CENTRIFUGATION:
Centrifugation
is a process that involves the use of centrifugal force for the
sedimentation of heterogeneous mixtures with a centrifuge used in industry and
in laboratory settings. The word “Centrifugal” came from two Latin words ‘Centrum’
which means ‘Center’ and ‘Fugere’ which means ‘To Flee’. Centrifugal force is
the apparent force that draws a rotating body away from the center of rotation.
It is caused by the inertia of the body.
is a process that involves the use of centrifugal force for the
sedimentation of heterogeneous mixtures with a centrifuge used in industry and
in laboratory settings. The word “Centrifugal” came from two Latin words ‘Centrum’
which means ‘Center’ and ‘Fugere’ which means ‘To Flee’. Centrifugal force is
the apparent force that draws a rotating body away from the center of rotation.
It is caused by the inertia of the body.
Centrifugal Force is
used to provide the driving force for two operations-
- To create a pressure difference in the
filtration process. - To reduce gravitational force in the
sedimentation process.
PRINCIPLES FOR CENTRIFUGATION:
Centrifugation
is based on the well-known principle that an object that is rotated about the center point at a constant radial distance from the point is acted upon by a
force.
is based on the well-known principle that an object that is rotated about the center point at a constant radial distance from the point is acted upon by a
force.
The
operations using centrifugal force are described by equations including the
gravitational constant. It is convenient, therefore, to measure the centrifugal
force in terms of a ratio to the gravitational force and this is known as the centrifugal effect, which is the number of times the centrifugal force is
greater than the gravitational force. The centrifugal effect is then inserted
in the appropriate equation with the gravitational force.
operations using centrifugal force are described by equations including the
gravitational constant. It is convenient, therefore, to measure the centrifugal
force in terms of a ratio to the gravitational force and this is known as the centrifugal effect, which is the number of times the centrifugal force is
greater than the gravitational force. The centrifugal effect is then inserted
in the appropriate equation with the gravitational force.
The centrifugal effect is obtained as follows-
Consider
a body of mass ‘m’ rotating in a circular path of radius ‘r’ at a velocity ‘v’.
The force acting on the body in a radial direction is given below-
a body of mass ‘m’ rotating in a circular path of radius ‘r’ at a velocity ‘v’.
The force acting on the body in a radial direction is given below-
F=mv²/r …………….. (1)
Here,
F=Centrifugal force
M= Mass of body
v= Velocity of body
r = Radius of the circle of
rotation.
rotation.
The same body will be acted upon by a
gravitational force
gravitational force
G=mg………………
(2)
(2)
Where,
G= Gravitational
force
force
g= Gravitational
constant
constant
The centrifugal effect
is the ratio of the two forces, so that
is the ratio of the two forces, so that
C=F/G
=(mv²)/mgr
=v²/gr
=((2πnr)²)/gr
[v=2πnr, where n=speed of rotation]
=4π²r²n²/gr
=4π²rn²/g
=(4π²n² d/2)/g
[r=d/2 ,where,d=diameter of rotation ]
=2π²n²d/g
So, the Centrifugal effect,
C=2π²n²d/g
The
gravitational constant has a value of 9.807 ms¯² so that the equation maybe
simplified to-
gravitational constant has a value of 9.807 ms¯² so that the equation maybe
simplified to-
Centrifugal
effect,
C=2.013n²d……….. (3)
effect,
C=2.013n²d……….. (3)
‘n’
is expressed as s¯¹ and ‘d’ is in m.
is expressed as s¯¹ and ‘d’ is in m.
From equation (3),
It is shown that c∝n²d
It is shown that c∝n²d
So, The centrifugal effect is directly proportional to the diameter and the square of
the speed of rotation.
the speed of rotation.
We
can conclude by the equation that we can modify a centrifugal machine as well
as a centrifugal effect by modifying the speed of rotation or the diameter of the
apparatus. But it is wise to modify the speed of rotation other than the
diameter. Increasing the diameter is not so effective, because after a certain
point it can produce tremendous pressure difference and it can break down the
apparatus. Besides, it is a very hazardous task. So, when the diameter is increased
then the rotating speed must be matched by calculation.
can conclude by the equation that we can modify a centrifugal machine as well
as a centrifugal effect by modifying the speed of rotation or the diameter of the
apparatus. But it is wise to modify the speed of rotation other than the
diameter. Increasing the diameter is not so effective, because after a certain
point it can produce tremendous pressure difference and it can break down the
apparatus. Besides, it is a very hazardous task. So, when the diameter is increased
then the rotating speed must be matched by calculation.
But it is easy to modify the speed of
rotation. By increasing the speed of rotation, we can increase the centrifugal
effect. Thus, tiny particles can be separated by centrifugation.
rotation. By increasing the speed of rotation, we can increase the centrifugal
effect. Thus, tiny particles can be separated by centrifugation.
