Implementation device and method for improving performance of Stirling engine

Abstract

The invention discloses an implementation device and method for improving the performance of a Stirling engine, a heater and a cooler of the implementation device are each provided with a double-coaxial circular pipe, and each double-coaxial circular pipe comprises an outer pipe, an inner pipe, an outer annular flow channel and an inner circular flow channel; an outer annular flow channel is formed between the outer wall face of the inner pipe and the inner wall face of the outer pipe, and an inner circular flow channel is defined by the inner wall face of the inner pipe. A groove rough surface, a spherical bulge rough surface, a spiral fin or a straight fin can be respectively arranged in the outer annular flow channel; the turbulence effect of the spiral fins or the straight fins is utilized to enhance the disturbance of a working medium in the outer annular flow channel, heat transfer enhances the heat exchange effect, and the heat exchange efficiency is improved; the inner circular flow channel is further provided with a heat preservation coating, the heat preservation coating is of a heat transfer weakening structure, and the heat preservation coating is located on the surface of the outer wall face of the inner circular flow channel or the surface of the inner wall face of the inner circular flow channel.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat exchange components of Stirling engines, and particularly relates to a device and method for improving the performance of Stirling engines. Background Art

[0002] A Stirling engine is an external combustion engine. The gas medium with work capacity inside it does not contact the external heat source, and has low requirements for the quality of the heat source. It can utilize renewable energy or traditional fossil fuels. In addition, the Stirling engine has low operating noise, high theoretical efficiency, and a compact structure, and has great potential for future applications. The actual energy utilization efficiency of a Stirling engine is closely related to the heat transfer process of its heater and cooler. Improving the heat transfer performance of the heater and cooler is crucial for improving its actual efficiency.

[0003] For Stirling engine heaters, fin - type and tube - type are currently the two most common types. Compared with fin - type heaters, tube - type heaters have a larger heat transfer capacity and are the most widely used. Currently, the main ideas for enhancing heat transfer in tube - type heat exchangers mainly include two aspects: (1) optimizing the arrangement of the heating tube bundles; (2) adding flow - disturbing or flow - guiding structures inside the heater. For idea (1), patents such as (CN209959367U Stirling engine heat exchanger) (CN 111720236 A Heater in Stirling engine) use the circumferential arrangement of U - shaped tube bundles to replace the equally - spaced arrangement of simple straight tubes to optimize the performance of the heater; patent (CN115075979A Stirling engine heater) uses concave - twisted tubes instead of U - shaped tubes to further improve the heat transfer performance of the heating tube bundles; patents such as (CN103195609A Device for improving the efficiency of the heating head of a solar Stirling engine) (CN104265499A Heat exchanger for the heating head of a solar Stirling engine) (CN102297040A A heat - collecting head for a solar Stirling engine) etc. adjust the layout of the tube bundles according to the external heat source conditions of solar energy, so that a larger proportion of the heating tubes can receive perpendicular solar irradiation; for idea (2), patents (CN111810314A A Stirling engine structure, CN111819354A Stirling engine with a gas passage arranged with three heat exchangers) add fin structures on the outer surface of the heating tube bundles to enhance heat transfer, the paper (Solomon et al. Computational analysis of external heat transfer for a tubular Stirling convertor) adds flow - guiding structures on the outer surface of the heating tube bundles to change the flow direction of the flue gas for heat transfer enhancement, patent (CN115163327A Device for improving the heat transfer effect of the external heat source of a Stirling engine) adds flow - disturbing structures in the space between the heating chamber and the heating tubes to disturb the flue gas flow field for heat transfer enhancement, and the paper (Xin et al. Study of heat transfer in oscillatory flow for a Stirling engine heating tube inserted with spiral spring) adds flow - disturbing components inside the heating tubes for heat transfer enhancement.

[0004] For Stirling engine coolers, finned or tubular structures are currently mostly used. The finned structure is simple but has a small heat exchange capacity and is only suitable for small-power Stirling engines. For tubular heat exchangers, the structural types mainly include coil type and shell-and-tube type, among which the shell-and-tube type is the most widely used. The main ideas for enhancing the heat transfer of tubular coolers include: (1) improving the form of the heat source; (2) changing the geometric dimensions or shapes of the tube types. For idea (1), the most commonly used cold sources in current Stirling engines are air or water. Among them, the cooling capacity of air is limited and it is only suitable for small-power Stirling engines. Water is the most widely used cold source at present, and there are also studies using a mixture of water and ethanol to enhance its cooling effect. Patent application (CN206016995 Stirling heat engine cooler using liquid metal for heat dissipation) uses liquid metal to replace the conventional cold source to enhance its heat transfer effect; for idea (2), patent application (CN108592660A A double-coil cooler for Stirling thermoelectric conversion device) aims at the coil-type cooler and invents a double-helix tube to replace the ordinary round tube and fins to enhance its heat exchange effect. Patent application (CN217029121U A Stirling engine cooler) proposes to use multiple capillary tubes to enhance the cooling effect of the cooler by reducing the diameter of the cooling tubes.

