RU2715733C1 - Working medium vaporizer for thermionic converters - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to the field of thermionic conversion of heat energy into electrical energy, specifically to working medium vapour sources for thermionic transducers (TIC), and can be used in caesium systems of thermionic nuclear power plants, thermionic power generating channels and assemblies, TIC, installations for research and testing of similar devices. Working mediums steam generator for thermionic converters is controlled by voltage variation between contacts connected to gas-permeable electrodes, using an electric circuit, which, in addition to the working medium vapour generator, comprises a variable electrical resistor, a switch, a paired switch and a constant voltage source.

EFFECT: technical result is expansion of functional capabilities of steam generator of working medium (use for supply of caesium or barium vapour), reduction of its sensitivity to level of operating temperature, increase in efficiency of thermionic conversion process, as well as reliability and service life of TIC.

4 cl, 3 dwg

Description

The invention relates to the field of thermionic conversion of thermal energy into electrical energy, and in particular, to sources of vapor of a working fluid for thermionic converters, and can be used as part of cesium systems of thermionic nuclear power plants (NPPs), thermionic electricity generating channels (EGCs) and assemblies, thermionic converters ( TEP), as well as installations for research and testing of such devices.

The presence of cesium vapor in the interelectrode gap (MES) of the TEC is necessary to reduce the work function of the electrons and compensate for their space charge. To reduce the work function of the emitter of promising high-temperature TECs, it is also proposed to use barium vapor in the MEZ. Maintaining the required vapor pressure of these working fluids at a level from zero to several Torr is carried out with the help of working fluid vapor generators (GPRT).

To supply the vapor of the working fluid (cesium or barium) to the TEC, an evaporative type HCPG is used, in which the working fluid is vaporized directly from the surface of the liquid phase, or fed into the evaporation zone communicating with the MEZ using capillary forces and porous wicks (patent RU No. 1786536 , IPC ⁵ H01J 45/00, publ. 01/07/1993), similar to how it is done in heat pipes. The disadvantages of this and similar evaporative devices are:

- a relatively low level of operating temperature (~ 550-650 ° K) of the liquid phase of cesium compared with the collector temperatures of the TEC (~ 850-1000 ° K), determined by the necessary pressure of its saturated vapors, makes it difficult to place the GPRT directly on and near the TEC;

- a strong dependence of the pressure in the MEZ, and, correspondingly, of the output parameters of the TEC on the temperature of the liquid phase of cesium in the hydroprocessing.

In addition, with the independent supply of cesium and barium from two similar hydrofracturing systems, the temperature of their liquid phases should be the same, which limits the possibility of optimizing the TEC operation mode according to the vapor pressure of these working bodies.

Cesium vapor generators are also known that are formed by decomposition of graphite and cesium compounds (Gverdtsiteli I.G. Kalandarishvili A.G., Tskhakaya V.K. Sources of cesium vapor based on cesium graphite for TEC. Pros. 3rd Internat. Conf. On Thermion Electr. Power Gener., Juelich, 1972, Vol. 3, p. 1139-1146.). The disadvantages of such hydroprocessing are:

- the risk of penetration of carbon compounds in the MEZ, which leads to a decrease in the efficiency of thermionic energy conversion and resource characteristics of the TEC;

- a small cesium capacity and the need for precise control of the operating temperature of cesium graphite (in the range of ~ 650-1000 ° K) as the cesium content in it decreases and to compensate for technological deviations of the parameters.

The closest to the claimed technical solution for a number of signs (different vapor pressure of the working fluid inside and outside the device, its recharge from the reservoir and the lack of direct contact of the liquid phase with the MEZ medium) is a GPRT, including a reservoir containing liquid cesium or a porous body impregnated with it, an electric heater and a hollow cylinder of cesium graphite. The inner cavity of the cylinder communicates with the reservoir, and its outer surface with the cavity of the MEZ (Patent RU No. 2464668, IPC H01J 45/00, publ. 20.10.2012). Due to the pressure difference inside and outside the cylinder, when it is heated, cesium evaporates from the outer surface and is simultaneously absorbed from the inner cavity.

