Abstract:
A continuous flow electric heater for heating liquid contained in a liquid container has a plurality of parallel tubular heating ducts (7b) each bounded by a tubular wall (ib) having upper and lower ends connected respectively to a lower inflow chamber (19b) and an upper outflow chamber (31). The inflow chamber (19b) forms a collector for solids which many separate from the liquid being heated and is defined by a pot-shaped body having a large area solids removal opening closed by a removable cover (25b) and providing access to the interior of the inflow chamber (19b) over the entire width thereof, thereby allowing full access to the interior of the ducts (7b). A tubular heating resistor (17b) is helically wound around each tubular wall portion (8b) to heat the liquid flowing therethrough. A common reception tube (27b) tangentially engaging each tubular wall (8b) between two adjacent turns of the heating resistor thereon removably receives the temperature sensor of a thermal cutout protector. The temperature sensor of a temperature regulator is removably received in the reception tube (35) located in the upper portion of the inflow chamber (19b).

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an electric heating means for liquid containers, particularly for hot water equipment, with at least one tubular heater. 
     For heating liquids in containers, such as hot water tanks, washing machines or the like, in general the heater is associated with the container in such a way that it heats the liquid therein until the desired temperature is reached. Despite possible liquid flow reactions due to the heating means, there are large temperature differences within the liquid in the container and efficiency is not always satisfactory. Particularly when heating hard water considerable solids in the form of lime are also deposited on the interior of the container and can lead to a further deterioration of efficiency, whilst also causing cross-sectional reduction preventing the liquid flow. Cleaning such containers for removing the solids is usually very complicated and time-consuming. 
     SUMMARY OF THE INVENTION 
     The problem of the present invention is to provide an electrical heating means for liquid containers, which ensures increased efficiency in a simple manner by a continuous removal of solids. 
     According to the invention this problem is solved by an electrical heating means of the aforementioned type, in that a continuous flow heater heated by tubular heaters is connected to the inlet and outlet sides of the container and has at least one lower collector for solids removal which can be emptied through a large-area opening. Thus, the liquid is uniformly heated to the desired temperature flowing in a circuit through the container and continuous flow heater, accompanied by a constant thorough mixing, so that the solids appear in the collector of the continuous flow heater and not in the container and can be much more easily removed therefrom than from said container. The liquid flow through the continuous flow heater and therefore through the container can be brought about, according to the invention, by a thermosiphon action and/or by a mechanical pump, such as a circulating pump. 
     A particularly advantageous construction of the invention is obtained in that the continuous flow heater has at least one flow heating duct, which is heated from at least one side remote from the side subject to the liquid action and in particular from the outside by means of the tubular heater. Thus, the tubular heater or heaters do not come directly into liquid contact and this in particular prevents local overheating and ensures a rapid heat transfer from the tubular heater to the liquid, because the tubular heater heats the heating duct wall in large-area manner and the liquid flows along said wall. Thus, the surfaces coming into contact with the liquid and in particular the liquid-carrying surfaces of the heating duct can be made very smooth and even, so that the tendency towards the deposition of solids is significantly reduced. 
     The thermosiphon action of the continuous flow heater can, e.g., be brought about in simple manner such that the inlet of the continuous flow heater, particularly the heating duct, e.g., directly emanating from the container, is made lower than the outlet, which also appropriately issues into the container. The inlet and outlet can be vertically superimposed or the outlet can be laterally displaced with respect to the vertical relative to the inlet. In both cases, there are appropriately linear flow paths within the continuous flow heater between the inlet and outlet. In the case of a sloping arrangement of the continuous flow heater, e.g., constructed in the manner of a heating cartridge, the angle of inclination can be adapted to the viscosity of the particular liquid to be heated in that said angle of inclination can be made shallower as the viscosity decreased. 
     A particularly compact heating means construction, which further improves efficiency, is obtained if the continuous flow heater is at least partly integrated into the container interior and in particular is attached as a shaft to the container bottom at the inlet and outlet sides. Thus, the continuous flow heater and container form a closed assembly and there are very short flow paths between the heater and the container. However, it is also conceivable to connect the continuous flow heater detachably to the container via pipe connections in the form of a separate unit. 
