THROUGHFLOW HEATER

Abstract

A throughflow heater comprises an outer surface encircling a longitudinal axis, inwardly adjoining the outer surface a conveying region for a fluid that is to be heated, inwardly adjoining the conveying region at a transition surface a heating layer with an electrical heating element and heat-conducting material, and an insulating core which extends centrally along the longitudinal axis and outwardly forms a support surface for the electrical heating element and the heat-conducting material. The thermal conductivity of the insulating core is lower than that of the heat-conducting material. The radial extent of a channel arranged in the conveying region is less than 1 mm.

Claims

1. The throughflow heater having an outer surface extending around a longitudinal axis and two end faces facing away from each other and extending transversely to the longitudinal axis, a lead-through area adjoining the outer surface on the inside for a fluid to be heated, a heating layer adjoining the lead-through area at a transition surface on the inside, said heating layer comprising an electric heating element and heat-conducting material, an insulating core extending centrally along the longitudinal axis and externally forming a support surface for the electric heating element and the heat-conducting material, wherein the thermal conductivity of the insulating core is lower than that of the heat-conducting material, the lead-through area comprises an inner sleeve at the transition surface, an outer sleeve at the outer surface, and between the inner and the outer sleeve at least one channel which extends between two terminals and around the longitudinal axis in a coiled manner and comprises in addition at least one coiled guide wall which extends from the outer surface against the transition surface and determines a rectangular channel cross-section with two long sides at the sleeves and two short sides at the guide wall, wherein in the cross-section of the coiled channel the length of the short, radially extending sides is smaller than 1 mm, preferably in the range of 0.8 mm to 0.4 mm, and especially the long sides are at least six times as large as the short sides.

2. A throughflow heater according to claim 1, wherein spacers which protrude radially over the support surface are provided in each case at both axial ends of the insulating core in at least three areas which are substantially uniformly distributed at regular intervals along the circumference, which ensure a central positioning of the insulating core within the inner sleeve and even at a small thickness of the heating layer prevent a direct contact between the electric heating element and the inner sleeve.

3. A throughflow heater according to one of the claim 1, wherein the insulating core comprises silicate ceramics and/or oxide ceramics and/or non-oxide ceramics, wherein the ceramic material is shaped and compacted by sintering to the insulating core, the thermal conductivity of the insulating core is at most half as large as the thermal conductivity of the heat-conducting material, the insulating core preferably comprises ceramic material whose thermal conductivity is less than 5 Wm.sup.1K.sup.1, in particular less than 3 Wm.sup.1K.sup.1, and whose electrical resistance at 20 C. to 120 C. is preferably greater than 10.sup.6 m, in particular greater than 10.sup.9 m.

4. A throughflow heater according to claim 1, wherein the outer surface, the transition surface, and the support surface are each formed in a substantially cylindrical shell-shaped manner with a circular cross-section, wherein the radius extends from the longitudinal axis to the support surface preferably at least over 70%, in particular at least over 80%, of the radius from the longitudinal axis to the transition surface.

5. A throughflow heater according to claim 1, wherein the insulating core comprises a cavity extending in the direction of the longitudinal axis and that in this cavity-, in a section of the longitudinal axis with a heating element arranged on the outside on the support surface, at least one overheating protection device is arranged, which on an electrical connection side is connected to a first electrical connection contact arranged at one end face and on the other electrical connection side is connected to a first contact of the electric heating element-, wherein preferably the cavity of the insulating core has a cavity axis which extends at a distance from the central longitudinal axis of the insulating core, so that the smallest distance between the at least one overheating protection device arranged in the cavity and the nearest region of the electric heating element corresponds to a predetermined distance.

6. A throughflow heater according to claim 1, wherein a second electrical connection contact is also arranged on the end face with the first electrical connection contact, which second electrical connection contact is connected to a second contact of the electric heating element, wherein in the insulating core, a bore extending parallel to the longitudinal axis is formed, through which an electrical connection of a contact of the heating element is guided against one of the two electrical connection contacts.

7. A throughflow heater according to claim 1, wherein the heating element is formed by a resistance wire which is wound as an electric heating coil from one end face to the other end face of the insulating core onto the support surface of the insulating core and the insulating core is electrically insulating due to a sufficiently high electrical resistance.

8. A throughflow heater according to claim 1, wherein the inner sleeve is closed off at one end face with a front surface in a cup-shaped manner and comprises a final plug on the end face facing away therefrom with the first electrical connection contact.

9. A throughflow heater according to claim 1, wherein the heat-conducting material is filled and pressed in a powdery manner between the inner sleeve and the insulating core, the heat-conducting material has a thermal conductivity above 5 Wm.sup.1K.sup.1, and the electrical resistance of the heat-conducting material at 20 C. to 120 C. is greater than 10.sup.6 m, preferably greater than 10.sup.9 m, and especially the heat-conducting material between the electric heating element and the transition surface preferably has a thickness of not more than 4 mm or optionally of not more than 2 mm, so that the heat emitted by the heating element reaches the lead-through area without disturbing time delay and the electric heating element is electrically insulated.

