A model for water vapour density in the unsaturated porous media.

The water vapour density is given by

\[ \rho_v = h\, \rho_{vS}, \]

where \(h\) is the relative humidity according to

\[ h=\exp \left({\frac{p}{\rho_w R T}}\right), \]

with \(R\) the specific gas constant for water vapour, and \(\rho_{vS}\), is the saturated vapour density given by

\[ \rho_{vS}=10^{-3}\, \exp({19.819-4975.9/T}). \]

The specific gas constant for water vapour \(R=461.6\,\text{J}\,\text{kg}^{-1}\text{K}^{-1}\), the value is calculated by \(R_g/M_w\) with \(R_g= 8.3144621\,\text{J}\,\text{mol}^{-1}\text{K}^{-1}\), the ideal gas constant, and \(M_w=0.018016\,\text{kg}\,\text{mol}^{-1}\), the molar mass of water.

The formula of this density model is presented on page 20 of [21].

In the application, the vapour density related terms in the mass balance equation are multiplied with \(1-S\) with \( S \), the water saturation. Therefore the application of the water vapour density model is naturally restricted in the unsaturated zones.

Note: The temperature must be greater then the freezing temperature. In the paper the offset is 273K, not 273.15 which might cause small inconsistencies.

It belongs to vapour_density. That means the name of this property is vapour_density. Besides, it has no parameter to be input.

Child parameters, attributes and cases

Additional info

Used in the following test data files