[0005] The above-mentioned methods for improving the performance of Stirling engine heaters and coolers can all improve the performance of the engine to a certain extent. Their innovative ideas are mainly based on the principle of enhanced heat transfer in general steady-state flow, and they conduct heat transfer enhancement design for Stirling engine heaters and coolers, rarely considering the particularity of the working fluid flow in the Stirling engine. For example, for heaters, existing research only enhances heat transfer, increases the energy exchange between the external heat source and the internal working fluid, raises the temperature of the internal working fluid, and improves the utilization efficiency of the heat of the external heat source; for coolers, existing research only enhances heat transfer, strengthens the cooling effect of the external cold source on the internal working fluid, reduces the temperature of the internal working fluid, and improves the energy transfer efficiency. These studies do not consider that the destinations of the working fluid in different flow directions are different and their heat demand targets are different. Summary of the Invention

[0006] The embodiments of the present invention provide a device and method for improving the performance of a Stirling engine. Since the working fluid in the Stirling engine is in a reciprocating oscillating flow state, the destinations of the working fluid flow in different flow directions are different and the expected effects are different. When the main flow direction of the working fluid is Compression Chamber → Cooling Tube → Regenerator → Heating Tube → Expansion Chamber (abbreviated as Compression → Expansion flow direction, see Figure 1) The destination of the working fluid flow is the expansion chamber, which generates a driving force on the driving wheel through thermal expansion. In this process, the better the heat transfer effect of the heating pipe, the more sufficient the power of the driving wheel of the Stirling engine. However, if the heat transfer performance of the cooling pipe is better, the temperature of the working fluid entering the expansion chamber will be reduced, and the power of the driving wheel will become weaker instead; when the main flow direction of the working fluid is expansion chamber → heating pipe → regenerator → cooling pipe → compression chamber (abbreviated as expansion → compression flow direction, see Figure 2 ) The destination of the working fluid flow is the compression chamber, which generates a driving force on the driving wheel through cold compression. In this process, the better the heat transfer effect of the cooling pipe, the more sufficient the power of the driving wheel of the Stirling engine. However, if the heat transfer effect of the heating pipe is better, the temperature of the working fluid entering the compression chamber will rise, and the power of the driving wheel of the Stirling engine will become weaker instead.

[0007] For the thermodynamic cycle of an ideal Stirling engine, during the isothermal expansion stage of heating, the heat source is turned on and the cold source is turned off (see Figure 1 );During the isothermal compression stage of cooling, the heat source is turned off and the cold source is turned on (see Figure 2 ). However, in the actual operation process, the frequency of the Stirling engine is relatively high, and the flow direction of the working fluid changes extremely fast. It is impossible to intermittently start and stop the external heat source and cold source. However, inspired by the ideal Stirling cycle process, different heat transfer control means can be considered for different flow directions of the reciprocating oscillating flow to reduce the gap between the actual cycle and the ideal cycle and improve the actual efficiency of the Stirling engine.

[0008] To solve the above problems, the technical solutions provided by the present invention are as follows:

[0009] The embodiment of the present invention provides a device for improving the performance of a Stirling engine, including a driving wheel (1), an expansion chamber (2), a connecting pipe (3), a heater (4), a heat source (5), a regenerator (6), a cold source (7), a cooler (8), a compression chamber (9) and a piston (10); the driving wheel (1) is connected to the expansion chamber (2) and the compression chamber (9) respectively through 2 pistons (10), the expansion chamber (2) is connected to the heater (4) through 1 connecting pipe (3), a heat source (5) is arranged outside the heater (4), the heater (4) is connected to the regenerator (6), the regenerator (6) is connected to the cooler (8), a cold source (7) is arranged outside the cooler (8), and the cooler (8) is connected to the compression chamber (9) through another connecting pipe (3); both the heater (4) and the cooler (8) are provided with double coaxial circular tubes.

[0010] In a preferred embodiment of the present invention, the double coaxial circular tube includes an outer tube (11), an inner tube (12), an outer annular flow channel (18) and an inner circular flow channel (19); an outer annular flow channel (18) is formed between the outer wall surface of the inner tube (12) and the inner wall surface of the outer tube (11), and an inner circular flow channel (19) is formed by enclosing the inner wall surface of the inner tube (12).

[0011] A groove rough surface (13), a spherical protrusion rough surface (14), a spiral fin (15) or a straight fin (16) can be respectively arranged in the outer annular flow channel (18). One edge of the spiral fin (15) is respectively arranged on the inner wall surface of the outer tube (11), or one side of the straight fin (16) is arranged on the inner wall surface of the outer tube (11). The flow disturbance of the working medium in the outer annular flow channel (18) is enhanced by the flow disturbance effect of the spiral fin (15) or the straight fin (16), its heat transfer effect is strengthened, and the heat exchange efficiency is increased; wherein, a heat preservation coating (17) is further arranged in the inner circular flow channel (19), the heat preservation coating (17) is a heat transfer weakening structure, and the heat preservation coating (17) is located on the outer wall surface or the inner wall surface of the inner circular flow channel (19).

[0012] In a preferred embodiment of the present invention, the double coaxial circular tube realizes the transformation of the working medium flow channel through a one-way valve, so as to achieve the purpose of directional heat transfer regulation; the working medium is helium, the radial cross sections of the outer tube (11) and the inner tube (12) are both circular, and the axis of the outer tube (11) is collinear with the axis of the inner tube (12), and the outer annular flow channel (18) or the inner circular flow channel (19) in which the working medium is located in different flow directions in the tube is different.

[0013] In a preferred embodiment of the present invention, the pitch of the spiral fin (15) is 20 mm, its fin height is 0.6 mm, and it is arranged in the outer annular flow channel (18).

[0014] In a preferred embodiment of the present invention, the pitch of the spiral fin (15) is 40 mm, its fin height is 0.6 mm, and it is arranged in the outer annular flow channel (18).

[0015] An embodiment of the present invention provides a method for improving the performance of a Stirling engine, including the following steps:

[0016] By means of a double coaxial circular tube, heat transfer in different directions is regulated through the transformation of the working fluid flow path. When the flow direction is from compression to expansion, the working fluid of the cooler (8) is transported through the inner circular flow path (19). At this time, the existence of the outer annular flow path (18) will increase the heat transfer resistance between the working fluid and the cold source (7), weakening the heat transfer process, reducing the temperature drop of the working fluid, while the working fluid of the heater (4) is transported through the outer annular flow path (18), and its heat transfer area with the heat source (5) is significantly increased compared with a single circular tube, strengthening the heat transfer, and increasing the temperature rise of the working fluid. Both of the above methods increase the temperature of the working fluid at the inlet of the expansion chamber (2), enhancing its work capacity. Conversely, when the flow direction is from expansion to compression, the working fluid of the heater (4) is transported through the inner circular flow path (19), weakening the heat transfer process, while the working fluid of the cooler (8) is transported through the outer annular flow path (18), strengthening the heat transfer process, thereby reducing the temperature of the working fluid entering the compression chamber and enhancing its work capacity.

