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INVENTION
Russian Federation Patent RU2124781

Quasivacuum thermionic converter thermal energy into electricity

Quasivacuum thermionic converter
Thermal energy into electricity

Name of the inventor: Majewski VA
The name of the patentee: Majewski, Vladimir Alexandrovich; Majewski Igor
Address for correspondence: 111402, Moscow, ul.Ketcherskaya 05.02.34, Mayevsky VA
Starting date of the patent: 1995.12.21

Usage: As a source of electrical energy in terrestrial and space environments. The technical result is to increase the efficiency and creates the conditions for reuse of heat generated at the anode to supply it to the cathode of the next cell for him. Quasivacuum thermionic converter comprises toothed electrodes and the opposite projections of one electrode and troughs opposite electrode installed shielding plate, the electrodes and the plates are mounted so that the vector of the magnetic field perpendicular to the surface of the electrodes and plates and the electrode-anode has a higher temperature than the electrode -cathode.

DESCRIPTION OF THE INVENTION

The invention relates to converting thermal energy into electrical energy, and more specifically - to direct heat thermionic conversion process and is intended to be used as sources of electrical energy in the terrestrial and space-based units.

Known thermionic converter of thermal energy into electrical energy, comprising a heated cathode and the anode is cooled, separated by an inter-electrode gap [1]. The temperature of the anode in such a converter lower cathode temperature, which eliminates the ability to reuse the heat generated at the anode, and limits the efficiency of the converter.

The object of the invention to provide an electric power generation in the converter at the anode, the cathode temperature greater and the use of heat released at the anode, the next element for heating the cathode.

This problem is solved so that in quasivacuum thermionic converter of thermal energy into electrical energy, comprising a toothed electrodes and generator magnetic field, the electrodes are made of flat plates with deposited on their surfaces with triangular grooves forming a periodic tooth system, wherein the opposite projections of the toothed electrode and depressions shield plates mounted opposite width (2-3) r l electrically connected with a corresponding electrode, where r n - electron Larmor radius of the transducer in a magnetic field and the magnetic field generator is set so that a uniform magnetic field perpendicular to the electrode surface.

FIG. 1 is a schematic diagram of a thermionic converter of the present invention is performed, Fig. 2 - electrode toothed surface, FIG. 3 - electrode circuit with oblique magnetic field, FIG. 4 - Timing circuit electrode and the electron trajectory in a magnetic field, FIG. 5 - Correlation of the electrodes on the position captured emission portion on the tooth surface with an inclination angle r for different values of L in FIG. 6 - the variation of the current density along the length of the electrode (Fig 1.) With shielding plates, FIG. 7 - transmitter electrode configuration and nature of the current density distribution along them, FIG. 8 - the current-voltage characteristic of the converter, FIG. 9 - estimation of the power density and the power density on the temperature of the electrodes and the interelectrode distance d and FIG. 10 - a system of coordinates to calculate the current value.

The converter operates as follows. As will be shown below, in a magnetic field perpendicular to the surface of the electrode gear, the average density of the emission current of the cavity is less than the average current density with the projection due to the greater proportion of emitted electrons captured by the adjacent emitting planes in the basin. Then, screening, respectively, the protuberances of one electrode and the opposite depression can increase or decrease the current to the electrode.

For example, if the transducer gap reflecting shielding plate installed, they strongly reduce the current from the electrode, against which the projections are located, and therefore the total current of electrons at the same temperature electrodes is directed to the electrode tabs which these plates screened.

Consider quasivacuum thermionic diode electrodes which are made of flat plates with their surfaces coated on the triangular grooves so that they form a periodic system tooth pitch 2a (Figs. 1 and 2). We find the emission current density distribution with this electrode in a uniform magnetic field perpendicular to its surface.

In [2] it is shown that if the magnetic field vector H is directed at an angle to the emitting surface (Fig. 3), with the current density of such a surface by capturing the emitted electrons rotating around the magnetic field lines with a radius r l emitting surface decreases to

j = j 0 sin .

