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Text 5. Heat Exchanger
A heat exchanger is a device built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. Heat exchangers are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, and natural gas processing. One common example of a heat exchanger is the radiator in a car, in which the heat source, being a hot engine-cooling fluid, water, transfers heat to air flowing through the radiator (i.e. the heat transfer medium).
Heat exchangers may be classified according to their flow arrangement. In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. In counter-flow heat exchangers the fluids enter the exchanger from opposite ends. The counter current design is most efficient, it can transfer the most heat from the heat (transfer) medium. In a cross-flow heat exchanger, the fluids travel roughly perpendicular to one another through the exchanger.
For efficiency, heat exchangers are designed to maximize the surface area of the wall between the two fluids, while minimizing resistance to fluid flow through the exchanger. The exchanger performance can also be affected by adding fins or corrugations in one or both directions, which increase surface area and may channel fluid flow or induce turbulence. The temperature across the heat transfer surface varies with position, but an appropriate mean temperature can be defined. In most simple systems this is the log mean temperature difference (LMTD).
Tubular heat exchangers consist of a series of tubes. One set of these tubes contains the fluid that must be either heated or cooled. The second fluid runs over the tubes that are being heated or cooled so that it can either provide the heat or absorb the heat required. A set of tubes is called the tube bundle and can be made up of several types of tubes: plain, longitudinally finned, etc.
Tubular heat exchangers are typically used for high pressure applications (with pressures greater than 30 bar and temperatures greater than 2600C). This is because they are robust due to their shape. There are several thermal design features that are to be taken into account when designing the tubes in heat exchanger. These include:
- Tube diameter: Using a small tube diameter makes the heat exchanger both economical and compact. However, it is more likely for the heat exchanger to foul up faster and the small size makes mechanical cleaning of the fouling difficult. To prevail over the fouling and cleaning problems, larger tube diameters can be used. Thus to determine the tube diameter, the available space, cost and the fouling nature of the fluids must be considered.
- Tube thickness: The thickness of the wall of the tubes is usually determined to ensure:
· there is enough room for corrosion;
· that flow-induced vibration has resistance.
- Tube length: Heat exchangers are usually cheaper when they have a smaller diameter and a long tube length. Thus, typically there is an aim to make the heat exchanger as long as physically possible whilst not exceeding production capabilities. However, there are many limitations for this, including the space available at the site where it is going to be used and the need to ensure that there are tubes available in lengths that are twice the required length (so that the tubes can be withdrawn and replaced). Also, it has to be remembered that long, thin tubes are difficult to take out and replace.
- Tube pitch: when designing the tubes, it is practical to ensure that the tube pitch (i.e., the centre-centre distance of adjoining tubes) is not less than 1.25 times the tubes outside diameter.
- Tube Layout: refers to how tubes are positioned.
Exercise 58. Make attributive word combinations using the words given in columns A and B.
| A | B |
| a) processing b) refinery c) exchanger d) contact e) gas f) bungle g) parts h) temperature i) plant j) flow |
Exercise 59. Give nouns related to the following verbs. Identify suffixes, if any. Translate the pairs.
Transform, measure, generate, attach, exchange, separate, refrigerate, process, arrange, enter, design, perform, add, resist, define.
Exercise 60. Find words in text 5 that can be used both as a noun and a verb. Translate the pairs.
| Model: force - to force сила - примушувати |
Exercise 61. Fill in the gaps with appropriate prepositions:
for, on, to, in, by, of, between, as.
1. Heated fluid is supplied … boilers. 2. Heat exchangers are used … high pressure applications. 3. Heat exchanger efficiency depends … several thermal design features, such as tube diameter, thickness, length and configuration. 4. The human lungs serve … an efficient heat exchanger due … their large surface area to volume ratio. 5. Heat exchangers occur naturally … the circulation system … fish and whales. 6. Tubular heat exchangers can be cleaned … different methods. 7. Heat exchangers are used … many industries. 8. Choosing the right heat exchanger requires some knowledge … the different heat exchanger types. 9. Direct contact heat exchangers involve heat transfer … hot and cold streams.
