OGS
[case] WaterVapourDensity

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

$h=\exp({\frac{p}{\rho_w R T}}),$

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.

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