Patent Description:
In the second place, the invention relates to a micro gas turbine comprising a compressor, a turbine, a combustor, and a heat exchanger as mentioned, the compressor being designed to take in and pressurize gas, the combustor being designed to take in pressurized gas from the compressor and to generate hot gas on the basis of fuel combustion, the turbine being designed to take in and expand hot gas generated by the combustor, and the heat exchanger being configured and arranged to pre-heat pressurized gas before being supplied to the combustor by allowing the pressurized gas to exchange heat with expanded gas obtained from the turbine.

The invention is especially applicable to the field of gas turbines, particularly micro gas turbines The micro gas turbine may be dimensioned to generate up to <NUM> kW electric power, or up to <NUM> kW electric power, for example. A possible application of micro gas turbines is an application for Combined Heat & Power (CHP), which does not alter the fact that other applications are feasible as well. Micro gas turbines and/or micro gas turbine based CHP systems may be used instead of conventional boilers in large houses, offices, plants, schools, stores etc., to mention one example, or may be used in hybrid electric vehicles so as to extend the range of such vehicles, to mention another example. In general, micro gas turbines are known for high reliability, low maintenance demand and low noise level, combined with high efficiency, low weight and low emissions.

A micro gas turbine typically comprises a compressor, a turbine and a particular type of heat exchanger called recuperator. During operation of a micro gas turbine, ambient air is injected and pressurized in the compressor. The compressed air is transported to the recuperator, where it is pre-heated. Further, the pre-heated air is supplied to a combustor for adding more heat so as to obtain a hot gas which is at a required temperature level and outputting the hot gas, the heat being generated by fuel combustion. The hot pressurized gas is supplied to the turbine where it expands and thereby provides mechanical power for both the compressor and a generator coupled to the turbine. The mechanical power of the generator is converted to electric power as a first type of output from the micro gas turbine. The expanded gas, which is still at an elevated temperature, is transported from the turbine to the recuperator for pre-heating incoming air compressed by the compressor, as mentioned. Residual heat still present in the gas after having flown through the recuperator is transferred to water in a gas-to-liquid heat exchanger, so that hot water is obtained as a second type of output from the micro gas turbine. As an alternative, ambient air from an air heating system can be heated by using an air handler, in case forced air heating is used in a building, as is often the case in North America.

The recuperator as used in the micro gas turbine is a gas-to-gas heat exchanger. It is a generally known fact that such recuperator is difficult to design and manufacture in view of the fact that the recuperator needs to be capable of operating under demanding circumstances including high temperatures, high temperature gradients, high pressure differentials between pressurized incoming air and exhaust flue gases, and a high rate of start-stops. In order to guarantee optimal operation of a micro gas turbine, effectiveness of a heat exchange process as facilitated by a recuperator needs to be high, more than <NUM>%, even about <NUM>%. What's more, pressure loss in a recuperator should be kept low, preferably below <NUM>%, as pressure loss involves a reduction of the expansion ratio through the turbine, which is detrimental to the power output. In order to comply with these demanding specifications, an optimal flow distribution within the heat exchanger is required, allowing the maximum available surface area to contribute to the heat exchange.

<CIT> discloses a heat exchanger according to the preamble of claim <NUM> and describes a heat exchanger which is a recuperator for a gas turbine in one of the possible embodiments thereof. In the heat exchanger, a first header (pipe) is arranged for inflow of a first fluid and a second header (pipe) for outflow of that first fluid, after it has been heated in the heat exchanger. The body of the heat exchanger consists of a stack of mutually spaced-apart substantially rectangular plates arranged between the inflow header and the outflow header of the first fluid with opposite edges respectively facing the headers. The plates are arranged in spaced-apart pairs which are sealed around their edges so as to provide respective sealed units, save only for ducting for inflow and outflow of the first fluid.

The pairs of plates are also mutually spaced apart, providing spacings therebetween which constitute a fluid flow path for a second fluid which thus flows over the outsides of the plate pairs. The inside of the inflow header communicates with the inside of the respective plate pairs by respective flexible curved tubes. Likewise, the inside of the outflow header communicates with the inside of the respective plate pairs by respective flexible curved tubes.

Each pair of plates has arranged thereon a plurality of pins, the pins having a function in enhancing the heat exchange surface. These pins both bridge the spaced-apart plates and extend into the spacings between the plate pairs. During the manufacturing process of the heat exchanger, connections between the plates and the pins are made by means of laser welding, wherein each of the pins is fixed to one of the two plates. In view of the fact that a heat exchanger may comprise hundreds of thousands of pins, this is a very laborious process. Also, making the curved tubes and connecting them between the headers and the plate pairs is an intensive process. The headers are composed of segments which are connected to the respective plate pairs. Consequently, the manufacturing process of the heat exchanger comprises a step of assembling the header by stacking the segments and subjecting them to a connecting action such as welding.

