Define mass flux and molar flux

Flux

The mass transfer flux of a given species is defined as the amount of that species in either mass or molar units which crosses a unit area in unit time.

Mass flux

The mass flux of species ' i ' is defined as the mass of species ' i ' that passes through a unit area per unit time.

• It denoted by a small letter
• n_i = mass flux with respect to a stationary/fixed observer

n_i = ρ_i (u_i-0) =ρ_i u_i                Kg / m².s

• 0 represent observer is stationary
• j_i = mass flux with respect to an observer moving with the mass average velocity u

j_i = ρ_i (u_i-u)                Kg / m².s

Molar flux

The molar flux of species ' i ' is defined as the moles of species ' i ' that passes through a unit area per unit time.

• It denoted by a capital letter
• N_i = mass flux with respect to a stationary/fixed observer

N_i = C_i (u_i-0) =C_i u_i                Kg / m².s

• 0 represent observer is stationary
• J_i = mass flux with respect to an observer moving with the molar average velocity U

J_i = C_i (u_i-U)                Kg / m².s