[0017] A preferred embodiment of the present invention specifically includes: the working fluid is helium, the outer tube (11) of the double coaxial circular tube has a diameter of 8 mm, the inner tube (12) has a diameter of 5.4 mm, the lengths of the outer tube (11) and the inner tube (12) are both 300 mm, and the wall thicknesses are the same, both 0.25 mm; the inlet temperature of the working fluid in the outer annular flow path (18) of the double coaxial circular tube is 575 K, and the inlet temperature of the working fluid in the inner circular flow path (19) of the double coaxial circular tube is the average temperature at the outer ring outlet; the heating wall temperature is 1000 K. When the maximum Reynolds number is 4180, compared with a smooth tube with the same flow area, in the forward process stage, the temperature rise at the inlet and outlet of the working fluid in the double coaxial circular tube is increased by 69.1 K; in the return process stage, the temperature rise at the inlet and outlet of the working fluid is reduced by 79 K.

[0018] A preferred embodiment of the present invention specifically includes: the working fluid is helium, and spiral fins (15) are added to the outer annular flow path (18) of the double coaxial circular tube, wherein one side of the spiral fins (15) is closely attached to the inner wall surface of the outer tube (11). Among them, the outer tube (11) of the double coaxial circular tube has a diameter of 8 mm, the inner tube (12) has a diameter of 5.4 mm, the lengths of the outer tube (11) and the inner tube (12) are both 300 mm, and the wall thicknesses are the same, both 0.25 mm. The pitch of the spiral fins (15) is 40 mm, and the fin height is 0.6 mm; the inlet temperature of the working fluid in the outer ring is 575 K, the inlet temperature of the working fluid in the inner circular flow path (19) is the average temperature at the outer ring outlet, the heating wall temperature is 1000 K. When the maximum Reynolds number is 4180, compared with a smooth tube with the same flow area, in the forward process stage, the temperature rise at the inlet and outlet of the working fluid in the double coaxial circular tube with built-in spiral fins is increased by 84.1 K. Compared with the double coaxial circular tube without spiral fins added, the temperature rise at the inlet and outlet of the working fluid can be increased by 15 K more; in the return process stage, the temperature rise at the inlet and outlet of the working fluid in the double coaxial circular tube with built-in spiral fins is reduced by 81.2 K compared with a smooth tube with the same flow area.

[0019] A preferred embodiment of the present invention specifically includes: helium is used as the working fluid. The outer tube (11) of the double coaxial circular tube has a diameter of 8 mm, and the inner tube (12) has a diameter of 5.4 mm. The lengths of both the outer tube (11) and the inner tube (12) are 300 mm, and the wall thicknesses of both are the same, which is 0.25 mm. Among them, the pitch of the spiral fin is 20 mm, and the fin height is 0.6 mm. The inlet temperature of the working fluid at the outer ring is 575 K, the inlet temperature of the inner flow channel is the average temperature at the outer ring outlet, and the heating wall temperature is 1000 K. When the maximum Reynolds number is 4180, compared with the smooth tube with the same flow area, in the process stage, the temperature rise at the inlet and outlet of the working fluid in the double coaxial circular tube with internal spiral fins is increased by 95.9 K. Compared with the double coaxial circular tube without spiral fins, the temperature rise at the inlet and outlet of the working fluid can be increased by 26.8 K more. In the return stage, the temperature rise at the inlet and outlet of the working fluid in the double coaxial circular tube with internal spiral fins is reduced by 68.5 K compared with the smooth tube with the same flow area.

[0020] Compared with the prior art, the embodiment of the present invention provides a device and method for improving the performance of a Stirling engine, having the following beneficial effects:

[0021] (1) The present invention discloses a method for regulating the oscillating flow and reciprocating bidirectional heat transfer of a Stirling engine. Inspired by the intermittent start and stop working processes of the heat / cold sources in the ideal thermodynamic cycle of the Stirling engine, the present invention innovatively proposes a heat transfer regulation method based on the difference in heat transfer requirements in the "forward" and "return" flow directions of the heater and the cooler, that is, the heater strengthens heat transfer in the flow direction to be heated and weakens heat transfer in the flow direction to be cooled; the cooler strengthens heat transfer in the flow direction to be cooled and weakens heat transfer in the flow direction to be heated.

[0022] (2) The present invention discloses a method for realizing the regulation of reciprocating bidirectional heat transfer by a double coaxial circular tube device. The research objectives of heat transfer regulation are usually divided into enhancing heat transfer or weakening heat transfer. The former is committed to improving the heat transfer effect, and the latter is to enhance the heat insulation performance as much as possible. The present invention proposes a solution for realizing the opposite heat transfer regulation effects in different flow directions through the idea of the inner and outer flow channels of the double coaxial circular tube, so as to enhance the work done by the working fluid entering the expansion chamber and the compression chamber, thereby realizing the improvement of the performance of the Stirling engine under certain external heat and cold sources.

