RU2542601C2 - Method of conversion of thermal energy into electric and device for its implementation - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to the electric thermomagnetic solid state devices intended for generation of electric energy by its direct conversion from thermal energy and can be used as a power supply for electric equipment. The invention concept is as follows: the method consists in that the conversion of thermal energy into the electric energy is performed by periodic change of the state of magnetisation of the thermosensitive ferromagnetic element (located in a gap of the magnetic conductor) heated up to the Curie temperature which is in a paraprocess phase corresponding to ferromagnetic material. The magnetisation of the thermosensitive ferromagnetic element is changed by cyclic change of the biasing current. The device contains a magnetic conductor 1 with a magnetic field source 2 in the gap of which the thermosensitive ferromagnetic element 3, the heater 4, the output winding 5, the input winding 6, the thermoinsulator 7, placed on the magnetic conductor, the exciting generator 8 connected to the input winding 6 and the electric energy storage 9 connected to the output winding 5, are located.

EFFECT: improvement of efficiency of the process of conversion of thermal energy into the electric.

2 cl, 4 dwg

Description

The invention relates to electric thermomagnetic devices on a solid, designed to generate electrical energy by directly converting it from thermal energy, and can be used as a power source for electrical equipment.

Known methods and devices for converting thermal energy into electrical energy, based on the Peltier effect (Seebeck) [1, 2, etc.].

Their common disadvantage is low efficiency and limited capacity.

There is a method of direct conversion of heat of the medium into electricity, based on a non-linear voltage capacitance with a non-linear dielectric [3].

The disadvantage of this method is the need to use sufficiently high operating voltages, which significantly limits the scope of such converters.

Known methods and devices implemented by thermomagnetic generators [4, 5], directly converting thermal energy into electrical energy by periodically heating and cooling the ferromagnetic core of a nonlinear inductor near the Curie point.

The disadvantage inherent in these methods is low efficiency, which is associated with the need to use relatively long processes of thermal cycling of magnetic materials.

The closest in technical essence to the claimed is a method of direct conversion of thermal energy into electrical energy [6] (prototype), which consists in periodically changing the magnetization state of the thermosensitive ferromagnetic element located in the gap of the magnetic circuit by periodically heating and cooling in the vicinity of the Curie point of the thermosensitive ferromagnetic element in the paraprocess phase.

A device for implementing the prototype method consists of a magnetic circuit, a magnetic field source connected to the magnetic circuit, in the gap of the magnetic circuit there is a thermosensitive ferromagnetic element, a heater and a cooler, which respectively provide heating or cooling of the thermosensitive ferromagnetic element, the output winding located on the magnetic circuit.

The disadvantage of the prototype is the low efficiency due to the use of the inertial process of thermal cycling of ferromagnetic material.

The invention solves the problem of increasing the efficiency of the process of converting thermal energy into electrical energy.

This is achieved by the fact that when implementing the method of converting thermal energy into electrical energy to excite an alternating electric current, the magnetization state of the thermally sensitive ferromagnetic element located in the magnetic circuit gap heated to the Curie temperature corresponding to the ferromagnetic material in the paraprocess phase is carried out periodically, according to the invention, the magnetization of the thermally sensitive ferromagnetic element is carried out by cyclic changing the bias current.

The claimed method is implemented by a device for converting thermal energy into electrical energy, containing a magnetic circuit with a magnetic field source, in the gap of which there is a thermosensitive ferromagnetic element, an output winding located on the magnetic circuit, a heater of a thermosensitive ferromagnetic element, in the construction of which, according to the invention, a thermal insulator is inserted that insulates the magnetic circuit from a heated thermosensitive ferromagnetic element, the input winding placed on the magnetic circuit, ge nerator-exciter connected to the input winding, and an electric energy storage device connected to the output winding. A material with a Curie point close to ambient temperature, such as gadolinium, can act as a thermosensitive ferromagnetic element. It is possible to use a battery connected via an diode to the output winding as an electric energy storage device.

A comparative analysis of the features of the claimed method and the prototype method shows that the claimed method differs in that the set of essential features is changed, the conditions for the action associated with the change in the magnetization of the heat-sensitive ferromagnetic element located in the gap of the magnetic core are changed. It is carried out by cyclically changing the bias current.

A comparative analysis of the device that implements the prototype method, and the device that implements the claimed method, shows that the set of essential features has been changed:

- introduced elements: thermal insulator, input winding, exciter generator and electrical energy storage device;

- the connections between the elements have been changed: the magnetic circuit is separated from the thermosensitive ferromagnetic element using a thermal insulator; the exciter generator is connected to the input winding; electric energy storage device is connected to the output winding;

- Forms of elements execution have been clarified: a material with a Curie point corresponding to the ambient temperature, for example gadolinium, has been proposed as a thermosensitive ferromagnetic element, which allows using the surrounding atmosphere as a heat source; An electric energy storage device may be a battery connected to the output winding through a diode.

The invention is illustrated graphically (Fig. 1-4).

In FIG. 1 shows a diagram of a device that implements the proposed method.

In FIG. Figure 2 shows the dependence of the initial magnetic permeability and the relative tangent of the angle of magnetic losses on the amplitude value of the intensity of an alternating magnetic field.

In FIG. Figure 3 shows the temperature dependence of the initial magnetic permeability.

In FIG. Figure 4 shows the dependence of magnetic permeability on the intensity of an external alternating magnetic field at a temperature close to the Curie temperature and bias by an external constant magnetic field.

A device that implements the proposed method (Fig. 1) contains a magnetic circuit 1 with a magnetic field source 2, a thermosensitive ferromagnetic element 3 located in the gap of the magnetic circuit, a heater 4 of the thermosensitive ferromagnetic element, an output winding 5 located on the magnetic circuit, an input winding 6 also located on magnetic circuit, thermal insulator 7, an insulating magnetic circuit from a heated thermosensitive ferromagnetic element, an exciter generator 8 connected to the input winding, and an electric storage device energy 9 connected to the output winding.

When implementing the proposed method, the thermosensitive ferromagnetic element 3, isolated from the magnetic circuit 1 using a heat insulator 7, is heated to a temperature close to the Curie temperature. Using the source of the magnetic field 2 and through the magnetic circuit 1, the thermosensitive ferromagnetic element 3 is transferred to the initial stage of the para process. From the output of the generator-exciter 8 to the input winding 6 serves a sequence of pulses. With the arrival of each of the pulses in the input winding 6, the process of increasing current begins. With increasing current, the total magnetic field strength increases, and, as a result, the magnetic permeability of the thermosensitive ferromagnetic element 3 decreases, since the latter is in a paraprocess state. The input winding 6, located on the magnetic circuit 1, in the gap of which is located a thermosensitive ferromagnetic element 3, forms a nonlinear inductance with a negative reactance. The energy accumulated by such a nonlinear inductance may exceed the energy given by the source. At the end of the pulse in the input winding 6 in the output winding 5 located on the same magnetic circuit 1 as the input winding 6, the self-induction emf is excited, the energy of which is consumed by the drive 9. Separation of the energy storage cycles by the input coil and the energy consumption of the drive can be carried out by any of known methods, for example, using switching devices or using a diode, as is done in the latter case in the proposed device.

As follows from the foregoing, in contrast to the prototype, when implementing this method of converting thermal energy into electrical energy, there is no fundamental need for thermal cycling and, therefore, additional energy costs for periodic heating and cooling of the working fluid — a thermally sensitive ferromagnetic element located in the gap of the magnetic core — are eliminated. The temperature of the magnetic circuit can always be maintained at the required level by adjusting the flow rate of the coolant by any of a variety of known methods. Thus, the goal of the invention is achieved - increasing the efficiency of the process of converting thermal energy into electrical energy.

The total capacity of the proposed source of electricity can be increased by parallelizing a large number of such sources, which can be made miniature constructively.

Any source can be used as a heat source: from radiant to organic.

If the temperature sensing element of ferromagnetic material used with the Curie point corresponding to the ambient temperature, such as gadolinium (Curie point - t _k = 17 °), then the role of the heat source may perform the ambient atmosphere.

As an energy storage device, a battery connected to the output winding through a diode can be used, which eliminates the reverse discharge of the battery.

