EP2410813B1 - Electric heater and continuous-flow heater - Google Patents

Description

The present invention relates to an electric radiator according to the preamble of claim 1, wherein the radiator has a first tube for receiving a heating element, which is electrically insulated from the tube wall of the first tube, and to be flowed through by a fluid to be heated second tube, and a water heater with such an electric radiator.

Electric heaters, for example, for heating a liquid fluid such as water, are divided in principle according to their design in tubular heating systems or bare wire systems. Tubular heater systems are characterized in that an electrical heating element is arranged outside the fluid flow and thus there is no direct contact between the fluid to be heated and the electric heating element. Such a radiator is eg in the German patent DE 39 05 398 C1 shown. The radiator has substantially a flow tube for carrying out the water to be heated and a heating coil for heating the water. The heating coil is arranged in a metal tube, which is spirally wound around the flow tube. For electrical insulation of the heating coil relative to the metal tube wall, the metal tube is filled with magnesium oxide powder, which completely covers the heating coil. The metal tube is soldered to the flow tube, wherein to increase the contact area between the flow tube and the metal tube and thus to improve the heat transfer from the heating coil to the water, the metal tube has a triangular cross-section. However, it has been shown that the energy losses of this radiator are quite high and, in particular in the case of damage to the solder joint, there is no sufficient heating of the water. Furthermore, in order to prevent calcification of the flow tube, the surface available for heat transfer to the water must be as large as possible, whereby such a tubular heater takes up relatively large space.

Bare wire systems are characterized in that an electrical heating element is arranged in the fluid flow and thus a direct contact between the heating element and the fluid. Such a radiator is eg in the German patent DE 28 03 951 C1 shown. The radiator has a flow channel for defining a heating path for the water to be heated, in which a heating coil is arranged without electrical insulation. As a result, the water is under tension, so that in the water, a leakage current according to its electrical conductivity flows. In order not to endanger the user of such a radiator, the flow channel is made of a material with a high insulation resistance such as plastic. In addition, upstream of the flow channel, a water supply path and downstream of the flow channel, a water overrun of one non-conductive material is provided. The bare wire bodies offer much better efficiencies than the tubular heaters, but are not approved in every country.

The DE 20 2010 006 739 U1 relates to a water heater, which shows an electric heater whose tubular heater is arranged in a sheet metal profile and stored in this via radial webs. The tubular heater is surrounded by a plurality of fluid-carrying tubes, which are guided by the webs and spaced from the tubular heater.

The DE 10 2007 056169 A1 relates to an electric heater having a tubular heater in a fluid-carrying outer tube. The tubular heater is arranged coaxially to the outer tube and is supported by webs on this.

The DE 22 18 796 B relates to a water heater, which shows an electric heater, the tubular heater is arranged inside the tube in a fluid-conducting outer tube. The tubular heater is arranged coaxially to the outer tube and is supported on this radial ribs on this.

Object of the present invention is to provide an electric heater which eliminates the aforementioned disadvantages and in an electrically insulated heating coil has a high energy efficiency, and to provide a water heater with such an electric radiator.

This object is achieved by an electric heater with the features of claim 1 and by a water heater with the features of claim 12.

Advantageous embodiments and further developments, which are individually or in combination replaceable with each other, are the subject of the respective dependent claims.

An electric heater according to the invention has a first tube for receiving a heating element, which is electrically insulated from the tube wall of the first tube, and a second tube to be flowed through by a fluid to be heated. According to the invention, the second tube is an outer tube and the first tube is an inner tube arranged in the interior of the outer tube.

Thus, according to the invention, the fluid flowing through the outer tube, for example water, completely flows around the inner tube having the heating coil so that the heat transfer surface corresponds in principle to a lateral surface of the inner tube and the fluid is heated rapidly. As a result, a much better heat transfer is achieved in comparison to known tubular heaters, so that the used electrical energy is available to a greater extent for heating the fluid and the radiator according to the invention thus has an improved efficiency. At the same time the energy loss is reduced, so that the radiator according to the invention has a significantly improved efficiency over known tubular heaters. The risk of calcification is greatly reduced by the increased heat transfer surface of the radiator. In addition, the radiator is made compact by the internal arrangement of the inner tube or the heating coil.

According to the invention, the inner tube is supported via ribs with a high thermal conductivity, in particular via metallic ribs, on the inner wall of the second tube or outer tube. On the one hand, a stable positioning of the inner tube in the outer tube is achieved and on the other heat-conducting bridges between the inner tube and the outer tube created whereby not only the wall or lateral surface of the inner tube serves as a heat transfer surface, but also the rib surfaces, which thus the heat radially into the outer tube, whereby the heating of the fluid is further accelerated.

In a preferred embodiment, the ribs are formed as partitions that divide the interior into a plurality of channels. As a result, the heat transfer surface is increased not only in the radial direction, but also in the axial direction, whereby an even faster heating of the fluid takes place. However, the partitions may also be installed in addition to the ribs. Likewise, the ribs and / or the intermediate walls may be formed as webs, radial projections of the inner tube and the like.

In order to achieve that the ribs or intermediate walls are sufficiently heated over their entire radial extent, an embodiment provides for the intermediate walls to be wedge-shaped in the radial direction.

According to the invention, the heating coil with the magnesium powder is accommodated in a metal tube, which is inserted into the inner tube and, for example, soldered to it to produce a high thermal conductivity. This variant is very simple can be produced because the metal tube rolled and thus the recorded magnesium oxide powder can be highly compressed.

Preferably, the outer tube is made of a material having a high thermal conductivity, so that the heat is also introduced into the wall of the outer tube via the ribs or the partition walls, whereby the heat transfer surface is further increased. In this embodiment, heat is released into the fluid over all side surfaces of the channels, so that it is heated almost from all sides and thereby almost uniformly over its cross section and is heated even faster and in particular energy efficient.

In order to prevent the outer tube radiating its heat radially outward, an embodiment provides a thermal insulation to the sheathing of the outer tube.

The heat transfer between the inner tube, the intermediate walls and the outer tube can be improved if the radiator is formed as an integral component with a high thermal conductivity such as a metal profile. The component can be produced for example by a generative manufacturing process or particularly simple, fast and inexpensive by an extrusion process. However, the inner tube, the outer tube and the ribs can also be designed as subsequently to be interconnected individual components. Likewise, the ribs or at least some of the ribs may be integrally formed with the outer tube or the inner tube.

In one embodiment, the outer tube is made of a material with poor thermal conductivity, such as, e.g. Plastic or with a thermal conductivity which is less than the thermal conductivity of the inner tube and / or the ribs or partitions. As a result, the heat loss through the outer tube without insulation is very low. Likewise, the production is simplified.

An embodiment provides end caps for the frontal or axial closing of the channels, each having a connecting piece as a liquid inlet or liquid outlet, a radially inner inner wall to the frontal support have on the inner tube and a radially outer outer wall to the frontal support on the outer tube. The end caps, which are preferably plastic-based injection-molded parts, allow a reliable sealing of the channels and in particular a spatial and electrically insulating separation of necessary fluid and electrical power connections.

In a variant, the inner wall and the outer wall form an annular space into which the respective connecting piece opens or from which it extends, and which allows a uniform and fluidically favorable distribution of the inflowing fluid into all channels or a correspondingly uniform removal.

In an alternative variant, the end caps are designed so that the individual channels are connected in a meandering manner and thus define a single multiple deflected flow channel. This can be achieved, for example, by forming a plurality of deflection regions in the end caps between the outer wall and the inner wall, each of which produces a fluid connection between two adjacent parallel channels. As a result, the water is guided longer along the heated channel surfaces and thus more heat can be transferred to the water at the same heat output over a longer compared to the previous variant period.

The inner wall may have an axially close opening for receiving an electrical connector for the heating coil.

A preferred instantaneous water heater is provided with an electric heater according to the invention and is characterized in particular by high efficiency, high safety, low calcification, a compact design and cost-effective production.