[0023] (3) The present invention further enhances its heat transfer regulation performance by further strengthening and weakening the design of the inner and outer flow channels of the double coaxial circular tube. Further strengthening designs include but are not limited to surface treatment, using special-shaped tubes, and inserting objects inside the tube, etc.; further weakening designs include but are not limited to using heat insulation materials, heat insulation coatings, etc. Brief Description of the Drawings

[0024] To more clearly illustrate the technical solutions in the embodiments or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0025] Figure 1 This is a schematic diagram of the working medium main flow direction of the Stirling engine provided by the embodiment of the present application being from compression to expansion, and a schematic diagram of working with only the heat source and the cold source closed under ideal conditions.

[0026] Figure 2 This is a schematic diagram of the working medium main flow direction of the Stirling engine provided by the embodiment of the present application being from expansion to compression, and a schematic diagram of working with only the cold source and the heat source closed under ideal conditions.

[0027] Figure 3 This is a schematic diagram of the flow of the working medium in different flow channels of the double coaxial circular tubes of the heater and the cooler when the Stirling engine is in the compression-to-expansion flow direction provided by the embodiment of the present application.

[0028] Figure 4 This is a schematic diagram of the flow of the working medium in different flow channels of the double coaxial circular tubes of the heater and the cooler when the Stirling engine is in the expansion-to-compression flow direction provided by the embodiment of the present application.

[0029] Figure 5 This is a schematic diagram of the inner wall of the outer ring pipe of the double coaxial circular tubes of a single Stirling engine provided by the embodiment of the present application having an inwardly concave rough surface structure.

[0030] Figure 6 This is a schematic diagram of the inner wall of the outer ring of the double coaxial circular tubes of a single Stirling engine provided by the embodiment of the present application having a spherical convex rough surface structure.

[0031] Figure 7 This is a schematic diagram of the double coaxial circular tube structure of a single Stirling engine provided by the embodiment of the present application with spiral fins arranged in the outer annular flow channel.

[0032] Figure 8 This is a schematic diagram of the double coaxial circular tube structure of a single Stirling engine provided by the embodiment of the present application with straight fins arranged in the outer annular flow channel.

[0033] Figure 9 This is a schematic diagram of the double coaxial tube of a single Stirling engine provided by the embodiment of the present application, where the outer tube is a three-headed spiral corrugated special-shaped tube.

[0034] Figure 10 This is a schematic diagram of the heat transfer weakening structure of the inner circular flow channel pipe wall of the double coaxial circular tubes of a single Stirling engine provided by the embodiment of the present application using a thermal insulation coating.

[0035] Figure 11 Schematic diagram of the single - cylinder Stirling engine's double - coaxial triangular tube structure provided by the embodiment of the present application.

[0036] Figure 12 Schematic diagram of the single - cylinder Stirling engine's double - coaxial rectangular tube structure provided by the embodiment of the present application.

[0037] Figure 13 Schematic diagram of the single - cylinder Stirling engine's double - coaxial hexagonal tube structure provided by the embodiment of the present application.

[0038] Figure 14 Schematic diagram of the single - cylinder Stirling engine's straight - tube double - coaxial circular tube structure provided by the embodiment of the present application.

[0039] Figure 15 Schematic diagram of the single - cylinder Stirling engine's U - shaped double - coaxial circular tube structure provided by the embodiment of the present application.

[0040] Figure 16 Schematic diagram of the straight - row structure of the tube cluster composed of multiple double - coaxial circular tubes provided by the embodiment of the present application.

[0041] Figure 17 Schematic diagram of the circumferential circular - ring arrangement structure of the tube cluster composed of multiple double - coaxial circular tubes provided by the embodiment of the present application.

[0042] Reference numerals in the drawings: 1. Driving wheel; 2. Expansion chamber; 3. Connecting pipe; 4. Heater; 5. Heat source; 6. Regenerator; 7. Cold source; 8. Cooler; 9. Compression chamber; 10. Piston; 11. Outer tube; 12. Inner tube; 13. Grooved rough surface; 14. Spherical - protrusion rough surface; 15. Spiral fin; 16. Straight fin; 17. Thermal insulation coating; 18. Outer annular flow channel; 19. Inner circular flow channel. Detailed implementation manners

[0043] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application. When referring to the "upper", "lower", "front", "rear", "left", "right", etc. used for the installation position or direction of the structure or components in this embodiment, they are based on the orientation of the given drawings. They are only for the convenience of expression to distinguish the relative positions of the components or directions, and do not represent the orientation when the calibration device or components in this embodiment are in use.

[0044] Figure 1 - Figure 2It is a schematic diagram of the main flow direction of the working fluid of a Stirling engine, including the compression → expansion main flow direction and the expansion → compression main flow direction, and also shows the start and stop conditions of the heat source and the cold source under ideal conditions. Figure 3 - Figure 4 It is a schematic diagram of the double coaxial circular tube flow channel design and the working fluid flow direction of the Stirling engine of the present invention. Figure 5 - Figure 9 It is a schematic diagram of the enhanced heat transfer device for the outer annular flow channel in the double coaxial circular tubes of the Stirling engine of the present invention. Figure 10 It is a schematic diagram of the weakened heat transfer device for the inner circular flow channel in the double coaxial circular tubes of the Stirling engine of the present invention. Figure 11 - Figure 13 It is a schematic diagram of the tube shapes of different radial cross-sections of the double coaxial tubes of the Stirling engine of the present invention. Figure 14 - Figure 15 It is a schematic diagram of the tube shapes of different axial cross-sections of the double coaxial circular tubes of the Stirling engine of the present invention. Figure 16 - Figure 17 It is a schematic diagram of different tube cluster arrangement methods of the double coaxial circular tubes of the Stirling engine of the present invention. Explanation: Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 have the same purpose, which is to increase the heat transfer enhancement ability of the outer annular flow channel. But different methods are used, which are divided into three major categories: rough surfaces ( Figure 5 , Figure 6 ), inserts ( Figure 7 , Figure 8 ), and special-shaped tubes ( Figure 9 ). Figure 10 The purpose is to weaken the heat transfer ability of the inner circular flow channel, and the method used is the thermal insulation coating.

