WO2012112055A1

WO2012112055A1 - Bellows heat exchanger for a heating machine, heat pump, expander or compressor

Info

Publication number: WO2012112055A1
Application number: PCT/NO2012/050022
Authority: WO
Inventors: Harald Nes RISLÅ; Nikolas Aulin Paldan
Original assignee: Viking Heat Engines As
Priority date: 2011-02-14
Filing date: 2012-02-14
Publication date: 2012-08-23
Also published as: NO20110247A1

Abstract

A device for heat exchange in a heat engine, a heat pump, an expander or a compressor that utilizes a working fluid for energy conversion and a thermo fluid for heat transmission is described, the heat engine, the heat pump, the expander or the compressor having at least one working mechanism (1) including at least one variable-volume-chamber housing (100), and the variable-volume-chamber housing (100) forming at least one variable-volume chamber (150), the at least one working mechanism (1) including at least one displacement mechanism (200), and there being at least one internal heat exchanger (300) in thermal contact with at least one of the at least one variable-volume chamber (150), the heat exchang er (300) surrounding and/or being surrounded by the variable volume chamber (150) and being formed as a bellows.

Description

BELLOWS HEAT EXCHANGER FOR A HEAT ENGINE, HEAT PUMP, EXPANDER OR COMPRESSOR

A device for heat exchange in a heat engine, a heat pump, an expander or a compressor that uses a working fluid for energy conversion and a thermo fluid for heat transmission is described, the heat engine, heat pump, expander or compressor having at least one working mechanism including at least one variable-volume-chamber housing, and the variable-volume- chamber housing forming at least one variable-volume chamber, the at least one working mechanism including at least one displacement mechanism, and there being at least one internal heat exchanger in thermal contact with at least one of the at least one variable-volume chamber.

There are many heat-engine technologies that utilize heat supplied from an external heat source, so-called external- heat engines, as opposed to internal -combustion engines, in which heat is supplied in consequence of the internal combustion of a fuel. All heat engines utilize a working fluid, and in an external-heat engine, the heat is supplied to the working fluid through a heat exchanger. An example of an external-heat engine is the Stirling engine.

Precisely because all the heat that is converted in an external-heat engine is to be transferred by means of one or more heat exchangers, the design thereof is an important factor to achieve an efficient design. To achieve good heat exchange in a heat engine, it is important to achieve a high heat- transmission coefficient between the working fluid and the heat exchanger. Similarly, it is important to achieve a high heat-transmission coefficient between the heat transmission fluid, hereinafter called the thermo fluid, and the heat exchanger, so that the total heat-transmission coefficient between the thermo fluid and the working fluid will be high. The thermo fluid is the fluid that transports the heat between the heat engine and an external heat or cold reservoir and may, in the simplest case, be air, water or exhaust gas. As a rule, the heat exchanger will separate the two fluids from each other, as the heat exchanger generally forms a mechanical barrier between the two.

In the simplest case, a heat exchanger may be a metal plate which functions as an interface between two fluids that are each in contact with a respective side of the metal plate, s that heat may be transferred between them through the materi al of the metal plate. To achieve a high heat-transmission coefficient it is important, among other things, that the heat exchanger has a small thickness of material (thin walls in the interface between the two fluids. If not, the thermal resistance between the two fluids will be relatively large and the thermal conductivity of the heat exchanger correspondingly low.

In conventional external-heat engines based on the piston principle, it is common for the cylinder wall also to function as a heat exchanger. As a plain cylinder has only a lim ited surface, given by the length and diameter of the cylinder, it may be advantageous to make use of measures to increase this surface. A common measure is to make internal heat-exchanger fins on the cylinder wall, but this results i the dead volume, that is to say the volume which cannot be displaced by the piston, increasing. As unnecessary dead volume generally has a negative effect on the efficiency, there are limits to how much dead volume may be allowed. But in some cases, increasing the heat-exchanger surfaces at the cost of increased dead volume will still be worthwhile.

