Heat exchanger for combustion engine with external combustion

Abstract

The description relates to a heat exchanger for a hot gas engine having at least one cylinder and a regenerator arranged externally around the cylinder. According to one exemplary embodiment, the heat exchanger comprises: a main body and a cover plate, the rear side of which is fixedly connected to a front side of the main body; first channels which run from the front side of the main body through the main body and open into the interior of the cylinder; second channels which run from the front side of the main body through the main body and open into the interior of the regenerator; and connecting channels which are incorporated into the front side of the main body and / or into the rear side of the cover plate. Each of the connecting channels connects one of the first channels to one of the second channels. The main body has, on a rear side, a collar which, in the installed state, bears against an inner side of a flange of a container. In some exemplary embodiments, the container is used to receive a liquid medium (e.g. molten metal) for storing heat. In other exemplary embodiments, the container can be a firing chamber, a vessel for fluidized bed material, a radiation receiver for concentrated solar energy or a furnace for thermal processes.

Description

Heat exchanger for internal combustion engine with external combustion TECHNICAL FIELD

[0001] The present description relates to the field of thermodynamic machines, in particular to a heat exchanger for introducing thermal energy into the process gas of a hot air engine. BACKGROUND

[0002] It is known that heater heat exchangers in Stirling engines are often equipped with a series of small tubes through which the process gas flows and is heated. The tubes are often equipped with ribs or fins to create more surface area for heat transfer. The ends of the tubes open into the expansion cylinder on one side and the engine's regenerator on the other. Regarding the prior art, reference is made to publications EP 19 883 52 A2, WO 2009 / 082997 A2, and US Pat. No. 3,861,146.

[0003] The disadvantage of these designs is that they are not suitable for certain types of heat transfer. If, for example, the radiant energy of a radiator is to be used efficiently, homogeneous, well-absorbing surfaces are more suitable. However, hot gases from biomass combustion, which carry dust and ash residues, are only suitable to a limited extent. They can quickly clog the spaces between the tubes or fins, which can lead to component failure. Heat input using liquid metals such as aluminum or sodium that are in contact with the heat exchanger is also difficult. Such melts contract during the transition from the liquid to the solid phase, which can inevitably lead to the deformation of the tubes and subsequently to the breakage of the component. It can also be problematic to introduce heat into the solidified metal between the tubes in order to get from the solid phase back to the liquid phase.

[0004] The inventor has set himself the task of creating a heat exchanger for a hot gas engine that at least partially overcomes the above-mentioned disadvantages and is suitable for a variety of applications (in particular for heat input using liquid metals). SUMMARY

[0005] The above-mentioned object is achieved by the device according to claim 1 and the system according to claim 8. Various embodiments and further developments are the subject of the dependent claims.

[0006] The description relates to a heat exchanger for a hot gas engine with at least one cylinder and a regenerator arranged externally around the cylinder. According to one exemplary embodiment, the heat exchanger comprises: a base body and a cover plate, the rear side of which is firmly connected to a front side of the base body; first channels, which run from the front side of the base body through the base body and open into the interior of the cylinder; second channels, which run from the front side of the base body through the base body and open into the interior of the regenerator; and connecting channels, which are incorporated into the front side of the base body and / or the rear side of the cover plate. Each of the connecting channels connects one of the first channels to one of the second channels. The base body has a collar on a rear side, which, when installed, rests against the inside of a flange of a container.In some embodiments, the container serves to hold a liquid medium (e.g., molten metal) for heat storage. In other embodiments, the container can be a combustion chamber, a vessel for fluidized-bed material, a radiation receiver for concentrated solar energy, or a furnace for thermal processes.

[0007] In contrast to the known, usually prismatically arranged tube structures, the heat exchanger according to the exemplary embodiments described here is designed in the form of a flat, slightly curved or conical disc. For the sake of simplicity, the following description assumes a flat cover plate. However, this (and the underlying front side of the base body) does not necessarily have to be flat. Both the entire (e.g. circular) front side of the cover plate and an annular part of the rear side of the base body (the aforementioned collar) are intended to introduce thermal energy into the interior of the heat exchanger (i.e., into the space between the cover plate and the base body). It is understood that the cover plate and the collar of the base body do not necessarily have to be circular, even if this can be advantageous for design and assembly.

