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Conversion electrical energy thermal or electric heating has four main types, according to which industrial electric furnaces are classified; 1) electric heating through resistance; 2) arc electric heating; 3) mixed electric heating; 4) induction heating.
Electric heating of metallurgical furnaces has significant advantages compared to heating as a result of combustion of carbonaceous fuel: the ability to obtain very high temperatures of up to 3000°C or more with the concentration of high temperature zones in certain areas of the working space of the 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 fumes; high thermal efficiency, reaching 70-85%; small amount of gases and dust; possibility of complex mechanization and automation; culture and cleanliness of workplaces; the ability to use any gas environment and vacuum.
The disadvantages of electric heating include: high electricity consumption, which significantly exceeds consumption in other industries national economy, and design limitations 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, the listed disadvantages will lose their significance.
The total active or watt power of a three-phase electric furnace installation P is determined by the formula
Electric heating through resistance
This type of electric heating has several varieties. Based on the method of heat generation, a distinction is made between indirect and direct heating; highest value and indirect heating is widespread in furnace technology, characterized by the fact that heat is released in special heating elements (resistances) and is transferred from them to the material being processed by heat transfer. Based on the temperature of the furnace working space, heating is distinguished; low temperature in the range of 100-700°, medium temperature 700-1200° and high temperature 1200-2000°.
At low temperature heating, very great value has heat exchange between the heater and the material by convection, which is intensified in every possible way by forced circulation at high speeds of gas or air inside the liver. During medium-temperature and high-temperature heating, especially in the absence of forced circulation of gases, the main amount of heat is transferred from the heaters to the materials being processed by radiation. For electric resistance furnaces, high temperature heating is of only limited importance.
Electric heating by resistance found greatest application for drying and firing of 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 domestic needs. Since, however, with indirect heating the size of the heating elements increases, and their placement in the working space of the furnace turns out to be difficult, the upper limit of the power of electric resistance furnaces is limited to 600-2000 kW.
For the normal process of converting electrical energy into thermal energy and long-term stable operation, heating elements must have the following qualities: high electrical resistivity, allowing for a sufficient cross-section of the elements and a limited length; small electric temperature coefficient, limiting the difference in electrical resistance of the heated and cold heater to constant electrical properties in time; heat resistance and non-oxidation; heat resistance, i.e. sufficient mechanical strength at high temperatures; constancy of linear dimensions; good workability 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 carbon materials used in the form of carbon, graphite or carborundum rods.
The determination of the dimensions of heating elements can be scientifically justified by the joint solution of two basic equations that describe the essence of the work of heaters - the power equation and the heat transfer equation. Since the heating element is integral part electrical purpose, then to obtain the required power it must have certain dimensions and resistance. On the other hand, all the thermal energy obtained in the heating element as a result of the conversion of electrical energy 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 permissible limits for the material, which will lead to destruction of the heater.
Based on the solution of the power equation for heating elements of any shape and material, a 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 of the heater, masonry and material A.D. Svenchansky analyzed the heat transfer conditions for various real heaters and compiled graphs and tables with which you can find the value of w.
Electric arc heating
This type of electric heating is used in high-temperature high-power electric furnaces mainly for smelting various materials. If an arc burns between the electrode and the material processed in the furnace, then such furnaces are called furnaces direct action 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 arc furnaces have the highest thermal efficiency, especially with closed arc, since they contain best conditions for heat exchange between the arc and the material, allowing the material to be heated quickly and with limited heat loss to very high high temperature.
Direct arc furnaces are most widely used for the smelting of steel and ferroalloys, smelting and refining of copper and nickel and processing of 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 immersing the electrodes in the material layer will lead to a short circuit. Closed arc operation is possible when the materials and products being processed have limited (non-metallic) electrical conductivity. Indirect arc furnaces are used in cases where the contact of the processed material with the arc deteriorates the quality of the products or increases losses, for example, when melting some non-ferrous metals and alloys (brass, bronze, etc.). It should be especially emphasized that electric arc heating, unlike resistance heating, does not have any restrictions on the total power of the furnaces.