Using a recuperator in a micro gas turbine involves a significant improvement of the efficiency of the micro gas turbine. However, due to its complex design and related laborious manufacturing process, the recuperator is a very expensive component of the micro gas turbine, which determines to a considerable extent the production cost of the micro gas turbine. It is an object of the invention to simplify the design of a heat exchanger which is suitable for use as a recuperator in a micro gas turbine, by simplifying the design of the cells and possibly also other components of the heat exchanger, preferably without introducing disadvantageous effects such as a reduction of efficiency or a reduction of reliability.

In view of the foregoing, the invention provides a heat exchanger comprising a stack of cells, each of the cells including a pair of mutually spaced-apart plates which is configured and arranged to define an internal fluid flow path of the cell, particularly between two inner surfaces of the plates facing each other, and an external fluid flow path of the cell, particularly at two outer surfaces of the plates facing away from each other, wherein the plates are connected to each other along the periphery thereof, except at positions where at least one inlet to and at least one outlet from the internal fluid flow path are located, and wherein a plurality of heat exchange elements is arranged in each of the fluid flow paths, the cell comprising at least one supply conduit extending from the at least one inlet to the internal fluid flow path; a housing enclosing the stack of cells; and a supply header for supplying fluid to the internal fluid flow path of the respective cells, the at least one inlet to the internal fluid flow path of the respective cells being connected to the supply header through the at least one supply conduit of the cells, wherein the at least one supply conduit of the respective cells has at least one flexible portion that is compressible and expandable in a direction in which the at least one supply conduit extends, and wherein the at least one flexible portion of the at least one supply conduit includes a bellows-shaped pipe portion.

A notable feature of each of the cells of the heat exchanger according to the invention is that the at least one supply conduit of the cell, i.e. a conduit that is arranged for providing access to the internal fluid flow path and that is associated with the inlet to the internal fluid flow path to that end, has at least one flexible portion, particularly at least one flexible portion that is compressible and expandable in a direction in which the at least one supply conduit extends. According to the invention the at least one flexible portion of the at least one supply conduit is designed so as to include a bellows-shaped pipe portion. In this way, complex design features such as the flexible curved tubes known from <CIT> can be omitted while the ability of the design to compensate for heat expansion effects is maintained. It may even be so that it is sufficient to have flexibility at one side of the cell only. In such a case, it is preferred if flexibility is realized at the relatively cold side of the cell, as the choice of possible materials and shapes of components is the largest at that side, whereas at the other side, the choice is restricted due to the higher temperature requirements. Further, the at least one supply conduit may comprise a nozzle pipe portion which diverges in the direction of the at least one inlet to the internal fluid flow path. Such a nozzle pipe portion does not need to be of complex design and may simply be a partially flattened pipe portion, for example.

In a practical embodiment of the heat exchanger according to the invention, the plurality of heat exchange elements of a fluid flow path are defined by at least one discrete spatial component incorporating at least a portion of the plurality of heat exchange elements and being at least connected to an adjacent one of the plates. In that way, it is not necessary to rely on providing a plurality of pins or similar elements for increasing the surface area available for heat exchange and optimizing a fluid spreading effect across the plates so as to obtain an equal distribution of the fluid across the plates. Instead, discrete spatial components are used for realizing a plurality of heat exchange elements in the various fluid flow paths. Consequently, in a manufacturing process of a cell for a recuperator, there is no need for laser welding hundreds of thousands of pins which need to be positioned either individually or in groups, and there is no need for specific tooling like casting dies, orbital welding equipment and a customized pin welding machine. Also, there is no need for other tooling like expensive stamps as conventionally used in a process of making recuperators of the type called primary surface recuperators. For the sake of completeness, in conformity with the above explanation of the functionality of the pins of the heat exchanger known from <CIT>, it is noted that the heat exchange elements are elements which are configured to increase the heat exchange surface of the heat exchanger. Advantageously, the heat exchange elements also have a function in spreading fluid across the plates. The fact is that optimizing effectiveness of the heat exchanger is closely related to optimizing the flow distribution. In practical situations, the design of the heat exchange elements is at the same time aimed at minimizing the extent to which the presence of the heat exchange elements contributes to a pressure drop in the heat exchanger.

