RU2464668C1 - Device to supply vapour of caesium into thermionic converter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device is proposed to supply vapour of caesium into a thermionic converter of a thermionic converter, comprising a source of caesium vapour, made of pyrolytic oriented caesium graphite, and placed in a body with a heater installed on it, at the same time the source of caesium vapour is arranged in the form of a hollow cylinder placed between two plates sealing the upper and lower planes of the cylinder, the upper of which is solid, at the same time the cylinder cavity is connected with a reservoir with a source of liquid caesium condensate, the inner volume of which is tightly closed with a source of vapour from a working volume. On the reservoir with liquid caesium condensate there is a heater installed and a nozzle with a valve, and the source of caesium condensate is arranged in the form of a capillary structure with liquid caesium condensate.

EFFECT: higher capacitance by caesium.

3 cl, 2 dwg, 1 tbl

Description

The invention relates to thermionic conversion of thermal energy into electrical energy and relates to devices for supplying cesium vapor to the interelectrode gap of a thermionic converter (TEC), where an adjustable supply of cesium vapor, a wide range of operating temperatures, and an increased cesium capacity are required.

In thermionic converters, cesium atoms perform several functions simultaneously:

- adsorbed on the surface of the TEC electrodes regulate the electron work function;

- ionizing on the hot surface of the emitter or in the interelectrode gap in the case of the implementation of the arc mode compensate for the spatial electron charge, which limits the passage of the electron current through the interelectrode gap.

Known devices for supplying cesium vapor containing a metal tank with liquid cesium condensate (see Kalandarishvili A.G. Sources of the working fluid for thermionic energy converters. - 2nd edition, add. - M .: Energoatomizdat, 1993 - p. 14, 30-31).

Heating the temperature of the tank with liquid cesium condensate, cesium steam is supplied with an optimal pressure of about several hundred pascals, which corresponds to a tank temperature of about 550-650 K.

However, such devices for supplying cesium vapor have several disadvantages:

- low optimum operating temperature of about 550-650 K, which in some cases complicates the temperature binding of the device to the installation;

- the presence of a liquid phase during operation of a thermionic installation in zero gravity conditions can cause technical difficulties;

- a sharp dependence of the output electrical parameters on the temperature of the tank.

Known devices (see Kalandarishvili A.G. Sources of the working fluid for thermionic energy converters. - 2nd edition, add., - M .: Energoatomizdat, 1993 - p. 203, Alleau T., Devin V., Lesneur R. Application of graphite-cesium compounds in thermionic converters. Pros. Internat. Conf. On Thermion. Electr. Power Gener., Lond., Sept. 1965, p.11-19. Kravchenko Yu.A., Stolyarov GA Sources of cesium vapor with pressed and pyrolytic graphite for TEC, Gverdtsiteli IG, Kalandarishvili AG, Tskhakaya VK Sources of cesium vapor based on cesium graphite for TEC. Pros. 3 ^rd Internat. Conf. On Thermion. Electr . Power Gener., Juelich, 1972, Vol.3, p.1139-1146), in which cesium vapor is fed into the interelectrode gap of the thermionic converter from a reservoir in which one of the graphite and cesium compounds is placed.

In these devices, cesium vapor is supplied from the solid phase, and the optimum operating temperature ranges from 650 to 1000 K, depending on the content of cesium in graphite. With an increase in the optimum operating temperature (which is associated with a decrease in the amount of cesium in graphite), the dependence of the output electric parameters on the temperature of the tank with a block of cesium graphite becomes more gentle.

The prototype is a device for supplying cesium vapor to a TEC thermionic converter containing a cesium vapor source made of pyrolytic oriented cesium graphite. The cesium vapor source is placed in a tank with a heater installed on it, the tank is connected to the TEP working volume

(See Gverdtsiteli I.G., Kalandarishvili A.G., Tskhakaya V.K. Sources of cesium vapor based on cesium graphite for TEC. Pros. 3 ^rd Internat. Conf. On Thermion. Electr. Power Gener., Juelich, 1972 Vol.3, p. 1139-1146).

As sources of cesium vapor in TEC, the compounds C ₁₀ Cs and C ₂₄ Cs, which have the highest capacity, which correspond to the following equilibrium reactions, are mainly used:

12C ₁₀ Cs⇔5C ₂₄ Cs + 7Cs,

3C ₂₄ Cs⇔2C ₃₆ Cs + Cs

The main disadvantage of such devices is the small cesium capacity. A large cesium capacity is necessary for devices with long-term operation of the TEC. In this mode of operation of the TEC, the working volume of the converter and the interelectrode gap (MEZ) are cleaned of residual gases by pumping cesium vapor through the MEZ, which leads to irreversible loss of cesium mass.

The table “The amount of cesium in layered graphite compounds per 1 g of pyrographite” provides calculated and experimental data on the amount of cesium per 1 g of pyrolytic graphite for various two-phase cesium-graphite systems.

Table Reaction Payment Experiment 5C ₈ Cs⇔4C ₁₀ Cs + Cs; 0.277 0.150 12C ₁₀ Cs⇔5C ₂₄ Cs + 7Cs; 0.647 0.525 3C ₂₄ Cs⇔2C ₃₆ Cs + Cs; 0.154 0,112 4C ₃₆ Cs⇔3C ₄₈ Cs + Cs. 0.077 0.923

The technical result to which the invention is directed is to increase the capacity of the device for cesium, which leads to an increase in the duration of operation of the TEC, and ensuring a wide range of operating temperatures.