Electric arc heating consists of the process of converting electricity into heat, which occurs in a burning arc, and the process of heat exchange between the arc, the material and the lining. The description of the laws of the first process is the subject of the so-called arc theory and especially the high-power alternating current arc. A significant contribution to the development of 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. The issues of heat exchange between the arc, material and lining were dealt with by D.A. Diomidovsky, N.V. Okorokov and others.
An electric arc can be produced using direct or alternating current, but all industrial furnaces usually operate on alternating current. To ensure stable arc burning and limit current surges during short circuits, an inductive reactance is connected in series with it in the electrical circuit, absorbing a small fraction of the active power. With alternating current, during each half-cycle the network voltage and current reach a maximum and pass through zero. In Fig. 21, a shows the theoretical curves of the instantaneous value of the current and arc voltage Id and Ud and the supply voltage Uist. When the source voltage begins to increase after crossing zero, the arc is ignited only when the ignition voltage U1 is reached. From this moment, a current appears in the circuit, increasing along a periodic curve that is different from a sinusoid. The arc extinguishes at the attenuation voltage, i.e., before the source voltage crosses zero, and at this moment the current stops. After crossing zero, all the described phenomena are repeated. Thus, the current in the arc flows intermittently and the arc either lights up or goes out. The duration of interruptions in arc burning depends on many factors and, 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 sequential inclusion of inductive reactance in the arc circuit, as can be seen from Fig. 21, b and c.
The study of the differential equation of an alternating current arc, which has active and inductive resistance in the circuit, determined the ratio of the values of inductive X and active R resistance, ensuring continuous arcing at given source voltages Uist and arc Ud (Fig. 22).
The efficiency of arc heating is very to a large extent depends on the electrical mode of the burning arc and, first of all, on the 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 selected according to factory practice in the range from 100 to 600 V, with higher voltages usually adopted for high-power arc furnaces and for furnaces with a closed arc. The relationship between the maximum operating voltage Uline and the rated power of the furnace Pnom is usually expressed by the empirical formula
where k and n are empirical coefficients having different 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 higher voltage is more rational, as it reduces electricity losses and increases the length and thermal radiation of the arc. The upper voltage limit (600 V) is mainly determined by the conditions of electrical insulation of the furnace and the safety of operating personnel.
After determining the voltage value, the choice of other indicators of the electrical mode of an electric furnace installation with arc heating - optimal current strength, cos φ and efficiency - is made according to its operating characteristics. The performance characteristics of arc furnaces are determined by constructing pie charts: for existing factory furnaces they are taken from nature, for newly designed furnaces - according to calculated data.
For the theory of arc heating and the 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 its infancy. initial stage its development and requires further in-depth development.
Mixed electric heating
This type of heating, which is the result of combined heat release in an electric arc and in the resistance of a layer of charge or melts, is of primary importance for ore-thermal furnaces that smelt ferroalloys, cast iron and process ore raw materials and intermediate products of non-ferrous metallurgy and the chemical industry.
at most difficult case electric current, passing through the arc and layers of charge, slag and metal, is converted into thermal energy Qarc, Qcharge, Qslag, Qmetal, furnace Рtotal represents the sum of the listed heat releases. The principle diagram for calculating all these heat releases and their connection with the geometry of the hearth of ore-thermal furnaces was at one time illuminated by the author, but for an accurate calculation of heat releases, a lot of data is still missing on the thermal characteristics of the arc, the electrical resistance of the charge and melts, the shape and size of the conductive sections, etc. . p. Accordingly, the method for calculating ore-thermal electric furnaces proposed by the author is still indicative and has limited application.
For non-ferrous metallurgy, ore-thermal furnaces are of greatest importance, operating with electrodes immersed in a thick layer of slag, in which mixed electric heating occurs, consisting of two main components: Qarc and Qslag.
