The role of heat engines in drilling. The role of heat engines in human life

It is currently impossible to name any area production activities person, wherever used thermal installations. Space technology, metallurgy, machine tool building, transport, energy, Agriculture, chemical industry, production food products- not far full list industries National economy, where it is necessary to decide scientific and technical issues related to heating installations.

In heat engines and thermal installations, heat is converted into work or work into heat.

A steam turbine is a heat engine in which potential energy the steam turns into kinetic, and kinetic into mechanical energy of rotation of the rotor. The turbine rotor is directly connected to the shaft of the working machine, which can be an electric generator, a propeller, etc.

The use of heat engines in railway transport especially large, because With the advent of diesel locomotives on railways, the transportation of the bulk of goods and passengers in all directions has been facilitated. Diesel locomotives appeared on Soviet railways more than half a century ago, on the initiative of V.I. Lenin. Diesels drive the diesel locomotive directly, and with the help of an electric transmission - generators electric current and electric motors. On the same shaft with each diesel locomotive there is a direct current generator. The electric current generated by the generator enters the traction motors located on the axles of the diesel locomotive. A diesel locomotive is more complex than an electric locomotive and costs more, but it does not require a contact network or traction substations. The diesel locomotive can be used wherever it is installed railways, and this is its huge advantage. Diesel is an economical engine; the diesel locomotive has enough fuel for long haul. To transport large and heavy cargo, heavy trucks were built, where instead of gasoline engines more powerful diesel engines appeared. The same engines operate on tractors, combines, and ships. The use of these engines greatly facilitates human work. In 1897, the German engineer R. Diesel proposed a compression ignition engine that could run not only on gasoline, but also on any other fuel: kerosene, oil. The engines were also called diesels.

The history of heat engines goes back a long way. More than two thousand years ago, in the 3rd century BC. era, the great Greek mechanic and mathematician Archimedes built a cannon that fired using steam.

There are hundreds of millions of heat engines in the world today. For example, engines internal combustion installed on cars, ships, tractors, motor boats, etc. The observation that changes in the temperature of bodies are constantly accompanied by changes in their volumes dates back to distant antiquity, however, the definition absolute value the relationship of these changes belongs only to modern times. Before the invention of thermometers, such definitions, of course, could not be thought of, but with the development of thermometry, an accurate study of this connection became absolutely necessary. Moreover, at the end of the last 18th century and the beginning of the present 19th century, a lot of various phenomena, which encouraged me to take careful measurements of the expansion of bodies due to heat; these were: the need to correct barometric readings when determining altitudes, the determination of astronomical refraction, the question of the elasticity of gases and vapors, the gradually increasing use of metals for scientific instruments and technical purposes, etc.

First of all, naturally, I turned to the definition of air expansion, which in its magnitude was most striking and seemed most easily measurable. Many physicists soon received a large number of results, but some of them are quite contradictory. Amonton to regulate his normal thermometer measured the expansion of air when heated from 0° to 80° R and relatively accurately determined it to be 0.380 of its volume at 0°. On the other hand, Nuge in 1705, using a slightly modified device, once obtained a number twice as large, and another time a number even 16 times larger. La Hire (1708) also received 1.5 and even 3.5 instead of the Amonton number. Goakesby (1709) found the number 0.455; Kryukius (1720) -- 0.411; Logs -- 0.333; Bonn -- 0.462; Muschenbreck -- 0.500; Lambert (“Pyrometrie”, p. 47) - 0.375; Deluc -- 0.372; I. T. Meyer - 0.3755 and 0.3656; Saussure -- 0.339; Vandermonde, Berthollet and Monge received (1786) - 0.4328. Priestley, who obtained a number of 0.9375 significantly deviating from the true number for the expansion of air, argued, moreover, that oxygen, nitrogen, hydrogen, carbonic acid, vapors of nitric, hydrochloric, sulfuric, hydrofluoric acids and ammonia - they all differ in their expansion from air. G. G. Schmidt (“Green’s Neues Journ.”, IV, p. 379) obtained for the expansion of air the number 0.3574, for oxygen 0.3213, and finally, for hydrogen, carbonic acid and nitrogen 0.4400, 0 .4352, 0.4787. Morveau and Duvernoy sided with Priestley's opinion, but generally found that the expansion of gases is not entirely proportional to the change in temperature.

Theoretical material

Since ancient times, man has wanted to be free from physical effort or to ease it when moving something, to have greater strength, speed.

Legends were created about airplane carpets, seven-league boots and wizards carrying a person to distant lands with the wave of a wand. When carrying heavy loads, people invented carts because it’s easier to roll. Then they adapted animals - oxen, deer, dogs, and most of all horses. This is how carts and carriages appeared. In carriages, people sought comfort, improving them more and more.