[0008] A key feature of the heat transfer to the process gas of the hot gas engine is a channel structure (the aforementioned connecting channels) located inside the disc (i.e., between the cover plate and the base body), through which the compressed working gas flows. The channels through which the working gas flows are distributed as evenly as possible, ensuring a uniform specific heat input per unit area. This serves to avoid significant temperature differences within the heat exchanger, which can lead to thermal stresses (with correspondingly undesirable consequences).

[0009] Both the front and back provide surfaces for heat transfer. At the front (where the cover plate is located), the entire (e.g. circular) surface is used. At the opposite back of the disc (where the aforementioned collar of the base body is located), additional heat is introduced into the heat exchanger via the annular surface of the aforementioned collar. There, heat is transferred to the base body by heat conduction via a metal ring (e.g. a flange) against which the collar of the base body rests. The metal ring, in turn, has thermal contact with its surroundings at its outer radial edge, which, if designed accordingly, can transfer considerable heat energy into the metal ring. This can be achieved, for example, by welding the ring (e.g. the flange) into the metallic wall of a vessel (or mounting it to it in some other way).As mentioned, the vessel can be a furnace, a vessel for liquid metal, or the like. In this respect, a portion of the vessel's wall acts as an additional heat transfer surface, supporting the entire outer surface of the heat exchanger to achieve greater heat transfer performance.

[0010] The design described above is important because the size of the disc and thus the length and consequently the volume of the internal channel structures (especially the connecting channels) can be kept relatively compact. This not only has a positive influence on the strength (and reduces the negative effects of thermal stresses), but it also provides the basis for the smallest possible volume in the channels for the process gas. In Stirling engines in particular, this volume is also referred to as the "harmful volume" or "dead volume" and should be kept as small as possible in terms of the achievable specific power. The specific heat transfer into the working gas is due to the high pressure that occurs in powerful In Stirling engines, the pressure can reach average values ​​of 100 bar and more, which is very high compared to the outer surface of the heat exchanger, where normally only atmospheric pressure conditions prevail. BRIEF DESCRIPTION OF THE ILLUSTRATIONS

[0011] The invention is explained in more detail below using the examples shown in the figures. The illustrations are not necessarily to scale, and the exemplary embodiments described here are not limited to the aspects shown. Rather, emphasis is placed on illustrating the principles underlying the exemplary embodiments. Regarding the figures:

[0012] Fig. 1 shows a section through the central axis of the expansion cylinder and the heat exchanger including its immediate surroundings.

[0013] Fig. 2 shows a view from the direction “A” indicated in Fig. 1.

[0014] Fig. 3 shows a fastening aid of the invention.

[0015] Fig. 4 shows a section of a radiation receiver for a solar mirror.

[0016] Fig. 5 is a horizontal section through a vessel with a built-in heat exchanger, primarily for liquid metals as heat storage.

[0017] Fig. 6 shows another section through the vessel from Fig. 5. DETAILED DESCRIPTION

[0018] In the exemplary embodiments described below, the heat exchanger is shown in conjunction with a Stirling engine. However, the use of the heat exchanger is not limited to Stirling engines. The concepts described are also applicable to other types of thermodynamic machines in which heat must be introduced into a process gas, such as the aforementioned Ericsson engine or Joule engine.

[0019] The exemplary embodiments described here relate to a heat exchanger for introducing thermal energy into the working gas of a thermodynamic machine (in particular a Stirling engine). An example is shown in Fig. 1. Fig. 1 shows a heat exchanger 1.4 for a hot-gas engine 1 (e.g., a Stirling engine) with at least one cylinder 1.1 and a regenerator 1.2 arranged externally around the cylinder 1.1. The heat exchanger has a base body 1.41 and a cover plate 1.45, the rear side of which is firmly connected to a front side of the base body 1.41 (e.g., by means of a joining process for producing high-temperature-resistant connections).