According to a first feasible example, each cell may comprise at least one discrete spatial component which includes a wire wound to a coil. In that case, it is practical if the cell comprises a plurality of such spatial components and the spatial components are positioned so as to extend alongside each other in a substantially parallel arrangement, at the same time being arranged in such particular way that fluid flows are not blocked and flow distribution is optimized. The windings of the coils have a similar effect on the heat exchange process and the spreading of the fluid to be subjected to the heat exchange process as the conventional pins. The coils may be of a generally flattened design so as to keep a dimension of the cell perpendicular to the plates within acceptable limits. According to a second feasible example, the cell may comprise at least one discrete spatial component which includes a wire mesh. In that case, it is even more simple to cover an area of the cell with heat exchange elements. A wire mesh may be provided in any suitable form, wherein the wire mesh may be folded in any suitable way. Further, a wire mesh may particularly comprise a woven structure of fibers or a non-woven structure of fibers. For example, the wires of a wire mesh may be arranged in a woven structure in the form of an open mattress. Providing a wire mesh, a wire coil or another type of discrete spatial component involves providing a plurality of heat exchange elements in one go or in only one handling step, whereas providing pins involves providing a plurality of heat exchange elements in a one-by-one process. Examples of another type of discrete spatial component include foils, louvres, elongated ribs of any suitable shape, metal foam, etc..

It may be so that when at least one discrete spatial component is used in the internal fluid flow path as defined between the plates, a discrete spatial component is connected to only one of the plates, especially when another discrete spatial component is present in the internal fluid flow path as well and is connected to the other of the plates. On the other hand, it may be so that only one layer including discrete spatial component(s) is present in the internal fluid flow path, wherein the at least one discrete spatial component is connected to both plates. In any case, the invention offers a possibility of realizing a cell having a kind of sandwich structure comprising two plates, two outer layers including heat exchange elements, and an intermediate layer including heat exchange elements.

It is not necessary to use discrete spatial components of only one design throughout the cell, although it may be practical to do so. For example, the invention covers embodiments of the cell comprising both wire coils and wire meshes in the respective fluid flow paths, and also embodiments of the cell which are provided with wire coils of two types, namely wire coils which are wound in two opposite directions, i.e. clockwise and counterclockwise directions, in which case pairs of intertwined coils of two types may be used.

If the heat transfer effect of the discrete spatial components on the plates is less than as would be the case when conventional pins would be used, the heat transfer effect can easily be put to the required level by designing the plates with larger dimensions and/or increasing the number of cells intended for use in a heat exchanger, which does not require any change of the basic set-up of the heat exchanger.

As is the case in the art, the plates may be of a generally planar design, wherein it may be practical if the plates are not curved and have a substantially rectangular periphery. In any case, it is practical if the plates and other components of the cell are made of a metal material. In view of the fact that the cell is subjected to high temperatures during use thereof, at least at one side, which may be higher than <NUM>, even up to <NUM>, <NUM> or higher, it may be advantageous to use a material commonly known as Inconel, which is material from a family of austenitic nickel-chromium-based high-performance alloys. As used in the context of the invention, the content of nickel of the nickel alloys may be typically higher than <NUM>%. Examples of heat resistant material include Aisi <NUM>, Inconel (Alloy) <NUM>, Inconel (Alloy) <NUM>, Inconel (Alloy) <NUM>. It is to be noted that it may be practical to use Inconel only at a side of the cell that is subjected to the highest temperatures and to use other materials at another side so as to save costs. In case discrete spatial components including a wire wound to a coil are used, this can easily be realized by arranging Inconel wire coils only at one side of the cell and arranging wire coils made from another material at another side.

For the purpose of discharging fluid from the internal fluid flow path of the respective cells, it is practical for the heat exchanger to comprise a discharge header. According to the invention, the discharge header may be of a far more simpler design than a conventional stack of segments that need to be interconnected, comprising a connection plate provided with slotted discharge openings, the connection plate being arranged against the cells, and each of the slotted discharge openings being aligned with an outlet of an internal fluid flow path of a cell. This design of the discharge header enables an option according to which the discharge header is composed of only the connection plate and a closure component at the position of the stack of cells, the connection plate and the closure component jointly forming a pipe-like entirety. It will be understood that forming a pipe-like entirety on the basis of no more than two components being generally dimensioned in a longitudinal direction of the entirety involves a simpler manufacturing process than forming a pipe-like entirety on the basis of a stack of segments, practically more than two segments. Also, providing a connection plate and a closure component as mentioned allows for simplification of a process of welding the cells to the header, as it this allows for welding the cells to the connection plate first and subsequently closing the header by means of the closure component. If the header would be provided in the form of a pipe from the start, welding of the cells to the header should be done on the inside of the pipe, which would be far more bothersome. It is possible to use pipe parts of a suitable heat resistant material, but it is also possible for both the connection plate and the closure component to be manufactured from a thin plate that is bended to the shape as desired.

In any case, for the purpose of supplying fluid to the internal fluid flow path of the respective cells, the heat exchanger comprises a supply header, and the at least one inlet to the internal fluid flow path of the respective cells is connected to the supply header through the at least one supply conduit of the cells. According to the invention, the supply header may be of a far more simpler design than a conventional stack of segments that need to be interconnected, comprising a connection plate having supply openings, wherein the at least one supply conduit of the cells is connected to the connection plate at the position of a supply opening. In conformity with the above explanation of possibilities relating to the discharge header, it may be so that the supply header is composed of only the connection plate and a closure component at the position of the stack of cells, the connection plate and the closure component jointly forming a pipe-like entirety.

