14. Mixers and agitators. Extruders.

In moat processes, there is a Deed to mix two different liquids, or a solid with, a liquid, or a gas with a liquid. In; order to best accomplish this, a rotating mixer is often used. Some of the duties required of such equipment! heat transfer, chemical reaction, crystallization, leaching, gas dispersion and absorption, fermentation, hydrogenation, and solids suspension. Several types of mixers^are available for these tasks.

Of all the rotating equipment mixers are the least susceptible to scientific calculations. Their selection requires close cooperation between vendor and user, especially for new-type processes. Mixer manufacturers generally have laboratories available for determining the best type of mixer in combination with the tank or vessel required for a process...

When deciding whether a mixer should be top-entering/ bottom-entering, or side-entering, several factors have to be considered. Is there enough headroom available? Are solids to be suspended from the bottom of the tank? Would the material being mixed prove dangerous to personnel if a lesk occured? This would preclude the Use of a bottom-entering mixer or side-entering mixer unless very special precautions were taken with respect to seal leakage.

Unless vortexing is desired, baffles should be used, especially for reactor-type vessels. For critical services in continuous operation, steady bearings should be avoided, since they are normally a maintenance item. An overhung shaft of large diameter can be used, but in this case the physical weight of the shaft must be considered.

There are batch and continuous mixers.

The Farrel Continuous Mixer. This type of mixer ,1s widely used in polymer production. The mixer takes ingredients into one end, mixes them, and discharges them from the other end continuously.

Discharge from the mixer is in the form of a thick ribbon that can be-handled as such, or guillotined into blocks. The machine requires a second-stage device to produce a final product, since it does not develop sufficient pressure to extrude the polymer through a die. This second stage is usually a single-screw extruder equipped with a die.

The single-screw extruder is basically a drag pump that conveys and forces the polymer through a die. The die Bay be provided with a slot for sheet extrusion, or with holes for standing or face cutting.

Commentary

1. ... since they are normally a maintenance item -... так как они /шурболизаторы потока/ представляют собой детали, часто требующие текущего ремонта

Words and word combinations :

1. mixer = agitator - мешалка, смеситель

2. leaching - выплачивание

3. hydrogenation - гидрирование

4. susceptible - поддающийся

5. tank - бак, цистерна

6. vessel - резервуар, сосуд

7. headroom - габаритная высота

8. bottom - дно

54

59

9. leak = leakage - утечки, просачивание

10. to preclude - предоа?враш;ашь

11. precaution - мера предосторожноса?и

12. with respect to - в отношении

13. seal - заделка, запайка

14. vortexing - взвихривание

15. baffle = bearing - 'турболизатор потока

16. overhung shaft - свободно установленный вал /стержень/

17. batch mixer - мешалка периодического действия continuous mixer - мешалка непрерывного действия

18. ingredient - составная часть, ингредиент

20 21 22 23 25

19. to extrude - выталкивать, выдавливать die - фильера

single-screw extruder - одночервячный экструдер drag pump - тяговый насос

slot - вырез, шлиц, щель 24. stranding - выпуск нити face outting - профилирование

Exercises

I. Translate the following sentences paying attention to the meaning of the word "available" :

1. Mixer manufacturers generally have laboratories available for determining the best type of mixer in combination with a tank.

2. Of all the instruments available a thermometer is the most suitable for measuring temperature.

3. In manufacturing plastics, greatly improved methods are available.

4. All of our available energy hag come from the sun.

5. We must learn to increase the efficiency of our use of fuel and to make available new sources of energy.

6. These tickets are available for 3 days only.

7. What we are interested to know is what fraction of the available energy we get in the form of useful work.

8. This device is not available for use now.

II. Translate the following sentences. Mind the meaning of the words "should" and "would":

Answer the following questions

1. en

   What purposes are agitators Used for?

2. What duties are required of rotating mixers? .

3. How can the best type of a mixer for a given process selected? 4. What factors have to be considered when deciding whether

mixer should be top-entering, bottom-entering, or side-tering?

5. In what cases are baffles used?

6. What types of mixers do you know?

7. How does the Farral continuous mixer operate?

8. Why does this machine require a seconds-stage device

9. What can you say about a single-screw extruder?

be

- I

l.I knew that, we should make the experiment. 2. You should examine all the properties of this substance ve­ry carefully. 3. If I could, I should help him in his investigation, 4. I should like to visit this new. laboratory.

5. It is necessary that this experiment should be done in our laboratory,

6. You must leave your home earlier lest you should be late for the lesson.

7. They would repeat their experiment many times, if the results were unsatisfactory.

8. The inventor would spend much time in the laboratory.

9. The engineer said that they would use this device in their laboratory.

56

57

10. It would be very difficult to carry out this research without electronic equipment.

11. Would this material prove dangerous to personnel if a leak occurred?

12. The metal would not melt without being heated for a long time.

13. Switch off the device lest it should be overheated.

III. Ask questions on all the parts of the following { sentences:

1. My friend carries out many interesting experiments in і our laboratory.

2. The first atomic power station was built in the USSR in І June 1954.

IV. Translate the following text using a dictionary?

Safety Precautions

Men working with machines, sharp tools, motors, elect­ricity, toxic or inflammable material must always be careful and always on guard. They must do what they are told so as to avoid accidents. The things they do to avoid accidents are called safety precautions. To save his eyes, the welder must use his mask. The electrician must check that the current is turned off before he starts to handle radios and other electrical machinery. The fitter must use a machine with guards on the moving parts where his clothing may catch. Those who work near or with inflammable material must always have the thought of fire in back of their minds.