Where

j 0 - density of the emission current.

If the angle of inclination of the vector H is equal to the tooth surface l and r << a, where r n - electron Larmor radius of the circle, the current density to the surface of the element remote from the edge of the tooth at a distance z >> r l (. Figure 4), is j z = 0,7 j 0.

However, in areas the size - r l in the vicinity of the tooth boundaries changing. At the top of the tooth proportion of trapped electrons is reduced due to a decrease in the electrode surface, which can capture electrons. Indeed, in the limit as z -> 0 the current density can be obtained by integrating the emission spectrum for electrons whose velocity is directed away from the emitted their electrode. Then, for a point B in the case of By integrating the emission spectrum in the range - (FIG. 10), j B = 0,85j 0; j B> j Z.

At the trough of the tooth electron capture increases due to electron capture surface adjacent tooth. The value of the share of the trapped electrons, seems to depend on the magnetic field strength, but can not be less than 0 0,5j. For this reason, at the point A

j A <j 0 and 0.5 · j B> j Z> j A .

The amount of current density at the remaining portions in this range should change monotonically.

Solution of the problem and the current density calculations to the tooth surface depending on the magnitude of the magnetic field based on electron capture both surfaces of the tooth are shown below.

When deciding it was assumed that in the diode mode is implemented and that quasivacuum

, R d d,

Where

- The electrochemical potential of the plasma electrode space;

- The work function of the electrode material;

r d - Debye radius;

d - value of electrode spacing. In this case, we can assume that the emission current density on the surface is determined by the equation of Richardson,



Where

A - Richardson constant;

T - the temperature of the electrode;

k - is Boltzmann's constant,

and the existence of retarding the electrons near-electrode potential drop V = - is taken into account in this equation by replacing on . It is possible and to argue that the presence of such a jump all the electrons that reach the electrode surface, it will be captured. Furthermore, it was assumed that the electric field is absent in the volume other than the Debye layer relatively thin, i.e. dY / d Z, dY / d Y = 0.

The calculation results confirm the previously made of the qualitative analysis of the findings. FIG. 5 shows the proportion of trapped electrons PICKUP S = 1 - j Z / j 0 for different parts of the tooth. Each curve corresponds to a value of H and L, respectively, r.

Numerical calculations showed that applies to z >> r lj Z = 0,7j 0, j B = 0,85j 0 and j A = 0,45j 0.

It is necessary to pay attention to the dependence of j from r l. R less than n, the less the length over which the change of j A and j B to j Z. The more r l, especially over long distances from the projection and the depression extends the influence of peripheral values j, which corresponds to a qualitative idea of the mechanism of capture of electrons in the system.

Feature emission spectrum with a toothed electrode in a magnetic field perpendicular to the surface, it is strong enough uneven length. Current density varies periodically (with period 2a); protrusion is in maximum, the minimum in the depressions. If the shield plates of the emitting or reflecting different portions of the electrode, it is possible to obtain different values ​​of the total current with a toothed electrode.

For example, if the reflecting screens installed opposite the projections, the current with such an electrode is reduced more than the case of installing such screens opposite the depressions. If used as a screen plate of the same material as the emitter, the installation of a tine should experience a decrease in current, and when a depression opposite the increase in current is observed, as current density at the depression is less than the current density with a plane electrode.

Using such a toothed emitters partial screening surfaces as electrodes quasivacuum thermionic diode can receive the resultant electrical current, even if the temperature is the same.

We note that the situation has not changed, if the toothed electrode has a two-dimensional geometry, ie, protrusions are formed as pyramids or cones.

Let's consider some possible schemes of such diodes. Suppose, for example, a diode is formed by two toothed electrodes offset from each other by a distance "a", so that the electrode tabs are opposite one another depressions (FIG. 1). Suppose now that the opposite upper electrode projections screens are installed, reflecting the electrons, and the diode is placed in a uniform magnetic field intensity vector is perpendicular to the surface of the electrodes and the reflecting plates. As screens can be used, such as plates with a higher work function; the width of the plate (2-3) r l.

