Necessary conditions for the operation of heat engines

The creation and development of thermodynamics was caused, first of all, by the need to describe the work and calculate the parameters thermal machines . thermal machines, or heat engines, are designed to obtain technical (useful) work due to the heat released due to chemical reactions (fuel combustion), nuclear reactions or for other reasons, such as heating by solar energy.

From consideration of the basic principles of operation of heat engines, regardless of their design, it follows that the continuous conversion of thermal energy into mechanical work done in them with the help of auxiliary body , called in thermodynamics working body . As noted earlier, the most suitable as working bodies in their physical properties is gases and vapors of liquids, since they are characterized by the greatest ability to change their volumes when changing R And T .

In addition, the operation of these machines is possible only if two indispensable conditions are met. First condition is that any heat engine must operate cyclically, that is, the working body, performing a series of expansion and contraction processes over a certain period of time, must return to its original state. This cycle must be repeated during the entire period of operation of the machine, and, depending on the design of the heat engine, individual parts of the cycle can be carried out in different parts of it. constituent parts. In the absence of a cycle, for example, in any process of only gas expansion in the working chamber (engine cylinder internal combustion, channels of working blades of steam and gas turbines) of a heat engine, respectively, there will come a moment when R And T working fluid will become equal to R And T environment, and this will stop getting work. In this case, you can get only a limited amount of work. To obtain work again, it is necessary either to return the working fluid to its original state during the compression process, or to somehow remove the spent working fluid from the working chamber and fill this chamber with a new portion of this body. From the point of view of thermodynamic analysis of the operation of a heat engine, it is not at all necessary to deal with new portions of the working fluid, since for the process of converting thermal energy into mechanical work, it does not matter whether the old working fluid remains in the working chamber or a new one is introduced. Therefore, it can be assumed that the cylinder of a heat engine contains the same amount of working fluid, which, cyclically passing through a series of changes in its state from initial to final and vice versa, converts thermal energy into mechanical work.

v

P

v2

v1

R 1

R 2

q 1

q2

Fig.6.6.1. Heat engine cycle

Consider the circular cycle of the heat engine shown in the figure. In the process of expanding the working fluid along the line 1-3-2 to it from a source of thermal energy with a temperature T 1 , i.e. from a hot heat source , heat is supplied in the amount q 1 . As a result, there is an additional increase in the volume of the working fluid. Thus, the expansion of the working fluid is carried out both by reducing the pressure in the working chamber and by increasing its temperature. However, to obtain mechanical work, the process of expansion of the heated working fluid in the working chamber must be carried out under a certain counterpressure from the side of the movable surfaces of the working chamber. This results in a positive specific mechanical work l 1 , namely the work of expansion of the working body, is equivalent to the area S 1-3-2-6-5-1 . Upon reaching point 2, the working fluid must be returned to its original state, that is, to point 1. To do this, you need to compress the working fluid.

In order for a heat engine to continuously produce mechanical energy, the expansion work of the working fluid must be more work its compression. So the compression curve 2-4-1 must lie below the expansion curve. If the compression process goes along the line 2-3-1 , then no technical, that is, useful, work will be received, since in this case it will be l 1 = l 2 , Where l 2 is the negative specific work of compression of the working fluid. Therefore, in order to obtain useful work, it is necessary to reduce the pressure of the working fluid during the expansion process due to the removal of part of the heat from it. q 2 to a heat source with a lower temperature T 2 , i.e. to a cold heat source . Respectively, l 2 equivalent to area S 2-4-1-5-6-2 . As a result, each kilogram of the working fluid makes per cycle useful work l c, which is equivalent to the area S 1-3-2-4-1 , bounded by the cycle contour. So for continuous work a heat engine requires a cyclic process in which heat is supplied to the working fluid from a hot source q 1 and is removed from it to a cold source of heat q 2 . The presence of at least two heat sources with different temperatures - hot and cold - is the second necessary condition for the operation of heat engines. .

