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And maintenance of heat exchangers
Heat exchangers are widely used in industry both for cooling and heating large scale industrial processes, some of which include:
- waste water treatment;
- petroleum industry;
- wine-brewery industry;
- refrigeration system.
The type and size of heat exchanger can be tailored to suit a process depending on the type of fluid, its place, temperature, density, viscosity, pressure, chemical composition and various other thermodynamic properties.
There are three main types of flows in heat exchangers.
1.Countercurrent Flow: both fluids flow in opposite directions, and are used for liquid-liquid heating, condensing and gas cooling applications. Units are usually mounted vertically when condensing vapour and horizontally when condensing high concentrations of solids.
2.Cross Flow: one liquid is in cross flow to another. This type of flow is suitable for handling low density gases.
3.Direct current / Uniflow: both fluids flow in one direction. They are widely used for cooling and heating large scale industrial processes.
In many industrial processes there is waste of energy or heat. Heat exchangers can be used to recover heat and put it to use by heating a different stream in the process. This practice saves a lot of money in industry as the heat supplied to other streams from the heat exchangers would otherwise come from an external source which is more expensive and more harmful to the environment.
In the waste water treatment industry heat exchangers play a vital role in maintaining optimal temperatures within anaerobic digesters so as to stimulate the growth of microbes which remove pollutants from the waste water.
In commercial aircraft heat exchangers are used to take heat from the engine oil system to heat cold fuel. This improves fuel efficiency, as well as reduces the possibility of water freezing.
In addition to heating up or cooling down fluids in just a single phase, heat exchangers can be used either to heat a liquid to evaporate (or boil) it or to cool a vapour and condense it to a liquid. In chemical plants and refineries heat exchangers are used to heat incoming fluid in distillation towers.
Heating and power plants which have steam-driven turbines commonly use heat exchangers to boil water into steam. Heat exchangers or similar for producing steam from water are often called boilers or steam generators.
In the nuclear power plants called pressurized water reactors, special large heat exchanger passes heat from the primary (reactor plant) system to the secondary (steam plant) system, producing steam from water. All fossil-fuelled and nuclear power plants using steam-driven turbines have surface condensers to convert the exhaust steam from the turbines into water for re-use.
One of the widest uses of heat exchangers is for air conditioning of buildings and vehicles. This class of heat exchangers is commonly called air coils, or just coils due to their serpentine internal tubing. In vehicles, heat coils are often called heater cores.
In nature the human lungs also serve as an extremely efficient heat exchanger due to their large surface area to volume ratio.
“Countercurrent” heat exchangers occur naturally in the circulation system of fish and whales. Arteries carrying warm blood are intertwined with veins carrying cold blood to exchange heat with the cold venous blood. This reduces the overall heat loss in cold water. “Heat exchangers” are also present in the tongue of whales as large volumes of water flow through their mouths.
Heat exchangers need to be disassembled and cleaned periodically. Tubular heat exchangers can be cleaned by such methods as acid cleaning, sandblasting, high-pressure water jet or drill rods.
In large-scale cooling water systems, water treatment such as purification, addition of chemicals is used to minimize fouling of the heat exchanger equipment.
Exercise 67. Translate the following word combinations and use them in sentences of your own.
Waste water treatment, save a lot of money, external source of heat, harmful to the environment, play a vital role, remove pollutants, engine oil system, thermal power plant, steam-driven turbine, nuclear power plant, fossil-fuelled power plant, similar units, incoming fluid, overall heat loss, high-pressure water jet.
Exercise 68. Write adjectives related to the following nouns. Name suffixes used to form adjectives. Translate the derivative chains.
Use, industry, viscosity, commerce, harm, environment, efficiency, chemistry, simplicity, variety, practice, tube, vein, artery, period, purification, waste, nucleus, nature, difference, expense, heat, possibility, addition, system, circle, blood, presence, method..
Exercise 69 Give corresponding adverbs. Translate the pairs.
Recent, rapid, current, complete, common, good, fast, extreme, late, natural, efficient, hard, final, easy, full, main, wide, direct, usual, horizontal, vertical, periodical, primary.
Exercise 70. Put the adjectives and adverbs in brackets into the comparative or superlative form.
- Oil is (important) of all fossil fuels today.
- External source of heat is (expensive) and (harmful) to the environment than heat supplied by heat exchange.
- Shell and tube exchangers are (efficient) for cooling and heating large scale industrial processes.
- Plate heat exchangers have (large) surface area and fluid flow passages for heat transfer than tubular heat exchangers.
- Direct contact heat exchangers are used (often) in air conditioning and humidification.
- One of the (wide) uses of heat exchangers is for air conditioning of buildings and vehicles.
- Thin-walled heat exchangers can (easily) be damaged or destroyed than others.
- Spiral heat exchangers may be used to have (little) pressure drop, (high) thermal efficiency and (low) energy costs.
