Conversion of thermal energy into electrical and thermoelectric energy. Converting thermal energy into mechanical work How is the conversion of thermal energy into electrical work

Electric current is a directed movement of electrical particles. When moving particles collide with ions or molecules, the kinetic energy of moving particles is partially transferred to ions or molecules, as a result of which the conductor is heated. Thus, electrical energy

is converted into heat, which is spent on heating the wire and dissipated into the environment.

Conversion speed electrical energy into thermal is determined by the power:

R =UI

or considering that U= Ir, we get:

P=UI=I 2 r.

Electrical energy converted into heat

W = Pt = Prt.

Q=I 2 rt.

The resulting expression, which determines the relationship between the amount of heat released, current strength, resistance and time, was found experimentally in 1844 by the Russian academician E. X. Lenz and at the same time by the English scientist Joule. It is now known as the Joule-Lenz law: the amount of heat generated by the current in the conductor is proportional to the square of the current, the resistance of the conductor and the time of passage of the current a.

The conversion of electrical energy into heat is useful application in a variety of heating and lighting fixtures and devices.

In other devices and devices, the conversion of electrical energy into thermal energy is an unproductive expenditure of energy (losses) that reduces their efficiency. In addition, heat, causing these devices to heat up,

limits their load, and when overloaded, the temperature increase can lead to damage to the insulation or to a reduction in the life of the installation.

Example1 -7. Determine the amount of heat released in the heating device during 15 min, if the resistance of the device is 22 om, and the mains voltage is 110 in.

Current strength

I= U: r= 110: 22 = 5a

The amount of heat released in the device,

Q= I 2 rt = 5 2 22 15 60 = 49 500 j.

Article on the topic of Conversion of electrical energy into heat

When current passes through a conductor with resistance, electrically charged particles collide with ions and molecules of the substance. In this case, the kinetic energy of moving particles is transferred to ions and molecules, which leads to heating of the conductor.

E.Kh. Lenz (1804-1865).

The rate of the considered transformation of electrical energy into thermal energy is characterized by the power

keeping in mind that we get:

The amount of electrical energy converted into heat during time t,

Since in the SI system the unit of energy and the unit of heat is the joule, the heat released by the current in the resistance

The resulting dependence was established experimentally in 1844 by the Russian academician E. X. Lenz and at the same time the English scientist Joule and is called the Joule-Lenz law: the amount of heat released by the current in the conductor is proportional to the square of the current strength, the resistance of the conductor and the time of passage of the current.

Conversion of electrical energy into thermal energy electric ovens and various heating appliances has a useful application. AT electrical machines ah and devices, the conversion of electrical energy into thermal energy is an unproductive expenditure of energy, that is, energy losses that reduce their efficiency. Heat, causing heating of these devices, limits their load; In the event of an overload, an increase in temperature can damage the insulation or shorten the service life of the installation.

The invention is intended for use in the field of energy, transport, aviation and astronautics, where big role plays an increase in the efficiency of thermal 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 steam-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. There is a known method of converting thermal energy into mechanical energy in a closed process with heat supply from the combustion of solid, liquid or gaseous fuel 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 stage. 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 to enable the use of low-grade heat, such as solar heat, heat environment and others. The problem is solved by the fact that in the method of converting thermal energy into mechanical energy by using two dissimilar working bodies, their separate compression, heat supply, mixing, adiabatic expansion of the mixture to obtain mechanical work, cooling and separation of the mixture into working bodies, 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) are used as working bodies, heat is supplied to the working bodies separately, and after the expansion of the mixture, heat is regenerated to the original working bodies. 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 gas mixture 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 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, such as 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 A mixture of working fluids expands adiabatically to a pressure of P "cm to obtain 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 to them 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 heat of the environment (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.

Technical field

The invention relates to methods and devices for converting thermal energy into electrical energy and can be used as an autonomous source of electrical energy, using for heating, for example, solar thermal energy or any other heat source.

