FLUIDHEIZER

Description

[0001] The invention relates to a fluid heater according to the preamble of claim 1.

[0002] A basic structure of such a fluid heater is disclosed, for example, in EP 2 499 436 B1 by the applicant. The fluid heater disclosed in this document has a housing in which a heating element in the form of a coiled tubular heater is accommodated. In the illustrated embodiment, the heating element is designed as a wire resistance heating element. The housing is designed with an inlet and an outlet for the fluid to be heated. An electronics housing, which houses the power electronics for controlling the tubular heater, is attached to a cover surface of the fluid-conducting housing. In multi-stage fluid heaters, several such heating elements / tubular heaters are provided, which are then controlled accordingly via the power electronics.

[0003] One requirement for such fluid heaters with wire resistance heating elements is that overheating of the fluid heater or heating elements must be reliably prevented if the water heater runs dry. This can be achieved, for example, by measuring the temperature in the fluid heater using suitable temperature sensors, and then switching off or reducing the heating element via the power electronics if a specified maximum temperature is exceeded.

[0004] An alternative possibility is to detect the fill level of the fluid heater and to only control the heating element when a sufficient fill level of the medium - usually water mixed with glycol - is guaranteed.

[0005] Capacitive sensors, for example, can be used to detect the fill level and are installed in the fluid housing. The disadvantage of this solution is that the fill level can only be detected locally at the sensor location, meaning that partial dry running in other areas cannot be reliably detected. Furthermore, capacitive sensors are relatively expensive, and it also requires a comparatively high level of effort to design the fluid heater housing appropriately for the sensor's positioning.

[0006] The documents US 2005 / 045621 A1 and EP 1 559 391 A2 disclose related prior art.

[0007] In contrast, the invention is based on the object of creating a fluid heater in which overheating is avoided with little device-related effort.

[0008] This object is achieved by a fluid heater having the features of patent claim 1.

[0009] Advantageous further developments of the invention are the subject of the subclaims.

[0010] The fluid heater according to the invention has a housing through which a fluid flows, in which a heating element for heating the fluid is housed. The fill level is measured by utilizing existing components in that spaced-apart components on the housing and the heating element form an electrode and a counter electrode of a capacitor, respectively. The dielectric of the capacitor is formed, in particular, by the fluid to be heated. The capacitor is wired in such a way that the fill level of the fluid can be determined from a change in the capacitance of this integrated capacitor.

[0011] The dielectric constants of air (empty space) and fluid are different, so the capacitor's capacitance changes depending on the fill level. Power electronics with a corresponding software algorithm can then evaluate the detected signal and generate a corresponding warning or fill level information, or reduce the power of the heating elements. This type of solution has the advantage of enabling quantitative fill level monitoring. Furthermore, by combining existing components, the design is extremely cost-effective, with the fill level being detected regardless of position and with a fast response time. This fast response time is particularly important to prevent overheating of the system, which can also be partially made of plastic.

[0012] In other words, the change in the fill level results in a change in the capacitor capacitance, so that if a limit value is undershot, it can be concluded that the fluid heater is partially or generally running dry and the heating element can be switched off or regulated down accordingly until the predetermined fill level is reached.

[0013] In one embodiment of the invention, the housing-side component forming an electrode / counter electrode is a housing wall, preferably a housing shell or an inner tube, which is encompassed by the heating element.

[0014] The component forming an electrode / counter electrode on the heating element side can be a metallic sheath or a heating wire of a heating element designed as a tubular heater.

[0015] Of course, other components of the heating element can also be used, or components of heating elements that have other designs.

[0016] In a preferred embodiment of the invention, the housing wall is made of plastic, wherein the conductivity is then achieved by providing the housing wall with an electrode coating or an electrode plate (for example as a sheet metal, foil, metal mesh).

[0017] The electrodes and counter electrodes of the capacitor formed from the components of the fluid heater can also be connected to form two or more capacitors connected in series.

[0018] In a multi-stage fluid heater, several heating elements are accommodated in the housing, whereby each heating element can be assigned a capacitor of the above-described design.

[0019] In one embodiment of the invention, the fluid heater is designed with an inner tube that determines the fluid flow, which in turn can be separated into several galvanic areas, each of which is assigned a heating element.

[0020] The fluid heater is particularly simple in design if the heating element is a coiled tubular heater constructed with a heating wire (resistance wire) arranged in a jacket tube and insulated from it by means of insulation, for example made of MgO.

