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Product Name: Separation Technology

Centrifugal Separation Technology


Centrifugal Separation Technology is the most widely used method for separating fluids with different densities. It is also used in separating solids from liquids or solids from gasses.

The need to separate different liquid phases and solids from each other is part of practically every industrial process. Huading has more than half a century of experience in meeting this requirement using either separator or decanter technology. And our products perform this crucial function exceptionally well.

The product range is based on centrifugal separation machines for separating liquids from each other or for removing solid particles from liquids.  All these centrifugal separation machines are based on density difference.

Sedimentation
Terminal free settling velocity of a spherical particle under gravitational force can be determined by the Newton's law:


Where
u,   m/s       settling velocity
d,   m          particle diameter
g,   m/s2     acceleration of gravity
ρ1  Kg/m3   density of particle
ρ2  Kg/m3   density of liquid
CD              drag coefficient

CD  has been found to be a function of Reynolds Number. If the flow around the particle is laminar Re < 0.6 then CD =24/Re. In this case, we can reduce the equation of settling velocity to :

Where
u ,  m/s       settling velocity
d,   m          particle diameter
g,   m/s2     acceleration of gravity
ρ1  Kg/m3   ensity of particle
ρ2  Kg/m3   ensity of liquid
μ    Pas       fluid dynamic viscosity

This expression is the Stoke's law of the terminal settling velocity of a spherical particle under laminar flow conditions.


Centrifugation
If the settling is carried out in a centrifugal field instead of gravitational, then we have to deal with a centrifugal acceleration, which is not constant like "g", but increases as the distance of the particle from the axis of the rotation of the vessel and as the angular velocity (See Fig .1.). Sedimenting centrifuges use centrifugal force to accelerate the sedimentation process. By rotating the process fluid, the sedimentation rate can be increased by a factor of several thousands compared to static sedimentation or settling. In applications, in which centrifuges are used, the static sedimentation velocity is between 10-9 and 10-4 m/s. To accelerate the process, centrifuges apply centrifugal forces of 500-30000g.

Fig.1. Principal analogy between sedimentation and centrifugation

The factor Z= rω2/g specifies how much greater the sedimentation rate of a particle is in a centrifugal field as compared with the gravitational field.

The next figure illustrates a centrifugal separator for removing solid particles from liquids.


Accelerating the separation process
In essence, a centrifuge is a settling tank whose base is wrapped around a centre line. Rotating this entire unit rapidly means that the effect of gravity is replaced by a controllable centrifugal force that can have an effect up to 10,000 times greater.

This force is then used to separate liquids from other liquids and solids efficiently and with great accuracy, and in a manner that is easy to control.

In the centrifugal field, under the action of centrifugal force, when the denser solids are subjected to centrifugal forces, they are forced outwards against the rotating bowl wall, while the less dense liquid phases form concentric inner layers.