WO2023048667A1

WO2023048667A1 - Heat transfer system for stirling engines

Info

Publication number: WO2023048667A1
Application number: PCT/TR2021/051275
Authority: WO
Inventors: Nevzat ÇİFTÇİ
Original assignee: Ciftci Nevzat
Priority date: 2021-09-27
Filing date: 2021-11-23
Publication date: 2023-03-30
Also published as: TR2021015056A2

Abstract

The present invention relates to a transfer system of Stirling engines or stirling heat pumps that heats and cools the air before it enters the cylinder, and to its cooling or heating units. There is a two-way air path for inlet and outlet of the air between the cylinders as two-way system in the inventive heat transfer system. The air goes to the hot cylinder and heats the path, the air goes to the cold cylinder cools the path. The invention is particularly a two-way heat transfer system, it relates to allowing the use of large volumes of heating and cooling devices in a remote location from the Stirling engine. Thus, Stirling engines are suitable for the use of sources such as solar energy. It is possible to use devices such as Stirling pumps or engine radiators away from the engine by means of the inventive heat transfer system. And it becomes suitable for use in heating and cooling systems.

Description

HEAT TRANSFER SYSTEM FOR STIRLING ENGINES

Field of the Invention

The present invention particularly relates to the formation of cooling or heating units as a heat transfer system in Stirling engines or Stirling heat pumps.

The inventive heat transfer system relates to the separation of the air from one cylinder to the other by heating the same into two paths, and again from one cylinder to the other by cooling the same.

The present invention relates to pipes, valves, regenerators and heat transfer devices that transmit air by cooling the same from the hot cylinder to the other and heating the same from the cold cylinder to the other in the two-way heat transfer system.

State of the Art

Stirling engines are generally a hot-cold two-cylinder engine group that operates as the air moves from cylinder to cylinder and is heated and cooled.

Stirling engines are engines that are not used commercially, although they have high thermodynamic efficiency and operate with all kinds of fuels. The most important reason for this is the difficulty in transferring the heat to the gases inside the engine and the low heat transfer efficiency. The inventive heat transfer system transfers the external heat to the engine air quickly and efficiently.

The heat exchange of the air circulating in the engine is provided from the cylinder surface in existing Stirling engines. Large surface elements such as radiators or heat exchangers located at the cylinder inlet transfer heat in the inventive heat transfer system. The heat transfer rates of said elements are higher than the cylinders and the heating time is earlier. And their internal volume can be quite small. Furthermore, it does not affect the heating or cooling of the air since the outlet ways of the air coming out of the cylinders of said elements are different. Operation of existing Stirling engines

The Stirling cycle consists of two isothermal state changes and two isochoric state changes. The Stirling cycle can be carried out, for example, using a machine with two pistons and a regenerator. (https://de.wikipedia.org/wiki/Stirling-Kreisprozess)

Two volume changes and two temperature changes occur in the state of the gases in the Stirling cycle. These state changes can usually be accomplished with two pistons and a regenerator, or with a piston, a displacer and a regenerator. The regenerator is a device with heat storage property that provides air passage between the hot cylinder and the cold cylinder. Said regenerator stores the heat of the hot air passing through it and gives it back by heating the cold air while the cold air is passing. Thus, the engines reuse the waste heat.

There are 3 commonly known types of Stirling engines. Alpha, beta and gamma. Their operating principles and thermodynamic cycles are the same.

An alpha Stirling engine has two cylinders, one hot and the other cold, and two pistons and a regenerator. The pistons of the alpha Stirling engine are connected to the crankshaft such that they move at an angle of around 90 degrees. The alpha Stirling cylinders in the figures are at right angles to each other and the piston rods are connected to the crankshaft at the same point so that the pistons move at a 90 degree angle. The smaller the angle of the pistons, the higher the compression ratio.

Beta Stirling engine has a single cylinder, a piston, a displacer and a generator. The hot cylinder is the hot zone of the cylinder and the cold cylinder is the cold zone of the cylinder in the beta Stirling engine. Displacer is the device that displaces the air between the hot and cold zones of the cylinder. The beta type has a piston that moves at an angle of around 90 degrees and a displacer. The displacer displaces the air in the hot zone and the cold zone in the cylinder. In some models, the air passes through the interval between the displacer and the cylinder, the surface between the displacer and the cylinder becomes the regenerator. Gamma Stirling engine is the engine that operates with the same principle as beta Stirling. However, there is a separate cylinder for air exchange.

State changes of Stirling engine gases occur in 4 times. These are as follows:

1 ) Compression time: The air is cooled in the cold cylinder and the pressure is reduced, the piston or pistons compress the air.

2) Heating time: The pistons push the cold cylinder air through the regenerator into the hot cylinder. The displacer pushes the air in beta Stirling engine.

3) Expansion time: The heated air in the hot cylinder expands and pushes the piston or pistons.

4) During the cooling time; the pistons push the hot cylinder air through the regenerator into the cold cylinder. The displacer pushes the air from the hot region of the cylinder to the cold region in a beta Stirling engine.

The air movements of the inventive heat transfer system takes place during heating and cooling times.

Heat transfer of the Stirling motors:

The cylinder surfaces are heated and cooled in the existing Stirling engines. The engine air is heated and cooled by the cylinder surfaces. Heat transfer time is short. The larger the cylinder, the smaller the surface-volume ration and the lower the heat transfer. It is also harmful for excessively hot cylinders and heat escape increases. Heat-transferring gases such as helium or hydrogen are used and the cylinder surface is enlarged so as to transfer heat quickly. Another problem is that heating and cooling are inseparable from the cylinders.

Stirling engines are devices that have a heat pump when powered by an external power. There is no change in the way it operates. The hot cylinder will still be hot, but it will be in the function of giving heat. The cold cylinder will still be cold, but it will be in the function where it takes heat from the environment. Aims of the Invention

The aim of the invention is to increase the efficiency of Stirling engines and Stirling heat pumps.

Another aim of the invention is to make a Stirling engine suitable for use as a heat pump system that can be used for both heating and cooling.

Another aim of the invention is to develop a heat transfer system that gives heat to the environment by means of the heating device in which the crankshaft can be rotated from the outside by an engine or power, and takes heat from the environment by means of the cooling device.

Another aim of the invention is to provide a flexibility and efficiency which allows the Stirling engines to operate as an engine when heat sources such as solar energy is highly available and as a heat pump at other time while for example generating electricity.

Another aim of the invention is to develop a heat transfer systems that enables the transfer of external heat to the engine air quickly and efficiently so as to make various heat sources and heat transfer devices to be used in Stirling engines.

In summary, the inventive Stirling heat transfer system has been developed so as to solve the following problems.

1 - Energy loss

2- Heat transfer difficulty

3- Heat transfer inefficiency

4- Additional structures for heat transfer

5- Excessive cylinder temperature

6- Heat escape from the hot cylinder surface.

7- dependency on light gases such as hydrogen, helium

8- Cylinder volume limitation

9- Low compression rate

10- Excessive coolant consumption 11 - Worthless waste heat.

Brief Description of Drawings

Figure 1 : A) is a cross-sectional view of the inventive heat transfer device during the heating time on alpha Stirling engine.

Figure 1 : B) is a cross-sectional view of the inventive heat transfer device during the cooling time on alpha Stirling engine.

Figure 2: A) is a cross-sectional view of the inventive heat transfer device during the heating time on alpha Stirling engine using Tesla valve.

Figure 2: B) is a cross-sectional view of the inventive heat transfer device during the cooling time on alpha Stirling engine using Tesla valve.

Figure 3: A) is a cross-sectional view of the inventive heat transfer device during the heating time on beta Stirling engine.

Figure 3: B) is a cross-sectional view of the inventive heat transfer device during the cooling time on beta Stirling engine.

