Centrifugation. Centrifugation: types and application of the method The centrifugation method is based on

Centrifugation is the separation of mechanical mixtures into their component parts.
by the action of centrifugal force. Devices used for this
targets are called centrifuges.
The main part of the centrifuge is the rotor with mounted
It has slots for centrifuge tubes. The rotor rotates with
high speed, as a result of which significant damage is created
magnitude of centrifugal forces, under the influence of which
mechanical mixtures are separated, for example
sedimentation of particles suspended in a liquid.

Processes occurring in a centrifuge

The following processes are separated in centrifuges:
1) Centrifugal filtration.
2) Centrifugal settling.
3) Centrifugal clarification.

Centrifugal filtration

Centrifugal filtration is
process of separating suspensions in centrifuges with
holey drums. Inner surface
of such a drum is covered with filter cloth.
The suspension is thrown towards the
drum walls, while the solid phase remains on
surface of the fabric, and the liquid under the influence
centrifugal force passes through the sediment layer and
the fabric is removed out through the holes in the drum.
Centrifugal filtration usually consists of
three sequential physical processes:
1)filtration with the formation of precipitate;
2) sediment compaction;
3)removal of liquid retained from the sediment
molecular forces;

Centrifugal settling

Centrifugal settling
Centrifugal settling - separation process
suspensions in centrifuges having drums with
solid walls. The suspension is injected into the lower
part of the drum and under the influence of centrifugal force
thrown against the walls. A layer forms at the walls
sediment, and the liquid forms the inner layer and
is forced out of the drum entering the separation
suspension. The liquid rises to the top,
pours over the edge of the drum and is removed
out.
In this case, two physical processes occur:
1) Sedimentation of the solid phase.
2) Sediment compaction.

Centrifugal clarification

Centrifugal clarification - separation process
thin suspensions and colloidal solutions. So
it is carried out in solid drums.
According to its physical essence, centrifugal
clarification is a process
free deposition of solid particles in the field
centrifugal forces.
In drums with solid walls
emulsions are also separated. Under
components due to centrifugal force
emulsions according to density
are arranged in the form of delimited layers:
outer layer of liquid with higher density
and an inner layer of lighter liquid.
Liquids are discharged separately from the drum.

In clinical and sanitary laboratories
centrifugation is used
for separating red blood cells from
blood plasma, blood clots from
serum, dense particles from
liquid part of urine, etc. For
used for this purpose or
manual centrifuges, or
electric driven centrifuges,
whose rotation speed
can be adjusted.
Ultracentrifuges, speed
rotation of the rotors of which
exceeds 40,000 rpm,
usually used in
experimental practice
for organelle separation
cells, colloidal compartments
particles, macromolecules,
polymers.

Use of centrifugation in parasitology

The method is used to differentiate complex
blood mixture, urine or feces, followed by
isolating helminths from it for further
studying under a microscope and fixing the material. IN
centrifugation process present in the sample
parasites pass through the filter and accumulate in
lower conical compartment of the test tube. Filter mesh
with specially sized cells
in a test tube is located vertically, as a result
what happens horizontal (lateral)
sample filtration. As a result, rude
particles of undigested food, fiber settle in
mixing chamber, and parasites and their eggs
pass through the filter unhindered. So
Thus, parasites concentrate in
surface layer of fine sediment, and
the laboratory doctor can only carefully select
sample for microscopy using
automatic pipette and apply it to
slide.

Centrifugation method in cytology

Differential method
centrifugation is used for
fractionation of cells, i.e. their separation
contents into fractions depending on specific
weight of various organelles and cellular inclusions.
To do this, finely ground cells are rotated in
a special device - an ultracentrifuge. IN
resulting from centrifugation of cell components
precipitate from solution, located in
according to its density. More dense
structures settle at lower rates
centrifugation, and less dense ones - at high
speeds The resulting layers are separated and studied
separately.