State of the art

The prior art means and methods for converting thermal energy into electrical energy (see US 4381463 A, 04/26/1983; US 4454865 A, 06/19/1984), using solar energy to heat the working fluid. The principle of operation of the known methods and devices is based on the convection circulation of an electrically conductive working fluid and its passage through a magnetohydrodynamic generator to generate electrical energy. The disadvantages of the known methods and devices are: the complexity of implementation, economic inefficiency, environmental friendliness, due to the use of liquid metals, in particular mercury, as a working fluid.

A power plant device is known (see JPS 62272860 A, 11/27/1987) using an ionized liquid passing through a magnetohydrodynamic generator as an electrically conductive medium. disadvantages known device are, in particular: the complexity of manufacturing, low reliability, due to the operation of the device at high pressures.

Known conversion device solar energy into electric (see US 4191901 A, 03/04/1980), using an organic liquid as a working medium. The disadvantages of the known device, in particular, are: the complexity of the design and low reliability due to the need for its operation at high pressures to ensure the passage of the working medium through the magnetohydrodynamic generator.

As the closest analogue, the method and device for converting thermal energy, known from RU 2013743 C1, 05/30/1994, are taken. The known method includes cyclic heating and evaporation of the liquid, transportation of its vapors, their further condensation in the zone located above the evaporation zone, and the direction of the liquid from the condensation zone to the energy conversion device. The known device contains a liquid in a closed circuit, including a heater-evaporator connected in series, a condenser and an energy converter. The condenser is installed higher than the heater-evaporator, and all elements of the device are connected by a heat-insulated pipeline. The disadvantages of the known device and method, as well as the above-mentioned means and methods, are: the complexity of implementation, low reliability, due to the need to provide reinforced hermetic connections of elements for operation at high pressures.

Disclosure of invention

The objective of the invention is to develop a solution for converting thermal energy into electrical energy, devoid of the shortcomings of known means and methods for this purpose.

The technical result of the proposed invention is to simplify the implementation of the method, the design of the device, improve reliability, durability, environmental friendliness and economy, expand the scope.

The technical result is achieved in a method for converting thermal energy into electrical energy, including cyclic heating and evaporation of the liquid, transporting its vapors, their further condensation in the zone located above the evaporation zone, and directing the liquid from the condensation zone to the energy conversion device. At the same time, a part of the heated liquid is directed directly to the energy conversion device, forming a convection circuit, to the condensation zone, together with vapors, by means of an airlift, another part of the liquid is transported and the liquid from the condensation zone is used to accelerate the liquid in the convection circuit, and atmospheric pressure is provided in the condensation zone. pressure.

Heating and evaporation of the liquid can be carried out using solar energy.

The technical result is achieved in a device for converting thermal energy into electrical energy, containing a liquid in a closed circuit, including a heater-evaporator, a capacitor and an energy converter connected in series with the help of a heat-insulated pipeline. At the same time, an additional convection circuit for liquid is formed in it by means of additional connection outlet of the heater-evaporator with an energy converter, an airlift is installed between the heater-evaporator and the condenser, and the condenser is connected to the energy converter through a convection circuit with the possibility of accelerating the flow of liquid along the circuit, and the condenser is configured to provide atmospheric pressure in it.

As an energy converter, a magnetohydrodynamic generator or a turbine with a generator can be used.

The liquid may contain salt and/or antifreeze and carbon nanotubes. And water can be used as the liquid itself.

The evaporator heater may be configured to receive thermal energy from the sun. In this case, in the case of an opaque liquid, the heater-evaporator is made transparent, and in the case of a transparent liquid, the heater-evaporator is made opaque. The evaporator heater may include heat exchange fins. In a transparent heater-evaporator, heat exchange fins are located inside it, and in an opaque heater-evaporator, heat exchange fins are made on its heated side and face inward. Heat transfer fins are made of dark or black plastic or blackened copper.

Brief description of the drawings

1 is a schematic view of a device for converting thermal energy into electrical energy using a transparent liquid.

2 is a schematic view of a device for converting thermal energy into electrical energy using an opaque or translucent liquid.