[0020] The (heater) heat exchanger thus comprises a disc- or plate-shaped design consisting of a base plate (which is part of the main body 1.41 of the heat exchanger) and the cover plate 1.45. First channels 1.44 and second channels 1.43 (bores) are arranged in the main body 1.41. The first channels 1.44 run from the front of the main body 1.41 through it and open into the interior of the cylinder 1.1. The second channels 1.43 also run from the front of the main body 1.41 through it, but open into the interior of the regenerator 1.2. Also shown in Fig. 1 is the displacer piston of the Stirling engine arranged in the cylinder 1.1. The interior of the regenerator 1.2 can, for example, be arranged in a ring around the central axis of the expansion cylinder 1.1. The heater heat exchanger, which may be disc- or plate-shaped, is located at the front end of cylinder 1.1. It is irrelevant whether cylinder 1.1 and the base body 1.41 of the heat exchanger are realized as a single part or are assembled from several parts. In the example shown, the base body 1.41 of the heat exchanger and the cylinder 1.1 form an integral component.

[0021] A structure of connecting channels 1.42 is incorporated into one or both of the plates (i.e., the front of the base body 1.41 or the back of the cover plate 1.45, or both). This structure, once the base and cover plates are joined together, creates a closed and gas-tight channel structure for the flowing working gas. Each of the connecting channels 1.42 connects one of the first channels 1.44 (leading into the cylinder interior) with one of the second channels 1.43 (leading into the regenerator). This means that the connecting channels 1.42 end at the bores 1.43 and 1.44, thus connecting the cylinder interior with the regenerator (see also Fig. 2).

[0022] A further aspect of the exemplary embodiments described here is, for example, that the outer edge region of the base body (the base plate) can be installed in a form-fitting manner into the wall of a container (e.g., a vessel, a combustion chamber, or the like), and that the inner wall of the container surrounding the heat exchanger forms a surface that absorbs heat and transfers it via a contact surface primarily to the rear side of the base body 1.41 (i.e., to the side of the heat exchanger facing away from the heat source). The aforementioned contact surface is made possible by a collar C arranged on the rear side of the base body 1.41, which, when installed, rests against an inner side 3.1 of a flange 3.0 of a container. As mentioned at the beginning, the container can fulfill different functions (e.g., combustion chamber, a vessel for liquid metal, or the like).The contact surface in the area of ​​the collar C enables heat conduction from the container into the back of the base body 1.41 of the heat exchanger, which overall increases the heat transfer capacity.

[0023] The collar C on the rear of the base body 1.41 is not necessarily flat. The collar and thus the contact surface between the base body 1.41 and the tank wall (flange 3.0) can, for example, also be slightly conical. The contact surface in the area of ​​the collar C is close to the connecting channels 1.42 and heat can therefore be introduced into the connecting channels 1.42 over a short distance. This heat is introduced from the flange 3.0, which in turn has a good heat-conducting connection to the tank wall 3.1 or the like, via the contact surface into the base body 1.41 of the heat exchanger. The flange 3.0 can also be considered part of the tank wall. In the example shown, the flange 3.0 is welded into the tank wall 3.1. It is understood that the flange 3.0 can also be mounted to the tank wall 3.1 in another way. The flange 3.0 can also be an integral part of the tank wall.To improve the efficiency of the rear heat input, the flange 3.0 can have a relatively thick wall thickness (thicker than the vessel wall (3.1)) in order to transfer the radial heat flow from the surrounding vessel wall 3.1 well to the contact point C. The heat transfer at the contact point in the area of ​​the collar C can be further improved, for example, with a high-temperature thermal paste.

[0024] Two possible applications are shown in Fig. 1. The left half generally represents the installation of the device in a container, ie the mounting on its wall 3.1. The flange 3.0 serves - in addition to the heat conduction function already explained - also for positioning the heat exchanger 1.4, whereby the heat exchanger can be fastened by means of a split pressure ring 2.2, which is supported on the cylinder wall of the cylinder 1.1 and is able to press the collar C of the base body 1.41 firmly against the flange 3.

[0025] The aforementioned thrust ring 2.2 is therefore part of a clamping device (see also Fig. 3), with the thrust ring 2.2 resting against an outer side of the flange 3.0 and supported against an outer wall of the base body 1.41 (any part arranged around the cylinder 1.1). The thrust ring 2.2 can be pressed by means of screws against a conical section of the outer wall of the base body 1.41, thereby pressing the collar C of the base body 1.41 against the inner side 3.1 of the flange 3.0.

