture transport interface associated to the relative humidity variable.
You can also select None from either list to uncouple the node from a physics interface. If the physics interface is removed from the Model Builder — for example, Heat Transfer in Building Materials is deleted — then the Heat transfer list defaults to None as there is nothing to couple to.
Latent Heat
The multiphysics coupling adds the following latent heat source qevap on surfaces due to evaporation and condensation:
where gevap is the evaporative flux and Lv is the latent heat of evaporation.
To neglect the latent heat effects in the heat transfer equation, clear the Include latent heat source on surfaces check box.
Evaporative Cooling of Water: Application Library path Heat_Transfer_Module/Phase_Change/evaporative_cooling
Location in User Interface
Context Menus
Multiphysics>Heat and Moisture
when a heat transfer interface with Building Material feature is active together with a moisture transport interface with Building Material feature; or when a heat transfer interface with Fluid or Moist Air feature is active together with a moisture transport interface with Moist Air feature.