[sayan_bose]

Fluent solves the convective term of species transport equation as

∂(F_i φ_k )/(∂x_i )

where φ is the kth scalar, x_i is the space coordinate, and F_i is the user defined mass flux which is calculated as

F=area intg of(rhoV.dA) rho=density, v=vel vec, dA= area vector

the F or the mass flux that it calculates is the mass flux of what, the scalr phi or the fluid.
thanks in advance