Device for Ohmic Heating Fluids

Abstract

A heater for heating a conductive liquid includes a two-dimensional array of parallel rod-shaped electrodes (22, 122, 322, 422, 522), a power supply with multiple poles, and a power switch for connecting different electrodes to different poles, such that current flows through the liquid between the electrodes. The array preferably includes outer electrodes defining the boundaries (24, 424) of the array and inner electrodes disposed within these boundaries. The array can have regular or irregular spacing between the electrodes. The array can provide a variety of different connection schemes to vary the resistance between the poles, thereby changing the heating rate. The array can be arranged to provide substantially equal current through the three poles of a three-phase power supply.

Description

[0001] Cross-references to related applications

[0002] This application is a partial continuation of U.S. Patent Application No. 16 / 346,354, filed April 30, 2019, which is the national phase of PCT International Application No. PCT / US2017 / 060192, filed November 6, 2017, which in turn claims the benefits of U.S. Provisional Patent Application No. 62 / 458,201, filed February 13, 2017, and U.S. Provisional Application No. 62 / 418,493, filed November 7, 2016, the disclosures of which are incorporated herein by reference. Background Technology

[0003] This disclosure relates to an ohmic fluid heating device and a method for heating a fluid. The ohmic fluid heater can be used to heat conductive fluids, such as drinking water. Such a heater typically includes multiple electrodes spaced apart from each other. These electrodes are in contact with the fluid to be heated, such that the fluid fills the space between adjacent electrodes. Two or more electrodes are connected to a power source, such that different potentials are applied to the different electrodes. For example, when operating the ohmic heater using a common alternating current power source (e.g., power available from a household electrical outlet), at least one electrode will be connected to a pole with an alternating potential, while at least one other electrode will be connected to the opposite pole with a neutral or grounded pole. Current flows through the fluid in at least one space between the electrodes, and electrical energy is converted into heat energy through the resistance of the fluid.

[0004] Controlling the rate at which electrical energy is converted into heat energy in a heater (the heating rate) is desirable to ensure the heated fluid reaches the desired temperature. Researchers have proposed altering the heating rate by mechanically moving electrodes closer together, thereby changing the resistance between them. However, this arrangement requires complex mechanical components, such as moving parts exposed to the fluid. Furthermore, it is difficult to make such a mechanical structure respond quickly to rapidly changing conditions. For example, if an ohmic heater is used in a "sudden heating" arrangement to heat water supplied to bathroom fixtures such as shower heads, water continuously flows directly into the fixture through the heater while it is in use. If the user (e.g., by opening a valve on the fixture) suddenly increases the water flow rate, the heater should react rapidly to increase the heating rate, thereby maintaining the water supplied to the fixture at a substantially constant temperature.

[0005] An ohmic heater with a power switch and a large number of electrodes is also proposed to selectively connect different electrodes to the poles of a power source. For example, the electrode array can be arranged linearly with spaces between the electrodes. The array includes two electrodes at the ends of the array and multiple intermediate electrodes between the two end electrodes. To provide a minimum heating rate, the end electrodes are connected to the opposite pole of the power source, and the intermediate electrodes are isolated from the power source poles. Current flows from one end electrode through fluid in a first space to the nearest intermediate electrode, then through fluid in the next space to the next isolated electrode, and so on, until it reaches the last intermediate electrode and flows from the last intermediate electrode to the other end electrode. Thus, the fluid in all spaces is electrically connected in series between the two end electrodes. This connection scheme provides high resistance and a low heating rate between the poles of the power source.

[0006] For maximum heating rate, all electrodes are connected to poles such that each electrode is connected to the opposite pole of its next nearest neighbor. In other words, spare electrodes are connected to the hot and neutral poles. In this configuration, the fluid in each space is directly connected between the poles of the power source and in parallel with the fluid in each of the other spaces. This connection scheme provides minimal resistance between the poles. Intermediate heating rates can be achieved by connecting various electrode combinations to the poles of the power source. For example, in one such connection scheme, two of the intermediate electrodes are connected to the opposite poles of the power source, and the remaining electrodes are electrically isolated from the poles of the power source. The connected intermediate electrodes are separated from each other by some other intermediate electrodes and spaces, such that the fluid in only a few spaces is connected in series between the poles. This connection scheme provides a higher resistance between the poles than in the maximum heating rate scheme but lower than in the minimum heating rate scheme. For fluids with known conductivity, different connection schemes will provide different resistances between the poles, thus providing different heating rates. Because the resistance of a known connection scheme decreases with increasing conductivity, the parameter referred to herein as “specific resistance” is used in this disclosure to characterize a circuit or part of a circuit having elements electrically connected by fluids. Specific resistance is the ratio of the resistance of a circuit or part of a circuit to the resistivity of the fluid in the circuit.