Exercise 62. Use the proper Active or Passive form of the verbs in brackets.
1. A heat engine is a physical or theoretical device that (convert) thermal energy to mechanical work. 2. John Ericsson (develop) an external heated engine. 3. A fire-tube boiler usually (have) a comparatively low rate of steam production, but high steam storage capacity. 4. For much of the Victorian ‘age of steam’, the only material used for boiler making (be) the highest grade wrought iron. 5. The first piston engine (build) in 1697 by Thomas Savery. 6. Recently the company (start) producing spiral heat exchangers. 7. Heat exchangers (use) in industry both for cooling and heating large scale industrial processes. 8. The source of heat for a boiler (be) combustion of any of several fuels, such as wood, coal, oil or natural gas. 9. A variety of companies (start) using water borne oscillation technology to prevent biofouling. 10. Nuclear fission (use) as a heat source for generating steam. 11. Tube diameter and length must (take) into account when designing tubular heat exchangers. 12. Plate heat exchangers usually (make) of aluminum alloys.
Exercise 63. Work in pairs. Make questions for each answer below with reference to text 5.
1. Heat exchangers are widely used in space heating, refrigeration, air conditioning, power plants, etc. 2. One common example of a heat exchanger is a car radiator. 3. Heat exchangers may be classified according to their flow arrangement. 4. The countercurrent design is the most efficient. 5. Tubular heat exchangers consist of a series of tubes. 6. Plate heat exchangers are usually made of aluminum alloys to provide higher heat transfer. 7. Heat exchangers are widely used for air conditioning of buildings and vehicles. 8. Plate heat exchangers need to be disassembled and cleaned periodically. 9. In commercial aircraft, heat exchangers are used to take heat from the engine oil system to heat cold fuel. 10. The log mean temperature difference is a measure of the effectiveness of the heat exchanger in transferring heat energy.
Exercise 64. Translate into English.
1. Теплообмінники широко використовуються як у промисловості, так і в домашньому господарстві. 2. Конструкція теплообмінника визначається типом рідини та її термодинамічними властивостями. 3. Найпростіша модель теплообмінника складається з двох прямих з’єднаних труб, якими тече рідина певної температури. 4. Теоретично у теплообмінниках повинні використовуватись довгі труби малого діаметру, проте у таких трубах швидко утворюється накип, який важко вичищати. 5. Трубчасті теплообмінники дуже часто застосовують для охолодження газів і рідин на нафтоочисних заводах. 6. Річна вода використовується як охолоджуюча рідина у теплообмінниках. 7. Накип та осад зменшують ефективність процесу теплообміну. 8. На літаках теплообмінники є невід’ємною частиною мастильної системи двигуна.
Exercise 62. Memorize the following words and word combinations to text 6.
Large-scale – великомасштабний
waste – марнотрата
waste water – стічна / відпрацьована вода
wine-brewery industry – виноробна промисловість
save – заощаджувати; економити
treatment – оброблення
tailored – розрахований; пристосований
density – густина, щільність
viscosity – в’язкість
otherwise – інакше; а то; а ні, то
digester – автоклав; варильний котел
pollutant – забруднююча речовина
freezing – замерзання; заморожування
evaporate – випаровувати(ся)
condense – конденсувати
incoming – вхідний
distillation – дистиляція, перегонка; ректифікація
anaerobic – анаеробний
distillation tower – дистиляційна / перегінна колона
direct current / uniflow heat exchanger – прямоточний теплообмінник
steam generator – парогенератор, паровий котел
surface condenser – поверхневий конденсатор
air coil – змійовик
serpentine – змієвидний; змійовик
lungs – легені
artery – артерія
vein – вена
countercurrent heat exchanger – теплообмінник із зустрічними потоками
intertwine – переплітатися
whale - кит
tongue – язик
disassemble –демонтувати
acid – кислота
cross flow heat exchanger – теплообмінник з поперечними / перехресними потоками
sandblasting – піскоструменеве очищення
drill rod – бур
purification – очищення
jet – струмінь
Exercise 66. Read and translate text 6.Make up the plan of its key ideas.