Modern technology enables great variation in how heat exchangers may be formed, and then in particular with a view to utilization in heat engines or heat pumps. An interesting, reasonable and easily available technical solution lies within the area of metal bellows which may be formed in many different ways. The advantage of metal bellows is that they exhibit great strength, while, at the same time, the thickness of material is minimal across the entire surface. In, for example, a cylinder that has the function of a heat exchanger, in which cooling ribs have been made to increase the surface, there will be a considerable thermal resistance between the outside and the inside of the cylinder, as the heat will have to be transported through the material of both the cylinder and the ribs before it may be transmitted to the medium on one side or the other.

A metal bellows has the advantage of enabling a design with a cylindrical outline, while, at the same time, the thickness of material will substantially be small over the entire active heat-exchanger area as it is only the pleating of the plate material that increases the surface and not the material itself, as in a cylinder with circumferential heat- exchanger ribs .

A metal bellows, and in particular a metal bellows in which the different pleats are circular, will also exhibit high mechanical strength in consequence of its design, which is very favourable in applications in which, at times, different fluids are under great pressure, like in a heat engine or a heat pump. US Patent 5,638,898 (Gu) shows this principle utilized in a shell-and-tube heat exchanger, in which the extent of corrugations of the tubes follows the axial direction, so that the surface is increased.

A radial metal bellows in a heat engine will also give some increased dead volume, but in contrast to a cylinder with added heat-exchanger ribs, the heat-transmission coefficient will be very hig across its entire surface, as the thickness of material is small and varies little. This gives a net positive effect, and even with a small cylinder diameter, if it is a case of a piston engine, there are, in principle, no limits to how large the heat-exchanger surfaces may be made.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art .

The object is achieved through features which are specified in the description below and in the claims that follow.

The invention relates to a device for heat exchange in a heat engine, a heat pump, an expander or a compressor that uses a working fluid for energy conversion and a thermo fluid for heat transmission, the heat engine, heat pump, expander or compressor having at least one working mechanism including at least one variable-volume-chamber housing, the variable- volume-chamber housing forming at least one variable-volume chamber, the at least one working mechanism including at least one displacement mechanism, and there being at least one internal heat exchanger in thermal contact with at least one of the at least one variable-volume chamber, characterized by the heat exchanger surrounding and/or being surrounded by the variable-volume chamber and being formed as a bellows . The heat exchanger may include first and second heat- exchanger surfaces that are thermally connected by a heat- exchanger wall having high thermal conductivity.

The first heat-exchanger surface may be in thermal contact with the variable-volume chamber.

The heat exchanger and a surrounding or surrounded heat- exchanger housing may form a fluid flow passage which is in fluid communication with a thermo fluid inlet and a thermo fluid outlet.

The second heat-exchanger surface may be in thermal contact with the fluid- flow passage.

The heat exchanger may substantially occupy an annular volume .

The heat exchanger may substantially have an equal thickness of material across the portion of the heat-exchanger wall that abuts the fluid flow passage.

There may be stiffening elements arranged in the pleats of the heat exchanger.

There may be braces arranged between the periphery of the bellows heat exchanger and surrounding elements.

The braces may be provided as raised parts formed as profile pressed out from the neutral axis of the heat-exchanger wall Alternatively, the braces may be formed as separate stiffening elements. Alternatively the braces may be provided as a combination of raised parts, formed as profiles pressed out from the neutral axis of the heat-exchanger wall, and separate stiffening elements.

The separate stiffening elements may be connected to the heat-exchanger walls by means of fastening means taken from the group consisting of adhesives, welding or soldering connections, screws and rivets.

The bellows heat exchanger may substantially be formed out of a metal or an alloy of metals.

The bellows heat exchanger may be formed of several heat- exchanger sections joined together by means of a fastening means .

The bellows-heat-exchanger sections may be joined together by welding .