10. Centrifugation in botany and plant physiology

Centrifugation allows you to obtain various
fractions of subcellular particles and explore
properties and functions of each faction in
separately. For example, from spinach leaves you can
isolate chloroplasts, wash them with
repeated centrifugation in an appropriate
environment from cell fragments and examine them
behavior in various experimental
conditions or determine their chemical composition.
Further you can, using various modifications
techniques, destroy these plastids and isolate
through
differential centrifugation (repeatedly
of particle deposition at various values
acceleration) their constituent elements. So
by means of which it was possible to show that plastids contain
structures characterized by a very ordered
structure - the so-called grana; all grains
are located within the limiting chloroplast
membranes (chloroplast shell). Advantages
this method is simply invaluable because it
allows us to reveal the existence
functional subunits that make up
larger subcellular particles; in particular,
using method

11. Centrifugation method in virology

The Bracquet density gradient centrifugation method can be
use for both selection and retrieval
quantitative characteristics of plant viruses. As it turned out,
This method is fraught with many possibilities even today
widely used in the field of virology and molecular
biology. When conducting research using
density gradient centrifugation centrifuge tube
partially filled with a solution whose density decreases in
direction from the bottom to the meniscus. To create a gradient when
most commonly used in the fractionation of plant viruses
sucrose. Before centrifugation begins, virus particles may
be either distributed throughout the entire volume of the solution, or applied to
the top of the gradient. Brakke proposed three different techniques
density gradient centrifugation. With isopycpic
(equilibrium) centrifugation process continues until
until all particles in the gradient reach a level where the density
environment is equal to their own density. Thus,
particle fractionation occurs in this case in accordance with
differences in their density. Sucrose solutions do not have
sufficient density for isopycnal separation of many
viruses. During high-speed zonal centrifugation, the virus
First, a previously created gradient is applied. Particles
each type is sedimented through a gradient in the form of a zone,
or strips, at a speed depending on their size, shape and
density. Centrifugation is completed when the particles
still continue to sediment. Equilibrium zonal
centrifugation is similar to high-speed zonal
centrifugation, but in this case centrifugation

12. Difficulties in using the centrifugation method

Application of the differential centrifugation method
is associated with many methodological difficulties. Firstly, when
The release of particles can damage their structure. That's why
it was necessary to develop special methods for destroying cells,
which would not cause damage to the structure of subcellular
factions. Secondly, since subcellular particles have
membranes, in the process of their secretion may arise
various osmotic effects. Therefore, in order to
so that the ultrastructure of the objects under study is not destroyed
even when isolating them, it is necessary to carefully select the composition
environment in which cell destruction and sedimentation occurs
particles. Finally, washing away subcellular particles
(resuspension of them in the medium and subsequent repeated
centrifugation) may result in the loss of some
substances contained in them, which under the influence of diffusion forces
go into solution.
Because of this, it can sometimes be difficult to understand which small molecules
are really elements of the structures under study, and which
were simply adsorbed on their surface during the release process.
This situation makes it difficult to accurately determine some
functional properties of selected objects.

What is centrifugation? What is the method used for? The term "centrifugation" means the separation of liquid or solid particles of a substance into various fractions using centrifugal forces. This separation of substances is carried out through the use of special devices - centrifuges. What is the principle of the method?

Centrifugation principle

Let's look at the definition in more detail. Centrifugation is the effect on substances through ultra-high-speed rotation in a specialized apparatus. The main part of any centrifuge is the rotor, which contains nests for installing test tubes with material that is subject to separation into separate fractions. When the rotor rotates at high speeds, the substances placed in the test tubes are separated into different substances according to the density level. For example, centrifuging groundwater samples separates the liquid and precipitates the solid particles it contains.

Author of the method

For the first time it became known what centrifugation is after experiments conducted by scientist A.F. Lebedev. The method was developed by a researcher to determine the composition of soil water. Previously, for these purposes, settling of liquid with subsequent separation of solid samples from it was used. The development of the centrifugation method made it possible to cope with this task much faster. Thanks to this separation, it became possible to extract the solid portion of substances from a liquid in dry form within a matter of minutes.

