The Penman-Millington-Quirk (PMQ) Vapour diffusion model.

The vapour diffusion can be described by [28], [29],

$D_v=D_0 \left(\frac{T}{273.15}\right)^{n} D_{vr},$

where $D_{0}$ is the base diffusion coefficient with default value $2.16\cdot 10^{-5}$ ${\text m}^2 \text{Pa}/(\text{s}\text{K}^{n})$ , $n$ is the exponent with default value 1.8, $D_{vr}$ is the the relative diffusion coefficient, and $T$ is the temperature.

The Penman–Millington–Quirk (PMQ) model [28] is given as

$D_{vr}=0.66 \phi \left(\frac{\kappa}{\phi}\right)^{\frac{12-m}{3}},$

where $\phi$ is the total porosity, $\kappa$ is the air filled porosity, and $m$ is a fitting parameter. The air filled porosity is defined as $\kappa = \phi-\theta = \phi -S_L \phi$ with $\theta$ the liquid content, and $S_L$ the liquid saturation.

According to the study presented in [28], $m=6$ is the best fitting parameter for the sieved, repacked soils that the authors tested. Therefore, $m=6$ is used in the implementation, which gives

$D_{vr}=0.66 \phi (1 - S_L )^2.$

Note: In order to maintain consistency with the implementation of the computations of other vapor-related parameters, $\phi (1 - S_L )$ is removed from the implementation for this class and is multiplied back in the local assembler.

Child parameters, attributes and cases

Additional info

Used in the following test data files