Let's carry out the theoretical justification of the proposed method and device. The exciter generator forms a sequence of rectangular pulses. With the arrival of each of the pulses to the input winding, the process of increasing current begins in it. With increasing current in the input winding, the magnetic field strength changes and, as a result, the magnetic permeability of the thermally sensitive ferromagnetic element located in the gap of the magnetic circuit, and therefore the inductance of the input winding (set of elements: a thermosensitive ferromagnetic element and a magnetic circuit with a magnetic field source, will be called magnetic core, bearing in mind that the input and output windings are located on the magnetic circuit). This fact was noted by Stoletov (Stoletov’s magnetization curve). The differential equation describing the process of current flow in the solenoid during the action of the pulse has the form:

- магнитный поток;

- ток, протекающий в катушке; L₀ - индуктивность соленоида без учета магнитной проницаемости магнитного сердечника; r - сопротивление нагрузки; µ(H) - магнитная проницаемость магнитного сердечника, причем

; E - импульсное напряжение, приложенное ко входной обмотке в течение длительности импульса

.Where

- magnetic flux;

- current flowing in the coil; L ₀ is the inductance of the solenoid without taking into account the magnetic permeability of the magnetic core; r is the load resistance; µ (H) is the magnetic permeability of the magnetic core, and

; E is the pulse voltage applied to the input winding during the pulse duration

.

We rewrite equation (1) in a slightly different way:

и ток

являются величинами взаимозависимыми, и, следовательно, форма зависимости

повлияет на форму временной зависимости тока.As can be seen from (2), the relative magnetic permeability

and current

are interdependent quantities, and therefore the form of dependence

will affect the shape of the time dependence of the current.

The shape of the magnetic permeability curve depends not only on the magnetic field generated by the current, but also on many other factors: the material of the thermosensitive ferromagnetic element, applied mechanical stresses, current frequency, temperature, shape of the magnetic core, etc. In particular, as an example, for ferrite rings of the 10000NM type with an initial magnetic permeability µ _n = 10000 intended for operation in weak magnetic fields, this curve has the form shown in FIG. 2 [7]. As can be seen from the figure, with increasing magnetic field strength, the magnetic permeability first increases, reaching a maximum value of µ _n + Δµ, and then decreases.

In the absence of external magnetic fields, when a thermosensitive ferromagnetic element is cooled below the Curie temperature, a definite configuration of spontaneous magnetization regions is formed in it, called a domain structure. Each domain is magnetized to saturation, the magnetization vector in them is oriented along a certain direction, called the axis of easy magnetization. The existence of a domain structure determines the high susceptibility of a ferromagnet to magnetization. The course of the magnetization curve is determined by the processes of the emergence, formation, and disappearance of domains.

The placement of a ferromagnetic material in a uniform external magnetic field leads to the instability of domains with magnetization against an external magnetic field and to increase the stability of domains with magnetization along the field, which causes an increase in the volume of some domains due to a reduction in the volume of other domains by shifting the domain boundaries or by rotating the magnetization in the domains.

It is known that at the beginning of magnetization the process proceeds mainly due to the displacement of the domain walls to approximately 0.5 · Δµ + µ _n (Fig. 2). In this case, the magnetization of the sample depends linearly on H. With a further increase in the external magnetic field, two processes occur. The first is the destruction of the domain structure: the disadvantageously magnetized domains are compressed and their number decreases. A further increase in the field leads to the disappearance of such domains by end collapse. The second process is the transformation of domain structures into domains with magnetization along the field due to the rotation of the magnetization. As a result, a single-domain saturation state is formed in the saturation field H _s . A subsequent increase in the external field strength is the final stage of magnetization and is known by the term para-process or true magnetization. This stage is characterized by the orientation in the field H of elementary carriers of magnetism (spin magnetic moments of electrons or magnetic moments of ions), which remained not rotated in the direction of the resulting magnetization due to the disorganizing effect of thermal motion. With an increase in H (if H> H _s ), the magnetization tends to the value of absolute saturation, i.e. to that which a ferromagnet would have at absolute zero temperature. In most cases, the paraprocess gives a small increase in magnetization; therefore, the magnetization process is considered almost complete when the ferromagnetic core reaches a state of technical saturation.