The heat exchanger may comprise a holder component for supporting the cells on the supply header. Such a holder component may be shaped like a rack or a plurality of adjacent racks, for example, in which case the rack may be designed so as to be capable of receiving and holding a portion of the respective cells. Contrariwise, in commonly known designs, the cells are interconnected, whereby a kind of monolithic block structure is obtained, which involves high internal thermal stress levels.

The invention also relates to a micro gas turbine comprising a compressor, a turbine, a combustor, and a heat exchanger of the design as described in the foregoing, the compressor being designed to take in and pressurize gas, the combustor being designed to take in pressurized gas from the compressor and to generate hot gas on the basis of fuel combustion, the turbine being designed to take in and expand hot gas generated by the combustor, and the heat exchanger being configured and arranged to pre-heat pressurized gas before being supplied to the combustor by allowing the pressurized gas to exchange heat with expanded gas obtained from the turbine. As mentioned in the foregoing, efficiency of a micro gas turbine is significantly improved when a recuperator is used. In a practical embodiment, the internal fluid flow path of the cells of the heat exchanger is in communication with the compressor for taking in pressurized gas from the compressor, and the external fluid flow path of the cells of the heat exchanger is in communication with the turbine for taking in expanded gas from the turbine. Thus, in such an embodiment, relatively high pressure is prevailing between the plates of each of the cells of the heat exchanger during operation of the micro gas turbine. Especially in case the cells of the heat exchanger comprise at least one discrete spatial component which is located in the internal fluid flow path and which is connected to both plates, the heat exchanger is very well capable of withstanding the relatively high pressure.

When the invention is put to practice, especially when at least one discrete spatial component incorporating at least a portion of the plurality of heat exchange elements applied in the cell, the cell may be manufactured on the basis of a method in which two plates and at least three discrete spatial components for defining a plurality of heat exchange elements extending from at least one surface of the plates are provided and stacked so as to obtain a stack including successively a first outer layer including at least one spatial component, a first plate, at least one intermediate layer including at least one spatial component, a second plate, and a second outer layer including at least one spatial component, and in which connections between the plates and the spatial components are made so as to obtain a stacked entirety. As explained earlier, using discrete spatial components for defining a plurality of heat exchange elements extending from at least one surface of the plates allows for having a manufacturing process that is far less complicated than a conventional process in which the heat exchange elements are connected to the plates on a one-by-one basis.

Connections between the plates and the discrete spatial components can be made by any suitable connecting technique. Assuming that the plates and the spatial components are made of a metal material, vacuum brazing is an advantageous example of such a technique, in view of the fact that when vacuum brazing is applied, making the connections basically requires no more than providing the plates with a suitable filler agent, assembling the stack of plates and spatial components, and heating the stack in an oven while exerting pressure on the stack.

As mentioned in the foregoing, the following options are applicable to the manufacturing method of the cell. In the first place, it may be so that at least one layer including at least one discrete spatial component is realized by disposing on a plate a plurality of spatial components which include a wire wound to a coil in a configuration in which the spatial components extend alongside each other in a substantially parallel arrangement. In the second place, it may be so that the stacked entirety of two plates and at least three discrete spatial components is made by providing only three spatial components which include a wire mesh besides the two plates, in which case the manufacturing process of the cell is even more simplified. In the third place, it is practical for the plates to be connected to each other along the periphery thereof, except at positions for having at least one inlet to and at least one outlet from an internal fluid flow path as defined between the plates. In the process, welding may be used as a suitable connecting technique, although other possibilities are also covered by the invention. In any case, according to the invention, as a step in the manufacturing method of the cell, irrespective of whether or not the cell is designed with discrete spatial components as mentioned, the stacked entirety of two plates and at least three discrete spatial components is provided with at least one supply conduit having at least one flexible portion that is compressible and expandable in a direction in which the at least one supply conduit extends, wherein the at least one supply conduit is connected to the stacked entirety at the position of the at least one inlet to the internal fluid flow path.

The individual cells are suitable to be used for manufacturing a heat exchanger. Such a heat exchanger is made by arranging the cells in a stack and enclosing the stack of cells in a housing.

As mentioned in the foregoing, the following options are applicable to the process of composing a heat exchanger of a number of cells. In the first place, it may be so that a discharge header for discharging fluid from an internal fluid flow path as defined between the plates of the respective cells is made by providing a connection plate having slotted discharge openings, arranging the connection plate against the cells and aligning each of the slotted discharge openings with an outlet of an internal fluid flow path of a cell, providing a closure component, and interconnecting the connection plate and the closure component so as to form a pipe-like entirety. In the second place, it may be so that a supply header for supplying fluid to an internal fluid flow path as defined between the plates of the respective cells is made by providing a connection plate having supply openings, connecting the at least one supply conduit of the cells to the connection plate at the position of a supply opening, providing a closure component, and interconnecting the connection plate and the closure component so as to form a pipe-like entirety. In the third place, it may be practical if a holder component is provided and arranged for supporting the cells on the supply header, which holder component may particularly be shaped like a rack or a plurality of adjacent racks, in which case the rack may be designed so as to be capable of receiving and holding a portion of the respective cells.