[0045] Such as Figure 1 - Figure 17As shown in the figure, an implementation device for improving the performance of a Stirling engine provided by an embodiment of the present invention includes a driving wheel 1, an expansion chamber 2, a connecting pipe 3, a heater 4, a heat source 5, a regenerator 6, a cold source 7, a cooler 8, a compression chamber 9, and a piston 10. The driving wheel 1 is connected to the expansion chamber 2 and the compression chamber 9 respectively through 2 pistons 10. The expansion chamber 2 is connected to the heater 4 through a connecting pipe. A heat source 5 is arranged outside the heater 4. The heater 4 is connected to the regenerator 6. The regenerator 6 is connected to the cooler 8. A cold source 7 is arranged outside the cooler 8. The cooler 8 is connected to the compression chamber 9 through a connecting pipe. Both the heater 4 and the cooler 8 are provided with double coaxial circular tubes. The structure of the Stirling engine in this embodiment is not limited and can be of the α type, β type, or γ type. The number of cylinders of the Stirling engine is not limited and can be single-cylinder, double-cylinder, or multi-cylinder. The type of the heater is not limited and can be a tube bundle heater, a finned heater, or other forms of heaters. The type of the cooler is not limited and can be a tube bundle cooler, a finned cooler, or other forms of coolers. The arrangement mode of the tube bundle of the tube bundle heat exchanger is not limited and can be that multiple identical U-shaped tubes are circumferentially arranged in a circular ring shape, or other shapes and other arrangements. The type of the external heat source is not limited and can be renewable energy such as solar energy and biomass energy, or traditional heat sources such as fossil fuels. The type of the external cold source is not limited and can be cooling water, or cooling air, etc. The type of the working medium in the tube is not limited and can be helium, hydrogen, air, nitrogen, etc.

[0046] For the outer flow channel of the double coaxial circular tube, if only relying on the circular ring structure to increase the heat transfer area, the degree of strengthening the heat transfer effect is limited. The present invention proposes that the heat transfer performance can be further improved by using rough surfaces, inserted turbulators, etc. The type, structure, and size of the strengthening elements are selected according to the heat transfer regulation requirements. For the inner flow channel of the double coaxial circular tube, if only relying on the outer circular ring to increase the thermal resistance, the degree of weakening the heat transfer is limited. The present invention proposes to improve the heat transfer weakening performance by adding a thermal insulation coating on the inner circular tube wall surface, and the material, thickness, and position of the thermal insulation coating need to be adjusted according to the regulation requirements.

[0047] Specifically, as Figures 5 to 10 , the double coaxial circular tube includes an outer tube 11, an inner tube 12, and an outer annular flow channel 18 is formed between the outer wall surface of the inner tube 12 and the inner wall surface of the outer tube 11. The inner wall of the inner tube encloses an inner circular flow channel 19. The outer annular flow channel 18 can be further provided with a groove rough surface 13, or a spherical protrusion rough surface 14, or a spiral fin 15, or a straight fin 16, etc. of the heat transfer strengthening structure, which disturb the flow of the working medium in the outer annular flow channel and enhance the heat transfer process. The inner circular flow channel can be further provided with a heat transfer weakening structure such as a thermal insulation coating 17, such as arranging the thermal insulation coating 17 on the outer wall surface or the inner wall surface of the inner circular flow channel.

[0048] Specifically, one edge of the spiral fin 15 or the straight fin 16 is arranged on the inner wall surface of the outer tube 11. By using the flow disturbing effect of the spiral fin or the straight fin, the disturbance of the working medium in the outer annular flow channel 18 is enhanced, the heat transfer is strengthened, its heat exchange effect is improved, and the heat exchange efficiency is increased.

[0049] The double coaxial circular tubes achieve the transformation of the working medium flow channel through a one-way valve, so as to achieve the purpose of directional heat transfer regulation. Inside the Stirling engine, when the working medium flows from the compression chamber to the expansion chamber, the cold-end working medium is transported through the inner circular flow channel 19, while the hot-end working medium is transported through the outer annular flow channel 18. Conversely, when the working medium flows from the expansion chamber to the compression chamber, the hot-end working medium is transported through the inner circular flow channel 19, while the cold-end working medium is transported through the outer annular flow channel 18.

[0050] The working medium is helium. The radial cross-sections of the outer tube 11 and the inner tube 12 are both circular, and the axis of the outer tube 11 is collinear with the axis of the inner tube 12. The flow of the working medium in different reciprocating directions is arranged in different flow channels, and the heat transfer regulation effects of opposite reciprocating different processes are completed.

[0051] In a specific example, the working medium is helium. The radial cross-sections of the outer tube 11 and the inner tube 12 are both circular. The pitch of the spiral fin 15 is 20 mm, and the fin height is 0.6 mm. It is arranged in the outer annular flow channel 18, where one side of the spiral fin 15 is closely attached to the inner wall surface of the outer tube 11. See Figure 7 and the axis of the outer tube 11 is collinear with the axis of the inner tube 12. The flow of the working medium in different directions inside the tube is arranged in two different flow channels (the outer annular flow channel 18 and the inner circular flow channel 19).

[0052] In another specific example, the working medium is helium. The radial cross-sections of the outer tube 11 and the inner tube 12 are both circular. The pitch of the spiral fin 15 is 40 mm, and the fin height is 0.6 mm. It is arranged in the outer annular flow channel 18, where one side of the spiral fin 15 is closely attached to the inner wall surface of the outer tube 11. See Figure 7 and the axis of the outer tube 11 is collinear with the axis of the inner tube 12. The flow distribution of the working medium in different directions inside the tube is arranged in two different flow channels (the outer annular flow channel 18 and the inner circular flow channel 19).