From experimental observations made by different authors, it follows that at a fixed external field strength with increasing temperature, the magnetic permeability also increases, reaching a maximum near the Curie point. These observations are confirmed by data taken from [7], shown in FIG. 3. This fact is explained by the fact that with an increase in thermal fluctuation fluctuations of the crystal lattice, the probability of destruction of the domain structure or rotation of the magnetization of unprofitable magnetized domains increases. Domains are “pushed” by heat to the magnetization state corresponding to the external field intensity vector, i.e. in this temperature range, heat energy is partially spent on increasing the internal magnetic field of the magnetic core. If the temperature begins to exceed the boundary of the Curie point, the crystal lattice vibrations become so significant that the temperature begins to work against the magnetic field, destroying the domain structures.

It follows from the foregoing that the inductor will much more efficiently accumulate energy in a magnetic field if the thermosensitive ferromagnetic element of the magnetic core is heated to a temperature close to the Curie point, and an alternating magnetic field changes the intensity in the decay portion of the magnetic permeability curve corresponding to the state of the para process. A shift into this region is not difficult to ensure by applying an external magnetic field, for example, using a permanent magnet.

, где

(справедливо для соленоида). Выбор вида зависимости не носит принципиального характера. Достаточно, чтобы эта зависимость отражала общую тенденцию, соответствующую состоянию парапроцесса. В данном случае такая зависимость выбрана исключительно из желания упростить аналитические выкладки и, следовательно, изложение сути процесса. С учетом выбранной зависимости дифференциальное уравнение (2) может быть приведено к виду:In this region, the first derivative of magnetic permeability from the intensity of the variable component of the magnetic field will be negative. The principle of selecting a work area is illustrated in FIG. 4. Let on the selected site, this dependence has the character of the form:

where

(valid for solenoid). The choice of the type of dependence is not fundamental. It is enough that this dependence reflects the general tendency corresponding to the state of the para-process. In this case, such a dependence is chosen solely from a desire to simplify analytical calculations and, therefore, an account of the essence of the process. Given the selected dependence, differential equation (2) can be reduced to the form:

The solution to this equation is known:

The cycle of converting the energy of the magnetic field of the output winding into current in the pause between pulses of the exciter-generator is described by the differential equation:

, где

. С учетом последнего получим:R is the payload

where

. Given the latter we get:

It should be noted that in expressions (5) and (6), the differentials dH and di are negative, since the current decreases. Hence the minus sign in expression (6).

After separating the variables and integrating the right and left sides of the equation, we will have:

- ток на момент окончания действий импульса генератора-возбудителя, определим постоянную интегрирования

. Подставив постоянную интегрирования в уравнение (7), после несложных преобразований получим:By setting the initial conditions t = 0 and

- current at the time of the end of the pulse of the generator-exciter, we define the integration constant

. Substituting the integration constant in equation (7), after simple transformations, we obtain:

As can be seen from relation (8), at the initial time, the expression in parentheses under the exponent is zero. As the current decreases, the expression in parentheses increases and, being positive, slows down the current decay process. As a result, this is expressed in the additional energy released on the load.

, затраченную источником за время действия импульса, и энергию, отданную индуктивностью в нагрузку

во время паузы, нетрудно рассчитать по формулам:Energy

consumed by the source during the pulse, and the energy given by the inductance to the load

during a pause, it is easy to calculate by the formulas:

Let us evaluate the effectiveness of the proposed method by comparing these energies. Let the magnetic core and the thermosensitive ferromagnetic element constituting the magnetic core be made of a 10,000 NM ferrite ring with sizes: D = 38 mm, d = 24 mm, h = 7 mm. The input and output windings are absolutely identical and have two hundred turns N = 200 with a wire resistance of r = 2 Ohms. The length of the winding l = 60 mm. Then n = 3.3 · 10 ³ . The inductance of coils with such sizes without taking into account the magnetic permeability of the core will be:

. График этой зависимости помещен на фиг.5. Отсюда значение k=5000, значение µ_n=12700. Пусть на выходе генератора-возбудителя формируется импульсная последовательность с параметрами: амплитуда импульса - E=12 В; длительность импульса

мс и длительность паузы -

мс. Выходная обмотка подключена к нагрузке сопротивлением R=100 Ом. Тогда энергия, затраченная источником в течение одного импульса, составит:

