EP0880640A1

EP0880640A1 - Cyclic-operation heat engine

Info

Publication number: EP0880640A1
Application number: EP97905088A
Authority: EP
Inventors: Albert V. Serogodski; Bernhard Schaeffer
Original assignee: Dokowa Gesellschaft Zur Entwicklung Dezentralokologischer Energiewandler Mbh & Co KG
Current assignee: Dokowa Gesellschaft Zur Entwicklung Dezentralokologischer Energiewandler Mbh & Co KG
Priority date: 1996-02-26
Filing date: 1997-02-26
Publication date: 1998-12-02
Also published as: HUP9901286A2; WO1997032114A1; AU1877097A; NO983902D0; HUP9901286A3; NO983902L; DE19608300A1

Abstract

The cyclic-operation heat engine proposed has a closed space, which contains a working fluid, plus heat-exchange means by means of which heat is supplied to and extracted from the working fluid. The working fluid used is a multi-component mixture. The ratio of the components in the multi-component mixture, as well as the operating-pressure and operating-temperature range of the heat engine, are chosen such that, within a given pressure range, the temperature of the mixture decreases less, compared with the behaviour of a single-component working fluid, when the pressure decreases and increases less when the pressure increases, or remains approximately constant, or even decreases when the pressure increases and increases when the pressure decreases. The multi-component mixture may include nitrogen and butane, nitrogen and carbon dioxide or hydrogen and carbon dioxide.

Description

Cyclic heat engine

Technical field

The invention relates to a heat engine working with a cyclic process, comprising

(a) an enclosed space in which a working medium is enclosed,

(b) heat exchange means by means of which heat is supplied to and removed from the working medium.

Such heat engines convert heat energy into work. The efficiency of a heat engine is defined as the ratio of work done A to supplied heat energy Q _to

(1) η = A / Q _2U .

In an idealized cycle without losses, for example according to Carnot, it can be shown that (2) η = A / Q _zu = (Q _zu - Qab) / Qzu '

where Q _{ab is} the dissipated thermal energy.

Underlying state of the art

Such heat engines are generally known, for example, as so-called hot-air machines and are described in many thermodynamics textbooks, for example "Thermodynamics" by E. Schmidt, 9th edition, Springer-Verlag 1962, pp. 132-138. Two piston machines (or turbo machines) are connected to one another via a line system with two heat exchangers. Air is the working medium in the piston machines, the pipe system and the heat exchangers. Depending on the structure of the hot air machine, the working medium can go through various processes. For example, the compression and expansion can be adiabatic (Joule process) or isothermal (Ericson process). In practice, however, such idealized processes can only be approximated.

Heat engines are disclosed in several different publications, by means of which the efficiency of the heat engine is to be improved:

DE 41 01 500 AI discloses a working with a cycle heat engine with a cylinder chamber which is limited by a piston. A quantity of an evaporable liquid is provided in the cylinder chamber as a working medium at an initial temperature. In a first phase of work, the volume of the Cylinder chamber from an inner dead center by moving the piston outwards to an outer dead center. At bottom dead center, the movement of the piston is stopped for a predetermined period of time. As a result, condensation of the supercooled vapor of the liquid is initiated. This leads to a sudden drop in pressure. In a second working phase, the piston is then moved to the inner dead center. The cooled condensate is heated to the initial temperature using a heat exchanger. In DE 41 01 500 AI, the working medium consists of only one component.

From DE 42 44 016 C2 a heat engine of the type mentioned is known, in which the working medium is a two-substance mixture of nitrogen and butane. The heat engine consists of a boiler kept at a temperature of 104.5 ° C. and a cylinder connected to the boiler and a heat exchanger arranged in the boiler, which cylinder is closed by a piston. The ratio of the concentrations of nitrogen and butane and the starting temperature (boiler temperature) are chosen so that the two-component mixture at the starting temperature is in the range of retrograde condensation and the starting temperature is between the critical temperatures of nitrogen and butane. The efficiency of a heat engine is to be improved by using such a two-substance mixture. This is achieved in that the expansion of the volume of the two-component mixture in the area of retrograde condensation takes place so rapidly that the formation of condensate is delayed. At the outer dead center of the piston, the system emerges from it unstable state into equilibrium. As a result of the special behavior of the two-substance mixture (kinking of the isobars at the phase boundary), this is associated with a drop in pressure. This increases the work done for a given heat supply and thus improves the efficiency of the heat engine.

The properties of multi-substance mixtures are described, for example, in a book by Stephan and Mayinger "Thermodynamics Fundamentals and Technical Applications", 11th edition, volume 2, Springer-Verlag, in particular pp. 59-67.

Disclosure of the invention

The invention has for its object to improve the efficiency of a heat engine of the type mentioned.

According to the invention this object is achieved in that

(c) the working medium is a multi-substance mixture and

(d) the mixing ratio of the multicomponent mixture, the working pressure range and the working temperature range of the heat engine is chosen such that, based on the behavior of a single-substance working medium, the temperature of the multicomponent mixture in a certain pressure range decreases less with decreasing pressure and rises less with increasing pressure. Such behavior of the working medium has a favorable effect on the efficiency. The amount of heat Q _ab to be dissipated then becomes smaller and thus the efficiency η greater (cf. Eq. (2)).