     As a further development of the invention, the continuous flow heater is provided on the inlet side with a downflow duct, via which the in each case cooler liquid can flow out of the container and directly into the heater. The downflow duct is preferably at least partly located in the heating duct having a rising flow direction and/or is approximately equiaxial to the heating duct, so that in the path from the container to the heating zone of the continuous flow heater, the liquid is not subject to any further cooling and a very space-saving continuous flow heater construction is obtained. 
     A very favourable liquid flow behaviour is obtained in that the upper end of the downflow duct, which is in particular located above the container bottom, is higher than the continuous flow heater outlet, which is in particular level with the container bottom, so that despite a virtually random container shape a favourable circuit flow within the container is obtained. This is further improved in that at least one flow guiding member for the continuous flow heater outlet flow is provided which is directed away from the downflow duct inlet flow. The flow guidance member is preferably formed by the end of the downflow duct, which is widened in funnel-shaped manner and covers the outlet of the heating duct. In the case of an equiaxial arrangement of the downflow duct and heating duct, as well as with a horizontal outlet or flow guidance member within the container, the heated liquid coming from the continuous flow heater is directed away from the central axis of the flow guidance member and introduced into the container, whilst the liquid flowing to the heater is concentrated in an area immediately around said central axis. 
     Existing containers, e.g. burner-heated hot water boilers can benerally be readily reequipped to the inventive construction, if the continuous flow heater is constructed for connection to the outside of the container and preferably has connecting openings at the inlet and outlet sides at right angles to the heating duct for connecting to an upright container wall. The continuous flow heater can be connected to the container in electrically insulatable isolated manner, so that electrolysis problems are not of concern. In the case where the continuous flow heater is connected to the outside of the container, this can e.g. be achieved in that the liquid-carrying connections contain, in the form of intermediate members, hose portions made from non-conductive material, e.g., plastic. The connections between the continuous flow heater and container can be constructed in such a way that the heater is only carried by these connections and consequently requires no further support or fixing. 
     To further increase efficiency and improve maintenance, two or more separate heating ducts, particularly identical and/or parallel heating ducts, emanate from the collector and preferably issue into a mixing casing upstream of the continuous flow heater outlet. On the side of the mixing casing facing the inlet to the heating ducts it is in particular provided with a closable access opening, so that direct inspection and cleaning of the interior of the heating ducts is readily possible. 
     A simple heating means construction is obtained in that the heating duct, which in particular may be cross-sectionally annular, and/or the downflow duct is in each case formed by a pipe. 
     The use of pipes, particularly cylindrical pipes also offers the possibility of fitting the tubular heaters very simply in good thermally conducting connection. According to the invention this can be achieved in that the tubular heater is fitted to the continuous flow heater or heating duct, particularly as a prestressed or biased coil, and is thermally conductively combined with the associated wall by alloying or some similar solder-like connection. 
     It is conceivable to make the collector and/or continuous flow heater such that the collector is accessible through the upper, large-area opening of the heater, e.g. through the downflow duct, for emptying purposes. However, emptying is much simpler if the collector has a base cover and/or is formed by a pot or the like removable from the continuous flow heater, so that the collector can be simply emptied from the bottom. If a sliding check valve or the like is provided in each line connection of the continuous flow heater with the container, it is possible to clean the collector at any time independently of the emptying of the container by shutting off the line connection or connections. 
     For temperature regulation or running dry protection purposes, it is advantageous to provide adjacent to the tubular heater and/or in the liquid flow path in the continuous flow heater at least one reception tube for the removable arrangement of the sensor of a temperature regulator. Thus, the temperature is monitored by means of the sensor in or on the continuous flow heater instead of in the container, so that further simplification of maintenance and assembly of the electrical heating means is obtained. 
     In order to obtain a particularly effective protection against running dry, the reception tube for the temperature sensor is appropriately soldered adjacent to the tubular heater to the latter and/or to the wall of the heating duct or is fixed by clips which closely surround it in thermally conducting manner. 
     Other than for hot water boilers and the like, the inventive construction is particularly advantageous as a heating register for washing machines, dishwashers, etc. The heating means according to the invention can also be used for heating liquids other than water, e.g. frying fat for deep fat fryers, where once again the provision of a continuous flow heater permits simple cleaning of the fryer container and simple removal of the solids obtained when frying. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in greater detail hereinafter relative to non-limiting embodiments and the attached drawings, wherein show: 
     FIG. 1 An axial section through a heating means according to the invention. 
     FIG. 2 A plan view of the heating means according to FIG. 1. 
