Moist Air (HT Interface)
This node should be used to model heat transfer by convection and diffusion in moist air, by using moisture-dependent thermodynamics properties. It solves Equation 6-4, with the density ρ (SI unit: kg/m3), the heat capacity at constant pressure Cp (SI unit: J/(kg·K)), and the thermal conductivity k (SI unit: W/(m·K)) defined as a function of the quantity of vapor in the moist air.
Model Input
This section has fields and values that are inputs to expressions that define material properties. If such user-defined property groups are added, the model inputs appear here.
Temperature
This section is available when temperature-dependent material properties are used. By default the temperature of the parent interface is used and the section is not editable. To edit the Temperature field, click Make All Model Inputs Editable (). The available options are User defined (default), Common model input (the minput.T variable, set to 293.15 [K] by default) and all temperature variables from the physics interfaces included in the model. To edit the minput.T variable, click the Go to Source button (), and in the Common Model Inputs node under Global Definitions, set a value for the Temperature in the Expression for remaining selection section.
Absolute Pressure
The absolute pressure is used in some predefined quantities that include the enthalpy (the energy flux, for example).
It is also used if the ideal gas law is applied. See Thermodynamics, Fluid.
The default Absolute pressure pA is User defined. When additional physics interfaces are added to the model, the absolute pressure variables defined by these physics interfaces can also be selected from the list. For example, if a Laminar Flow interface is added you can select Absolute pressure (spf) from the list. The Common model input option corresponds to the minput.pA variable, set to 1 [atm] by default. To edit it, click the Go to Source button (), and in the Common Model Inputs node under Global Definitions, set a value for the Pressure in the Expression for remaining selection section.
Velocity Field
The default Velocity field u is User defined. For User defined enter values or expressions for the components based on space dimensions. Or select an existing velocity field in the component (for example, Velocity field (spf) from a Laminar Flow interface). The Common model input option corresponds to the minput.u variable. To edit it, click the Go to Source button (), and in the Common Model Inputs node under Global Definitions, set values for the Velocity components in the Expression for remaining selection section.
Concentration
This section can be edited anytime a material property is concentration dependent; for example, when the Fluid type is set to Moist air with Input quantity set to Concentration.
From the Concentration c (SI unit: mol/m3 or kg/m3) list, select an existing concentration variable from another physics interface, if any concentration variables exist, User defined to enter a value or expression for the concentration, or Common model input which corresponds to the minput.c variable.
Thermodynamics, Fluid
The available Input quantity options to define the amount of vapor in the moist air are the following:
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Vapor mass fraction ω to define the ratio of the vapor mass to the total mass.
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Concentration to define the amount of water vapor in the total volume. If selected, a Concentration model input is added in the Model Inputs section.
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Moisture content xvap, also called mixing ratio or humidity ratio, to define the ratio of the water vapor mass to the dry air mass.
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Relative humidity (the default), a quantity defined between 0 and 1, where 0 corresponds to dry air and 1 to a water vapor-saturated air. The Relative humidity, temperature condition and Relative humidity, absolute pressure condition must be specified.
Depending on the selected Input quantity, enter values or expressions for the User defined option, select an ambient value (for example, an Ambient relative humidity defined in an Ambient Thermal Properties node under Definitions), or select a value from a Moisture Transport interface.
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Moist Air Fluid Type
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Theory for Heat Transfer in Fluids
With certain COMSOL products, the Viscous Dissipation (for heat generated by viscous friction), Pressure Work, and Convectively Enhanced Conductivity subnodes are available from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu.
When Surface-to-surface radiation is activated, the Opacity (Surface-to-Surface Radiation interface) subnode is automatically added to the entire selection, with Transparent option selected. The domain selection can’t be edited. To set some part of the domain as opaque, add a new Opacity (Surface-to-Surface Radiation interface) subnode from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu.
Evaporative Cooling of Water: Application Library path Heat_Transfer_Module/Phase_Change/evaporative_cooling
For a detailed overview of the functionality available in each product, visit http://www.comsol.com/products/specifications/
Location in User Interface
Context menus
 Heat Transfer in Moist Air>Moist Air
Heat Transfer in Building Materials>Moist Air
Ribbon
Physics Tab with Heat Transfer in Moist Air or Heat Transfer in Building Materials selected:
Domains>Moist Air