RU2827399C1 - Thermal unit of stirling engine - Google Patents

Abstract

FIELD: engine building.

SUBSTANCE: invention relates to the field of propulsion engineering, namely to engines operating according to the Stirling cycle. Thermal unit of Stirling engine contains in-series connected heater 1, regenerator 2 and cooler 3, formed by displacer cylinder 5 with installed in it displacement piston and external cylinder 4 with a gap between them, filled with metal spirals 10a, 10b with high heat conductivity in the area of heater 1 and cooler 3 and heat accumulating material 11 in the area of regenerator 2. Heater 1 and cooler 3 contain jackets 8, 9 located outside external cylinder 4 with hot and cold heat carrier, respectively, containing inlet and outlet branch pipes. Lower part of external cylinder 4 is connected to manifold 14, containing the axial channel with displacement piston rod 15 and channel 16 of communication with the working cylinder, and upper parts of both cylinders 4, 5 end with heads of cylinders 6, 7, at the same time in the centre of cylinder head of displacer 7 there is hole 13.

EFFECT: increasing the efficiency of the thermal unit of the Stirling engine due to more efficient heat transfer from the walls of the heater and cooler cylinders to the working fluid, as well as simplifying the design.

1 cl, 2 dwg, 1 tbl

Description

The invention relates to the field of engine building, namely to the design of a thermal unit for engines operating on the Stirling cycle, and can be used in various Stirling engine installations used in isolated areas, in outer space, etc., and where it is ineffective or impossible to use internal combustion engines, as well as steam engines or turbines.

A Stirling engine is known [RU 2100634, published 27.12.1997], containing at least one displacer cylinder, in which a displacer piston moves, dividing the volume of the cylinder into hot and cold cavities. In this case, a heater, a regenerator and a cooler are installed in series in the line connecting the hot and cold cavities. The cooler contains a cylindrical cooling jacket filled with cooling liquid and enclosing the cylinder with the piston, equipped with two annular collectors connected to the liquid inlet and outlet pipes. The cooler, made as a "pipe in pipe", contains annular channels formed by means of bushings with internal holes located uniformly along the diameter of the cylinder in the cooling jacket, through which the working fluid circulates.

The disadvantage of this device is the insufficient heat exchange of the cylindrical walls of the cooler channels with the working environment, which reduces the efficiency of the engine.

A Stirling engine is known [RU 2008489, published 28.02.1994], comprising at least one cylinder with an upper cover-heater facing an external heat source, a displacement and working pistons placed in the cylinder and dividing its volume into a hot cavity, a cold cavity and a buffer cavity, a cooler, a regenerator and a heater, installed in series in a line connecting the hot and cold cavities, wherein the heater is made in the form of a disk with profiled channels placed in it, one part of which connects the hot cavity with the periphery of the disk, which is communicated with the other part of the channels connecting the periphery of the disk with the regenerator, wherein the heater channels are made in the form of a cylindrical pipe truncated along a generatrix, facing with its larger surface towards the heat source.

The disadvantage of this engine is the need to use a disk with channels in the heater, which has great rigidity and thickness in order to withstand the high pressure of the working fluid (gas) inside. The second disadvantage is that in order to provide the required heat flow, it is necessary to use large dimensions of the heater disk, which complicates the use of this design in multi-piston engines. The third disadvantage is the low efficiency of heat transfer in the cooler, which contains a channel in which the working fluid is cooled by cooling the walls of the outer jacket of the cooler with a cold coolant circulating in it.

The closest technical solution selected as a prototype is the Stirling engine thermal block [RU 2788798, published 24.01.2023], consisting of a heater, regenerator, cooler and displacer cylinder connected in series with a piston-displacer installed in it. The heater and cooler have jackets into which a hot or cold coolant is supplied through the inlet and outlet pipes to transfer or remove heat from external sources. The volume formed by the gap between the internal surfaces of the heater or cooler and the displacer cylinder is filled with a bulk material with good gas permeability and thermal conductivity, which exchanges heat with the working fluid.