Centrifugation steps

Differential centrifugation begins with the settling of substances that are subject to research. This material processing occurs in settling devices. During settling, particles of matter are separated under the influence of gravity. This allows you to prepare substances for better separation using centrifugal forces.

Next, the substances in the test tubes undergo filtration. At this stage, so-called perforated drums are used, which are intended to separate liquid particles from solid ones. During the presented activities, all sediment remains on the walls of the centrifuge.

Advantages of the method

Compared to other methods aimed at separating individual substances, such as filtration or sedimentation, centrifugation makes it possible to obtain a sediment with a minimum moisture content. The use of this separation method allows the separation of fine suspensions. The result is the production of particles with a size of 5-10 microns. Another important advantage of centrifugation is the ability to perform it using equipment of small volumes and dimensions. The only drawback of the method is the high energy consumption of the devices.

Centrifugation in biology

In biology, the separation of substances into individual substances is resorted to when it is necessary to prepare preparations for examination under a microscope. Centrifugation here is carried out using complex devices - cytorotors. In addition to slots for test tubes, such devices are equipped with sample holders and all kinds of slides of complex design. The design of the centrifuge when conducting research in biology directly affects the quality of the materials obtained and, accordingly, the amount of useful information that can be gleaned from the analysis results.

Centrifugation in the oil refining industry

The centrifugation method is indispensable in oil production. There are hydrocarbon minerals from which water is not completely released during distillation. Centrifugation makes it possible to remove excess liquid from the oil, increasing its quality. In this case, oil is dissolved in benzene, then heated to 60 o C, and then subjected to centrifugal force. Finally, measure the amount of remaining water in the substance and repeat the procedure if necessary.

Blood centrifugation

This method is widely used for medicinal purposes. In medicine, it allows you to solve the following number of problems:

1. Obtaining purified blood samples for plasmapheresis. For these purposes, the formed elements of blood are separated from its plasma in a centrifuge. The operation makes it possible to rid the blood of viruses, excess antibodies, pathogenic bacteria, and toxins.
2. Preparing blood for donor transfusion. After the body fluid is separated into separate fractions by centrifugation, the blood cells are returned to the donor, and the plasma is used for transfusion or frozen for later use.
3. Isolation of platelet mass. The substance is obtained from the resulting mass and is used in surgical and hematology departments of medical institutions, in emergency therapy, and operating rooms. The use of platelet mass in medicine makes it possible to improve blood clotting in victims.
4. Synthesis of red blood cells. Centrifugation of blood cells occurs through delicate separation of its fractions according to a special technique. The finished mass, rich in red blood cells, is used for transfusion during blood loss and operations. Red blood cells are often used to treat anemia and other systemic blood diseases.

In modern medical practice, many new generation devices are used, which make it possible to accelerate a rotating drum to a certain speed and stop it at a certain moment. This allows blood to be more accurately separated into red blood cells, platelets, plasma, serum and clots. Other bodily fluids are examined in a similar way, in particular, substances in urine are separated.

Centrifuges: main types

We figured out what centrifugation is. Now let's find out what devices are used to implement the method. Centrifuges can be closed or open, mechanically or manually driven. The main working part of hand-held open instruments is a rotating axis located vertically. In its upper part there is a perpendicularly fixed bar where movable metal sleeves are located. They contain special test tubes that are narrowed at the bottom. Cotton wool is placed at the bottom of the sleeves, which avoids damage to the glass test tube when it comes into contact with metal. Next, the apparatus is set in motion. After some time, the liquid separates from the suspended solids. After this, the manual centrifuge is stopped. A dense, solid sediment concentrates at the bottom of the test tubes. Above it is the liquid part of the substance.

Closed mechanical centrifuges have a large number of sleeves to accommodate test tubes. Such devices are more convenient compared to manual ones. Their rotors are driven by powerful electric motors and can accelerate to 3000 rpm. This makes it possible to carry out better separation of liquid substances from solid ones.

