a0	Superficial area	m−1
Ap	Total area of particles	m²
c	Extract concentration on fluid phase	kg·m−3
D	Diffusivity of the solute inside the particle	m2·s −1
Di	Internal diffusion coefficient	m²·s−1
e	Extract mass in regard to N	-
G	Particle size	mesh
h	Bed height	m
h	Axial coordinate	m
J	Mass transfer rate	kg·s−1·m−3
K	Inaccessible solute mass inside the solid particles	kg
K	Equilibrium coefficient	m3·kg−1
kf	Mass transfer coefficient for fluid phase	m·s−1
ks	Mass transfer coefficient for solid phase	m·s−1
kTM	Internal mass transfer coefficient	m·s−1
l	Characteristic dimension	m
Mt	Mass extracted at a given time	g
M ∞	Mass extracted in an infinite time	g
N	Solid phase mass free from solute	kg
n	Number of the series expansion	-
O	Initial solute mass in solid phase	kg
P	Easily accessible solute mass	kg
P	Pressure	bar
p	Descriptive p-value level	-
Q	Solvent flow rate	g·s−1
q	Specific quantity of solvent	-
q	Extract fraction in solid phase	kg·kg−1
qm	Specific amount of solvent at the beginning of extraction in the interior of particles	-
qn	Specific amount of solvent at the end of the extraction of easily accessible solute	-
q0	Initial concentration of extract in solid phase	kg·kg−1
q*	Concentration in the solid–fluid interface	kg·kg−1
$\dot{q}$	Solvent mass flow in regard to N	s−1
r	Particle radius	m
T	Temperature	°C
t	Extraction time	s
ti	Time for internal diffusion	s
u	Solvent superficial velocity	m·s−1
V	Extractor volume	m³
x	Fraction of solute in the solid phase (solute free basis)
x 0	Initial concentration of free solute in the solid phase (mass fraction)
xk	Initial extract concentration inside the solid particles (mass fraction)
xp	Easily accessible solute concentration (mass fraction)
y	Solute fraction in fluid phase (free basis)
yr	Extract solubility on solvent
W	Sovová model parameter for the slow extraction period
Z	Sovová model parameter for the rapid extraction period
zw	Boundary coordinate between fast and slow extraction
Greek Letters
$\epsilon$	Porosity	-
μ	Constant related to the particle geometry	-
ρ	Solvent density	kg·m−3
ρs	Solid phase density	kg·m−3