Moist Air (Heat Transfer Interface)
This node should be used to model heat transfer by convection and diffusion in moist air, using moisture-dependent thermodynamics properties. It solves Equation 6-5, with density ρ (SI unit: kg/m3), heat capacity at constant pressure Cp (SI unit: J/(kg·K)), and thermal conductivity k (SI unit: W/(m·K)) defined as a function of the amount of vapor in moist air.
Model Input
This section contains fields and values that are inputs for expressions defining material properties. If such user-defined property groups are added, the model inputs appear here.
Temperature
This section is available when material properties are temperature-dependent. 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 Default Model Inputs node under Global Definitions, set a value for the Temperature in the Expression for remaining selection section.
Absolute Pressure
Absolute pressure is used in certain predefined quantities that include enthalpy (the energy flux, for example).
The default Absolute pressure pA is taken from Common model input. It corresponds to the minput.pA variable, set to 1 atm by default. To edit it, click the Go to Source button (), and in the Default Model Inputs node under Global Definitions, set a value for the Pressure in the Expression for remaining selection section. 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 last option is User defined.
Concentration
This section can be edited whenever a material property is dependent on concentration, for example, when the Fluid type is set to Moist air with the Input quantity set to Concentration.
In the Concentration c (SI unit: mol/m3 or kg/m3) list, select an existing concentration variable from another physics interface, if there are concentration variables, User defined to enter a value or expression for the concentration, or Common model input that corresponds to the minput.c variable.
Heat Convection
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 Default Model Inputs node under Global Definitions, set values for the Velocity components in the Expression for remaining selection section.
Thermodynamics, Moist Air
The Input quantity options available to define the amount of vapor in moist air are as follows:
Vapor mass fraction ω to define the ratio between vapor mass and total mass.
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.
Moisture content xvap, also called mixing ratio or humidity ratio, to define the ratio between water vapor mass and dry air mass.
Relative humidity ϕw (default), a quantity defined between 0 and 1, where 0 corresponds to dry air and 1 to air saturated with water vapor. The Relative humidity, temperature condition and Relative humidity, absolute pressure condition should 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 Properties node under Definitions), or select a value from a Moisture Transport interface.
With some 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.
Evaporative Cooling of Water: Application Library path Heat_Transfer_Module/Phase_Change/evaporative_cooling
Location in User Interface
Context Menus
Ribbon
Physics tab with Heat Transfer in Solids and Fluids, Heat Transfer in Solids, Heat Transfer in Fluids, Heat Transfer in Porous Media, Heat Transfer in Building Materials, or Bioheat Transfer selected: