Apparatus and method for converting thermal energy

Abstract

An apparatus for converting thermal energy into mechanical energy by a cycle, having a heat exchanger, a reservoir for an operating medium, a feed line, a turbine, and a return line having at least one recovery device is described. In order to also be able to utilize waste heat for the generation of electrical energy, the turbine is embodied as a disc rotor turbine. A method for converting thermal energy into mechanical energy in a cycle is also described, in which thermal energy is supplied to an operating medium in a reservoir, the operating medium evaporates and/or a pressure in the operating medium is increased, whereupon the operating medium releases energy in a turbine, after which the operating medium is returned to the reservoir.

Claims

1. A method for converting thermal energy into mechanical energy in a cycle, using an apparatus including a heat exchanger, a reservoir for an operating medium, a feed line, a turbine embodied as a disc rotor turbine, and a return line having at least one recovery device, the method comprising: supplying thermal energy to the operating medium in the reservoir, wherein at least one of the operating medium evaporates or a pressure in the operating medium is increased, whereupon the operating medium releases energy in the disc rotor turbine, after which the operating medium is returned to the reservoir, and wherein a full condensation of the operating medium occurs in the disc rotor turbine, whereby a separate condenser can be eliminated.

2. The method according to claim 1, wherein CO.sub.2 is used as the operating medium.

3. The method according to claim 1, wherein the operating medium absorbs the thermal energy at a pressure of up to 73 bar and thereby evaporates.

4. The method according to claim 1, wherein the operating medium reaches a supercritical state at a pressure of more than 74 bar and the full condensation takes place in the turbine.

5. The method according to claim 4, wherein the operating medium reaches a supercritical state at a pressure of more than 100 bar.

6. The method according to claim 1, wherein pressure and temperature are measured in the return line and compared with a pressure and a temperature in the feed line, wherein a flow rate of the operating medium in the return line is regulated by a valve arranged in the return line.

7. The method according to claim 1, wherein the return of the operating medium from the disc rotor turbine to the reservoir takes place with a pressure increase in the operating medium by the recovery device with which a chronologically alternating force is applied to the operating medium.

8. The method according to claim 1, wherein the operating medium is set in oscillation by the recovery device.

9. The method according to claim 8, wherein the oscillation of the operating medium is generated by a resonant tube.

10. The method according to claim 8, wherein the oscillation of the operating medium is generated by a spring-loaded mass.

11. The method according to claim 10, wherein the mass is damped.

12. The method according to claim 8, wherein the operating medium one of comprises a magnetic fluid or is formed by a magnetic fluid, and the oscillation is generated by an alternating magnetic field.

13. The method according to claim 8, wherein the operating medium is set in resonance by the recovery device.

Description

(1) Additional features, advantages, and effects of the invention follow from the exemplary embodiments described below. In the drawings which are thereby referenced:

(2) FIG. 1 shows an apparatus according to the invention;

(3) FIG. 2 shows an apparatus according to the invention with a resonant tube system;

(4) FIG. 3 shows an apparatus according to the invention with a spring-loaded, undamped mass;

(5) FIG. 4 shows an apparatus according to the invention with a spring-loaded and damped mass;

(6) FIG. 5 shows an apparatus according to the invention with field coils inside a closed volume;

(7) FIG. 6 shows an apparatus according to the invention with field coils outside a dosed volume.

(8) FIG. 1 shows a diagram of an apparatus 1 according to the invention for carrying out a cycle according to the invention, wherein heat is converted into mechanical energy and further into electrical energy.

(9) The apparatus 1 is essentially composed of a turbine 2, a reservoir 3 for the operating medium, a heat exchanger 4, a feed line 5 between the reservoir 3 and turbine 2 in order to convey an operating medium from the reservoir 3 to the turbine 2, a return line 6 after the turbine 2 in order to convey the operating medium from a turbine outlet back to the reservoir 3, a valve 7 for regulating a flow.

(10) Furthermore, a pressure sensor 8 is provided with which the valve 7 can be controlled.

(11) In order to convey the operating medium from the turbine outlet to the reservoir 3, wherein a higher pressure prevails in the reservoir 3 than at the turbine outlet, a recovery device 9 is provided in the return line 6.

(12) CO.sub.2 is preferably used as an operating medium, since it has a low boiling point. The critical point is at 31? C. and 73.9 bar. For CO.sub.2, a phase transition between liquid and gaseous already occurs at a pressure of approximately 72 bar at a temperature of only 30? C., whereby a phase transition can be utilized for energy absorption and release even with a heat supplied at low temperatures. Thus, the operating medium in the reservoir can be present, for example, at a pressure of 72 bar, wherein waste heat is supplied thereto at a temperature of 40? C. by means of the heat exchange, wherein the operating medium evaporates, whereupon it is depressurized to a pressure of approximately 64 bar in the turbine, thereby cooling to an ambient temperature of 20? C., for example, and fully condensing, wherein work is outputted via the turbine.

(13) Alternatively, it can also be provided that the operating medium is present in the reservoir (3) at a pressure of more than 74 bar, for example at approximately 100 bar, and reaches a supercritical state through a supply of heat, from which state it fully condenses to a gaseous state and, simultaneously or subsequently, to a liquid state in the turbine (2).