[0026] On the right side of Fig. 1, an example of the integration of the device into a combustion chamber is shown. It depicts a ceramic tube 3.2 as the end of a combustion zone of a furnace. The flue gases 4.1 exit radially from the combustion zone in a gap between heat exchanger 1.4 and the end of the combustion tube 3.2 and enter an annular channel that is located between the outer surface of the combustion tube 3.2 and the inside of the vessel wall 3.1. There, heat is introduced into the wall 3.1 and conducted via the flange 3.0 to the collar C of the heat exchanger 1.4. If the front surface (i.e., the cover plate 1.45) of the heat exchanger 1.4 is directed towards the flame or embers of the furnace, intensive heat input occurs in three ways: (1.) through the radiation power 4.0 of the flame or embers, (2.) through convection of the flue gas flow 4.1 at the front of the heat exchanger, and (3.) through heat conduction via the contact point between the flange 3.0 and the base body 1.41 (at the collar C).

[0027] Fig. 2 shows the view “A” according to Fig. 1 of the heat exchanger 1.4, but without the cover plate 1.45, so that the view of the base plate (the front of the base body 1.41) and its channel structure (first and second channels 1.44, 1.43, connecting channels 1.42) is clear. It can be seen that the connecting channels 1.42 are arranged at a largely constant distance from each other in order to ensure heat extraction via the to keep the entire surface largely homogeneous. Also shown are the through holes 1.43 (second channels) in the regenerator 1.2 and the through holes 1.44 (first channels) in the cylinder chamber 1.1. On the left-hand side, an annular surface R is indicated, the surface of which transfers heat via the hidden flange 3.0 (indicated by dashed lines) to the rear side (at the collar C) of the heat exchanger. If the annular surface R marked with the arrows with a diameter D2 of 1.41 Dl is selected, approximately twice the area of ​​the end face of the heat exchanger 1.4 (corresponds to the area of ​​the cover plate 1.45) is available as a heat input surface.

[0028] An example of the clamping device mentioned is shown in Fig. 3. This comprises a two-part clamping ring 2.2, which is used to mount the heat exchanger 1.4 is used on flange 3.0. The split ring, in conjunction with a conical surface on the outer wall of the base body 1.41 of the heat exchanger or the cylinder 1.1, is able to press the rear of the heat exchanger 1.4 (namely, the collar C) firmly against the flange 3.0 to ensure good heat transfer at the contact point. For this purpose, clamping screws can press the two parts of the clamping ring 2.2 together in a diametrical direction. High-temperature thermal pastes can be used to support heat transfer. Another particular advantage is that the ring's clamping screws are no longer in the high-temperature area and can therefore be easily removed at any time. It goes without saying that other clamping ring designs that achieve essentially the same or a similar result can also be used.

[0029] Fig. 4 illustrates an application of the invention in connection with a radiation receiver of a solar mirror. This means that the container 3.1 serves as a radiation receiver, with the lid of the container 3.1 being designed as a flange 3.0 in the example shown. Heat is introduced exclusively by concentrated radiation 4.0, which is partially reflected from the cylindrical outer wall onto the cover plate 1.45. The absorbed portion is directed to the flange 3.0 and introduced into the heat exchanger on its rear side at collar C.

[0030] Fig. 5 and 6 are two representations of a system in which the heat exchanger 1.4 is mounted in a wall of a container 3.1, in which a (e.g. liquid) A heat storage medium is arranged. The system can be part of a so-called Camot battery, in which, for example, electrical energy is temporarily stored as heat, which can later be converted back into electrical energy (e.g., with the help of a Stirling engine and a generator driven by it). The heat storage medium can be a molten metal (e.g., liquid aluminum or sodium), molten salt, or similar.

[0031] The majority of the heat is transferred into the heat exchanger 1.4 via the cover plate 1.45. A partial surface of the wall of the vessel 3.1 conducts the heat of the melt via the flange 3.0 to the rear of the heat exchanger 1.4, where it is introduced into the rear of the heat exchanger at the collar C. The front side (cover plate 1.45) is in direct contact with the melt (see also Fig. 6). This means that the cover plate 1.45 of the heat exchanger 1.4 is located below the surface O of the liquid heat storage medium. The design of the vessel can be selected according to the properties of the melt, for example, a prismatic, truncated cone, or hemispherical design.