Implementation of the invention

The proposed invention is intended for converting thermal energy into electrical energy and can be used as an autonomous source of electrical energy, both for individual household use and for industrial use. As heat sources, you can use fuel sources, radioisotope, nuclear (nuclear reactor heat), solar, waste heat, as well as heat from any sources that emit waste heat (exhaust, furnace gases, etc.). The proposed solution can work in the system, for example, by combining it with solar-powered heating and hot water devices, such as solar collectors.

The essence of the proposed method is to provide double-circuit system movement of fluid flows, one of which uses convection as driving force, and in the other, an airlift is used, followed by the use of the potential energy of the gravitational field to accelerate the flow of fluid in the convection circuit. An embodiment of the proposed method is given below in the description of the device operating on its basis.

The device for implementing the method of converting thermal energy into electrical energy (Figure 1) contains a heater-evaporator 1 connected in series in a closed circuit with heat exchange ribs 2, an airlift 3, a condenser 4, an ejector 5 and an energy converter 6. The output of the heater-evaporator 1 is additionally connected to the inlet of the intake of the ejected medium of the ejector 5, the nozzle of which is connected to the condenser 4. Connections between the elements of the device are made using heat-insulated pipes. The condenser 4 is located higher relative to the heater 1, and a branch pipe 7 is made in it, which serves to equalize the internal pressure of the vapor-liquid medium with atmospheric pressure and the operation of the airlift 3. Through the pipe 7 it is possible to top up the liquid, in case of evaporation and lowering of the level, at other times it is closed with a dust filter or membrane.

All elements of the device, with the exception of the energy converter 6, can be made of plastic, such as polycarbonate. Heat exchange fins 2 can be made of either dark or black plastic or blackened copper. The energy converter 6 can be a magnetohydrodynamic generator (MHD generator) or a liquid turbine with a generator.

Liquid 8 may contain salt and/or antifreeze and carbon nanotubes, and water itself can be used as the liquid itself. The percentage composition of the fluid components is selected from the necessary operational, technical and economic requirements. So, for example, adding antifreeze to the liquid allows the device to operate at low temperatures, the addition of salt also affects the lowering of the freezing point of the liquid and increases its electrical conductivity. The addition of carbon nanotubes to the composition of the liquid affects the intensity of heat transfer and electrical conductivity. Additionally, dyes can be introduced into the composition of the liquid, affecting its transparency for various options execution of the device, which will be shown below.

One embodiment of the device uses a clear liquid (Figure 1). The device for converting thermal energy into electrical energy works as follows. For example, solar energy is used as a heat source, which can be either direct or reflected using a reflector. When thermal (solar) energy enters the heater-evaporator 1, the liquid 8 is heated, which begins convection movement along the circuit (convection circuit), including the heater-evaporator 1, ejector 5, energy converter 6. To improve heat transfer, increase the intensity of heating and vaporization of the liquid 8, with low irradiance, it is possible to use heat exchange ribs 2. When using a transparent liquid, the heater-evaporator 1 is made opaque, and the heat exchange ribs 2 are made on its heated side and face inward. With an increase in the temperature of liquid 8, the boiling process begins and part of it passes into gaseous state(steam), forming a mixture of liquid and vapor. Due to the difference between steam pressure and atmospheric pressure provided by the branch pipe 7 in the condenser 4, the liquid 8 begins to rise through the air lift 3 into the condenser 4. As the liquid 8 accumulates in the condenser 4, it is directed to the nozzle of the ejector 5. Due to the height difference between the condenser 4 and the ejector 5, the liquid 8 at the condenser outlet 4 has potential energy, which in the ejector 5 turns into kinetic energy and is transferred to the fluid flow 8 in the convection circuit, accelerating its movement along the circuit.

When using an MHD generator as an energy converter 6, electrical energy is generated due to the passage of an electrically conductive liquid 8 through it. In the case of using a turbine with a generator, the energy of the fluid flow 8 is converted into mechanical energy of turbine rotation and then into electrical energy. The electrical energy received at the converter 6 is sent to the consumer.