[0053] The outer annular flow channel 18 and the inner circular flow channel 19 of the double coaxial circular tubes are arranged coaxially and have the same tube length. Then, several similar double coaxial circular tubes are used to form a heater tube cluster and a cooler tube cluster, which serve as the heater and cooler of the Stirling engine. The purpose of directional heat transfer regulation is achieved through the transformation of the working medium flow channel: during the compression → expansion flow direction, the working medium of the cooling tube is transported through the inner circular flow channel to weaken the heat transfer process, while the working medium of the heater is transported through the outer annular flow channel to strengthen the heat transfer process; conversely, during the expansion → compression flow direction, the working medium of the heater is transported through the inner circular flow channel to weaken the heat transfer process, while the working medium of the cooler is transported through the outer annular flow channel to strengthen the heat transfer process.

[0054] The shape of the double coaxial circular tube is not limited. From the perspective of the radial cross-sectional shape, it can be a double coaxial triangular tube, a double coaxial rectangular tube, a double coaxial elliptical tube or other shaped tubes. From the perspective of the axial cross-sectional shape, it can be a straight tube, a U-shaped tube or other shaped tubes. The structural dimensions of the double coaxial circular tube are not limited, and the cross-sectional areas of the inner circular tube and the outer ring tube are not limited. It is preferred that the areas of the two are equal.

[0055] Furthermore, the means to improve the heat transfer effect of the outer annular flow channel of the double coaxial circular tube include but are not limited to: rough surfaces, special-shaped tubes, and flow disturbance elements inserted into the tube. The type of rough surface is not limited, including but not limited to grooved surfaces, raised surfaces, fins, ribbed surfaces, etc. The type of special-shaped tube is not limited, including but not limited to elliptical tubes, triangular tubes, rectangular tubes, spiral corrugated tubes, etc. The type of insert in the tube is not limited, including but not limited to twisted tapes, coils, various vortex generators, etc. The means to further weaken the heat transfer effect of the inner circular flow channel include but are not limited to: using thermal insulation materials and thermal insulation coatings.

[0056] According to the difference in heat transfer requirements of the oscillating flow in the "forward" and "reverse" flow directions, a method for directional regulation of its heat transfer performance: for the heater, during the compression → expansion flow direction, strengthen its heat transfer process to improve the work ability of the working fluid entering the expansion chamber, while during the expansion → compression flow direction, do not enhance the heat transfer as much as possible or even weaken the heat transfer process to reduce the cooling burden on the working fluid by the regenerator and cooler; for the cooler, during the expansion → compression flow direction, strengthen its heat transfer process to enhance the work performance of the working fluid in the compression chamber, while during the compression → expansion flow direction, do not enhance the heat transfer as much as possible or even weaken the heat transfer to reduce the heating burden on the working fluid by the regenerator and heater. In short, heat transfer enhancement should be carried out during the stage when the heat source and the cold source should be turned on, and heat transfer weakening should be carried out during the stage when they should be turned off, while the traditional heat transfer regulation method can only achieve one of heat transfer enhancement or weakening.

[0057] An embodiment of the present invention provides a method for improving the performance of a Stirling engine, which is realized by an apparatus for improving the performance of a Stirling engine as described in the above embodiment, and includes the following steps: By using a double coaxial circular tube and changing the working fluid flow path, the heat transfer in different directions is regulated. When the flow direction is from compression to expansion, the working fluid of the cooler 8 is transported through the inner circular flow path 19. At this time, the existence of the outer annular flow path 18 will increase the heat transfer resistance between the working fluid and the cold source 7, weakening the heat transfer process, reducing the temperature drop of the working fluid, while the working fluid of the heater 4 is transported through the outer annular flow path 18, and its heat transfer area with the heat source 5 is significantly increased compared with a single circular tube, strengthening the heat transfer, and increasing the temperature rise amplitude of the working fluid. Both of the above methods improve the temperature of the working fluid at the inlet of the expansion chamber 2, enhancing its work capacity; conversely, when the flow direction is from expansion to compression, the working fluid of the heater 4 is transported through the inner circular flow path 19, weakening the heat transfer process, while the working fluid of the cooler 8 is transported through the outer annular flow path 18, strengthening the heat transfer process, thereby reducing the temperature of the working fluid entering the compression chamber and enhancing its work capacity. Refer to Figure 3 and Figure 4 。

[0058] Example 1

[0059] Taking the double coaxial circular tube heater of a Stirling engine as an example for research, the working fluid is helium. When the working fluid is in the process flow direction from compression to expansion, it flows in the outer annular flow path 18 to enhance heat transfer; conversely, when the working fluid is in the return flow direction from expansion to compression, it flows in the inner circular flow path 19 to weaken heat transfer. Among them, the outer tube 11 of the double coaxial circular tube has a diameter of 8 mm, the inner tube 12 has a diameter of 5.4 mm, the lengths of the outer tube 11 and the inner tube 12 are both 300 mm, and the wall thicknesses are the same, both 0.25 mm; the inlet temperature of the working fluid in the outer annular flow path 18 of the double coaxial circular tube is 575 K, and the inlet temperature of the working fluid in the inner circular flow path 19 of the double coaxial circular tube is the average temperature at the outlet of the outer ring; the heating wall temperature is 1000 K. It can be obtained from the research that when the maximum Reynolds number is 4180, compared with a smooth tube with the same flow area, in the process stage, the temperature rise at the inlet and outlet of the working fluid in the double coaxial circular tube is increased by 69.1 K; in the return stage, the temperature rise at the inlet and outlet of the working fluid is reduced by 79 K. It can be found that using a double coaxial circular tube instead of a smooth tube significantly increases the temperature of the working fluid entering the expansion chamber, enhancing the work capacity of the working fluid entering the expansion chamber, and at the same time reducing the temperature of the working fluid entering the regenerator, reducing the cooling burden on the working fluid by the regenerator and the cooler.

