Evaporation vessel and electrode arrangement for an electrode evaporator having a dummy electrode
BACKGROUND OF THE INVENTION 
     The invention relates to an electrode arrangement for an evaporation vessel of an electrode evaporator and to an evaporation vessel for an electrode evaporator, having an electrode arrangement which comprises at least two electrodes which are held in the vessel wall and can be electrically connected from outside the evaporation vessel. 
     Electrode evaporators are known as vapour generators, in the case of which a single-phase or multi-phase alternating current is passed through the water via two or more electrodes and the water itself is used as the heating resistance for generating the heat which is required for evaporation. They are mainly used in air humidifiers for ventilation and air-conditioning systems or for direct room air humidification. 
     The apparatuses and, in particular, the evaporation vessels must be designed very differently (in particular with respect to the number, shape and arrangement of the electrodes) depending on the required power and as a function of the properties of the electrical mains, which differ very much depending on the point of use and the geographical region (different rate of voltages, number of phases etc.). In the case of the known electrode evaporators, on the one hand, for the manufacturer, this means that he must produce a large number of different apparatus types and, on the other hand, for the wholesaler and retailer, it means that he must keep a large number of different apparatuses and spare parts. 
     SUMMARY OF THE INVENTION 
     It is thus an object of the present invention to propose a design refinement of an evaporation vessel and electrodes which allows a large range of different apparatus types to be provided, in a variable construction, using a small number of different components. 
     The behaviour of the electric field can be influenced, as the person skilled in the art will see immediately, by insertion of a dummy electrode, that is to say of a part which is electrically conductive but is not connected electrically or is connected to a neutral conductor, into the electrode arrangement. By suitable selection of the size and shape of the dummy electrode, the operation of the electric field can be matched to different requirements, so that the other (active) electrodes require less matching or do not need any matching at all. Only a few electrode types are thus required to cover a wide range of apparatuses. 
     For symmetry reasons, as a rule it will be expedient to arrange the dummy electrode in the centre of the electrode arrangement, that is to say more precisely, coaxially with respect to the central axis of symmetry of the arrangement which is formed by the other electrodes. A hollow cylinder is proposed as a simple, advantageous shape for the dummy electrode; however, any desired shapes, even complex shapes, are in principle conceivable, depending on the application. 
     In addition, using a dummy electrode, a further problem, which is also known to the person skilled in the art under the term &#34;leakage current&#34;, can be solved in a simple manner. Specifically, if the dummy electrode is arranged such that, for example with its lower section, it electrically screens the region in the vicinity of the water inlet and outlet, the formation of electrical potential differences in this region is thus prevented, which otherwise can generate an undesirable and dangerous electrical current in the emerging water when (electrically conductive) water is allowed to flow out. 
     A further way of making a wide range of configurations possible using a small number of electrode types is achieved according to the invention as follows: a plurality of bushings are provided in the wall of the evaporation vessel, in which bushings an electrode can be held by means of a special plug-in part. This allows electrodes to be arranged at different positions and in different orientations, so that different arrangements can be implemented using the same electrode type. The plug-in part is provided with a latching device which, on the one hand, holds the plug-in part, which is inserted into a bushing, such that it automatically latches and, on the other hand, can be released again by hand without any tools if it is intended to remove the plug-in part or the electrode again. 
     This design refinement furthermore makes it possible for the electrodes to be installed and removed quickly and represents a considerable simplification in comparison with the conventional type of construction, in the case of which the electrodes are firmly inserted in the evaporation vessel, are frequently injection-moulded directly in the vessel wall or are then screwed tight. 
     The simplicity of the installation and removal of the electrodes achieved in this way, as well as the advantages which result in cleaning and servicing, are extremely advantageous, particularly from the ecological viewpoint, since electrodes which have become unuseable as a result of mineral deposits after a specific life can now be replaced independently of the evaporation vessel, and can possibly even be cleaned and reused. In comparison with conventional apparatuses, this means less waste and a considerable reduction in the environmental contamination since, until now, once the life had expired, that is to say as soon as the mineral deposits are excessive, the entire evaporation vessel must be replaced together with the electrodes since removal of the electrodes is either completely impossible or would then be much too costly. 
     During assembly of an evaporation vessel for a specific apparatus type, matching electrodes are installed in a suitable position and orientation by means of plug-in parts which are inserted into suitably selected bushings. A certain amount of variability is in principle achieved in this case if only one of the electrodes can be installed in this way however, in a preferred embodiment, all the electrodes are held in one or more of the bushings by means of the said plug-in parts. Unused bushings can be sealed using additional plug-in parts. 