[0007] Typically, the switch is an electrically controllable switch, such as a semiconductor switching element (e.g., a thyristor). This type of ohmic heater can quickly switch between connection schemes, thus enabling switching between different heating rates. This type of heater does not require any moving parts in contact with the fluid to control the heating rate. However, this type of ohmic heater can only select from a set of resistivities determined by the physical configuration of the electrodes, thus incrementally selecting the heating rate. Under certain conditions, the available heating rate may not match the heating rate required to produce the desired fluid temperature. These drawbacks become more pronounced for heaters used under a range of different conditions, such as fluids with significantly different conductivity, different flow rates of the fluid passing through the heater, different fluid inlet temperatures, and different fluid outlet temperatures. For example, if the heater provides a set of different resistivities between the highest and lowest resistivities, only a small subset of the usable resistivities will be available for regulating the temperature of a particular fluid, where the highest resistivity enables a low heating rate with a fluid having relatively high conductivity, and the lowest resistivity enables a high heating rate with a fluid having low conductivity. Adding more electrodes increases the cost and size of the heater. Furthermore, additional electrodes can create redundant connection schemes, allowing different connection schemes to provide the same specific resistance between the poles of the power supply. In this case, additional electrodes offer no advantage.

[0008] One solution to this problem is disclosed in U.S. Patents 7,817,906 and 8,861,943, the disclosures of which are incorporated herein by reference. As disclosed therein, arranging electrodes in a manner with non-uniform resistivity between adjacent electrode pairs, such as non-uniform spacing, enables the provision of an ohmic heater suitable for operation under a wide range of conditions. Ideally, the resistivity between adjacent electrode pairs is chosen such that, for a given fluid conductivity, the available power levels using different connection schemes encompass a series of non-redundant resistivityes extending over a very wide range. For example, such a heater can provide a resistivity of 60 or greater in a substantially logarithmic series, i.e., a series of resistivityes, such that the ratio between each resistivity and the next lower resistivity is substantially constant. This arrangement provides an efficient solution that has been commercially used in demanding applications, such as instantaneous heaters for domestic hot water.

[0009] However, further improvements are still needed. For example, electrodes in the form of conductive plates have been used in commercial implementations of the heaters disclosed in the aforementioned '706 and '943 patents. These electrodes are arranged within an insulating housing such that the plates subdivide the interior of the housing into channels. The housing includes pathways to guide fluid through these channels. While this arrangement works well for medium-sized, mass-producible heaters (e.g., domestic water heaters for private residences or apartments), it is not the optimal choice for large industrial and commercial heaters. Such heaters are typically made to custom dimensions to fit the application. The cost of designing and manufacturing complex insulating housings to accommodate the specific electrode setup required for a custom arrangement can be substantial. Furthermore, if the components are subjected to conditions such as extreme pressure and temperature that may be encountered in industrial and commercial heaters, the components may be damaged and may be difficult to repair or replace. Attached Figure Description

[0010] Figure 1 This is a cross-sectional schematic diagram of a heater according to an embodiment of the present invention;

[0011] Figure 2 Yes Figure 1 A schematic diagram of the circuit in the heater;

[0012] Figure 3 This is a perspective view of a heater according to another embodiment of the present invention;

[0013] Figure 4 yes Figure 3 A partial sectional view along line 4-4;

[0014] Figure 5 This is a cross-sectional schematic diagram of a heater according to another embodiment of the present invention;

[0015] Figure 6 This is a cross-sectional schematic diagram of a heater according to another embodiment of the present invention;

[0016] Figure 7 This is a schematic diagram of a circuit according to another embodiment of the present invention;

[0017] Figure 8 Is with Figure 7 A cross-sectional view of a heater used in conjunction with the circuitry;

[0018] Figure 9 , 10 11 and 12 are shown Figure 8 A schematic diagram of some connection modes used in the operation of the heater;

[0019] Figure 13 This is a schematic diagram of an electrode array in a heater according to another embodiment of the present invention. Detailed Implementation

[0020] A heater according to one embodiment of the present invention includes a housing 20 and a plurality of rod-shaped electrodes extending within the housing in the plane of the figures, the electrodes being arranged in an irregular two-dimensional array. Figure 1 As shown, these electrodes are cylindrical, therefore, as Figure 1 The cross-section shown in the diagram indicates that these electrodes are circular. In this irregular array, each electrode has multiple adjacent electrodes. For example, electrodes 22a, 22b, 22c, and 22d are all adjacent to electrode 22e. Unless otherwise stated, the position of a rod-shaped or cylindrical electrode as used herein refers to the position of the electrode's axis. Electrodes 22b, 22c, 22d, 22f, and 22g are referred to herein as "outer electrodes" because they collectively define the outer boundary 24 of the array. As mentioned in this disclosure, the outer boundary 24 of the array is a polygon formed by the shortest possible combination of imaginary straight lines, such that the axes of all electrodes lie within or on the outer boundary, wherein the imaginary straight lines extend between the axes in a plane perpendicular to the axis 26 of some of the electrodes 22. In contrast, electrodes 22e, 22a, and 22h are referred to herein as inner electrodes because their axes 26 lie within but not on the outer boundary 24.

[0021] exist Figure 1 In the irregular array shown, the electrodes are spaced at many different distances from each other. Figure 1 The array is two-dimensional and irregular because... Figure 1 In the diagram, the spacing between the axes of the electrodes is represented by arrows X and Y in two directions perpendicular to the axis of the electrode.