The bellows heat exchanger may be formed by electrofabrica- tion .

The bellows heat exchanger may be formed out of one piece of material .

The bellows heat exchanger may be formed by fluid forming.

The thermo fluid may be included in a closed circuit.

The working mechanism may be arranged to let the working fluid alternate between the liquid and gas phases.

The working fluid may have a normal boiling point lower than 100 °C.

In what follows, an example of a preferred embodiment is described, which is visualized in the accompanying drawings, in which :

Figure 1 shows, in an axial section, a principle drawing of a working mechanism provided with a work housing that, together with a displacement mechanism (shown in a lower position here) , forms a variable-volume chamber surrounded by an annular bellows heat exchanger which constitutes part of the work housing

Figure 2 shows a view corresponding to that of figure 1 but with the displacement mechanism in an upper position;

Figure 3 shows, on a larger scale, an axial section of a first exemplary embodiment of a bellows heat exchanger formed out of one piece of material;

Figure 4 shows an axial section of a second exemplary embod iment of the bellows heat exchanger formed in one piece of material;

Figure 5 shows an axial section of a second exemplary embod iment of the bellows heat exchanger formed out of several pieces of material, the different pieces being connected by means of a fastening means, for example a weld seam, a solder seam, glue or the like ;

Figure 6a shows an axial section of a further exemplary embodiment of the bellows heat exchanger with stiffening elements arranged between the different corrugation segments;

Figure 6b shows a radial section of the bellows heat exchang er of figure 6a;

Figure 7a shows an axial section of an annular bellows heat exchanger with a heat-exchanger housing, in which the radial extent of the corrugation segments is relatively small;

Figure 7b shows a plan of the bellows heat exchanger of figure 7a; Figure 8a shows an axial section of an annular bellows heat exchanger, in which the radial extent of the corrugation segments is relatively large;

Figure 8b shows a plan of the bellows heat exchanger of figure 8a;

Figure 9a shows an axial section of an annular bellows heat exchanger, in which radial stiffening elements have been formed to provide a stiffening effect mainly in the axial direction;

Figure 9b shows a radial section of the bellows heat exchanger of figure 9a;

Figure 10a shows an axial section of an annular bellows heat exchanger, in which independent, radial stiffening elements have been fitted to provide a stiffening effect mainly in the axial direction;

Figure 10b shows a radial section of the heat exchanger of figure 10a;

Figure 11 shows a radial section of an annular bellows heat exchanger with inclined, radial stiffening elements which, in addition to providing a stiffening effect in the axial direction, may also encourage a rotating fluid flow;

Figure 12a shows an axial section of an annular bellows heat exchanger, in which the longitudinal axis of the corrugated segments is arranged in the axial direction of the variable-volume chamber; and gure 12b shows a radial section of the heat exchanger

figure 12a. In the description of the invention, reference is made to elements in a device for heat exchange in a heat engine, a heat pump, an expander or a compressor as it is shown in figures 1 and 2, the device elements being identified by reference numerals that are shown in one or more of the figures l-12b.

