Ohmic heater with multiple operating states

Abstract

The ohmic heater includes a structure 20 having a flow path extending in a flow direction D, a first pair of electrodes 34a, 34b, and a second pair of electrodes 36a, 36b. The electrodes in each pair are adjacent to each other in the flow direction and spaced apart in a direction perpendicular to the flow direction, and the electrode pairs are spaced apart in the flow direction. Electrical circuits 40, 42, 44, 46, 48, and 50 are operable to apply a voltage (i) between the electrodes 34a, 34b in the first pair, (ii) between the electrodes 36a, 36b in the second pair, or (iii) between at least one electrode 34a in the first pair and at least one electrode 36b in the second pair, and the applied voltage may be varied. The heater can respond to changing conditions, such as changes in the conductivity of the liquid flowing through the heater.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 937,877, filed November 20, 2019. [Background technology]

[0002] The present disclosure relates to an ohmic liquid heating device and a method for heating a liquid. The ohmic liquid heating device includes a structure containing a liquid to be heated and a plurality of spaced electrodes. The electrodes contact the liquid to be heated, with the liquid filling the space between the adjacent electrodes. A voltage is applied between the electrodes, causing a current to flow between the electrodes through the liquid, resulting in heating of the liquid by power lost due to the liquid's own electrical resistance. The heating rate varies with the square of the current and is inversely proportional to the electrical resistance of the liquid between the energized electrodes. The current varies with the electrical conductivity of the liquid. For a liquid of a given conductivity, the current varies with the spacing between the electrodes. Closely spaced electrodes provide a low-resistance current path, resulting in a high current and a high heating rate. The current and heating rate also vary with the area of the electrodes, with larger electrodes providing a high current. In this disclosure, the term "resistivity," used to characterize a circuit or portion of a circuit having elements electrically connected by a liquid, refers to the ratio of the electrical resistance of the circuit or portion of the circuit to the electrical resistivity of the liquid in the circuit. For example, the ohmic heater described in Patent Document 1 uses multiple electrode pairs of different sizes so that each pair of electrodes defines a different resistivity. The electrodes of each pair are plate-like elements facing each other with a gap between them. The liquid flow path extends sequentially through the gaps created by the various pairs. A desired heating rate is achieved by selecting electrode pairs and connecting each pair of electrodes to both poles of a power supply. The heater disclosed in Patent Document 2 uses a generally similar configuration, but further controls the heating rate by rapidly opening and closing switches that connect each pair of electrodes to the power supply so as to vary the average voltage applied over time in a pulse-width modulation manner. Patent Document 3 also discloses another ohmic heater that utilizes multiple electrode pairs. However, further improvements may be desirable. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Canadian Patent No. 1291785 [Patent Document 2] International Publication No. 2009 / 100486 [Patent Document 3] U.S. Patent No. 8,532,474 Summary of the Invention

[0004] According to one aspect of the present invention, an ohmic heater (ohmic heater) is provided. The ohmic heater according to this aspect of the present invention preferably comprises a structure having a flow path formed therein extending in a downstream direction. Preferably, the heater comprises a first pair of electrodes arranged in the flow path adjacent to each other in the downstream direction and spaced apart in a direction perpendicular to the downstream direction. Preferably, the heater also comprises a second pair of electrodes arranged downstream of the first pair of electrodes in the flow path. The second pair of electrodes are adjacent to each other in the downstream direction within the flow path and spaced apart in a direction perpendicular to the downstream direction. By way of example only, the structure may comprise an elongated tube formed from a dielectric material, with the first pair of electrodes facing each other at a certain position along the tube and the second pair of electrodes facing each other at another position downstream from the first electrodes. In this example, the tubular dielectric structure may define an elongated passage extending between the first electrode and the second electrode. The heater also preferably includes an electrical circuit operable in at least three states. These states preferably include (i) a first state in which the circuit applies a voltage across a first pair of electrodes, (ii) a second state in which the circuit applies a voltage across a second pair of electrodes, and (iii) a third state in which the circuit applies a voltage across at least one of the first pair of electrodes and at least one of the second pair of electrodes. Each state preferably results in a different resistivity. In the third state, current flows along the length of the flow path between the first pair of electrodes and the second pair of electrodes. In the example described above, current flows through the liquid in the elongated passage along the length of the passage. As described further below, this state may result in a significantly higher resistivity than in the first or second states. The heater preferably provides a wide range of resistivity in a compact structure. Preferably, the electrical circuit is operable to vary the average voltage applied to the electrodes. The combined effect of adjusting the resistivity through a change in state and varying the voltage allows a wide range of operating conditions to be met, such as different liquid conductivities, different thermal requirements, etc., without exceeding the limits of the electrical circuit.