The invention will be further elucidated on the basis of the following description of an example of a recuperator and various components thereof. Reference will be made to the drawing, in which equal reference numerals indicate equal or similar components, and in which:.

The figures relate to a recuperator <NUM> having features according to the invention, as will now be explained. The recuperator <NUM> as shown and described represents only one example of many possibilities existing within the framework of the invention.

In the shown example, the recuperator <NUM> is intended to be used as a gas-to-gas heat exchanger and is particularly suitable for application in the context of a micro gas turbine, which does not alter the fact that application of the recuperator <NUM> in other contexts is feasible as well.

<FIG> provides a view of the exterior of the recuperator <NUM>, showing a housing <NUM> of the recuperator <NUM> that serves as an outer shell enclosing various components of the recuperator <NUM>. <FIG> shows interior components of the recuperator <NUM>, particularly an assembly of a stack <NUM> of cells <NUM>, a supply header <NUM> and a discharge header <NUM>. The stack <NUM> of cells <NUM> and the discharge header <NUM> are also shown in <FIG>, wherein further the supply header <NUM> is partially shown as well. <FIG> shows a single cell <NUM> from the stack <NUM> of cells <NUM> of the recuperator <NUM>.

Each of the cells <NUM> used in the shown recuperator <NUM> comprises a pair <NUM> of mutually spaced-apart plates <NUM>, <NUM> having a substantially rectangular periphery and being generally planar, i.e. free from curves. This particular design of the plates <NUM>, <NUM> is not essential within the framework of the invention, and the present disclosure of various special features of the invention is not limited to this particular design. The plates <NUM>, <NUM> are connected to each other along the periphery thereof so as to delimit an internal space, except at positions where an inlet <NUM> to and an outlet <NUM> from the internal space are located. In particular, the plates <NUM>, <NUM> may be provided with edges of a special design which can be welded and/or brazed together during the manufacturing process of the cell <NUM>, without a need for using an additional frame or the like. Preferably, the connection is made along a line that is practically in the middle of the two plates <NUM>, <NUM>, so that it is ensured that local thermal stresses during the welding process will not cause deformation of the cell <NUM>, particularly one of the plates <NUM>, <NUM>. During operation of the recuperator <NUM>, the internal space of the cells <NUM> serves as an internal fluid flow path. Further, a plurality of heat exchange elements <NUM> is arranged in the internal fluid flow path, and also on the two outer surfaces 22a, 23a of the plates <NUM>, <NUM> facing away from each other, i.e. in an external fluid flow path of the cell <NUM>.

As can be seen in <FIG>, the cell <NUM> has a layered structure, comprising successively a first outer layer <NUM> of heat exchange elements <NUM>, a first plate <NUM>, an intermediate layer <NUM> of heat exchange elements <NUM>, a second plate <NUM>, and a second outer layer <NUM> of heat exchange elements <NUM>. In respect of the intermediate layer <NUM> of heat exchange elements <NUM>, it is noted that this layer <NUM> may comprise heat exchange elements <NUM> which are connected to both plates <NUM>, <NUM>, but it is also possible for this layer to comprise heat exchange elements <NUM> which are connected to only one of the plates <NUM>, <NUM>, wherein it may be so that a number of heat exchange elements <NUM> is connected to the first plate <NUM> and that the rest of the heat exchange elements <NUM> is connected to the second plate <NUM>. However, in view of having optimal mechanical strength of the cell <NUM>, the first option is preferred, as in that case, the plates <NUM>, <NUM> are not only connected to each other along the periphery thereof, but also through the plurality of heat exchange elements <NUM>. Thus, the cell <NUM> can be very well made suitable for applications involving relatively high pressures.

According to an advantageous option, the heat exchange elements <NUM> are not provided as individual components, but are arranged on the respective plates <NUM>, <NUM> as part of a discrete spatial component comprising a plurality of heat exchange elements <NUM>. In the example as shown in the figures, each layer <NUM>, <NUM>, <NUM> of heat exchange elements <NUM> comprises a number of discrete spatial components <NUM> in the form of elongated wire coils. As illustrated in <FIG>, the wire coils <NUM> of each layer <NUM>, <NUM>, <NUM> are arranged so as to extend substantially parallel to each other.

