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uclchem / UCLCHEM

UCLCHEM - A gas-grain chemical code for Astrochemistry.
MIT License
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Grain variables #6

Closed jonholdship closed 4 years ago

jonholdship commented 4 years ago

The grain surface area per hydrogen atom (GRAIN_AREA=2.4d-22) is precalculated

but we have everything we need to do this consistently by setting average grain radius (GRAIN_RADIUS) and calculating surface area of a dust grain from that. Then dividing byGAS_DUST_DENSITY_RATIO which is 1/n_d (the fractional abunance of dust grains).

Without it, our grain treatment is not entirely consistent.

jonholdship commented 4 years ago

Rawlings et al. 1992 treatment has a numerical factor and grain area per H atom of 2.4d-22. We've replaced the numerical factor with a clearer variable. Grain area has also been reduced by a factor of 0.6. This is the result of assuming spherical grains of 0.1 um rather than original average r^2 from a grain size distribution.

In a way, the area is a worse approximation to true value but it is internally consistent at least.