[0005] According to further aspects of the present invention there is provided a cleaning appliance such as a dishwasher incorporating a heater as described above, and a method of heating a liquid. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a schematic partial cross-sectional view of a heater according to one embodiment of the present invention; [Figure 2] FIG. 10 is a schematic partial cross-sectional view showing a heater according to another embodiment of the present invention. [Figure 3] 10 is a schematic partial cross-sectional view of a heater according to a further embodiment of the present invention; [Figure 4] FIG. 10 is a schematic perspective view showing a pair of electrodes usable in yet another embodiment of the present invention. [Figure 5] FIG. 10 is a fragmentary view showing a portion of a heater according to yet another embodiment of the present invention. [Figure 6] FIG. 10 is a schematic diagram showing a dishwasher according to yet another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0007] A heater according to one embodiment of the present invention includes a structure 20 having a flow channel 22 formed therein, the flow channel 22 extending in a downward direction, as indicated by arrow D in FIG. 1 , from an inlet end 24 to an outlet end 26. The flow channel 22 has a straight portion adjacent the inlet end 24, another straight portion adjacent the outlet end 26, and an elongated passage 30 connecting the two straight portions. In this embodiment, the elongated passage 30 is curved, but the particular shape shown is entirely arbitrary, and the passage 30 may be straight or include multiple curved portions. Also, while the structure 20 is shown as a unitary tubular body, it may be formed from multiple elements connected to define a flow channel. As discussed herein, the downward flow direction at any point along the flow channel should be considered to be the direction of the centerline 32 of the flow channel. Similarly, a direction perpendicular to the downward flow direction is a direction perpendicular to the centerline at any point along the flow channel. The centerline 32 is a line passing through the center of the flow channel area along the flow channel 22. Of course, in the case of a flow channel having a circular cross-section, the center of area is simply the center of the circle of the cross-section.

[0008] The first pair of electrodes 34a and 34b is disposed in a straight portion of the flow path 22 adjacent to the inlet end 24. Therefore, the elongated passage 30 is downstream of the first pair of electrodes. The electrodes 34a and 34b in the first pair are adjacent to each other in the downstream direction. In this embodiment, the electrodes 34a and 34b are the same size and aligned in the downstream direction, so that the electrodes face each other throughout their entire range from upstream to downstream. The electrodes 34a and 34b in the first pair are spaced apart in a direction perpendicular to the downstream direction. The electrodes may have a generally plate-like or sheet-like structure. In this embodiment, the electrodes 34a and 34b are attached to the wall of the structure 20, but this is not required, and the electrodes may be spaced apart from the wall if necessary. Meanwhile, the electrodes should be disposed in the flow path 22 so that they contact the liquid flowing through the flow path. Desirably, the structure 20 is formed entirely or partially from a dielectric material so that the structure does not form an electrical connection between the electrodes. The second pair of electrodes 36a and 36b is positioned in a straight portion of the flow path adjacent to the downstream end 26. Thus, the passage 32 is located downstream of the first pair 34 and upstream of the second pair 36. The second pair of electrodes is configured similarly to the first pair, such that the electrodes 36a and 36b are adjacent to each other and aligned in the downstream direction, but spaced apart in a direction perpendicular to the downstream direction. The spacing between the second pair of electrodes may be the same as or different from the spacing between the first pair of electrodes. In this particular embodiment, the second electrodes 36a and 36b are larger in area and closer to each other than the first electrodes 34a and 34b. Therefore, the conduction path through the liquid in the flow path between the electrodes 36a and 36b has a lower resistivity than the conduction path through the fluid between the electrodes 34a and 34b in the first pair.

