Old and Modern Theories of Heat

Famous People

Gas Burners

Gas is known to be burnt in many industrial furnaces used for heat treating, metal melting, steam generation etc., as well as in commercial applications such as pizza ovens, baker’s ovens, dishwashers, etc., because of its cleanliness, ease of control of furnace atmosphere, ability to produce a long slow burning flame with uniform and gradual energy liberation, and ease of temperature regulation. Environmentally, natural gas burns cleaner than other fossil fuels, such as oil and coal, and produces less greenhouse gases. For an equivalent amount of heat, burning natural gas produces about 30% less carbon dioxide than burning petroleum and about 45% less than burning coal. Thus, power generation using natural gas is the cleanest source of power using fossil fuels, and this technology is widely used wherever gas can be obtained at a reasonable cost.

A gas burner is a device that burns a continuous stream of a flammable gas, such as natural gas. The amount of air mixed with the gas stream affects the completeness of the combustion reaction in the flame. Less air provides an incomplete and thus cooler reaction, while a gas stream well mixed with air provides a complete and hotter reaction. For steam generation, where a short flame is desired in order to reduce the required furnace volume, the burner is expected to provide for rapid and thorough mixing of the fuel and air in the correct proportions for good combustion. For such applications, a good burner is primarily a proportioner and a mixing device. When a molecule of combustible gas is mixed with the oxygen at a temperature above the ignition temperature, combustion is practically instantaneous. In industrial furnaces where long "lazy" flames are desired, slow and gradual mixing of the air and fuel in the furnace is required.

Natural gas is used for steam generation in gas producing areas and in areas where coal is not available at a competitive price. It is also used extensively in coal or oil-fired units during the summer months, when the houses are not heated so there is a temporary surplus of natural gas. Because of the variable or seasonal supply of gaseous fuels, combination burners have been developed to permit the simultaneous burning of the available gas together with pulverized coal or oil.

· Transcribe the following words, practice reading them, give Russian equivalents:

Burner, furnace, oven, environment, fossil fuel, carbon dioxide, cycle, surplus, simultaneous, pulverize, molecule, combustible, oxygen, instantaneous.

· Are the following sentences true or false? Correct the false sentences

1. Burning natural gas in industrial furnaces has many disadvantages.

2. Gas is never used in coal and oil-fired units.

3. Combination burners permit the burning of gas together with pulverized coal and oil to

produce steam.

4. Combustion is instantaneous when combustible gas is mixed with oxygen at a

temperature below the ignition temperature.

5. In industrial furnaces rapid and thorough mixing of the fuel and air in the correct

proportions are necessary for good combustion.

· Answer the questions.

1. What are the advantages of burning gas in industrial furnaces?

2. What is the role of air in a gas burner?

2. In what regions is gas used for steam generation?

3. What conditions are necessary for instantaneous combustion of gas?

4. What kind of flame is desired for steam generation, and why?

5. How can short and long flames be achieved?

6. What is the advantage of combination burners?

Joseph Louis Gay-Lussac (1778-1850)

Gay Lussac was a French chemist and physicist. He grew up during both the French and Chemical Revolutions. When he was about twenty-four years old, Gay-Lussac formulated the law that a gas expands linearly with a fixed pressure and rising temperature. He did this in 1802, but the discovery later became known as Charles's Law, in honor of Jacques Charles, who had arrived at nearly the same conclusion 15 years earlier but had not published it. Gay Lussac made several daring ascents of over 7,000 meters above sea level in hydrogen-filled balloons. That allowed him to investigate other aspects of gases. He gathered magnetic measurements at various altitudes, took pressure, temperature, and humidity measurements and samples of air, which he later analyzed chemically. Perhaps what he is most well-known for is the Law of Combining Volumes of Gases which states that the volumes of reacting gases and their products at the same temperature and pressure can be expressed as ratios of small whole numbers. E.g. hydrogen combines with oxygen in a 2:1 ratio by volume to produce a volume of water vapor equal to the initial volume of hydrogen or twice the initial volume of oxygen. Gay-Lussac was respected by his colleagues for his careful, elegant, experimental work. He devised many new types of apparatus such as the portable barometer, an improved pipette and burette.