Figures 1 and 2 show the device in a preferred embodiment, in which a working mechanism 1 is provided with a piston 200 which oscillates in a cylinder chamber 150, also called a variable-volume chamber, formed by a cylinder 100. A connecting rod 60 connects the piston 200 to a crank shaft 50 and provides conversion of the translatory movement of the piston 200 into rotation of the crank shaft 50, like in common motor solutions. The piston 200 is provided with seals 210, for example ordinary piston springs, which provide sufficient sealing during operation. Further, a bellows heat exchanger 300 is arranged, surrounding the cylinder chamber 150. The bellows heat exchanger 300 is provided with a first heat- exchanger surface 301 that is in thermal connection with a second heat-exchanger surface 302, these forming two opposite surfaces of a heat-exchanger wall 350 of the heat exchanger 300. The first heat-exchanger surface 301 is further in thermal contact with the cylinder chamber 150, as it forms part of the surrounding wall of the cylinder chamber 150. The second heat-exchanger surface 302 is correspondingly in thermal contact with a fluid-flow passage 610 which is formed by a heat-exchanger housing 600 surrounding the heat exchanger 300, a clearance being provided between the heat exchanger 300 and the heat-exchanger housing 600. The heat exchanger 300 provides for heat supply to a working fluid during expansion in the cylinder chamber 150 and heat removal from the working fluid during compression in the cylinder chamber 150, as a thermo fluid which is flowing through the fluid-flow passage 610 supplies or receives heat to/from the working fluid through the heat-exchanger wall 350. The thermo fluid flows in and out of the fluid-flow passage 610 between the heat exchanger 300 and the heat-exchanger housing 600 by a thermo fluid inlet 500 and a thermo fluid outlet 510 being arranged in the heat-exchanger housing 600. The working fluid flows in and out of the cylinder chamber 150 by a working- fluid inlet 400 and a working-fluid outlet 410 being arranged in the cylinder housing 100. The moment of injection of the working fluid, and the amount, pressure et cetera may be controlled by means of known control principles. In a heat engine or a heat pump, work will be exchanged between the working fluid and the working mechanism 1 by thermal energy being converted into mechanical energy or vice versa, the heat exchanger 300 exchanging heat between the thermo fluid and the working fluid.

The heat exchanger 300 is formed as a bellows, a bellows giving the great advantage of enabling a large heat-exchanger surface, while, at the same time, the thickness of material may be kept small and equal in nearly the entire heat- conducting surface. In addition, bellows are inexpensive to produce, and have very good mechanical strength, so that they may also stand up to operation under high pressure, even though the thickness of material is small, which is essential in any heat engine or heat pum .

In exemplary embodiments shown in figures 9a-11, the heat exchanger 300 is provided with several braces 310, so that high working pressure will not cause significant deformation or dislocation of the heat-exchanger wall 350 in the axial direction. The braces 310 may also have a stabilizing effect in other directions, for example in the radial direction. The braces 310 may be formed as elongated raised parts, also called ribs 311, that have been pressed out in the plate ma- terial of the heat exchanger 300 (see figures 6a-6b and 9a- 9b) . The braces 310 may also be separate stiffening elements 312 which have been put into the pleats of the heat-exchanger wall 350, possibly also between the heat-exchanger wall 350 and other adjacent components, such as the heat-exchanger housing 600 (see figures lOa-ll) . The advantage of using separate stiffening elements 312 is that they will reduce the dead volume of the device by the very fact of the stiffening elements 312 occupying some volume, which may be very favourable in, for example, a heat engine or a heat pump. A combination of pressed-out ribs 311 and separate stiffening elements 312 may also be used.

The heat-exchanger wall 350 and/or the stiffening elements 310 may further be made with additional formations, so that further adjustment, control or distribution of the working- fluid or thermo fluid flow may be achieved. This measure may also contribute to controlling and possibly enhancing turbulence if desirable. Figure 11 further shows how the direction of the stiffening elements 312 may contribute to controlling a fluid flow in the heat exchanger 300 during operation, which is illustrated here by deflection from the radial direction, so that a working fluid, for example, may achieve a more circular direction of flow, if desirable.

In one embodiment, the heat exchanger 300 is formed by one metal piece being shaped by means of fluid forming. Fluid forming gives the advantage of enabling large series to be produced very cheaply, without the need of putting together several independent pieces of material, which will increase the price. It is assumed, however, that there are several favourable production methods for heat exchangers of this kind.

In one embodiment, the heat exchanger 300 is of such a design that it occupies substantially an annular volume. In this way, it may surround the cylinder chamber 150 and thus occupy as little space as possible in the device, because there will then be good utilization of volume. However, the heat exchanger 300 according to the invention is not limited to the annular form, as the principle described may also be used for, for example, plane heat exchangers, for example for use on an end surface of the cylinder chamber 150.