Features of preparing tubes for centrifugation

Test tubes used for centrifugation must be filled with the test material of identical mass. Therefore, special high-precision scales are used for measurements here. When it is necessary to balance numerous tubes in a centrifuge, the following technique is used. After weighing a couple of glass containers and achieving the same mass, one of them is left as a standard. Subsequent tubes are equilibrated with this sample before being placed into the apparatus. This technique significantly speeds up work when it is necessary to prepare a whole series of tubes for centrifugation.

It is worth noting that too much of the test substance is never placed in test tubes. Glass containers are filled in such a way that the distance to the edge is at least 10 mm. Otherwise, the substance will flow out of the test tube under the influence of centrifugal force.

Supercentrifuges

To separate the components of extremely thin suspensions, it is not enough to use conventional manual or mechanical centrifuges. In this case, a more impressive effect on substances from centrifugal forces is required. When implementing such processes, supercentrifuges are used.

The devices of the presented plan are equipped with a blind drum in the form of a tube of small diameter - no more than 240 mm. The length of such a drum significantly exceeds its cross-section, which makes it possible to significantly increase the number of revolutions and create a powerful centrifugal force.

In a supercentrifuge, the substance being tested enters the drum, moves through the tube and hits special reflectors, which throw the material onto the walls of the device. There are also chambers designed for separate removal of light and heavy liquids.

The advantages of supercentrifuges include:

• absolute tightness;
• the highest intensity of substance separation;
• compact dimensions;
• the ability to separate substances at the molecular level.

In conclusion

So we found out what centrifugation is. Currently, the method finds its application when it is necessary to isolate precipitates from solutions, purify liquids, and separate components of biologically active and chemical substances. Ultracentrifuges are used to separate substances at the molecular level. The centrifugation method is actively used in the chemical, oil, nuclear, food industries, as well as in medicine.

Centrifugation method- this is the separation (division) into components of various heterogeneous mixtures using centrifugal force. To accomplish this, specialized devices called centrifuges are used.

The main part of any centrifuge is a rotor with nests into which test tubes are installed. During ultra-high-speed rotation, a centrifugal force arises in the system, which contributes to separation of the processed substance by density- for example, the solid particles present in the liquid are “sedimented”. The centrifugation method is used in almost all areas of human activity: in science and medicine, industry, agriculture, in everyday life and in technological fields.

Various centrifugation methods

To separate substances, another method of sedimentation can be used - sedimentation, when separation occurs under the influence of gravity. As a rule, treatment in settling devices precedes centrifugation and is a preparatory stage of work.

The centrifugation method itself is divided into sedimentation, filtration and clarification.

Filtration carried out using a perforated drum on which a filter medium is installed. Liquid passes through it freely under the influence of centrifugal force, while solid particles remain outside. For defending Drums with solid walls are used, into the lower part of which the suspension is supplied. During the process, sediment is released on the walls, and the liquid forms an inner layer, then overflows over the edge.

And finally lightening also occurs in solid drums, representing a process of free sedimentation of particles under the influence of a centrifugal field.

Characteristics of centrifugation methods

In their physical essence, filtration and sedimentation methods are very different.

In settling drums processing is carried out to purify a liquid, the content of contaminants and impurities in which is quite insignificant, by compacting the sediment and settling solid particles.

At the same time, this differs radically from the process using gravity - primarily due to the fact that settling is a fairly uniform process, and centrifugation, due to the non-parallelism of the centrifugal field lines, is a rather inconsistent method. The two methods are inherently different, and this must be taken into account.

Filtration centrifugation the structure is somewhat more complicated, since it usually occurs in three stages: first there is the formation of sediment, then compaction, then the elimination of liquid. Filtration by centrifugal force is also very different from filtration using “normal” gravity. Only the first stage can be called similar.

Use of centrifugation in different areas

The method has become widespread and is used in almost any field of activity. You can meet it in biology and medicine, laboratory diagnostics, and the food industry; it has long and successfully replaced the more traditional and less efficient processes of filtering, squeezing and cleaning.