10. A throughflow heater according to claim 1, wherein the coiled guide wall is formed on the outer sleeve or optionally on the inner sleeve or preferably inserted as an intermediate part between the inner and the outer sleeve.

11. A throughflow heater according to claim 1, wherein the outer sleeve is tightly connected at at least one end face to the inner sleeve.

12. A throughflow heater according to claim 1, wherein the outer sleeve is tightly connected at one end face to a hood-shaped cover and the cover comprises one of the two terminals, which preferably extends in the direction of the longitudinal axis and is arranged in particular in the center of the cover.

13. A throughflow heater according to claim 1, wherein at least two sections of the heating element are arranged on the support surface of the insulating core, which each comprise a wound electrical resistance wire and electrical connecting leads feeding said wire.

14. The use of a throughflow heater according to one of the preceding claims for heating water, wherein the electrical supply of the electric heating element is controlled by a controller which at least determines whether the heating element is to be electrically powered or whether no heat should be generated.

15. The use according to claim 14, wherein the throughflow heater makes the respective heating of the water adaptable to a selectable consumption temperature, in particular with an adjustment of the heating power and at least one temperature measurement and/or flow rate measurement.

Description

[0066] Further details of the invention will become apparent with reference to the following description of an embodiment schematically illustrated in the drawings, wherein:

[0067] FIG. 1 shows a longitudinal section through a throughflow heater (AA according to FIG. 2);

[0068] FIG. 2 shows a view of the end face with the electrical terminal contacts;

[0069] FIG. 3 shows a cross-section BB according to FIG. 1;

[0070] FIG. 4 shows a cross-section CC according to FIG. 1;

[0071] FIG. 5 shows a perspective view of the throughflow heater;

[0072] FIG. 6 shows a longitudinal section through a throughflow heater with a hood-shaped cover;

[0073] FIG. 7 shows a side view of the throughflow heater according to FIG. 6; and

[0074] FIG. 8 shows a perspective view of the throughflow heater according to FIG. 6.

[0075] FIGS. 1 to 5 show a throughflow heater 1 with an outer surface 3 extending around a longitudinal axis 2 and two end faces 4 extending transversely to the longitudinal axis 2 and away from each other. A lead-through area 5 for a fluid to be heated adjoins the outer surface 3 on the inside. In the illustrated embodiment, the lead-through area 5 comprises an inner sleeve 6 and an outer sleeve 7, wherein these two sleeves 6, 7 are tightly connected to each other at the two end faces 4. Between the inner and the outer sleeve 6, 7, a channel 8 is formed, which extends between two terminals 9 and 10 wound around the longitudinal axis 2 and comprises in addition at least one coiled guide wall 11. The coiled guide wall 11 extends in longitudinal section and in cross-section in a radial direction from an area at the outer surface 3 against a region at a transition surface 12 on the inner side of the inner sleeve 6 directed against the longitudinal axis 2.

[0076] In the illustrated embodiment, the coiled guide wall 11 is formed on the outer sleeve, or the channel 8 is incorporated into the outer sleeve 7 so that the guide wall 11 projects from the outer surface 3 against the longitudinal axis 2. It would also be possible that the guide wall 11 is formed on the outer side of the inner sleeve 6 or inserted as an intermediate part between the inner and the outer sleeve 6, 7.

[0077] In the inner sleeve 6, or within the transition surface 12, an insulating core 13 is arranged, whose jacket surface forms a support surface 15 for a heating element 16 in the form of an electrical resistance wire wound on the support surface 15. The heating element 16 or the resistance wire wound onto the support surface 14 from one face end of the insulating core 13 to the other is thus an electric heating coil. The heating element 16 forms a heating layer 17 together with the heat-conducting material arranged between the support surface 15 and the transition surface 12.

[0078] For optimal positioning or centering, the insulating core 13 comprises at both axial ends in each case at least three spacers 14 protruding radially beyond the support surface at substantially uniform intervals along the circumference, which ensure a distance between the support surface 15 and the inner sleeve. Even with a small thickness of the heating layer 17, direct contact between the electric heating element and the inner sleeve is prevented. Both the insulating core 13 and also the heat-conducting material of the heating layer 17 have a sufficiently high electrical resistance, so that the supplied current flows only through the heating wire.

[0079] In the illustrated embodiment, the inner sleeve 6 is formed of metal and closed off in a cup-shaped manner at an end face 4 with a metallic front surface 6a. Between the inner sleeve 6 and the insulating core 13, powdery heat-conducting and electrically insulating material, such as magnesium oxide, is filled. In order to achieve the desired high thermal conductivity, the powdery material is compacted. The volume of the filled inner sleeve can be reduced by means of a rolling process by radially constricting and/or by pressing in the front surface 6a, so that the powdery material is compressed and the cavities are displaced. At the of the metallic front surface 6a facing away from end face 4, a final plug 18 is attached.

