COMSOL 6.2 - 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.

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.

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 field, click (

). The available options are (default), (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 button (

), and in the node under , set a value for the in the section.

Absolute pressure is used in certain predefined quantities that include enthalpy (the energy flux, for example).

The default pA is taken from . It corresponds to the minput.pA variable, set to 1 atm by default. To edit it, click the button (

), and in the node under , set a value for the in the 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 interface is added you can select from the list. The last option is .

This section can be edited whenever a material property is dependent on concentration, for example, when the is set to with the set to .

In the c (SI unit: mol/m3 or kg/m3) list, select an existing concentration variable from another physics interface, if there are concentration variables, to enter a value or expression for the concentration, or that corresponds to the minput.c variable.

The default u is . For enter values or expressions for the components based on space dimensions. Or select an existing velocity field in the component (for example, from a interface). The option corresponds to the minput.u variable. To edit it, click the button (

), and in the node under , set values for the components in the section.

The options available to define the amount of vapor in moist air are as follows:

•

to define the amount of water vapor in the total volume. If selected, a model input is added in the section.

•

xvap, also called mixing ratio or humidity ratio, to define the ratio between water vapor mass and dry air mass.

•

ϕw (default), a quantity defined between 0 and 1, where 0 corresponds to dry air and 1 to air saturated with water vapor. The

and

should be specified.

Depending on the selected , enter values or expressions for the option, select an ambient value (for example, an defined in an node under ), or select a value from a Moisture Transport interface.

	Theory for Heat Transfer in Moist Air

	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

	For a detailed overview of the functionality available in each product, visit https://www.comsol.com/products/specifications/

Physics tab with , , , , , or selected: