A Area

C Concentration

C* Concentration at equilibrium with the bulk partial pressure

C Average concentration

D Diffusivity

H Henry's constant j Diffusion rate k Film coefficient

K Overall mass transfer coefficient

I Length of a solid cylinder

L Time lag for unsteady-state mass transfer

M Molecular weight n Mole number

N Mass flux per unit area

N Total mass flux

P Pressure

P* Pressure at equilibrium with the bulk concentration

Q Total amount of substance being diffused in time t r Radius r Mean capillary radius

R Gas constant

S Solubility t Time

T Temperature v Velocity

V Volume

X Molecular fraction y Small distance of transfer

Y Total distance of transfer


0 Properties at initial time

1,2 Properties at positions 1 and 2, respectively

A Properties of matter A

AB Properties of A when transferred through B

Ai Properties of A at the boundary layer b Properties of bulk, or when binding effect is present

B Properties of matter B

BA Properties of B when transferred through A

d Properties due to diffusion e Properties at equilibrium g Properties in the gas phase

1 Properties at the interface

I Properties in the liquid phase m Arithmetic mean value

/nln Logarithmic mean value p Properties of protein t Properties at time t



Diffusivity reduction factor


Diffusion cell constant




Porous fraction of solid or membrane

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