RU2778028C1 - Stirling engine heating head - Google Patents

Abstract

FIELD: engine building.

SUBSTANCE: invention relates to the field of engine building, namely to the heating heads of the Stirling engine. A heating head of a Stirling engine is proposed, containing an inner cylinder 4 and an outer power cylinder 2, between which there are internal longitudinal ribs 7, and on the outer surface of the outer power cylinder 2 external radial ribs 6. A piston 5 is installed in the inner cylinder 4. In the outer power cylinder 2 holes were made to obtain thermal bridges 3 by pouring cast copper or aluminum alloys. A cover is additionally fixed to the heating head from above and a flange from below, while thermal bridges 3 form one solid part with internal longitudinal 7 and external radial 6 ribs, as well as with a cover fixed from above and from below a flange.

EFFECT: increase in engine efficiency, increase in the temperature of the working gas in the heating head.

4 cl, 2 tbl, 4 dwg

Description

The invention relates to the field of engine building, namely to the heating heads of the Stirling engine. These engines have found application in the national economy as a mini-CHP, power plants for ships, cars; in space to power the onboard systems of spacecraft; in military equipment, namely in submarines for recharging batteries and powering the propulsion engine.

Known heater head for composite modules of the Stirling engine (patent US No. 4768342, IPC F02G 1/04, publ. 21.04.1986).

The essence of the invention lies in the fact that the heater head is a pressure vessel with a top wall and a side wall connected to it. The former interacts with one end of the displacer piston to form an expansion space, and the latter interacts with the displacement piston cylinder to define an annular heat exchange area in close proximity to the expansion space and in open communication with it. The displacer piston is installed with the possibility of reciprocating motion in the displacer cylinder. In one embodiment of the invention, the engine working gas occupying the expansion space and the heat exchange area is heated by a plurality of heat pipes sealed through the wall of the pressure vessel into the heat exchange area from an external manifold through which the heated fluid is pumped. In another embodiment, a plurality of heat exchange tubes extending through the heat exchange zone are connected between external inlet and outlet manifolds to transport heated fluid through the heat exchange zone.

The disadvantage of this invention is the complexity of the design, due to the fact that it is necessary to solder a lot of pipes to the side and top walls of the heater, including the collector walls. This method requires many technological operations, and the solder joints must be tight and withstand high temperatures, pressure and heated fluid (molten sodium or a low-melting alloy consisting of sodium and potassium) for a long time.

The closest technical solution is a device for heat transfer at high temperature (DE patent No. 4219583, IPC F02G 1/43, 1/055, publ. 15.06.1992).

A device for transferring heat at high temperature to a gaseous working medium in a high-temperature power housing or a heating machine operating in a closed cycle process with an intermittently moving piston, the working gas in two separated cylindrical spaces, which is connected by a combination of a heater, a regenerator and a cooler, flows forward and back in alternating flow directions. The power housing consists of an inner cylinder and an outer cylinder with longitudinal ribs, which are located between the inner and outer cylinders and are heat-conducting, rigid and resistant to high temperatures connections, and on the outer surface of the outer cylinder, radially mounted ribs.

The disadvantage of this invention is that the outer cylinder, as a rule, has a significant wall thickness, because it experiences high temperature and pressure. The outer cylinder is made of a heat-resistant corrosion-resistant alloy with a low coefficient of thermal conductivity, therefore, the heat flow towards the working gas and its temperature decrease, as a result of which the efficiency of the Stirling engine decreases. In addition, brazed seams, as a rule, are porous along the walls of the cylinder and must work at high temperatures for a long time. The porosity of brazed joints has a bad effect on heat transfer from the outer ribs to the cylinder wall and from the cylinder wall to the ribs.

The objective of the present invention is to provide a Stirling engine heating head with increased thermal conductivity from the external heating medium to the working gas.

The technical result achieved by using the present invention is:

- increasing the temperature of the working gas in the heating head;

- increasing the efficiency of the engine.

To solve this problem and achieve a technical result, a Stirling engine heating head is claimed, containing an inner cylinder and an outer power cylinder, between which there are internal longitudinal ribs, and external radial ribs on the outer surface of the outer power cylinder. A piston is installed in the inner cylinder. Holes are made in the external power cylinder for obtaining thermal bridges by pouring cast copper or aluminum alloys, a cover is additionally fixed to the heating head from above and a flange from below, while thermal bridges form one single piece with internal longitudinal and external radial ribs, as well as with a fixed top cover and bottom flange. The outer power cylinder can be made welded and obtained by casting, or the outer power cylinder can be made non-welded and obtained by drawing. The shape and number of holes for thermal bridges, as well as their location in the external power cylinder, is selected depending on the size of the heating head.

In most high-performance Stirling engines, the working fluid is under pressure in a sealed welded housing, and the heating head experiences high temperatures of ≈500°C and above. In this regard, the engine head is made of heat-resistant corrosion-resistant alloys. The technical inconsistencies in designs with a finned heating head are:

1) heat-resistant corrosion-resistant alloys, as a rule, have a low coefficient of thermal conductivity, therefore, the heat flux towards the working fluid and its temperature decrease, as a result of which the efficiency of the Stirling engine decreases, this follows from formula (1)

- температура рабочего тела в нагревательной головке;where

- temperature of the working fluid in the heating head;

- температура рабочего тела в холодильнике;

- temperature of the working fluid in the refrigerator;

2) with an increase in the maximum pressure in the cycle, the output power of the engine increases, this follows from formulas (2), (3). However, this leads to an increase in the wall thickness of the engine head, and, consequently, to a decrease in the heat flux towards the working fluid, as a result of which the efficiency of the Stirling engine decreases.

where A is work;

- максимальное давление в цикле;

- maximum pressure in the cycle;

V - volume;

t - time;

N is power.