[0009] The heater also includes a variable voltage power supply 40. The power supply 40 has a first pole 42 and a second pole 44. In this example, the first pole 42 is the neutral pole and the second pole 44 is the "hot" pole. The power supply 40 is configured to provide power and apply a voltage between the poles 42 and 44, which can be controlled and varied as needed over an operating range of voltages. Typically, the power supply applies an alternating voltage to the hot pole while maintaining the neutral pole at a fixed voltage, which may be close to or equal to ground.

[0010] One electrode 34a in the first pair is permanently connected to the neutral pole 42 of the power supply, and the other electrode 34b in the first pair is connected to the hot pole 44 of the power supply through a switch 46. The electrode 36a in the second pair is connected to the neutral pole 42 of the power supply through a switch 48, and the other electrode 36b in the second pair is connected to the hot pole 44 of the power supply through another switch 50. Although the switches 46, 48, and 50 are shown in Figure 1 as conventional mechanical switches, most typically the switches 46, 48, and 50 are semiconductor switches such as FETs, MOSFETs, etc. that can be electrically controlled.

[0011] The heater further includes an array of sensors for detecting one or more conditions of the electrical circuitry, the liquid passing through the heater, and both. For example, in this embodiment, the sensors include a current sensor 52 for detecting current from power supply 40 and a voltage sensor 54 for detecting voltage between poles 42 and 44. The sensors in this embodiment further include sensors capable of detecting one or more conditions of the liquid passing through the heater, such as an inlet temperature sensor 56 located upstream of a first pair of electrodes 34a, 34b, an outlet temperature sensor 56 located downstream of a second pair of electrodes 36a, 36b, and a flow sensor 58 located within the flow path for measuring the flow rate of the liquid through the flow path. Not all of the sensors shown in FIG. 1 need necessarily be included.

[0012] The heater also includes a controller 60. The controller 60 is connected to the switches 46, 48, and 50 and the power source 40, so that the controller can independently command each of these switches to a conducting closed state or a non-conducting open state. The controller is also connected to the power source 40 and commands the power source to increase or decrease the applied voltage between the poles 42 and 44. The controller 60 is also connected to the sensors mentioned above, so that the controller can receive signals from the sensors. The connections between the controller and the sensors are omitted in FIG. 1 for clarity. The controller 60 may include conventional analog-digital circuitry to perform the operations described below. Most typically, the controller includes a digital processor and a memory containing instructions that direct the processor to perform the operations. The controller also typically includes appropriate circuitry for interfacing with the sensors and switches, such as analog-to-digital and digital-to-analog conversion circuitry.

[0013] 1, all switches 46, 48, and 50 are open and the heaters are inactive. By closing switch 48 and leaving switches 48 and 50 open, electrodes 34a and 34b in the first pair can be selected for connection to power supply 40, thus placing the electrical circuit in a first state. In this state, electrodes 34a and 34b are connected to opposite poles of the power supply, so that a voltage difference is applied between electrodes 34a and 34b. In this state, current flows between the electrodes through the liquid present in flow path 22. Similarly, by opening switch 48 and closing switches 48 and 50, the controller can select electrodes 36a and 36b in the second pair and connect both electrodes to poles 42 and 44 of the power supply. In this state, current flows between electrodes 36a and 36b through the fluid in the space between them. Because electrode 34a in the first pair remains connected to the neutral pole, some current may flow from electrode 36b through the liquid in elongated passageway 30 to electrode 34a. However, the resistivity between electrodes 36a and 36b in the second pair is significantly less than the resistivity between electrode 36b in the second pair and electrode 34a in the first pair due to the elongated, relatively narrow current path through the liquid in passageway 30. Therefore, current will primarily flow between electrodes 36a and 36b.

[0014] Controller 60 is also operable to place the circuit in a third state in which switches 46 and 48 are open and switch 50 is closed. In this state, the only inter-pole current path of the power supply through either of these electrodes exists between electrode 36b of the second pair and electrode 34a of the first pair, via passage 30. If desired, the controller is operable to place the circuit in a fourth state in which electrodes 34a and 34b are connected to opposite poles of a power supply and electrodes 36a and 36b of a second pair are connected to opposite poles of a power supply.