Claims

C l a i m s

A device for heat exchange in a heat engine, a heat pump, an expander or a compressor which utilizes a working fluid for energy conversion and a thermo fluid for heat transmission, the heat engine, heat pump, expander or compressor having at least one working mechanism (1) including at least one variable-volume- chamber housing (100), and the variable-volume-chamber housing (100) forming at least one variable-volume chamber (150) , the at least one working mechanism (1) including at least one displacement mechanism (200) , and there being at least one heat exchanger (300) in thermal contact with at least one of the at least one variable-volume chamber (150) , c h a r a c t e r i z e d i n that the heat exchanger (300) surrounds and/or is surrounded by the variable-volume chamber (150), and is formed as a bellows.

The device according to claim 1, wherein the heat exchanger (300) includes first and second heat-exchanger surfaces (301, 302) which are thermally connected by a heat-exchanger wall (350) having high thermal conductivity .

The device according to claim 2, wherein the first heat-exchanger surface (301) is in thermal contact with the variable-volume chamber (150) .

The device according to claims 1 to 3, wherein the heat exchanger (300) and a surrounding or surrounded heat-exchanger housing (600) form a fluid-flow passage (610) which is in fluid communication with a thermo fluid inlet (500) and a thermo fluid outlet (510) .

5. The device according to any one of claims 2 to , wherein the second heat-exchanger surface (302) is in thermal contact with the fluid-flow passage (610) .

6. The device according to any one of the preceding

claims, wherein the heat exchanger (300) substantially occupies an annular volume.

7. The device according to any one of the preceding

claims, wherein the heat exchanger (300) has substantially equal thickness of material across the portion of the heat-exchanger wall (350) abutting the fluid- flow passage (610) .

8. The device according to any one of the preceding

claims, wherein stiffening elements (310) are arranged in the pleats of the heat exchanger (300) .

9. The device according to any one of the preceding

claims, wherein braces (310) are arranged between the periphery of the bellows heat exchanger (300) and surrounding elements (600) .

10. The device according to one or both of the claims 8 and 9, wherein the braces (310) are provided as raised parts (311) formed as profiles pressed out from the neutral axis of the heat-exchanger wall (350) .

11. The device according to one or both of the claims 8 and 9, wherein the braces (310) are provided as separate stiffening elements (312) .

12. The device according to one or both of the claims 8 and 9, wherein the braces (310) are provided as a combination of raised parts (311) , formed as profiles pressed out from the neutral axis of the heat- exchanger wall (350) , and separate stiffening elements (312) .

13. The device according to claim 11 or 12, wherein the separate stiffening elements (312) are connected to the heat-exchanger wall (350) by means of fastening means taken from the group consisting of adhesives, welding or soldering connections, screws and rivets.

14. The device according to any one of the preceding

claims, wherein the bellows heat exchanger (300) is substantially formed out of a metal or an alloy of metals .

15. The device according to any one of the preceding

claims, wherein the bellows heat exchanger (300) is formed of several heat-exchanger sections (380) joined together by means of a fastening means (390) .

16. The device according to claim 15, wherein the bellows- heat-exchanger sections (380) are joined together by welding .

17. The device according to any one of claims 1 to 14, wherein the bellows heat exchanger (380) is formed by electrofabrication .

18. The device according to any one of claims 1 to 14, wherein the bellows heat exchanger (380) is formed out of one piece of material .

19. The device according to any one of claims 1 to 14, wherein the bellows heat exchanger (300) is formed by fluid forming.

The device according to claim 1, wherein the thermo fluid is included in a closed circuit.

21. The device according to claim 1, wherein the working mechanism (1) is arranged to let the working fluid alternate between the liquid and gas phases.

22. The device according to claim 1, wherein the working fluid has a normal boiling point lower than 100 °C.