     FIG. 3 A section along line III--III of FIG. 1. 
     FIG. 4 A further embodiment of a heating means in a representation corresponding to FIG. 1. 
     FIG. 5 A plan view of the heating means according to FIG. 4. 
     FIG. 6 A detail of FIG. 4 on a larger scale. 
     FIG. 7 Another embodiment of a heating means in a view on the connection side. 
     FIG. 8 The heating means according to FIG. 7 in side view. 
     FIG. 9 A section along line IX--IX of FIG. 7. 
     FIG. 10 A detail of FIG. 8 in sectional, larger-scale representation. 
     FIG. 11 A detail of FIG. 10 in a further embodiment. 
     FIG. 12 A further embodiment of a heating means in part sectional view. 
     FIG. 13 A further embodiment of a heating means in a representation corresponding to FIG. 7. 
     FIG. 14 The heating means according to FIG. 13 in side view. 
     FIG. 15 The heating means according to FIG. 13 in plan view. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The heating means 1 according to FIGS. 1 to 3 is associated with a container 2, e.g. a hot water boiler, which is provided with supply and drain lines (not shown) for the liquid to be heated. Container 2 is substantially symmetrical to a vertical central axis 3 and with respect to its central axis, said heating means is entirely located in central axis 3. Heating means 1 is positioned in the vicinity of an opening 5 on the bottom 4 of container 2 and partly projects through the central, e.g. circular opening 5 into the container interior 6. 
     Heating means 1 has a vertical, cross-sectionally circular heating duct 7, which is radially outwardly bounded by a tubular wall 8 and radially inwardly by a tubular wall 9 which is equiaxial to wall 8. Wall 9 surrounds or bounds a downflow duct 10 positioned equiaxially in heating duct 7 and only separated from the latter by wall 9. The lower end of duct 10, roughly in the plane of the lower end of wall 8, is level with the circular liquid inlet 11 for the heating duct 7. At the upper end, tubular wall 8 has a flange 12 for the sealed fixing to the underside of the container bottom 4, the width of opening 5 being at least as large as the greatest width of heating duct 7. The upper end of heating duct 7, level with said flange 12, forms its circular liquid outlet 13 issuing directly into container 6. The upper end of wall 9 or the downflow duct 10 is widened in obtuse-angled, funnel-shaped manner 14 just above liquid outlet 13 to a width which is greater than the maximum width of outlet 13 or the heating duct 7 which has substantially constant cross-sections over its height. Thus, the upper end of wall 9, apart from an inlet for the downflow duct 10 constricting in funnel-shaped manner downwards to the width of duct 10, forms an annular flow guidance member, which slopes upwards in axial section and is positioned annularly around the central axis 3. In plan view on the heating means, said guidance member completely covers the outlet 13 of heating duct 7. Thus, the flow guidance member 14 effectively separates the liquid flow guided into heating means 1 from the liquid flow guided from heating means 1 into container 2. Therefore the heated liquid leaving heating means 1 is uniformly upwardly guided about central axis 3 along the wall of container 2, is deflected downwards in the upper region of container 2 and is finally supplied in circuit to the downflow duct 10 again for further heating purposes. 
     The outer wall 8 of heating duct 7 is provided on the outside 16, remote from inside 15 and which is subject to liquid action and namely on the outer circumference thereof with an electric tubular heater 17, which is fixed in closely engaging and therefore good heat conducting manner to said side 16, e.g. by soldering or the like. The tubular heater surrounds wall 8 in helical manner and it is possible to provide two or more helical heater coils, which can be switched in separately in the manner of a multiple coil, so as to have the possibility of operating the heating means 1 at different power levels. The tubular heater 17 extends substantially over the entire length of heating duct 7 or wall 8. 
     Below the inlet 11 to heating duct 7 is provided a deflecting and collecting space 18, whose central axis coincides with central axis 3 and whose width is at least as great as the maximum width of the heating duct 7, so that the heating duct 7 is open over its entire cross-sectio downwards to collector 18. Collector 18 is formed by a pot 19, which is fixed in easily detachable, but sealed manner to a lower flange 20 of wall 8. The liquid passing out of the lower outlet of downflow duct 10, located in the plane of inlet 11, is deflected in collector 18 radially outwards and upwards into heating duct 7, the solids dropping into the relatively low-flow lower region of the collector 18 and depositing on the bottom thereof. Any solids depositing on the walls of heating duct 7, some of which regularly break off as a result of the thermal stresses which occur, also tend to drop to the bottom of collector 18 due to the relatively low flow rate in duct 7. Following the removal of pot 19, it is possible to empty the same and then heating duct 7 is completely accessible from below over its entire height, so that its walls can easily be cleaned. 
