10. Heat exchangers

A heat exchanger, in the narrow sense, is a vessel in which an outgoing processed, hot liquid transfers some of its heat to an incoming cold liquid to be processed. An alternative term is heat interchanger. The amount of heat so transferred is not lost to the process but is used over again; its equivalent need not be supplied by new fuels it may be considered as cycled heat. Hot gases end vapors similarly may be enabled to pass part of their heat to the incoming cold liquid. A heat exchanger, ' .still in the narrow sense, may also transfer in the opposite direction, for example, in an interchanger in which an outgoing cold gas takes up the heat of the incoming warmer gas, as in a liquid-air plant. In the widest sense, a heat exchanger is any device at all which makes possible a heat transfer from one fluid to another through a containing wall.

For the moment, let us consider the heat exchanger in which an outgoing hot liquid transfers its heat to an incoming cold one. One type which is widely used, largely because of its compactness, is the "shell-and-tube" type, consisting of a cylindrical shell within which lies a bundle of tubes, either straight or coiled in the form of U-tubes. Another type is the multitube type, containing numerous (perhaps 40) separate tubes, within each of which an inner tube carried the cold liquid.

Shell-and-Tube-Heat Exchangers. For the shell-and-tube exchanger, there is no rule which dictates which liquid should travel through the shell and which through the tubes: the selection depends upon a number of considerations. In general, the hot liquid should travel through the shell and the cold liquid in the tubes. A-wide variety of further considerations will govern the final selection. Thus, in an exchanger for a caustic solution which is to be built partly of nickel, and partly of steel, the tube side would be selected for the travel of the caustic solution, because less nickel would be required on that side to provide all nickel passages.

Another example' would be that of a dirty fluid to be treated with a clean liquid. The dirty liquid would be sent through the tubes, irrespective of temperatures, for the tubes may be cleaned on their inner side comparatively easily.

Multiple-type Exchangers. Another type of heat exchanger for liquids is the multitude type, in which each inner tube with its outer tube forms a separate unit, and many units (as many as 40) are combined. The flow of the liquids through all the tubes is truly countercurrent. The advantage possessed by this type is that each unit acquires a definite temperature essentially uniform for the single unit, so that once the apparatus is operating, the strains are constant. The multitude exchanger is not adapted to the handling of large volumes of liquids.

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Words and word combinations;

1. to process - обрабатывать

2. interchanger - обменник

heat interchanger - теплообменник

3. to transfer - передавать, переносить

4. over again - много раз, повторно

5. to cycle - совершать цикл

6. to pass - передавать

7. plant - I) завод, фабрика, 2) силовая установка, агрегат

8. to contain - вмещать, содержать в себе

9. because of - из-за, вследствие

10. shell -корпус, остов, оболочка

11. tube - труба

12. bundle - пачка, связка

13. to coil - наматывать; свертывать

14. selection - выбор

15. solution - раствор

16. passage - прохождение

17. to treat - обрабатывать

18. irrespective - независимо от

19. multiple - составной

20. unit - блок

21. as many as 40 - до сорока (блоков)

22. countercurrent - противоТ'ок

23. strain - напряжение

Answer the following questions;

1. What is a heat exchanger?

2. For what purpose are heat exchangers used?

3. What types of heat exchangers do you know?

4. What does the "shell-and-tube" heat exchanger consist of?

5. Which liquid should travel through the shell and which through the tubes? Is there a strict rule for it?

Give some

examples.

6. How many separate units are combined in a multiple-type exchanger?

7. What tubes does each separate unit consist of?

8. What is the advantage of a multiple-type exchanger?

Exercises

I. Translate the following sentences. Mind the functions of the infinitives:

1. The problem to be studied is of great importance for the development of chemistry.

2. To separate iron from sulphur is an easy task»

3. The function of a boiler is to transfer heat to the weter in the most efficient manner. »

4. Mechanization is to be distinguished from more primitive . tool using.

5. Lomonosov is known to have been one of the greatest men of science.

6. We know the thermometer to be an instrument for measuring temperature. "

7. When a structure or a machine is to be built, suitable materials are to be chosen for the parts.

8. Silicon is said to pla.7 an important part in the inorganic world.

9. To dissolve rubber, benzene is used.

10. Water to be used for drinking should be thoroughly purified.

11. Gold was probably one of-the first metals to attract the attention of men.

II. Ask questions on all the parts of the following

sentences?

1. Liquid products from the plant can be skipped by

rail, truck or pipeline.

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2, The engineers of our plant constructed a new electrical de-vise last year.