Figure 4: A) is a cross-sectional view of the inventive heat transfer device during the heating time on beta Stirling engine using Tesla valve.

Figure 4: B) is a cross-sectional view of the inventive heat transfer device during the cooling time on beta Stirling engine using Tesla valve

Figure 5: A) is a cross-sectional view of a different version of the inventive heat transfer device during the heating time on alpha Stirling engine.

Figure 5: B) is a cross-sectional view of a different version of the inventive heat transfer device during the cooling time on alpha Stirling engine.

Figure 6: A) is a cross-sectional view of a different version of the inventive heat transfer device during the heating time on alpha Stirling engine. Figure 6: B) is a cross-sectional view of a different version of the inventive heat transfer device during the cooling time on alpha Stirling engine.

Figure 7: A) is a cross-sectional view of a different version of the inventive heat transfer device during the heating time on beta Stirling engine.

Figure 7: A) is a cross-sectional view of a different version of the inventive heat transfer device during the cooling time on beta Stirling engine.

Reference Numbers:

01 . Heat transfer system

02. Alpha Stirling engine

03. Beta Stirling engine

10. Regenerator

14. Check valve

15. Tesla valve

17. Piston

18. Displacer

18a. Free displacer

19. Crankshaft

21 . Hot cylinder (hot side of cylinder in beta Stirling and gamma Stirling engines)

22. Hot pipe

23. Heating device

25. Heating device valve

31 . Cold cylinder (cold side of cylinder in beta Stirling and gamma Stirling engines)

32. Cold pipe

33. Cooling device

35. Cooling device valve

Double square bracket arrows indicate the direction of the check valves

Hollow arrows indicate inter-cylinder air flow.

Line arrows show heater or coolant movement. Detailed Description of the Invention

The figures show the operation of the inventive heat transfer device and the movements of Stirling engines during heating and cooling times.

There is usually only one airway between the cylinders of the Stirling engine with the regenerator (10). The heat transfer system (01 ) transforms the air path between the cylinders (21 , 31 ) with additional devices into two inlet and outlet paths. One of these devices is the heating device (23) and it transfers air from the regenerator (10) to the hot cylinder (21 ), the other one is the cooling device (33) and transfers air from the regenerator to the cold cylinder (31 ).

The inlet and outlet of the air are provided in two separate ways, in the simplest way, by means of check valves (14). Tesla valves (15) or various valves can be used instead of check valves. The directions of the check valves are in the direction of providing the above-mentioned air flow.

Thus, the cold pipe (32) that transfers air from the cold cylinder (31 ) to the regenerator (10) and the hot pipe (22) that transfers air from the hot cylinder (21 ) to the regenerator (10) are parts of the intermediate pipe of the classical Stirling engine and are unidirectional with the check valves (14).

The way the air transmitted from the hot cylinder (21 ) to the cold cylinder (31 ) consists of the hot pipe (22), the regenerator (10) and the cooling device (33) respectively. In this way, the flow direction of the check valves (14) is towards the cold cylinder (31 ). The air passes this way by being cooled down.

The way the air transmitted from the cold cylinder (31 ) to the hot cylinder (21 ) consists of the cold pipe (32), regenerator (10) and the heating device (23) respectively. In this way, the flow direction of the check valves (14) is towards the hot cylinder (21 ). The air passes this way by being heating.

The common area through which the air passes is the regenerator (10). Said regenerator (10) can be made as a heat exchanger in some models, and the hot air and cold air paths can be made completely separate. Examples of this are shown in Figure 5, Figure 6, and Figure 7. Stirling engines can be made without a regenerator, but they have not been considered as economical. In this case, there are only the heating device (23) and the cooling device (33) between the two cylinders.

In some of the figures, there is also a heating device valve (25) and a cooling device valve (35) but in the open passive state. Its operation is shown in Figure 7.

