NAME
MassDiffusivity
SYNOPSIS
MassDiffusivity(real(in) :: xtemp, real(in) :: xden, real(in) :: massfrac, real(out) :: diffusivity)
DESCRIPTION
A generic mass diffusivity routine. Just returns a constant diffusivity from the run-time parameter, 'diff_spec_D'
ARGUMENTS
xtemp : temperature (in K) xden : density (in g/cm**3) massfrac : mass fractions of the composition diffusivity : mass diffusivity