Abstract
The invention relates to a heating system (200) for heating of a fluid. The heating system comprises a supply connection (201) in fluid communication with a supply of fluid to be heated. It further comprises a structured body (108) arranged for heating of the fluid during use of the heating system. The structured body comprises a macroscopic structure (21) of electrically conductive material, the macroscopic structure comprising at least one channel (22) through which the fluid can flow. The heating system further comprises at least two conductors (103,114) configured to electrically connect the structured body to at least one electrical power supply. The at least two conductors are electrically connected to the structured body at a first end (204) and at a second end (205), respectively, of a conductive path within the structured body. The structured body is configured to direct an electrical current to run along the conductive path from the first end to the second end thereof. The electrical power supply is configured to heat at least part of said structured body to a temperature of below 400° C. by passing an electrical current through said structured body during use of the heating system.
Claims
1. A heating system for heating of a fluid, said heating system comprising: a supply connection in fluid communication with a supply of fluid to be heated; a structured body arranged for heating of said fluid during use of the heating system, said structured body comprising a macroscopic structure of electrically conductive material, the macroscopic structure comprising at least one channel through which the fluid can flow, at least one inlet port through which the fluid to be heated can flow from the supply connection and into the at least one channel, at least one outlet port through which heated fluid can flow out of the at least one channel, and at least two conductors configured to electrically connect the structured body to at least one electrical power supply, wherein the at least two conductors are electrically connected to the structured body at a first end and at a second end, respectively, of an electrically conductive path within the structured body, wherein the structured body is configured to direct an electrical current to run along the conductive path from the first end to the second end thereof, and wherein said electrical power supply is configured to be used to heat at least part of said structured body to a temperature of below 400° C. by passing an electrical current through said structured body during use of the heating system.
2. Heating system according to claim 1, wherein the macroscopic structure is a sintered or oxidized powder metallurgical structure.
3. Heating system according to claim 2, wherein the macroscopic structure is manufactured by a method comprising the following steps: preparing a paste by mixing at least: a powder comprising metal, a binder in an amount of 2 to 8 weight % of the paste, liquid, such as water, in an amount of 5 to 25 weight % of the paste, transferring the paste to an extruder, extruding the paste into a green body by using an extrusion pressure (P) of more than 50 bar, drying the green body, and sintering or oxidizing the dried green body to bond the powder together and thereby form the macroscopic structure.
4. Heating system according to claim 1, wherein the macroscopic structure has a varying electric resistivity in a direction extending from the inlet port to the outlet port.
5. Heating system according to claim 1, wherein the macroscopic structure has a varying electric resistivity transverse to a direction extending from the inlet port to the outlet port.
6. Heating system according to claim 4, wherein the varying electric resistivity has been obtained by a method of manufacturing comprising the following steps: preparing a plurality of pastes comprising: at least a first paste having a first composition, and at least a second paste having a second composition, transferring the plurality of pastes into a supply chamber of a processing equipment, shaping a green body from the plurality of pastes by forcing the pastes from the supply chamber through a die of the processing equipment, and sintering or oxidizing the green body to obtain the macroscopic structure having a varying electric resistivity along a longitudinal direction of the macroscopic structure, the longitudinal direction corresponding to the direction of movement of the pastes through the die, and the varying electric resistivity resulting from the first composition being different from the second composition.
7. Heating system according to claim 6, wherein: the first paste comprises metal powder with a first alloy composition, ceramic powder, and a first binder, the second paste comprises metal powder with a second alloy composition and a second binder, and wherein the first alloy composition and the second alloy composition both consist of at least one chemical element, and wherein the chemical elements are chosen so that, for each of the chemical elements being present in an amount higher than 0.5 weight % in each of the alloy compositions, that chemical element is comprised both in the first and second alloy composition, and for the chemical elements being present in the first alloy composition in amounts of up to 5.0 weight %, the amount of that chemical element differs by at most 1 percentage point between the first and second alloy compositions, and for the chemical elements being present in the first alloy composition in amounts of more than 5.0 weight %, the amount of that chemical element differs by at most 3 percentage point between the first and second alloy compositions.
8. Heating system according to claim 1, wherein the macroscopic structure comprises a plurality of longitudinally extending channels.
9. Heating system according to claim 1, wherein the macroscopic structure is made from a non-corrosive material or is provided with a coating, such as a coating of non-corrosive material, at least on surfaces being in contact with the fluid during use of the heating system.
10. Heating system according to claim 1, wherein the connections between the at least two conductors and the structured body are established by sintering.