Figure 1 : A) The inventive heat transfer device (01 ) is on the alpha Stirling engine (02) and is at the heating time. The air flow takes place respectively through the cold cylinder (31 ), the cold pipe (32), the regenerator (10), the heating device (23) and the hot cylinder (21 ). In Figure 1 B), the inventive heat transfer device (01 ) shown in Figure 1 A, is in its cooling time. The air flow takes place respectively through the hot cylinder (21 ), the hpt pipe (32), the regenerator (10), the cooling device (33) and the cold cylinder (31 ). In the figure, there is the heating device valve (25) and the cooling device valve (35), but both valves (25, 35) are in the open position.

Figure 2: It is an alpha Stirling engine (02) using Tesla valves (15) and the air flow is the same as shown in figure 1 .

Figure 3: The inventive heat transfer system (01 ) is on the beta Stirling engine (03). The structure and operation of the inventive heat transfer system (01 ) is the same as described in alpha Stirling engine (02) in figure 1 .

Figure 4: It is a beta Stirling engine (03) using Tesla valves (15) and the air flow is the same as shown in figure 3.

Figure 5: The regenerator (10) is in the form of a heat exchanger. The air flow paths are completely separated. Since the airway does not intersect, the number of check valves (14) has been decreased. The heating device valve (25) and the cooling device valve (35) are positioned and their operation is not shown. Other properties an operation mode is shown in Figure 1 .

Figure 6: It is an alpha Stirling engine (02) as in Figure 5, and Tesla valves (15) are used instead of check valves (14), heating device valve (25) and cooling device valve (35). Figure 7: The inventive heat transfer system (01 ) is shown on the beta Stirling engine (03). However, in said system, the displacer is not connected to the crank (19) and is replaced by the air movements in the cylinder. The regenerator (10) is in the form of a heat exchanger. The air flow paths are completely separated. Since the airway does not intersect, the number of check valves (14) has been decreased. The heating device valve (25) and the cooling device valve (35) are positioned and their operation is not shown. In Figure 7A, the piston (17) has completed its compression and the heating device valve (25) has opened and remains open for more than 90 degrees. And the gases released from the heating device 23 push the free displacer (18a) and the piston (17). In Figure 7B, the cooling device valve (35) has opened after the piston (17) has expanded. First the gases on the hot side are sucked and then the check valve (14) is opened and the air enters the cold cylinder (31 ) by means of the vacuum created in the cooling device (33). Thus, the air in said cold cylinder (31 ) is compressed.

Although not shown on the figures, pumps placed on the inventive heat transfer system (01 ) in beta Stirling engine (03) and gamma Stirling engines can function as the displacer (18). Although the cold and hot air zone are separate in said cylinder, there is no displacer between them. Or, when the heating device valve (25) is turned to the open position, it functions like a pump towards the cold cylinder (31 ) with the pressure effect created by the heating device (23), discharging the hot air from the heating device and vacuuming the cold air from the cold cylinder (31 ) therein. In case the amount of air taken in and discharged out during this process is adjusted, the displacer (18) function is provided. Similarly, if the cooling device valve (35) is activated, the opposite process will be realized. The hot cylinder (21) will suck its air, that is, the hot air, and will be pumped to the cold cylinder (31 ), that is, to the cold side of the cylinder, with the air flow rate. This process can partially or completely replace the displacer function in the beta Stirling engine (03). Or, a displacer, which is not connected to the crankshaft (19) and moves with air pressure, can be placed between them. The structure and operation of the inventive heat transfer system (01)

The subject of the invention is the heat transfer system (01 ) for Stirling engines (02, 03). There are two systems that perform heating and cooling. The system that heats the air transmits the air in the cold cylinder (31 ) to the hot cylinder (21 ) by heating the same. The system that cools the air is transmitted by cooling the air in the hot cylinder (21 ) to the cold cylinder (31 ). There are check valves (14) that determine the flow path in these systems.