[0021] Of course, the heating elements can also have other designs.

[0022] The fluid can, for example, be water mixed with glycol.

[0023] As explained above, the fluid heater is preferably designed with power electronics that controls the heating elements depending on the capacitance of the capacitor or the fill level and, if necessary, emits a warning signal.

[0024] Preferred embodiments of the invention are explained in more detail below with reference to schematic drawings. They show: Figure 1 an exploded view of an embodiment of a fluid heater according to the invention; Figure 2 a cross section through a fluid heater according to Figure 1 ; Figure 3 a longitudinal section of the fluid heater according to Figure 1 and Figures 4 to 11 Schematic representation of possibilities to design components of a fluid heater according to the Figures 1 to 3 to be connected as a capacitor.

[0025] Figure 1shows an exploded view of some components of a fluid heater 1 that are essential for understanding the invention. Accordingly, the heater has a multi-part fluid-conducting housing with a lower shell 2 and a cover plate 4, onto which the electronics housing (not shown) with the power electronics is placed. In the illustrated embodiment, the lower shell 2 is made of a metallic material and is soldered or otherwise connected to the cover plate 4, which is also made of a metallic material. A guide plate 6, the function of which will be discussed later, is arranged in the lower shell 2, parallel to the cover plate 4.

[0026] The fluid is fed via an inlet 8 into the interior space defined by the lower shell 2 and the cover plate 4 or the guide plate 6 and then flows heated over a Figure 1drain 10 located below. Inlet 8 and outlet 10 are each designed as pipe sockets that are attached to the lower shell 2 and to which fluid lines are connected.

[0027] The fluid is heated by three heating elements 12, 14, 16 arranged in series, whose connections 18, 20 (only two connections in Figure 1 provided with reference numerals) penetrate through recesses in the guide plate 6 and the cover plate 4 in a sealing manner into the electronics housing (not shown) and are contacted there with the power electronics.

[0028] In the illustrated embodiment, the heating elements 12, 14, 16 are designed as helical tubular heaters. The basic structure of such tubular heaters is described, for example, in DE 10 2015 118 718 A1 of the applicant. Such a tubular heater has, for example, an approximately centrally arranged wire resistor (heating wire), which is arranged coaxially within a jacket tube and embedded in an insulating fill, preferably consisting of MgO. Further details of such a tubular heater will be described later with reference to Figure 2 explained.

[0029] As in Figure 1 As shown, the terminals 18, 20 of each heating element 12 project upwards towards the guide plate 6 and cover plate 4 - these terminals 18, 20 are connected to the wire resistance elements.

[0030] The coiled heating elements 12, 14, 16 surround an inner tube 22, also called a displacement tube, which ensures that the fluid flows around the heating elements 12, 14, 16 as it flows through and is thus in optimal thermal contact with the heating elements 12, 14, 16, so that a fast, effective heat exchange is guaranteed.

[0031] The guide plate 6 has a Figure 1 downwardly projecting connecting piece 24, to which the inlet 8 is attached. The fluid then flows via this inlet 8 and the connecting piece 24 to the Figure 1 visible top of the guide plate 6 and flows further in the direction of the arrow to an opening 26, through which it passes downwards into the actual housing interior. The fluid then flows, partially guided by the inner tube 22, along the heating elements 12, 14, 16 to the outlet 10 and exits the fluid heater 1 heated through the outlet.

[0032] Figure 2shows a cross section of the fluid heater 1 according to Figure 1 . In this illustration, one can see the tub-like lower shell 2, which - as explained - is made of a metallic material in this embodiment. The connections 18, 20 of the heating elements (in Figure 2 The terminals 18, 20 are connected to the wire resistor 30, indicated by a dotted line. As explained, this is embedded in an insulator 32, made of MgO, for example, which is inserted into a coiled jacket tube (metallic sheath of the heating element) 34.

[0033] According to the presentation in Figure 2the inner tube 22 is inserted precisely into the space encompassed by the jacket tube 34, so that the space through which the fluid flows is essentially limited to the outside by the lower shell 2 and the guide plate 6 and to the inside by the inner tube 22.