Due to the uneven distribution of bulk material by volume and the lack of reliable thermal contact of its particles with the walls of the heater and cooler, the heating block has zones with different hydraulic resistance and heat transfer coefficients, and a decrease in the volume of bulk material as a result of thermal deformations during the operation of the heating block leads to a decrease in heat transfer to the working fluid, which is the main disadvantage of the heating block.

The technical result of the invention is an increase in the efficiency of the Stirling engine thermal block due to more efficient heat transfer from the walls of the heater and cooler to the working fluid, as well as a simplification of the design.

The technical result is achieved in that the thermal block of the Stirling engine contains a heater, a regenerator and a cooler connected in series, formed by a displacer cylinder with a piston-displacer installed in it and an outer cylinder with a gap between them, filled with metal spirals with high thermal conductivity in the area of the heater and cooler and heat-accumulating material in the area of the regenerator, the heater and cooler also contain jackets with hot and cold coolant, respectively, located outside the outer cylinder, containing an inlet and outlet branch pipes, wherein the lower part of the outer cylinder is connected to a manifold containing an axial channel with a piston-displacer rod located in it and a communication channel with the working cylinder, and the upper parts of both cylinders end with cylinder heads, wherein an opening is made in the center of the displacer cylinder head.

The essence of the invention is explained by graphic materials:

- figure 1 - thermal block of the Stirling engine;

- figure 2 - cross-section of the heating block heater.

The Stirling engine body block, as shown in Figure 1, includes the following main parts:

1 - heater;

2 - regenerator;

3 - cooler;

4 - outer cylinder;

5 - displacer cylinder;

6 - outer cylinder head;

7 - displacer cylinder head;

8 - heater jacket;

9 - cooling jacket;

10a - heating coils;

10, - cooler spirals;

11 - heat-accumulating material;

12 - piston-displacer;

13 - hole in the cylinder head of the displacer;

14 - collector;

15 - piston rod;

16 - communication channel with the working cylinder.

As shown in Figures 1 and 2, the claimed thermal block of the Stirling engine contains a heater 1, a regenerator 2 and a cooler 3 arranged in series. The heater 1 of the thermal block is formed by the upper part of the outer cylinder 4 and the displacer cylinder 5, ending with cylinder heads 6 and 7, respectively, as well as a heater jacket 8, equipped with inlet and outlet pipes (not separately marked with numbers in the figures), in which the hot coolant circulates. The gap between the walls of the outer cylinder 4 and the displacer cylinder 5 is filled with metal spirals 10a.

The cooler of the thermal block 3 is formed by the lower part of the outer cylinder 4 and the displacer cylinder 5, as well as the cooler jacket 9, equipped with inlet and outlet pipes, in which the cold coolant circulates. The gap between the walls of the outer cylinder 4 and the displacer cylinder 5 in the cooler 3 is also filled with metal spirals 10b.

Metal spirals 10a and 10b are made of metal with high thermal conductivity. These spirals are tightly laid in the gap between the cylinder walls in layers around the circumference of the gap so as to ensure good thermal contact between the spiral turns and the cylinder walls 4 and 5, as well as low gas-dynamic resistance for the movement of the working fluid.

Regenerator 2 is also formed by an outer cylinder 4 and a displacer cylinder 5, the gap between which is filled with heat-accumulating material 11.

Inside the cylinder of the displacer 5 there is a piston-displacer 12, shown in Figure 1 at the lower "dead" point. For the passage of the working fluid through the heater 1, the regenerator 2 and the cooler 3, an opening 13 is made in the upper part of the head of the cylinder of the displacer 7.

The outer cylinder 4 is fixed in its lower part to the manifold 14, containing an axial channel (not separately marked in the figures), in which the piston rod of the displacer 15 moves, rigidly connected to it. The manifold also contains a communication channel with the working cylinder 16, through which the working fluid (gas) from the under-piston space enters the working cylinder of the engine.