It is extremely important to emphasize that everything is warm q 1 received by the working fluid from a hot source cannot be converted into work. Part q 1 , that is q 2 , must necessarily be given to another body (bodies) with a lower temperature. Such a body can be atmospheric air, large volume water and the like. Numerous attempts to create a heat engine in which everything is warm q 1 would turn into work, that is, there would be equality q 2 = 0, inevitably ended in failure. Such a machine, which could convert all the heat supplied to it into work, was called perpetual motion machine of the second kind , or perpetuum mobile (perpetuum mobile) second kind . All the experimental material accumulated by science shows that such an engine is impossible.

Once again, we note that the presence of a cold heat source and the transfer of part of the heat received from the hot source to it is mandatory, since otherwise the operation of a heat engine is impossible. Indeed, to obtain continuous mechanical work, it is necessary to have a flow of energy, in this case heat flow. If there is no cold source, then the working fluid will inevitably come into thermal equilibrium with the hot source and the heat flow will stop.

1-3-2 And 2-4-1 will accordingly look like:

q 1 = + Du+ l 1 ;

Quantities q 2 And l 2 must be taken modulo, which will avoid confusion with the signs y q 2 , since the heat leaving the system has a minus sign. The internal energy of the working fluid for the cycle should not change, and therefore before Du in the equations directly opposite algebraic signs are put down. Adding these equations, we get:

q 1 - | q 2 | = q c = l 1-½ l 2 ½ = l c, (6.6.1)

Where q c - part of the heat of the hot source, converted into work in the cycle; l c – cycle work 1-3-2-4-1 .

Since in the case under consideration l 1 > l 2 , then the cycle work is positive. It, as shown by (6.6.1), is equal to the difference between the heat supplied and removed in the cycle.

Conversion efficiency q 1 V l c evaluated thermal (thermodynamic, thermal) thermal engine cycle efficiency:

. (6.6.2)

Thus, the thermal efficiency of a heat engine cycle is the ratio of the useful work obtained in the cycle l c to all the heat introduced into the working fluid q 1 .

A cycle consisting of reversible processes is called ideal. In this case, the working fluid in such a cycle should not be subjected to chemical changes. If at least one of the processes included in the cycle is irreversible, then the cycle will no longer be ideal. To perform an ideal cycle in a heat engine (engine), there must be no thermal and mechanical losses. Such a machine is called an ideal heat engine (ideal heat engine).

Because ½ q 2½> 0, then h T< 1.0, that is, the efficiency of a heat engine, even an ideal one, will always be less than 1.0. The results of studies of ideal cycles can be transferred to real, that is, irreversible, processes of real heat engines by introducing experimental correction factors.

Relation (6.6.2) is a mathematical expression of the principle of equivalence of thermal and mechanical energy. If a cold source is excluded from the heat engine circuit, then formally the principle of equivalence will not be violated. However, as noted above, such a machine will not work.

Cycles resulting in positive work, that is, when l 1 > l 2 , are called direct cycles , or heat engine cycles . These cycles are used by internal combustion engines. jet engines, gas and steam turbines and so on.

If the cycle shown in Fig. 6.6.1 is presented as flowing in the opposite direction, that is, along a closed curve 1-4-2-3-1 (see Fig. 6.6.2), then for its implementation it is necessary to spend work l c, which will be already negative and equivalent to the area S 1-4-2-3-1 . The cooled body in such a machine is a cold heat source, and the heated body is the environment, that is, a hot heat source. Such cycles are called refrigeration cycles, or refrigeration (reverse) cycles.

To support low temperature cooled body, it is necessary to continuously remove heat from it q 2 , which enters the working fluid from a cold source. This withdrawal in the refrigeration cycle is carried out in the process 1-4-2 expansion of the working fluid, which perceives this heat and performs at the same time positive work l 2 , equivalent to the area
S 1-4-2-6-5-1 . The return of the working fluid to its original state occurs in the process of compression along the curve 2-3-1 located above the curve of the expansion process, that is, in a process occurring at higher temperature conditions. This makes it possible to transfer the heat removed from the working fluid q 1 a hot source of heat, which is usually the environment. Negative work is expended on compression l 1 determined on the area chart S 2-3-1-5-6-2 .

v

P

v2

v1

R 1

R 2

q 1

q2

Rice. 6.6.2. Chiller cycle

The equation of the 1st law of thermodynamics for processes 1-4-2 And 2-3-1 taking into account the algebraic signs in front of the components, respectively, have the form:

q2 = + Du+ l 2; -½ q 1 ½ = - Du- ½ l 1½.

Adding by parts of both equations gives:

q 2 - ½ q 1 ½= - (½ l 1 ½ - l 2) = -½ l c ½ (6.6.3)

½ q 1½= q 2+½ l c.½ (6.6.4)

This expression shows that heat q 1 , transferred to a hot heat source, is made up of heat q 2 , which entered the working fluid from a cold heat source, and the work of the cycle l c. Because ½ l 1 ½ > l 2 , That l c < 0 и, следовательно, для непрерывной работы холодильной машины необходимо затрачивать работу. Таким способом осуществляется передача тепла с низшего температурного уровня на высший, то есть производится охлаждение некоторых частей OS and created in right place temperature is lower than the temperature OS . According to the refrigeration (reverse cycle) refrigeration machines, heat pumps and so on.

The efficiency of the refrigeration machine is evaluated by the so-called coefficient of performance e, determined by the ratio of the limited capacity of useful heat taken from the cold source q 2 to the work done l c:

. (6.6.5)

The coefficient of performance characterizes the efficiency of heat transfer from a cold heat source to a hot heat source. It will be the greater, the greater the amount of heat q 2 will be taken from a cold heat source and transferred to a hot heat source and the less work will be spent on it l c. Unlike thermal (thermodynamic, thermal) efficiency h T the coefficient of performance 𝜺 can be greater, less and equal to one.

In the refrigerator q 1 released into the environment, which is source of unlimited capacity . Therefore, the refrigeration machine can be used not only for cooling various bodies, but also for heating the room. Indeed, even an ordinary household refrigerator, while cooling the products placed in it, simultaneously heats the air in the room. The principle of dynamic heating was proposed by W. Thomson and is the basis for the operation of modern heat pumps . Heat pumps are machines whose main product is heat. q 1 transmitted to a source of limited capacity . Their effectiveness is assessed heating coefficient , which is the ratio of the heat transferred to the consumer q 1 To l c:

In this case, warm q 2 is taken from a source of unlimited capacity (atmospheric air, large volumes of water, rock mass).

The advantage of a heat pump over electric heater It consists in the fact that not only the electrical energy converted into heat is used for heating the premises, but also the heat taken from the environment. Therefore, the efficiency of heat pumps can be much higher than the efficiency of electric heaters.

The combination of the engine cycle and the heat pump or refrigeration cycles is a cycle thermal transformer , which allows you to pump heat from a source with one T to the source on the other T during the combined cycle. The purpose of a thermal transformer is to change the heat potential. If the transformer is designed to produce heat at a lower T, than the original T hot spring, then such a transformer is called lowering . If heat is received in the transformer at T higher than the original heat, then such a transformer is called raising .

Thus, the operation of any heat or refrigeration machine is possible only if there are two sources of heat: hot and cold.

Machines in which the internal energy of the fuel is converted into mechanical energy are called thermal engines. These include: internal combustion engines, steam and gas turbines, jet engines. Let us find out what conditions are necessary for the internal energy of the fuel to be converted into the mechanical energy of the working shaft of the engine in a heat engine.

The substance that does work in a heat engine is called working body. In steam engines, this is steam, and in an internal combustion engine, a jet engine, and a gas turbine, it is gas. As the theory of heat engines shows, in order for the working fluid to continuously perform work in them, it is necessary to have a heater and a refrigerator in the engine. A device in which the working fluid is heated by the energy of the fuel is called heater(steam boiler, cylinder). A device in which the working fluid is cooled after doing work is called refrigerator(atmosphere, a condenser in which the exhaust steam is cooled by running water and turns into water).

Let's do the following experiment (Fig. 30). Take a U-shaped tube filled with water. One elbow of the tube is connected to a heat receiver (in which the working fluid is located - gas), in the other knee there is a float A. We will alternately heat the heat receiver with a spirit lamp and lower it into cold water. The spirit lamp acts as a heater for the working fluid, cold water as a refrigerator. The operation of such a model of a heat engine consists in a repeating process - raising and lowering water along with a float. It happens like this: the working fluid (gas), heating up in the heater and expanding, does the work of raising the water with the float; in order for the working fluid to be able to do work again, it is cooled in a refrigerator, and then heated again. While this process will be repeated - the model of such an engine will work.

The heat engine runs continuously. This happens because in it the processes that occur with the working fluid are periodically repeated: it heats up, expands, does work, cools, heats up again, etc. (Trace this in the operation of an internal combustion engine. So, for the operation of a heat engine, it is necessary to have: a heater, a working fluid and a refrigerator.

For periodically repeating processes, a law was discovered according to which it is impossible to carry out such a periodically repeating process, the only and end result which would be the complete conversion of the amount of heat received from the heater into work. In relation to a heat engine, this means: the amount of heat received by the working fluid from the heater cannot be fully used to perform work, since the process of complete transition of the internal energy of the random movement of a large number of molecules into the mechanical energy of the movement of the body (engine piston, turbine impeller) is impossible. ).

In order for the working fluid to do work again and again in real heat engines, the spent portion of the working fluid is removed from the engine to the refrigerator, that is, to the atmosphere, or to the condenser for heating water, or for heating (Fig. 31). At the same time, in order to remove as little work as possible, the temperature and pressure in the refrigerator are always lower than in the working chamber of the engine. Due to the difference between the work of steam and the work to remove it, the engine does useful work. From an energy point of view, the process occurring in heat engines is as follows (Fig. 32): the working fluid receives from the heater the amount of heat Q n, part of which gives to the refrigerator Q x , and due to the remainder, it does the work A \u003d Q n - Q x.

There are many uses for heat engines. Carburetor engines, for example, are applied in cars, motorcycles; diesel engines - in tractors, cars heavy duty, diesel locomotives, motor ships, sea vessels; steam turbines - in power plants; gas turbines - in power plants, gas turbine locomotives, in blast furnaces for driving blowers, are part of one of the types of jet engine; jet engines - in aviation, in rockets.

A heat engine converts heat into work, in other words, it takes heat from some bodies and transfers it to other bodies in the form of mechanical work. In order to carry out this transformation, it is necessary to have two differently heated bodies, between which heat exchange is possible. For brevity, we will call the hotter body the heater, and the colder one the refrigerator. In the presence of such two bodies, the process of converting heat into work is drawn as follows: an expandable body (working body) is brought into contact with a heater. Heat is taken from the heater and used for the work of expansion, which is given to the surrounding bodies. Further, the working fluid is brought into contact with the refrigerator, to which it gives off heat

due to the work performed by external forces on the working body.

To obtain a continuously operating heat engine, it is necessary to end the compression stroke at the point at which the expansion stroke began; in short, the process must be cyclical. working body after each cycle, it returns to its original state. The law of conservation of energy therefore requires that the energy received from the surrounding bodies be equal to the energy transferred to the surrounding bodies. From the medium received: heat during expansion and work A 2 during compression of the working fluid. Given to the environment: work A! when expanding the body and heat when contracting. Therefore, or When the cycle is carried out clockwise, the work of compression less work extensions. Therefore, the last equality expresses the simple fact that the net work transferred by the working body external environment, is equal to the difference in heat received from the heater and given to the refrigerator. Accordingly, the coefficient useful action cycle, and hence the entire machine, will be equal to

The described process of operation of a heat engine is, of course, an abstract scheme. However, the most essential features of each heat engine are conveyed by this scheme. The working fluid is an expanding and contracting gas or steam, the environment plays the role of a refrigerator. The heater is a steam boiler or, in internal combustion engines, a combustible mixture.

The same three systems are also necessary for a refrigeration machine in which the cycle takes place in reverse side. The principle of operation of this machine is as follows: the expansion of the working fluid is performed when it is in contact with the refrigerator. This cools the cold body even more, which is the task of the refrigeration machine. Further, in order for the cycle to become possible, it is necessary to compress the working fluid and transfer the heat received from the refrigerator. This is done when the working fluid comes into contact with the heater. Thus, a hotter body heats up even more. The "unnatural" transfer of heat from a less heated body to a more heated body is "paid for" by work. Indeed, when the cycle is performed counterclockwise, the equality of the energy transferred to the medium and the energy taken from the medium (i.e., or where we still refer index 1 to the part of the process that occurs upon contact with a hotter body) has the following meaning : the amount of heat removed from the system must be compensated by an equal amount of mechanical work.

The second law of thermodynamics imposes some condition on the operation of a heat engine. If we assume the process is reversible, then the change in the entropy of the working fluid after passing through the cycle should be equal to zero. In other words, change

entropy during expansion should equal (with the opposite sign) the change in entropy during compression, i.e.

In the case of an irreversible process, the entropy of a closed system consisting of a heater, a refrigerator and a working fluid will increase and therefore

(We remind you that there is an algebraic quantity. The heat entering the system is considered positive.) Calculating the values ​​of these integrals for specific processes, in some cases it is quite easy to find the value of the maximum efficiency of a particular cycle of a heat engine.

« Physics - Grade 10 "

What is a thermodynamic system and what parameters characterize its state.
State the first and second laws of thermodynamics.

It was the creation of the theory of heat engines that led to the formulation of the second law of thermodynamics.

The reserves of internal energy in the earth's crust and oceans can be considered practically unlimited. But to solve practical problems, having energy reserves is still not enough. It is also necessary to be able to use energy to set in motion machines in factories and plants, vehicles, tractors and other machines, to rotate the rotors of generators. electric current etc. Mankind needs engines - devices capable of doing work. Most of the engines on Earth are heat engines.

Heat engines - These are devices that convert the internal energy of the fuel into mechanical work.

The principle of operation of heat engines.

In order for the engine to do work, a pressure difference is needed on both sides of the engine piston or turbine blades. In all heat engines, this pressure difference is achieved by increasing the temperature working body(gas) hundreds or thousands of degrees above ambient temperature. This increase in temperature occurs during the combustion of fuel.

One of the main parts of the engine is a gas-filled vessel with a movable piston. The working fluid in all heat engines is a gas that does work during expansion. Let's denote the initial temperature of the working fluid (gas) through T 1 . This temperature in steam turbines or machines acquires steam in a steam boiler. in internal combustion engines and gas turbines temperature rise occurs when fuel is burned inside the engine itself. The temperature T 1 is called heater temperature.

The role of the refrigerator

As work is done, the gas loses energy and inevitably cools to a certain temperature T 2 , which is usually somewhat higher than the ambient temperature. They call her refrigerator temperature. The refrigerator is the atmosphere or special devices for cooling and condensing exhaust steam - capacitors. In the latter case, the temperature of the refrigerator may be slightly lower than the ambient temperature.

Thus, in the engine, the working fluid during expansion cannot give all its internal energy to do work. Part of the heat is inevitably transferred to the refrigerator (atmosphere) together with the exhaust steam or exhaust gases internal combustion engines and gas turbines.

This part of the internal energy of the fuel is lost. A heat engine performs work due to the internal energy of the working fluid. Moreover, in this process, heat is transferred from hotter bodies (heater) to colder ones (refrigerator). circuit diagram heat engine is shown in Figure 13.13.

The working fluid of the engine receives from the heater during the combustion of fuel the amount of heat Q 1, does work A "and transfers the amount of heat to the refrigerator Q2< Q 1 .

In order for the engine to work continuously, it is necessary to return the working fluid to its initial state, at which the temperature of the working fluid is equal to T 1 . It follows from this that the operation of the engine occurs according to periodically repeating closed processes, or, as they say, according to a cycle.

Cycle is a series of processes, as a result of which the system returns to its initial state.

Coefficient of performance (COP) of a heat engine.

The impossibility of complete conversion of the internal energy of the gas into the work of heat engines is due to the irreversibility of processes in nature. If heat could spontaneously return from the refrigerator to the heater, then the internal energy could be completely converted into useful work using any heat engine. The second law of thermodynamics can be formulated as follows:

Second law of thermodynamics:
impossible to create perpetual motion machine of the second kind, which would completely convert heat into mechanical work.

According to the law of conservation of energy, the work done by the engine is:

A" \u003d Q 1 - | Q 2 |, (13.15)

where Q 1 - the amount of heat received from the heater, and Q2 - the amount of heat given to the refrigerator.

The coefficient of performance (COP) of a heat engine is the ratio of work A "performed by the engine to the amount of heat received from the heater:

Since in all engines some amount of heat is transferred to the refrigerator, then η< 1.

Maximum efficiency value thermal engines.

The laws of thermodynamics allow us to calculate the maximum possible thermal efficiency an engine operating with a heater having a temperature of T 1 and a refrigerator with a temperature of T 2 , and also to determine ways to increase it.

For the first time, the maximum possible efficiency of a heat engine was calculated by the French engineer and scientist Sadi Carnot (1796-1832) in his work “Reflections on the driving force of fire and on machines capable of developing this force” (1824).

Carnot came up with the ideal heat engine ideal gas as a working body. An ideal Carnot heat engine operates in a cycle consisting of two isotherms and two adiabats, and these processes are considered reversible (Fig. 13.14). First, a vessel with gas is brought into contact with a heater, the gas expands isothermally, doing positive work, at a temperature T 1 , while it receives an amount of heat Q 1 .

Then the vessel is thermally insulated, the gas continues to expand already adiabatically, while its temperature decreases to the temperature of the refrigerator T 2 . After that, the gas is brought into contact with the refrigerator, under isothermal compression, it gives off the amount of heat Q 2 to the refrigerator, compressing to a volume V 4< V 1 . Затем сосуд снова теплоизолируют, газ сжимается адиабатно до объёма V 1 и возвращается в первоначальное состояние. Для КПД этой машины было получено следующее выражение:

As follows from formula (13.17), machine efficiency Carnot is directly proportional to the difference absolute temperatures heater and refrigerator.

The main meaning of this formula is that it indicates the way to increase the efficiency, for this it is necessary to increase the temperature of the heater or lower the temperature of the refrigerator.

Any real heat engine operating with a heater having a temperature T 1 and a refrigerator with a temperature T 2 cannot have an efficiency exceeding the efficiency of an ideal heat engine: The processes that make up the cycle of a real heat engine are not reversible.

Formula (13.17) gives a theoretical limit for the maximum value of the efficiency of heat engines. It shows that a heat engine is more efficient, the greater the temperature difference between the heater and the refrigerator.

Only at the temperature of the refrigerator, equal to absolute zero, η = 1. In addition, it has been proved that the efficiency calculated by formula (13.17) does not depend on the working substance.

But the temperature of the refrigerator, the role of which is usually played by the atmosphere, practically cannot be lower than the ambient temperature. You can increase the temperature of the heater. However, any material (solid body) has limited heat resistance or heat resistance. When heated, it gradually loses its elastic properties, and when sufficiently high temperature melts.

Now the main efforts of engineers are aimed at increasing Engine efficiency by reducing the friction of their parts, fuel losses due to its incomplete combustion, etc.

For steam turbine the initial and final steam temperatures are approximately as follows: T 1 - 800 K and T 2 - 300 K. At these temperatures, the maximum efficiency is 62% (note that efficiency is usually measured as a percentage). The actual value of the efficiency due to various kinds of energy losses is approximately 40%. Diesel engines have the maximum efficiency - about 44%.

Environmental protection.

It is hard to imagine modern world without heat engines. They provide us with a comfortable life. Heat engines drive vehicles. About 80% of electricity, despite the presence of nuclear power plants, is generated using heat engines.

However, during the operation of heat engines, inevitable environmental pollution occurs. This is a contradiction: on the one hand, every year humanity needs more and more energy, the main part of which is obtained by burning fuel, on the other hand, combustion processes are inevitably accompanied by environmental pollution.

When fuel is burned, the oxygen content in the atmosphere decreases. In addition, the combustion products themselves form chemical compounds harmful to living organisms. Pollution occurs not only on the ground, but also in the air, since any aircraft flight is accompanied by emissions of harmful impurities into the atmosphere.

One of the consequences of the operation of the engines is the formation of carbon dioxide, which absorbs infrared radiation from the Earth's surface, which leads to an increase in the temperature of the atmosphere. This so-called Greenhouse effect. Measurements show that the temperature of the atmosphere rises by 0.05 °C per year. Such a continuous increase in temperature can cause the ice to melt, which in turn will lead to a change in the water level in the oceans, i.e., to the flooding of the continents.

Let's note one more negative moment when using heat engines. So, sometimes water from rivers and lakes is used to cool engines. The heated water is then returned back. The increase in temperature in water bodies disrupts the natural balance, this phenomenon is called thermal pollution.

For environmental protection, various cleaning filters preventing release into the atmosphere harmful substances engine designs are being improved. There is a continuous improvement of fuel, which gives less harmful substances during combustion, as well as the technology of its combustion. Actively developed alternative sources energy using wind, solar radiation, nuclear energy. Electric vehicles and vehicles powered by solar energy are already being produced.

heat engine - a device that converts the internal energy of a burnt fuel into mechanical energy. Types of heat engines : 1) internal combustion engines: a) diesel, b) carburetor; 2) steam engines; 3) turbines: a) gas, b) steam.

All these heat engines have a different design, but consist of three main parts : heater, working medium and refrigerator. Heater provides heat to the engine. working body converts part of the heat received into mechanical work. Fridge takes some of the heat from the working fluid.

T1– heater temperature;

T2– refrigerator temperature;

Q1- heat received

from the heater;

Q2- heat given off

refrigerator;

A"- work done

engine.

The operation of any heat engine consists of repetitive cyclic processes - cycles. Cycle - this is such a sequence of thermodynamic processes, as a result of which the system returns to its initial state.

Efficiency factor (COP) a heat engine is the ratio of the work done by the engine to the amount of heat received from the heater: .

The French engineer Sadi Carnot considered ideal heat engine with an ideal gas as the working fluid. He found the best ideal cycle heat engine, consisting of two isothermal and two adiabatic reversible processes - carnot cycle . The efficiency of such a heat engine with a heater at a temperature and a refrigerator at a temperature of: . Regardless of the design, choice of working fluid and type of processes in a heat engine, its efficiency cannot be greater than the efficiency of a heat engine operating according to the Carnot cycle and having the same heater and cooler temperatures as this heat engine.

The efficiency of heat engines is low, so the most important technical task is to increase it. Heat engines have two significant shortcomings. First, most heat engines use organic fuel, the extraction of which quickly depletes the resources of the planet. Secondly, as a result of fuel combustion, a huge amount of harmful substances is released into the environment, which creates significant environmental problems.

The discovery in 1850 by the German physicist R. Clasius is associated with the study of the issue of the maximum efficiency of thermal engines second law of thermodynamics : such a process is impossible in which heat would spontaneously transfer from colder bodies to hotter bodies.

Physical quantities and their units of measurement:

Name value	Designation	Unit	Formula
Relative molecular weight	M r(uh er)	dimensionless quantity
Mass of one molecule (atom)	m0	kg
Weight	m	kg
Molar mass	M
Amount of substance	ν (nude)	mole(mol)	;
Number of particles	N(en)	dimensionless quantity
Pressure	p(pe)	Pa(pascal)
Concentration	n(en)
Volume	V(ve)
Average kinetic energy forward movement molecules		J(joule)
Celsius temperature	t	°C
Temperature Kelvin	T	TO(kelvin)
Root mean square velocity of molecules
Surface tension	σ (sigma)
Absolute humidity	ρ (ro)
Relative Humidity	φ (fi)	%
Internal energy	U(y)	J(joule)
Job	A(A)	J(joule)
Quantity of heat	Q(ku)	J(joule)