WO2010060756A1

WO2010060756A1 - Heat exchanger with thermal protection

Info

Publication number: WO2010060756A1
Application number: PCT/EP2009/064554
Authority: WO
Inventors: Andrea Virzi; Duilio Capraro
Original assignee: IRCA SpA Industria Resistenze Corazzate e Affini
Current assignee: IRCA SpA Industria Resistenze Corazzate e Affini
Priority date: 2008-11-03
Filing date: 2009-11-03
Publication date: 2010-06-03
Anticipated expiration: 2011-05-03
Also published as: ITRM20080587A1; IT1391845B1

Abstract

A flow-heating system for liquids, in particular for producing hot water or steam, equipped with at least one thermal protection accommodated at the end of the electric heater (8). Such a heating system comprises at least two tubes thermally connected to each other or forming part of a single structure obtained by extrusion. One of the tubes allows the water to pass, the other or others accommodate the heating resistive wire (5). The thermal protection or thermal fuse (1) is assembled at the end of the electric heater (8) as described below. It is engaged on a connector (2), which is mechanically and electrically connected in turn to an electric connection (3) coined on the inner connector (4) on which the resistive wire (5) of the electric heater (8) is welded.

Description

HEAT EXCHANGER WITH THERMAL PROTECTION Field of the invention

The present invention relates to a heat exchanger for heating fluids, in particular for heating water, e.g. in coffee makers, provided with overheating protection.

State of the art

Various solutions are provided in the state of the art with regards to the integration of overheating protection devices in elements for heating water passing through a conduit and separated from the heating resistors.

In one of these solutions, there is a single profile obtained by extrusion; two side tubes act as electric heaters; a steel tube is accommodated in the central tube for the water passing, or the water or other fluid passage may be the central cavity of the extruded shape.

A second solution consists of two integral U-folded tubes; the outer tube is for the water passing, the inner one contains the electric heater.

The overheating protection devices of this types of heat exchangers are normally accommodated on a metal bracket made of materials having a high heat conductivity (e.g. aluminium), which is fixed to the heating element in advance, by arc welding or brazing.

The metal bracket carrying the overheating protection is suitably positioned to allow the transmission effectiveness of the thermal signal. It is normally integral with the fluid passing tube.

Such an overheating protection arrangement is not free from possible false electric and/or thermal contacts according to the quality of either the welding of the metal bracket or the assembly of the protection itself on the bracket. This problem distorts the intervention conditions of the device in case of faulty operation of the electric heater.

The electric connection in heat exchangers so assembled is complex; whereby the use of a number of wirings is needed, which weigh on the final cost of the heating system along with the metal bracket and the thermal protections (normally consisting of thermostat and thermal fuse accommodated in a pre-formed ceramic component with a metal bottom facing the bracket).

A solution for integrating a heat exchanger and an overheating protection different from the previous ones is further known as disclosed in patent document WO0152601. In this solution the inner connector, on which the resistive wire of the electric heater is welded, is coined onto the rheophore of the thermal protection and the same is accommodated in a recess of the insulating washer which closes the electric heater. The thermal protection is mounted when assembling the heater.

The problems related to this type of overheating protection integration mainly concern the dimensional development of the heater itself, impacting on the final cost and volume of the object. Indeed, the overheating protection must be appropriately spaced apart from the resistive wire so as to prevent premature intervention or undergo thermal aging during its working life, which would impair the intervention thereof. As a consequence, the heater has a longer longitudinal development, with higher cost of materials and difficulty of accommodation in the use devices, such as coffee makers, which usually require compact volumes. Summary of the invention