The cell <NUM> according to the shown example is made by providing the two plates <NUM>, <NUM> and a plurality of wire coils <NUM>, and making a stack <NUM> of a first number of wire coils <NUM> in the substantially parallel arrangement as mentioned, the first plate <NUM>, a second number of wire coils <NUM> in the substantially parallel arrangement as mentioned, the second plate <NUM>, and a third number of wire coils <NUM> in the substantially parallel arrangement as mentioned. The stack <NUM> may be prepared for vacuum brazing, i.e. provided with a suitable filler agent at appropriate places before putting the stack <NUM> together and exerting pressure on the stack <NUM> once it has been put together, and heated in an oven so that the various layers <NUM>, <NUM>, <NUM> of heat exchange elements <NUM> and the plates <NUM>, <NUM> get interconnected. Interconnecting the plates <NUM>, <NUM> along the periphery thereof is then performed after the vacuum brazing has taken place, or this is done by vacuum brazing as well. The high temperature vacuum brazing process may be carried out in any useful way, wherein it is possible to use foil, powder or paste for making the necessary interconnections. In order to avoid high costs of the brazing process, it may be practical to make use of disposable ceramic strips and metal clips for holding the ceramic strips at edge positions on the stack <NUM>.

During operation of the recuperator <NUM>, one fluid is made to flow through the internal fluid flow path of the cell <NUM>, while another fluid is made to flow through the external fluid flow path of the cell <NUM>. The heat exchange elements <NUM> have a function in enhancing heat exchange between the two fluids. In the first place, the heat exchange elements <NUM> constitute an enlargement of the surface at which heat exchange can take place. In the second place, the heat exchange elements <NUM> assist in spreading the fluids across the plates <NUM>, <NUM>. In the third place, the presence of the heat exchange elements <NUM> in the cell <NUM> contributes to the mechanical integrity of the cell <NUM>, as the plates <NUM>, <NUM> are not only interconnected along the periphery thereof, but may also be interconnected through the heat exchange elements <NUM>. This aspect of the use of heat exchange elements <NUM> in the cell <NUM> is especially advantageous in view of the fact that this enables the cell <NUM> to withstand relatively high pressures at the position of the internal space thereof. The various wire coils <NUM> used in the cell <NUM> may be adjusted to specific operational circumstances, especially as far as the choice of material is concerned. Wire coils <NUM> which are arranged at a side of the cell <NUM> that may be expected to get very hot may be made of another material than wire coils <NUM> which are arranged at a colder side of the cell <NUM>.

The discrete spatial components used in the cell <NUM> for defining the heat exchange elements <NUM> do not necessarily need to comprise the wire coils <NUM> as shown. Alternative embodiments of the spatial components are feasible within the framework of the invention. For example, wire meshes may be used in the cell <NUM>, wherein it may be so that dimensions of the wire meshes are chosen such that a layer <NUM>, <NUM>, <NUM> of heat exchange elements <NUM> can be realized by means of only one wire mesh. In general, the spatial components are designed so as to provide heat exchange elements <NUM> in a fluid flow path for interacting with a flow of fluid, wherein it is advantageous if the heat exchange elements <NUM> are shaped so as to realize an as large as possible heat exchange surface at minimal pressure loss across the cell <NUM>.

Besides the pair <NUM> of plates <NUM>, <NUM> and the layers <NUM>, <NUM>, <NUM> of heat exchange elements <NUM>, the cell <NUM> comprises a supply conduit <NUM> extending/ projecting from the inlet <NUM>. In the recuperator <NUM>, the cell <NUM> is connected to the supply header <NUM> through the supply conduit <NUM>, as can be seen in <FIG> and <FIG>. In the shown example, the supply conduit <NUM> comprises two distinctive portions, namely a bellows-shaped pipe portion <NUM> which is designed to compensate for heat expansion effects and to thereby avoid distortion effects, and a nozzle pipe portion <NUM> which diverges in the direction of the inlet <NUM>. In the recuperator <NUM>, the supply conduit <NUM> is connected to the supply header <NUM> through the bellows-shaped pipe portion <NUM> at the one side thereof, and to the plates <NUM>, <NUM> at the position of the inlet <NUM> through the nozzle pipe portion <NUM> at the other side thereof. Both the bellows-shaped pipe portion <NUM> and the nozzle pipe portion <NUM> are of a basic, simple design so that the manufacturing process of the supply conduit <NUM> of the cell <NUM> can be fast and efficient. In a general sense, when the supply conduit <NUM> comprises something like at least one flexible portion <NUM> that is compressible and expandable in a direction in which the supply conduit <NUM> extends, which direction may also be referred to as a longitudinal direction of the supply conduit <NUM>, the supply conduit <NUM> is suitable to compensate for heat expansion effects, wherein there is no need for complex measures involving high costs, a bulky/spacious design etc..