The device can operate at a low heat flux and at very negative temperatures, when the evaporation of the liquid 8 is not possible. In this case, the energy conversion in the device occurs due to the operation of the convection circuit.

The second version of the device, shown in figure 2, works by analogy with the first option. The difference is the use of a transparent heater-evaporator 1. An opaque or translucent liquid 8 is used to absorb solar energy in it. disappears completely.

The proposed method and design of a device for converting thermal energy into electrical energy does not require the provision of sealed seams and materials designed to operate at high pressures, which makes it possible to simplify and reduce the cost of the implementation of the method and the design of the device, to increase their reliability and durability during operation. The possibility of using various energy converters and operation in a wide temperature range expands the scope of the invention. In addition, due to the design features and principle of operation, the device can be made of plastic and use environmentally friendly liquids, which increases its environmental friendliness and efficiency, unlike similar devices that use freon, mercury, etc. as liquids.

Thus, the proposed solution provides the above technical result.

It should be noted that the description of the invention and the drawings are given only as an example and do not limit the possible modifications of the technical solution within the framework of the proposed formula.

1. A method for converting thermal energy into electrical energy, including cyclic heating and evaporation of a liquid, transporting its vapors, their further condensation in a zone located above the evaporation zone, and directing the liquid from the condensation zone to an energy conversion device, characterized in that part of the heated liquid it is sent directly to the energy conversion device, forming a convection circuit, into the condensation zone, together with vapors, by means of an airlift, another part of the liquid is transported and the liquid from the condensation zone is used to accelerate the liquid in the convection circuit, and atmospheric pressure is provided in the condensation zone.

2. The method according to claim 1, characterized in that a magnetohydrodynamic generator or a turbine with a generator is used as an energy converter.

3. The method according to claim 1, characterized in that the liquid contains salt and/or antifreeze and carbon nanotubes.

4. The method according to claim 1, characterized in that water is used as the liquid.

5. The method according to claim 1, characterized in that the heating and evaporation of the liquid is carried out using solar energy.

6. A device for converting thermal energy into electrical energy, containing a liquid in a closed circuit, including a heater-evaporator, a condenser and an energy converter connected in series with the help of a heat-insulated pipeline, characterized in that an additional convection circuit for liquid is formed in it by means of an additional connection of the heater output - an evaporator with an energy converter, an airlift is installed between the evaporator heater and the condenser, and the condenser is connected to the energy converter through a convection circuit with the possibility of accelerating the liquid flow along the circuit, and the condenser is configured to provide atmospheric pressure in it.

7. The device according to claim 6, characterized in that a magnetohydrodynamic generator or a turbine with a generator is used as an energy converter.

8. Device according to claim 6, characterized in that the liquid contains salt and/or antifreeze and carbon nanotubes.

9. The device according to claim 6, characterized in that water is used as the liquid.

10. The device according to claim 6, characterized in that the heater-evaporator is configured to receive thermal energy from the sun.

11. The device according to claim 10, characterized in that in the case of an opaque liquid, the evaporator heater is transparent, and in the case of a transparent liquid, the evaporator heater is opaque.

12. The device according to claim 11, characterized in that the heater-evaporator contains heat exchange fins.

13. The device according to claim 12, characterized in that in a transparent heater-evaporator the heat exchange fins are located inside it, and in an opaque heater-evaporator the heat exchange fins are made on its heated side and face inward.

14. The device according to claim 12, characterized in that the heat exchange fins are made of dark or black plastic, or blackened copper.

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The invention relates to the conversion of thermal energy into electrical energy and can be used as an autonomous source of electrical energy, using for heating, for example, solar thermal energy or any other heat source. The device for implementing the method contains a heater-evaporator 1 with heat exchange fins 2, an airlift 3, a condenser 4, an ejector 5, an energy converter 6, a branch pipe 7. Liquid 8 circulates inside the device. The technical result consists in simplifying the implementation of the method, design, increasing reliability, durability , environmental friendliness and efficiency, expanding the scope. 2 n. and 12 z.p. f-ly, 2 ill.