It is the object of the present invention to provide a heat exchanger with overheating protection which solves the aforesaid problem. It is the object of the present invention a heat exchanger for heating fluids which, in accordance with claim 1 , comprises a tubular structure; overheating protection means for protecting against overheating of the heat exchanger, arranged outside the tubular structure; at least one electric resistor arranged inside the tubular structure adapted to produce heat; fastening means integrally attached at one end of the electric resistor and forming the electric connection with power supply means; an insulating element arranged between the tubular structure and the overheating protection means; a connecting element between the electric resistor and the overheating protection means, wherein the connecting element is electrically conducting and is solidarily connected to the fastening means. The heat exchanger for heating fluids of the invention is typically of the flow type, with overheating protection means integrated with at least one of its ends adapted to the electric connection. The thermal protection or thermal fuse is mechanically engaged on an appropriately dimensioned connector, which in turn is engaged on an intermediate electric connection incorporated in the insulating washer and on which the inner connector carrying the welded resistive wire is coined. Such an integration of the overheating protection means ensures greater thermal sensitivity of the protection itself in case of faulty operation of the electric heater, the protection itself not being in contact with another element except for the connector which leads to the heating resistive wire. In case of faulty operation, and thus of temperature exceeding the maximum operating temperature, no other heat dissipating component, such as for example an insulating washer of known devices, is in contact therewith, and the susceptibility of the device is improved. Another advantage of the invention is that the overheating protection may be connected to the electric wiring harness and later engaged, e.g. after manufacturing the heater, in the specific connector. Thereby, the electric and thermal connections are simultaneous, and furthermore the overheating protection device is not subjected to any of the mechanical stresses which may be associated to a normal manufacturing process, which could impair mechanical - and thus electric - integrity of the heat exchanger. As a whole, integrating the overheating protection means in the heat exchanger is simplified as compared to known solutions, both at operative level (low-effort mechanical engagement) and with regards to the number of involved components and/or wiring harnesses. Furthermore, such a type of integration of overheating protection means in all the described variants ensures better exploitation of the available development for accommodating the so-called hot part, i.e. the one at the resistive wire. The dependent claims describe preferred embodiments of the invention, thus being an integral part of the present description. Brief description of the drawings

Further features and advantages of the present invention will be more apparent in view of the detailed description of preferred, but not exclusive, embodiments of a heat exchanger illustrated by way of non-limitative example, with the aid of the accompanying drawings, in which:

Fig. 1 is a partial side view of the longitudinal section according to the S-S plane in figure 4 of a heat exchanger of a first variant according to the invention; Fig. 2 is a partial side view of the longitudinal section according to the S-S plane in figure 4 of a heat exchanger of a second variant according to the invention; Fig. 3 is a partial side view of the longitudinal section according to the S-S plane in figure 4 of a heat exchanger of a third variant according to the invention;

Fig. 4 shows cross section views with respect to the longitudinal axis of two alternative variants of the heat exchanger of the invention.

The same reference numbers are used to identify the same constructional elements in the various figures.

Detailed description of preferred embodiments of the invention

With particular reference to figure 1 , which illustrates a first embodiment of the invention, the heat exchanger 8 comprises an external tube 7, preferably made of aluminium or aluminium alloys, which may correspond to one of the cavities of a single extruded profiled element comprising two or more cavities, of which at least one forms a passage for the fluid to be heated, while one or more cavities accommodates the heater. Different embodiments, which do not limit the number of cavities or conduits, are shown in cross section in fig. 4. The resistive wire 5 wound in a spiral is longitudinally centred within such a tube 7. The heating resistive wire 5 and the external tube 7 are electrically spaced by an electrically insulating filler 9 of known type with excellent thermal conduction properties, such as for example magnesium oxide. The wire 5 is welded to the inner connector 4, also incorporated in the aforesaid filler. The inner connector 4 is in turn connected, for example by coining, to the electric connection pin 3 accommodated within the insulating washer 6. The interior of such an insulating washer is suitably shaped to provide an abutting reference for pin 3.

When manufacturing the heat exchanger, the pre-assembled set of wire 5, connector 4, pin 3 and washer 6 is inserted, during the step of filling, into the tube

7 with the magnesium oxide at one or both ends of the heat exchanger 8 where the electric connection to the external power supply is provided.

The second connector 2, advantageously in the form of an elastic fastening terminal, is then engaged to the pin 3 with a low mechanical effort and the connector 2 is thus ready for accommodating the overheating protection means, typically a thermal fuse 1 but other equivalent means may also be used, as they are or already pre-assembled on the wiring harness. Alternatively, according to manufacturing needs, such a thermal fuse may be accommodated later or in another place.