[0015] As previously mentioned, these two pairs of electrodes are configured to have different resistivities. Therefore, the heater can provide four different resistivities overall. These resistivities can be selected to cover a wide range with relatively large steps between the resistivities. Typically, the power supply 40 has a finite operating range. For example, a voltage source will typically be capable of applying a voltage between poles 42 and 44 up to a predetermined maximum voltage and a current up to a maximum current through the poles and switch without damaging the power supply or switch. Desirably, the resistivities provided in the various states are selected so that for any liquid of conductivity within a predetermined range, any heating rate within a predetermined operating range of heating rates can be provided by selecting one of the states previously described and adjusting the power supply through states within that operating range.

[0016] In one embodiment, the controller may implement a simple control scheme using the outlet temperature of the fluid from the heater, as sensed by outlet temperature sensor 58, as the primary input. In this control scheme, the controller first selects the state with the highest resistivity, i.e., the third state in this example, with electrodes 36b and 34a connected to the poles. With the circuit in this state, the controller applies a low voltage between poles 42 and 44 and operates the power supply to gradually increase the voltage until the output temperature reaches a desired setpoint value or until the applied voltage reaches a predetermined switching threshold voltage, which may be at or slightly below the maximum operating voltage of the power supply. If the threshold voltage is reached before the output temperature reaches the setpoint value, the controller selects the state with the next lowest resistivity, i.e., the first state, in which the first pair of electrodes 34a and 34b is selected, and reduces the voltage applied by the power supply. The controller then gradually increases the voltage applied by the power supply until the desired outlet temperature is achieved or another predetermined switching threshold voltage is reached. Once the predetermined switching threshold voltage is reached, the controller again reduces the voltage applied by the power supply and switches to the second state, which has the next lowest available resistivity—in this example, the second pair of electrodes 36a and 36b. Once the threshold switching voltage is reached, the controller then switches to the fourth state, which has the lowest available resistivity. Of course, if the fluid temperature rises above the desired setpoint temperature, the controller performs the same steps in reverse, first reducing the voltage provided by the power supply to the selected minimum voltage threshold, and then switching to a higher resistivity state once the minimum voltage threshold is achieved. If desired, the controller may monitor the current detected by the current sensor 52 and, if the current increases to a maximum threshold, reduce the voltage, switch to a higher resistivity state, or both. This situation may occur, for example, if the liquid's conductivity increases significantly.

[0017] In a more sophisticated control scheme, the controller may obtain data indicative of the liquid's conductivity by placing the circuit in one of the above states, momentarily energizing the power supply to apply a low voltage between the poles, and measuring the current using sensor 52. The applied voltage may be measured using sensor 54 or may be known with sufficient accuracy from the voltage commanded by the controller. The known current and voltage, along with the known resistivity between the poles in each state, can be used to calculate the conductivity. The controller may use data from input temperature sensor 56 and flow rate sensor 58 to estimate the heating rate that will raise the liquid's temperature to the desired set point, and may select the circuit state and applied voltage to achieve the required heating rate while maintaining the circuit within its operating range.

[0018] A heater according to another embodiment of the present invention (FIG. 2) is the same as the heater described above with reference to FIG. 1, except as noted below. In the heater of FIG. 2, the power source is a fixed-voltage power source, such as a public power connection. A controller 160 varies the voltage by pulse-width modulation. Thus, the controller 160 controls the average voltage applied to selected electrodes by repeatedly opening and closing one or more switches associated with the selected electrodes. In a first state, with electrodes 34a and 34b selected, the controller may be configured to repeatedly open and close switch 46. In a second state, with electrodes 36a and 36b selected, the controller may repeatedly open and close one or both of switches 48 and 50. Similarly, in a third state, the controller opens and closes switch 50. Otherwise, the system operates as described above. In other words, the controller can control the average voltage applied to selected electrodes by controlling the voltage applied by the power source, as in FIG. 1, or by controlling the duty cycle of the connection between the selected electrodes and the power source, as in FIG. 2.

[0019] Another embodiment of the heater (FIG. 3) is similar to the heater described above, except that the heater includes a first pair of electrodes 234a and 234b, a second pair of electrodes 236a and 236b, and a third pair of electrodes 237a and 237b. In this embodiment, the structure 220 includes a flow path 222 having a first elongated passage 230 between the first and second pairs of electrodes and a second elongated passage 231 between the second pair of electrodes 236a and 236b and the third pair of electrodes 237a and 237b. Again, the electrodes of each pair are positioned adjacent to one another in the downstream direction along the flow path. However, in this particular embodiment, the electrodes 236a and 236b of the second pair are positioned so as to overlap, and the electrodes 237a and 237b of the third pair do not overlap one another in the downstream direction D along the flow path. In this embodiment, the various pairs of electrodes are also configured so that each pair of electrodes provides a different resistivity.