[0022] The heater includes circuitry (such as...) Figure 2As shown, the circuit includes a power supply 36 with two conductors, 38 and 40. These conductors are connected to a power source (e.g., a utility power supply). These conductors are arranged such that different potentials can be applied to electrodes 38 and 40 during operation. For example, electrode 40 may be a neutral conductor receiving a neutral voltage, typically close to ground, while electrode 38 may be a “thermal conductor” for receiving an AC voltage supplied by a utility power supply. This particular power supply is a single-phase power supply because only one AC voltage is used. A power switch 48 is connected between electrodes 22 and power supply 36, and power switch 48 is arranged such that each electrode can be connected to one of electrodes 38 and 40 or isolated from the electrodes. As used in this disclosure, the term “switch” includes mechanical switches that can be manually actuated or actuated by a device such as a relay, and also includes solid-state devices that can be actuated to switch between a non-conductive state with very high impedance and a conductive state with very low impedance. Examples of solid-state switches include elements such as triacs, MOSFETs, thyristors, and IGBTs. In the specific arrangement described, two separate unipolar switches are associated with each electrode 22, each switch being operable such that the associated electrode is connected to a different pole, and the electrode is isolated from both poles when both switches are open. However, this arrangement can be replaced by any other electrically equivalent switch arrangement.

[0023] In operation, a conductive fluid, such as a conductive liquid like drinking water, flows through the housing 20, filling the space within the housing and contacting the surfaces of the electrodes 22. One or more electrodes 22 are connected to the hot electrode 38 via a power switch 48, while one or more electrodes 22 are connected to the neutral electrode 40, allowing current to flow between the different electrodes through the fluid contained within the housing. The current varies inversely proportional to the resistance between the electrodes. The resistance between the electrodes depends on the specific resistance of all current paths, which are formed in parallel by the fluid connecting the pairs of electrodes to the different poles. Furthermore, in this arrangement, there are conductive paths through the fluid between a given electrode and each of the alternate electrodes. For example, if only electrodes 26c and 22g are connected to opposite poles, current will flow between these electrodes. Because other electrodes, such as electrodes 22e and 22h, are positioned in the current flow path, and these electrodes are conductive, some current will flow through them, and the resistivity of the current path between electrodes 22c and 22b will be significantly different from the hypothetical system without electrodes 22e and 22h. If only adjacent electrodes 22c and 22b were connected to opposite poles, current would flow between these electrodes. Current flows through all the fluid within the chamber, but the main flow path lies near the straight line connecting the two electrodes. Therefore, the presence of other electrodes (such as electrode 26e) will affect the current to some extent, but this effect is small compared to the effect of electrodes 22e and 22h in the previous example. Because the distances between different electrodes through the fluid are different, and the effects of other electrodes are also different, the resistivity between two electrodes in different pairs is different. In this respect, the internal electrodes help to provide a wide range of resistivity between poles 38 and 40, which can be formed by connecting different electrodes to the poles, thus allowing the heater to provide a wide range of heating rates and a large number of different heating rates within this range. This wide range of heating rates can be provided in a compact unit. In particular, the component can be compact in its dimensions transverse to the axis of the electrode. This is especially ideal when the liquid to be heated is under pressure, necessitating that the housing containing the electrode be a pressure vessel. The cost and weight of the pressure vessel walls required to withstand a given pressure increase with increasing vessel cross-sectional dimensions.

[0024] The heater discussed above also includes optional control circuitry 56 (such as...). Figure 2(As shown). Although specific control circuitry is shown and discussed herein, it should be understood that the heater can be controlled by a manual control switch, and the control circuitry is optional. Specific control circuitry 56 includes a control processing unit 58 and one or more sensors for detecting one or more operating parameters of the heater. In one example, one or more sensors may consist only of an outlet temperature sensor (not shown), which is physically mounted in or near the outlet of housing 20 to detect the temperature of the fluid discharged from the heater. The temperature sensor may include conventional elements such as one or more thermocouples, thermistors, and resistive elements whose resistance changes with temperature. Control processing unit 58 is connected to power switch 48 such that control processing unit 58 can actuate the switch to provide the various connection schemes discussed. Control processing unit may include memory 70, such as non-volatile memory, random access memory, or other conventional storage elements. The memory ideally stores at least some data of the various connection schemes obtainable through the operation of the switch. Data in the table for each connection scheme may include settings for each power switch 48 to form a specific connection scheme, as well as data explicitly or implicitly specifying the stored connection schemes sorted by their specific resistance. For example, the data for each connection scheme could include the specific resistance between the poles of that connection scheme, or equivalent data (such as the resistance or conductivity values ​​of the various connection schemes), all of which are measured or calculated for a space filled with a fluid of a given conductivity. Alternatively, the explicit data might simply be the ordinal number of each connection scheme. In the example of implicit ordering, data specifying the switching settings for each connection scheme could be stored at addresses in memory, such that the data at the least significant address specifies the switching setting for the connection scheme with the lowest specific resistance, the data at the next least significant address specifies the data for the connection scheme with the next lowest specific resistance, and so on.