In the system that heats the air, the air in the cold cylinder (31 ) passes through the cold pipe (32), the regenerator (10), and the heating device (23) during the heating time, and enters the hot cylinder (21 ) as heated. The check valves (14) in this path are directed to the hot cylinder. Thus, the heating of the air takes place before the hot cylinder (21 ). In addition, heating can be performed with a check valve (14) at the inlet of the device (23) and a heating device valve (25) at the outlet. The necessity of making the heating device 21 with two valves is to keep it open during the heating time and closed at other times.

In the system that cools the air, the air in the hot cylinder (21 ) passes through the hot pipe (22), the regenerator (10), and the cooling device (33) during the cooling time and enters the cold cylinder (31 ) as it cools. The check valves (14) in this path are directed to the cold cylinder (31 ). Thus, cooling takes place before the cold cylinder (31 ). Furthermore, the cooling device (33) can be produced with a check valve (14) at its outlet and a cooling device valve (35) at its inlet. The two valves (14, 25) are for keeping the cooling device (33) on during the cooling time and off at the other times.

The heating device valve (25) is more necessary if the internal volume of the heater (23) is large and far from the engine. The heating device valve (25) and the check valve (14) together convert the heating device (23) into a closed environment. A mechanical, electronic or hydraulic mechanism connected to the crankshaft (19) may open the heating device valve (25) during the heating time and keep it closed at other times. Or a mechanism that keeps it on when the air pressure of the hot cylinder (21 ) is higher than the pressure of the cold cylinder (31 ), and off at other times may control the heating device valve (25).

The cooling device valve (35) is more necessary if the internal volume of the cooling device (33) is large and far from the engine. It makes the cooling device (33) closed with the check valve (14). A mechanical, electronic or hydraulic mechanism connected to the crankshaft (19) may open the cooling device valve (25) during the cooling time and keep it closed at other times. Or a mechanism that keeps it on when the air pressure of the hot cylinder (21 ) is lower than the pressure of the cold cylinder (31 ), and off at other times may control the heating device valve (35).

The inventive heat transfer system (01 ), Stirling engine (02, 03) can be used as a heat pump. In this case, the crankshaft is rotated by means of an external engine or power. In this case, the heating device (23) gives heat to the environment, while the cooling device (33) receives heat from the environment.

Thus a Stirling engine (02, 03) can operate as an engine when heat sources such as solar energy are highly available and as a heat pump at other times while generating electricity. It can be used for heating and cooling. If the electric generator is designed to convert to an electric engine when necessary, the same device is both an engine and a heat pump without requiring an additional device. Such a Stirling engine can operate as an engine when heat sources such as solar energy is plentiful while at other times, it can operate as a heat pump and can be used for heating and cooling.

Advantages of the inventive heat transfer system:

Stirling engines (02, 03) are engines that are not used commercially, although they have high thermodynamic efficiency and operate with all kinds of fuels. The most important reason for this is the difficulty in transferring the heat to the gases inside the engine and the low heat transfer efficiency. The inventive heat transfer system transfers the external heat to the engine air quickly and efficiently.

The heat exchange of the air circulating in the engine is provided from the cylinder surface in the existing Stirling engines (02, 03). In the inventive heat transfer system (01 ), large-surface instruments such as radiators or heat exchangers located at the entrance of the cylinders (21 , 31 ) transfer heat. Their heat transfer rates are higher than the cylinders (02.03) and the heating time is earlier. And their internal volume can be quite small.

Models with heating device valve (25) and cooling device valve (35) and radiator or heat exchanger used as heating device (23) or cooling device (33) can be located far from the system and operate with atmospheric air. The fluid that releases heat comes out at a temperature close to the inlet temperature of the fluid that receives heat in radiators or heat exchangers. Thus most of the heat is used. However, the heating fluid has to leave the hot cylinder at a higher temperature in the traditional Stirling engine.

Furthermore, they transfer heat in the best manner with their large surfaces, which can be tens of times higher than the cylinder.

Contributions of the inventive heat transfer system

Radiators or heat exchangers have large surfaces and most of the heat is received because there is heat exchange.

The main advantage of the invention is that it effectively heats and cools the air without entering the cylinders.