The conversion of electrical energy into thermal or electric heating has four main varieties, according to which industrial electric furnaces are classified; 1) electric heating through resistance; 2) electric arc heating; 3) mixed electric heating; 4) induction heating.
Electric heating of metallurgical furnaces has significant advantages over heating by burning carbonaceous fuels: the possibility of obtaining very high temperatures up to 3000°C or more with a concentration of high temperature zones in certain sections of the working space of furnaces; ease and smoothness of regulation of the value and distribution of temperature in the working space; cleanliness of the working space and the ability to avoid contamination with ash, sulfur, gases and various impurities: low loss of metals with slag, dust, gases and due to waste; high thermal efficiency, reaching 70-85%; small amount of gases and dust; the possibility of complex mechanization and automation; culture and cleanliness of workplaces; the ability to use any gas medium and vacuum.
The disadvantages of electric heating include: high electricity consumption, significantly exceeding consumption in other industries National economy, and design limitation of performance and power for some types of electric furnaces. In the future, due to an increase in the capacity and number of power plants, a decrease in the cost of electricity and an increase in the power and productivity of electric furnaces, these shortcomings will lose their significance.
The total active or watt power of a three-phase electric furnace installation P is determined by the formula

Electrical heating through resistance

This type of electric heating has several varieties. According to the method of heat release, indirect and direct heating are distinguished; highest value and distribution in furnace technology has indirect heating, characterized by the fact that heat is released in special heating elements (resistances) and transferred from them to the material being processed by heat transfer. According to the temperature of the working space of furnaces, heating is distinguished; low temperature in the range of 100-700°, medium temperature 700-1200° and high temperature 1200-2000°.
With low-temperature heating, heat exchange between the heater and the material is of great importance by convection, which is intensified in every possible way by forced circulation at high speeds of gas or air inside the furnaces. During medium and high temperature heating, especially in the absence of forced circulation gases, the main amount of heat is transferred from the heaters to the processed materials by radiation. For electric resistance furnaces, high temperature heating is only of limited value.
Electric resistance heating has found the greatest application for drying and firing materials, heating and heat treatment of metals and alloys, melting low-melting metals - tin, lead, zinc, aluminum, magnesium and their alloys, as well as for laboratory and household needs. Since, however, with indirect heating, the size heating elements increases, and placing them in the working space of the furnace is difficult, the upper limit of the power of electric resistance furnaces is limited to 600-2000 kW.
For the normal course of the process of converting electrical energy into thermal energy and long-term stable operation, the heating elements must have the following qualities: high electrical resistivity, allowing a sufficient cross-section of the elements and their limited length; small electrical temperature coefficient, which limits the difference in the electrical resistance of a heated and cold heater, constancy electrical properties in time; heat resistance and non-oxidation; heat resistance, i.e. sufficient mechanical strength at high temperatures; constancy of linear dimensions; good machinability of the material (weldability, ductility, etc.). These requirements are best met by alloys of nickel, chromium, iron (nichrome, fechral and heat-resistant steel) used in resistance electric furnaces in the form of wire or tape, and carbonaceous materials used in the form of carbon, graphite or carborundum rods.
The determination of the dimensions of the heating elements can be scientifically substantiated by the joint solution of two basic equations that describe the essence of the work of the heaters - the power equation and the heat transfer equation. Because the heating element is integral part electrical purpose, then in order to obtain the necessary power, it must have certain dimensions and resistance. On the other hand, all the heat energy received in the heating element as a result of electricity conversion must be transferred by heat transfer to the processed materials and the furnace lining, for which it is necessary to have a certain surface, temperature and heat transfer coefficient. If the heat transfer of the heating element does not correspond to the heat release occurring in it, the element will overheat, and its temperature may exceed the allowable limits for the material, which will lead to the destruction of the heater.
Based on the solution of the power equation for heating elements of any shape and material, the general formula is derived

When calculating the dimensions of the heater, the value of w must exactly correspond to its specific heat transfer, which is found by solving the corresponding heat transfer equation for the heater, masonry and A.D. material. Svenchansky analyzed the heat transfer conditions for various real heaters and compiled graphs and tables that can be used to find the value of w.