     As a result of the described construction, heating means 1 has a continuous flow heater 21 integrated with container 2 and which heats the content of the latter in circuit. The actual heating zone is located in the vicinity of heating duct 7, where the flow is directed from bottom to top according to arrow 22. 
     In FIGS. 4 to 15 corresponding parts are given the same reference numerals as in FIGS. 1 to 3, but followed by the letter a in FIGS. 4 to 6, b in FIGS. 7 to 10, c in FIG. 11, d in FIG. 12 and e in FIGS. 13 to 15. 
     In the embodiment according to FIGS. 4 to 6, the container bottom 4a is provided with a bottom flange 5a, to which is fixed, by its upper flange 12a, the tubular wall 8a bounding the heating duct 7a on a radially outer circumference. The two engaging flanges are secured with a detachable profile ring 23, whilst interposing a ring seal 24 engaging round the same. 
     Wall 8a extends over the entire height of the continuous flow heater 21a, so that it also simultaneously bounds collector 18a and projects downwards by the height of collector 18a with respect to the lower end of wall 9a. To the lower end of wall 8a is fixed a detachable bottom cover 25, so that the interior of wall 8a is accessible over the entire width through the removal of cover 25. The upper end of wall 9a forms a plurality of roughly radially outwardly projecting fastening plates 26 uniformly distributed about the central axis 3a and which are fixed by bent or offset ends to the inside of the container bottom 4a. Thus, following the removal of wall 8a, the outside of wall 9a is readily accessible. 
     As can in particular be seen in FIG. 6, the tubular heater 17a, can also be flattened for engagement on the associated side 16a of wall 8a, e.g. can be given a triangular cross-section, so that there is an even better heat transfer from tubular heater 7a to wall 8a. Adjacent tubular heater 17a, at least one reception tube 27 is fixed in good heat conducting manner to the same side 16a of wall 8a and serves to receives the temperature sensor 28 of a temperature regulator, e.g. filled with an expansion fluid. In the same or a similar manner, it is also possible to provide a reception tube for a temperature sensor of a running dry protection means, said reception tube being appropriately in direct thermally conducting contact with the tubular heater. 
     FIGS. 7 to 10 show a continuous flow heater 21b having openings 29, 30 for connection to the container (not shown) transversely or at right angles to the flow direction indicated by arrow 22b of several heating ducts 7b. Pot 19b defining the collector 18b has its opening closed by a detachable cover 25b on the underside. To the upper base of pot 19b are connected three parallel and identical pipe sections 8b, which are in a common axial plane and in each case bound one heating duct 7b, being provided on the outer circumference with a separate helical tubular heater 17b. The internal spacing between adjacent pipe sections 8b is smaller than the diameter thereof. The upper ends of the pipe sections and therefore heating ducts 7b are connected to the bottom of an also pot-shaped, common mixing casing 31, whose upper pot opening is also closed by an easily detachable cover 32. The inflow connection opening 29 of the continuous flow heater 22b is provided in a wall of pot 19b, whilst the outlet connecting opening 30 axially parallel thereto and vertically superimposed with respect thereto is located on the associated wall of mixing casing 31. The two connecting openings 29, 30 can be formed by projecting connecting pieces 33, 34. As a result of this construction, the continuous flow heater 21b can be simply subsequently joined to the outside of a container. In addition, following the removal of covers 35b, 32, the heating ducts 7b are easily accessible for cleaning or other purposes. 
     On the outsides of pipe sections 8b is fixed a common reception tube 27b for a temperature sensor having a running dry protection function. The reception tube 27b tangentially engaging on all pipe sections 8b is positioned between each heating duct 7b between two turns of the associated tubular heater 17b, which can be in direct contact therewith. The temperature sensor is inserted in reception tube 27b, which is open at one end, so that it can always be removed again and, e.g., replaced. The same applies with respect to a second reception tube 35, which is provided in the liquid flow path within the continuous flow heater 21b, namely in the upper region of collector 18b. The closed end of reception tube 35 is positioned within collector 18b, whilst the other open end of the sealed reception tube 35 passing outwards through a wall of heater 21b is positioned in freely accessible manner on the outside of heater 21b. Thus, the associated temperature sensor, which is appropriately associated with a temperature regulator, can be replaced at any time. For this purpose, the reception tubes are substantially linear or only slightly curved, so that the temperature sensor can be adequately easily inserted and removed. 