Industrial centrifuges They have greater power and a more complex rotor design, thanks to which a lot of substances can be processed simultaneously. They are used in agriculture for extracting honey from honeycombs and cleaning grain, separating fat from milk by separation, and they are also very common in the field of ore beneficiation. You can even find a centrifuge in a laundry room - there they spin clothes after washing.

Laboratory centrifuges with a fairly slow rotor speed are used for separating blood serum, urine sediments, for serological studies and for sedimentation of red blood cells. Laboratory varieties are further divided into clinical, stationary, refrigerated, tabletop and corner small: each is used in its own area of ​​laboratory research, depending on the goals and objectives of the medical center.

Preparative centrifugation is one of the methods for isolating biological material for subsequent biochemical research. Allows you to isolate a significant number of cellular particles for a comprehensive study of their biological activity, structure and morphology. The method is also applicable for isolating basic biological macromolecules. Area of ​​use: medical, chemical and biochemical research.

Classification of preparative centrifugation methods

Preparative centrifugation is carried out using one of the following methods:

Differential. The method is based on the difference in the sedimentation rate of particles. The material under study is centrifuged with a gradual increase in centrifugal acceleration. At each stage, one of the medium fractions is deposited at the bottom of the test tube. After centrifugation, the resulting fraction is separated from the liquid and washed several times. Zone-speed. The method is based on layering the test medium on a buffer solution with a known continuous density gradient. The sample is then centrifuged until the particles are distributed along the gradient, forming discrete bands (zones). The density gradient allows you to eliminate mixing of zones and obtain a relatively pure fraction.

• Isopycnic. It can be carried out in a density gradient or in the usual way. In the first case, the processed material is layered onto the surface of a buffer solution with a continuous density gradient and centrifuged until the particles are separated into zones. In the second case, the medium under study is centrifuged until a sediment of particles with a high molecular weight is formed, after which the particles under study are isolated from the resulting residue.
• Equilibrium. It is carried out in a density gradient of heavy metal salts. Centrifugation allows you to establish the equilibrium distribution of the concentration of the dissolved test substance. Then, under the influence of centrifugal acceleration forces, the particles of the medium are collected in a separate zone of the test tube.

The optimal methodology is selected taking into account the goals and characteristics of the environment being studied.

Classification of preparative laboratory centrifuges

Depending on the design features and operational characteristics, preparative centrifuges can be divided into 3 main groups:

General purpose. Maximum speed – 8,000 rpm with relative centrifugal acceleration up to 6,000 g. Universal laboratory centrifuges are equipped with angular rotors or rotors with hanging containers for storing biological material. They are distinguished by a large capacity from 4 dm 3 to 6 dm 3, which allows the use of standard centrifuge tubes with a volume of 10-100 dm 3 and vessels with a capacity of no more than 1.25 dm 3. Due to the peculiarities of fastening the rotor to the drive shaft, the tubes or vessels must be balanced and differ in weight by a maximum of 0.25 g. It is not permissible to operate the centrifuge with an odd number of tubes. When the rotor is partially loaded, containers with the test medium should be placed symmetrically relative to each other, thereby ensuring their uniform distribution relative to the axis of rotation of the rotor.

• Express. Maximum speed – 25,000 rpm with relative centrifugal acceleration up to 89,000 g. To prevent heating due to friction forces arising during rotation of the rotor, the working chamber is equipped with a cooling system. They are equipped with angular rotors or rotors with hanging containers for placing biological material. Capacity of high-speed preparative
  centrifuges – 1.5 dm 3 .
• Ultracentrifuges. Maximum speed – 75,000 rpm with relative centrifugal acceleration up to 510,000g. To prevent heating due to friction forces arising during rotation of the rotor, they are equipped with a cooling system and a vacuum unit. Ultracentrifuge rotors are made of ultra-strong titanium or aluminum alloys. To reduce vibrations due to uneven filling, the rotors have a flexible shaft.