- River water is often used as cooling water so fouling is the (serious) problem in some heat exchangers.
- The (common) example of a heat exchanger is a radiator in a car.
Exercise 71. Translate and comment upon the following verb forms.
are used, can be recovered, will be removed, is producing, is being carried, need to be disassembled, must be cleaned, has converted, have been built, may have been damaged.
Exercise 72. Complete the sentences putting the verbs in brackets into correct Active or Passive tense forms.
- The shell (make) of steel and (stiffen) to provide higher corrosive resistant tubes.
- To overcome corrosion some manufactures (provide) higher corrosive resistant tubes.
- As the steam flow (cause) the turbine to rotate, the electric generator (turn) and electricity (produce).
- This technology must (improve) the quality of heat exchangers.
- The tube may (make) up of materials having different chemical composition.
- Heat exchangers (classify) according to their flow arrangement.
- Heat exchangers need (disassemble) and (clean) periodically.
- Heat (take) from the engine oil system to (heat) cold fuel.
- Heat exchangers can (use) either to (heat) a liquid or (cool) vapour.
- Exhaust steam from the turbines (convert) into water for re-use.
Exercise 73. Work in pairs. Translate the questions into English and find the correct answers.
| 1. Для чого використовують теплообмінники? | a) Tubular heat exchangers are cleaned by such methods as acid cleaning, sand blasting, high-pressure water jets or drill rods. |
| 2. Від чого залежить тип і розмір теплообмінника? | b) Heat exchangers are used in industry both for cooling and heating large scale industrial processes. |
| 3. Що називається конденсатором у теплотехніці? | c) They convert the exhaust steam from turbines into water for re-use. |
| 4. Яким чином працюють теплообмінники на теплоелектростанціях? | d) The type and size of heat exchanger depends on thermodynamic properties of fluid. |
| 5. Які технології застосовують для очищення труб теплообмінників? | e) A condenser is the commonly used term for a water cooling shell and tube heat exchanger. |
Exercise 74. Translate into English.
1. Конденсатор в теплотехніці – це теплообмінник, який використовують для конденсації пари шляхом охолодження. 2. Теплообмінники застосовують на теплових і атомних електростанціях для конденсації відпрацьованої в турбінах пари. 3. Теплообмінники поділяються на прямоточні, теплообмінники із зустрічними та перехресними потоками в залежності від напрямку потоку рідини. 4. У процесі експлуатації труби теплообмінника забруднюються, що призводить до зниження ефективності роботи турбіни. 5. Сучасні конструкції теплообмінників дозволяють виконувати механічне очищення труби на певній ділянці без зупинки процесу. 6. Тип і розмір теплообмінника залежать від тиску та інших термодинамічних властивостей. 7. На літаках теплообмінники є складовою частиною системи змащення двигуна і використовуються для нагрівання палива. 8. Додавання хімічних речовин до рідини зменшує утворення накипу у трубах.
Exercise 75. Discuss the following questions in groups.
1.How are shell and tube heat exchangers cleaned?
2.How often is it necessary to clean tubular heat exchangers? Why?
3.What do heat exchangers serve for in heating and power plants?
4.Why are heat exchangers used in aircraft engine oil system?
Exercise 76. Choose the correct verb form.
1. The word ‘energy’ … from Greek word.
a) derived;
b) derive;
c) derives;
d) have derived.
2. The Laws … on the idea of conservation of energy.
a) based;
b) will base;
c) is based;
d) are based.
3. This point of view … by many scientists.
a) shared;
b) is shared;
c) were shared;
d) are shared.
4. Heat … from a hot area to a cold area.
a) is moved;
b) move;
c) moves;
d) have moved.
5. Thermodynamics … by second year students.
a) are studied;
b) study;
c) were studying;
d) is studied.
6. The science … of need to increase the efficiency of early steam engines.
a) developed out;
b) have developed out;
c) develops;
d) will develop.
7. Energy … in many ways.
a) are measured;
b) measure;
c) measures;
d) is measured.
8. Energy … in one form or another.
a) have existed;
b) are existing;
c) existed;
d) has existed.
9. The term thermodynamics … by James Joule in 1859.
a) coined;
b) coins;
c) have been coined;
d) was coined.
10. The new textbook on thermodynamics already … .
a) was writing;
b) has been written;
c) wrote;
d) will write.
11. The type and size of heat exchanger …
a) choose;
b) can be chosen;
c) is choosing;
d) must have chosen.
12. Heat exchangers play a vital role in … optimal temperatures.
a) maintain;
b) maintains;
c) maintained;
d) maintaining.
13. James Joule who … in the 19th century discovered that heat is a type of energy.
a) live;
b) has lived;
c) lived;
d) lives.
14. There … nothing to transfer the energy from the Sun to the Earth.
a) be;
b) being;
c) is;
d) are.