[0020] In this embodiment, electrode 234a in the first pair is also permanently connected to the neutral pole 242 of power supply 240, while the other electrodes are connected to the poles of the power supply through switches 246, 248, 250, 251, and 253. Again, the controller is operable to place the circuit in one of the previously described states while electrodes 237a and 237b are disconnected from the power supply. The controller is also operable to place the circuit in another state. For example, the controller can select only the third electrode pair such that electrodes 237a and 237b in the third pair are connected polarly. In yet another state, electrode 237b of the third pair is connected to the hot pole 244, electrode 237a of the third pair is disconnected from the neutral pole, electrode 236a of the second pair is connected to the neutral pole, and electrode 236b of the second pair is disconnected from the hot pole. In this state, poles 244 and 242 are electrically connected to each other through the liquid in second passage 231. Because second passage 231 has a different configuration than first passage 230, the resistivity between the poles in this state is different from the resistivity in the third state described above, where current flows through the liquid in first passage 230. In yet another state, electrode 237b in the third pair is connected to the hot pole, electrode 234a in the first pair is connected to the neutral pole through a permanent connection, and the other electrodes are disconnected. In this state, the current path between the poles of the power supply exists in series through the liquid in passage 231 and the liquid in passage 230. Such a current path provides the highest available resistivity.

[0021] 1 and 2, power supply 240 may be a variable voltage power supply controlled by controller 260 as previously described. In other configurations, power supply 240 may be a fixed voltage power supply as shown in FIG. 2, and controller 260 may be configured to repeatedly open and close switches in current paths through selected electrodes to provide pulse width modulation of the applied voltage. As will be appreciated, further embodiments using a greater number of electrode pairs are available.

[0022] In the previously described embodiment, the electrodes are plate-like structures extending along both sides of the flow path. However, other configurations are also possible. For example, as shown in FIG. 4, the pair of electrodes may include an elongated rod-shaped electrode 334b extending in the downstream direction of the flow path and a tubular electrode 334a surrounding the rod-shaped electrode. In this case, the inner diameter of the tubular electrode 334a is larger than the outer diameter of the rod-shaped electrode 334b, so that the electrodes are spaced apart from each other along a radial direction R that intersects with the downstream direction of the flow path. Many other electrode configurations are also possible.

[0023] Typically, the heater includes safety features such as ground electrodes (not shown) located in the flow path upstream and downstream from the electrodes connectable to a power source, the ground electrodes being permanently connected to ground potential.

[0024] In another variation, one or both electrodes in a pair of electrodes may be configured as several segments. As shown in FIG. 5, the pair of electrodes includes a first electrode 532a formed as a single unit element and a second electrode formed as two segments 534b1 and 534b2. Both segments of the second electrode are arranged adjacent to the first electrode in the downstream direction. The first electrode 534a is connected to one pole 542 of a power supply through a switch 548. The segments 534b1 and 534b2 of the second electrode are connected to the other pole 544 of the power supply through separate switches 548 and 549, respectively, so that each segment can be connected or disconnected to the pole of the power supply independently of the other segment. This configuration can be used to change the effective area of the segmented electrodes. Therefore, it can be used to change the resistivity of selected segments of the electrodes, for example, the resistivity between the first and second electrodes of the pair or the resistivity between the segmented electrode and other electrodes of the pair. Such a configuration can be applied to any or all of the electrode pairs.

[0025] In the embodiment shown in Figures 1-3, one electrode is permanently connected to the neutral pole, which may be connected to the neutral pole through a separate switch operated by the controller if desired.

