Study Set Content:
Settling of particle or floccules under gravitational force in
liquid dosage form.
Sedimentation
Velocity of sedimentation expressed by
Stokes Equation:
Stokes Equation:
sedimentation velocity in cm/sec
v
diameter of particle
d
density of disperse phase
ps
density of disperse media
po
acceleration due to gravity
g
viscosity of disperse medium in poise
n
Limitation of Stoke’s Equation
a. Spherical particles in a very dilute suspension (0.5 to 2 gm per
100 ml)
b. Particles which freely settle without collision.
c. Particles with no physical or chemical attraction
SEDIMENTATION PARAMETERS
Sedimentation volume (F) or Height (H) for flocculated
suspensions:
Sedimentation volume is a ratio of the ultimate
volume of sedimentation (Vu) to the original volume of
suspension (Vo) before settling
Sedimentation volume
is a ratio of the ultimate
volume of sedimentation (Vu) to the original volume of
suspension (Vo) before settling.
Definition: Sedimentation volume
F =
Vu / Vo
final or ultimate volume of sediment
Vu
original volume of suspension before settling
Vo
has values ranging from less than one to greater than one.
F
When F < 1 then
Vu
When F = 1 then
Vu=Vo
The system (F=1) is said to be n flocculation equilibrium and show no
clear supernatant on standing