[0060] Example 2

[0061] Taking the Stirling engine double coaxial circular tube heater as the research object, and adding spiral fins to its outer annular flow channel, where one side of the spiral fins is closely attached to the inner wall surface of the outer tube, and helium is used as the working fluid. When the working fluid is in the process flow direction of pressure → expansion, it flows in the outer annular flow channel with spiral fins 15 added to enhance heat transfer; on the contrary, when the working fluid is in the return flow direction of expansion → pressure, it flows in the inner circular flow channel 19 to weaken heat transfer; among them, the diameter of the outer tube 11 of the double coaxial circular tube is 8 mm, the diameter of the inner tube 12 is 5.4 mm, the lengths of the outer tube 11 and the inner tube 12 are both 300 mm, and the wall thicknesses are the same, both 0.25 mm. Among them, the pitch of the spiral fins 15 is 40 mm, and the fin height is 0.6 mm; the inlet temperature of the working fluid in the outer ring is 575 K, the inlet temperature of the inner circular flow channel 19 is the average temperature at the outlet of the outer ring, and the heating wall temperature is 1000 K. The research shows that when the maximum Reynolds number is 4180, compared with the smooth tube with the same flow area, in the process stage, the temperature rise at the inlet and outlet of the working fluid in the double coaxial circular tube with built-in spiral fins is increased by 84.1 K. Compared with the double coaxial circular tube without spiral fins added, the temperature rise at the inlet and outlet of the working fluid can be increased by 15 K more. In the return stage, the temperature rise at the inlet and outlet of the working fluid in the double coaxial circular tube with built-in spiral fins is reduced by 81.2 K compared with the smooth tube with the same flow area. It can be found that after arranging the spiral fins in the outer annular flow channel, the temperature of the working fluid entering the expansion chamber can be further increased, and the work capacity of the working fluid entering the expansion chamber is improved.

[0062] Example 3

[0063] Taking the Stirling engine with a double coaxial circular tube and an internal spiral fin heater as an example for research, helium is used as the working fluid. When the working fluid is in the process flow direction of compression → expansion, it flows in the outer annular flow path with the spiral fin 15 added, enhancing heat transfer; on the contrary, when the working fluid is in the return flow direction of expansion → compression, it flows in the inner circular flow path 19, weakening heat transfer. In the third embodiment, the outer tube 11 of the double coaxial circular tube has a diameter of 8 mm, the inner tube 12 has a diameter of 5.4 mm, the lengths of the outer tube 11 and the inner tube 12 are both 300 mm, and the wall thicknesses of both are the same, which is 0.25 mm. Among them, the pitch of the spiral fin is 20 mm, and the fin height is 0.6 mm. The inlet temperature of the working fluid at the outer ring is 575 K, the inlet temperature of the inner flow path is the average temperature at the outlet of the outer ring, and the heating wall temperature is 1000 K. The research shows that when the maximum Reynolds number is 4180, compared with the smooth tube with the same flow area, in the process stage, the temperature rise at the inlet and outlet of the working fluid in the double coaxial circular tube with internal spiral fins is increased by 95.9 K. Compared with the double coaxial circular tube without spiral fins added, the temperature rise at the inlet and outlet of the working fluid can be increased by 26.8 K more; in the return stage, the temperature rise at the inlet and outlet of the working fluid in the double coaxial circular tube with internal spiral fins is reduced by 68.5 K compared with the smooth tube with the same flow area. It can be found that using the double coaxial circular tube heater with internal spiral fins significantly increases the temperature of the working fluid entering the expansion chamber. When the fin pitch decreases, the effect of increasing the outlet temperature is more obvious, further enhancing the work capacity of the working fluid entering the expansion chamber.

[0064] Although the present invention has been disclosed above with the preferred embodiments, the above preferred embodiments are not intended to limit the present invention. Those of ordinary skill in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the scope defined by the claims.

Claims

1. A device for improving the performance of a Stirling engine, characterized in that: The invention comprises a driving wheel (1), an expansion chamber (2), a connecting pipe (3), a heater (4), a heat source (5), a heat regenerator (6), a cold source (7), a cooler (8), a compression chamber (9) and a piston (10); the driving wheel (1) is connected to the expansion chamber (2) and the compression chamber (9) respectively through two pistons (10); the expansion chamber (2) is connected to the heater (4) through a connecting pipe (3); a heat source (5) is arranged outside the heater (4); the heater (4) is connected to the heat regenerator (6); the heat regenerator (6) is connected to the cooler (8); a cold source (7) is arranged outside the cooler (8); the cooler (8) is connected to the compression chamber (9) through another connecting pipe (3); the heater (4) and the cooler (8) are both provided with double coaxial circular tubes.

2. A device for improving the performance of a Stirling engine according to claim 1, characterized in that: The double coaxial circular tubes comprise an outer tube (11), an inner tube (12), an outer annular flow channel (18) and an inner circular flow channel (19); an outer annular flow channel (18) is formed between the outer wall surface of the inner tube (12) and the inner wall surface of the outer tube (11), and an inner circular flow channel (19) is formed on the inner wall surface of the inner tube (12); The outer annular flow channel (18) is provided with a groove rough surface (13), a spherical protrusion rough surface (14), a spiral fin (15) or a straight fin (16), one edge of the spiral fin (15) is provided on the inner wall surface of the outer tube (11), or one side of the straight fin (16) is provided on the inner wall surface of the outer tube (11), and the turbulent effect of the spiral fin (15) or the straight fin (16) is utilized to enhance the disturbance of the working medium in the outer annular flow channel (18), strengthen its heat transfer effect, and increase the heat exchange efficiency; wherein, the inner circular flow channel (19) is further provided with a thermal insulation coating (17), and the thermal insulation coating (17) is a heat transfer weakening structure, and the thermal insulation coating (17) is located on the outer wall surface of the inner circular flow channel (19) or the inner wall surface of the inner circular flow channel (19).

