pyrcel.thermo.dv

pyrcel.thermo.dv(T, r, P, accom=1.0)

Diffusivity of water vapor in air, modified for non-continuum effects.

The diffusivity of water vapor in air as a function of temperature and pressure is given by

\[\begin{equation} D_v = 10^{-4}\frac{0.211}{P}\left(\frac{T}{273}\right)^{1.94} \tag{SP2006, 17.61} \end{equation}\]

where \(P\) is in atm [SP2006]. Aerosols much smaller than the mean free path of the air surrounding them (\(K_n >> 1\)) perturb the flow around them moreso than larger particles, which affects this value. We account for corrections to \(D_v\) in the non-continuum regime via the parameterization

\[\begin{equation} D'_v = \frac{D_v}{1+ \frac{D_v}{\alpha_c r} \left(\frac{2\pi M_w}{RT}\right)^{1/2}} \tag{SP2006, 17.62} \end{equation}\]

where \(\alpha_c\) is the condensation coefficient (constants.ac).

Parameters:

Tfloat

ambient temperature of air surrounding droplets, K

rfloat

radius of aerosol/droplet, m

Pfloat

ambient pressure of surrounding air, Pa

accomfloat, optional (default=:const:constants.ac)

condensation coefficient

Returns:

float

\(D'_v(T, r, P)\) in m^2/s

See also

dv_cont

neglecting correction for non-continuum effects

References

[SP2006]

Seinfeld, John H, and Spyros N Pandis. Atmospheric Chemistry and Physics: From Air Pollution to Climate Change. Vol. 2nd. Wiley, 2006.