(14) With corresponding pressure conditions in the apparatus (1), it can also be provided that an at least partial phase transition of the operating medium to a solid state takes place in the turbine at a temperature of 20? C., for example, so that dry ice particles form which are also unproblematic for the turbine (2) due to the use of a disc rotor turbine. As a result, heat accumulating at a low temperature of only 40? C., for example, can also be utilized to generate electricity.

(15) Of course, other operating media such as refrigerants can also be used, for example 8744 or R134a.

(16) The heat from a heat source 10 is supplied to the operating medium via a heat exchanger 4 arranged in the reservoir 3. Either primary energy or preferably waste heat, for example from an industrial process, with a temperature of approximately 40? C. can thereby be used. Heat sources with a lower temperature can also be used, however. It is thus especially beneficial that solar energy can also be utilized.

(17) A disc rotor turbine is used as a turbine 2. This is also known as a boundary-layer turbine 2 or Tesla turbine 2. This disc rotor turbine comprises multiple discs rotatably arranged next to one another on an axle, which are arranged in a casing with side walls, an inlet opening, and an outlet opening. A stream of the operating medium, up to now usually water, is conducted parallel to the discs onto said discs through the inflow opening. Due to an adhesion force, the discs are then set in motion about the axle. The stream is decelerated by a friction. The stream is redirected onto a circular path by the side walls and thereby continues to drive the discs. Since only the bearings of the axle need to have low tolerances and no highly resilient materials are required, the production costs are also low and a long service life can be expected. Because a higher viscosity arises due to the condensation of the operating medium in the turbine 2, the discs are also driven more powerfully as a result. In typical turbines 2 with blades, a condensation would severely damage said blades. The energy extraction then subsequently takes place by a pressure reduction in the operating medium in the turbine 2.

(18) To control the cycle, pressure and temperature are measured at the turbine outlet in the return line 6 and compared with the pressure and the temperature in the feed line 5. The cycle can thereupon be regulated via a valve 7 arranged in the return line 6 in order to regulate the flow rate. In this manner, a very good load regulation is possible with simultaneously low complexity.

(19) The operating medium is then supplied to a recovery device 9 after the valve 7, which device is embodied as a pump in this case.

(20) In the exemplary embodiments illustrated in FIG. 2 through FIG. 6, the recovery device 9 is embodied to set the operating medium in vibration in order to overcome a pressure difference between the turbine outlet and the reservoir 3.

(21) FIG. 2 shows an apparatus 1 according to the invention with a recovery device 9 embodied as a resonant tube 11. Here, a fluid column of the operating medium can vibrate back and forth in a volume 12 in a pipe-like form, and can thus be in self-resonance, for example, and, in combination with a valve, can therefore overcome the pressure difference between the return line 6 of the turbine 2 and the feed line 5 between the reservoir 3 for the operating medium and the turbine 2. A vibration excitation can, for example, occur by an electromagnetically driven membrane.

(22) In FIG. 3, a further variant of an apparatus 1 according to the invention is illustrated with a spring-loaded mass 13. Here, using this mass 13, which can be a membrane, for example also a piston, inside a closed volume 12, the vibrations are excited in the operating medium and the operating medium is brought into resonance in the volume, which causes the amplitude to proceed to rise accordingly. In the state of resonance, only a fraction of the excitation energy originally used is required, which leads to an improved efficiency and ensures a particularly efficient transport of the operating medium into the reservoir 3. Here, the closed volume 12 is illustrated as a cylinder in which the mass 13 can vibrate by means of a spring 14. The vibrations are thereby generated through the use of external energy, for example electromechanical energy.

(23) FIG. 4 shows an apparatus 1 similar to that illustrated in FIG. 3. Here, however, the mass 13 is hindered from excessive amplitudes, which could have negative effects in the system, by means of a damper 15. Nevertheless, a pressure difference between the return line 6 of the turbine 2 and the feed line 5 between the reservoir 3 for the operating medium and the turbine 2 can also be overcome easily in this case.

(24) A further possibility for generating an oscillation is illustrated in FIG. 5. Here, the oscillation is generated by means of a magnetic fluid which is set in vibration by field coils 16, wherein an alternating electromagnetic field can be generated with the field coils 16.

(25) To control the flow direction of the operating medium, an additional one-way valve 17 is provided in this case between the valve 7, which is only used here to regulate the flow rate, and the recovery device 9. Alternatively, the flow direction in the apparatus 1 can, of course, also be ensured by a correspondingly embodied valve 7, so that no additional one-way valve 17 is required.

(26) The one-way valve 17 can, similarly to the valve 7, of course also be provided after the recovery device 9, or between the recovery device 9 and the reservoir 3.

(27) In the variant according to FIG. 5, the field cods 16 are arranged inside a closed volume 12.

(28) A similar variant is illustrated in FIG. 6, although here, in contrast to FIG. 5, the field coils 16 are arranged outside the closed volume 12, for example a cylinder. Because the electromagnetic field generated using the field coils 16 can penetrate into the volume 12, a vibration excitement of the magnetic fluid is also possible here.

(29) With the apparatus 1 described above and the method according to the invention, previously unutilized waste heat can be converted into electrical energy under economically beneficial conditions. For example, industrial waste heat in the temperature range of approximately 40? C. to over 300? C., can thereby be used for conversion into electricity. Solar heat can also be utilized for additional electricity generation. Because the system is inherently closed, it can also be used beneficially and advantageously in remote regions without connection to other power supply lines.