Devices for ohmically heating a fluid
A heater for heating a conductive liquid includes a two-dimensional array of rod-like electrodes ( 22, 122, 322, 422, 522 ) extending parallel to one another, an electrical power supply having a plurality of poles, and power switches to connect different ones of the electrodes to different poles so that current flows between the poles through the liquid. The array desirably includes outer electrodes defining the boundary ( 24, 424 ) of the array and inner electrodes disposed within this boundary. The array may have regular or irregular spacings between the electrodes. The array can provide numerous different connection schemes to vary the electrical resistance between the poles and thus vary the heating rate. The array can be arranged to provide substantially equal currents through three poles of a three-phase power supply.
1 . A liquid heater comprising:
(a) a chamber configured to receive a liquid passing therethrough along a flow direction between an inlet and an outlet;
(b) a plurality of rod-like electrodes disposed within the chamber and extending substantially parallel to one another along a direction transverse to the flow direction, the electrodes being spaced apart from one another in an irregular two-dimensional array wherein, for at least some of the electrodes, distances between a given one of the electrodes and two other ones of the electrodes which are closest to the given one of the electrodes are unequal;
(c) a three-phase electrical power supply having three poles, the power supply being operable to supply alternating potentials offset by 120° in phase to the respective poles;
(d) power switches electrically connected between at least some of the electrodes and the poles, the power switches being operable to selectively connect each of the electrodes to one the poles and to selectively disconnect each of the electrodes from the poles so as to form current paths between electrodes connected to different ones of the poles through the liquid disposed in the chamber; and
(e) a control processing unit coupled to the power switches and configured to actuate the power switches according to switch setting data retrieved from a memory, the memory storing a plurality of predefined connection schemes;
wherein the connection schemes include electrode groupings having three-fold symmetry about a central axis and define current paths between pairs of poles of the three-phase power supply with substantially equal specific resistance.
2 . A liquid heater comprising:
(a) a chamber configured to receive a liquid passing therethrough along a flow direction between an inlet and an outlet;
(b) a plurality of rod-like electrodes disposed within the chamber and extending substantially parallel to one another along a direction transverse to the flow direction, the electrodes being disposed a two-dimensional array including outer electrodes cooperatively defining an outer boundary of the array and inner electrodes disposed within the boundary;
(c) a three-phase electrical power supply having three poles, the power supply being operable to supply alternating potentials offset by 120° in phase to the respective poles;
(d) power switches electrically connected between at least some of the plurality of electrodes and the poles, the power switches being operable to selectively connect each of the electrodes to one or another of the poles and to selectively disconnect each of the electrodes from the poles so as to form current paths extending through the liquid disposed in the chamber between electrodes connected to different ones of the poles; and
(e) a control processing unit coupled to the power switches and configured to actuate the power switches according to switch setting data retrieved from a memory, the memory storing a plurality of predefined connection schemes;
wherein the connection schemes include electrode groupings having three-fold symmetry about a central axis and define current paths between pairs of poles of the three-phase power supply with substantially equal specific resistance.
3 . The heater as claimed in claim 2 wherein the array includes a plurality of rows of electrodes extending in a first direction with the electrodes within each row spaced apart from one another in the first direction and aligned with one another in a second direction orthogonal to the first direction, the rows being spaced apart from one another in the second direction.
4 . The heater as claimed in claim 3 wherein the electrodes within at least one of the rows are disposed at unequal intervals in the first direction.
5 . The heater as claimed in claim 4 wherein the electrodes are disposed in columns extending in the second direction, the electrodes disposed in each column being aligned with one another in the second direction, the columns being spaced apart from one another at unequal intervals in the first direction.
6 . The heater as claimed in claim 2 wherein the outer electrodes are disposed along an outer circle around a central axis and extend parallel to the central axis.
7 . The heater as claimed in claim 6 wherein the inner electrodes are disposed along one or more inner circles coaxial with the outer circle.
8 . The heater as claimed in claim 6 wherein the inner electrodes are disposed along a single inner circle coaxial with the outer circle.
9 . The heater as claimed in claim 8 wherein M inner electrodes are disposed along the single inner circle and N outer electrodes are disposed along the single outer circle, and N>M.
10 . The heater as claimed in claim 9 wherein the outer electrodes are disposed at equal circumferential spacings and the inner electrodes are disposed at equal circumferential spacings.
11 . The heater as claimed in claim 10 wherein N=2M, and wherein each inner electrode is disposed at a circumferential location midway between the circumferential locations of two of the outer electrodes.
12 . The heater as claimed in claim 7 wherein the inner electrodes include intermediate electrodes disposed on an intermediate circle of smaller diameter than the outer circle and innermost electrodes disposed on an inner circle of smaller diameter than the intermediate circle.
13 . The heater as claimed in claim 2 wherein the array includes three groups of electrodes having N-fold symmetry about a central axis, and wherein the power supply is a three-phase power supply having three poles, the power switches being operable to select sets of connected electrodes so that the connected electrodes includes corresponding electrodes from each group so that the connected electrodes define current paths having three-fold symmetry about the central axis.
14 . The heater as claimed in claim 13 wherein N is 3 or a multiple of 3.
15 . The heater as claimed in claim 14 wherein the electrodes of each group are disposed at irregular radii from the central axis, and at irregular intervals in the circumferential direction around the axis.
16 . The heater as claimed in claim 14 wherein the power switches are operable to select the three sets of connected electrodes so that the connected electrodes provide current paths having equal current flows between the poles of the power supply, and so that the connected electrodes include other electrodes which provide current paths having unequal current flows between the poles of the power supply, and so that the paths of equal current flow carry at least the majority of the current flowing between the poles.
17 . A liquid heater comprising:
(a) a chamber;
(b) a plurality of rod-like electrodes disposed within the chamber and extending substantially parallel to one another, the electrodes being disposed a two-dimensional array;
(c) a three-phase electrical power supply having three poles, the power supply being operable to supply different electrical potentials to different ones of the poles;
(d) power switches electrically connected between at least some of the plurality of electrodes and the poles, the power switches being operable to selectively connect each of the electrodes to one or another of the poles and to selectively disconnect each of the electrodes from the poles so as to form current paths extending through liquid disposed in the chamber between electrodes connected to different ones of the poles and
(e) a control processing unit coupled to the power switches and configured to actuate the power switches based on switch setting data retrieved from a memory, the memory storing a plurality of predefined connection schemes, wherein the connection schemes include groupings of electrodes defining current paths having three-fold symmetry about a central axis and substantially equal specific resistances between the poles of the three-phase power supply;
wherein the electrodes are arranged in a hexagonal array including outer electrodes cooperatively defining an outer boundary of the array in the shape of a regular hexagon and inner electrodes disposed within the boundary and defining at least one inner hexagon, the array including rows extending along three sets of row axes disposed at 60° angles to one another, the row axes in each set being uniformly spaced and the spacings between row axes of the three sets being equal to one another, the row axes intersecting one another to form a grid of equilateral triangles, the electrodes being disposed at the vertices of the equilateral triangles, the power switches being operable to connect three sets of the electrodes to the respective poles so that the electrodes connected to the poles have three-fold symmetry around a central axis and define current paths between the poles having three-fold symmetry around the central axis.