Дж, а энергия, отданная в нагрузку в течение паузы:

Дж. При расчете энергии, отданной в нагрузку, ток в нагрузке определялся путем решения дифференциального уравнения (6) методом Рунге-Кутта. Прирост энергии за период импульсной последовательности составит: ΔW=3,01·10^-3 Дж или за секунду ΔW^*≈0,214 Дж/с.As an approximating dependence for μ (H), we choose a dependence of the form:

. A graph of this dependence is placed in figure 5. Hence the value of k = 5000, the value of µ _n = 12700. Let an impulse sequence with the following parameters be formed at the output of the exciter-generator: pulse amplitude - E = 12 V; pulse duration

ms and pause duration -

ms The output winding is connected to a load of resistance R = 100 Ohms. Then the energy spent by the source during one pulse will be:

J, and the energy given to the load during a pause:

J. When calculating the energy delivered to the load, the current in the load was determined by solving differential equation (6) using the Runge-Kutta method. The energy gain over the period of the pulse sequence will be: ΔW = 3.01 · 10 ^-3 J or per second ΔW ^* ≈0.214 J / s.

The essence of the above confirms the conclusion that, in contrast to the prototype, when implementing this method of converting thermal energy into electrical energy, there is no fundamental need for thermal cycling and, therefore, additional energy costs for periodic heating and cooling of the working fluid — the magnetic circuit — are eliminated. The temperature of the thermosensitive ferromagnetic element can always be maintained at the required level by adjusting the flow rate of the coolant by any of a variety of known methods. Thus, the goal of the invention is achieved - increasing the efficiency of the process of converting thermal energy into electrical energy.

The total capacity of the proposed source of electricity can be increased by parallelizing a large number of such sources, which can be made miniature constructively.

Any source can be used as a heat source: from radiant to organic.

If the temperature sensing element of ferromagnetic material used with the Curie point corresponding to the ambient temperature, such as gadolinium (Curie point - t _k = 17 °), then the role of the heat source may perform the ambient atmosphere.

As an energy storage device, a battery connected to the output winding through a diode can be used, which eliminates the reverse discharge of the battery.

The technical result from the use of the claimed technical solutions in comparison with the prototype is to increase the efficiency of the process of converting thermal energy into electrical energy.

List of sources used

1. Landau L.D., Lifshits E.M. Theoretical Physics: Textbook. manual: For universities. In 10 vol. T. VIII. Electrodynamics of continuous media. - 4th ed., Stereo. - M .: Fizmatlit, 2000 .-- 656 p.

2. Patent No. 2419919, IPC H01L 35/02, 2008. Thermoelectric element.

3. Patent No. 2227947, IPC H01M 14/00, H02N 11/00, 2002. Capacitive converter of heat of the medium into electricity.

4. Copyright certificate No. 141560, cl. 21G, 35, 1961. A method for directly converting thermal energy into electrical energy.

5. Copyright certificate No. 811466. M. cl. H02N 11/00, 1981. Thermomagnetic generator.

6. Copyright certificate No. 1015457, cl. H01L 31/04, H02N 11/00, 1983. Magnetothermal generator.

7. OJSC "Ferroribor":

http://www.rusgates.ru/company/soft_magnetic/the_properties_of_ferrites__grades/highly_permeable_ferrite/index.php

Claims (2)

1. The method of converting thermal energy into electrical energy, which consists in periodically changing the magnetization state of the thermally sensitive ferromagnetic element located in the gap of the magnetic circuit, heated to the Curie temperature corresponding to the ferromagnetic material in the para-process phase, characterized in that the magnetization state of the thermally sensitive ferromagnetic element carried out by cyclically changing the bias current. 2. A device for converting thermal energy into electrical energy, containing a magnetic circuit with a magnetic field source, in the gap of which a thermosensitive ferromagnetic element is located, an output winding located on the magnetic circuit, a heater of a thermosensitive ferromagnetic element, characterized in that a thermal insulator is introduced that insulates the magnetic circuit from the heated thermosensitive ferromagnetic element , an input winding located on the magnetic circuit, an exciter generator connected to the input winding, electrical energy storage device, connected to the output winding.

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