A separate category should include specially designed preparative centrifuges designed to carry out certain types of research and solve specific problems. This group includes centrifuges with heating jackets, refrigerated centrifuges and other similar equipment.

Features of the rotor design in preparative centrifuges

Preparative centrifuges are equipped with angular or horizontal rotors:

Angled rotors - test tubes are located at an angle of 20-35° to the axis of rotation during centrifuge operation. The distance traveled by the particles to the corresponding wall of the test tube is small, and therefore their sedimentation occurs quite quickly. Because of the convection currents that occur during centrifugation, fixed-angle rotors are rarely used to separate particles whose size and properties cause significant differences in settling rates. Horizontal rotors – tubes in this type of rotor are mounted vertically. During the rotation process, under the influence of centrifugal force, the vessels with the processed material move to a horizontal position. These design and operation features make it possible to reduce convection phenomena, so rotors of this type are optimal for separating particles with different sedimentation rates. The use of sectorial tubes allows for an additional reduction in the effects of vortex and convection phenomena.

The type of rotor determines the scope of use of the equipment. The ability to change the rotor allows you to use the same centrifuge model to solve diverse problems. Medical centrifuges for the Centurion laboratory are available in floor-standing or tabletop versions, which makes it possible to use the equipment in any room, regardless of the available space.

Lecture No. 5

The separation of liquid heterogeneous mixtures is effectively carried out by the centrifugation method, based on the use of centrifugal force. Devices in which liquid heterogeneous mixtures are separated under the influence of centrifugal force are called centrifuges.

The centrifugation method is widely used in various fields of technology; The number of types and designs of centrifuges is very large.

The main part of the centrifuge is a drum (a rotor with solid or perforated walls), rotating at high speed on a vertical or horizontal shaft. The separation of heterogeneous mixtures in centrifuges can be carried out either by the principle of settling or by the principle of filtration. In the first case, drums with solid walls are used, in the second - with holes; drums with holes are covered with a filter. If the walls of the drum are solid, then the material, under the influence of centrifugal force, is arranged in layers according to its specific gravity, and a layer of material with a high specific gravity is located directly next to the walls of the drum. If the walls of the drum have holes and are equipped on the inner surface with a filter partition, for example a filter cloth, then the solid particles of the mixture remain on the filter partition, and the liquid phase passes through the pores of the solid sediment and the filter partition and is removed from the drum. The liquid phase separated in a centrifuge is called centrate.

Centrifugal force; separation factor. When the centrifuge drum and the liquid in it rotate, centrifugal force arises as an inertial force.

С=m W 2 / r (1)

m-weight of a rotating body (fluid) in kgf;

r - radius of rotation in m

W - peripheral rotation speed in m/s;

The peripheral rotation speed is defined as:

W=ω r = 2 π n r/60 (2)

n- number of revolutions per minute;

ω-angular velocity of rotation in radians

g-gravity acceleration in m/sec 2, if m=G/g, then centrifugal force WITH, acting on a rotating body with mass m and weight G, is equal to C= G(2π n r/60) 2 /rg Or C ≈ G n 2 r/900 (3)

Equation (2.3) shows that an increase in centrifugal force is more easily achieved by increasing the number of revolutions than by increasing the diameter of the drum. Small-diameter drums with a high number of revolutions can develop greater centrifugal force than large-diameter drums with a low number of revolutions.

Thus, the centrifugal force acting on a particle can be greater than the force of gravity as many times as the acceleration of the centrifugal force is greater than the acceleration of gravity. The ratio of these accelerations is called separation factor and denote Kr:

W 2 / r – acceleration of centrifugal force.

Taking G=1n, we get: Kr=n 2 r /900

For example, for a centrifuge with a rotor with a diameter of 1000 mm (r=0.5 m) rotating at a speed of n=1200 rpm, the separation factor will be 800. The separating effect of the centrifuge increases in proportion to the value of Kp.