The present invention is particularly suitable for providing a compact heater for an electrical domestic appliance, in particular a water heater for heating water, which has a high efficiency in an insulated heating coil.

Other advantageous embodiments of the present invention are the subject of further subclaims.

Figur 1

einen Querschnitt durch einen erfindungsgemäßen Heizkörper,

Figur 2

eine perspektivische Ansicht eines Metallprofils des Heizkörpers aus Figur 1, und

Figur 3

einen ausschnitthaften Längsschnitt durch den Heizkörper aus Figur 1, der über eine Endkappe verschlossen ist.

In the following, a preferred embodiment of the invention is explained in more detail with reference to schematic representations. Show it:

FIG. 1

a cross section through a radiator according to the invention,

FIG. 2

a perspective view of a metal profile of the radiator FIG. 1 , and

FIG. 3

a partial longitudinal section through the radiator FIG. 1 which is closed by an end cap.

According to FIG. 1 has a radiator 1 according to the invention, in particular for a household appliance such as a water heater, for heating water, an outer tube 2, an inner tube 4 and a plurality of ribs 6a, 6b, 6c, .... The inner tube 4 is coaxial with the outer tube 2 in whose interior 8 is arranged and connected via the ribs 6a, 6b, 6c, integral with the outer tube 2. As in FIG. 2 Shown are the outer tube 2, the inner tube 4 and the ribs 6a, 6b, 6c, ... formed as a cylindrical one-piece metal profile 10, which is for example an extruded profile. It consists of a material or an alloy with a high thermal conductivity such as copper and is corrosion resistant to the respective fluid to be heated.

The ribs 6a, 6b, 6c,... Extend radially outward from the inner tube 4 and are formed as axially oriented partitions which divide the inner space 8 into a plurality of parallel channels 12a, 12b, 12c, ... subdivide, which are arranged circumferentially of the inner tube 4.

In the inner tube 4, an electric heating coil 14 is arranged, which is electrically insulated from the tube wall 18 of the inner tube 4 via an electrically insulating powder 16, for example magnesium oxide powder, positioned in the inner tube 6. The heating coil 14 is preferably made of copper and has such a diameter or internal resistance that it heats up when energized.

The ribs or intermediate walls 6a, 6b, 6c,... Are each tapered outwards in the radial direction and have a wedge-like cross section. In the embodiment shown, eight equally formed partitions 6a, 6b, 6c, ... are provided.

The channels 12a, 12b, 12c, ... serve to receive the water to be heated. They and thus the outer tube 2 are flowed through in the longitudinal direction of the water and each have an approximately trapezoidal, equal in cross-section. According to the number of partitions 6a, 6b, 6c, ... eight channels 12a, 12b, 12c, ... are formed. The energy transferred per unit area to the water can be optimized by increasing the number of partitions 6a, 6b, 6c, ..., thereby reducing calcification of the water-bearing channels 12a, 12b, 12c, ....

To improve the efficiency of the radiator 1 according to the invention, the outer tube 2 is circumferentially encased by a thermal insulation 20.

As soon as the heating coil 14 is energized, it heats up. The heating coil 14 releases heat to the tube wall 18 of the inner tube 4 via the magnesium oxide powder. From the inner tube wall 18, the heat is introduced via the heating intermediate walls 6a, 6b, 6c, ... in the wall 22 of the outer tube 4. Thus, all, the channels 12a, 12b, 12c, ... forming side surfaces of the metal profile 2 are heated and the water flowing through is virtually fully from the axial, radial and circumferential direction is heated and a correspondingly fast and efficient heating of the water takes place.

The radiator 1 can as in FIG. 3 shown closed in each case via an end cap 24 at the end. The end cap 24, which is preferably a plastic-based injection molded part, has a cylindrical outer wall 26, a cylindrical inner wall 28 extending coaxially with the outer wall 26, and a radial connecting piece 30 for connecting a cold water inlet or a hot water outlet. In addition, the end cap 24 has a tapered outer wall portion 32 which is extended beyond the inner wall 28 in the axial direction and is formed by a radial downgrading of the outer wall 26.