[0032] If the heat exchanger 1.4 is mounted in the vessel 3.1 at a height close to the liquid level O (see Fig. 6), a thermosiphon effect occurs, leading to a certain circulation of the melt. The thermosiphon effect is triggered by the increase in the density of the part of the melt immediately surrounding the heat exchanger 1.4, caused by the heat removal. This causes this denser (and consequently heavier) part of the melt to sink. This behavior can be used in thermal batteries to utilize as much of the volume in the vessel as possible for heat dissipation. In this context, it can be advantageous for the vessel 3.1 to be inclined. According to Fig. 6, the heat exchanger is arranged on a side surface of the vessel 3.1 below (but close to) the surface O of the liquid medium, and the central axis of the vessel is inclined with respect to the vertical.

[0033] The heat storage medium is not necessarily liquid metal; heated sand or other granular (grain-like) storage material (bulk material) such as aluminum oxide, ceramic sand, or the like can also be used. Transfer of heat energy, if possible from the entire volume of the container, can be achieved, for example, by circulating the sand. Methods for circulating sand and other bulk materials are known and range from simple mechanical methods, such as screw conveyors or the like, to fluidization using hot air, similar to that used in fluidized-bed combustion. For example, air can be sucked from the surface of a sand bed and reintroduced into the bottom via a nozzle plate (cf. Grace JR: "High-Velocity Fluidized Bed Reactors," in: Chemical Engineering Science, Vol. 45, Issue 8, pp. 1953-1966, 1990).

Claims

PATENT CLAIMS 1. A heat exchanger (1.4) for a hot gas engine with at least one cylinder (1.1) and a regenerator (1.2) arranged outside the cylinder (1.1), the heat exchanger comprising: a base body (1.41) and a cover plate (1.45), the rear side of which is firmly connected to a front side of the base body (1.41), first channels (1.44) which run from the front side of the base body (1.41) through the base body (1.41) and open into the interior of the cylinder (1.1), second channels (1.43) which run from the front side of the base body (1.41) through the base body (1.41) and open into the interior of the regenerator (1.2); and Connecting channels (1.42) which are incorporated into the front side of the base body (1.41) and / or into the rear side of the cover plate (1.45), wherein each of the connecting channels (1.42) connects one of the first channels (1.44) to one of the second channels (1.43), wherein the base body (1.41) has a collar (C) on a rear side which, in the installed state, rests against an inner side (3.1) of a flange (3.0) of a container.

2. The heat exchanger according to claim 1, further comprising: a clamping device with a split pressure ring (2.2) which rests on an outer side of the flange (3.0) and is supported on an outer wall of the base body (1.41).

3. The heat exchanger according to claim 1, wherein the pressure ring (2.2) is pressed by means of screws against a conical section of the outer wall of the base body (1.41), whereby the collar (C) of the base body (1.41) is pressed against the inner side (3.1) of the flange (3.0).

4. The heat exchanger according to one of claims 1 to 3, wherein the cover plate (1.45) is substantially flat.

5. The heat exchanger according to claim 4 wherein the cover plate (1.45) lies in a plane which is normal to a longitudinal axis of the cylinder (1.1).

6. The heat exchanger according to one of claims 1 to 5, wherein the first channels (1.44) and the second channels (1.43) end in a central region of the base body (1.41) and wherein the connecting channels (1.42) run from the central region of the base body (1.41) to the edge of the base body (1.41) and back again into the central region.

7. The heat exchanger according to one of claims 1 to 6, wherein a high-temperature thermal paste is arranged between the collar (C) of the base body (1.41) and the flange (3.0).

8. A system comprising: a container (3.1) with a flange (3.0) for receiving a heat storage medium; a hot gas engine with at least one cylinder (1.1) and a regenerator (1.2) arranged externally around the cylinder (1.1); and a heat exchanger according to one of claims 1 to 7.

9. The system according to claim 8, wherein the heat storage medium is a molten metal, in particular an aluminum or sodium melt.

10. The system according to claim 8, wherein the heat storage medium is a granular medium, in particular sand 11. The system according to claim 9, wherein the container (3.1) has a central axis and the heat exchanger is arranged on a side surface of the container (3.1) below but close to the surface of the liquid medium, so that a convection flow is created by removing heat from the liquid medium at the heat exchanger (thermosiphon effect).

12. The system according to any one of claims 8 to 11, further comprising: a device for circulating the heat storage medium.

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