DE102008050653B4 - Heat engine according to the pulse tube principle - Google Patents

Abstract

Heat engine according to the pulse tube principle with at least one expander (2), which comprises a cylinder and a piston or a membrane, and at least one fluidically coupled to the expander (2) thermal head, which consists of the fluidic series connection of a cooler (3 or 4) , a pulse tube (7 or 8), a heater (9 or 10) and a regenerator (11 or 12), characterized in that the regenerator (11 or 12) of the at least one thermal head fixed to the pulse tube (7 or 8) is connected.

Description

The invention relates to a fast-running heat engine with external heating, whose moving parts are located exclusively on the side of the lower temperature level. It is z. As used in combined heat and power plants, central power plants, industrial plants and motor vehicles and allows the use of heat fluxes at a temperature level of 150 to 2000 ° C. The life of the heat engine is thus as high as the usual life of power plants and heating systems.

For the generation of mechanical or electrical energy from heat flows, complex heat engines with internal heating are often used.

Also known are combined heat and power plants, in which the heat generated during operation is not used exclusively for heating, but also with the help of slow-running heat engines with external heating for the generation of electrical energy. The heat engines used are based on the Stirling or Ericssen principle, and although simpler, as heat engines with internal heating, still constructed comparatively complicated.

In addition, are out US 2003/0019218 A1 and US 5,435,136 A Pulse tube heat engines, which are used to drive gas chillers; In this case, parts of the cold part of the pulse tubes are functionally combined with parts of the drive. The use of pulse tubes makes it possible to produce heat engines with a more compact and simpler structure.

In DE 100 01 460 A1 discloses a pulse tube power amplifier consisting of a continuous mechanical compression device, a regenerator, gas heater, pulse tube, and gas cooler assembly, and a base realization of four valves sitting in the piping between the assemblies. The pulse tube power amplifier is provided as a drive device for other cycles.

Both solutions employ a pulse tube operating on the alpha-stirling principle, wherein instead of an active compressor, a passive resonant compressor is used, which is functionally arranged in front of the cooler and mechanically damped. Because of this, these pulse tube heat engines are applicable only to low power systems (50 W max.) And low power count requirement.

The main disadvantage of these pulse tube heat engines, however, is that they, like all other heat engines currently used, have at least two moving parts, between which a power transmission occurs. One of the moving parts (piston or regenerator) is exposed to temperatures close to the heat flow temperature (typically 600 to 1200 ° C) while the other moving part is on the cold side of the heat engine.

The transmission of force between the two moving parts is problematic since, on the one hand, large forces have to be transmitted to the relatively widely separated parts, which requires transmission elements (eg piston rods) with a large diameter, but, on the other hand, in order to keep the loss heat flows low, the heat flow between the two parts must be kept as small as possible.

On the high temperature side, sealing and lubrication also presents difficulties. Often, therefore, larger tolerances / gaps are allowed there, which, however, cause increased dead volumes, shuttle and outflow losses. On the other hand, precisely fitting seals for high temperatures, such. B. by liquid metals (lead) or solid lubricants (eg., Boron Nitride), only consuming and expensive materials.

The moving parts on the high temperature side are also subject to very high wear, which greatly reduces the life and durability of the heat engines.

The invention has for its object to eliminate the disadvantages of the prior art. In particular, a heat engine with external heating is to be created, whose moving parts are located exclusively on the side with the lower temperature level. The heat engine should be made compact and fast running. In addition, it should be reachable with her high lifetimes.

This object is achieved by the characterizing features of claim 1. Further advantageous embodiments and uses emerge from the claims 2 to 9.

It is based on a heat engine with external heating according to the pulse tube principle, which consists of at least one expander comprising a cylinder and a piston or a membrane, and at least one fluidically coupled to the expander thermal head, which consists of a series circuit of a radiator, a Pulse tube, a heater and a regenerator.

According to the invention, the regenerator is firmly connected to the pulse tube. As a result, the heat engine, in contrast to all other heat engines currently in use, be carried out without moving parts on the hot side. The only moving part of the heat engine, namely the piston or the membrane of the expander, is located in the cold area. The operation of the machine is made possible by generating a working integral by means of a temperature wave. The heat engine is fast running and works on the pressure chamber principle (analogous to Stirling engines), ie not thermoacoustically.

The functional process of the heat engine consists of the two working cycles of compression and expansion. During compression, the working fluid (typically working gas) is pushed out of the expander via the piston / membrane and into the regenerator via the radiator, pulse tube and heater. Expansion is the reverse process.

With the heat engine according to the invention, the problems described above, which occur in the guide, sealing and lubrication, are avoided. In addition, neither the usual high mechanical wear of the moving parts at high temperatures nor the loss of efficiency due to loss of heat flows caused by the mechanical coupling elements occur. With the heat engine therefore much longer lifetimes can be achieved compared to conventional machines. In addition, it is possible to build the heat engine very compact.

The piston or the membrane can also be made with relatively low mass; Thus, without much technical effort quickly running heat engines can be produced.

To increase the efficiency of the heat engine is provided that the regenerator of the at least one thermal head is not, as usual, maintained at a constant temperature level, but in the regenerator, a temperature gradient is set. For this purpose, a cooler is mounted on the side facing away from the heater of the regenerator, whereby a temperature reduction along the regenerator is effected. The temperature of the regenerator consequently decreases steadily with increasing distance from the heater. A falling in the direction of the regenerator along the heater temperature profile is proven to be advantageous for the efficiency of the heat engine.

The filler material of the regenerator consists of felt, mesh or open-pored metal foam. Depending on the working fluid and the working temperature stainless steel, copper or aluminum is used.

In a preferred embodiment, the piston (or the membrane) of the expander is mounted in the cylinder in free-swinging fashion and each of the two working spaces formed by the piston / membrane is fluidically coupled to the respective cooler side of a separate thermal head. Thus, using only one expander, the workload per cycle is doubled. Depending on the design of the expander, the machine can be designed either as a resonant or a non-resonant heat engine.

The two thermal heads are constructed identically and are operated in push-pull, d. H. if the compression takes place in one thermal head, the expansion takes place in the other.

A further increase in performance is achieved with an embodiment in which, in each case on the side facing away from the heater of the regenerators of the two thermal heads, a radiator, which can be flowed through by the working fluid, is mounted and both radiators are fluidly connected by means of a throttle. Since the two thermal heads are operated in push-pull, it is achieved that in each case the volume of one thermal head, the other thermal head is available as a gas ballast.

To increase the performance while maintaining the high-speed operation, several of such heat engines constructed from an expander with two thermal heads can be cascaded in the form of a multi-cylinder system. Also conceivable are systems in which a plurality of thermal heads are fluidically coupled to an expander or a plurality of expanders to a thermal head to increase the power.

In a preferred variant, the heat engine is used to drive an electric linear generator. As generators systems with moving magnet, moving coil, moving coil and magnetic core, piezoelectric or other generators can be used. It is also possible, the heat engine as a linear mechanical drive, for. B. for the operation of a pump to use.

It is also possible to use the heat engine as a rotary drive, wherein z. B. a Connecting rod or the eye of a crank loop is mounted centrally on the piston. However, occur due to tilting moments higher forces between the piston and cylinder wall, so it is necessary to operate the heat engine with higher center pressures. Although higher mid-pressures are in principle advantageous, since at higher mean pressures greater work integrals (higher powers) are achieved, with too high mean pressures, however, there is a risk that damage components of the heat engine.

The invention will be explained in more detail with reference to three embodiments; show:

1 : a heat engine with regenerators at a constant temperature level;

2 a heat engine with temperature reduction along the regenerators;

3 : a heat engine with temperature reduction along the regenerators and fluidic connection of the cold ends of the regenerators.

How out 1 As can be seen, the heat engine consists of regenerators 11 . 12 at a constant temperature level from an expander 2 , comprising a cantilevered cylinder and a piston, and two thermal heads, each consisting of the fluidic series circuit of the radiator 3 . 4 , the pulse tube 7 . 8th , the heater 9 . 10 and the regenerators 11 . 12 put together. The two identically constructed thermal heads are lined with the sides on which the radiator 3 . 4 each fluidically to one of the two by the piston and the cylinder of the expander 2 connected workrooms coupled.

The piston of the expander 2 carries the magnet system of the electrodynamic linear generator 1 ; the induction coil and the magnetic yoke are located in the stator of the generator 1 ,

The coolers 3 . 4 have about the ambient temperature while the heaters 9 . 10 are approximately at the temperature level of the heat flow used. Depending on the heat source (combined heat and power plant, central power plant, industrial plant or motor vehicle), the temperature of the heater is typically 600 to 2000 ° C. With modifications, however, temperatures as low as 150 ° C can already be used with the heat engine. The regenerators 11 . 12 are each thermally to the heater 9 . 10 coupled and are set by means of a cooling device to a constant temperature, which is below the heater temperature, but above the radiator temperature.

During compression, the working fluid (working gas) is compressed in one of the working spaces of the expander and in each case via the radiator 3 . 4 , the pulse tube 7 . 8th and the heater 9 . 10 in the regenerator 11 . 12 pushed the fluidically coupled to the working space thermal head. The working gas has when crossing the pulse tube 7 respectively. 8th in the heater 9 respectively. 10 a temperature that is above the heater temperature for most of the compression process, so over the wall of the heater 9 respectively. 10 only a little heat is given off to the working gas. In the regenerator 11 respectively. 12 the excess temperature of the working gas is delivered to its filling material, which consists of open-pore foam made of stainless steel. The compression is polytropic (generally sub-isothermal), as a result of which only a slight pressure builds up during compression.

