DIFFUSION_COEFFICIENTΒΆ

The phase molecular diffusion coefficients may be entered in the GAS_WATER mode. These are entered in FLUID_PROPERTY blocks. See example:

FLUID_PROPERTY
  PHASE LIQUID
  DIFFUSION_COEFFICIENT 2.0d-9
/
FLUID_PROPERTY
  PHASE GAS
  GAS_DIFFUSION_COEFFICIENT 2.0d-5
/

The diffusion coefficients are entered in m2/sec.

If not entered, the diffusion coefficients default to the following values:
  • liq_diff_coeff = \(1.0 \times 10^{-9} m^2 /\mbox{sec}\)

  • gas_diff_coeff = \(2.13 \times 10^{-5} m^2 / \mbox{sec}\)

Internally the simulator uses the liquid molecular diffusion as entered by the user, while it modifies the gas molecular diffusion with corrections that accounts for pressure and temperature:

\[D_{\mbox{gas}} = \mbox{gas_diff_coeff} \frac{101235}{P} \left[ \frac{T+273.15}{273.15} \right]^{1.8}\]

Note that the pressure and temperature in the equation above are in Pascal and degree Celsius.