[0025] The control processing unit 58 also includes a logic unit 72 connected to the memory 70. The logic unit has one or more conventional driver circuits (not shown) connected to the output of the power switch 48, for example, by means of a driver circuit configured to convert signals provided by the logic unit into appropriate voltages or currents to drive a switch. The logic unit may include a general-purpose processor, hard-wired logic circuitry, a programmable gate array, or any other logic element capable of performing the operations discussed herein, programmed to perform the operations discussed herein. Although the term "unit" is used herein, this does not require that the elements constituting a unit be located in separate locations. For example, portions of the control processing unit or portions of the logic unit may be located in physically separate locations and may be operatively connected to each other via any communication medium.

[0026] In operation, the control processing unit can initiate heater operation by retrieving switch setting data for the connection scheme with the highest specific resistance (lowest heating rate) and setting the switch accordingly, thus setting that connection scheme as the first one in use. After startup, the control processing unit periodically compares the fluid outlet temperature determined by the outlet temperature sensor with the set temperature. If the outlet temperature is lower than the set point temperature by a preset tolerance, the control processing unit retrieves switch setting data for a connection scheme with a lower specific resistance than the currently used connection scheme to provide a higher heating rate and sets the switch accordingly. This process is repeated cyclically until the outlet temperature reaches the set point. If the outlet temperature is higher than the set point by a preset tolerance, the control processing unit selects a connection scheme with a higher specific resistance in the next cycle to reduce the heating rate. In this way, the control circuit eventually stabilizes at a certain heating rate that allows the fluid to reach the desired output temperature. Ideally, the control system actuates the switch to change the control scheme when the AC voltage applied to the hot electrode 38 of the power supply is zero or close to zero. This zero-crossing period occurs twice in each cycle of the conventional AC waveform. This setup minimizes the generation of switching transients and electrical noise. In some other embodiments, the control logic can use the measured current between the electrodes and the measured flow rate of the liquid to determine the predicted temperature increase within the heater, and add the predicted temperature increase to the measured inlet temperature of the liquid entering the heater to reach the predicted outlet temperature. If the predicted outlet temperature is lower than the setpoint temperature by more than a preset tolerance, the control logic switches to a connection scheme with lower specific resistance to increase the current. If the predicted outlet temperature is higher than the setpoint temperature, the control logic takes the opposite action.

[0027] The heater circuit may optionally include one or more shunt buses 52 and shunt switches 50, which are operable to connect each electrode to one or more shunt buses and disconnect each electrode from one or more shunt buses. Each shunt bus can be used to establish a low-resistance conductive path between any two electrodes not connected to a pole. In the example above, only electrodes 22c and 22g are connected to opposite poles of the power supply; the other electrodes are disconnected from the poles of the power supply and also from the shunt buses, resulting in a relatively high specific resistance of the current path. However, if electrodes 22h and 22e are both connected to shunt buses, the conductive path will be a combination of two parallel paths: a first path, as described above, directly from electrode 22c to electrode 22g, and a second path, from electrode 22c to electrode 22e, through the shunt bus to electrode 22h, and from electrode 22h to electrode 22g. Because shunt switches 50 and shunt buses 52 have very low impedance, the path through electrodes 22e and 22h, as well as the shunt buses, will dominate. In this case, the specific resistance between electrodes 22c and 22g will be much lower. When a shunt bus is included, additional connection schemes with different specific resistances are provided. These additional connection schemes are included in data specifying various connection schemes and their specific resistances stored in the memory 70 of the control processing unit 58, and the control processing unit is connected to the shunt switch 50, thereby enabling the control processing unit to open and close the shunt switch as needed.

[0028] Rod-shaped electrodes greatly simplify the structure of the heater. For example, as... Figure 3 As shown, the housing can be an elongated hollow body 102 having a pair of end walls 104 and 106. A cylindrical electrode 122 extends through a hole 108 in the end wall 104. Figure 4 Although in order to clearly explain in Figure 3Only two cylindrical electrodes 122 are depicted, but in reality, the electrode array ideally comprises multiple electrodes extending parallel to each other and parallel to the elongation axis 110 of the body 102. The electrodes can be easily positioned in any desired array by forming holes 108 in a desired configuration, which facilitates the customization of heaters for specific applications. No complex baffle system is required to guide fluid through separate pathways between the electrodes. The end walls of the hollow body can be constructed of insulating materials (such as polymers) or conductive materials (such as metals) and are equipped with insulating sleeves (not shown) within the holes 108. The exposed ends 125 of the electrodes can be easily connected to a circuit. Individual electrodes passing through the end walls can be secured and sealed to the end walls using any known techniques typically used to secure elements such as tubes passing through walls. For example, the seal can be formed by an O-ring 126 located in a groove 128 on the electrode, and the electrode can be secured by engaging a thread (not shown) on the electrode with a corresponding thread (not shown) in the hole 108. The electrodes can be easily disassembled, serviced, or replaced as needed. An inlet (not shown) and an outlet (not shown) are provided in opposite end walls 104 and 106 so that fluid flows through the interior of the heater.