The value of K for cyclones is on the order of hundreds. And for centrifuges - about 3000, thus, the driving force of the sedimentation process in cyclones and centrifuges is 2-3 orders of magnitude greater than in settling tanks. Thanks to this, the productivity of cyclones and centrifuges is higher than the productivity of settling tanks, and small particles can be effectively separated in them: in centrifuges with a size of about 1 micron. In cyclones - about 10 microns.

From a comparison of the equations it is clear that the separation factor K p is numerically equal to the centrifugal force that develops during the rotation of a body weighing 1 kg.

Characteristics of centrifugation processes . As mentioned above, centrifugation can be carried out by the principle of settling (in solid drums) or by the principle of filtration (in perforated drums). In their physical essence, both processes differ from each other. In addition, there are separate varieties of each of these processes, which are determined by the content of the solid phase and the degree of its dispersion, as well as the physical properties of the suspension.

Centrifugation in settling drums is carried out both to purify liquids from contaminants contained in small quantities (liquid clarification) and to separate suspensions containing a significant amount of solid phase (settling centrifugation).

Centrifugation in settling drums generally consists of two physical processes: sedimentation of the solid phase (the process follows the laws of hydrodynamics) and compaction of the sediment; The basic laws of soil mechanics (dispersed media) apply to the latter process.

Up to a certain concentration limit of the solid phase (equal to approximately 3-4% by volume), its deposition in the settling drum occurs without the formation of an interface between the solid and the liquid. With increasing concentration, such a surface is formed due to the enlargement and sedimentation of solid particles in the liquid.

The centrifugation process in settling drums is fundamentally different from the separation process in settling tanks. In the latter, the deposition rate can practically be considered constant, since the process occurs in a gravitational field, the acceleration of which does not depend on the coordinates of the falling particle.

Acceleration of the field of centrifugal forces is a variable quantity and depends, at a constant angular velocity, on the radius of rotation of the particle. In addition, the lines of force of the centrifugal field are not parallel to each other and, therefore, the direction of action of the centrifugal forces will be different for different particles (not lying on the same radius of rotation).

Therefore, the laws of settling processes cannot be extended to the centrifugation process in settling drums.

The separation capacity of settling centrifuges is characterized by the performance index (sigma) Σ, which is the product of the area of ​​the cylindrical settling surface F in the rotor and the separation factor Kp.

Σ=F Kr (1), Kr= W2/rg ≈n2 r/900, whence Σ /F=Kr (2)

Considering that the separation factor expresses the ratio of the settling rates of particles in the settling centrifuge and settling tank, in accordance with equality (2), the value of Σ should be considered equal to the area of ​​the settling tank, equivalent in performance for a given suspension to the centrifuge in question. The performance index reflects the influence of all design features of the precipitation centrifuge that determine its separation ability.

When determining the productivity of batch settling centrifuges, it is necessary to take into account the time spent on starting, braking and unloading the centrifuge. Determining the productivity of a filter centrifuge is as difficult as determining the productivity of any filter.

Even more complex is the process of centrifugation in filter drums. The process occurs in three stages:

formation of sediment, compaction of sediment, and finally removal from the pores of the sediment of liquid retained by capillary and molecular forces.

As a result, the entire process of centrifugal filtration cannot be identified with conventional filtration that occurs under the influence of gravity. Only its first period is fundamentally close to conventional filtration and differs from it only in the magnitude of the hydraulic pressure of the liquid flowing through the sediment layer under the influence of centrifugal forces. During this period, moisture in the sediment is in free form and is removed from it most intensively. The second period is similar to the corresponding period during settling centrifugation and, finally, the third is characterized by the penetration of air into the compacted sediment, i.e. mechanical drying of the sediment

The duration of the above periods depends on the physical properties and concentration of the suspensions, as well as on the characteristics of the centrifuge.

The complexity and diversity of centrifugation processes makes it difficult to develop a theory of the process (especially its kinetics) and precise methods for calculating centrifuges.

Centrifuge performance. Typically, the productivity of centrifuges is expressed by the volume of suspension entering the centrifuge per unit time (l/hour), or the weight of the sediment obtained after centrifugation (kg/hour).