     As already mentioned, different rotation orientations can be provided for the same electrode, for example a) bent towards the vessel wall and b) away from it. Interacting positioning means are expediently constructed on the plug-in part and on the evaporation vessel in order to define one or more rotation orientations of the electrode or the axial alignment of the plug-in part in the bushing. Such positioning means can, for example, comprise a special shape of the cross-sectional contour of the bushing and plug-in part or can also be implemented using positioning studs and corresponding recesses for accommodating the positioning studs in the other part. 
     Very frequently, further functional parts, for example sensors for the water level and the like, must be arranged in the interior of the evaporation vessel as well as the electrodes. These further functional parts are also advantageously held in one of the bushings by means of a plug-in part. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment is described in the following text in order to explain the invention in more detail, with reference to the attached drawings, in which: 
     FIG. 1 shows an evaporation vessel according to the invention, in a perspective, partially cut-away illustration, 
     FIG. 2 shows a plan view of the evaporation vessel in FIG. 1, 
     FIG. 3 shows, in a perspective illustration, the cover of the evaporation vessel having two active electrodes, which are installed therein, and one dummy electrode, together with a sieve having holding elements for supporting the electrodes in their lower region, 
     FIG. 4 shows a vertical section of a plug-in part, which is inserted into a bushing in the cover of the evaporation vessel, together with a plug for the electrical connection of the electrode, 
     FIG. 5 shows a side view of the plug-in part in FIG. 4, 
     FIG. 6 shows a plan view of the plug-in part in FIG. 5, 
     FIG. 7 shows a vertical section of a bushing, which section is rotated through 90° with respect to FIG. 4, 
     FIG. 8 shows a partially cut-away side view of the plug-in part, rotated through 90° with respect to FIG. 5, 
     FIG. 9, FIG. 10, FIG. 11 and FIG. 12 show different possible electrode arrangements in a schematic illustration, viewed from above, 
     FIG. 13 shows a preferred embodiment of the connection of the cover and lower part of the evaporation vessel, using a side view of the lower part and the cover separated therefrom, 
     FIG. 14 shows a plan view of the lower part of the evaporation vessel, and 
     FIG. 15 shows a partial side view of the closed evaporation vessel, viewed from direction A in FIG. 13. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1, 2 and 13 show the evaporation vessel which is designated by 2 in its totality. It is normally located in a housing 4 (which is indicated by dashed lines in FIG. 1) of an air humidifier. Those details of such an apparatus, such as the water connection, vapour distributor, electronic controller etc., which are not essential in the present context and are known to the person skilled in the art are not illustrated. The evaporation vessel 2 consists of a lower part 6, in whose base a water inlet and outlet 8 is arranged, and of a cover 10 having a vapour outlet 12. Supporting feet 14 which are integrally formed on the lower part and on which the lower part can be erected in a free-standing manner during installation or servicing tasks can furthermore be seen. 
     A number of bushings, seven altogether, are constructed in the cover 10, four of which, which are designated by 16.1, are arranged relatively close to the edge and three, which are designated by 16.2, are arranged relatively close to the centre of the cover. Plug-in parts 18 can be inserted into these bushings 16.1 and 16.2 respectively, by means of which plug-in parts 18 electrodes can be held in the cover 10, as is described in more detail below. 
     For better clarity, the illustrations in FIGS. 1 and 2 show only a single plug-in part 18 inserted in one of the bushings 16.1, which plug-in part 18 carries a rod 20, which is part of an electrode. An arrangement of three electrodes can be seen in FIG. 3, consisting of two identical electrodes 22 which are &#34;real&#34; in the normal sense, that is to say are connected to a supply voltage in operation, and of an electrode 24 which is designed as a dummy electrode. A further electrode 22, which would be arranged towards the observer, is omitted in the figure (cf. FIG. 11). As has already been described in general above, the dummy electrode 24 is not connected to a supply voltage but is held in an electrically insulated manner in the wall of the evaporation vessel 2, or is possibly connected to a neutral conductor. It is used to a certain extent passively in order to influence the electric field which is generated by the active electrodes 22. 
     In the case of the exemplary embodiment shown here, each electrode 22 consists of a rod 20 and an electrode body 22.1 attached thereto, and the electrode 24 consists of two rods 20 and an electrode body 24.1 which is attached to these rods. Both the rods 20 and the electrode bodies 22.1 and 24.1 respectively are manufactured from an electrically conductive material, preferably metal. All the electrodes are held in the cover 10 by means of plug-in parts which are in each case attached to one of the rods 20, to be precise the electrodes 22 in bushings 16.1 and the dummy electrode 24 in bushings 16.2. 
     As can be seen in FIGS. 1 and 3, retaining elements 26 can be provided for supplementary stabilization of the electrodes, which retaining elements 26 are fitted on a sieve 28, for example being integrally formed, which sieve 28 is normally present anyway and is arranged in the evaporation vessel at the bottom. In the case of the exemplary embodiment, the retaining elements 26 are constructed as sleeves into which the lower ends of the rods 20 are inserted. 
