Symbols used
Aj	Slope term of the Yt function in Model B and C for each particle size quantile j (10, 50, 90), kg0.4/(m2.4s1.8)
Aj*, Aj**	Intermediately derived slope terms of Yt function for each particle size quantile j (10, 50, 90)
a	The average frequency of drug particle compressions, 1/min
API	Active pharmaceutical ingredient
Bj	Intercept term of the Yt function for each particle size quantile j (10, 50, 90)
BI	Brittleness index, m−1/2
BL	Bead loading, % v/v
c	Fractional volumetric bead loading in the drug suspension–beads mixture
C	Rate constant
CPS	Crosslinked polystyrene
D	Diameter, m
e	Restitution coefficient
E	Mill-scale efficiency correction factor
g 0	Radial distribution function at contact
h	Thickness of the powder bed, m
H	Hardness, Pa
k	Apparent breakage rate constant, 1/min
K c	Fracture toughness, Pa.m1/2
Kt	Arrhenius equation for the temperature impact
m	Mass, kg
MHD	Microhydrodynamic model
Nj	Shape factor of the Yt transform for each particle size quantile j (10, 50, 90)
N 1	Exponent for the stirrer speed effect
N 2	Exponent for the bead loading effect
N 3	Exponent for the bead density effect
N 4	Exponent for the bead size effect
N 5	Exponent for the tip diameter effect
N 6	Exponent for the suspension viscosity effect
N 7	Exponent for the suspension density effect
N t	Number of turnovers
P	Power, W
P ax	Axial pressure, Pa
P rad	Radial pressure, Pa
P v	Power density, W/m3
Pe	Peclet number
PR	Poisson ratio
PSD	Particle size distribution
Q	Volumetric flow rate or pumping rate of the suspension, m3/s
R	Radius, m
R diss	Effective drag coefficient
Re	Reynolds number
S	Specific breakage rate, 1/min
t	Milling time, min
T	Temperature, °C
U tip	Tip speed, m/s
V	Volume, mL
xj	Particle size for each particle size quantile j (10, 50, 90), m
YM	Young’s modulus, Pa
Yt	Transform of the dependent variable Y
YSZ	Yttrium-stabilized zirconia
Greek letters
ε	Powder compact out-of-die porosity
ε coll	Energy dissipation rate due to partially inelastic bead–bead collisions, W/m3
ε ht	Power spent on shear of milled suspension of the slurry at the same shear rate but calculated (measured) when no beads were present in the flow, W/m3
ε m	Nondimensional bead–bead gap thickness at which the lubrication force stops increasing and becomes a constant, –
ε visc	Energy dissipation rate due to both the liquid–beads viscous friction and lubrication, W/m3
ε	powder compact out-of-die porosity
γ	Mass concentration, g/mL
λ	Lumped parameters of the microhydrodynamic model
θ	Granular temperature, m2/s2
μ	Viscosity, Pa.s
ρ	Density, kg/m3
σax	Axial stress, Pa
σrad	Radial stress, Pa
τ	Mean residence time for the single pass, min
ω	Rotational speed of the rotor, 1/min
Indices
10	10% passing size of the cumulative PSD
50	Median particle size of the cumulative PSD
90	90% passing size of the cumulative PSD
a	agitator
batch	Batch
b	Bead
c	Out-of-die compacts
inf	Infinity
j	Index for particle size quantile
lim	Grinding limit
m	Mill chamber
p	Particle
ref	Reference values used to make variables nondimensional
s	Suspension