Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
  • F24H1/00—Water heaters, e.g. boilers, continuous-flow heaters or water-storage heaters
  • F24H1/10—Continuous-flow heaters, i.e. heaters in which heat is generated only while the water is flowing, e.g. with direct contact of the water with the heating medium
  • F24H1/12—Continuous-flow heaters, i.e. heaters in which heat is generated only while the water is flowing, e.g. with direct contact of the water with the heating medium in which the water is kept separate from the heating medium
  • F24H1/121—Continuous-flow heaters, i.e. heaters in which heat is generated only while the water is flowing, e.g. with direct contact of the water with the heating medium in which the water is kept separate from the heating medium using electric energy supply
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
  • F24H1/00—Water heaters, e.g. boilers, continuous-flow heaters or water-storage heaters
  • F24H1/18—Water-storage heaters
  • F24H1/20—Water-storage heaters with immersed heating elements, e.g. electric elements or furnace tubes
  • F24H1/201—Water-storage heaters with immersed heating elements, e.g. electric elements or furnace tubes using electric energy supply
  • F24H1/202—Water-storage heaters with immersed heating elements, e.g. electric elements or furnace tubes using electric energy supply with resistances
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
  • F24H9/00—Details
  • F24H9/0005—Details for water heaters
  • F24H9/001—Guiding means
  • F24H9/0015—Guiding means in water channels
  • F24H9/0021—Sleeves surrounding heating elements or heating pipes, e.g. pipes filled with heat transfer fluid, for guiding heated liquid
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
  • F24H9/00—Details
  • F24H9/12—Arrangements for connecting heaters to circulation pipes
  • F24H9/13—Arrangements for connecting heaters to circulation pipes for water heaters
  • F24H9/133—Storage heaters
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
  • F24H9/00—Details
  • F24H9/18—Arrangement or mounting of grates or heating means
  • F24H9/1809—Arrangement or mounting of grates or heating means for water heaters
  • F24H9/1818—Arrangement or mounting of electric heating means
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
  • F24H9/00—Details
  • F24H9/40—Arrangements for preventing corrosion
  • F24H9/45—Arrangements for preventing corrosion for preventing galvanic corrosion, e.g. cathodic or electrolytic means
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
  • F24H9/00—Details
  • F24H9/40—Arrangements for preventing corrosion
  • F24H9/45—Arrangements for preventing corrosion for preventing galvanic corrosion, e.g. cathodic or electrolytic means
  • F24H9/455—Arrangements for preventing corrosion for preventing galvanic corrosion, e.g. cathodic or electrolytic means for water heaters

Definitions

• the invention relates to a tubular-shaped heating element for use, in particular, with boilers for sanitary purposes and household electrical appliances in general.
• the heating devices currently used in the aforesaid boilers are generally the so-called 'armoured electrical resistors'. These are constituted of an resistive electric f ament immersed in a chemically inert, electrically insulating powder, which is, in its turn, pressed into a hermetically sealed metal pipe.
• the optimal thermal power dispensable per unit of surface (normally called the 'thermal load') is usually approximately 8.5W/cm2 for boiler resistors and 5W/cm2 for dishwasher resistors, which are also designed to run dry during the drying phase.
• Electric storage heaters are generally characterised by a flange onto which one or more electrical resistors are mounted, a thermostat sheath containing one or more temperature sensors and, possibly, an anticorrosion device constituted of a magnesium anode or a cathodic protection device electrode.
• the inlet pipe which is very short, just penetrates the tank and the said pipe dispenses the cold water into the bottom of the said tank.
• the output pipe runs through the whole tank to draw the hot water from the highest part.
• the minimum installed power in this type of boiler is approximately 1,200/1,500W.
• the so-called "under-the-sink” electric storage heaters are small boilers located inside the sink unit. To make the attachment to the tap unit easier, these boilers are mounted upside down and, consequently, so that the cold water is inserted in the lower part and the hot water is drawn from the upper part, the pipe that normally acts as the inlet pipe is then attached to the output and vice-versa.
• the fast-acting electric boilers are similar in construction to the storage heaters, except that they may have a smaller tank to suit the function they have to fulfil, they have a higher level of installed power and, for safety reasons, they are often of the so-called "free-discharge” kind, i.e. the water contained in the tank is at room pressure.