[0029] like Figure 5 As shown, a heater according to another embodiment of the present invention includes entry and exit points. Figure 5 The accompanying figure shows an array of rod-shaped electrodes 322 extending parallel to each other in the plane direction. In this embodiment, the array is partly regular and partly irregular. Electrodes are arranged in columns 301 extending in the direction indicated by arrow "Y" and in rows extending in the direction indicated by arrow "X" and perpendicular to the direction Y, both directions being perpendicular to the axis of the electrodes. For example, electrodes 322aa, 322ab, and 322ac constitute column 301a, while electrodes 322aa, 322ba, 322ca, 322da, and 322ea constitute row 303a. The electrodes in each row are arranged at the same position in the Y direction, and the electrodes are regularly spaced apart from each other in the Y direction such that the distance between adjacent rows 303 in the Y direction is equal. The electrodes in each column are arranged at the same position in the X direction. However, the distance C between adjacent columns is not equal, so that the columns are irregularly spaced apart from each other in the X direction. For example, the distance C between columns 301a and 301b is... ab It must be greater than the distance C between columns 301b and 301c. bc .exist Figure 5 In the array shown, the electrodes located in the outer columns 301a and 301e, and the electrodes located in the outer rows 303a and 303c, constitute the outer electrodes and define the boundary of the array, while the electrodes that are not located in the outer rows or columns (electrodes 322bb, 322cb and 322db) constitute the inner electrodes within the boundary.

[0030] Figure 5 The array shown is housed within a housing 320 with insulating walls. In the specific embodiment described, the housing is configured such that the liquid passing through the heater flows primarily in a direction transverse to the axis of the electrodes (i.e., the X direction described in this case), from inlet 307 to outlet 309 through the array. Similarly, complex structures are not required to guide the fluid through the individual spaces of the array. Alternatively, the fluid may flow generally in a direction parallel to the axis of the electrodes.

[0031] Electrode 322 is connected to a power source similar to that described above, such that each electrode can be connected to one or the other pole of the power source, or can remain disconnected. In the case where the power source includes a shunt bus as described above, the power source can connect two or more electrodes disconnected from the electrodes to the shunt bus as described above. This type of array can provide a variety of combinations of current paths, which provide a variety of different resistivity ratios between the poles of the power source.

[0032] In the references mentioned above Figure 5 In the variations of the array discussed, some or all of the intervals between columns can be equal to each other. In the extreme case where all intervals C are the same, the array is a perfectly regular array. However, even in this case, a large number of conduction schemes with different specific resistances can be provided. As mentioned above, combining... Figure 1 The heater shown has a resistivity between designated electrode pairs connected to different poles of the power supply that is affected by other electrodes, and this effect varies with the position of the other electrodes relative to the connected electrode pairs. This effect increases the number of different conductivity schemes the array can provide. For example, in... Figure 5 In the array shown, the resistivity between electrodes 322aa and 322ab will differ from that between electrodes 322ba and 322bb. The latter electrode pair (322ba and 322bb) has four adjacent other electrodes, while the former electrode pair (322aa and 322bb) has only two adjacent other electrodes. Generally, the resistivity between a pair of electrodes set at a given distance from each other will differ from the resistivity between a pair of electrodes comprising one or more inner electrodes set at the same distance from each other. This effect is greater in compact arrays where the distance between electrodes is relatively small. One measure of compactness is the average distance between adjacent electrodes. For example, the average distance can be less than five times the average diameter of a single electrode, more preferably less than three times the average diameter of a single electrode, and even more preferably less than twice the average diameter of a single electrode.

[0033] Another embodiment of the present invention ( Figure 6 The provided heater includes a housing 420 and an array of rod-shaped electrodes 422, the array having an outer electrode disposed on an outer circle 401 having a radius R around a central axis 410.O Although circle 401 is shown as a solid line for clarity, circle 401 is the trajectory of the electrodes, not a physical structure. Twelve outer electrodes are provided, separated by regular circumferential intervals α, where α = 30°. Thus, the outer electrodes define the boundary of the array as a regular twelve-sided polygon 424. Figure 6 Only a portion of it is depicted. The array also includes six inner electrodes 423, which are arranged at regular circumferential intervals of 2α on an inner circle 403 coaxial with the outer circle and the central axis 410, the radius of which is R. I Less than R O The first 423a of the inner electrode is offset by α / 2 degrees from the first 422a of the outer electrode in the circumferential direction around the central axis 410. Therefore, each spaced inner electrode 423 is also located in the middle of the circumferential position between the two closest outer electrodes. All electrodes extend parallel to each other and parallel to the central axis 410. Also in this embodiment, each electrode can be connected to either pole of the power supply or remain disconnected from the power supply. If a shunt bus is provided, the electrode disconnected from the power supply can be connected to the shunt bus. Similarly, although the array of electrodes has a degree of regularity, it provides a large number of unique resistivities between various electrode combinations. In variations of this arrangement, the circumferential spacing between the inner electrodes 423, the circumferential spacing between the outer electrodes 442, or both can be completely or partially irregular. In further variations, additional electrodes can be added within the array, and these electrodes can be arranged at positions on other circles. In yet another variation, the inner electrodes can be arranged on an inner circle that is not on the same axis as the outer circle.