These ratios become even more favorable if the mixing ratio of the multicomponent mixture, the working pressure range and the working temperature range of the heat engine are chosen so that the temperature of the multicomponent mixture remains approximately constant when the pressure changes.

Even more favorable ratios for the efficiency are obtained if the mixing ratio of the multicomponent mixture, the working pressure range and the working temperature range of the heat engine are chosen so that the temperature of the multicomponent mixture drops with increasing pressure and increases with decreasing pressure.

Surprisingly, it has been shown that there are mixtures of substances with such behavior. Such behavior shows, for example, a multi-component mixture of nitrogen and butane in a mixing ratio of approximately 10% nitrogen and 90% butane. A multicomponent mixture of nitrogen and carbon dioxide in a mixing ratio of approximately 10% nitrogen and 90% carbon dioxide also exhibits this behavior, as does a multicomponent mixture of hydrogen and carbon dioxide in such a mixing ratio. It has also been shown experimentally that this behavior is promoted by adding water in small amounts.

An embodiment of the invention is explained below with reference to the accompanying drawings.

Brief description of the drawings

Fig.l is a schematic representation and shows a

Heat engine of the type here.

FIG. 2 shows in a p-V diagram the changes in the working medium during a cycle in a heat engine.

3 shows in a diagram measurements of the adiabatic exponents K for a mixture of nitrogen and carbon dioxide in various mixing ratios.

Preferred embodiment of the invention

The mode of operation of a heat engine is to be described with reference to FIG. 1. A first turbine is designated 10 and a second turbine 12. A shaft 14 extends through the two turbines 10 and 12. For example, a generator (not shown) for generating electricity can be connected to the shaft 14. The first turbine 10 is located on the so-called cold side and the second turbine 12 on the so-called warm side of the heat engine.

The two turbines 10 and 12 are connected to one another via a line system. A first line 16 connects the first turbine 10 to the cold side inlet of a first heat exchanger 18. The warm side outlet of the first heat exchanger 18 is connected via a line 20 to the cold side inlet of a second heat exchanger 22. The output of the warm side of the second heat exchanger 22 is connected to the second turbine 12 via a line 24. A line 26 connects the second turbine 12 to the input of the warm side of the first heat exchanger 18. The output of the cold side of the first heat exchanger 18 is connected via a line 20 to the input of the warm side of a third heat exchanger 30. The cold side output of the third heat exchanger 30 is connected to the first turbine 10 via a line 32. This system forms a closed system in which the working medium of the heat engine is enclosed. The working medium flows in the direction of the arrows in FIG. 1.

The warm side inlet and the cold side outlet of the second heat exchanger 22 are connected to a first boiler 38 via lines 34 and 36. The cold side inlet and the warm side outlet of the third heat exchanger 30 are connected via lines 40 and 42 to a second boiler 44. The first boiler 38 is kept at a temperature T ₂ . The second boiler 44 is kept at a temperature T ₄ , where T ₂ > T ₄ . The working medium is compressed in the first turbine 10 to the pressure p _λ . It then flows via line 16 into the first heat exchanger 18. Here, the working medium is heated from the temperature T _x to a temperature T _w . This takes place in the counterflow process by simultaneous cooling of the working medium coming from the second turbine 12. The working medium then flows further via line 20 into the second heat exchanger 22. Here the working medium is heated from the temperature T _w to the temperature T ₂ . This takes place in the countercurrent process by simultaneous cooling of the medium coming from the first boiler 38. The working medium is then expanded in the second turbine 12, as a result of which work is performed. The working medium leaves the second turbine 12 under the pressure p ₃ and at the temperature T ₃ . It flows via line 26 into the first heat exchanger 18 and is cooled here to a temperature T _k . The working medium then flows further via line 28 into the third heat exchanger 30. Here the working medium is cooled from the temperature T _k to the temperature T _t . This is done in a countercurrent process by simultaneous heating of the medium coming from the second boiler 44.

By the first heat exchanger 18, it is not possible to the working medium from the line 16 to the temperature T ₂ of

To heat working medium from line 26 or that

Cool the working medium from line 26 to the temperature Υ _{1 of} the working medium from line 16. So T ₂ > T _w > T _k > T ₁ always applies. Fig. 2 shows a pV diagram and swapped the changes in state of the working medium during a passage through the heat engine. The mode of operation of the described heat engine is to be explained on the basis of this state diagram:

The working medium leaves the first turbine 10 at a pressure p _x and at a temperature ^r T ₁ . This corresponds to point I in FIG. 2.

In a first working phase, the working medium is heated approximately isobarically (p ₁ = p ₂ ) from the temperature T _λ to a temperature T ₂ , the volume of the working medium increasing from a volume V _x to a volume V ₂ . The temperature of the working medium is increased from T _x to T _w in the first heat exchanger 18 and T _w to T ₂ in the second heat exchanger 22.