However, in this case, there remains the need to maintain the temperature of graphite, which differs from the temperature of the TEC collector, as well as the danger of the penetration of carbon compounds into the MEZ. In addition, this device is not suitable for supplying barium.

The objective of the invention is the expansion of the functionality of the hydroprocessing (using cesium or barium vapor), reducing its sensitivity to the level of operating temperature, increasing the efficiency of the process of thermionic conversion, as well as the reliability and resource of TEC.

The problem is solved by using a known barogalvanic cell as a vapor generator for the thermionic converter, which uses a solid electrolyte placed between two gas-permeable electrodes communicating with isolated cavities containing vapor of a substance whose ions provide the conductivity of this electrolyte, and pressure vapor in the cavities differ from each other ("Energy conversion device comprising a solid crystalline electrolyte and a solid reaction zone separator", US patent No. 353516 3, declared on November 21, 1966, published on October 20, 1070; according to the Russian classification, the generally accepted name is: “one-component electrochemical converter with different pressure of the active substance in the electrodes” - L. A. Kvasnikov, R. G. Tazetdinov. Regenerative fuel cells. Moscow , "ATOMIZDAT", 1978, p. 18-21).

When using the barogalvanic cell as a hydroprocessing, its working substance is cesium or barium, present in the liquid phase or in the form of easily decomposing compounds in a cavity isolated from the MEZ. The pressure in this cavity will be equal to the saturated vapor pressure of these substances. In this case, the electromotive force (emf) of the baro-galvanic cell is determined in accordance with the Nernst formula:

Where:

T _c is the temperature of the liquid phase or decomposing compound;

P _Cs - saturated vapor pressure of the working fluid at this temperature,

P _MEZ - pressure in the cavity in communication with the MEZ;

z is the degree of ionization (equal to 1 for cesium or 2 for barium);

R = 8.3145 J / (mol⋅K) - universal gas constant;

F = 96485 C / mol - the Faraday number.

To simplify the design of the TEC, the temperature of the working substance, as well as the temperature of the solid electrolyte, it is advisable to maintain close to the temperature of the collector of the TEC. In FIG. 1 shows a graph of dependence (1) in the range of values of cesium pressure in the MEZ characteristic for the TEC, is indicated in FIG. 1, as P _MEZ , and the temperature of the collector, which coincides with the temperature of the liquid phase or decomposable compound, indicated in FIG. 1, as T _s. The use of the barogalvanic cell for a new purpose, namely, as a generator of the working fluid vapor for a thermionic converter, is due to the reduced dependence of the emf pressure and temperature, as well as the ability to control the ion current flowing through the electrolyte.

The essence of the claimed technical solution is illustrated by schematic depictions of a barvoltaic cell used as a vapor generator of the working fluid, shown in section in FIG. 2, as well as the electrical circuit for controlling this generator shown in FIG. 3.

Information confirming the possibility of carrying out the invention.

The working fluid steam generator shown in FIG. 2, contains a flask 1 of solid electrolyte with ion conductivity of the TEC working fluid, separating the metal reservoir for the working fluid 2 and the pipe 3, connected to the cavity of the TEC MEZ. The ceramic-metal pressure seal 4 provides a tight connection of these structural elements and their electrical isolation from each other. For current collection from the inner and outer surfaces of the flask 1, gas-permeable electrodes 5 and 6 are used in the form of electrically conductive wicks, as well as electrical contact 7 on the reservoir of the working fluid 2 and electrical contact 8, which is under a common electric potential with pipe 3.

As a solid electrolyte in the proposed HRPT, flasks made of mixed aluminum oxides and a working fluid can be used, made by electrochemical replacement of sodium with cesium or barium atoms in beta-alumina, which is formed by the technology used to make the electrolyte for sodium-sulfur batteries (J. Sadworth , A. Tilly. Sodium Sodium Batteries. Moscow, Mir, 1988). The gas-permeable electrodes can be metal grids, or wicks of wire, shavings and foil, which are in electrical contact with a solid electrolyte, and the electrode 6, which does not have direct contact with the MEZ medium, can also be made of carbon fiber.