[0034] Three-phase power is typically used to power large industrial and commercial electrical equipment with power consumption in the kilowatt range or higher. A power supply 536 for a three-phase power source includes three poles 540, 542, and 546, which can be connected to a three-phase common circuit (not shown) to receive equal-amplitude alternating potentials with phase offsets of 120° (i.e., phase angles of 0°, 120°, and 240°) from each other. Similarly, a power switch 548 is provided for selectively connecting each pole to one of the poles. For clarity, Figure 7Only two electrodes 522 are depicted, typically with the same setup of a power switch 548 for each electrode. The power switch is depicted as including three switches associated with each electrode, allowing any electrode to be connected to any pole. However, in most cases, it is not necessary to include all of these switches. For example, the power switch may include only a single switch for each electrode, allowing a specified electrode to be connected to one of the poles or remain disconnected. In this case, the power switches associated with different electrodes are configured to connect different electrodes to different poles. Optionally, one or more shunt buses 552 and shunt switches 550 may also be provided. In three-phase operation, current flows through the electrodes and through the current path in the fluid between each pair of poles (i.e., between poles 540 and 542, between poles 540 and 544, and between poles 542 and 544). Figure 7 In the operation of the three-phase power supply shown, it is highly desirable to maintain the three currents being equal to each other. In other words, the resistance between each pair of electrodes should ideally be equal to the resistance between the other pairs of electrodes. Assuming that the resistivity of the fluid in contact with the electrodes is the same along every current path in the fluid, the specific resistance between each pair of electrodes should be equal.

[0035] A kind of compatible Figure 7 heaters used with power sources such as Figure 8 As shown. The heater includes electrodes 522 disposed within an insulating housing 520. The electrodes are preferably positioned as follows: Figure 8 The hexagonal lattice shown is positioned accordingly. Similarly, all electrodes 522 are rod-shaped and extend parallel to each other into and out of the plane of the figure. In the hexagonal lattice, the electrodes are arranged in rows at 60° angles to each other, with the center of each electrode positioned on the row axis extending along the row direction. Figure 9 (represented as A, B, and C). Although for clarity, Figure 9 Only a few row axes are depicted, but similar row axes extend along other rows of electrodes. The row axes, parallel to each other, are arranged at equal intervals to define intersections at the vertices of multiple equilateral triangles, and the array's axes are positioned at at least some vertices. Similarly, the array includes an outer electrode defining an outer regular hexagon and an inner electrode defining an inner hexagon in this embodiment. The row axes also define a central vertex 510. The central axis extends parallel to the axis of the electrodes through the central vertex, and the array has six-fold symmetry about the central axis.

[0036] The same array can also be described as having electrodes arranged on a coaxial circle, wherein all electrodes positioned on the inner hexagon are located around a radius R around the central vertex. I On the inner circle (not shown), the electrode is located at the corner of the outer hexagon, on a radius of R coaxial with the inner circle and the central vertex 510. O On the outermost circle (not shown), Figure 9The electrode on the outer hexagonal side, as shown in the shaded area, is positioned on a radius of R that is coaxial with both the inner and outer circles. INT On the middle circle (not shown), where R I <R INT <R O .

[0037] In the connection scheme, the power supply is arranged to connect at least some of the electrodes to the poles of the power supply, such that the connected electrodes include three sets of electrodes connected to different of the poles 540, 542, and 544 of the power supply. Figure 7 ). Figure 9 The image depicts a connection scheme in which the first group of electrodes 522a, the second group of electrodes 522b, and the third group of electrodes 522c are shown with different crosshairs. In this particular scheme, all electrodes 522 of the array are connected to poles to provide a low specific resistance between poles. In another mode, ( Figure 10 Each group of electrodes 522a, 522b, and 522c comprises only one electrode, which are external electrodes located at the corners of the hexagonal array to provide a very high resistivity between the electrodes, thereby providing a minimal heating rate. In this mode, the remaining electrodes are disconnected from the power supply. Numerous intermediate schemes for providing many different resistivities between the electrodes can be formed. Figure 11 An intermediate scheme is shown. In each of the above connection schemes, the electrode of each connection and the corresponding electrodes of the other two sets are positioned at the vertex of an equilateral triangle whose center is located on the central axis of the array. For example, as Figure 11 As shown, electrodes 522a1, 522b1, and 522c1 are positioned at the vertices of one equilateral triangle, while electrodes 522a2, 522b2, and 522c2 are positioned at the vertices of another equilateral triangle. In other words, in each connection scheme discussed above, the connection electrode of each is positioned at the location of the connection electrodes of the other group, which are rotated 120° about the central axis 510 from the location of the other group. In these connection schemes, the electrode groups have triple symmetry about the central axis. Therefore, these electrode groups provide substantially uniform current paths between all three pairs of poles of the power supply, and the effect of adjacent electrodes on the current path will be the same. Therefore, these connection schemes provide substantially equal specific resistances between the poles. In other connection schemes, for example... Figure 12 In the scheme described herein, the connected electrodes 522a, 522b, and 522c are positioned at the vertices of an equilateral triangle not centered on the central axis 512. The conduction loops have equal lengths and will have equal specific resistances except for any differences that may be caused by differences in the effects of adjacent electrodes.