     In the case of the continuous flow heater according to FIGS. 7 to 9, the tubular heaters 17c according to FIG. 11 can also have flattened engagement faces or a triangular cross-section. 
     The continuous flow heater 21d according to FIG. 12 is also constructed for arrangement on the outside of a container. The cross-sectioally circular heating duct 7d is bounded by two coaxial, tubular walls 8d, 9d, the outer wall 8d being provided on the outside with at least one tubular heater 7d and the inner wall 9d on the inside with at least one tubular heater 17d, so that a greatly enlarged contact surface is provided for heating the liquid flowing through heating duct 7d. Such a construction would also be conceivable in the case of the provision of a downflow duct according to FIGS. 1 to 6, the wall of said duct then being positioned within the inner tubular heater 17d. To increase efficiency or avoid heat losses, the outer tubular heater 17d or the associated wall 8d is covered by a thermal insulation 36 and the inner tubular heater 17d with a thermal insulation 37. The inner insulation 37 can completely fill the inner cavity of wall 9d. The inflow connecting opening 29d of the continuous flow heater 21d or the associated connecting piece 33d is appropriately provided on the pot 19d adjacent to collector 18d and which can e.g. be detachably screwed on to an outer thread of the outer tubular wall 8d. If the inner wall 9d is also fixed to this pot 19d, on detaching said pot, it can be completely removed from outer wall 8d, thereby permitting very simple cleaning of the complete continuous flow heater 21d. 
     As shown in FIGS. 13 to 15, the inner wall 9e of the annular heating duct 7e, which in this case differs in cross-section from a circular shape, can also be arranged in suspended manner in the outer wall 8e. The upper end of wall 9e is fixed to a switch box 38 for the tubular heater 17e, which simultaneously forms the upper, detachable end cover of outer wall 8e. Thus, inner wall 9e, including the tubular heater 17e can be removed upwards out of the outer wall 8e together with the switch box 38. In the represented embodiment, tubular heaters 17e are only provided on the inside of inner wall 9e. 
     Pot 19e bounding the collector, which is shown in the removed state in FIG. 14, is detachably fixed to the underside of outer wall 8e, so that it can be emptied at all times. If pot 19e and switch box 38 are removed, then the complete inner area surrounded by wall 8e is freely accessible for maintenance purposes. 
     As is further shown in FIG. 14, container 2e, indicated by dot-dash lines, is provided on an upright or vertical container wall 39 with two parallel, substantially vertically superimposed connecting pieces, whose reciprocal spacing is adapted to the spacing between connecting pieces 33e, 34e. The connecting pieces of the continuous flow heater 21e are connected to the connecting pieces of container 2e via fitted connecting sleeves 40 made from rubber or some similar material and sleeves 40 are, e.g., secured with clips. As a result the continuous flow heater 21e can at any time be completely removed from container 2e. 
     A continuous flow heater is also conceivable, whose outer wall has a bulging, flattened or oval shape corresponding to wall 8e in FIG. 15 and on to whose outside is wound at least one tubular heater, as in the embodiment according to FIGS. 7 to 9. The top and/or bottom of the wall can be closed by in each case one removable, cross-sectionally corresponding cover, which has a connecting piece for the supply or removal of the liquid to be heated. Furthermore, the wall can be formed from portions assembled in the longitudinal direction, whereof each carries at least one separate tubular heater, so that by adding or removing such portions, which can have an identical construction, it is possible to increase or decrease the caloric power of the continuous flow heater. Appropriately the portions engaged by their end faces in positive, sealed manner in one another, said faces being constructable in such a way that they are also suitable for the positive sealed engagement of the end covers. As a result of the flattened construction of the continuous flow heater, favourable dimensions for a space-saving location are provided. The outer wall of the continuous flow heater can also be given a drum shape, e.g. can bulge towards the centre of its length, in such a way that its cross-sections are smaller in the vicinity of its ends than in the vicinity of the centre of its length.