Arc electric heating

This type of electric heating is used in high-temperature electric furnaces of high power, mainly for melting various materials. If the arc burns between the electrode and the material processed in the furnace, then such furnaces are called direct-acting furnaces with a dependent arc: open - visible (Fig. 20, a) or closed - invisible arc immersed in a layer of charge or melt (Fig. 20, b ). If the arc burns between the electrodes and does not directly come into contact with the materials and products processed in the furnace, then such furnaces are called indirect furnaces with an independent arc (Fig. 20, c). Direct-acting arc furnaces, especially with a closed arc, have the highest thermal efficiency, since they have the best conditions for heat exchange between the arc and the material, allowing the material to be heated quickly and with limited heat loss to a very high temperature.

Direct-acting arc furnaces are most widely used for smelting steel and ferroalloys, smelting and refining copper and nickel, and processing various ore raw materials. When melting metals or alloys with high (metallic) electrical conductivity, you can only work with an open arc burning on the surface of the material, since immersion of the electrodes in the layer of material will lead to a short circuit. Closed arc operation is possible when the processed materials and products have limited (non-metallic) electrical conductivity. Indirect arc furnaces are used in cases where the contact of the processed material with the arc worsens the quality of the products or increases losses, for example, when melting some non-ferrous metals and alloys (brass, bronze, etc.). It should be emphasized that electric arc heating, unlike resistance heating, does not have any restrictions on the total power of furnaces.
Arc electric heating consists of the process of converting electricity into heat, occurring in a burning arc, and the process of heat exchange between the arc, material and lining. The description of the regularities of the first process is the subject of the so-called theory of the arc, and especially of the arc alternating current high power. A significant contribution to the development of the arc theory was made by V.V. Petrov, V.F. Mitkevich, S.I. Telny, I.T. Zherdev, K.K. Khrenov, G.A. Sisoyan and others. D.A. Diomidovsky, N.V. Okorokov and others.
An electric arc can be obtained with direct and alternating current, but all industrial furnaces usually run on alternating current. For stable burning of the arc and limiting current surges during short circuits, an inductive reactance is included in series with it in the electrical circuit, absorbing a small fraction of the active power. With alternating current, during each half-cycle, the mains voltage and current strength reach a maximum and pass through zero. On fig. 21, a shows the theoretical curves of the instantaneous value of the current and arc voltage Id and Ud and the voltage of the supply source Uist. When the source voltage begins to rise after the zero crossing, the arc is ignited only when the ignition voltage U1 is reached. From that moment on, a current appears in the circuit, increasing along a periodic curve other than a sinusoid. The arc dies out at the attenuation voltage, i.e., before the source voltage crosses zero, and at this moment the current stops. After passing through zero, all the described phenomena are repeated. Thus, the current in the arc is intermittent and the arc is ignited, then extinguished. The duration of interruptions in arc burning depends on many factors, in particular, on the material of the electrodes, the degree of heating of the furnace space, etc. It is clear that an intermittent arc reduces the efficiency of arc heating and therefore conditions must be created to ensure continuous burning of the alternating current arc. The main means for continuous burning of an alternating current arc is the series inclusion of an inductive resistance arc in the circuit, as can be seen from fig. 21b and c.
Study differential equation arc of alternating current, which has active and inductive resistances in the circuit, determined the ratio of the values ​​of inductive X and active R resistances, which ensures continuous arc burning at given source voltages Uist and arc Ud (Fig. 22).