• the instant electric boilers are characterised by a very small storage tank or by the fact that they do not have a storage tank (it is replaced by a long piece of piping which is heated by electrical resistors), by a high level of electric power (even as high as 20kW) and, for safety reasons, these too are often of the 'free-discharge' kind.
• the armoured electrical resistors mentioned earlier are generally used. In certain phases of the washing programme, when immersed in water, these resistors heat the water, in other phases, when the device is dry, the said resistors proceed to dry the crockery.
• the aforesaid armoured resistors have some drawbacks, a first of which is represented by the complex production process.
• a further drawback of this type of commonly known resistance is constituted by the distribution of the thermal power achieved with a looped or spiral-shaped resistor: all forms require costly specific equipment.
• the drawbacks of the current electric storage heaters are constituted, above all, by the need for a flange, as a sealing element, and a support for at least one or more resistors, a sheath for one or more thermostat probes, and, possibly, a magnesium anode or a cathodic protection system electrode.
• a further drawback of this kind of boiler is that the water must be stored at at least the usage temperature, but normally at much higher temperatures than the fast-acting boilers or even higher than the instant boilers, with a lower level of installed power but with greater heat loss and lime-scale deposits forming faster, these latter having an effect on the corrosion.
• a further drawback is that it is impossible, without using a comphcated-shaped resistor, to concentrate a significant amount of the thermal power in the lower part of the tank in order to guarantee more uniform temperatures with less heat loss keeping the average temperature unchanged.
• a still further drawback is constituted by the fact that with the armoured electrical resistors it is impossible to heat the water a final time when it is drawn from the device.
• the said resistors are constituted of a metal support base, generally
• AISI 430 steel capable of diffusing the thermal energy emitted and guaranteeing the adhesion of the overlaying layers even if heat expansion occurs.
• this metal support base - one or more layers of dielectric material
• printed resistor will be used to indicate the whole unit constituted of the actual printed circuit and the layers of dielectric material underneath and above it, whether the circuit was made using a screen-printing technology or any other circuit printing technology.
• the thermal loads obtainable with the printed resistors obviously depend on the capacity for heat elimination but, while the there are no particular increases in the cost of producing relatively low thermal loads in relation to those generally used in the sector, these can still be extremely high (at least 18-20W/cm2).
• the printed resistors can also function dry because they can resist up to 700° C in the air (250°C at the welded points on the electric terminals).
• the subsequent layers can also be placed on curved surfaces.
• the feeder cables are connected electrically to the printed resistive circuit at the end of the printed circuit, by welding in two points which are intentionally not covered by the second group of layers of dielectric material.
• a first aim of this invention in a device for heating water such as an electric boiler or a dishwasher in which it is necessary to provide electric resistive means of heating the water and, possibly, means of checking the temperature of the water and/or, possibly, electrochemical means of preventing corrosion, consists in reducing the components required to realise the aforesaid means.
• a second aim consists in simplifying the construction of one or more of the aforesaid heating, temperature checking and corrosion prevention means.
• a third aim consists in snnplifying the mounting of one or more of the aforesaid means on a device for heating water.
• a fourth aim consists in limiting the lime-scale deposits that form on the aforesaid heating means.
• a fifth aim consists in the possibility of emninating the support flange from one or more of the aforesaid means.
• a further aim consists in the possibility of distributing the thermal power to be emitted by the aforesaid heating means better.
• a still further aim, for a storage heater consists in enabling the water to be heated fully at the moment it is drawn, using the same heating means that heat the stored water.
• a still ftuiher and final aim consists in reducing the manufacturing costs.
• a heating element constituted of a tubular element designed to pipe water (for sanitary purposes at least) and to whose external and/or internal surfaces are apphed one or more resistors printed in the way determined above.