[0034] As in Figure 2 As indicated, the level measurement is carried out by a capacitor 36, which is not used as an additional component as in the prior art, but is formed by existing components of the fluid heater 1. In the illustrated embodiment, a "plate" / electrode of the capacitor 36 is formed by the jacket tube 34. The counter electrode (further "plate") is Figure 2 In the embodiment indicated, the fluid contained in the previously described interior forms the dielectric of the capacitor 36, the capacitance of which depends on the fill level.

[0035] This capacitor 36 is connected to the power electronics via control lines not shown, so that the detected signal can be evaluated via evaluation electronics and the fill level can be determined accordingly.

[0036] Figure 3 shows a longitudinal section of a further embodiment of a fluid heater 1. In this illustration, one can clearly see the three heating elements 12, 14, 16 with the respective tubular heaters, whose connections 18 protrude through the guide plate 6 and the cover plate 4 into the electronics housing 28 indicated by dashed lines.

[0037] In the area of ​​the two heating elements 12, 16, a capacitor 36a, 36b is formed, wherein one electrode is again formed by the jacket tube 34, while the counter electrode in the embodiment according to Figure 3 formed by the metallic inner tube 22. In the variant according to Figure 3A further capacitor 38a, 38b is formed in each case, one electrode ("plate") of which is formed by the wire resistor or the associated terminal 18, while the other "plate" (counter electrode) of the capacitor 38a is then in turn formed by the jacket tube 34. The dielectric of this capacitor 38a,b is then formed by the insulation.

[0038] As also illustrated by the further figures 4 to 12, according to the invention, components of the fluid heater 1 which are already present are used to enable a capacitive level measurement. Figure 4 shows again a circuit diagram of the Figure 2 explained embodiment, wherein the lower shell 2 and one of the heating elements 12 are shown in a highly simplified manner. Instead of the circular real coil according to Figure 2 the tubular heater is in the Figures 4 to 11 symbolized by a rectangular frame.

[0039] The connections 18, 20 of the heating element 12 are also only indicated. As already shown in Figure 2 As explained, one electrode ("plate") of the capacitor 36 is formed by the jacket tube 34 of the heating element 12, while the counter electrode (further "plate") is formed by the metallic lower shell 2 of the housing.

[0040] Between these two capacitor plates is the fluid, whose fill levels 40a, 40b are shown in two exemplary states. Depending on the fill levels 40a, 40b, the capacitance of capacitor 36 changes due to the different dielectric constants of air and water (glycol), so that a corresponding signal can be evaluated via the power electronics. This basic principle applies to all variants described below.

[0041] In the embodiment according to Figure 5Two capacitors 36a, 38a are connected in series, with one electrode of capacitor 38a being formed by terminal 18, i.e., by the wire resistor (heating wire), while the counter electrode of capacitor 38a is formed by the jacket tube 34. An advantage of such a solution is that the already existing terminal 18 can also be used to contact the capacitor 38a with the power electronics, so that no additional contact components need to be provided.

[0042] An electrode of the further capacitor 36a is also formed by the jacket tube 34. The further counter electrode of the second capacitor 36a is in the Figure 5 illustrated embodiment is again carried out by the lower shell 2.

[0043] In the embodiment according to Figure 6The lower shell 2 is made of a non-conductive plastic. The electrode of the capacitor 36 is then formed by a metallic electrode element 42 connected to the lower shell 2, which can be, for example, a sheet or plate inserted into the plastic material, a metallic foil, or a metallic coating, thus forming the counter electrode of the capacitor 36. The further electrode of the capacitor 36 can then in turn be formed by the jacket tube 34.

[0044] Figure 7 then shows a variant whose basic structure is already in Figure 5 However, instead of the metallic lower shell 2, as in the embodiment according to Figure 4 , a plastic lower shell 2 is used, which is provided with a metallic electrode element 42 in order to be able to take over the function of a capacitor plate. The embodiment according to Figure 7corresponds to that of Figure 5 , so that further explanations are unnecessary.

[0045] Figure 8 shows a variant in which the inner tube 22, also symbolized as rectangular, forms a counter electrode of the capacitor 36, while the other electrode is formed by the jacket tube 34. The lower shell 2 is not part of the capacitor 36.

[0046] The inner tube 22 can then be made of a metallic material or of plastic. In the latter case, the inner tube 22 - similar to the lower shell 2 in the embodiments according to the Figures 6 and 7 - by a coating, an inserted foil or an inserted metallic electrode element.