The desire of people to increase speed also accelerated the change of events in the history of transport development. From the Greek "autos" - "oneself" and the Latin "mobilis" - "mobile" in European languages The adjective “self-propelled” was formed, literally “automobile”.

It applied to watches, automatic dolls, to all sorts of mechanisms, in general, to everything that served as a kind of addition to the “continuation”, “improvement” of a person. In the 18th century, they tried to replace manpower with steam power and applied the term “car” to trackless carts.

Why is the age of a car started from the first “gasoline cars” with an internal combustion engine, invented and built in 1885-1886? As if forgetting about steam and battery (electric) crews. The fact is that the internal combustion engine made a real revolution in transport technology. For a long time, it turned out to be the most consistent with the idea of ​​a car and therefore retained its dominant position for a long time. The share of vehicles with internal combustion engines today accounts for more than 99.9% of global road transport.<Приложение 1>

Main parts heat engine

IN modern technology mechanical energy is obtained mainly from the internal energy of the fuel. Devices in which internal energy is converted into mechanical energy are called heat engines. To perform work by burning fuel in a device called a heater, you can use a cylinder in which gas is heated and expanded and moves a piston.<Приложение 3>The gas whose expansion causes the piston to move is called the working fluid. The gas expands because its pressure is higher than the external pressure. But as the gas expands, its pressure drops, and sooner or later it will become equal to the external pressure. Then the expansion of the gas will end and it will stop doing work.

What should be done so that the operation of the heat engine does not stop? In order for the engine to operate continuously, it is necessary that the piston, after expanding the gas, returns to its original position each time, compressing the gas to its original state. Compression of a gas can only occur under the influence of an external force, which in this case does work (the gas pressure force in this case does negative work). After this, gas expansion and compression processes can occur again. This means that the operation of a heat engine must consist of periodically repeating processes (cycles) of expansion and compression.

Picture 1

Figure 1 graphically depicts the processes of gas expansion (line AB) and compression to the original volume (line CD). The work done by the gas during the expansion process is positive (AF > 0) and is numerically equal to the area of ​​the figure ABEF. The gas work done during compression is negative (since AF< 0) и численно равна площади фигуры CDEF. Полезная работа за этот цикл численно равна разности площадей под кривыми АВ и CD (закрашена на рисунке).

The presence of a heater, working fluid and refrigerator is essential necessary condition for continuous cyclic operation of any heat engine.

Heat engine efficiency

The working fluid, receiving a certain amount of heat Q1 from the heater, gives part of this amount of heat, equal in modulus |Q2|, to the refrigerator. Therefore, the work done cannot be greater than A = Q1 -- |Q2|. The ratio of this work to the amount of heat received by the expanding gas from the heater is called the efficiency of the heat engine:

The efficiency of a heat engine operating in a closed cycle is always less than one. The task of thermal power engineering is to make the efficiency as high as possible, that is, to use as much of the heat received from the heater as possible to produce work. How can this be achieved?

For the first time, the most perfect cyclic process, consisting of isotherms and adiabats, was proposed by the French physicist and engineer S. Carnot in 1824.

Carnot cycle.

Let us assume that the gas is in a cylinder, the walls and piston of which are made of a heat-insulating material, and the bottom is made of a material with high thermal conductivity. The volume occupied by the gas is equal to V1.

Figure 2

Let's bring the cylinder into contact with the heater (Figure 2) and allow the gas to expand isothermally and do work. The gas receives a certain amount of heat Q1 from the heater. This process is graphically represented by an isotherm (curve AB).

Figure 3

When the gas volume becomes equal to a certain value V1"< V2, дно цилиндра изолируют от нагревателя, после этого газ расширяется адиабатно до объема V2, соответствующего максимально возможному ходу поршня в цилиндре (адиабата ВС). При этом газ охлаждается до температуры T2 < T1.

The cooled gas can now be compressed isothermally at temperature T2. To do this, it must be brought into contact with a body having the same temperature T2, i.e., with a refrigerator, and the gas must be compressed by an external force. However, in this process the gas will not return to its original state - its temperature will always be lower than T1.

Therefore, isothermal compression is brought to a certain intermediate volume V2">V1 (CD isotherm). In this case, the gas gives up a certain amount of heat Q2 to the refrigerator, equal to the work of compression performed on it. After this, the gas is compressed adiabatically to volume V1, while its temperature rises to T1 (adiabatic DA) Now the gas has returned to its original state, in which its volume is V1, temperature is T1, pressure is p1, and the cycle can be repeated again.

So, in the ABC section the gas does work (A > 0), and in the CDA section the work is done on the gas (A< 0). На участках ВС и AD работа совершается только за счет изменения внутренней энергии газа. Поскольку изменение внутренней энергии UBC = -UDA, то и работы при адиабатных процессах равны: АВС = -АDA. Следовательно, full time job, performed per cycle, is determined by the difference in work performed during isothermal processes (sections AB and CD). Numerically, this work is equal to the area of ​​the figure bounded by the ABCD cycle curve.