Unit X. The Infinitive Construction Introduced by the Preposition ‘’for’’

Read the following sentences. State the voice and the tense forms of the predicates. Translate the sentences into Russian, paying attention to the infinitive construction.

1. The temperature was too low for the substance to ignite.

2. For these experiments to be carried out successfully we shall follow some rules.

3. A new computer program is needed for these data to be processed as soon as possible.

4. For this effect to be understood researchers carried out a lot of experiments.

5. The speed of the particles is too high for us to study in detail.

6. The time taken for equilibrium conditions to occur is small.

7. The lithium nucleus is too small for so many collisions to occur.

8. For a force to exist there must be two objects involved.

9. Here is one more point for the speaker to explain.

10. The tendency was for the steam to condense.

11. For a reaction to take place, an A molecule must first meet a B molecule.

12. It is possible for the reaction to occur.

13. The only conclusion for him to make was the following.

14. The tendency for the substance to become ionized at high temperatures was investigated.

15. It is not usual for the phosphatic uranium materials to be used as a commercial source for uranium.

· Read the following text. Find the predicate in each sentence and state the voice and tense form. Which of the sentences contain the infinitive construction?Translate the text into Russian.

Till the eighteenth century, scientists considered heat to be an invisible fluid with special properties called caloric (теплород) (from the Latin word for heat). They believed the caloric to flow from one body to another. According to this theory while a body was heated, the caloric particles were attracted to each individual molecule but repelled each other. The more caloric the molecule had, the more the substance expanded.

The expansion of gases according to this theory was explained in the following way. The theory said that gases expanded much more than solids because each gas molecule was so thickly coated with caloric that the caloric repelling force between molecules was greater than any attracting force.

The caloric theory seemed to have explained a lot of things about heat. But experiments found more and more points for which the caloric theory could not provide explanation. For them to be explained a new theory was needed.

In 1738, Swiss scientist Daniel Bernoulli published Hydrodynamica which laid the basis for the kinetic theory of gases. In this work, Bernoulli positioned the argument, still used to this day, that gases consist of great numbers of molecules moving in all directions, that their impact on a surface causes the gas pressure that we feel, and heat is simply the kinetic energy of their motion. The faster the molecule move, the higher is the temperature of the molecule. In other words, the temperature of a body increases when kinetic energy increases. The new theory was given the name of kinetic theory (from the Greek word kino which means 'movement'). Later the kinetic theory was developed by such scientists as Count Rumford, James Clark Maxwell, and others.

According to the molecular-kinetic theory, the molecules of a solid body are always in a state of slight vibration about their fixed positions. The higher the temperature of a body, the more widely all the molecules vibrate, each of the molecules moving slightly apart from the others. The lower the temperature of a body, the less widely its molecules vibrate, moving closer to each other. Due to such changes, bodies either expand or contract.

· Transcribe the following words, practice reading them, give Russian equivalents:

Theory, century, scientist, invisible, substance, tiny, surround, expand, expansion, experiment, provide, explanation, elaboration, vibrate, collide

· Are the following sentences true or false? Correct the false sentences

1. According to the kinetic theory heat was considered to be an invisible fluid with

special properties.

2. Scientists believed caloric to repel the molecules of a substance.

3. Caloric theory explained all the things about heat.

4. The molecules of a solid body do not move.

5. Bodies can either expand or contract because of temperature changes.

6. According to the kinetic theory, heat is considered to be a form of energy.

· Answer the questions.

1. What theory of heat existed until the 18-th century?

2. What did the scientists of the past call ‘caloric’?

3. How did the caloric theory explain the expansion of substances with heat?

4. Why was a new theory of heat needed?

5. What is heat according to the new theory?

6. What does the temperature of the molecule depend on according to the new theory of

heat?

7. Why was the new theory named ‘kinetic theory’?

8. Do the molecules of a solid body remain motionless?

9. Why do bodies expand or contract according to the kinetic theory?

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