At the position of the stack <NUM> of cells <NUM>, the supply header <NUM> comprises a connection plate <NUM> having supply openings <NUM>, as can be seen in <FIG>. The connection plate <NUM> is shown separately in <FIG>. The supply conduit <NUM> of each of the cells <NUM> is connected to the supply header <NUM> at a position of one of the supply openings <NUM> of the connection plate <NUM>. At the position of the stack <NUM> of cells <NUM>, a pipe-like appearance of the supply header <NUM> is obtained by means of a curved closure component <NUM> which is designed to be joined to the connection plate <NUM> along longitudinal edges thereof. A suitable connecting technique such as welding may be used for assembling the supply header <NUM>. For the purpose of avoiding a situation in which the cells <NUM> are supported on the supply header <NUM> only through the supply conduit <NUM>, which would put construction requirements on the supply conduit <NUM>, a rack-like holder component <NUM> is arranged so as to extend from the connection plate <NUM> of the supply header <NUM> and to engage with edge portions of the stack <NUM> of plates <NUM>, <NUM> and layers <NUM>, <NUM>, <NUM> of heat exchange elements <NUM>.

There is no need for compensating for heat expansion effects at both sides of the stack <NUM> of cells <NUM>, and therefore, it is sufficient for the cells <NUM> to comprise a conduit <NUM> having a flexible portion <NUM> at only one side thereof, provided that the flexible portion <NUM> is designed to cover a complete possible displacement range of components. Hence, the stack <NUM> of plates <NUM>, <NUM> and layers <NUM>, <NUM>, <NUM> of heat exchange elements <NUM> can be connected directly to the discharge header <NUM>. In view thereof, the discharge header <NUM> comprises a connection plate <NUM> provided with slotted discharge openings <NUM>. The connection plate <NUM> is shown separately in <FIG>. Each of the cells <NUM> is received in the connection plate <NUM> at a position in which a discharge opening <NUM> is open to the outlet <NUM> of the cell <NUM>. At the position of the stack <NUM> of cells <NUM>, a pipe-like appearance of the discharge header <NUM> is obtained by means of a curved closure component <NUM> which is designed to be joined to the connection plate <NUM> along longitudinal edges thereof. A suitable connecting technique such as welding may be used for assembling the discharge header <NUM>. In the shown example, both the connection plate <NUM> and the closure component <NUM> are designed as half pipes so that a complete pipe is obtained when the connection plate <NUM> and the closure component <NUM> are put together.

As mentioned earlier, the recuperator <NUM> is intended to be used as a gas-to-gas heat exchanger and is particularly suitable for application in the context of a micro gas turbine. <FIG> shows a scheme of various components of a micro gas turbine <NUM>, wherein fluid flows are indicated by means of large arrows. The micro gas turbine <NUM> may be dimensioned to generate up to <NUM> kW electric power, for example. Besides the recuperator <NUM>, the micro gas turbine <NUM> comprises a compressor <NUM>, a turbine <NUM>, a combustor <NUM>, a high speed generator <NUM>, a heat exchanger <NUM> and an exhaust <NUM>. The high speed generator <NUM> is arranged on a common shaft <NUM> of the compressor <NUM> and the turbine <NUM>. When the micro gas turbine <NUM> is operated, air is input to the compressor <NUM> and fuel is input to the combustor <NUM>. The compressor <NUM> acts to compress the air and to thereby pressurize the air to about <NUM> bar. The compressed air is supplied to the recuperator <NUM> where it is pre-heated under the influence of heat exchange with exhaust gas from the turbine <NUM>. The compressed air is supplied to the combustor <NUM> which is configured and arranged to output hot gas under the influence of heat generated by fuel combustion. The hot pressurized gas is expanded in the turbine <NUM>, on the basis of which mechanical power is obtained that is used for powering both the compressor <NUM> and the high speed generator <NUM>. In the process, the common shaft <NUM> performs a rotary movement as indicated by means of a small bent arrow.

Exhaust gas from the turbine <NUM> is supplied to the recuperator <NUM> for heating compressed air from the compressor <NUM>, as mentioned. After having passed the recuperator <NUM>, the gas from the turbine <NUM> is made to flow through the heat exchanger <NUM> and finally through the exhaust <NUM>. The heat exchanger <NUM> serves to heat a suitable medium such as water. Thus, output of the micro gas turbine <NUM> is realized at the heat exchanger <NUM>, as mentioned, and the high speed generator <NUM>, wherein it is noted that the latter is designed to be used to convert mechanical power to electric power.

In the recuperator <NUM>, the low pressure hot gas from the turbine <NUM> is made to flow through the external fluid flow path of the various cells <NUM>, whereas the high pressure cold air from the compressor <NUM> is made to flow through the internal fluid flow path of the various cells <NUM>. In this respect, it is noted that the relatively hot side of the recuperator <NUM> is at the discharge header <NUM>, whereas the relatively cold side of the recuperator <NUM> is at the supply header <NUM>. In view thereof, it is advantageous to have the means for compensating for heat expansion at the side of the supply header <NUM>, as is the case in the shown example where a bellows-shaped pipe portion <NUM> is incorporated in a supply conduit <NUM> of the cells <NUM>. The same is applicable to the nozzle pipe portion <NUM> of the supply conduit <NUM> of the cells <NUM>.

