Friday, March 18, 2016

What are the Principle of Separation in the Purifier?


An Oil Purifier separates various contaminants to oil in such specific condition (Al+Si,
sludge, water, etc.) to maintain oil characteristics to certain limits. Oil that is fed into
an engine requires controlled characteristics to maintain the engine operational
reliability and extend the life usage.

Principle of Separation

When separation process is required, two conditions could be met:
a. to separate solid particles from a liquid, e.g. sludge / dirt from oil.
b. to separate liquids of different densities which are mutually insoluble e.g. water
from oil.
i. Separation by Gravity
When liquid is filled in the tank and stored in some period of time, separation by
gravity is conducted except when the liquid is emulsified.
In case of the oil, the sediments such as sludge, dirt, etc., tends to stay at the
bottom, the water is in the center and the oil floats above the water inside the
tank. The separation is acted due to the gravitational force from earth.
This type of separation is normally takes place in the oil settling tanks and service
tanks. As the difference in their densities is very less, the separation process is
very slow and is not sufficient to provide oil in a condition which can be used
directly in the system.

ii. Separation by Centrifugal Force
When centrifugal force is applied, the main separating force is equal to the
difference between the centrifugal force acting on the solid and water, and the
centrifugal force acting on the oil due to the difference in the density.

As per Stokes’ law, the separating force in centrifugal separation can be
expressed as:
F= ( d3v2/6r) x ( 2- 1)
d = diameter of particle
v = linear velocity of particle
r = radius of rotation of particle

In the formula above, the separating force acting between the two liquids or liquid
and solid particle is directly proportional to the difference in their densities and the
square of linear velocity. This method of separation is very useful when the
difference in densities of water and oil in a mixture is very less. Since the
separation force is directly proportional to square of linear velocity, it can be
increased many fold by rotating the container at permissible high speed.
When a centrifugal force is acting in the rotating container, all solid particles and
water which is heavier than oil is displace outward from the center of rotation.
The lighter liquids tend to form in the center and moves upward. Centrifugal force
application increases the separation process in a rotating container.
A centrifugal purifier is essentially a container which is rotated at high speed
while contaminated oil is force through, and rotates with the container. However,
only material that are insoluble in the oil can be separated by centrifugal force,
distillate e.g., gas oil cannot be separated from lubricating oil, nor salt can be
removed from sea water by centrifugal force. Water can be separated from oil
because water and oil does not form a true solution when they are mixed.
Furthermore, there must be a difference in the specific gravities of the materials
before they can be separated by centrifugal force.
In a centrifugal purifier, the separated water is discharged from water outlet, the
oil from the clean oil outlet and the solid remain in the rotating unit. The
separation by centrifugal force is further affected by the size of the particles, the
viscosity of the fluids, and the time during which the materials are subjected to
the centrifugal force. In general, the greater the difference in specific gravity
between the substances to be separated and the lower the viscosity, in case of
fuel oil the greater will be the rate of separation.

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