To this end, a device is proposed for supplying cesium vapor to a TEC thermionic converter containing a cesium vapor source made of pyrolytic oriented cesium graphite and placed in a housing with a heater installed on it, while the cesium vapor source is made in the form of a hollow cylinder placed between the sealing upper and the lower plane of the cylinder by two plates, the upper of which is solid, while the cylinder cavity is connected to the reservoir with a source of cesium liquid condensate, internal the first volume of which is sealed off by the steam source from the working volume of the TEC.

At the same time, a heater and a pipe with a valve are installed on the tank with liquid cesium condensate.

In this case, the cesium source is made in the form of a capillary structure with liquid cesium condensate.

Figure 1 and 2 shows a schematic diagram of the design of the device, which contains:

1. the main working volume associated with the interelectrode gap of the TEC;

2. a pipe connecting the cesium vapor source with the TEC interelectrode gap;

3. bellows;

4. movable continuous plate;

5. a hollow cylinder made of cesium oriented graphite;

6. stainless steel case;

7. fixed plate;

8. a heater for heating cesium graphite;

9. tank;

10. high-temperature valve;

11. capillary structure filled with liquid cesium condensate;

12. a heater for heating the liquid condensate of cesium;

13. thermionic energy converter;

14. output choke;

15. cesium absorber block made of oriented pyrographite;

16. pipe connecting the working volume of the TEC with the vacuum system.

The proposed device operates as follows.

After the entire device is degassed through valve 10, cesium is filled with a hollow cylinder of cesium oriented graphite 5 and capillary structure 11, after which valve 10 is hermetically closed. The cylinder cavity is connected to the reservoir 9, the upper plane is hermetically sealed by a continuous metal plate 4, which is attached to a bellows 3 connected to the housing of the device 6, made, for example, of stainless steel. This fastening makes it possible to compensate for the expansion of pyrolytic graphite during heating and saturation with cesium. The lower plane of the cylinder 5 is sealed by a plate 7 with an opening connecting the internal cavity of the cylinder 5 with a reservoir of cesium 9. When the cesium condensate 11 is heated by the heater 12, pyrolytic graphite 5 is recharged during operation. The amount of cesium mass charged into the capillary structure 11 is each time determined by the life of the cesium vapor source and the plant as a whole. Such a device makes it possible to ensure the required cesium mass flow rate, provided that the sorption isostere (the dependence of the cesium vapor pressure on the temperature of the tank 9) for cesium liquid condensate should always exceed the sorption isostere for the selected steam source based on cesium graphite, which is automatically implemented in this device.

Example.

In order to ensure stable long-term operation of the thermionic energy converter 13, it is necessary to continuously clean the interelectrode gap 17 and the TEC working volume from residual gases throughout the entire period of operation. The most promising from the point of view of purification of residual gases is their emission through a special throttle 14 with further pumping through the pipe 16 using a vacuum system. However, along with the residual gases, a certain mass of cesium is also ejected. Therefore, additional requirements are imposed on the sources of cesium vapor that ensure the operation of the TEC - they must have a certain capacity by weight of cesium, the specific value of which depends on the service life of the product and on the adopted cleaning system, which determine the daily mass flow rate of the working fluid (cesium).

Typically, mass cesium consumption of about 0.5 g / day is sufficient for effective cleaning.

An experimental setup for studying the proposed device for supplying cesium vapor in the mode of mass flow of cesium 0.5 g / day is presented in figure 2.

As a source of cesium vapor, cesium graphite of the composition C ₈ Cs was selected (the weight of pure graphite was 5 grams), the temperature of which was maintained by the heater 8 constant and equal to about 800 K. 20 grams of liquid cesium condensate was distilled into the internal volume of the tank 9. At a temperature of 800 K, the compound C ₈ Cs corresponds to a two-phase equilibrium reaction

5C ₈ Cs⇔4C ₁₀ Cs + Cs;

according to which, with 5 grams of graphite, in the case of using a prototype, a source of cesium vapor without replenishment from the internal volume of liquid cesium condensate, the maximum capacity (see table above) corresponds to 1.5 g of cesium. In this case, the pressure of saturated cesium vapor from cesium graphite will be maintained at a constant level.

In our case, the proposed device was used, which was connected to an experimental installation (see Figure 2), in which the cesium 5 vapor source was made on the basis of cesium graphite with the composition C ₈ Cs. Similarly, sources of rubidium and potassium vapor can be made.

In the process of operation of the TEC in the mode with the consumption of cesium, the steam source 5 was continuously fed by cesium atoms from liquid condensate. The flow of directed cesium vapor from cesium graphite 5 fell into the working volume 1 and penetrated through the pipe 2 into the working volume of the TEC 13 and, falling into the electrode gap 17 of the TEC, captured the residual gases, which through the output choke 14 entered the absorbent block of the working fluid (cesium) based on pyrographite 15, which selectively adsorbed cesium atoms and passed residual gases through the pipe 16 to vacuum pumping.

In this case, the mass consumption of cesium was determined by the output choke 14 and was approximately 0.5 g / day.

The tests showed that the device for supplying cesium vapor provides stable operation of cesium steam TEP in operation with a mass flow rate of cesium of about 0.5 g / day for about 1000 hours.

Claims (3)

1. A device for supplying cesium vapor to a thermionic converter (TEC) containing a cesium vapor source made of pyrolytic oriented cesium graphite and placed in a housing with a heater installed on it, characterized in that the cesium vapor source is made in the form of a hollow cylinder located between two plates sealing the upper and lower planes of the cylinder, the upper of which is solid, while the cylinder cavity is connected to the reservoir with a source of cesium liquid condensate, the internal volume which is sealingly overlapped by the source of steam displacement. 2. The device according to claim 1, characterized in that a heater and a pipe with a valve are installed on the reservoir with liquid cesium condensate. 3. The device according to claim 1, characterized in that the source of cesium condensate is made in the form of a capillary structure with liquid cesium condensate.

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