måndag 27 februari 2012

Conductivity and diffusivity

It appears as if I have in some previous posts confused myself, and possibly some others, by not making an appropriate distinction between heat conductivity k and diffusivity D. According to Fourier's law, under stationary conditions the heat flux F is given by

F = -k*dT/dx.

The diffusivity D is proportional to k but also inversely proportional to the density. In particular this means that my attemps to motivate the existence of a stratosphere through a reduction in air density does not follow directly from the heat equation. (A note of caution is perhaps appropriate here, since I think that the heat equation was first formulated for solids and not gases). However, I think that the overall "thickness" of the atmosphere must come into play somehow. How to motivate this seems to be an open question and what is perhaps lacking is an adequate theory for heat conduction in the atmosphere.

This article could perhaps provide some information though.

Inga kommentarer:

Skicka en kommentar