Only part of the amount of heat QT received from the heater, equal to QT1- |QT2|, is actually converted into useful work. So, in the Carnot cycle useful work A = QT1 - |QT2|.

Internal energy reserves in earth's crust and oceans can be considered practically unlimited. But having energy reserves is not enough. It is necessary to be able to use energy to set in motion machine tools in factories and factories, vehicles, tractors and other machines, to rotate the rotors of electric current generators, etc. Humanity needs engines - devices capable of doing work.

The irreversibility of processes in nature imposes certain restrictions on the possibility of using internal energy to perform work in heat engines.

The role of heat engines in the development of thermal power engineering and transport. Most of the engines on Earth are heat engines, i.e. devices that convert the internal energy of fuel into mechanical energy.

Of greatest importance is the use of heat engines (mainly powerful steam turbines) in thermal power plants, where they drive the rotors of electric current generators. More than 80% of all electricity in our country is generated at thermal power plants.

Heat engines, steam turbines - also installed on all nuclear power plants. At these stations to get steam high temperature The energy of atomic nuclei is used.

Further, all major types of modern transport predominantly use heat engines. On road transport use piston internal combustion engines with external education combustible mixture (carburetor engines) and engines with the formation of a combustible mixture directly inside the cylinders (diesels). The same engines are installed on tractors, which are indispensable in agriculture.

In railway transport until the middle of the 20th century. The main engine was a steam engine. Now they mainly use diesel locomotives with diesel units and electric locomotives. But electric locomotives also ultimately receive energy mainly from thermal engines of power plants.

Water transport uses both internal combustion engines and powerful steam turbines for large ships.

In aviation, piston engines are installed on light aircraft, and turbojet and jet engines, which also belong to thermal engines, are installed on huge airliners. Jet engines are also applied to space rockets.

Without heat engines, modern civilization is unthinkable. We would not have an abundance of cheap electricity and would be deprived of all forms of rapid transport.

The main condition for the operation of heat engines. In all heat engines, fuel during combustion increases the temperature of the working fluid by hundreds or thousands of degrees compared to the environment. In this case, the pressure of the working fluid increases compared to the pressure environment, i.e. the atmosphere, and the body does work due to its internal energy. The working fluid of all heat engines is gas.

No heat engine can operate at the same temperature of its working fluid and the environment. Able thermal equilibrium no macroscopic processes occur; in particular, no work can be done.

A heat engine performs work using internal energy in the process of transferring heat from hotter bodies to colder ones. In this case, the work performed is always less than the amount of heat received by the engine from the hot body (heater). Some of the heat is transferred to a colder body (refrigerator).

The role of the refrigerator. Let's find out why, when a heat engine operates, some of the heat is inevitably transferred to the refrigerator.

During adiabatic expansion of gas in a cylinder (Fig. 45), work is done due to a decrease in internal energy without heat transfer to the refrigerator. According to formula (4.14). In an isothermal process, all heat transferred to the gas turns out to be equal to work; .

However, in both the first and second processes, work is done during a single expansion of the gas to a pressure equal to the external one (for example, atmospheric pressure). The engine must be running long time. This is only possible if all parts of the engine (pistons, valves, etc.) make movements that are repeated at certain intervals. The engine must periodically return to its original state after one operating cycle; or the engine must undergo a time-invariant (stationary) process (for example, continuous rotation of a turbine).

To return the gas in the cylinder to its original state, it must be compressed. To compress a gas, work must be done on it. The work of compression will be less than the work done by the gas itself during expansion if the gas is compressed at a lower temperature, and therefore at a lower pressure, than what happened during the expansion of the gas. To do this, it is necessary to cool the gas before compression or during the compression process, transferring a certain amount of heat to the refrigerator.

In engines used in practice, the completed work (exhaust) gas (or steam) is not cooled before subsequent compression, but is released from the engine and the next operating cycle begins with a new portion of gas. The exhaust gas has a higher temperature than the surrounding bodies and transfers some heat to them.

To rotate a steam turbine, hot steam under high pressure is continuously supplied to its blades, which, after completing the work, is cooled and removed from the turbine. As the steam cools and condenses, it transfers heat to surrounding bodies.

In a steam turbine or machine, the heater is a steam boiler, and the refrigerator is the atmosphere or special devices for cooling and condensing exhaust steam - condensers. In internal combustion engines, an increase in temperature occurs when fuel is burned inside the engine, and the “heater” is the hot combustion products themselves. The refrigerator also serves as an atmosphere into which exhaust gases are released.

The schematic diagram of a heat engine is shown on the color inset. The working fluid of the engine receives an amount of heat from the heater, does work A and transfers the amount of heat to the refrigerator

Another formulation of the second law of thermodynamics. The impossibility of completely converting internal energy into work in heat engines that periodically return to their original state is due to the irreversibility of processes in nature and underlies another formulation of the second law of thermodynamics.