11. Heating system according to claim 1, wherein the structured body is built-up of two or more macroscopic structures which have been mutually joined by an electrically conducting connection.
12. Heating system according to claim 11, wherein the macroscopic structure is a sintered or oxidized powder metallurgical structure wherein the macroscopic structures have been joined by sintering.
13. Heating system according to claim 1, wherein the first end and the second end of the electrically conductive path to which the at least two conductors are electrically connected are located at an end of the structured body comprising the inlet port.
14. Heating system according to claim 13, wherein: the conductors are arranged at opposite sides of the heating system and both extend in the same direction parallel to a longitudinal direction of the structured body, and the structured body comprises electrically insulating regions so that the conductive path runs in a meandering manner between the first end and the second end of the conductive path.
15. Heating system according to claim 1, further comprising an outer housing enclosing at least a part of the structured body and forming a fluid tight enclosure extending from the inlet port to the outlet port.
16. Method of heating a fluid to a temperature of below 400° C. by use of a heating system according to claim 1.
17. Method according to claim 16, wherein the fluid is a liquid, such as water, which is heated to a temperature of below 100° C., such as between 50 and 100° C., such as between 70 and 100° C.
18. Method according to claim 16, wherein the fluid, such as being a gas, is heated to a temperature of between 200 and 400° C., such as between 300 and 400° C.
19. Method according to claim 16, further comprising a step of transferring the heated fluid from the at least one outlet port to a storage for storing the heated fluid as an energy reservoir.
20. Heating system according to claim 3, wherein the macroscopic structure is a sintered or oxidized powder metallurgical structure, and wherein the macroscopic structure has a varying electric resistivity in a direction extending from the inlet port to the outlet port.
Description
BRIEF DESCRIPTION OF THE FIGURES
[0105] The heating system according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.
[0106] FIG. 1 shows schematically a heating system according to the present invention.
[0107] FIG. 2 shows schematically examples of possible designs of the structured body of the heating system.
[0108] FIG. 3 is a flow-chart of some of the steps of a possible method of manufacturing a macroscopic structure for use in a heating system.
[0109] FIG. 4 shows schematically a processing step of a possible method of manufacturing a macroscopic structure for use in a heating system.
[0110] FIG. 5 shows schematically a macroscopic structure having a varying electric resistivity in a direction extending from the inlet port to the outlet port.
[0111] FIG. 6 shows schematically a method of manufacturing the macroscopic structure in FIG. 5.
[0112] FIGS. 7 to 10 show schematically cross-sectional views of different embodiments of a heating system according to the present invention.
[0113] FIG. 11 shows schematically how a system according to the present invention provides for a more uniform temperature distribution than a known system.
DETAILED DESCRIPTION OF AN EMBODIMENT
[0114] FIG. 1 shows schematically an embodiment of a heating system 200 for heating of a fluid. The heating system 200 comprises a supply connection 201 in fluid communication with a supply of fluid to be heated (not shown). The supply of fluid can be a part of the heating system 200 or an external supply. A structured body 108 is arranged for heating of the fluid during use of the heating system 200. The structured body 108 comprises a macroscopic structure 21 of electrically conductive material. In some embodiments of the invention, the macroscopic structure 21 forms all of the structured body 108. The macroscopic structure 21 comprises at least one channel 22 through which the fluid can flow. In the illustrated embodiment, there are a plurality of parallel channels 22. The heating system 200 comprises an inlet port 202 through which the fluid to be heated can flow from the supply connection 201 and into the channels 22 and an outlet port 203 through which heated fluid can flow out of the channels 22. Conductors 103, 114 electrically connect the structured body 108 to an electrical power supply (not shown).
[0115] The conductors 103, 114 are electrically connected to the structured body 108 at a first end 204 and at a second end 205, respectively, of a conductive path within the structured body 108. In the illustrated embodiment, the conductive path runs from an upper end of the structured body 108 to a lower end of the structured body 108. In other embodiments, the conductive path runs in different ways as will be exemplified in FIGS. 7 to 10. The structured body 108 is configured to direct an electrical current to run along the conductive path from the first end 204 to the second end 205 thereof. The electrical power supply is used to heat at least part of said structured body 108 to a temperature of below 400° C. by passing an electrical current through said structured body 108 during use of the heating system 200. In the embodiment illustrated in FIG. 1, the heating system 200 is provided with gaskets 206 at the inlet port 202 and at the outlet port 203 to ensure a fluid tight connection to a pipe 207 through which the fluid to be heated flows into the system and to a pipe 208 through which the heated fluid flows out of and away from the heating system 200. The resistance of the structured body is a function of the electric resistivity, the cross sectional area perpendicular to the current, and the length of the current path, and it can be determined using Ohm's law. In more advanced cases, finite element analysis can be used to calculate the current given the electrical potential (voltage) or vice versa. Having both the current and voltage, the resistance is voltage divided by current. These parameters can be used in the design of the heating system for a given application; i.e. for a given fluid, flow rate etc. Having the resistance, a suitable power supply can be found. The power from the supply is voltage times current. The necessary power for heating the fluid is calculated using thermodynamics.