The efficiency of arc heating depends to a very large extent on electric mode burning arc and, first of all, on the values ​​of voltage and current.
At present, a scientifically based method for determining the most advantageous voltage for powering arc furnaces has not yet been created. Therefore, the voltage is chosen according to factory practice in the range from 100 to 600 V, and more high voltage generally accepted for high power arc furnaces and closed arc furnaces. The relationship between the maximum operating voltage Ulin and the rated power of the furnace Рnom is usually expressed by the empirical formula

where k and n are empirical coefficients having various meanings depending on the type of furnace and the nature of the process. For example, for arc steel-smelting furnaces k = 15; n = 0.33. Working at increased voltage is more rational, as it reduces power losses and increases the length and thermal radiation of the arc. The upper voltage limit (600 V) is mainly due to the conditions electrical insulation furnace and the safety of the attendants.
After determining the voltage value, the choice of other indicators of the electric mode of the electric furnace installation with arc heating - the optimal current strength, cos φ and efficiency - is made according to its performance characteristics. The operating characteristics of arc furnaces are found by constructing circular diagrams: for existing factory furnaces they are taken from nature, for newly designed furnaces - according to calculated data.
For the theory of arc heating and calculation of arc furnaces, the process of heat exchange between the burning arc and the materials processed in the furnace is of great importance. However, the theory of heat transfer in the working space of arc furnaces is still in development. initial stage its development and requires further in-depth development.

Mixed electric heating

This type of heating, which is the result of joint heat release in the electric arc and in the resistance of the charge layer or melts, is of primary importance for ore-thermal furnaces that smelt ferroalloys, cast iron and process ore raw materials and semi-products of non-ferrous metallurgy and the chemical industry.
in the most difficult case electricity, passing through the arc and layers of charge, slag and metal, is converted in them into thermal energy Q of the arc, Q charge, Q slag, Q metal, furnace Rtot represents the sum of the listed heat releases. The principle scheme for calculating all these heat releases and their connection with the geometry of the hearth of ore-thermal furnaces was once covered by the author, but for an accurate calculation of heat release, there are still very few data on the thermal characteristics of the arc, the electrical resistance of the charge and melts, the shape and size of the conductive sections, etc. Accordingly, the method proposed by the author for calculating ore-thermal electric furnaces is still indicative and has limited application.
For non-ferrous metallurgy, ore-thermal furnaces operating with electrodes immersed in thick layer slag, in which mixed electric heating occurs, consisting of two main components: Qarc and Qslag.
M.S. Maksimenko proposed to divide all electrothermal processes into two main groups; 1) processes in which the fraction of energy absorbed in the arc p is greater than the fraction of energy absorbed in the charge and melts 2) processes in which p

Induction electric heating

Induction electric heating is carried out according to the principle of a transformer, in which secondary winding closed on. itself, as a result of which the induced electric current is converted into thermal energy. The role of the secondary winding is usually played by the heated material itself. The electrical energy supplied to the primary winding (inductor) makes a complex transition into the energy of a rapidly changing magnetic field, which, in turn, again passes into the secondary circuit into electrical energy, which is converted here due to the resistance of the circuit into thermal energy. If the material being heated is ferromagnetic, then part of the energy of the alternating magnetic field is converted into thermal energy directly, without conversion into electrical energy.
The most widespread in technology are two types of induction furnaces: 1) furnaces with an iron core; 2) coreless furnaces - high frequency.

Iron core furnaces have circuit diagram(Fig. 23, a), similar to the circuit of a conventional transformer, in which the primary winding is mounted on an iron core, and the secondary is represented by a closed ring of molten metal, i.e., combined with the load. As a result of vigorous circulation, the metal heated in the annular channel rises up into the working space of the furnace and, in contact with the charge located there, heats and melts it.
Coreless furnaces in their scheme represent an air transformer (Fig. 23, b), the primary winding of which is copper coil- the inductor, and the secondary is the metal charge itself, loaded into the crucible.
The effective value of the induced electromotive force E. in, depends on the amplitude value of the useful magnetic flux Fm, wb, alternating current frequency f, per / sec, the number of turns of the winding w, and is expressed by the formula