At the beginning of expansion, the working gas first takes heat from the regenerator 11 respectively. 12 on. When the working gas flows back from the regenerator 11 respectively. 12 in the heater 9 respectively. 10 the temperature of the working gas is below that of the heater 9 respectively. 10 , In the heater 9 respectively. 10 The working gas takes heat from the walls of the heater 9 respectively. 10 and expands. Due to the expansion of the working gas increases, although at the same time the piston of the expander 2 runs back and thus the total volume of the system is increased, first the pressure of the working gas. As soon as the working gas is largely warmed up, it expands more slowly and the pressure drops.

Due to the asymmetry of the inlet conditions of the working gas in the heater with respect to the compression and expansion of an asymmetry of the working integral with respect. The two working cycles causes, ie the heat engine is under heat absorption from the heater 9 respectively. 10 Net work done.

When operating the heat engine with regenerators 11 . 12 occur at a constant temperature level, due to the sudden transition from the high temperature of the heater 9 . 10 to the lower temperature of the regenerators 11 . 12 , comparatively high heat losses on. The heat losses and thus the efficiency of the heat engine can be reduced by in the regenerators 11 . 12 a temperature gradient is set. This is done in each case at the heater 9 . 10 opposite side of the regenerators 11 . 12 the two thermal heads a regenerator cooler 5 . 6 appropriate ( 2 ), the temperature degradation along the regenerators 11 . 12 causes, ie the temperature in the regenerators 11 . 12 decrease with increasing distance from the heater. The coolers 5 . 6 are designed so that they can be flowed through by the working gas, but form closed spaces. They thus act as buffer spaces, which improve the heat transfer at the cold ends of the regenerators 11 . 12 Contribute by avoiding the stagnation of the working gas.

A further improvement in the efficiency of the heat engine can be achieved when the ends of the regenerator coolers 5 . 6 by means of a throttle line 14 are connected ( 3 ). Since the two thermal heads are operated in push-pull, it is achieved in each case that the volume of one thermal head is available to the other as a gas ballast.

LIST OF REFERENCE NUMBERS

1

generator

2

expander

3

Radiator of the first thermal head

4

Radiator of the second thermal head

5

Regenerator cooler of the first thermal head

6

Regenerator cooler of the second thermal head

7

Pulse tube of the first thermal head

8th

Pulse tube of the second thermal head

9

Heater of the first thermal head

10

Heater of the second thermal head

11

Regenerator of the first thermal head

12

Regenerator of the second thermal head

13

exhaust duct

14

choke line

Claims (9)

Heat engine according to the pulse tube principle with at least one expander ( 2 ), which comprises a cylinder and a piston or a membrane, and at least one fluidically to the expander ( 2 ) coupled thermal head, from the fluidic series connection of a cooler ( 3 respectively. 4 ), a pulse tube ( 7 respectively. 8th ), a heater ( 9 respectively. 10 ) and a regenerator ( 11 respectively. 12 ), characterized in that the regenerator ( 11 respectively. 12 ) of the at least one thermal head fixed to the pulse tube ( 7 respectively. 8th ) connected is. Heat engine according to claim 1, characterized in that on the heater ( 9 respectively. 10 ) side facing away from the regenerator ( 11 respectively. 12 ) a regenerator cooler ( 5 respectively. 6 ), the setting of a temperature gradient in the regenerator ( 11 respectively. 12 ) serves. Heat engine according to claim 1 and 2, characterized in that the regenerator ( 11 respectively. 12 ) includes open-pored metal foam. Heat engine according to claim 1 to 3, characterized in that the piston or the membrane of the expander ( 2 ) is mounted cantilever in the cylinder, wherein each of the two chambers formed by piston or diaphragm and cylinder is fluidically coupled to a separate thermal head. Heat engine according to claim 4, characterized in that the two thermal heads are constructed identically. Heat engine according to claim 5, characterized in that in each case at the heater ( 9 . 10 ) facing away from the regenerators ( 11 . 12 ) of the two thermal heads, a fluid-flowable by the regenerator cooler ( 5 . 6 ) is fluidically and thermally coupled and both regenerator coolers ( 5 . 6 ) by means of a throttle line ( 14 ) are fluidly connected. Heat engine according to claim 4 to 6, characterized in that it comprises a plurality of expander each having two fluidically coupled thermal head modules, wherein the pistons or membranes of the expander are mechanically coupled in the form of a multi-cylinder system. Use of the heat engine according to claim 1 as a drive of an electric linear generator. Use of the heat engine according to claim 1 as a linear motor.

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