M.S. Maksimenko proposed dividing 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 the secondary winding is short-circuited. 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. Electrical energy supplied to the primary winding (inductor) makes a complex transition into the energy of a rapidly alternating magnetic field, which, in turn, is again converted into electrical energy in the secondary circuit, which is converted here due to the resistance of the circuit into thermal energy. If the heated material is ferromagnetic, that part of the energy of the alternating magnetic field is converted into thermal energy directly, without converting into electrical energy.
Two types of induction furnaces are most widespread in technology: 1) furnaces with an iron core; 2) furnaces without a core - high-frequency.
Iron core furnaces have schematic 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 winding 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, coming into contact with the charge located there, heats and melts it.
Furnaces without a core, in their diagram, represent an air transformer (Fig. 23, b), the primary winding of which is a copper coil - an inductor, and the secondary winding is the metal charge itself loaded into the crucible.
Effective value of the induced electromotive force E. in, depends on the amplitude value of the useful magnetic flux fm, vb, alternating current frequency f, per/sec, number of winding turns w, and is expressed by the formula
In furnaces with an iron core, the value is quite large due to the concentration of the useful magnetic flux in the core, while in furnaces without a core the value is small due to large magnetic dispersion. As a result, in induction furnaces with an iron core, the required value of electromotive force E is easily achieved using alternating current with normal and reduced frequencies (f The main advantages of induction heating are the following: heat release directly in the mass of the heated material, which reduces the role of heat exchange processes, ensures more uniform heating of the material and significantly increases the thermal efficiency of induction furnaces; exceptional cleanliness of the furnace working space (due to the absence of fuel combustion products, heating element materials and electrodes that pollute it), which makes it possible to obtain especially pure metals and alloys; complete isolation the working space of the furnaces from ambient air and smelting in a vacuum or in a protective gas atmosphere; the possibility of obtaining a very high temperature, limited only by the properties of the heated material and refractory masonry; energetic mixing of melts by electromagnetic and thermal 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 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; the complexity of the electrical equipment of coreless furnaces, requiring special high-frequency alternating current sources and capacitor banks of significant capacity; limited durability of the lining of the channels of furnaces with an iron core and the crucibles of coreless furnaces: low heating temperature of the slag.
The advantages of induction heating have made it widespread. Iron core induction furnaces are currently the main unit for melting and casting non-ferrous metals and producing 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 operating at final stages are also used. Induction heating is widely used in machine-building plants for heat treatment of various metal workpieces and products.
The theory of iron core induction furnaces is based on the theory of single-phase two-winding iron core transformer. The difference between a conventional transformer and an induction furnace with an iron core is 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 through the secondary current I2 and the actual active resistance of the metal in channel r2 by the formula
The power lost in the inductor (electrical losses) Rel is expressed through 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 processed charge and through the air.
The frequency f of the alternating current supplying the inductor depends on the capacity (power) of the induction furnace and the resistivity of the processed charge p2. Research shows that the larger the furnace capacity and its dimensions, in particular the diameter of the charge d, cm, and the smaller resistivity 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 high-capacity (power) coreless furnaces, it turned out to be possible to use a lower frequency of alternating current, down to the normal 50 Hz.
The active power of a 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 laws of the processes of fuel combustion and the conversion of electrical energy into heat, the following most important tasks on theory, operation and design of metallurgical furnaces:
a) choice of heating system for furnaces (carbon fuel or electricity);
b) selection of the type and grade of fuel and its combustion system;
c) selection of parameters of electricity and the system for converting it into thermal energy;
d) calculations of fuel combustion processes;
e) selection and calculation of combustion devices;
f) calculation and design of electric furnaces.
The number of digital gadgets is constantly increasing. TO cell phone a mobile radio station, a GPS navigator and a camera were added.
Carrying around a full pot of spare batteries for all this electronic fraternity is difficult, and in the cold season it is also pointless - their capacity and power are low temperatures are greatly reduced.
Therefore, every traveler would like to acquire a device that converts the energy available on a hike into electricity.
Thermal generators turned out to be very practical - sources that require heat to operate. What is the principle of their operation based on and how you can make thermoelectric generators with your own hands - this will be discussed in this article.
Thermoelectromotive force occurs in a closed loop when two conditions are met:
- If it consists of at least two conductors made of different materials.
- If all heterogeneous sections included in the contour have different temperatures(at least in the connection area).
In physics this phenomenon called the Seebeck effect.
The magnitude of thermoEMF depends on the type of materials and their temperature difference.
It is determined by the formula:
E = k (T1 – T2),
- Where T1 and T2 are the temperature of the conductors;
- K – Seebeck coefficient.
The highest performance is achieved by circuits consisting of dissimilar semiconductors (having p- and n-conductivity). In metals, the Seebeck effect is minor, with the exception of some transition metals and their alloys, such as palladium (Pd) and silver (Ag).
Heat exchangers are widely used in everyday life. It can be done quite easily - assembly instructions are presented in the article.
Step-by-step instructions for covering a fireplace with your own hands are presented.
Did you know that as little as 12 volts can serve as a heat source? Follow the link for instructions on making a 12 Volt heater with your own hands.
Operating principle
Solving the problem of producing electricity from thermal energy requires, as they say in science, the opposite. The opposite of the Seebeck effect is the Peltier effect, which consists of changing the temperatures of two dissimilar semiconductors combined in a closed circuit when passing through them DC: one of them heats up, the second cools down.
If the direction of the current is changed, the direction will also change heat flow: the first semiconductor will cool down, and the second will heat up. The most commonly used semiconductors are a solid mixture of silicon with germanium and bismuth telluride.
Peltier effect
The effect discovered by Jean Peltier has been widely used in various fields human life, where refrigeration machines are required, but it is not possible to use a compressor heat pump using freon. Therefore, it was his name that was used to name the devices produced for this purpose - Peltier elements.
But if such an element or, as it is also called, a thermoelectric cooler is influenced from the opposite side, that is, a temperature difference is created on its semiconductors, then we will get the Seebeck effect: the Peltier element will turn into a direct current source.
Thermal generator design
So, the idea of a thermal generator is quite simple: you need to take a Peltier element and strongly heat one of its surfaces. In factory-made generators, gas burners are used for this. But creating such a device at home is quite difficult - it is difficult to ensure stable combustion of the flame for a long time.
Therefore, craftsmen prefer a simpler version of the thermogenerator, which we will now talk about.
DIY making
Schematically, the structure of a homemade thermoelectric power plant can be represented as follows:
- We place the Peltier element at the bottom of a deep vessel - a bowl or mug.
- Next, we’ll insert another one into this vessel: if bowls are used, you’ll need the same one; if your choice fell on mugs, then the second one should be slightly smaller than the first.
- We will connect a voltage converter to the wires removed from the Peltier element.
- Fill the inner container with snow or cold water, after which we put the entire structure on fire.
After some time, the snow will melt, turn into water and boil. The productivity of the generator will decrease, but the tourist will have the opportunity to drink hot tea. After drinking tea, you can fill the generator with a new portion of snow.
The more thermoelements (they are also called branches) the Peltier element you purchased has, the better. You can use a device of the TEC1-127120-50 brand - it has 127 of them. This element is designed for currents up to 12A.
Work order
Now let's look at the process of creating a homemade thermal generator in detail:
- The surface of each vessel at the point of contact with the Peltier element should be leveled and cleaned, which will ensure maximum heat transfer. For a perfect fit, you can polish the bottoms with a piece of felt greased with GOI paste, fixed in the spindle of an electric drill.
- We connect wires from an electric stove equipped with heat-resistant insulation to the contacts of the Peltier element. In the absence of such, you can use, for example, MGTFE-0.35 wire, wrapping it in heat-resistant fabric.
- Having lubricated the bottom of one of the vessels with thermal conductive paste, for example, KPT-8, we place a Peltier element on it. The wires connected to it should be positioned so that their ends are outside the container.
