GB2268381A - Electric heating of resistive liquid - Google Patents

Abstract

An electrical heater has a generally sandwich structure comprising at least two electrode plates 11. A plate of electrically insulating material 12 is interleaved between the or each pair of adjacent electrode plates and mounted on a common axle for rotation through a selected angle out of position between respective electroplates. A corresponding selected proportion of the surface area of the electrode plates is therefore exposed to liquid in which the heater is at least partially immersed. The liquid is heated by electric current passing through the electrode plates and liquid therebetween. The heating is controllable by selecting the angle of rotation and thus the area of the electrode plates fully exposed to the liquid. <IMAGE>

Description

ELECTRICAL HEATER This invention relates to electrical heaters and more particularly to an electrical heater adapted for heating a liquid in which it is at least partially immersed.

Heretofore the practice generally has been to heat liquids by means of an electrical resistance wire generally coiled upon an insulating ceramics support and which may be located outside a tank in which the liquid is to be heated or alternatively within the tank so as to be immersed in the liquid. Heating tends to be relatively slow and there is a relatively high consumption of energy. The heating wire and/or the tank may be damaged if the level of liquid within the tank is insufficient to fully cover an immersed heating wire or fails as a result of the boiling off of the liquid.

In general some form of switch and/or thermostat must be connected in series with the heating wire for controlling the heater.

The present invention represents a wholly different approach.

In accordance with the present invention, we provide an electrical heater adapted for heating a liquid in which it is at least partially immersed, the heater having a generally sandwich structure, comprising at least two electrode plates with a plate of electrically insulating material interleaved between the or each pair of adjacent electrode plates, the or each insulating plate being mounted on a common axle for rotation through a selected angle out of position between respective electrode plates so that a corresponding selected proportion of the surface area of the electrode plates is exposed to liquid in which the heater is at least partially immersed, the liquid being arranged to be heated in use by electric current passing through the electrode plates and liquid therebetween, the resultant heating being controllable by selecting the angle of rotation and thus the area of the electrode plates fully exposed to the liquid.

The sandwich structure may be of a multi-layer nature with a plurality of electrode plates connected in common to a first electric line and a second plurality of electrode plates connected in common to a second electric line. There may be at least one further electrode plate connected to an earth line.

The invention is hereinafter more particularly described by way of example only with reference to the accompanying drawings in which: Fig. 1 shows a generally perspective view of a preferred embodiment of heater constructed in accordance with the present invention; Fig. 2 shows the heater of Fig. 1 with the insulating plates partly rotated out of position between the respective electrode plates; Fig. 3 is an exploded perspective view of the heater of Figs. 1 and 2; Fig. 4 is a sectional view of the heater showing the internal structure; and Fig. 5 shows the heater of Figs. 1 to 4 mounted within a tank for heating a liquid.

The illustrated embodiment of heater has a multi-layer generally sandwich structure comprising a plurality of electrode plates 11 with interleaved plates of electrically insulating material 12. The electrode plates are suitably made of a material which is proof to high temperatures such as stainless steel. The insulating plates may be made of ceramic and are mounted on a common axle 17 which is rotatable so that the insulating plates as a whole may be rotated through a selected angle out of position between respective electrode plates as shown in Fig. 2 so that a corresponding selected proportion of the surface area of the electrode plates is exposed to liquid in which the heater is at least partially immersed.

It will be seen that while the insulating plates 12 are all essentially semicircular in shape and have a key-shaped opening for receipt of the common axle 17, the electrode plates while generally semicircular in shape have outwardly extending tabs for several purposes to be explained. At the centre of the semi-circle there is an opening. The arrangement is such that the insulating plates keyed to the axle rotate with it whereas the electrode plates' do not.

The sandwich structure of the heater is maintained by a frame which comprises a generally yoke-shaped piece 15 having a first elongate member which extends along the diameter of the structure on its underneath side in the orientation illustrated in the drawings and a pair of elongate side members which extend perpendicularly thereto so as to extend across the thickness of the sandwich. These members, as illustrated are of channel-shaped cross-section, so as to receive therein insulating blocks 13 which have a plurality of openings 131 therein for receiving corresponding tabs of the electrode plates. As a result the electrode plates are fixed to the yoke. The main portion of the frame is completed by a second elongate member 14 which extends across the diameter of the semicircle on the upper side of the heater in the orientation shown in the drawings.