[0026] The heaters described above can provide a variety of conduction paths with different resistivities using a relatively small number of electrodes and switches. While heaters such as those described herein can be used in any application requiring heating of a liquid, they are particularly useful when the conductivity of the liquid is expected to change over a wide range during operation of the heater. For example, heaters used to heat water in cleaning appliances such as clothes washers or dishwashers can vary over a very wide range of conductivity during operation. The water supply to the cleaning appliance is typically potable water, and its conductivity can vary depending on factors such as the dissolved mineral content of the water. Furthermore, as the cleaning appliance operates, its conductivity generally increases as electrolytes, such as ionic components of soap and materials washed off from the items to be washed, are added to the water during the wash cycle. Heaters such as those described above can be configured to provide a wide range of resistivities so that the components of the electrical circuit remain within their operating range despite dramatic changes in conductivity. Furthermore, the heaters can provide this capability in a very compact structure. The portion of the structure providing the elongated passageway can comprise a tube of essentially any configuration. In some embodiments, the tubes may extend around other components of the appliance. For example, the washing appliance shown in FIG. 6 has a housing 501 defining a washing chamber 501. The housing includes a rack (not shown) that supports items to be washed, in this case dishes 505, within the washing chamber. A pump 507 is configured to circulate a washing liquid, such as water, through the washing chamber, for example, by forcing the liquid through a sprayer 509, thereby contacting the items to be washed. A heater, as previously described, includes a structure 520 with a flow path (not shown) for the washing liquid, which is connected to an outlet of the pump and the sprayer 509. A portion of the heater structure 520 typically surrounds the pump, thereby occupying space within the appliance that would otherwise be wasted.

[0027] In the heaters described so far, the passages extending between the electrode pairs are elongated and have a relatively small cross-sectional area. That is, the cross-sectional area of each passage is smaller than the area of the electrode, and the length of the passage is greater than the distance between the electrodes in each pair. Thus, in the heaters described above, the conductive path extending through the passages has a greater resistivity than any of the conductive paths between the electrodes in a given pair. However, if the electrodes in a given pair are widely spaced apart and the passage between the pairs is short, the conductive path through the passages can have a lesser resistivity than the conductive path between the electrodes in the pair.

[0028] The features disclosed in the various embodiments described above may be interchanged between different embodiments. For example, the electrode structures shown in Figures 3, 4, and 5 may be utilized in any of the heaters of Figures 1 and 2. Therefore, the foregoing description should be considered illustrative rather than limiting.

Claims

1. (a) a structure provided with a flow path extending in a downstream direction; (b) a first electrode pair disposed in the flow path, adjacent to each other in the flow direction, and spaced apart from each other in a direction perpendicular to the flow direction; (c) a second electrode pair disposed downstream of the first electrode pair in the flow path, wherein the second electrode pair is disposed adjacent to one another in the downstream flow direction and spaced apart from one another in a direction perpendicular to the downstream flow direction, and the structure includes a dielectric wall that forms an elongated passage constituting a part of the flow path between the first electrode pair and the second electrode pair; and (d) an electrical circuit operable in at least three states; Equipped with The at least three states are: (i) a first state in which the circuitry applies a voltage between the first pair of electrodes; (ii) a second state in which the circuitry applies a voltage between the second pair of electrodes; (iii) a third state in which the circuit applies a voltage between at least one electrode in the first pair and at least one electrode in the second pair, wherein in the third state, only a current path through any of the plurality of electrodes exists between one electrode in the second pair and one electrode in the first pair through the elongated passageway, and current flows through a liquid in the passageway; Including, Ohmic heater.

2. The circuit comprises: one or more sensors for detecting one or more conditions of the circuit, one or more conditions of the liquid passing through the flow path, or one or more conditions of the circuit and one or more conditions of the liquid passing through the flow path; a controller that sets the circuit in one of the first state, the second state, and the third state in response to a signal from at least one of the sensors; The heater of claim 1 , comprising:

3. 3. The heater of claim 2, wherein the controller controls an average voltage in response to a signal from at least one of the sensors while maintaining the circuit in one of the first state, the second state, and the third state.

4. 2. The heater of claim 1, wherein the resistivity of the circuit in the third state is greater than the resistivity of the circuit in the first state and the second state.

5. the first pair of electrodes are at least partially aligned with one another in the downstream direction; The heater of claim 1 , wherein the electrodes in the second pair are at least partially aligned with one another in the downstream direction.

6. the circuit comprises a power supply having two poles; the circuit is operable in a fourth state, in which the electrodes in the first pair are connected to opposite poles of the power supply and the electrodes in the second pair are also connected to opposite poles of the power supply; The heater of claim 1 .