- Lubricate the Peltier element on top with thermal paste again and insert a second container of a suitable size into our mug or bowl (you will need to cut off the handle of the mug).
- The space between the containers must be filled with heat-resistant sealant (you can buy a composition for repairing exhaust pipes at a car store). It will serve as thermal insulation between the hot and cold sides of the generator and additional protection for wires.
Camping electricity generator
The protruding ends of the wires can be glued to the side of the mug with fabric tape.
Converter manufacturing
During the experiment, a thermogenerator installed on an electric stove, in the presence of snow in the internal container, provided an EMF of 3V and a current of 1.5A. After the snow turned into water and boiled, the power of the generator dropped three times (the voltage was 1.2V).
To use such a device as charger For a phone or other gadget that requires a stable voltage of 5 V or 6.5 V, it must be equipped with a voltage converter.
Let's consider two options.
Option 1
The easiest way is to use the KR1446PN1 microcircuit, equipped with a DIP housing, as a converter.
It is produced in Russia and can be easily found in a radio parts store or on the radio market.
It is not forbidden to use more powerful analogues, but they are all produced in miniature surface-mount packages, so you will have to suffer with wiring.
The input of the microcircuit is supplied with voltage from the Peltier element, and it turns on in the “5 Volt” (standard) mode. In parallel with the Peltier element, a sufficiently powerful shunt diode should be soldered to the input of the voltage converter. It will prevent current from flowing into reverse direction, if the opposite temperature effect is exerted on the generator.
For example, being filled hot water it may be inadvertently installed on some cold surface.
To the output of the converter you need to solder a cable from an old charger suitable for our model of phone or camera, as well as a 5 V LED indicator.
The disadvantage of this option: the microcircuit proposed as a converter limits the power of the generator, since the current at its output does not exceed 100 mA. Thus, the Peltier element is used by approximately 20%, which will only be sufficient for older models of phones.
To be able to charge more powerful devices, you need to use a more sophisticated version of the voltage converter.
Option 2
A more powerful converter can be assembled using a two-stage circuit using a pair of MAX 756 microcircuits. So that when the consumer is disconnected, the generated current does not go to waste, we will equip the converter with built-in batteries. Connected in series, they are included in the load of the first stage through a switch, diode and current-limiting resistor. The cascade itself is configured for the “3.3 Volt” output mode.
To the output of cascade No. 1 we connect cascade No. 2, configured to the “5 Volt” output mode. Both stages are implemented according to the diagram given in the documentation for the MAX 756 chip (published on the Internet). The only difference is the chain feedback cascade No. 2 (between the output of the cascade and leg No. 6 of its microcircuit) is complemented by a sequence of 3 silicon diodes located with the anode towards the output.
The simplest camping thermogenerator
This improvement will allow you to receive a voltage of 6.5 V at idle (required for charging some electronic devices).
To simplify the circuit, you can use the MAX 757 chip, which is equipped with a separate feedback output.
The interface of this converter corresponds to USB Type A. But if you intend to connect a USB device to it, then it is better to remove the sequence of diodes from the feedback circuit of the 2nd stage so that the output voltage returns to the level of 5 V.
This version of the converter cannot be connected to USB-Host type ports.
Variation on a theme...
The Peltier element can simply be attached to a stake stuck into the ground near the fire.To create sufficient temperature gradient, both of its surfaces must be equipped with finned radiators.
On the surface on the flame side, the radiator should have an increased area, and its fins should be installed horizontally.
A smaller radiator is installed on the opposite side of the element, and its fins are vertical.
Heating radiators can be installed differently depending on the type heating system– single-pipe or double-pipe. and tips on where to install them - read carefully.
How to repair circulation pump with your own hands? The main types of breakdowns and methods for eliminating them are presented.
Video on the topic
The method is carried out by using one or more closed turns of an electric current conductor as a heating element, forming the secondary winding of an electric transformer, and introducing the coolant into contact with the surfaces of the conductor. The invention improves the reliability of electrical energy conversion during heat exchange. 1 salary, 1 ill.
The invention relates to technology for converting electrical energy into heat and creating heat exchange. It can be used to heat fluid in engine preheating systems internal combustion, heating and hot water supply industrial enterprises and residential buildings, for heating plasma and other substances. There is a known method of converting electrical energy into heat and creating heat exchange, based on the direct passage of electric current through the coolant, created by supplying mains voltage through current leads to the electrodes (see A.P. Althauzen et al., “Low-temperature electric heating”, Moscow, Energy, 1968). It is used to heat liquids, concrete, and to thaw soil, ore, sand and other substances. The main disadvantages of this method are the increased electrical hazard due to the relatively high voltage(380 V or 220 V), as well as the dependence of electric heating and heat transfer on the electrical resistance of the coolant. In particular, special additives are added to the heated water to ensure a given value of electrical resistance. There is a known method of converting electrical energy into heat and creating heat exchange between a heating element and a coolant, including supplying power to the heating element, which is a metal tube, inside of which there is a heating coil pressed into a special filler, passing an electric current through the heating coil (see A. P. Althauzen et al., “Low-temperature electric heating”, Moscow, Energia, 1968). This method has become widespread in various areas national economy. The tubular electric heater (TEH) can be placed in water, salts, liquid metal, mold, crankcase of internal combustion engine, etc. However, the heated coil is supplied electrical voltage directly from the supply network, and the relatively high voltage cannot be reduced electrical resistance spiral, which entails the need for electrical insulation of the spiral to ensure electrical safety and which in turn reduces the thermal conductivity between the spiral and the metal tube, and therefore worsens the heat exchange between the heating element (ohm) and the coolant as a whole. The electrical insulation of the spiral does not exclude the possibility of its electrical breakdown and contact with the metal tube of the heating element (a) electric potential, which leads to the need for its grounding. In addition, the heating element(s) have a limited service life due to burnout of the coil. There is a known method of converting electrical energy into heat and creating heat exchange, called "Resistance welding" (see N.S. Kabanov, "Welding on contact machines", Moscow, ed. " graduate School", 1985; Y.N. Bobrinsky and N.P. Sergeev, "Design and adjustment of contact welding machines", Moscow, publishing house "Machine Building", 1967; V.G. Gevorkyan, "Fundamentals of welding", Moscow, publishing house . "Higher School", 1991). this method the heating element and coolant is the metal being welded, which closes the secondary winding of the welding transformer, as a result of which an electric current sufficient to heat and weld the metal flows through a closed circuit. In this case, each turn of the secondary winding of the transformer is a separate source of electricity, since it covers the same magnetic flux created in the magnetic core by the primary winding of the transformer. This method is a prototype. The disadvantage of this method is that it is only applicable for coolants with relatively low electrical resistance. In the case of using a liquid, for example water, it would be necessary to abandon the voltage reduction using a transformer, and the method would turn into the first one considered with all its disadvantages. The safety and reliability of converting electrical energy into heat and the efficiency of heat transfer in the proposed method are achieved by using a closed turn of an electric current conductor or several turns forming the secondary winding of the transformer as a heating element and introducing the coolant into contact with the surfaces of the conductor. When a turn of the conductor covering the magnetic circuit of the transformer is closed, an EMF is induced in it that is less than that supplied to the primary winding in the number of its turns, which ensures electrical safety, and the current flowing through the closed turn increases sharply due to the low electrical resistance of the turn and heats it regardless of the electrical coolant resistance. At the same time, direct contact of the coolant with the surfaces of a closed coil of conductor increases the efficiency of heat transfer due to sharp decline heat losses. Conditions can be created that exclude the possibility of coil burnout, which ensures the reliability of the conversion. The drawing shows an example of equipment that implements the proposed method. The method is carried out as follows. Using switch K, the primary winding of the transformer with the number of turns W 1 is connected to the alternating current network. In the magnetic circuit 1, an alternating magnetic