• - Figure 1 is a section drawing of a heating element according to a preferred embodiment of the invention applied to the interior of a hot water storage tank;
• FIG. 2 is a total view of the heating element as per the embodiment in the previous figure
• FIG. 3 is a section drawing, along the main axis, of the same elements shown in the previous figure;
• FIG. 4 is an enlarged section drawing, at right angles to the main axis, of a general heating element
• - Figure 5 is a schematic diagram of a possible variant of the invention shown in figures 2 and 3, showing the flow of water inside the heating element during the heating phase of the said water and during the drawing phase;
• FIG. 6 is a schematic diagram of a further possible variant of what is shown in figure 2;
• FIG. 7 shows, extremely schematically, a fast-acting boiler using heating elements according to a variant of this invention
• FIG. 8 shows a total view of the heating element according to a further embodiment of the invention.
• the heating element 1 is shown inside the tank 2 of a storage heater.
• the heating element 1 is the hot water output pipe from the tank 2.
• the heating element 1 is constituted of: a piece of piping 3 made of any material compatible with the printed resistor technology and with the chemical, physical and mechanical stresses to which the said piping 3 will be subjected, e.g. AISI 430 steel; a printed resistor 4 and, lastly, a pipe coupling 5.
• the pipe coupling 5 is fitted with suitable connection means 6 and 7, for example, threaded bushings, to fix respectively, the said coupling 5 to both the tank 2, by means of a ring nut 8, welded to the tank 2 itself, and also to the hot water distribution system (not shown).
• the coupling 5 is also fitted with suitable connectors 9 for the electricity supply to the printed resistor 4, the said connectors 9 being connected electrically to the printed resistor 4 and insulated electrically from the remaining elements in a commonly known way not shown in the figure.
• figure 4 there are (from the inside to the outside of the heating element 1): a possible layer of material 14 on which it is difficult for lime- scale to form deposits, such as polypropylene; the piping 3 onto which the subsequent printed resistor 4 will be apphed, the said printed resistor 4 being constituted of one or more layers of a dielectric material anchored to the base of the support constituted by the piping 3; the actual resistive printed circuit and one or more external layers of a dielectric material.
• Last to be shown is a possible sheath 15 designed to protect the printed resistor 4 against abrasion.
• Figure 5 which constitutes a possible variant of the invention as indicated in figure 3, shows, with arrows, the circulation direction the water will assume during the two functioning modes of a storage heater.
• the openings 10. a and 11. a, fitted with deflectors 12 positioned towards the inside, constitute, respectively, variants of the openings 10 and 11.
• Figure 6 shows a possible variant of figure 5, where the openings lO.b and ll.b are made in the piping 3 in a position with the section enlargements 13.
• Figure 7 shows, mounted on a small tank 2.1, elements already shown in the previous figures: the arrows indicate the inlet and output water flow directions; although not shown in the figure, also the tank 2.1, in the same way as for the piping 3 in the previous figures, and at least for its entire cylindrical part, can constitute the support base for a printed resistor 4.1 completely identical to the printed resistor 4.
• the other elements indicated are identical or equivalent to those shown in the previous figures. Therefore, the fast-acting kind of boiler shown in the figure is fitted with at least two printed resistors: the aforementioned printed resistor 4.1 and the printed resistor 4 , the base element of which is constituted of a piece of piping 3 of the hot water output kind.
• FIG. 8 shows a heating element 1.1 according to a second embodiment of the invention which is suitable for heating water circulating in a piece of piping incorporated into a household appliance such as, for example, an instant boiler or a dishwasher.
• the said heating element 1.1 is fitted with one or more printed resistors 4, supported by a piece of piping 3.1 and fitted with two bushings 5.1 or equivalent means of connecting the said heating element 1.1 respectively to an input pipe for water to be heated and an output pipe for heated water.
• the other elements indicated are identical or equivalent to those shown in the previous figures. There will now follow a detailed description of the characteristics of the heating element 1 according to this invention.
• the printed resistor 4 has been drawn in the figure indifferently, whether it is constituted of fretwork or a spiral wound around the piping 3. In actual fact, this could have any route which does not intersect itself, the route could even be irregular to vary the thermal load along the length of the heating element in the most suitable way. There could be, for example, a double spiral route with a constant pitch which begins and ends at the pair of connectors 9, or a double spiral with a variable pitch.
• each said resistor term ating in a respective pair of connectors 9 with a view to make it possible to modulate the thermal power emitted by inserting one or more of the said printed resistors 4.
