A

half the thickness of the liquid (volume per unit area) in case of finite volume of liquid

a

length of the edge of a cube, considered as a model for the volume/area ratio

?

ratio of the volumes of the liquid and of the sheet, per unit area, in Equation (4.14)

? _n

positive roots of the Equation (4.22). Table is given in the Appendix

C _x,t, C _L,t

concentration of diffusing substance at position x, on the side at position L, at time t, respectively

C _in, C _?, C _eq

concentration of diffusing substance, initially, and after infinite time, respectively, and at equilibrium with that in the surrounding, liquid or gas

CGS

Centimetre, gram, second system of physical units

D

diffusivity (coefficient of diffusion) expressed in: cm ²/s, square length/unit time

F _x,t

flux of matter at position x and time t (mass per unit area and per unit time)

h

coefficient of convection expressed in cm/s

K

partition factor shown in Equation (4.15), dimensionless number

L

half the thickness of the sheet (of thickness 2L); thickness of the package

M _t, M _?

amount of matter transferred by diffusion after time t, infinite time, respectively

n

integer

PET

polyethylene terephthalate

PVC

polyvinyl chloride

q _n

non-zero positive roots of Equation (4.13)

S

area of the sheet in contact with the liquid

x, t

coordinate along which the diffusion occurs, and time, respectively

D t/L ²

dimensionless number, expressing time

h L/D

dimensionless...