7. the circuit comprises a power supply having two poles; In the third state, the only current path between the poles of the power source through any of the plurality of electrodes exists between one electrode in the second pair and one electrode in the first pair through the passage. The heater of claim 1 .

8. A heater according to any one of claims 1 to 7; a housing defining a cleaning chamber in which items to be cleaned are held; a pump for supplying cleaning fluid through the heater and into the cleaning chamber so that the cleaning fluid can contact the articles in the cleaning chamber; A cleaning device comprising:

9. (a) passing a liquid in a downward direction through a first pair of electrodes adjacent to each other in the downward direction and spaced apart in a direction perpendicular to the downward direction, then through an elongated passage formed by a dielectric wall, and then through a second group of electrodes adjacent to each other in the downward direction and spaced apart in a direction perpendicular to the downward direction; (b) operating an electrical circuit to apply a voltage between the electrodes in the first pair in a first state, between the electrodes in the second pair in a second state, and between at least one electrode in the first pair and at least one electrode in the second pair in a third state, wherein only a current path through any of the electrodes exists through the elongated passage between one electrode in the second pair and one electrode in the first pair, and current flows through a liquid in the elongated passage; (c) detecting a condition of at least one of the liquid and the circuit; (d) controlling the electric circuit to select one of the first state, the second state, and the third state in response to at least one state detected in step (c); A method for heating a liquid, comprising:

10. 10. The method of claim 9, further comprising the step of controlling the electrical circuitry to vary the average voltage applied in response to at least one condition detected in step (c).

11. operating the circuit includes connecting a plurality of the electrodes to opposite poles of a power source; In the third state, the only current path between the poles of the power source through any of the plurality of electrodes exists between one electrode in the second pair and one electrode in the first pair through the passage.

11. The method according to claim 9 or 10.

12. the circuit comprises a power supply having two poles; The step of operating the circuit also includes operating the circuit in a fourth state, wherein in the fourth state, the electrodes in the first pair are connected to opposite poles of the power supply and the electrodes in the second pair are also connected to opposite poles of the power supply.

11. The method according to claim 9 or 10.

13. The dielectric wall forms a tubular, elongated passage that constitutes the entire flow path between the first electrode pair and the second electrode pair, and the dielectric wall surrounds the entire flow path around an axis extending in the downstream direction, forming the tubular, elongated passage; In the third state, only the current path through any of the plurality of electrodes exists between one electrode of the second electrode pair and one electrode of the first electrode pair through the tubular, elongated passage, and a current flows through a liquid in the tubular, elongated passage. The heater of claim 1 .

14. The electric circuit has a power source having two poles and varying a voltage applied between the two poles, The electrical circuit comprises: (i) the first state in which the circuit applies a variable voltage between electrodes of the first electrode pair; (ii) the second state in which the circuit applies a variable voltage between the electrodes of the second electrode pair; (iii) a third state in which the circuit applies a variable voltage between at least one electrode in the first electrode pair and at least one electrode in the second electrode pair, wherein in the third state, the only current path through any of the plurality of electrodes exists between at least one electrode in the second electrode pair and at least one electrode in the first electrode pair through the tubular, elongated passageway, and current flows through a liquid in the tubular, elongated passageway; and operating in at least three states, including the electric circuit has a first resistivity between the electrodes of the first electrode pair in the first state, the electric circuit has a second resistivity between the electrodes of the second electrode pair in the second state, the second resistivity being different from the first resistivity, and the electric circuit has a third resistivity between at least one electrode of the second electrode pair and at least one electrode of the first electrode pair in the third state, the third resistivity being greater than the first resistivity and the second resistivity. The heater of claim 13.

15. A heater as described in claim 1, wherein in the third state, only the current path through any of the plurality of electrodes passes through an electrode in the second electrode pair and an electrode in the first electrode pair, and does not pass through any electrodes other than the electrode in the second electrode pair and the electrode in the first electrode pair.

16. A heater as described in claim 1, wherein the cross-sectional area of the elongated passage is smaller than the area of the first electrode pair and the second electrode pair, and the length of the elongated passage is greater than the distance between the electrodes in the first electrode pair and greater than the distance between the electrodes in the second electrode pair.

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