• An important aspect of this invention is the fact that, using the same technology, and at the same time as the printed resistors 4 are printed, electrical circuits can be printed for connecting various electrical or electronic components to the exterior of the tank electrically. These said components could be useful if mounted along the heating element, the said heating element acting as a support for the said components.
• the said components are welded in a commonly known way to one end of the printed electric circuits, in the most suitable position along the heating element, and insulated electrically from the surrounding environment; the other end of the said circuits terminates, with suitable electrical connectors, in position with the pipe coupling.
• the said components can be, for example, temperatures sensors (e.g.
• the temperature sensors can also be constituted of a printed resistive track with a resistivity level dependant enough on the temperature to be measured.
• the route of the printed sensor can be constituted of a track which is long enough to increase the total resistance, thus facihtating the measuring of the resistor as a function of the temperature change.
• one or more openings 10, constituted of 4mm holes are sufficient to guarantee the recirculation without the cold water eddying when the water is drawn from the tank
• the diameter of the heating element 1 can be made wide enough to permit a sufficiently active natural circulation inside it without any openings 10 being necessary.
• the speed of the water when it is drawn from the tank is high enough or sufficiently frequent to ensure a constant washing and so prevent or remove lime-scale deposits.
• a layer of non-stick material 14 for the lime-scale inside the piping 3 such as polypropylene.
• an external anti-abrasion jacket for the most external layer of insulating material constituting the printed resistor 4.
• a protective sheath 15 made of a suitable material, but it could also be useful to have the said protective sheath 15 made of a material designed to act as an electrode for the cathodic protection, as described in full in another patent filed at the same time, by the same applicant.
• the said protective sheath 15 can be constituted of a sacrificial metal tubular element to protect the apparatus against corrosion (in general a magnesium anode). With any commonly known means or the means described earlier, the said electrode or the said anode are suitably connected electrically to the metal tank to be protected.
• the heating element 1 permits the functioning to be flexible, which is impossible with the commonly known armoured electrical resistors.
• a boiler generally keeps the water at 70-75°C, while the usage temperature is generally 40° C. If little water is required and the user wishes to limit the heat loss, the storage temperature can be lowered to the usage temperature, but never below.
• the heating element 1 the water can kept at slightly lower temperature than the usage temperature and it can be reheated during the drawing phase, activating the printed resistor 4.
• the said electrical resistor 4 it is necessary for the said electrical resistor 4 to be operated by a thermostat during the storage phase and by a flow sensor unit, such as a pressure switch or a flow switch, during the water-drawing phase.
• the heating element 1 is shown as a pipe for drawing the hot water from a storage heater but, alternatively, this can take the form of the input pipe, as in the case of the 'under-the- sink' boiler or both the inlet pipe suitably extended inside the tank, and the output pipe for a better distribution of the thermal power in the most suitable areas.
• Figure 7 instead, shows a fast-acting boiler fitted with at least two printed resistors which are separated from each other physically.
• the first said resistor indicated with the number 4.1 and supported by the tank 2.1, can keep the water stored at a determined temperature, regulated by a suitable thermostat.
• the second, indicated with the number 4 and supported by the output pipe 3 can also heat the water during the drawing phase, regulated by a suitable flow sensor, such as a pressure switch or a flow switch.
• a single heating element 1 constituting the output pipe could perform both the pre-heating function during the storage phase and the final heating function during the drawing phase as long as the said heating element 1 has the openings 11 as shown in the figure.
• the heating element 1.1 shown constitutes, substantially, the entire water heating device.
• the metal base constituted by the piping 3.1 is made of any material compatible with the technology and the chemical, physical and mechanical stresses the element will be exposed to (including, in this case, the water mains pressure), for example AISI 430 steel.
• AISI 430 steel for example AISI 430 steel.
• two or more heating elements can be provided of the kinds 1 or 1.1, which are parallel to each other and coaxial, as shown in figure 7 for the fast-acting boiler. Alternatively, they are connected in series in a way not shown because it is obvious.
• the connectors 9 for connecting the heating element 1.1 electrically can be made, as well as in position with the pipe coupling, at any point on the external surface of the said heating element 1.1.