This formulation belongs to the English scientist W. Kelvin: it is impossible to carry out such a periodic process, the only result of which would be the production of work due to heat taken from one source.

Both formulations of the second law of thermodynamics mutually determine each other. If heat could spontaneously transfer from the refrigerator to the heater, then internal energy could be completely converted into work by any heat engine.

Heat engines are necessary to generate electricity to drive most transport vehicles.

Of greatest importance is the use of powerful steam turbines in power plants to rotate generator rotors. Steam turbines are also installed at nuclear power plants, where the energy of atomic nuclei is used to produce high-temperature steam.

Modern transport uses all types of heat engines. In cars, tractors, self-propelled combines, diesel locomotives, piston internal combustion engines are used, in aviation - gas turbines, in space rockets - jet engines.

Heat engines have some harmful effects on the environment:

1. Heat engine efficiency η < 50 %, следовательно, большая часть энергии топлива рассеивается в окружающем пространстве, вредно влияя на общую экологическую обстановку:
2. thermal power plants and cars emit fuel combustion products harmful to plants, animals and humans (sulfur compounds, carbon oxides, nitrogen oxides, etc.);
3. increased concentration carbon dioxide in the atmosphere increases" Greenhouse effect"Earth.

In this regard, the problem of nature conservation has become very important. To protect the environment it is necessary to ensure:

1. effective cleaning of exhaust gases emitted into the atmosphere;
2. using high-quality fuel, creating conditions for more complete combustion;
3. increasing the efficiency of heat engines by reducing friction losses and complete combustion of fuel, etc.

The use of hydrogen as a fuel for heat engines is promising: the combustion of hydrogen produces water. Intensive research is underway to create electric vehicles that can replace gasoline-powered cars.

Literature

Aksenovich L. A. Physics in high school: Theory. Tasks. Tests: Textbook. allowance for institutions providing general education. environment, education / L. A. Aksenovich, N. N. Rakina, K. S. Farino; Ed. K. S. Farino. - Mn.: Adukatsiya i vyakhavanne, 2004. - P. 165.

Technical thermodynamics. Basic concepts and definitions

Kartashevich, A.N., Kostenich, V.G., Pontalev, O.V.

K 27 Thermal engineering: course of lectures. Part 1. – Gorki: Belarusian State Agricultural Academy, 2011. 48 p.

ISBN 978-985-467-319-6

The main parameters and equations of state are considered ideal gases, concept and types of heat capacity, ideal gas mixtures and methods for determining their parameters. The formulations and basic provisions of the first and second laws of thermodynamics are given, as well as an analysis of the basic thermodynamic processes of ideal gases.

For students of specialties 1-74 06 01 – Technical support agricultural production processes, 1‑74 06 04 – Technical support for reclamation and water management works, 1‑74 06 06 – Logistics support for the agro-industrial complex.

Tables 4. Figures 27. Bibliography. 12.

Reviewers: A.S. DOBYSHEV, Doctor of Engineering. Sciences, Professor, Head. Department of Mechanization of Livestock Husbandry and Electrification of Agricultural Production (EI “BSAHA”); V.G. SAMOSYUK, Ph.D. econ. sciences, CEO Republican Unitary Enterprise "Scientific and Practical Center of the National Academy of Sciences of Belarus for Agricultural Mechanization".

UDC 621.1 (075.8)

BBK 31.3ya73

Heat is used in all areas of human activity - to generate electricity, drive vehicles and various mechanisms, heat premises, as well as for technological needs.

The main way to obtain heat today is the combustion of fossil fuels - coal, oil and gas, which satisfies about 90% of humanity's energy needs. Data on energy consumption in the world for last years and its distribution by species are presented in Table. 1 .

Table 1. Structure of world energy consumption in 1998–2008

As can be seen from the table. 1 data, global energy consumption is increasing from year to year. The population and human needs are constantly growing, and this causes an increase in energy production and the growth rate of its consumption.

However, the reserves of oil, gas and coal are not infinite and, according to forecasts, the explored resources may be enough: oil for 40 years, gas for 60 years, coal for 120 years. Natural uranium reserves are sufficient to meet the world's energy needs for approximately 85 years.

Another factor limiting the further increase in energy production by burning fuel is the ever-increasing pollution of the environment by its combustion products. No less dangerous is thermal pollution of the environment, leading to global warming and climate change, melting glaciers and rising sea levels.

In nuclear energy there are ecological problems other kind related to the need for burial nuclear waste, which also poses great difficulties.

To determine the most rational ways to use heat, analyze the efficiency of working processes of thermal installations and create new, more advanced types of thermal apparatus, knowledge is required theoretical foundations heating engineering.