In a second working phase, the working medium is expanded approximately adiabatically from the pressure p ₂ to a pressure p ₃ and expanded from the volume V ₂ to a volume V ₃ , the temperature decreasing from the temperature T ₂ to the temperature T ₃ .

In a third working phase, the working medium is cooled approximately isobarically (p ₃ = p ₄ ) from the temperature T ₃ to the temperature T ₄ , the volume of the working medium decreasing from the volume V ₃ to a volume V ₄ .

In a fourth working phase, the working medium becomes approximately adiabatic from the pressure p ₄ to the pressure p _: and compressed from the volume V ₄ to the volume V _x , the temperature changing from the temperature T ₄ to the temperature T _x .

The p-V diagram forms a closed curve that encloses a surface and is traversed clockwise. The heat engine therefore does mechanical work on every cycle.

In the exemplary embodiment described, the first turbine 10 works as a compressor and the second turbine 12 as a machine. The turbine 10 is driven by the turbine 12 via the shaft 14. It should be mentioned that not only turbines can be used, but also piston machines, for example. It should also be mentioned that the heat engine described here works according to the so-called Joule process. However, the invention is not limited to heat engines that work according to this working diagram, but applies to all heat engines.

According to the invention, a multi-substance mixture is now used as the working medium. In various experiments it has been shown that mixtures of approximately 90% carbon dioxide and approximately 10% nitrogen and mixtures of approximately 90% butane and approximately 10% nitrogen show remarkable properties. These properties are further enhanced when small amounts of water are added to the mixtures. The following effects have been observed experimentally: When nitrogen is introduced into a closed container filled with (gaseous and liquid) colonic dioxide at a temperature of 0 ° C., the pressure in the container increases, as expected. Surprisingly, the temperature drops to approx. -10 ° C. The same effect occurs with hydrogen instead of nitrogen, even in an increased form. This effect can also be observed at starting temperatures up to + 20 ° C. The effect is no longer observed above + 20 ° C. The drop in temperature with increasing pressure is only observed with small quantities of nitrogen. If the nitrogen content exceeds approx. 20%, the effect also disappears. So if you use a working medium of approx. 90% carbon dioxide and approx. 10% nitrogen in a heat engine, and keep T _x at 0 ° C (see FIG. 2), then the working medium becomes only in the compression in the turbine 10 little warmed up.

A mixture of approx. 90% butane and approx. 10% nitrogen behaves differently. If such a mixture is expanded from a pressure of approx. 127 bar to a pressure of approx. 100 bar at an initial temperature of 94 ° C., the temperature of the mixture increases to approx. 127 ° C. If the pressure is increased again to 127 bar, the temperature drops again to the initial temperature. In the case of known substances and mixtures of substances, one can expect a reversed behavior.

Another property of these mixtures of substances has a favorable effect on the efficiency η of a heat engine. It can be shown that with an adiabatic change in the state of a gas, the course of the curve is given by the equation (3) pV ^κ = C,

is very well described, where C is a constant.

Measurements of the adiabatic exponent K for a mixture of carbon dioxide and nitrogen in various concentrations at a temperature of 0 ° C. have shown that K has very low values below 1. These measurements are shown in Fig. 3. The top right in FIG. 3 shows the different values for K at nitrogen concentrations from C = 0.1 to C = 1.0.

The value of K has an effect on the decay of the adiabatic curve from point II to point III in the state diagram in FIG. 2. The smaller K is, the flatter this curve section and the flatter this curve section, the larger it becomes area enclosed by the curve and therefore also the work of the heat engine performed in each cycle. As a working medium in a heat engine, this property also gives a higher degree of efficiency than with conventional substances or mixtures of substances.

Claims

claims

1. Comprising thermal engine, containing

(a) an enclosed space in which a working medium is enclosed,

(b) heat exchange means by means of which heat is supplied to and removed from the working medium,

characterized in that

(c) the working medium is a multi-substance mixture and

(d) the mixing ratio of the multicomponent mixture, the working pressure range and the working temperature range of the heat engine is chosen so that, based on the behavior of a single-substance working medium, the temperature of the multicomponent mixture drops less in a certain pressure range with decreasing pressure and with increasing pressure Less pressure increases.

2. Heat engine according to claim 1, characterized in that the mixing ratio of the multi-substance mixture, the working pressure range and the working Temperature range of the heat engine is chosen so that the temperature of the multi-substance mixture remains approximately constant with a change in pressure.

3. Heat engine according to claim 1, characterized gekenn¬ characterized in that the mixing ratio of the multi-substance mixture, the working pressure range and the working temperature range of the heat engine is chosen so that the temperature of the multi-substance mixture decreases with increasing pressure and increases with decreasing pressure.

4. Heat engine according to one of claims 1-3, characterized in that the multi-substance mixture contains nitrogen and butane.

5. Heat engine according to one of claims 1-3, characterized in that the multi-substance mixture contains nitrogen and carbon dioxide.

6. Heat engine according to one of claims 1-3, characterized in that the multi-substance mixture contains hydrogen and carbon dioxide.

7. Heat engine according to one of claims 1-6, characterized in that the multi-substance mixture contains water.