3. A device for improving the performance of a Stirling engine according to claim 2, characterized in that: The double coaxial circular tubes realize the transformation of the working medium flow channel through a one-way valve, so as to achieve the purpose of directional heat transfer regulation; the working medium is helium, the radial cross-sections of the outer tube (11) and the inner tube (12) are both circular, and the axis of the outer tube (11) is colinear with the axis of the inner tube (12), and the outer annular flow channel (18) or the inner circular flow channel (19) where the working medium is located in different flow directions in the tube is different.

4. A device for improving the performance of a Stirling engine according to claim 3, characterized in that: The spiral fin (15) has a pitch of 20 mm and a fin height of 0.6 mm and is arranged in the outer annular flow channel (18).

5. The device for improving the performance of a Stirling engine according to claim 3, characterized in that: The spiral fin (15) has a pitch of 40 mm and a fin height of 0.6 mm and is arranged in the outer annular flow channel (18).

6. A method for improving the performance of a Stirling engine, characterized in that: The following steps are involved: By utilizing double coaxial circular tubes to transform the working fluid flow channel, directional heat transfer control is achieved: when the flow direction is from compression to expansion, the working fluid of the cooler (8) is transported through the inner circular flow channel (19). At this time, the existence of the outer annular flow channel (18) increases the heat exchange resistance between the working fluid and the cold source (7), weakens the heat transfer process, and reduces the temperature reduction of the working fluid. The working fluid of the heater (4) is transported through the outer annular flow channel (18). The heat exchange area between the working fluid and the heat source (5) is significantly increased compared with a single circular tube, the heat transfer is enhanced, and the temperature rise of the working fluid is increased. Both of the above methods increase the temperature of the working fluid at the inlet of the expansion chamber (2), thereby enhancing its working capacity. On the contrary, when the flow direction is from expansion to pressure, the working fluid of the heater (4) is transported through the inner circular flow channel (19), and the heat transfer process is weakened. The working fluid of the cooler (8) is transported through the outer annular flow channel (18), thereby enhancing the heat transfer process, thereby reducing the temperature of the working fluid entering the compression chamber and enhancing its working capacity.

7. A method for improving the performance of a Stirling engine according to claim 6, characterized in that: Specifically include: The working fluid is helium, the outer tube (11) of the double coaxial circular tube has a diameter of 8 mm, the inner tube (12) has a diameter of 5.4 mm, the outer tube (11) and the inner tube (12) are both 300 mm long, and the tube wall thickness is the same, both 0.25 mm; the working fluid inlet temperature of the outer annular flow channel (18) of the double coaxial circular tube is 575 K, and the working fluid inlet temperature of the inner circular flow channel (19) of the double coaxial circular tube is the average temperature at the outer annular outlet; the heating wall temperature is 1000 K, and when the maximum Reynolds number is 4180, compared with a light tube with the same flow area, in the process stage, the working fluid inlet and outlet temperature rise of the double coaxial circular tube is increased by 69.1 K; in the return stage, the working fluid inlet and outlet temperature rise is reduced by 79 K.

8. A method for improving the performance of a Stirling engine according to claim 6, characterized in that: Specifically include: The working medium is helium, and a spiral fin (15) is added to the outer annular flow channel (18) of the double coaxial circular tube, wherein one side of the spiral fin (15) is closely attached to the inner wall surface of the outer tube (11), the outer tube (11) of the double coaxial circular tube has a diameter of 8 mm, the inner tube (12) has a diameter of 5.4 mm, the outer tube (11) and the inner tube (12) are both 300 mm long, and the tube wall thickness is the same as 0.25 mm, wherein the spiral fin (15) has a pitch of 40 mm and a fin height of 0.6 mm; the working medium at the outer ring inlet temperature is 5 75K, the inlet temperature of the inner circular flow channel (19) is the average temperature at the outlet of the outer ring, the heated wall temperature is 1000K, and when the maximum Reynolds number is 4180, compared with the bare tube with the same flow area, in the process stage, the temperature rise of the working fluid inlet and outlet of the double coaxial circular tube with built-in spiral fins is increased by 84.1K, and compared with the double coaxial circular tube without adding spiral fins, the temperature rise of the working fluid inlet and outlet can be increased by 15K; in the return stage, the temperature rise of the working fluid inlet and outlet of the double coaxial circular tube with built-in spiral fins is reduced by 81.2K compared with the bare tube with the same flow area.

9. A method for improving the performance of a Stirling engine according to claim 6, characterized in that: Specifically include: The working fluid is helium, the outer tube (11) of the double coaxial circular tube has a diameter of 8 mm, the inner tube (12) has a diameter of 5.4 mm, the outer tube (11) and the inner tube (12) are both 300 mm long, the tube wall thickness is the same, both 0.25 mm, wherein the spiral fin pitch is 20 mm, and the fin height is 0.6 mm; the working fluid temperature at the outer ring inlet is 575 K, the inner flow channel inlet temperature is the average temperature at the outer ring outlet, the heating wall temperature is 1000 K, and when the maximum Reynolds number is 4180, compared with a bare tube with the same flow area, in the process stage, the working fluid inlet and outlet temperature rise of the double coaxial circular tube with built-in spiral fins is increased by 95.9 K, and compared with the double coaxial circular tube without adding spiral fins, the working fluid inlet and outlet temperature rise can be increased by 26.8 K; in the return stage, the working fluid inlet and outlet temperature rise of the double coaxial circular tube with built-in spiral fins is reduced by 68.5 K compared with the bare tube with the same flow area.

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