[0080] The insulating core 13 comprises a cavity 19 extending in the direction of the longitudinal axis 2. In this cavity 19, two overheating protection devices 20 are arranged in series in a section of the longitudinal axis 2 with a heating element 16 arranged on the outside of the support surface 15. A first electrical connection side of these overheating protection devices is connected via a first line 21 to a first electrical connection contact 23 arranged on the end face 4 with the plug 18. A second electrical connection side of the overheating protection devices 20 is connected via a second line 22 at the plug 18 to a first contact of the electric heating element 16 (not shown).

[0081] On the end face 4 with the first electrical connection contact 23, a second electrical connection contact 24 is arranged, which is connected to a second contact of the electric heating element 16. In order to lead an electrical line from the second electrical connection contact 24 to the second contact of the electric heating element 16 at the insulating core end, which faces the front surface 6a, a bore 25 extending parallel to the longitudinal axis 2 is formed in the insulating core 13. This bore 25 can also be used for fixing the first electrical connection contact 23. For fixing the second electrical connection contact 24, the insulating core 13 comprises at the end face 4 with the plug 18 an insertion opening 26.

[0082] In the operating state, the heat generated by the heating element 16 passes through the thin heating layer 17 with the heat-conducting material with only insignificant delay and reduction to the lead-through area 5. In the insulating core 13 with the lower thermal conductivity, only a small proportion of heat flows. If, however, due to a disturbance, the heat in the lead-through area 5 is not absorbed by the fluid to be heated, heat is increasingly also transferred to the insulating core 13 and thus to the overheating protection devices 20. In order to improve the heat conduction from the insulating core to the overheating protection devices 20, heat-conducting material is preferably introduced into the cavity 19 around the overheating protection devices 20.

[0083] The cavity 19 of the insulating core 13 has a cavity axis, which extends at a distance from the central longitudinal axis 2 of the insulating core 13, so that the smallest distance between overheating protection devices 20 arranged in the cavity 19 and the nearest region of the electric heating element 16 corresponds to a predetermined distance. With the choice of this distance, the delay or damping of the heat flow to the overheating protection device 20 can be influenced. The sensitivity of the overheat protection 20 is also selected according to the selected distance.

[0084] In the illustrated embodiment, the outer surface 3, the transition surface 12, and the support surface 15 are each formed substantially cylinder-jacket-shaped with a circular cross-section. The radius from the longitudinal axis 2 to the support surface 15 extends at least over 70%, in particular at least over 80%, of the radius from the longitudinal axis 2 to the transition surface 12.

[0085] FIGS. 6 to 8 show a throughflow heater 1 with a hood-shaped cover 28. The outer sleeve 7 is tightly sealed at one end face 4 with the hood-shaped cover 28. This cover 28 comprises the connection 9, which extends in the direction of the longitudinal axis and is formed in the center of the cover 28. The cover 28 connects the lead-through area 5 or the channel 8 between the inner sleeve 6 and the outer sleeve 7 via deflection regions with sufficiently large radii of curvature to the connection 9.

[0086] For channel formation, the throughflow heater 1 comprises a spring-shaped intermediate part 29 which is inserted between the inner and the outer sleeve 6, 7. In order to ensure that the intermediate part 29 is held in a desired position in the direction of the longitudinal axis and optionally in the circumferential direction, at least one dent 30 is formed after the desired positioning of the intermediate part 29 on the dome-shaped cover 28, so that the intermediate part 29 is tightly clamped. The hood-shaped cover 28 also has an alignment stop in the form of a recess 31. During assembly, the recess 31 is brought into engagement with a corresponding alignment element.

[0087] FIGS. 6 to 8 show an embodiment in which the heating element 16 is divided into two sections. The insulating core 13 comprises two partial areas 15a and 15b on the jacket surface formed on the support surface 15, which are separated from each other by a radial elevation 15c. On both partial areas 15a and 15b, an electrical resistance wire is wound in each case. Both wound resistance wires are each connected via feeding electrical connection lines to a pair of connection contacts 23, 24 or 27, wherein the connection contact 27 is provided for the second section. The electrical connection lines from the ends of the resistance wires to the three connection contacts 23, 24 and 27 are guided in corresponding bores 25, 26 through the insulating core 13. An electrical connection line is guided at the end facing away from the connection contacts 23, 24 and 27 of the insulating core 13 to the bore 26. In order to ensure that this electrical connection line is unable to come into contact with the metallic end face 5a of the inner sleeve 5, the insulating core 13 comprises a projection 13a projecting centrally against this end face. The insulating core 13 can thus be inserted as far into the inner sleeve 5 when assembling the throughflow heater 1 until the projection 13a is rests thereon. This ensures the correct positioning.