In furnaces with an iron core, the value is quite large due to the concentration of useful magnetic flux in the core, and in furnaces without a core, the value is small due to large magnetic dissipation. As a result, in induction furnaces with an iron core, the required value of the electromotive force E is easily achieved at alternating current with normal and reduced frequency (f The main advantages of induction heating are as follows: heat release directly in the mass of the heated material, which reduces the role of heat exchange processes, provides more uniform heating of the material and significantly increases the thermal efficiency of induction furnaces; exceptional cleanliness of the working space of furnaces (due to the absence of polluting products of combustion of fuel, materials of heating elements and electrodes), which makes it possible to obtain highly pure metals and alloys; the possibility of complete isolation of the working space of furnaces from the surrounding air and conducting melting in a vacuum or in a gas protective atmosphere; the possibility of obtaining a very high temperature, limited only by the properties of the heated material and refractory masonry; vigorous mixing of melts by electromagnetic and thermal and flows, allowing to obtain alloys of uniform chemical composition; high specific productivity of induction furnaces; high speed heating and melting; small losses of metals from waste; high technical culture of furnace units, absence of dust and gases.
The disadvantages of induction heating include: reduced power factor, since for furnaces with an iron core cos φ = 0.3 / 0.8 and for coreless furnaces cos φ = 0.03 / 0.1; limited size, power and capacity of induction furnaces compared to other units; complexity electrical equipment coreless furnaces requiring special high-frequency alternating current sources and high-capacity capacitor banks; limited resistance of the lining of the channels of furnaces with an iron core and crucibles of coreless furnaces: low temperature slag heating.
The advantages of induction heating have led to its widespread use. Iron core induction furnaces are currently the main equipment for melting and casting non-ferrous metals and the production of non-ferrous alloys. Coreless induction furnaces are used for melting non-ferrous and precious metals and for producing high-quality steel castings. In the metallurgy of copper, nickel and zinc, induction furnaces are also used, operating at final stages. Induction heating is widely used in engineering plants for heat treatment various metal blanks and products.
The theory of iron core induction furnaces is based on the theory of a single-phase two-winding iron core transformer. The difference between a conventional transformer and induction furnace with an iron core lies in the fact that in a transformer the secondary winding and the consumption network (load) are located at a considerable distance from one another, and in an induction furnace the secondary winding is combined with the load and is represented by a ring of molten metal.
The converted power Ppr can be expressed in terms of the secondary current I2 and the actual active resistance of the metal in the channel r2 by the formula

The power lost in the inductor (electrical losses) Rel is expressed in terms of the primary current I1 and the actual active resistance of the inductor winding

The total active (watt) power of an induction furnace with an iron core P will be

In the theory of induction furnaces without an iron core, these furnaces are considered as air transformers, in which, as a result of the absence of a closed iron magnetic circuit, magnetic fluxes pass through the mixture being processed and through the air.
The frequency of the alternating current supplying the inductor f depends on the capacity (power) of the induction furnace and the specific resistance of the processed charge p2. Studies show that the larger the capacity of the furnace and its dimensions, in particular, the charge diameter d, cm, and the lower the specific resistance of the molten metal p2. ohm/cm3, the lower the minimum frequency fmin, Hz; this dependence is expressed by the formula

Each furnace capacity and resistance corresponds to a certain optimal frequency of the supply current, at which the efficiency of the furnace reaches its maximum possible value. For coreless furnaces of high capacity (power) it was possible to use a reduced frequency of alternating current, up to the normal 50 Hz.
The active power of the coreless furnace Pa consists of the power converted in the charge and the power lost in the inductor, and is expressed by the formula

Based on the regularities of the processes of fuel combustion and the conversion of electrical energy into thermal energy, the following most important tasks in the theory, operation and design of metallurgical furnaces can be solved:
a) choice of furnace heating system (carbonaceous fuel or electricity);
b) selection of the type and grade of fuel and its combustion system;
c) the choice of parameters of electricity and the system for its conversion into thermal energy;
d) calculations of fuel combustion processes;
e) selection and calculation of combustion devices;
f) calculation and design of electric furnaces.