The claimed thermal block of the Stirling engine operates as follows.

The heat coming from the hot coolant circulating inside the jacket of the heater 8, connected by the inlet and outlet pipes to the external source of the hot coolant, is transferred through the wall of the outer cylinder 4 to the metal spirals of the heater 10a and, further, to the working fluid.

Similarly, the cooling of the working fluid occurs through its contact with the metal spirals of the cooler 10b, which transfers heat through the walls of the outer cylinder 4, cooled by the cold coolant circulating inside the cooler jacket 9, connected by inlet and outlet pipes to the source of the cold coolant.

Thus, the metal coils of the heater 10a are maintained at a high temperature close to the temperature of the hot coolant, and the metal coils of the cooler 106 are maintained at a low temperature close to the temperature of the cold coolant.

When the piston-displacer 12 moves upward from the lower "dead" point, the working fluid (gas) enters from the above-piston space through the opening in the cylinder head of the displacer 13 into the heater 1, where it is heated when passing through the metal spirals of the heater 10a. With further movement of the working fluid, its heat is transferred to the heat-accumulating material 11 of the regenerator 2. Further movement of the working fluid is accompanied by its cooling when passing through the metal spirals of the cooler 106.

The working fluid, having passed through the zones of the heater, regenerator and cooler, enters the sub-piston space, collects above the manifold 14 and through its gap with the displacer cylinder 5 and channel 16 is fed into the working cylinder.

When the working fluid moves into the under-piston space, it cools to a temperature close to the cooler temperature. At the same time, the pressure of the working fluid drops, transmitted through channel 16 to the working cylinder, where it is compressed.

When the working fluid moves into the above-piston space, it heats up to a temperature close to the heater temperature. At the same time, the pressure of the working fluid increases, which is transmitted through channel 16 to the working cylinder, where it performs useful expansion work.

An example of a specific implementation of a thermal block.

A thermal block of a Stirling engine, made in accordance with the description presented above, in which the heater and cooler in a gap of 3.5 mm between the outer cylinder and the displacer cylinder (the outer diameter of the displacer cylinder is 80 mm, the height is 210 mm) are filled with metal spirals made of 12X18N10T wire with a diameter of 0.5 mm. The outer diameter of the spirals in the initial state is 4 mm, the filling factor is 20%.

The hydraulic resistance and heat transfer coefficient were measured with the following parameters: coolant - air at atmospheric pressure, air flow rate at the inlet 0.0042 ^m3 /sec. The temperature of the coolant in the heater jacket is 250°C, cooler - 18°C, temperatures are measured with a K-type thermocouple. The hydraulic resistance was measured with a water differential pressure gauge.

The measured characteristics of the heat transfer efficiency of the claimed invention were compared with the characteristics of a prototype in which pieces of a metal spiral with a diameter of 3 mm and a height of 3 mm made of 12X18N10T wire with a diameter of 0.5 mm were used as a backfill material in the gap between the cylinders.

The results of the tests carried out are presented in the table below.

According to the data obtained during testing of the claimed invention, in comparison with the prototype, hydraulic losses were reduced by 3.9 times, and thermal power increased by 1.46 times, which confirms the claimed technical result.

Claims (1)

The thermal block of the Stirling engine contains a heater, a regenerator and a cooler connected in series, formed by a displacer cylinder with a piston-displacer installed in it and an outer cylinder with a gap between them, filled with metal spirals with high thermal conductivity in the area of the heater and cooler and heat-accumulating material in the area of the regenerator, the heater and cooler also contain jackets with hot and cold coolant, respectively, located outside the outer cylinder, containing an inlet and outlet branch pipes, wherein the lower part of the outer cylinder is connected to a manifold containing an axial channel with a piston-displacer rod located in it and a communication channel with the working cylinder, and the upper parts of both cylinders end with cylinder heads, wherein an opening is made in the center of the displacer cylinder head.

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