The end cap 24 engages with the tapered Außenwandungsabschnitt 32 an end wall portion 34 of the outer tube 2 and is supported with its outer wall 26 via a seal, not shown on the front side on the outer tube 2 and with its inner wall 28 via a seal not shown from the front side on the inner tube 4 from. As a result, between the outer wall 26 and the inner wall 28, an annular space 36 is formed, which extends radially over all channels 12a, 12b, 12c, ... and into which the connecting piece 30 opens or from which the connecting piece 30 extends.

The inner wall 28 also defines an axially close opening 38, in which an electrical connector 40 is inserted, which closes the inner tube 4 at the end and to which the heating coil 14 is electrically connected at the end.

Disclosed is an electric heater having a first tube for receiving a heating element, which is electrically insulated from the tube wall of the first tube, and to be flowed through by a fluid to be heated second tube, wherein the second tube is an outer tube and the first tube arranged in the interior of the outer tube inner tube.

LIST OF REFERENCE NUMBERS

1

radiator

2

outer ear

4

inner tube

6a, b, c, ...

rib

8th

inner space

10

metal profile

12a, b, c, ...

channel

14

heating coil

16

magnesia

18

pipe wall

20

insulation

22

wall

24

endcap

26

outer wall

28

inner wall

30

spigot

32

Außenwandungsabschnitt

34

wall section

36

annulus

38

opening

40

Connectors

Claims (12)

1. Electrical heater (1) having a first pipe (4) for receiving a heating element (14), which is electrically insulated from the pipe wall (18) of the first pipe (4), and having a second pipe (2) through which a fluid to be heated is to flow, wherein the second pipe (2) is an outer pipe and the first pipe (4) is an inner pipe disposed in the interior (8) of the outer pipe (2), and the inner pipe (4) is supported on the wall (22) of the outer pipe (2) via fins (6a, 6b, 6c...) with a high thermal conductivity, characterised in that the heating element (14) is disposed in a metal pipe which is inserted into the inner pipe (4) and is thermally connected to said inner pipe (4).
2. Heater according to claim 1, wherein the fins (6a, 6b, 6c...) are embodied as intermediate walls which divide the interior (8) into a plurality of channels (12a, 12b, 12c...).
3. Heater according to claim 1 or 2, wherein the fins or intermediate walls (6a, 6b, 6c...) end in a wedge-like manner in the radial direction.
4. Heater according to claim 1, 2 or 3, wherein the outer pipe (2) is manufactured from a material with a high thermal conductivity.
5. Heater according to one of the preceding claims, wherein the outer pipe (2) is enclosed by a thermal insulation (20).
6. Heater according to one of the preceding claims, wherein the inner pipe (4), the intermediate walls (6a, 6b, 6c...) and the outer pipe (2) are embodied as an integrated component (10).
7. Heater according to claim 1, 2 or 3, wherein the outer pipe (2) is manufactured from a material with a low thermal conductivity.
8. Heater according to one of the preceding claims, wherein end caps (24) for closing the channels (12a, 12b, 12c...) are provided with a connecting nozzle (30) as a fluid inlet or fluid outlet in each case, which end caps (24) have a radially-interior inner wall (28) for support on the end face of the inner pipe (4) and a radially-exterior outer wall (26) for support on the end face of the outer pipe (2).
9. Heater according to claim 8, wherein the inner wall (28) and the outer wall (26) form an annular space (36) into which the connecting nozzle (30) opens or from which said connecting nozzle (30) extends.
10. Heater according to claim 8, wherein the end caps (24) have a plurality of deflection areas for producing a fluid connection between adjacent channels (12a, 12b, 12c...).
11. Heater according to claim 8, 9 or 10, wherein the inner wall (28) delimits a paraxial opening (38) for receiving an electrical plug-in connector (40).
12. Continuous-flow heater having an electrical heater (1) according to one of the preceding claims.

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