The generator is controlled by varying the voltage between the contacts using the electric circuit shown in FIG. 3, which in addition to the GPRT contains variable electrical resistance R1, switch Pr1, paired switch Pr2 and a constant voltage source U.

The proposed HRT works as follows. In the position of the switch Pr1 opposite to that shown in FIG. 3, the constant voltage source is disconnected from the scram. In this case, with a high value of resistance R1, there is no ion current in the electrolyte, and the working fluid does not enter the cavity of the MEZ. A decrease in the magnitude of this variable resistance allows the ion current to pass through a flask of solid electrolyte under the influence of an emf arising from the difference in the vapor pressure of the working fluid in the reservoir and in the cavity of the MEZ. In this case, the working fluid is absorbed by the electrolyte on the gas-permeable electrode 6 and evaporates from the gas-permeable electrode 5 until the vapor pressures in the tank and in the MPZ are equal. The feed rate of the vapor of the working fluid is regulated by variable resistance, and the maximum value of this speed is limited by the value of the emf (1) and the internal electrical resistance of the HLRT. A further increase in the ion current and the feed rate of the working fluid is achieved by creating an additional potential difference between the electrical contacts 7 and 8 using an external constant voltage source U by setting the switch Pr1 in the one shown in FIG. 3 position. In this case, by varying the resistance R1, the supply of the working fluid can also be controlled. Transferring the pair switch Pr2 to the opposite position reverses the polarity of the source connection. In this case, the current through the electrolyte and the feed rate of the working fluid decrease again. If the reverse voltage exceeds the magnitude of the emf (1), the direction of the current in the electrolyte changes to the opposite and the working fluid begins to move away from the cavity of the MEZ back to the reservoir, and the vapor pressure of the working fluid in the MEZ decreases. The speed of this process can also be controlled by a variable resistance R1. In the future, since according to formula (1), when the vapor pressure of the working fluid in the MEZ decreases, the emf value increases, the total voltage between the gas-permeable electrodes becomes zero, the ion current through the electrolyte stops and the pressure stabilizes at the level determined by the value of U. Since the operating voltage of the TEC is comparable with the calculated values of the emf presented in the graph (see Fig. 1), this converter can also be used as a constant voltage source U for hydroprocessing.

Thus, the proposed technical solution allows to expand the functionality of the hydroprocessing (use cesium or barium as a working fluid), reduce its sensitivity to the level of the operating temperature, increase the efficiency of the process of thermionic energy conversion, as well as the reliability and resource of TEC.

Claims (7)

1. The vapor generator of the working fluid for thermionic converters, which is a barogalvanic element containing a reservoir with a working fluid - cesium, which is in the liquid phase or in the form of easily decomposable compounds; wherein the vapor generator of the working fluid is connected by a pipe to the cavity of the interelectrode gap of the thermionic converter; while the reservoir with the working fluid and the pipe are electrically isolated from each other, separated by a solid electrolyte with conductivity by the ions of the working fluid, and a solid electrolyte is placed between two gas-permeable electrodes, characterized in that the control of the working fluid vapor generator for thermionic converters is carried out by changing the voltage between the contacts connected to the gas-permeable electrodes using an electric circuit, which, in addition to the working fluid vapor generator, contains an alternating electrical resistance, a switch, a pair switch and a constant voltage source. 2. The vapor generator of the working fluid for thermionic converters according to claim 1, characterized in that the working fluid is barium. 3. The vapor generator of the working fluid for thermionic converters according to claim 1, characterized in that the solid electrolyte is made in the form of a flask from a mixture of aluminum oxides and a working fluid. 4. The working fluid vapor generator for thermionic converters according to claim 1, characterized in that the gas-permeable electrodes are metal grids or wicks of wire, shavings and foil that are in electrical contact with a solid electrolyte.

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