The cylinders are cooler and can be cooled.

Remote and large volume heating device or cooling device can be made by means of the control check valves.

As a heat pump, the air of the cylinders is used as a direct cooling device or heating fluid. Thus, the radiators that heat and cool the Stirling engine can be placed away from the engine.

Claims

CLAIMS A heat transfer system (01 ) that can be used in Stirling engines (02, 03) or Stirling heat pumps containing hot cylinders (21 ), cold cylinders (31 ) and pistons (17) moving therein; characterized in that; it comprises the following process steps;

- A cold pipe (32) that provides unidirectional air flow from the cold cylinder (31 ) to the regenerator (10) of the Stirling engine,

- A heating device (23) that heats the air that comes out of the cold cylinder (31 ) and passes through the regenerator (10) and transfers the same to the hot cylinder (21 ),

- A hot pipe (22) that provides unidirectional air flow from the hot cylinder (21 ) to the regenerator (10) of the Stirling engine,

- A cooling device (33) that heats the air that comes out of the hot cylinder (21 ) and passes through the regenerator (10) and transfers the same to the cold cylinder (31 ). A heat transfer system (01 ) according to claim 1 , characterized by providing the air flows according to claim 1 ; comprising; a check valve (14) oriented towards the hot cylinder (21 ) in the way of the heating device (23), a check valve (14) oriented towards the regenerator (10) between the hot cylinder (21 ) and the regenerator (10), a check valve oriented towards the cold cylinder (31 ) in the way of the cooling device (33), a check valve (14) for the regenerator (10) between the cold cylinder (31 ) and the regenerator (10). A heat transfer system (01 ) according to claim 1 and claim 2, characterized in that; it can use alternative valves such as Tesla valve or solenoid valve (14), or system controlled valves (14) on the cold pipe (32) and the heating device (23), which are opened at the heating time and closed at other times, valves (14) on the hot pipe (22) and the cooling device (23) that are opened during cooling time and closed at other times instead of the check valves (14) mentioned in Claim 2. A heat transfer system (01 ) that can be used in Stirling engines (02, 03) or Stirling heat pumps containing hot cylinders (21 ), cold cylinders (31 ) and pistons (17) moving therein; characterized in that; it comprises the following process steps;

- A heating device (23) that heats the air that comes out of the cold cylinder (31) and heats the air passing through the regenerator and transfer the same to the hot cylinder (21 ) at the heating time of the Stirling engine (02, 03),

- A cooling device (33) which provides the cooling of the air passing through the regenerator (10) from the hot cylinder (31 ) during the cooling time of the Stirling engine and transferring it to the cold cylinder (21 ) and closed at other times. A heat transfer system (01 ) according to claim 4, characterized by providing air flows according to claim 1 , comprising; a check valve (10) oriented towards the regenerator (10) between the hot cylinder (21 ) and the regenerator (10), a check valve (14) for the regenerator (10) between the cold cylinder (31 ) and the regenerator (10). A heat transfer system (01 ) according to claim 4, characterized in that; it comprises a valve (14) at its inlet or a check valve (14) whose direction is towards the hot cylinder (21 ), and a heating device valve (25) at its outlet such that the heating device (23) is closed and open. A heat transfer system (01 ) according to claim 4, characterized in that; it comprises a valve at the outlet or a check valve (14) whose direction is towards the cold cylinder (31 ) such that the cooling device (33) is closed and open, and a cooling device valve (25) at the inlet. 15 A heat transfer system (01 ) according to any of the preceding claims, characterized in that; it comprises a free displacer (18a) which is not connected to the crankshaft (19) and operates with air flows in the cylinder if it operates on a beta Stirling engine (03). A heat transfer system (01 ) according to claim 8, characterized in that; the air movement in the amount to push said free displacer (18a) is realized by opening and closing the heating device valve (25) and the cooling device valve (35) or by means of the pumps to be attached on the inventive heat transfer system (01 ).