flux arises, which induces an emf in the closed turns of conductors 2 and 3 and causes an electric current in them, heating them. Conductor 2 is made in the form of a pipe, conductor 3 is made of a closed bundle of copper wires. A cold coolant is introduced into input A, for example water, which enters inside conductor 2 and washes the outside of conductor 3. Heat exchange occurs through the interface between conductors 2 and 3 and the coolant, the coolant heats up and, due to convection, flows to output B. In one particular case, conductor 3 may be absent (it is needed when the electrical resistance of conductor 2 does not match the power of the transformer). In another particular case, in order to prevent heat dissipation from the outer surface of conductor 2, an electrical insulating pipe can be used instead of conductor 2, and then heat will flow into the coolant only from conductor 3. In the third case, the conductor can be the coolant itself, placed inside the insulating pipe or into a volume of another shape enclosing the magnetic circuit. An example of a specific implementation of the method. A stamped steel radiator of grade 2M3-500 was taken (see page 189, Reference special work edited by N.A. Kokhanenko, Moscow, ed. literature on construction, 1964) with an equivalent heating surface of 3.53 ecm (equivalent to an 11-section cast iron radiator M-140 according to GOST 8690-58) with a capacity of 13.3 liters. A closed coil was made from a steel pipe with a diameter of 3/4"" covering the magnetic circuit of a 1.5 kW power transformer. The input of turn A was connected to the output (pipe at the bottom of the radiator installed vertically), and the output of turn B was connected to the radiator inlet (pipe at the top) using rubber hoses. An expansion tank with a capacity of 0.25 liters was installed at the top of the radiator. Then the system (radiator - turn) was filled with water and the primary winding of the transformer was connected to a network with a voltage of 220 V. The temperature surrounding the radiator before turning on the transformer was 4.5 o C in a room volume of 300 m 3. After turning on the transformer, the electric voltage on the turn of 0.8 V and the electric current passing through the turn were measured, which amounted to 1875 A. After 20 minutes, the temperature of the water in the radiator increased to 96 o C (the initial water temperature was 12 o C), after which Using a thyristor control system, the power consumed from the network was initially reduced to 800 W, which ensured that the water temperature was maintained at 82 o C, and then after 2 hours to 500 W, which ensured that the water temperature was maintained at 60 o C. As a result, 4 -hour test, the room temperature reached 18 o C. The next day the system was turned on at a power consumption of 1.5 kW. After 4 hours, the room temperature reached 23 o C, after which the system was switched to 500 W consumption and operated for 1 month as a heating device. Tests were carried out on heating a heating system with a capacity of 150 liters using the proposed method with a power consumption of 800 W. During the tests, water heating was set from 16 o C to 58.5 o C in 7 hours, after which the system was switched to a mode that maintained the temperature at 58 o C with a power consumption of 500 W. Tests were carried out to introduce into a closed coil of a steel pipe a bundle of copper wires closed by soldering (conductor 3). As a result of the tests, it was established that, using conductor 3, it is possible to reduce the equivalent electrical resistance of closed turns within almost any limits and increase the power consumption until the transformer is fully loaded. Tests have shown the possibility of reducing electricity consumption by 1.5-2 times when using the proposed method in comparison with traditional ones.
Formula of invention
1. A method for converting electrical energy into heat and creating heat exchange between a heating element and a coolant, using as a heating element the secondary winding of an electric transformer, made in the form of a closed coil of conductor in the form of a pipe with a coolant inlet and outlet, characterized in that it provides coolant convection through heating element by connecting its inlet with the coolant outlet from the radiator, and the coolant outlet from the heating element with the radiator inlet, connections are made with hoses, the radiator is installed vertically so that the coolant outlet from the radiator is in its lower part, an expansion tank is installed in the upper part of the radiator and the entire system is filled with coolant and the transformer is connected to the network. 2. The method according to claim 1, characterized in that the closed turn in the form of a pipe is made of electrical insulating material, and one or more closed turns of the conductor are installed inside it.
DRAWINGS
MM4A Early termination of patent Russian Federation for an invention due to failure to pay the fee for maintaining the patent in force on time