Moist Air

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 6-3, 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 Inputs

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.

Absolute Pressure

The default pA is . 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.

Velocity Field

The defaultu 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).

Concentration

From the c (SI unit: mol/m3 or kg/m3) list, select an existing concentration variable from another physics interface, if any concentration variables exist, or select to enter a value or expression for the concentration. This section can be edited anytime a material property is concentration dependent; for example, when the is set to .

Thermodynamics, Fluid

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

•

ω to define the ratio of the vapor mass to the total mass.

•

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 of the water vapor mass to the dry air mass.

•

φref (the default), a quantity defined between 0 and 1, where 0 corresponds to dry air and 1 to a water vapor-saturated air. The and must be specified.

Depending on the selected , enter values or expressions for the option, select an ambient value (for example, an defined in the Ambient Settings section of a Heat Transfer or Heat Transfer in Shells interface), or select a value from a Moisture Transport interface.

Equivalent Conductivity for Convection

When the check box is selected, the fluid thermal conductivity is increased according to the Nusselt number to account for the contribution of the convective heat flux. In addition the user-defined or predefined velocity model input is ignored and the fluid velocity is set to zero. This check box is not selected by default and requires the Heat Transfer Module. See Equivalent Conductivity for Convection in Fluid node for details.


	Moist Air Fluid Type Theory for Heat Transfer in Fluids Equivalent Thermal Conductivity Correlations


	With certain COMSOL products, the Viscous Dissipation (for heat generated by viscous friction) and Pressure Work 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 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 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

Ribbon

Physics Tab with or selected: