transformation mechanical energy into electrical

Tolman effect. Tolman discovered the phenomenon of electron inertia in metals. When the conductor moves with acceleration, we can observe the potential difference at the ends of the conductor.

Triboelectricity - the occurrence of electric charges during the friction of two dissimilar bodies. When rubbing chemically identical bodies, a positive charge gets more dense of them. When two dielectrics are rubbed, the dielectric with the higher permittivity is positively charged. Substances can be arranged in triboelectric rows, in which the previous body is electrified positively, and the next negatively.

Acousto-electric effect - occurrence direct current EMF in a conducting medium (conductor, semiconductor) under the action of a traveling ultrasonic wave. The appearance of current is associated with the transfer of momentum from the ultrasonic wave to electrons. It is used to measure the intensity of ultrasound in solids, big role plays in the study of the structure of matter.

The piezoelectric effect is observed in anisotropic dielectrics, mainly in crystals of certain substances that have a certain, rather low symmetry. External mechanical forces, acting in certain directions on a piezoelectric crystal, cause not only mechanical stresses and deformations in it (as in any solid body), but also the appearance of bound electric charges of different signs on its surfaces. When the direction of mechanical forces is reversed, the signs of the charges become opposite. It has found wide application in pressure sensors, used to measure the level of vibrations, acoustic antennas, flaw detection, hydroacoustics, powerful sources of ultrasonic waves.

Converting thermal energy into electrical and thermoelectric energy

Pyroelectricity - the occurrence of electric charges on the surface of pyroelectrics when they are heated or cooled. One end of the pyroelectric is charged positively, and the other negatively, when cooled, vice versa. Pyroelectrics - dielectrics with spontaneous polarization, are used as indicators and radiation receivers.

Seebeck effect - thermoelectric effect, the occurrence of electro driving force in electrical circuit, consisting of series-connected dissimilar conductors, the contacts between which are at different temperatures. Can be used as a thermoelectric transducer.

The Peltier effect is the effect of generating or absorbing heat when an electric current flows through a junction of two metals, alloys, or semiconductors. It is used in thermoelectric cooling devices, thermoelectric converters.

Thomson effect - consists in the release or absorption of heat in a current-carrying conductor along which there is a temperature gradient, occurs in addition to the release of Joule heat. If there is a temperature gradient along the conductor through which the current flows, and the direction of the current corresponds to the movement of electrons from the hot end to the cold one, then when moving from a hotter to a colder area, the electrons slow down and transfer excess energy to the surrounding atoms (heat is released); at reverse direction current electrons, moving from a colder area to a hotter one, are accelerated by the thermoEMF field and replenish their energy due to the energy of the surrounding atoms (heat is absorbed).

Nernst-Ettingshausen effect - occurrence electric field in metals and semiconductors in the presence of a temperature gradient (difference) and an external magnetic field. Refers to the number of thermomagnetic phenomena.

Galvanomagnetic effects

Hall effect - occurrence of a transverse electric field and difference potentials in a conductor or semiconductor through which electricity, when placed in a magnetic field perpendicular to the direction of the current. Based on this effect, sensors for measuring magnetic fields are created.

Nuclear interactions

Stark effect. Splitting of the spectral lines of an atom in constant electric field for atoms with nonzero dipole moments, the line shift is proportional to the field strength E, i.e. depending on the direction of the field, the frequency will either increase or decrease; for non-polar dielectrics, the line shift is proportional to ЕІ. This is due to the fact that the molecule or atom acquires additional rotational energy. This phenomenon can be used for measurement purposes; for example, in measurements related to the definition (moisture, composition, structure, etc.).

Nuclear magnetic resonance (NMR). Qualitatively similar to EPR, but quantitatively different. On the basis of NMR, methods have been developed for measuring the strength of magnetic fields (magnetometers), methods for monitoring the course of chemical reactions.

The invention is intended for use in the field of energy, transport, aviation and astronautics, where an important role is played by increasing the efficiency of heat engines. The method of converting thermal energy into mechanical energy is carried out by using two dissimilar bodies in the gas phase, their separate compression, separate heat supply to the working bodies, mixing, adiabatic expansion of the mixture to obtain mechanical work, heat recovery, cooling and separation of the mixture. The invention makes it possible to increase the efficiency of the cycle and use low-grade heat. 1 z.p. f-ly, 1 ill.

The invention is intended for use in the field of energy, transport, aviation and astronautics, where an important role is played by increasing the efficiency of heat engines. There is a known method of converting thermal energy into mechanical energy, in which the air compressed in the compressor is fed into the combustion chamber, where heat is supplied in the cycle during fuel combustion, and the combustion products formed in it are fed into the steam-gas ejector, in which, when they are mixed with superheated steam formed in steam generator when heat is supplied to the water and the acceleration in the ejector steam nozzle converted into an active flow until high speed outflow, there is an increase in the speed of the combustion products due to the transfer of the kinetic energy of the steam to them, followed by an increase in the pressure of the combustion products in the composition of the vapor-gas mixture, which is expanded in the turbine, and through the system of regenerative water heating, after separation from the vapor-gas mixture of the combustion products, they are removed from the installation ( see RF patent N 2076929, IPC F 01 K 21/04, 1997). The disadvantage of this method are high costs heat to produce superheated steam, the use of a bulky system of regenerative water heating and significant losses during mixing in the ejector. A known method is known for converting thermal energy into mechanical energy in a closed process with heat supplied from the combustion of solid, liquid or gaseous fuels or from another source, in which an inert gas, such as xenon or CO 2 , is compressed in a compressor, heated in a gas heater and then expanded in the first gas turbine steps. Spent, but still possessing energy, gases enter the mixer, where they are mixed with a working medium, such as water, or freon, or steam of this medium. The working medium evaporates or overheats. The mixture enters the second gas turbine stage, where it expands. The exhaust mixture is fed from the second gas turbine stage to the condenser, and due to the condensation, the separation of the substances takes place again at the same time. The gas enters the compressor, and the working mixture into the liquid collector and through the pump into the heater or evaporator (see application DE N 3605466, IPC F 01 K 21/04, 1987). The disadvantage of this method are large heat losses and the bulkiness of the equipment used. Of the known methods for converting thermal energy into mechanical (electrical) energy, the closest is the method for converting thermal energy into mechanical energy by using two dissimilar working fluids, their separate compression, heat supply, mixing, adiabatic expansion of the mixture to obtain mechanical work, cooling and separation of the mixture into working fluids. body (see US patent, N 5444981, IPC F 01 K 21/04, 1995). In this conversion method, the turbine extracts useful energy at a lower pressure drop than would be required if only one working fluid was used. However, this method is applicable only for the use of high-potential heat of fuel combustion in the boiler and has an insufficiently high cycle efficiency. The use of a boiler as a heat source and the joint heating of mixed working fluids predetermine the choice of water and helium vapor as working fluids, which, accordingly, have insufficiently optimal thermophysical properties in the process of converting thermal energy. The disadvantage of this method is also the lack of a heat recovery process. The objective of the present invention is to increase the efficiency of the cycle and to obtain the possibility of using low-grade heat, such as the heat of the sun, the heat of the environment, etc. The problem is solved by the fact that in the method of converting thermal energy into mechanical energy by using two , mixing, adiabatic expansion of the mixture to obtain mechanical work, cooling and separation of the mixture into working fluids, according to the invention, heterogeneous bodies in the gas phase (He - CO 2 , He - N 2 , Ar - CO 2 , H 2 - N 2 or mixtures thereof), heat is supplied to the working fluids separately, and after the expansion of the mixture, heat is regenerated to the original working fluids. The problem is solved by the fact that the mixing of the working fluids is carried out in a gas ejector with a supersonic diffuser or a pulsating gas ejector. The drawing shows a T-S diagram of compression, heating, mixing, expansion of the mixture, heat recovery from the mixture at the inlet to the original gases, cooling and separation of gases. The processes of adiabatic separate compression 0-1 and 0-1 "of two various gases in the temperature range from T 0 to T 1 are shown with a dotted line, since they start from the same point with the parameters P 0 and T 0, and end at points 1 and 1 "due to the difference in the properties of the gases used. The gases are compressed, respectively, to pressures P 1 and P" 1, and then there are processes of isobaric separate heat supply 1-2 and 1"-2" from an external source to a temperature of 2. After the heat is supplied, the gases are mixed in the gas ejector - process 2 - P cm - 2 "at a temperature T cm = T 2. It is possible to re-mix the mixture of gases after the ejector with one of the working fluids to achieve the optimal parameters of the working mixture before expansion. The mixture of gases of the ejector expands in the process P cm - P "cm to a temperature T" cm with the production of mechanical (electrical) energy. In the process P "cm - P" "cm, heat is regenerated (isobaric heat removal from the mixture to the original working fluids). The temperature of the mixture is then reduced to T 1 . The process P"" cm P 0 is adiabatic, closes the thermodynamic cycle, and the mixture acquires the initial parameters P 0 and T 0 . At point 0, the mixture is cooled and separated into its original components using the energy of the main cycle. The method of converting thermal energy into mechanical energy is carried out as follows. Diverse working fluids in the gas phase, for example He - CO 2 , He - N 2 , Ar - CO 2 , H 2 - N 2 or mixtures thereof are separately compressed to pressures P 1 and P "1 and heat is separately supplied to them, for example heat sun, ambient heat or other low-grade heat (process 1-2 and 1 "-2"). Then the heated working fluids are mixed, for example, in a gas ejector (point P cm). diffuser. The mixture of working bodies adiabatically expands to a pressure of P "cm with mechanical work (or electrical energy). In the process P" cm - P "" cm, heat is regenerated. Heat is isobarically removed from the mixture and transferred to the original working fluids. The process P "" cm - P 0 is adiabatic, closes the thermodynamic cycle, and the mixture acquires the initial parameters P 0 and T 0 At point 0, the mixture is cooled and separated into its original components using the energy of the main cycle.Thus, in the proposed method for converting thermal energy into mechanical (electrical) energy, a multiloop closed thermodynamic cycle is carried out, in which heterogeneous working bodies after their compression and separate heat supply they are alternately mixed, then separated after the expansion of the mixture in the turbine.The positive effect of the use of such a cycle is explained by a sharp difference in the thermophysical properties of the gases used as working fluids and optimal parameters and properties of the mixtures obtained by mixing these gases in the ejector. All this makes it possible to increase the thermal efficiency of a heat engine and use low-potential environmental heat (or solar heating) as heating of working fluids.

CLAIM

1. A method for converting thermal energy into mechanical energy by using two dissimilar working fluids, their separate compression, heat supply, mixing, adiabatic expansion of the mixture to obtain mechanical work, cooling and separating the mixture into working fluids, characterized in that heterogeneous bodies in the gas phase (He - CO 2 , He - N 2 , Ar - CO 2 , H 2 - N 2 or mixtures thereof), heat is supplied to the working bodies separately, and after the expansion of the mixture, heat is regenerated to the original working bodies. 2. The method according to claim 1, characterized in that the mixing of the working fluids is carried out in a gas ejector with a supersonic diffuser.

The invention is intended for use in the field of energy, transport, aviation and astronautics, where an important role is played by increasing the efficiency of heat engines. The method of converting thermal energy into mechanical energy is carried out by using two dissimilar bodies in the gas phase, their separate compression, separate heat supply to the working bodies, mixing, adiabatic expansion of the mixture to obtain mechanical work, heat recovery, cooling and separation of the mixture. The invention makes it possible to increase the efficiency of the cycle and use low-grade heat. 1 z.p. f-ly, 1 ill.

The invention is intended for use in the field of energy, transport, aviation and astronautics, where an important role is played by increasing the efficiency of heat engines. There is a known method of converting thermal energy into mechanical energy, in which the air compressed in the compressor is fed into the combustion chamber, where heat is supplied in the cycle during fuel combustion, and the combustion products formed in it are fed into the steam-gas ejector, in which, when they are mixed with superheated steam formed in in the steam generator, when heat is supplied to the water and the acceleration in the ejector steam nozzle converted into an active flow until a high exhaust velocity is reached, the velocity of the combustion products increases due to the transfer of the kinetic energy of the steam to them, followed by an increase in the pressure of the combustion products in the composition of the vapor-gas mixture, which is expanded in the turbine, and through the system of regenerative water heating, after separation from the gas-vapor mixture of combustion products, they are removed from the installation (see RF patent N 2076929, IPC F 01 K 21/04, 1997). The disadvantage of this method is the high cost of heat to obtain superheated steam, the use of a bulky system of regenerative water heating and significant losses during mixing in the ejector. A known method is known for converting thermal energy into mechanical energy in a closed process with heat supplied from the combustion of solid, liquid or gaseous fuels or from another source, in which an inert gas, such as xenon or CO 2 , is compressed in a compressor, heated in a gas heater and then expanded in the first gas turbine steps. Spent, but still possessing energy, gases enter the mixer, where they are mixed with a working medium, such as water, or freon, or steam of this medium. The working medium evaporates or overheats. The mixture enters the second gas turbine stage, where it expands. The exhaust mixture is fed from the second gas turbine stage to the condenser, and due to the condensation, the separation of the substances simultaneously occurs again. The gas enters the compressor, and the working mixture into the liquid collector and through the pump into the heater or evaporator (see application DE N 3605466, IPC F 01 K 21/04, 1987). The disadvantage of this method are large heat losses and the bulkiness of the equipment used. Of the known methods for converting thermal energy into mechanical (electrical) energy, the closest is the method for converting thermal energy into mechanical energy by using two dissimilar working fluids, their separate compression, heat supply, mixing, adiabatic expansion of the mixture to obtain mechanical work, cooling and separation of the mixture into working fluids. body (see US patent, N 5444981, IPC F 01 K 21/04, 1995). In this conversion method, the turbine extracts useful energy at a lower pressure drop than would be required if only one working fluid was used. However, this method is applicable only for the use of high-potential heat of fuel combustion in the boiler and has an insufficiently high cycle efficiency. The use of a boiler as a heat source and the joint heating of mixed working fluids predetermine the choice of water and helium vapor as working fluids, which, accordingly, have insufficiently optimal thermophysical properties in the process of converting thermal energy. The disadvantage of this method is also the lack of a heat recovery process. The objective of the present invention is to increase the efficiency of the cycle and obtain the possibility of using low-grade heat, such as the heat of the sun, the heat of the environment, etc. The problem is solved by the fact that in the method of converting thermal energy into mechanical energy by using two dissimilar , mixing, adiabatic expansion of the mixture to obtain mechanical work, cooling and separation of the mixture into working fluids, according to the invention, heterogeneous bodies in the gas phase (He - CO 2 , He - N 2 , Ar - CO 2 , H 2 - N 2 or mixtures thereof), heat is supplied to the working fluids separately, and after the expansion of the mixture, heat is regenerated to the original working fluids. The problem is solved by the fact that the mixing of the working fluids is carried out in a gas ejector with a supersonic diffuser or a pulsating gas ejector. The drawing shows a T-S diagram of compression, heating, mixing, expansion of the mixture, heat recovery from the mixture at the inlet to the original gases, cooling and separation of gases. The processes of adiabatic separate compression 0-1 and 0-1 "of two different gases in the temperature range from T 0 to T 1 are shown by a dotted line, since they start from one point with parameters P 0 and T 0, and end at points 1 and 1" due to the difference in the properties of the gases used. The gases are compressed, respectively, to pressures P 1 and P "1, and then the processes of isobaric separate heat supply 1-2 and 1"-2" from an external source to a temperature of 2 proceed. After the heat is supplied, the gases are mixed in a gas ejector - process 2 - P cm - 2" at a temperature T cm \u003d T 2. It is possible to re-mix the mixture of gases after the ejector with one of the working fluids to achieve the optimal parameters of the working mixture before expansion. The ejector gas mixture expands in the process P cm - P "cm to a temperature T" cm to obtain mechanical (electrical) energy. In the process P "cm - P"" ​​cm, heat is regenerated (isobaric heat removal from the mixture to the original working fluids). In this case, the temperature of the mixture decreases to T 1. The process P "" cm P 0 is adiabatic, closes the thermodynamic cycle, and the mixture acquires the initial parameters P 0 and T 0. At point 0, the mixture is cooled and separated into its original components using the energy of the main cycle. The method of converting thermal energy into mechanical energy is carried out as follows. Diverse working fluids in the gas phase, for example He - CO 2 , He - N 2 , Ar - CO 2 , H 2 - N 2 or mixtures thereof are separately compressed to pressures P 1 and P" 1 and heat is separately supplied to them, for example, the heat of the sun, ambient heat or other low-potential heat (process 1-2 and 1"-2"). Then the heated working fluids are mixed, for example, in a gas ejector (point P cm). The most preferred is the mixing of working fluids in a gas ejector with a supersonic diffuser. The mixture of working fluids adiabatically expands to a pressure of P "cm with the production of mechanical work (or electrical energy). In the process P" cm - P "" cm, heat is regenerated. The heat from the mixture is isobarically removed and transferred to the original working fluids. The process P"" cm - P 0 is adiabatic, closes the thermodynamic cycle, and the mixture acquires the initial parameters P 0 and T 0 . At point 0, the mixture is cooled and separated into its original components using the energy of the main cycle. Thus, in the proposed method of converting thermal energy into mechanical (electrical) energy, a multiloop closed thermodynamic cycle is carried out, in which heterogeneous working bodies, after their compression and separate heat supply to them, are alternately mixed, then separated after the expansion of the mixture in the turbine. The positive effect from the use of such a cycle is explained by the sharp difference in the thermophysical properties of the gases used as working fluids and the optimal parameters and properties of the mixtures obtained by mixing these gases in the ejector. All this makes it possible to increase the thermal efficiency of a heat engine and use low-potential environmental heat (or solar heating) as heating of working fluids.

Claim

1. A method for converting thermal energy into mechanical energy by using two dissimilar working fluids, their separate compression, heat supply, mixing, adiabatic expansion of the mixture to obtain mechanical work, cooling and separating the mixture into working fluids, characterized in that heterogeneous bodies in the gas phase (He - CO 2 , He - N 2 , Ar - CO 2 , H 2 - N 2 or mixtures thereof), heat is supplied to the working bodies separately, and after the expansion of the mixture, heat is regenerated to the original working bodies. 2. The method according to claim 1, characterized in that the mixing of the working fluids is carried out in a gas ejector with a supersonic diffuser.

They are devices for the direct conversion of thermal energy into electrical energy. The principle of operation of TEG is based on the application of the Seebeck effect. With the help of this effect, in many energy systems (for example, in internal combustion engines), it is possible to convert uselessly lost (waste) thermal energy from the engine into electrical energy and use it to power various devices in the car. Thermoelectric generators can also be used in some power plants where the cogeneration method is used, i.e. in addition to the generated electricity, heat is generated, which is used for alternative purposes. Thermoelectricity can also be used in conversion systems solar energy.

The simplest semiconductor thermoelectric generator (thermoelement) consists of negative (n-type conductivity) and positive (p-type conductivity) branches. A material with electronic conductivity has a negative TEDS, and a material with hole conductivity has a positive one, so you can get greater value thermo-EMF (and therefore increased 77).

Rice. 4.54.

The electrical circuit of the running TEG consists of R- and i-branches of one or more thermoelements (Fig. 4.54), hot connecting plates (at a temperature T d) and cold (at temperature T) junctions and active load 7?.

When heating the hot junctions of the thermoelement to a temperature T g and heat dissipation O on cold junctions maintained at a temperature T, and also with an open circuit 7?, between the junctions, a temperature difference is stationary established (T r - T x). The heat flux through the thermoelement, in this case after some simplifications, can be written as

where k is the average value of the thermal conductivities of the branches in the temperature range Г g - Г x; BUT and / - cross-sectional area and length R- and i-branches, respectively.

The temperature difference at the junctions of the thermoelement causes thermal diffusion of carriers, as a result of which the hot junctions of the branches are depleted of electrons and holes, which are concentrated on the cold junctions. The violation of electrical neutrality creates a field directed from cold to hot regions, which prevents further thermal diffusion of carriers. Field and creates thermoelectromotive force V, arising at the ends of the open circuit of the thermoelement. The emerging EMF is proportional to the temperature difference and the difference in the TEMF coefficients of each branch:

At the moment the thermoelement closes to an external load 7? A direct current due to the Seebeck effect will flow in the circuit:

(YARTEG), solar concentrators various execution (STEG). It is tentatively assumed that with electrical powers from 1 to 10 kW on the space aircraft RITEG and STEG are expedient, and when elevated levels power (especially deep space) - YARTEG.

For cathodic protection main gas and oil pipelines from corrosion, in the absence of a power line along the route, TEGs operating on gaseous fuel. For the operation of automation of gas boreholes, TEGs are used that use the temperature difference between the environment and gas from the well. The disadvantages of TEG are relatively low (3-5%) energy conversion efficiency and significant (10-15 kg/kW) specific gravity. Surface density power TEG reaches 10 kW/m 2 (pa unit of the cross section of the element), and the volumetric power density is 200-400 kW/m 3 .

To obtain a standard operating voltage of 30 V in the TEG at a TEMF value of one thermoelement of 0.1-0.3 V, up to 100 elements must be connected in series to the battery. For spacecraft TEGs are created with a power from units to hundreds of watts. TEG cascade connection allows increasing the energy conversion efficiency up to 13%.

Thermoelectric generators are of low-temperature, medium-temperature and high-temperature types. Maximum working temperature low-temperature (most common) TEGs with standard sizes 3x3 and 4x4 cm 2 reaches 470-520 K. The voltage, current and power of such TEGs at cold and hot junction temperatures of 323 and 423 K are 2 V, 1 A and 2 W, respectively.

• Rice. 4.55. Type of industrial TEG (o) and its principle device(b) where r is the internal resistance of the thermoelement. The same current will cause the release and absorption of Peltier heat at the junctions of the p- and /7-branches of the thermoelement with metal plates. The movement of carriers will occur from hot to cold junctions, which corresponds to the absorption of Peltier heat at the hot junctions. In other words, all electric power generated by the thermoelement is the difference between the Peltier heats of the hot and cold junctions. Thermocouple efficiency for thermoelectric generators is estimated by the Ioffe relation (4.13). The fundamental advantages of TEG (Fig. 4.55) over other power sources are as follows: long service life that does not require special maintenance, and an almost unlimited shelf life with full readiness for operation at any time; stability in operation, stable voltage, impossibility of short circuit and idle mode, high reliability, stability of parameters;
• complete noiselessness in operation (due to the absence of moving parts) and vibration resistance. Due to the listed properties, TEGs are used in areas where ultra-reliable power sources are needed that have a long service life and do not require maintenance. They are used to supply electricity to equipment in hard-to-reach objects that are mounted in remote areas of the Earth - automatic weather stations, sea ​​lighthouses, spacecraft. In the future, such objects can be mounted on the Moon or on other planets. Radioactive isotopes (RTEG), nuclear reactors are used as heat sources for supplying TEG hot junctions.

The young French engineer N.S. Karnot decided to investigate the performance of thermal engines. His work "Reflections on the driving force of fire and on machines capable of developing this force" (1824), in which he formulated general and abstract methods for solving a special problem, went beyond the limits of a special study, laying the foundation new science - thermodynamics.

Analyzing the mechanism of action of heat engines, Carnot proceeded from the fact that their operation requires the presence of a temperature difference and then their equalization, just as the difference in water levels is necessary for the operation of water engines. Therefore, “the emergence of a driving force is due to steam engines not the actual waste of caloric, but its transition from a hot body to a cold one, i.e. restoring his balance. But does it determine the work done by the machine? After all, the process of temperature equalization is possible without any work, as with direct thermal contact. In order for work to be done, an intermediary is needed, a working substance that would be able to take heat from the heater (hotter body) at more high temperature and give it to the refrigerator (colder body) - at a lower one.

Carnot considered an ideal machine that would have greater efficiency than any real machine. It is ideal because there is no internal friction in it, and the process is characterized by only two temperatures.

Carnot's theorem proved in this work: the efficiency of any heat engine operating at temperatures is less than the efficiency of an ideal engine. Kar-

but did not calculate the coefficient useful action(efficiency), but indicated that it is proportional to the difference in temperature drop per unit of caloric:

Carnot's ideas did not arouse interest for 10 years, until Clapeyron published his book (1834), in which he gave an analysis of Carnot's work, translated it into mathematical language and somewhat improved the Carnot cycle itself - replaced it with another, now well-known cycle of two adiabats and two isotherms, called the Carnot cycle. Clapeyron was the first to use a graphic representation of reversible circular processes and calculated the work as the corresponding area on the graph.

The transformation of heat into work is important for practical purposes, as is the transformation of one form of energy into another. Let us turn to the scheme of operation of a heat engine. In the cylinder of the machine is placed at atmospheric pressure substance (gas) working body. Raise its temperature without changing the pressure, and the gas should expand. Piston re-

fits in the distance X, moreover, it will move against the external pressure of the atmosphere. If the area of ​​the piston is s, then work is done against a force equal to ps, as R is the force per unit area. The piston has moved a distance X, and work along the way. A minus sign is put here, since work is being done

gas that gives it away external environment moving in the opposite direction of the applied force. Since the work sx is a change in the volume of the gas and is equal to the heat,

spent on gas heating.

Let the gas under the piston in the cylinder be in equilibrium with environment. We will slowly push the piston out of the cylinder, without disturbing the balance at any given moment and keeping the temperature constant. This process corresponds to the empirical law of Boyle - Mariotte: pV= const. Point 7, representing the state of the gas, will move to the planes p, v- exactly 2. If, again, the gas is compressed slowly and at a constant temperature, then the point 2 back to the point 1 because the isothermal process is reversible. There is another reversible process in a perfectly thermally insulated vessel - adiabatic. This process is also very slow, so that the temperature during compression or expansion equalizes at all points, but varies with volume:

Both of these reversible processes are, of course, idealized, real processes can only approach them, since there are always some heat losses due to thermal insulation, viscosity of the medium, etc. The Carnot cycle consists of two isothermal and two adiabatic processes, which form on the graph in coordinates (p, v) curvilinear quadrilateral. Adiabats go steeper than isotherms, so they form sidelines, and isotherms form bases. Heat is supplied and removed during an isothermal process, so the upper isotherm corresponds to the expansion of the gas in thermal contact with the temperature heater T 1 , and the lower one - to compression upon contact with the refrigerator at a temperature T 2 . Let the gas receive heat from the heater Q 1, and gives off heat to the refrigerator Q2. Then for the whole cycle he will receive heat Q=Q 1 -Q2, equal to perfect work BUT. Work attitude BUT to the heat received from the heater (the main costs are associated with the heater, because it needs fuel), is called the efficiency of the heat engine: efficiency =

The efficiency of the engine is thus determined by the temperature difference between the heater and cooler divided by the temperature of the heater:

On fig. 4.3 graphically represents the perfect work at Q= A + Q 1 , The possibility of building a machine without a refrigerator, i.e. with efficiency = 1, which could convert all the heat borrowed from the heat reservoir into work, does not contradict the law of conservation of energy. In my own way practical value she is

would not be inferior to the perpetuum mobile, as it could do work at the expense of almost inexhaustible reserves internal energy contained in the water of the seas and oceans, in the atmosphere and bowels of the Earth. W. Ostwald called such a machine a perpetuum mobile of the second kind (in contrast to a perpetuum mobile of the first kind - perpetual motion machine producing work from nothing). Carnot proceeded from the idea of ​​the impossibility of a perpetual motion machine, based on the facts of numerous experiments, which was elevated to a postulate called the second law of thermodynamics.

Based on thermodynamics, W. Thomson (later Lord Kelvin) proposed an absolute temperature scale (see Fig. 4.1). He proceeded from the fact that the efficiency of all reversible engines is determined only by the absolute temperatures of the refrigerator and heater. The Carnot machine can be used to calibrate the scale if the melting point of the ice is fixed. Having carried out a Carnot cycle between a given body and melting ice and measuring the corresponding amounts of heat, it is possible to find from the direct proportionality of the amount of heat and temperatures absolute temperature(VK). Since 1954, according to the definition of the X General Conference on Weights and Measures, the temperature of the triple point of water (the point of equilibrium coexistence of ice, water and steam) is considered equal to (273.16 K) at a pressure of 6.09 hPa.

Is it possible to increase efficiency by lowering the refrigerator temperature? It would seem that efficiency = 1 at T 2= 0, but all gases begin to liquefy much earlier, i.e., they cease to be gases, therefore, the absolute zero of temperatures is unattainable. This is the content third law of thermodynamics, asserting that it is impossible to cool substances to a temperature absolute zero through finite number steps. Understanding this beginning requires an understanding of atomic structure substances, while other principles are a generalization of direct experience and do not depend on any assumptions. But: is it possible to increase the efficiency by increasing the temperature of the heater? All heat engineering develops along this path (plasma engines, for example, have a temperature of hot matter up to ), but this way

the increase in efficiency is slower than the decrease T 2 . And when they want to lower the temperature of the refrigerator, they usually forget that it takes work to do this, at least with the help of a liquid.

whom air. In refrigeration units, heat is taken from a cold body and given to a hot one, but only due to work from outside. The meaning of the second law of thermodynamics lies in the fact that it is impossible to continuously obtain work without having a reservoir of energy. For the Earth, this source of energy is the Sun. Solar-powered power plants and solar panels, and wind turbines. Their work does not contradict the second law of thermodynamics. In 1851, Kelvin formulated the second law in a different way: "It is impossible for a circular process, the only result of which would be the production of work by cooling the heat reservoir." Max Planck gave a similar formulation: "It is impossible to build a periodically operating machine, the only result of which would be to lift the load by cooling the heat reservoir." Therefore, sometimes they say: "The Thomson-Planck process is impossible." Clausius put forward the second postulate in this form: "Heat cannot spontaneously transfer from a less heated body to a more heated body." It can be shown that all these variants of the second law are equivalent and follow one from the other.