[0116] The heating system 200 as shown in FIG. 1 comprises an outer housing 209 enclosing the structured body 108 and forming a fluid tight enclosure extending from the inlet port 202 to the outlet port 203. In alternative embodiments (not shown), the structured body 108 has a design so that it in itself comprises an outer circumferential wall which provides a fluid tight barrier towards the exterior, the fluid tight barrier extending from the inlet port to the outlet port. The outer housing 209 as shown in FIG. 1 may also be provided with a surrounding outer electrically insulating covering and/or thermally insulating covering. Such a covering could e.g. be an integrated part of the outer housing 209.
[0117] As mentioned above, a heating system 200 according to the present invention may e.g. be used for heating of portable water, disinfection of water, evaporation of liquids i.e. making steam, and heating of steam.
[0118] The macroscopic structure 21 may be a sintered powder metallurgical structure. FIG. 2 shows schematically examples of possible designs of the structured body of the heating system. In FIGS. 2.a and 2.b, the structured body comprises one macroscopic structure 21, and in FIGS. 2.c and 2.d, the structured body 108 comprises two macroscopic structures 21 which have been joined in a manner which ensures that they form a coherent conductive path. FIG. 2.a shows a macroscopic structure 21 having one longitudinally extending channel 22, and FIG. 2.b shows a macroscopic structure 21 having a plurality of longitudinally extending internal channels 22 which are arranged in a regular pattern separated by walls 23. FIG. 2.c shows an embodiment wherein two macroscopic structures 21 in the form of block-shaped elements comprising longitudinally extending channels 22 are arranged next to each other side by side so that the structured body 108 has a number of channels 22 which is a sum of a number of channels 22 in the first macroscopic structure 21 and a number of channels 22 in the second macroscopic structure 21. FIG. 2.d shows another embodiment wherein the two macroscopic structures 21 are arranged so that the channels 22 of the macroscopic structures 21 are in continuation of each other. The macroscopic structures 21 in FIGS. 2.c and 2.d may have been joined by sintering in a manner that ensures a coherent electrically conductive structure.
[0119] Experiments performed during the development work leading to the present invention have shown that it is possible to manufacture macroscopic structures 21, wherein walls 23 forming the longitudinally extending internal channels 22 have a wall thickness of between 0.25 and 2 mm, such as between 0.25 and 1 mm, such as between 0.25 and 0.5 mm. In the embodiments shown in FIG. 2, the cross-sectional shape of the channels is quadratic, but any shape that is possible to manufacture, e.g. by extrusion, is covered by the scope of the present invention. The cross-sections of the channels may e.g. be circular or hexagonal. The outer geometry of the macroscopic structure may also differ from the ones shown in this and the following figures. It may e.g. be circular, hexagonal, or rectangular.
[0120] The macroscopic structure 21 can be manufactured by a method having the first steps that are shown as a flow-chart in FIG. 3. A paste 10 is prepared by first mixing a powder 11 and a binder 12 in an amount of 2 to 8 weight % of the paste 10. The powder 11 comprises metal and may also comprise ceramic. The liquid is in the following described as being water 13, but other liquids may also be used as mentioned above. It is added in an amount of 5 to 25 weight % of the paste 10. In the illustrated embodiment, the adding of water 13 and kneading to obtain a homogenous paste is performed in a kneader 30, such as a Z-blade kneader or sigma blade kneader. The prepared paste 10 is then transferred to an extruder 31, where it is extruded into a green body 20 as shown schematically in FIG. 4. This step is preferably performed by using an extrusion pressure P of more than 50 bar. In some embodiments of the invention, the extrusion pressure P is between 50 and 500 bar, such as between 50 and 200 bar, preferably between 60 and 160 bar. The green body 20 is then dried and sintered in order to obtain the final macroscopic structure to establish the macroscopic structure of a heating system, such as the one in FIG. 1.