[0047] Figure 9 shows an embodiment in which - similar to the embodiments according to the Figures 5 and 7- again two capacitors 36, 38 are formed, wherein the electrodes / plates of the capacitor 38 are formed on the one hand by the terminal 18 (wire resistor) and on the other hand by the jacket tube 34. The counter electrode of the second, series-connected capacitor 36 is - as in the embodiment according to Figure 7 - through the inner tube 22, while the further electrode is also formed by the jacket tube 34.

[0048] The Figures 10 and 11 show schematic diagrams of embodiments with two heating elements 12, 16. Apart from the number of heating elements, the embodiment according to Figure 10 in basic structure to that of Figure 3. Each of the heating elements 12, 16 is assigned two series-connected capacitors 36a, 38a; 36b, 38b, wherein the electrodes / plates of the capacitor 38a, 38b are each formed by the terminal 18 (wire resistor) on the one hand and the jacket tube 34 of the respective heating element 12, 16 on the other hand. The electrodes of the respective further capacitor 36a, 36b are then correspondingly formed by the jacket tube 34 and the inner tube 22. In this embodiment, no capacitor element is formed by the lower shell 2. As shown in Figure 10 As shown, the inner tube 22 forms an electrode common to both capacitors 36a, 36b.

[0049] Figure 11 shows a variant in which the inner tube is galvanically separated into inner tube areas 22a, 22b according to the number of heating elements 12, 16. This galvanic separation is in Figure 11indicated by the dashed vertical line. The formation of the capacitors 36a, 38a, 36b, 38b is then again carried out according to Figure 10 , wherein the housing-side counter electrode of the capacitors 36a, 36b are formed by the respective galvanically isolated regions of the inner tube 22a and 22b. The remaining structure corresponds to the embodiment according to the Figures 10 and 3 , so that further explanations are unnecessary.

[0050] Even in the Figures 10 and 11 In the embodiment shown, a terminal 18 is used to form / contact a capacitor component, so that the device-technical design of such a solution is simpler than in a solution in which additional contacting elements must be provided for the integrated capacitors 36, 38.

[0051] Disclosed is a fluid heater 1 with a capacitive level measurement. List of reference symbols:

[0052] 1 Fluid heater 2 Lower shell 4 Cover plate 6 Guide plate 8 Inlet 10 Outlet 12 Heating element 14 Heating element 16 Heating element 18 Connection 20 Connection 22 Inner tube 24 Connection piece 26 Breakthrough 28 Electronics housing 30 Wire resistor 32 Insulation 34 Jacket tube 36 Capacitor 38 Capacitor 40 Fill level 42 Metallic electrode element

Claims

1. A fluid heater having a housing through which a fluid can flow and in which at least one heating element (12, 14, 16) for heating the fluid is accommodated, characterized in that at least two housing-side and heating-element-side components spaced apart from each other form an electrode or a counter electrode of a capacitor (36) whose dielectric is formed by the fluid and which is connected to power electronics in such a way that the fill level (40) of the fluid heater (1) can be determined from a change in capacitance of the capacitor (36).

2. The fluid heater according to claim 1, wherein the housing-side component is a housing wall, preferably a lower shell (2) or an internal pipe (22), which is surrounded by the heating element (12, 14, 16).

3. The fluid heater according to claim 1 or 2, wherein the heating-element-side component is a metallic sheath, for example a casing tube (34) or a heating wire of the heating element (12, 14, 16).

4. The fluid heater according to claim 2, wherein the housing wall is made of plastic and is provided with a coating or an electrically conductive element such as an electrode sheet, an electrode foil or the like.

5. The fluid heater according to one of the preceding claims, wherein electrodes and counter electrodes form at least two capacitors (36, 38) connected in series.

6. The fluid heater according to one of claims 2 to 5, wherein a plurality of heating elements (12, 14, 16) are accommodated in the housing, wherein at least one capacitor (36, 38) is associated with each heating element (12, 14, 16).

7. The fluid heater according to claim 6, wherein the internal pipe (22) has a plurality of galvanically separated internal pipe portions (22a, 22b), each of which is assigned to a heating element (12, 14, 16) as a counter electrode.

8. The fluid heater according to one of the preceding claims, wherein the heating element (12, 14, 16) is a, preferably coiled, tubular heating element with a wire resistor / heating wire, which is arranged in a casing tube (34) and is spaced apart from the latter via an insulation (32).