[0038] While it is desirable to provide equal resistivity between the electrodes, perfect equality is not required. Therefore, connection schemes can include one or more electrodes connected to one or both poles in a manner that causes inequality. However, it is desirable to select electrodes such that at least a significant portion, or even most of, of the current flows through current paths with equal specific resistances. This can provide an additional heating rate different from that achievable with perfect equality, while introducing a limited amount of imbalance only in the currents of different phases. In a variation of this scheme, the electrodes causing unequal current flow can be cyclically connected. In each cycle, the electrode causing the unequal current to flow with maximum current through one pole is connected for a period of time, then disconnected and replaced by a second electrode, and then disconnected and replaced by a third electrode, wherein the second electrode is capable of causing a corresponding unequal current to flow with maximum current through the second pole, and the third electrode causes a corresponding unequal current to flow with maximum current through the third pole. The third electrode is disconnected and replaced by the first electrode at the start of the next cycle. In this way, the unequal current rotates between the electrodes, which disperses the effects of excess current between the phases.

[0039] Arrays other than regular hexagonal arrays can provide current paths with the aforementioned triple symmetry. For example, Figure 13 The electrode array shown comprises three groups of electrodes: 622a, 622b, and 622c. Electrodes within each group are shown in the same shade. Electrodes within each group are arranged with an irregular radius from the central axis 610 and at irregular intervals in the circumferential direction around the axis. However, multiple groups are aligned with each other, but each group is rotated 120° from the position of another group. A power supply is configured to connect the electrode groups such that the connected electrodes include corresponding electrodes from all three groups. Again, the array has triple symmetry about the central axis, thus the electrodes are located at the vertices of an equilateral triangle centered at the central axis 610.

[0040] When the shunt bus is used with an array having triple symmetry about the axis, three shunt buses are used such that a set of electrodes connected to each other through each bus is consistent with a set of electrodes connected through another bus, but rotated 120° from the position of the other set.

[0041] In the above discussion, it was assumed that the liquid passing through the heater has a uniform resistivity. However, the resistivity of most liquids varies with liquid temperature. When the liquid flow is primarily parallel to the axis of the electrodes, this effect tends to affect all current paths equally. If a hotter liquid has a lower resistivity, the portion of each current path closer to the downstream end of the electrode will carry a larger current than the portion closer to the upstream end in the same loop, but the relationship between the currents carried by different paths will not be affected. However, if the direction of the electrodes and fluid flow extends horizontally, convection may cause the hotter liquid to preferentially flow through those current paths arranged near the top of the array. When the array is connected to a three-phase power supply, this can lead to current asymmetry between the electrodes. To suppress this effect, blades (not shown) are provided within the housing to induce a rotating flow around the axis of the housing, causing the liquid to follow a roughly helical path. The same effect can also be achieved by configuring an inlet, an outlet, or both, such that the flow of liquid entering, exiting, or both from the housing will induce a rotating flow around the axis of the housing.

[0042] In each embodiment discussed above, the rod-shaped electrode is in the form of a straight cylinder. However, other elongated rod-shaped elements may also be used. For example, the rod-shaped element may be tapered. In other embodiments, the rod-shaped electrode may have a non-circular cross-sectional shape in the electrode region exposed to the liquid. These electrodes may typically be cylindrical or conical to provide a circular cross-sectional shape in the electrode region penetrating the wall of the housing.

[0043] In the embodiments discussed above, the electrodes have equal diameters. However, the diameters of the electrodes may not be equal. Furthermore, as... Figure 8 The lattice arrangement shown has all electrodes set at equal intervals. This arrangement may vary. For example, the diameter of the central circle could be slightly increased, causing the electrodes on the central circle to be further away from the central axis. In this case, as... Figure 12 As shown, the smaller triangular groups of the three connecting electrodes are not equidistant from each other, which may result in some phase inequality, but will also produce an additional characteristic specific resistance. Figure 8 The array is just one example of an array where the entire array has N-fold symmetry about the central axis, where N is 3 or a multiple of 3. Furthermore, Figure 8 The array comprises electrode subgroups with N-fold symmetry about other axes. Other arrays with one or both of these properties can be used to provide three-phase balance.

[0044] In all of the above arrangements, the number of electrodes can be changed as needed.

[0045] Since these and other variations and combinations of the features discussed above can be employed, the above description should be understood in an illustrative manner rather than as a limitation of the invention.

Claims

1. A liquid heater, comprising: (a) Chamber; (b) A plurality of rod-shaped electrodes disposed in the chamber and extending substantially parallel to each other, the electrodes being configured as a two-dimensional array, the array comprising an outer electrode that commonly defines an outer boundary of the array and an inner electrode disposed within the boundary, wherein the outer electrode defines an outer hexagon and the inner electrode defines an inner hexagon; (c) A power source having at least two poles, said power source being operable to provide different potentials to different poles; (d) A power switch electrically connected to at least some of the plurality of electrodes and the pole, the power switch being operable to selectively connect each of the electrodes to one or the other pole and selectively disconnect each of the electrodes from the pole, thereby forming a current loop between the electrodes connected to different poles by means of a liquid disposed in the chamber. The array includes multiple rows of electrodes extending in a first direction, wherein the electrodes in each row are spaced apart from each other in the first direction and aligned with each other in a second direction orthogonal to the first direction, the rows being spaced apart from each other in the second direction.