[0121] The macroscopic structure 21 may have a varying electric resistivity in a direction extending from the inlet port 202 to the outlet port 203; see FIG. 1. FIG. 5.a shows schematically an example of such a macroscopic structure 21 which has four regions 21a, 21b, 21c, 21d with different resistivities along the longitudinal direction of the macroscopic structure 21. FIG. 5.b shows a curve of the electric resistivity p as a function of position along the length X of the macroscopic structure 21 in FIG. 5.a. In this illustrated embodiment, the electric resistivity varies in steps and with a constant increase rate in the narrow regions around the borders between the different regions 21a, 21b, 21c, 21d. FIG. 5.c shows schematically an example of what could be an ideal curve for a given application of the heating system where a smooth change in electric resistivity p would be desired. FIG. 5.d shows an example of an actual curve for a macroscopic structure to be used in the application having the ideal curve as in FIG. 5.c.
[0122] The macroscopic structure 21 in FIG. 5 can be prepared as shown schematically in FIG. 6. FIG. 6.a shows the step of preparing a first paste 10a having a first composition, and a second paste 10b having a second composition. The first and second pastes 10a, 10b are then transferred into a supply chamber 35 of a processing equipment 31, which in FIG. 6.b is schematically shown as a piston extruder. The pastes 10a, 10b are forced from the supply chamber 35 through a die 32 of the processing equipment 31 to result in a green specimen 20 as shown in FIG. 6.c. By moving the piston 36 towards the die 32 at a constant speed, the green body 20 is formed by continuously forcing the pastes 10a, 10b through the die 32. As shown for this embodiment, the order in which the pastes 10a, 10b are transferred into the supply chamber 35 corresponds to the longitudinal direction of the macroscopic structure 21 being manufactured. After this shaping, and possibly a further step of drying, the green body is sintered to obtain the macroscopic structure 21 having a varying electric resistivity along a longitudinal direction thereof. As seen from FIG. 6, the longitudinal direction of the macroscopic structure 21 corresponds to the direction of movement of the pastes 10a, 10b through the die 32, and the varying electric resistivity p results from the first composition being different from the second composition.
[0123] In preferred embodiments of the invention, the first paste 10a comprises metal powder with a first alloy composition, ceramic powder, and a first binder. The second paste 10b comprises metal powder with a second alloy composition and a second binder. The first alloy composition and the second alloy composition both consist of a plurality of chemical elements. Each of the metal powders of the first paste 10a and of the second paste 10b may comprise one or more of the following chemical elements: iron, chromium, aluminium, cobalt, nickel, manganese, molybdenum, vanadium, and silicon. Examples of alloys that have been used in the development work leading to the present invention are FeCrAl, TWIP, 316L, and 17-4PH. However, the invention can be used for many other alloys.
[0124] The second paste 10b typically also comprises a ceramic powder. The ceramic powder used for the first and second compositions typically comprises one or more of the following: Alumina, Zirconia, Boron Nitride, Cordierite, and Silicon Nitride. In embodiments comprising ceramic powder, the different resistivities p in the pastes 10a, 10b are typically obtained by varying one or more of the following parameters: [0125] the volume ratio between the metal powder and the ceramic powder, [0126] the size of the ceramic particles, [0127] the shape of the ceramic particles, and [0128] the type of the ceramic material.
