Moisture Flux
Use this node to add moisture flux across exterior boundaries, with the option to account for latent heat source due to evaporation. A positive moisture flux adds moisture to the domain.
Moisture Flux
Click to select the General moisture flux (the default), Convective moisture flux, concentrations difference, or Convective moisture flux, pressures difference button.
General Moisture Flux
It adds g0 to the total flux across the selected boundaries. Enter a positive value for g0 to represent a moisture flux that enters the domain.
Convective Moisture Flux, Concentrations Difference
Several options are available to specify the Moisture transfer coefficient hm.
•
The default option is to enter a User defined value for hm.
•
With the From heat and moisture transport analogy option, the heat transfer coefficient h to be multiplied by the analogy factor to obtain the moisture transfer coefficient hm should be specified. It can be User defined (in this case the Absolute pressure, pA, the External temperature, Text, and the External relative humidity, should be specified) or selected from a list of heat transfer coefficients defined in Heat Flux features applied on the same boundary (in this case the external conditions defined in the corresponding Heat Flux feature are used).
•
For the External natural convection, Internal natural convection, External forced convection, and Internal forced convection options, the geometry and velocity parameters used in the correlation are the same as for the Heat Flux feature. Then the external conditions should be specified. First, set the Absolute pressure, pA. For User Defined, enter a value or expression. Else, select an Ambient absolute pressure defined in an Ambient Properties node under Definitions. In addition, enter an External temperature, Text. For User defined, enter a value or expression. Else, select an Ambient temperature defined in an Ambient Properties node under Definitions. Finally, set the External relative humidity, . Note that the relative humidity at the boundary is provided by the physics interface.
For all options except User defined, select the Specify the exponent in the analogy factor check box to set the variable n in Equation 4-174.
Convective Moisture Flux, Pressures Difference
Enter a value for the Moisture transfer coefficient βp. In addition, two options are available to specify the external conditions:
•
If Relative humidity is selected (the default), set the External relative humidity, and the External temperature, Text (used for the computation of the vapor saturation pressure). For User defined, enter values or expressions. Else, select an Ambient relative humidity and an Ambient temperature defined in an Ambient Properties node under Definitions. Convective moisture flux is defined by g0 = βp(psat(Text) − psat(T)).
•
If Partial vapor pressure is selected, enter an External partial vapor pressure, pv,ext. Convective moisture flux is defined by g0 = βp(pv,ext − psat(T)).
Evaporation
Select the Contributes to evaporation flux check box to define the moisture flux as an evaporation flux, and to contribute to the total latent heat source mt.q_evaptot.
Condensation Risk in a Wood-Frame Wall: Application Library path Heat_Transfer_Module/Buildings_and_Constructions/wood_frame_wall
Location in User Interface
Context Menus
Moisture Transport in Air>Moisture Flux
Moisture Transport in Building Materials>Moisture Flux
Ribbon
Physics Tab with interface as Moisture Transport in Air or Moisture Transport in Building Materials selected:
Boundaries>Moisture Flux