• the external surface can be insulated thermally and the power can be regulated using any commonly known means used for instant electric boilers.
• a heating element according to the invention can be used advantageously in a dishwasher. This is not very different from the version indicated with the number 1.1 in figure 8.
• the said heating element 1.1 is preferably positioned, in the dishwasher tray; the water delivered to the nozzles is made to circulate inside the pipe which gradually heats it up at each stage. For the drying phase, once the water has been drained away, the heating element functions dry.
• the printed resistor 4 or 4.1 can be apphed to the internal surface of the heating element 1 or 1.1 and also the heating element 1 or 1.1 can have different shaped sections (i.e. not circular) or be curved or convex, naturally within the limits of the forms permitted by the commonly known resistor printing technology.
• a first advantage of the heating element 1 is that, in a storage heater, the flange can be eliminated by simply providing the following: a threaded ring nut for fixing the heating element, a welded or screwed sheath for inserting the thermostat sensors and/or the cathodic anticorrosion protection electrode and/or a threaded ring nut for inserting a magnesium anode or an electrode. It has also been shown, though, that the heating element 1 can also support, all together, the sensor units, safety thermostats and anticorrosion protection electrodes or sacrificial anodes. Therefore it is possible, in some variants, to eliminate, not only the flange, but also the other hole in the tank 2, with the exception of the hole needed for the heating element according to the invention.
• this invention can also permit a significant reduction in the heat loss and lime-scale formations in the tank 2.
• the heating element according to the invention makes it possible to manufacture a fast-acting storage heater where the same heating element can pre-heat the water stored to the storage temperatures lower than those required and then complete the heating phase at the moment of use.
• An elect ⁇ cal resistor of the armoured kind for boilers usually has a thermal load, as mentioned earlier, of 8.5W/cm2 and it is subject to rapidly forming lime-scale deposits, which increase in direct proportion to the thermal load.
• a boiler output pipe is generally ! ⁇ " in diameter (i.e. 21mm): supposing the length is 600mm and the installed power is 1500W, the heating element 1 has a thermal load of less than 4W/cm2, less than half that of the armoured resistor, and it is possible to further reduce the thermal load by increasing the pipe diameter and its surface while keeping the surface of the printed resistor route unchanged without there being any significant increase in the cost.
• the heating element 1.1 preferably of the kind indicated for instant electric boilers, makes it possible to reduce the dimensions of these latter. Supposing the power is 20kW and the pipe has a diameter of %", as a thermal load of approximately 20W/cm2 is acceptable (since the water does not become stagnant, there is no risk of scaring), the length of the heating element is equal to approximately 1200mm, but, to limit the dimensions, the version produced in practice can also have two or more heating elements placed alongside or coaxially, or a pipe with a larger diameter.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Resistance Heating (AREA)
• Instantaneous Water Boilers, Portable Hot-Water Supply Apparatuses, And Control Of Portable Hot-Water Supply Apparatuses (AREA)
• Control Of Resistance Heating (AREA)
• Pipe Accessories (AREA)

Applications Claiming Priority (3)

Publications (2)

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Family Applications (1)

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• 2000
  • 2000-06-08 IT IT2000MO000122A patent/IT1315636B1/it active
• 2001
  • 2001-06-05 EP EP01945250A patent/EP1290381B1/de not_active Expired - Lifetime
  • 2001-06-05 CN CNB018107834A patent/CN1232781C/zh not_active Expired - Fee Related
  • 2001-06-05 DE DE60118378T patent/DE60118378T2/de not_active Expired - Lifetime
  • 2001-06-05 ES ES01945250T patent/ES2261423T3/es not_active Expired - Lifetime
  • 2001-06-05 AU AU2001267519A patent/AU2001267519A1/en not_active Abandoned
  • 2001-06-05 DK DK01945250T patent/DK1290381T3/da active
  • 2001-06-05 AT AT01945250T patent/ATE321985T1/de active
  • 2001-06-05 WO PCT/EP2001/006357 patent/WO2001094861A1/en active IP Right Grant
• 2003
  • 2003-12-11 HK HK03109001A patent/HK1056768A1/xx not_active IP Right Cessation

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