15. MEASUREMENT IN CHEMICAL ENGINEERING. TEMPERATURE.

The quality of performance of control systems is directly dependent, on the quality of measurement of the controlled process variables.

The principal process variables, approximately in descending order of the frequency of their occurrence in process systems, are temperature, pressure, flow rate, composition, and liquid level. Some of these variables, such as pressure, can be measured relatively directly. Others, such as temperature, can be measured only indirectly. Often the indirect measures are made by measuring another process variable. Indeed, all five process variables can be measured by means of a pressure measurement.

Temperature. Temperature is the most important process variable, but it is also, perhaps, the most difficult to measure. It is used sometimes as a measure of composition and sometimes as the principal control variable for chemical-reaction rate, product yield, human comfort, and countless other properties.

Unlike pressure, temperature cannot be measured directly. It must be inferred from its effect on volume, pressure, electromotive force, electric resistance, radiation intensity, and so on.

Temperature measurement below 500 °С (932 F) is called thermometry, and above that it is called pyrometry. The five chief methods of measurement are based on the properties of expansion, state of aggregation, electric resistance, thermoelectric potential, and radiation intensity.

The difficulties in measuring temperatures arise primarily from the fact that there are so many carriers for thermal energy. Consider a temperature sensor mounted in a hot gas stream flowing along "a pipe. In a steady-state condition all thermal fluxes and all temperatures will be constant in time, but the actual temperature of the gas near the

58

59

sensor may be quite different from the temperature of the sensor. If the walls of the pipe are cooler than the gas, the sensor temperature will be less than the gas temperature be-cause of radiant-energy transfer from sensor to wall and because of conductive transfer from sensor through mount to wall. Издав two energy fluxes from the sensor must be balanced by thermal transfer from the gas to the sensor by the convective and conductive transfer that results from a temperature difference between the gas, and the sensor.

The difficulties of temperature measurement of fluids are doubly confounded if very high velocities are involved, so that kinetic-energy effects contribute to the sensor temperature, and if chemical changes, such as dissociations at high temperatures, are occurring in the fluid.

Answer the following questions;

1. What principal process variables do you know?

2. Can temperature be measured directly?

3. What effect must temperature be inferred from?

4,. What temperature measurement is called thermometry (pyro-metry)

5. What are the five chief methods of measurement based on?

6. From what fact do the difficulties in measuring temperatures arise? Give some examples.

7. When are the difficulties of temperature measurement of fluids doubly confounded?

Words and word combinations:

1. variable - переменная величина

2. frequency - частота

3. occurrence - распространение, проявление 4. pressure давление

5. flow rate - скорость потока /течения/

6. level - уровень .

7. rate - скорость

8. product yield - выход продукции

9. to infer (from) - выводить /из/

10. expansion - расширение

11. aggregation - соединение частиц, агрегация

12. to mount - монтировать mount (n) - крепление, опора

13. convective transfer - конвективная теплопередача 14, to confound - спутывать, зд.; усложнять

15. dissociation - распад

Exercises I. Translate the following sentences paying attention to the meaning of the word "mean" :

1. In mechanics, force does not mean strength.

2. A number of various complicated problems has been solved by means of computers.

3. At any given temperature the molecules of gases have the same mean kinetic energy.

4. It is generally possible by suitable means to separate the constituents of solutions.

5. Pressure may be measured by the means of four types of meters»

6. The thermometer which you mean is not the only means of measuring temperature.

7. Communism means happiness to all people, progress of science and culture, and friendship among the nations.

8. In capitalist countries workers have no means to give the-ir children higher education.

9. This problem is by no means easy. We must solve it by all means.

10. Telegraph and telephone are means of communication.

60

61

II. Translate the following sentences into Russian. Define the "ing-forms":

1. The temperature of the melted ice rising, the movement of its molecules is speeded up.

2. They succeeded in getting good results after a number of tedious investigations.

3. The rate of evaporation also depends on evaporating surface.

4. Since gases expand on heating and contract on cooling, it is interesting to consider, what will happen if we conti-nue lowering their temperature.

5. Every liquid can have a definite vapour pressure, this pressure increasing with rising temperature.

6. In passing through the metal electrons must collide with many ions.

7. The steam expanding, its volume will increase.

8. In making up a condencer, one has to take into consideration its 3ise.

9- Having found the needed solvent, he could continue his experiment.

10. Scientists succeeded in developing means of obtaining a synthetic rubber with properties similar to these of na­tural rubber,

11. (When) heating this mixture it is important to cheek if it changes its colour.

12. In many experiments one should check the temperature of the substance being heated.

Ill, Make the following sentences' refer to the past and futures:

1. We must check the temperature of the substance,

over

2. Some thermocouples can measure temperatures 3000°F.

3. You may work in our laboratory.