- What is the equation for mass flux in terms of density and mean velocity?
- Which mean velocity would you use here: mass, mole, or volume?
- What is the equation for mass flux of species $A$?
- What is diffusion velocity, and how is it related to mass flux?
- What is a constraint on (or relation between) diffusion fluxes?
- What is the most physical driving force for diffusion of an ideal gas: mole fraction gradients, mass fraction gradients, or concentration gradients?
- In general, if we have $N$ species, how many species gradients directly affect the diffusion flux of the species?
- Write the formula for Fick’s law in terms of molar flux $J_i$.
- Convert that formula to the equation for mass flux $j_i$.
- What is the simplified form of Fick’s law for $j_i$ that we often use in combustion?