Thus, the recuperator <NUM> serves to heat up the air from the compressor <NUM>, that is to be supplied to the turbine <NUM> after having passed the combustor <NUM>, and to cool down the gas from the turbine <NUM>, wherein the air from the compressor <NUM> is transported to the cells <NUM> of the recuperator <NUM> through the supply header <NUM> and transported away from the cells <NUM> through the discharge header <NUM>. In the context of the micro gas turbine <NUM>, a temperature at the turbine side of the recuperator <NUM> may be as high as <NUM>°, or even <NUM> or higher, and both the temperature differential and the pressure differential across the recuperator <NUM> are relatively high as well, in view of the fact that a temperatures at the compressor side of the recuperator <NUM> may be about <NUM>, and the fact that the pressure of the air from the compressor <NUM> may be about <NUM> bar whereas the pressure of the gas from the turbine <NUM> is at ambient pressure. It appears in practice that the recuperator <NUM> of the design as shown in the figures and described in the foregoing maintains its functionality under the extreme circumstances, while realizing an efficient heat exchange process. Thus, the invention provides a recuperator <NUM> of a relatively uncomplicated design which is still capable of performing the heat exchange process as desired and meeting the various requirements as applicable to the process, and which has a lifetime that is at least comparable to that of a recuperator of a conventional design, such as the recuperator known from <CIT>. Compared to a recuperator of conventional design, a reduction of costs of more than <NUM>% can be realized.

It will be clear to a person skilled in the art that the scope of the invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the invention as defined in the attached claims.

Also, it will be clear to a person skilled in the art that various aspects are independently applicable. In this respect, it is noted that the following items are feasible:.

A possible summary reads follows. A heat exchanger <NUM> that is suitable to be used as a recuperator in a micro gas turbine <NUM> comprises a stack <NUM> of cells <NUM>. Each of the cells <NUM> includes a pair <NUM> of mutually spaced-apart plates <NUM>, <NUM> and layers <NUM>, <NUM>, <NUM> of heat exchange elements <NUM> arranged at the outer surfaces 22a, 23a of the plates <NUM>, <NUM> and between the plates <NUM>, <NUM>. Each of the layers <NUM>, <NUM>, <NUM> of heat exchange elements <NUM> preferably comprises at least one discrete spatial component <NUM> incorporating a plurality of heat exchange elements <NUM>. For example, each of the layers <NUM>, <NUM>, <NUM> of heat exchange elements <NUM> may comprise a number of wire coils <NUM> or a wire mesh. Further, both a supply header <NUM> and a discharge header <NUM> of the heat exchanger <NUM> are preferably composed of only two components <NUM>, <NUM>; <NUM>, <NUM> at the position of the stack <NUM> of cells <NUM>. Means for compensating for heat expansion effects are of uncomplicated design as well and comprise a bellows-shaped pipe portion <NUM> of a supply conduit <NUM>.

Claim 1:
Heat exchanger (<NUM>) comprising:
- a stack (<NUM>) of cells (<NUM>), each of the cells (<NUM>) including a pair (<NUM>) of mutually spaced-apart plates (<NUM>, <NUM>) which is configured and arranged to define an internal fluid flow path of the cell (<NUM>), particularly between two inner surfaces of the plates (<NUM>, <NUM>) facing each other, and an external fluid flow path of the cell (<NUM>), particularly at two outer surfaces (22a, 23a) of the plates (<NUM>, <NUM>) facing away from each other, wherein the plates (<NUM>, <NUM>) are connected to each other along the periphery thereof, except at positions where at least one inlet (<NUM>) to and at least one outlet (<NUM>) from the internal fluid flow path are located, and wherein a plurality of heat exchange elements (<NUM>) is arranged in each of the fluid flow paths, the cell (<NUM>) comprising at least one supply conduit (<NUM>) extending from the at least one inlet (<NUM>) to the internal fluid flow path;
- a housing (<NUM>) enclosing the stack (<NUM>) of cells (<NUM>); and
- a supply header (<NUM>) for supplying fluid to the internal fluid flow path of the respective cells (<NUM>), the at least one inlet (<NUM>) to the internal fluid flow path of the respective cells (<NUM>) being connected to the supply header (<NUM>) through the at least one supply conduit (<NUM>) of the cells (<NUM>);
characterized in that
- the at least one supply conduit (<NUM>) of the respective cells (<NUM>) has at least one flexible portion (<NUM>) that is compressible and expandable in a direction in which the at least one supply conduit (<NUM>) extends, wherein the at least one flexible portion (<NUM>) of the at least one supply conduit (<NUM>) includes a bellows-shaped pipe portion (<NUM>).