Then the electrons emitted by the electrode portions located opposite the screen, the counter electrodes do not fall, and after reflection from screens returned to emit their station. This decreases the current from the electrodes, the current from the electrode reflective screens which are located at the protrusions decreases strongly (Fig. 6). Thus, in the electrode gap due to different reflective screens reduce the current density at the projections and recesses and, as a consequence of different quantities of currents from the electrodes J 1 and J 2 there is a resultant flow of electrons from the electrode to the electrode 1, 2.

The situation changes fundamentally if not used the reflecting screen and the screen of the same material of which the main electrodes. In this case, the current from the electrode, which projections are situated opposite screen is reduced more, as current density with the protrusion is greater than the current density with a corresponding flat surface portion of the screen. In the examination, the results of which are shown in FIG. 6, for the values 1 and j j 2-1 assumed that the screen is electrically connected to one electrode, the protrusion which it escapes. However, the resulting current will not change direction, if the screen is connected to the electrode 2. In this arrangement the screen current density higher than the current density of the cavities against which the screen is. Thus, the replacement of emitting portions in the vicinity of emission projections or depressions tooth located opposite them flat screen emitting leads respectively to decrease or increase the current density in these areas, and hence the corresponding change in the total current from the electrode.

Maximum current difference when using emitting screens can be obtained in a system with two rows of screens. One of them is electrically connected with the electrode 1 and it shields the protrusions, the second - the electrode 2 and its cavity escapes. One of the possibilities of practical implementation of this scheme is shown in FIG. 7.

Let us estimate the volumetric power density, which can be obtained in this diode. We assume that implemented quasivacuum mode and therefore, the current-voltage characteristic of the element in the generation region is exponential (Fig. 8)

j = j kz exp (-V / kT),

Where

V - the voltage on the load;

j kz - short-circuit current.

Then, as is well known, the maximum power can be obtained at a voltage V = kT and hence the power density per unit surface

N = (j ks · kT) / e.

The adopted model j = ks j 2-1. Assuming that the change j Z, depending on z can be approximated by a linear law (see. FIG. 3, the curve for r l = 0.05 cm), it is easy to obtain that the characteristic value of the average current density

j 2-1 ~ 0,1j 0.

The element with the thermal ionization equilibrium cesium current density depends on the mean free path of electrons and the electrode temperature. N and W values ​​according to the temperature shown in FIG. 9. When using the volumetric capacity of the plane of tungsten electrodes may reach values of 0.1 - 1.0 MW / m 3. It was assumed that in the area of power generation is possible to obtain the specific content of the emission surface ~ 2 - 3 cm 2 / cm 3.

The main factor limiting the increase in power density is relatively high because of the low value of the degree of ionization of the plasma thermal equilibrium with practically acceptable value for the electrode gap, the mean free path of electrons and converter temperature. This limitation can be overcome in a system with a non-equilibrium plasma ionization. In this case, the reduction It can be achieved by additional supply of external energy for ionization and decrease the work function of the electrodes can be achieved by the introduction into the interelectrode gap, for example, barium vapors.

USED ​​LITERATKRA

1. ND Margulis. Thermionic (plasma) power converter. Gosatomizdat, 1961

2. Schock A. Effect of magnetic fields on themionic power genefatiors. J. Applied Phys, 31, N 11, p. 1978 - 1981, 1960.

CLAIM

Quasivacuum thermionic converter of thermal energy into electrical energy, comprising a toothed electrodes and generator magnetic field, wherein the electrodes are made of flat plates with deposited on their surfaces with triangular grooves forming a periodic tooth system, wherein the opposite projections of the toothed electrodes and troughs of the opposite set shielding plate width (2 - 3) r l electrically connected with a corresponding electrode, where r n - electron Larmor radius of the transducer in a magnetic field and the magnetic field generator is set so that a uniform magnetic field perpendicular to the electrode surface.

print version
Publication date 08.01.2007gg