2. The heater according to claim 1, wherein, The electrodes in at least one row of the row are arranged at unequal intervals in the first direction.

3. The heater according to claim 2, wherein, The electrodes are arranged in columns extending along a second direction, with the electrodes in each column aligned with each other in the second direction, and the columns being spaced apart from each other at unequal intervals in the first direction.

4. A liquid heater, comprising: (a) Chamber; (b) A plurality of rod-shaped electrodes disposed in the chamber and extending substantially parallel to each other, the electrodes being configured as a two-dimensional array, the array comprising an outer electrode that commonly defines an outer boundary of the array and an inner electrode disposed within the boundary; (c) A power source having at least two poles, said power source being operable to provide different potentials to different poles; (d) A power switch electrically connected to at least some of the plurality of electrodes and the pole, the power switch being operable to selectively connect each of the electrodes to one or the other pole and selectively disconnect each of the electrodes from the pole, thereby forming a current loop between the electrodes connected to different poles by means of a liquid disposed in the chamber. The outer electrode is arranged around the central axis along the outer circle and extends parallel to the central axis, while the inner electrode is arranged along one or more inner circles coaxial with the outer circle.

5. The heater according to claim 4, wherein, M inner electrodes are arranged along one of the one or more inner circles, and N outer electrodes are arranged along the outer circle, where N>M.

6. The heater according to claim 5, wherein, The outer electrodes are arranged at equal circumferential intervals, and the inner electrodes are arranged at equal circumferential intervals.

7. The heater according to claim 6, wherein, N = 2M, wherein each inner electrode is located at the middle of the circumferential position between the two outer electrodes.

8. The heater according to claim 4, wherein, The inner electrode includes an intermediate electrode disposed on a middle circle with a diameter smaller than that of the outer circle and an innermost electrode disposed on an inner circle with a diameter smaller than that of the middle circle.

9. A liquid heater, comprising: (a) Chamber; (b) A plurality of rod-shaped electrodes disposed in the chamber and extending substantially parallel to each other, the electrodes being configured as a two-dimensional array, the array comprising an outer electrode that commonly defines an outer boundary of the array and an inner electrode disposed within the boundary, wherein the outer electrode defines an outer hexagon and the inner electrode defines an inner hexagon; (c) A power source having at least two poles, said power source being operable to provide different potentials to different poles; (d) A power switch electrically connected to at least some of the plurality of electrodes and the pole, the power switch being operable to selectively connect each of the electrodes to one or the other pole and selectively disconnect each of the electrodes from the pole, thereby forming a current loop between the electrodes connected to different poles by means of a liquid disposed in the chamber. The array comprises three sets of electrodes with N-fold symmetry about a central axis, where N is 3 or a multiple of 3, and the power supply is a three-phase power supply with three poles. The power switch is operable to select the connected electrode sets such that the selected connected electrode sets include corresponding electrodes from each set, thereby allowing the selected connected electrode sets to define a current loop with triple symmetry about the central axis.

10. The heater according to claim 9, wherein, Each group of electrodes is positioned at an irregular radius from the central axis and at irregular intervals in a circumferential direction around the central axis.

11. The heater according to claim 9, wherein, The power switch is operable to select connected electrode groups such that the connected electrodes include corresponding electrodes from each group, such that the connected electrodes define current loops with triple symmetry about the central axis, thereby providing current loops with equal current flow between the poles of the power source, and such that the connected electrodes include other electrodes providing current loops with unequal current flow between the poles of the power source, and such that the loops with equal current flow carry at least most of the current flowing between the poles.

12. A liquid heater, comprising: (a) Chamber; (b) A plurality of rod-shaped electrodes disposed in the chamber and extending substantially parallel to each other, the electrodes being configured as a two-dimensional array, the array comprising an outer electrode that commonly defines an outer boundary of the array and an inner electrode disposed within the boundary; (c) A power source having at least two poles, said power source being operable to provide different potentials to different poles; (d) A power switch electrically connected to at least some of the plurality of electrodes and the pole, the power switch being operable to selectively connect each of the electrodes to one or the other pole and selectively disconnect each of the electrodes from the pole, thereby forming a current loop between the electrodes connected to different poles by means of a liquid disposed in the chamber. The electrodes are configured as a hexagonal array, the array including an outer electrode defining an outer regular hexagon and an inner electrode defining an inner hexagon; the array includes rows extending along three sets of row axes arranged at 60° angles to each other, the row axes of each set being evenly spaced and the spacing between the three sets of row axes being equal, the row axes intersecting to form an equilateral triangular grid, the electrodes being disposed at the vertices of the equilateral triangles, and the power supply being a three-phase power supply with three poles; The power switch is operable to connect the electrode group to the pole, such that the electrodes connected to the pole have triple symmetry about the central axis, and defines a current loop between the poles having triple symmetry about the central axis.

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