To solve this contradiction, a heating head of a Stirling engine with an external power cylinder is proposed, in which holes are made for obtaining thermal bridges by pouring cast copper or aluminum alloys, which form one single piece with internal longitudinal and external radial ribs (Fig. 1a)) with subsequent mechanical processing of the outer radial and inner longitudinal ribs and welding of the cover from above and the flange from below (Fig. 1b)). Thermal bridges form one solid piece with internal longitudinal and external radial ribs. In this case, the number of holes and their shape, location in the outer power cylinder can be any, depending on the size of the heating head.

The manufacturing technology of the external power cylinder depends on the overall dimensions and wall thickness. The dimensions and wall thickness of the outer power cylinder may be acceptable for manufacturing by drawing.

If the outer power cylinder is not welded and obtained by drawing, then the thermal bridges in it are made by pouring with cast copper or aluminum alloys (Fig. 2a)) followed by machining of the inner longitudinal and outer radial ribs (Fig. 2b)).

Thus, the design of the heating head with thermal bridges made of a copper or aluminum cast alloy will increase the heat flow towards the working fluid due to a higher thermal conductivity compared to heat-resistant corrosion-resistant alloys. This solution will increase the temperature of the working gas in the heating head, and, consequently, the efficiency of the Stirling engine, this can be seen from formula (1).

Thermal calculations were carried out, which showed that the temperature of the internal longitudinal ribs with thermal bridges (Fig. 3) is 110°C higher than without them (Fig. 4). The initial data used for the thermal calculation of the structure: the temperature of the outer radial ribs of the heater is 460°C; thermal power removed from the internal longitudinal ribs - 2000 W; material of the external power cylinder - steel 12X18H10T; material of thermal bridges, external radial and internal longitudinal ribs - M1 alloy.

In FIG. 1 shows a heating head obtained by casting and welding: a) a blank obtained by casting; b) heating head; c) external power cylinder.

In FIG. 1 positions are marked:

1 - cast copper or aluminum alloy;

2 - external power cylinder;

3 - thermal bridges;

4 - inner cylinder;

5 - piston;

6 - outer radial ribs;

7 - internal longitudinal ribs.

In FIG. 2 shows a heating head obtained by drawing and casting: a) a blank obtained by casting; b) heating head; c) external power cylinder.

In FIG. 2 positions are marked:

1 - cast copper or aluminum alloy;

2 - external power cylinder;

3 - thermal bridges;

4 - inner cylinder;

5 - piston;

6 - outer radial ribs;

7 - internal longitudinal ribs.

In FIG. 3 shows the thermal calculation of the heating head with thermal bridges.

In FIG. 4 shows the thermal calculation of the heating head without thermal bridges.

In static mode, when the product is not working, the external power cylinder of the Stirling engine is under pressure, while no heat is supplied from the heat source from the outside. The temperature of the outer power cylinder pos. 2, thermal bridges pos. 3, inner cylinder pos. 4, piston pos. 5, outer radial ribs pos. 6, internal longitudinal ribs pos. 7 is approximately equal to the environment.

The device operates as follows: heat is supplied from the outside heat source, while heat transfer occurs: 1) by convective heat exchange between the external heating medium and the outer radial ribs pos. 6; 2) thermal conductivity from the outer radial ribs pos. 6 through the outer power cylinder pos. 2 and through thermal bridges pos. 3 to the surfaces of the internal longitudinal ribs pos. 7; 3) convective heat transfer from internal longitudinal ribs pos. 7 to the working gas of the Stirling engine, the inner cylinder pos. 4 and piston pos. 5. During operation, the working gas inside the outer power cylinder is pressurized.

The materials that can be used for the manufacture of the outer power cylinder, inner cylinder and piston are shown in Table 1.

Materials that can be used for the manufacture of external radial fins, thermal bridges and internal longitudinal ribs are in table 2.

Claims (4)

1. The heating head of the Stirling engine, containing an inner cylinder and an outer power cylinder, between which there are internal longitudinal ribs, and on the outer surface of the outer power cylinder, external radial ribs, while a piston is installed in the inner cylinder, characterized in that the outer power cylinder is made holes for obtaining thermal bridges by pouring cast copper or aluminum alloys, a cover is additionally fixed to the heating head from above and a flange from below, while thermal bridges form one single piece with internal longitudinal and external radial ribs, as well as with a cover fixed from above and from below a flange. 2. The heating head of the Stirling engine according to claim 1, characterized in that the outer power cylinder is welded and obtained by casting. 3. The heating head of the Stirling engine according to claim 1, characterized in that the outer power cylinder is not welded and obtained by drawing. 4. The heating head of the Stirling engine according to claim 1, characterized in that the shape and number of holes for thermal bridges, as well as their location in the outer power cylinder is selected depending on the size of the heating head.

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