A second embodiment of the heat exchanger according to the invention is shown in detail in Fig. 2. The heater 8 comprises a tube 7, preferably made of aluminium or aluminium alloys, which may be one of the cavities of a single extruded profiled element in which there are two or more cavities or longitudinal conduits, as in the first embodiment described above. The heating resistive wire 5 wound in a spiral is longitudinally centred within the tube. The resistive wire 5 and the outer tube 7 are electrically spaced by magnesium oxide 9. The resistive wire 5 is welded to the inner connector 4, also incorporated in the aforesaid filler. The inner connector 4 is in turn connected by coining to a first end portion 20c, the one on the right according to the orientation of the figure, of the second connector 20. The second connector 20 is suitably shaped in three portions, two end portions 20a and 20c and one central portion 20b. The end portion 20a advantageously consists of an elastic fastening terminal, by virtue of the presence of the longitudinal slot 1 1 interrupting the wall, so as to provide an outer accommodation to the overheating protection means, typically the thermal fuse 1. The central portion 20b crosses the insulating washer 6a and is formed as a hollow tube with a longitudinal slot 12. The end portion 20c may also have a slot 13 for improving the fastening effect with the connector 4, if needed.

Also in this embodiment, the manufacturing is carried out by inserting the pre- assembled set of wire 5, connector 4, second connector 20 and washer 6a into this tube 7 during the step of filling the tube 7 with magnesium oxide, at one or both ends of the electric connection of the heater 8 where the electric connection to the external power supply is provided.

The thermal fuse 1 may then be accommodated by press-fitting or already pre- connected to the wiring harness.

Figure 3 shows a third variant of the heat exchanger 8 according to the invention. Also in this variant, in cross section, the heat exchanger may have the embodiments in figure 4.

The heat exchanger 8 comprises a tube 7, preferably made of aluminium or aluminium alloy, which may form one of the cavities of a single extruded profiled element. The resistive wire 5 wound in a spiral is longitudinally centred within such a tube. The wire 5 and the outer tube 7 are electrically spaced by magnesium oxide. The wire 5 is welded to the inner connector 4 also incorporated in the aforesaid filler. The inner connector 4 is in turn connected by coining to the rheophore 1 a of the thermal protection 1. Also in this variant, the heat exchanger 8 is assembled using the same methods described for the previous two variants. In all variants, the materials chosen for the elements described above and forming the connection between the electric wire 5 and the overheating protection means have high electric conductivity in order to minimize losses due to resistance. The advantages deriving from the application of the present invention are apparent from the description above:

- higher thermal sensitivity of the overheating protection means,

- simplified integration of the overheating protection in terms of operating method,

- simplified electric connections with fewer wiring harnesses and fewer constitutive components of the heat exchanger,

- possible cost reduction for the heat exchanger as a whole,

- improved electric and thermal connections as compared to the solutions of the state of the art in terms of safety and contact certainty.

Claims

1. A heat exchanger (8) for heating fluids comprising:

- a tubular structure (7),

- overheating protection means (1 ) for protecting against overheating of the heat exchanger (8), arranged outside the tubular structure,

- at least one electric resistor (5) arranged inside the tubular structure (7) adapted to produce heat,

- fastening means (4) integrally attached at one end of the electric resistor (5) and forming an electric connection to power supply means,

- an insulating element (6, 6a) arranged between the tubular structure (7) and the overheating protection means (1 ),

- a connecting element (1 a, 2, 20) between the electric resistor (5) and the overheating protection means (1 ), wherein the connecting element (1 a, 2, 20) is electrically conductive and is solidarily connected to the fastening means (4).

2. A heat exchanger according to claim 1 , wherein the overheating protection means are a thermal fuse (1 ).

3. A heat exchanger according to claim 2, wherein the connecting element (1 a) is a rheophore integral with the thermal fuse (1 ).

4. A heat exchanger according to claim 2, wherein the connecting element (2, 20) is a hollow cylindrical element (2, 20) mechanically engaged about the thermal fuse (1 ).

5. A heat exchanger according to claim 4, wherein the hollow cylindrical element (2, 20) has a thin wall with a longitudinal slot (1 1 , 12) interrupting the wall so as to produce an expansion force or radial elastic contraction suitable for the fixing to the thermal fuse.

6. A heat exchanger according to claim 4, wherein the fastening means (4) are fixed to one end of the protection means (1 ) by coining.

7. A heat exchanger according to any one of the preceding claims, wherein the tubular structure (7) is an extruded profiled element comprising at least one tube for the passing of the fluid to be heated, and at least one tube in which the at least one electric resistor (5) is inserted.