     The details of the bushing 16.1 or 16.2 respectively and the plug-in part 18 can best be seen in FIGS. 5 to 8. The bushings 16.1, 16.2 are essentially constructed identically so that the same plug-in part can be inserted into both. They have a circular cross-section and are surrounded by annular guide flanges 30 and 32 which support the plug-in part 18 at the sides. The contour of the plug-in part 18 is matched, in a tightly seating manner, to the bushing 16.1 or 16.2 respectively and the guide flanges 30, 32. A sealing ring is designated by 34. If an electrode is intended to be held by means of a plug-in part 18, then said electrode is firmly attached to the plug-in part. In the case of the exemplary embodiment which is shown, the rod 20 for this purpose extends through a central hole in the plug-in part 18; the upper end of the rod can thus at the same time be used as an electrical connecting pin for a connecting plug 36. 
     The plug-in part 18 has two elastically flexible tongues 38, which are provided at their free end with a latching stud 40, as a latching device which can hold the plug-in part 18 in one of the bushings 16.1, 16.2 such that it latches automatically. The latching stud 40 is formed such that it tapers in the shape of a wedge in the insertion direction and has a latching projection 42 which engages behind a latching edge 44, in this case the edge of the guide flange 30, when the plug-in part is inserted. If a plug-in part 18 is moved into one of the bushings 16.1, 16,2, then the wedge surfaces of the tongues 38 run onto the edge of the bushing and in consequence are bent so far inwards that the plug-in part can be moved further into its final position. The length of the tongues 38 is selected such that the latching stud 40 becomes free again precisely in the final position, is thus forced outwards by the elasticity of the tongues 38 and engages behind the latching edge 44. In order to remove the plug-in part from the bushing, the projecting ends of the two tongues 38 can be pressed towards one another, for example using two fingers, until the latch is released and the plug-in part can be removed. As can be seen in FIG. 4, furthermore, the connecting plug 36 can advantageously be Used for the purpose of securing the tongues 38 in their latching orientation. 
     According to a preferred embodiment, positioning studs 46 are provided on the plug-in part 18 and corresponding recesses 48, in the form of slots, are provided in the guide flange 32. The positioning studs 46 and recesses 48 form interacting positioning means which ensure that the plug-in part 18 can be inserted into one of the bushings 16.1, 16,2 only in specific axial alignments. In the design which is illustrated in FIGS. 4 to 8, for example, the plug-in part 18 can be inserted in only two orientations, which differ by rotation through 180° about the main axis of the plug-in part. 
     In order to illustrate the wide possibilities which the invention offers for implementing different electrode arrangements in the same evaporation vessel using only a small number of electrode types, four examples are given in FIGS. 9 to 12. The position of the rods 20 in this case corresponds in each case to one position--which can best be seen in FIG. 2--of the bushings 16.1 and 16.2 respectively. The arrangement in FIG. 9 is used for two-phase alternating current and comprises two electrodes 22 and a dummy electrode 24, both of the type which has already been described further above with reference to FIG. 3. The arrangement in FIG. 10 is suitable for three-phase alternating current, it consists of three electrodes 22 which, in contrast to FIG. 9, are aligned bent inwards. FIG. 11 shows the arrangement in FIG. 10, supplemented by a dummy electrode 24. Two possible orientations of the electrodes 22 are indicated here, one bent inwards and one bent outwards. The arrangement can be matched to different vapour powers by suitable selection of the orientation of the electrodes. An arrangement having totally different electrodes is illustrated, by way of a supplement, in FIG. 12. These are three large-area electrodes 50, as are used for so-called demineralized water. 
     In the case of a preferred embodiment of the evaporation vessel, illustrated in FIGS. 13 to 15, the connection between the lower part 6 and the cover 10 of the evaporation vessel 2 is designed in the manner of a bayonet fitting. This makes the handling during opening and closing of the vessel particularly simple since only a short rotation is necessary for this purpose, and thus simplifies, in particular, replacement of the electrodes by the user. The bayonet fitting is formed by a number of first, outwardly projecting studs 52 on the lower part 6 and a corresponding number of second, inwardly projecting studs 54 on an annular web 56 on the cover, which web 56 engages over the edge of the lower part and the first studs 52. The studs 52 and 54 have inclined surfaces 58 and 60 respectively which face one another when the cover is fitted and run in a slightly inclined manner with respect to the fitting plane so that the two parts are moved towards one another by rotating the cover relative to the lower part, until the edge of the lower part 6 is pressed against a sealing ring 62, which is inserted in the cover 10, and the fitting is firmly seated. Two ribs 64 and 66 respectively, which are integrally formed on the side, on the web 56 and on the lower part 6 respectively form an additional stop for the closing rotation.