In the arrangement shown in the drawings there is also an auxiliary frame member comprising a second generally yoke-shaped piece 16 which comprises a member adapted to extend across the thickness of the sandwich structure and which is generally channel-shaped so as to receive another insulating block 13 with openings 131 for the electrode tabs 24. Yoke member 16 also has respective elongate members which extend along a radius of the semicircular plates to the axle, and is mounted to the main portion of the frame at a position at 900 to the main diameter to embrace the sandwich structure.

While the electrode plates have commonly located tabs 24 for receipt in the openings 131 in the respective insulating blocks 13, it will be seen that certain of the electrode plates have additional tabs 18 in similar positions, others have alternative tabs 19 at other positions and one electrode plate has a tab 20.

The reason for this structure is quite straightforward.

Certain of the electrode plates, identified 111 in Fig. 3 have terminal tabs 18 adapted for connection to a terminal for connection to the live electric line; other electrode plates, identified 112 are adapted for connection via their terminal tabs 19 to the neutral electric line and the single electrode plate 113 having a terminal tab 20 is adapted for connection to an earth line. Thus, the illustrated heater is adapted for connection to the conventional mains electricity alternating supply. The heater is, of course, adapted for use only with liquids (such as aqueous liquids) which will conduct electricity at least over the short distances between individual electrode plates in the structure illustrated.Coupling of the heater as identified above, for example in the arrangement illustrated in Fig. 5 and with the electrode plates at least partially immersed in such a conducting liquid will result in heating of the liquid. Control of the extent and rate of heating is simple. By rotating the insulating plates 12 through a predetermined angle, a corresponding predetermined area of the electrode plates is fully exposed to the liquid in which they are immersed. The rate of heating will of course depend upon the surface area exposed. Some of the liquid may of course penetrate between the electrode plates and insulating plates since if rotation is to take place, these plates must not be tight, and to relieve any pressure resulting from expansion of heated liquid in this position, the electrode plates are provided with through holes 25 as illustrated so as to avoid damage thereto.

Even if the illustrated heater should only be partly immersed, it will still operate without damage since no electric current will pass between electrode plates which are not immersed.

It follows, therefore, that plates which are not immersed are not heated and therefore there is no danger of any damage resulting from incomplete immersion as would occur with prior art arrangements involving an electrical resistance heating wire.

The invention is not limited just to plates of generally semicircular configuration. While in general the insulating plates should have a common configuration and the electrode plates should similarly have a common configuration, it is by no means essential that these two common configurations be generally the same. Where they are dissimilar, the effect of relative rotation will be as in this case to partially expose areas of the electrode plates, thereby providing for a selected degree of heating in exactly the same way as with the semicircular plates of the presently illustrated preferred embodiment.

Claims (6)

1. An electrical heater adapted for heating a liquid in which it is at least partially immersed, the heater having a generally sandwich structure, comprising at least two electrode plates with a plate of electrically insulating material interleaved between the or each pair of adjacent electrode plates, the or each insulating plate being mounted on a common axle for rotation through a selected angle out of position between respective electrode plates so that a corresponding selected proportion of the surface area of the electrode plates is exposed to liquid in which the heater is at least partially immersed, the liquid being arranged to be heated in use by electric current passing through the electrode plates and liquid therebetween, the resultant heating being controllable by selecting the angle of rotation and thus the area of the electrode plates fully exposed to the liquid.

2. A heater according to Claim 1 wherein each of the said plates is of generally semicircular configuration, the sandwich structure of the heater being maintained by a frame comprising a generally yoke-shaped piece having a first elongate member extending along the diameter of the semicircular electrode plates and a pair of elongate side members extending perpendicularly thereto so as to extend across the thickness of the sandwich, and a second elongate member extending along the diameter of the semicircular electrode plates and being coupled to the aforesaid side members of the yoke on the opposite side of the sandwich from the diametric elongate member of the yoke, the axle being mounted for rotation in the two said elongate members.

3. A heater according to Claim 2, wherein the frame comprises a second generally yoke-shaped piece comprising a member adapted to extend across the thickness of the sandwich structure and respective elongate members adapted to extend along a radius of the semicircular plates to the axle, the second yoke being mounted two the frame provided by the first yoke and the said second elongate member at a position at 900 to the aforesaid diameter to embrace the sandwich structure.

4. Apparatus according to any preceding claim, wherein the said sandwich structure is of a multi-layer nature with a first plurality of electrode plates being connected in common to a first electric line and a second plurality of electrode plates being connected in common to a second electric line.

5. A heater according to Claim 4, wherein at least one further said electrode plate is connected to an earth line.

6. An electrical heater substantially as hereinbefore described with reference to and as shown in the accompanying drawings.