$c_{s,i}$	molar concentration of the s-th solute in the i-th compartment [mol/liter]
$C{l}_s$	Clearance rate of the j-th solute [mL/min]
$D_{e,s}$	Diffusivity of s-th solute in the i-th compartment [m2/s]
$d_i$	diameter of the i-th compartment [mm]
$F$	friction coefficient
$K_s$	overall mass transfer coefficient of s-th solute [m/s]
$k_{s,i}$	mass transfer coefficient of s-th solute in the i-th compartment [m/s]
$k_{s,mj}$	mass transfer coefficient of s-th solute in the j-th membrane layer
$L$	length of the fiber [mm]
N	total number of fibers [-]
NSh,i	Sherwood number in the i-th compartment [-]
NRe,i	Reynold number in the i-th compartment [-]
p	the ratio of solute radius to the pore radius
QB	the blood flow rate in the blood compartment [mL/min]
QD	the dialysate flow rate in the dialysate compartment [mL/min]
$r_1$	the inner radius of the fiber [mm]
$-r_2$	the radius up to the outer layer of the fiber [mm]
$r_3$	the radius of the concentric permeate channel [mm]
SD	steric hindrance factor at pore inlet
ui	axial velocity in the i-th compartment [m/s]
vi	radial velocity in the i-th compartment [m/s]
z	axial co-ordinate [m]
Subscript and superscript
B	blood
D	dialysate
e	effective
i	i-th compartment (B,m,D)
$in$	inlet
j	j-th membrane layer (skin, middle, bulk)
m	membrane
Greek symbols
${\delta }_j$	the thickness of the j-th membrane layer [mm]
${\varepsilon }_{mj}$	membrane j-th layer porosity [-]
${\mu }_i$	fluid viscosity in the i-th compartment [kg/ms]
${\rho }_i$	fluid density in the i-th compartment