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When Capillary model is set to Kelvin’s law (default), a Darcy’s law based on the capillary pressure is used. The capillary pressure is derived from the relative humidity by using Kelvin’s law, using the assumption that the liquid and gas phases are in equilibrium.
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When Capillary model is set to Diffusion, the capillary flux is derived from the gradient of the moisture content, and the Moisture diffusivity Dw.
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For User defined, set a value for the Capillary liquid flux density, glc, to characterize the liquid transport as a function of the moisture content.
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When Capillary model is set to Diffusion (default), the capillary flux is derived from the gradient of the moisture content, and the Moisture diffusivity Dw.
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When Capillary model is set to Pressure, the capillary flux is derived from the gradient of capillary pressure. In turn, the Pressure model gives the expression of the capillary pressure. Details are given below.
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For User defined, set a value for the Capillary liquid flux density, glc, to characterize the liquid transport as a function of the moisture content.
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When Pressure model is set to van Genuchten (default), the capillary pressure is calculated from the Entry capillary pressure pec (SI unit: Pa), for which the default value is 10[kPa], and two constitutive relation constants mvG (dimensionless), for which the default value is 0.3, and lvG (dimensionless), for which the default value is 0.5. This model also gives the value of the relative liquid water permeability κrl (dimensionless) and of the relative moist air permeability κrg (dimensionless). The first one is used to calculate the capillary liquid flux, and the second one is used in the Moisture Flow coupling.
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When Pressure model is set to Brooks and Corey, the capillary pressure is calculated from the Entry capillary pressure pec (SI unit: Pa), for which the default value is 10[kPa], and the pore size distribution index λp (dimensionless), for which the default value is 2. This model also gives the value of the relative liquid water permeability κrl and of the relative moist air permeability κrg. The first one is used to calculate the capillary liquid flux, and the second one is used in the Moisture Flow coupling.
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For User defined, set an expression for the Capillary pressure, pc, to characterize the liquid transport as a function of the liquid saturation. The default expression is 10[kPa]*(1-mt.sl).
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The liquid saturation, sl, is defined from the moisture storage function specified in the Hygroscopic Porous Medium parent node when Equilibrium between liquid and gas phases is set to Equilibrium formulation, and is a dependent variable when it is set to Nonequilibrium formulation.
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The liquid water properties are based on the temperature set in the corresponding model input in the Hygroscopic Porous Medium parent node.
The properties for phase distribution of moisture content in the porous material are specified in the Hygroscopic Porous Medium parent node.
The properties for moist air transport are specified in the Moist Air (Hygroscopic Porous Medium) subnode.
The solid matrix porosity and permeability are specified in the Porous Matrix (Hygroscopic Porous Medium) subnode.
When the parent Hygroscopic Porous Medium node is coupled to a Porous Medium node in a fluid flow interface through the Moisture Flow coupling, the porosity and moist air permeability are automatically shared and corrected for the computation of the Darcy velocity of moist air to account for the presence of liquid water.
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