BRIEF DESCRIPTION OF THE DRAWINGS
Further characteristics and advantages of the invention will emerge from the ensuing description with reference to the annexed plate of drawings, which are provided purely by way of non-limiting example and in which:
FIGS. 1 and 2 illustrate the conditions of operation in conventional thermoelectric generators, respectively of the type with gas-solid interface and solid-solid interface, according to what has already been described above;
FIG. 3 is a schematic perspective view of a cross section of the thermoelectric generator according to a first embodiment of the invention;
FIG. 4 illustrates a variant of FIG. 3;
FIG. 5 is a schematic cross-sectional view of a first embodiment of the invention;
FIG. 5A is a schematic illustration in perspective view and at an enlarged scale of a detail of FIG. 5;
FIG. 6 illustrates a variant that differs from that of FIG. 5 as regards the pre-arrangement of a combustion chamber;
FIG. 7 illustrates a further variant of FIG. 5, which differs in that it envisages two flows of fluid that, instead of having parallel and opposite directions, have directions orthogonal to one another; and
FIGS. 8, 9, 10 and 11 illustrate further alternative configurations of the generator according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIG. 3, number 1 designates as a whole an element of thermoelectric material in the form of a plate, that can be made in any known way and set between two pipes (or sections of pipe, as will be described in detail in what follows), which are designated, respectively, by 4 and 5 and, in the example illustrated, are each constituted by an extruded element of metal material with high thermal conductivity. As may be seen in the drawing, each pipe 4 has an outer wall defining two main plane and opposite faces 4a, 4b and, respectively, 5a and 5b, and two opposite longitudinal faces 4c, 4d and, respectively, 5c and 5d. The walls define a cavity of passage that is divided into a plurality of sub-channels 4e and 5e by a plurality of diaphragms 4f and 5f orthogonal to one another. The arrangement described above tends to provide a sort of hybrid between the two conventional solutions with gas-solid interface and solid-solid interface, illustrated in FIGS. 1 and 2. In other words, the thermoelectric generator according to the invention exploits the difference of temperature existing between two flows of fluid, but pre-arranges the diaphragms 4f and 5f in order to provide a very large heat-exchange surface that tends to bring the real temperature diagram Tr closer to the one illustrated in FIG. 2, instead of to the one illustrated in FIG. 1.
FIG. 4 illustrates a variant of FIG. 3, where each pipe or section of pipe 4, 5, instead of presenting the form of an extruded sectional element with the cavities of passage divided into a plurality of sub-channels, has only the outer walls 4a, 4b, 4c, 4d (and likewise 5a, 5b, 5c, 5d), the cavity of passage of the fluid being occupied by a porous material, designated as a whole by the reference number 6, such as for example a sponge made of material with high thermal conductivity (copper, aluminium, silicon carbide, etc.) in thermal contact with the outer walls mentioned above.
FIG. 5 illustrates a preferred embodiment, in which a thermoelectric generator is obtained, exploiting the scheme of FIG. 3, but dividing longitudinally both the pipe 4 for the first flow of fluid F1 and the second pipe for the second flow of fluid F2, as well as the layer of thermoelectric material 1, into a number of sections, each of which is respectively designated by 4, 5 and 1. The succession of sections 4 of the pipe for guiding the flow F1 and the succession of sections 5 of the pipe for guiding the flow F2 comprise, between each section and the other, a hollow spacer element 7 made of thermally insulating material (see FIG. 5A).
Furthermore, in the case of the embodiment illustrated in FIG. 5, each section 1 of the layer of thermoelectric material is separated from the contiguous one by a spacer element 8 made of thermally insulating material. Alternatively, it is also possible to provide simply an air gap, instead of the spacer 8.
Once again in the specific case of the embodiment illustrated in FIG. 5, each thermoelectric section 1 is made up of a plane distribution consisting of an array of a plurality of thermoelectric elements 9 connected electrically in series and thermally in parallel. The contacts of the thermoelectric cells can be connected to one another in series or in parallel.
The arrangement described above, with the division of the pipes into separate sections 4, 5 and spacer elements 7 made of thermally insulating material tends to guarantee that the heat transfer will occur only vertically (as viewed in the drawings) between facing sections 4, 5 through the corresponding thermoelectric sections 1, and there is instead substantially no heat transfer longitudinally along either of the two pipes for guiding the flows F1, F2.
FIG. 6 differs from FIG. 5 in that, in this case, the electric generator is associated to a combustion chamber 10 of any known type in such a way that the cold flow is constituted by the flow of fuel mixture at inlet to the combustion chamber 10, whilst the hot flow is constituted by the burnt gases at outlet from the combustion chamber 10. Of course, the combustion chamber is provided with means of any known type for triggering combustion in the combustion chamber 10. The combustion chamber 10 can also be obtained, according to known technologies, in the form of a combustion microchamber, for being integrated in a thermoelectric generator of reduced dimensions.
FIG. 7 is substantially similar to FIG. 5 and differs from this only in that the sections of pipe 4, 5 are arranged so as to guide respective flows of fluid F1 and F2 in directions orthogonal to one another.
FIGS. 8 to 11 illustrate further alternative configurations of an embodiment of the invention that envisages the use, as thermoelectric sections 1, of thermoelectric elements constituted alternately by elements of semiconductor material of type n and type p. In the case of said embodiment, the electrical contacts connected to the two opposite sides of each thermoelectric section 1 are constituted by the same sections of pipe 4, 5. In this case, the sections of pipe 4, 5 must necessarily be constituted by walls of electrically conductive material or in any case be coated with a layer of electrically conductive material.
In the case of FIG. 8, the sections of pipe 4, 5 are staggered with respect to one another in such a way that a single serpentine electrical circuit is obtained, which traverses the various thermoelectric sections 1 in succession.
FIG. 9 differs from FIG. 8 in that associated thereto is a combustion chamber 10, according to what has already been described above with reference to FIG. 6.
FIG. 10 differs from FIG. 8 in that therein the sections of pipe 4, 5 are set exactly facing and mating with one another. In this case, the electrical continuity through the various thermoelectric sections is ensured by electrical bridges that connect together in twos sections of pipe 4 that are adjacent to one another and sections of pipe 5 that are adjacent to one another. Preferably, said electrical bridges can be integrated in the spacer elements 7. For this purpose, some of the spacer elements 7 (drawn darker in FIG. 10) present the configuration that may be seen in FIG. 5A but are coated with a layer of electrically conductive material.
Finally, FIG. 11 differs from FIG. 10 only in that it envisages association of the thermoelectric generator to a combustion chamber 10, according to what has already been described above.
In all of the embodiments discussed above, the number of thermoelectric sections and of the sections of pipe can be any whatsoever. Furthermore, it is possible to envisage configurations different from the elongated rectilinear configuration, such as, for example, a configuration bent over a number of times on itself.
As already mentioned above, preferably the entire structure of the generator is insulated from the outside world with a layer of material with very low thermal conductivity, such as for example silica aerogel.
Furthermore, as also mentioned above, it is possible to envisage different materials for the different thermoelectric sections, according to the respective ranges of operating temperature, in order to obtain an optimal thermoelectric efficiency for each range of temperature.
In the embodiments that envisage it, the combustion chamber 10 described above can be replaced by any device capable of transferring solar energy to the incoming fluid in the form of heat, for example a device of the type usually referred to as “solar furnace”.
Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what is described and illustrated herein purely by way of example, without thereby departing from the scope of the present invention.
Patent Application
20080060695