[0129] FIG. 7 shows schematically a cross-sectional partial view of an embodiment of a heating system 200 according to the present invention. In this and the following embodiments, the heating system 200 is symmetrical, and the axis of symmetry is marked as number 101. The description will be given with reference to structured bodies 108 having a circular cross-section. However, similar details as shown in these figures could also be used for non-symmetrical designs of the heating system. The structured bodies 108 in FIGS. 7 to 10 are shown as one unit which could be either one macroscopic structure 21 or be assembled from a plurality of macroscopic structures 21, such as e.g. shown in FIG. 2.c. The heating system 200 in FIG. 7 is illustrated as having a first conductor 103 connected to the structured body 108 at an upper end (with respect to the figure) via an electrically conducting ring 107 that extends circumferentially around the structured body 108. The first conductor 103 is marked as being connected to the positive pole (marked as +) of the power supply. Furthermore, the heating system 200 has a second conductor 111 connected to the structured body 108 at a lower end (with respect to the figure) also via an electrically conducting ring 107 that extends circumferentially around the structured body 108. The second conductor 111 is connected to ground, marked as GND. In this embodiment, the second conductor 111 also forms a bottom flange used for the mounting of the heating system 200, e.g. to a carrying frame. The heating system 200 may comprise more connectors than the ones shown in the figures, such as connectors arranged symmetrically to the illustrated ones. The electrical connections between the conductors 103, 111 and the conducting rings 107 as well as between the conducting rings 107 and the structured body 108 may be established by any joining method that ensures an electrically conducting joint, such as by laser welding, arc welding, soldering, brazing, or sintering. A better connection may be established by additionally applying a pressure. The heating system 200 in FIG. 7 further comprises a top flange 102, which may be used for mounting of the heating system 200. The fluid may be led to and from the heating system 200 directly via the top and bottom flanges 102, 111 being in the form of tubes. Alternatively, the heating system 200 comprises additional tubes through which the fluid flows and to which the heating system is connected. In the embodiment in FIG. 7, O-rings 104 are arranged above and below the first conductor 103 to provide electric insulation as well as sealing. The O-rings 104 are arranged in engagement with horizontally extending parts of the top flange 102 and of the bottom flange 111. The heating systems shown in FIGS. 7 to 10 also comprise contact points marked as 105, 109, and 110. They could e.g. be established by welding, soldering, brazing, thermal spraying, or sintering. For some designs of the system, it may also be sufficient to obtain the necessary contact by ensuring that a mechanical pressure is applied and maintained during use of the system. Such a pressure might e.g. be obtained by the bolts and nuts used for the assembly of the components.
[0130] FIG. 8 shows schematically a cross-sectional partial view of another embodiment of a heating system 200 according to the present invention. Similar numbers are used in FIG. 8 for similar components as in FIG. 7; the description thereof will not be repeated. In FIG. 8, the first conductor 103 extends upwards between two parts of the top flange 102. The horizontally extending part of the top flange 102 is connected to the bottom flange 111 by use of a bolt-and-nut connection. In this embodiment, O-rings 104, 112 are arranged on both sides of the first conductor 103 as well as between the top flange 102 and the bottom flange 111. The upwardly extending part of the top flange 102 may be a pipe forming the supply connection 201 through which the fluid is led from the fluid supply an into the heating system 200 via the inlet port 202.
[0131] FIG. 9 shows schematically a cross-sectional partial view of another embodiment of a heating system 200 according to the present invention. In this embodiment, a second conductor 114 (marked with —) forms the electrical connection to the negative pole of the power supply. The conductors 103, 114 are electrically connected to the structured body 108 as described above. The two conductors 103, 114 of this embodiment are provided with outer threading engaged with nuts so that they are used for the mounting of the heating system 200 as shown in the figure. O-rings 112, 113 are arranged around the conductors 103, 114 to form the electrical insulation and sealing thereof.
[0132] FIG. 10 shows schematically a cross-sectional view of another embodiment of a heating system 200 according to the present invention. In this embodiment, the conductors 103, 114 establishing the connections to the positive and negative poles of the power supply are arranged at opposite sides of the heating system 200 and both extend upwards. The structured body 117 comprises electrically insulating regions 116 so that the conductive path runs in a meandering manner between the first end and second end 106 of the conductive path. The electrically insulating regions 116 may e.g. be formed by ceramic material, polymer material, or air gaps. Such a structured body 117 may e.g. be established by cutting slots in one macroscopic body 21, or it may be established by assembly of a plurality of macroscopic bodies 21. By a design of the heating system as exemplified in FIG. 10, the conductors 103, 114 can be arranged at the end of the structured body where the fluid to be heated flows into the at least one channel via an inlet port, i.e. the end where the fluid has not yet been heated by the heating system. By designing the structured body 117 so that the conductive path runs in a meandering manner between the first and second ends of the conductive path, a better utilization of the heating capacity of the whole volume of the macroscopic structure is obtained, because of the use of a larger surface area to establish the interface between the macroscopic structure and the fluid to be heated.
[0133] FIG. 11 illustrates schematically one of the advantages of a heating system according to the present invention, namely that the temperature is more homogeneous over the whole cross-section of the heat providing element than what would be the case for a system based on an external heating source arranged next to the heat providing element. The left system in FIG. 11 is a known system with an external heating source schematically illustrated as electrical coils 250. The heat providing element is the structured body 108 through which the fluid to be heated flows. The bold curve illustrates a typical temperature curve for such a system; i.e. a lower temperature in the central region of the structured body 108 than near the edges. The left system is a system according to the present invention, wherein the heating is provided via the structured body 108, i.e. across the whole cross-section. This results in a temperature curve, shown as the bold line, which is much closer to a desired temperature, shown as a dotted line.
[0134] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. Furthermore, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.
