Heat exchanger for fluids

Abstract

 The heat exchanger of the invention comprises substantially a U-shaped armoured resistance element (2) constructed of stainless steel and provided at its ends with insulators (4) from which push on connectors (6) emerge for connection to the electric mains cables.
A metal tube (8), preferably of stainless steel, but high nickel/chromium content alloys could be used, is wound as a spiral about the resistance element (2).
The tube (8) is secured by brazing with (nickel) alloys able to reliably withstand the maximum operating temperature of the resistance element and to adequately transmit the heat generated by the resistance element to the tube. The tube is provided at its ends with connectors (10) of gas type for its connection to the hydraulic circuit.
The resistance element (2) and the tube (8) are braze-welded to two C-shaped brackets (12) with their flanges (14) provided with holes (16) for fixing to a support structure (not shown in the drawings). The same brackets (12) are also used for mounting safety and/or operational thermostats.
A sleeve (18) is applied to the outer surface of the tube (8) at one of the two brackets, and houses internally a thermal fuse (not shown in the drawings) connected into the electrical network supplying the resistance element, to interrupt this supply when a predetermined temperature is exceeded.

Description

[0001] The present invention relates to a heat exchanger for fluids.

[0002] Heating devices used in household electrical appliances (washing machines, dishwashers, coffee makers, etc.) are known, the operating cycle of which uses heated water which is made to circulate through a suitable utilization circuit.

[0003] These technologies have also found application in other industrial and commercial sectors such as hot water sanitary equipment, collective cantering, steam generation, etc.

[0004] A first known type of heat exchanger consists of a body made of cast aluminium incorporating a resistance element and a spiral tube though which a fluid flows.

[0005] This heat exchanger has however the drawback of high cost and the impossibly of undergoing modification to meet unforeseen requirements.

[0006] Another heat exchanger consists of a double-U aluminium profile in which one tube houses the resistance element and the other forms the fluid collector.

[0007] This device has the drawback of high dispersion and requires specific equipment for its construction.

[0008] A third type of heat exchanger consists of an aluminium sleeve internally lined with Teflon and housing an armoured resistance element within the tube wall.

[0009] This heat exchanger has the drawback of high cost due mainly to the Teflon coating and its die casting procedure.

[0010] A fourth device consists of a resistance element spiral wound about a steel tube and braze-welded to it.

[0011] This device has the drawback of high dispersion and the high cost of the braze-welding equipment.

[0012] Another device consists of two aluminium plates forming the fluid circuit and incorporating the resistance element, which is fixed by pressure.

[0013] This device has the drawback of a high die cost and a high assembly cost for the various parts.

[0014] Another device consists of a stainless steel tube through which the fluid passes and in which a resistance element is welded.

[0015] This device has the drawback of limestone formation as the fluid is directly in contact with the resistance element, and is of high cost.

[0016] Moreover the aforesaid devices often require production technologies which may not be present on one and the same production site or which cannot coexist due to environmental conditions incompatible with consequent logistic problems for their completion.

[0017] An object of the invention is to eliminate these drawbacks by providing a heat exchanger which not only enables fluids to be heated but which for certain applications enables the fluid to be brought into the vapour phase.

[0018] Another object of the invention is to provide a heat exchanger having good thermal efficiency and a high modularity.

[0019] Another object of the invention is to enable adequate temperature control possibly by thermostats.

[0020] Another object of the invention is to achieve intrinsic "safety" against overtemperature, being constructed of materials which resist temperatures up to 650°0 without undergoing deterioration.

[0021] Another object of the invention is to provide a heat exchanger requiring low specific investment and hence having a competitive cost.

[0022] This and other objects which will be apparent from the ensuing description are attained by a heat exchanger as described in claim 1.

[0023] The present invention is further clarified hereinafter with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of heat exchanger according to the invention,

Figure 2 is a plan view thereof,

Figure 3 is a front view thereof, and

Figure 4 is a longitudinal section through a variant thereof.

[0024] As can be seen from the figures, the heat exchanger of the invention comprises substantially a U-shaped armoured resistance element 2 constructed of stainless steel and provided at its ends with insulator 4 from which push-on connectors 6 emerge for connection to the electric mains cables.

[0025] A metal tube 8, preferably of stainless steel, but high nickei/chromium content alloys could be used, is wound as a spiral about the resistance element 2.

[0026] The tube 8 is secured by brazing with (nickel) alloys able to reliably withstand the maximum operating temperature of the resistance element and to adequately transmit the heat generated by the resistance element to the tube. The tube is provided at its ends with connectors 10 of gas type for its connection to the hydraulic circuit.

[0027] The resistance element 2 and the tube 8 are braze-welded to two C-shaped brackets 12 with their flanges 14 provided with holes 16 for fixing to a support structure (not shown in the drawings). The same brackets 12 are also used for mounting safety and/or operational thermostats.

[0028] A sleeve 18 is applied to the outer surface of the tube 8 at one of the two brackets, and houses internally a thermal fuse (not shown in the drawings) connected into the electrical network supplying the resistance element, to interrupt this supply when a predetermined temperature is exceeded.

[0029] This system presents low thermal inertia, but should it be necessary to increase it a steel profile of high thermal mass can be applied (by welding in parallel with or on a higher level than the spiral tube). This variant is considered useful for various applications, such as vapour phase generation.

[0030] In the embodiment shown in figure 4, the resistance element 2 comprises at one end a seat into which a hollow sleeve 20 is inserted, housing a thermal fuse 22 which is connected at its ends to the push-on connector 6 and, respectively, to a terminal pin 24 connected to the resistive spiral 26.

[0031] A resin seal 28 separates the magnesium oxide 30 insulating the resistive spiral 26, from the sleeve 20.

[0032] From the aforegoing it is apparent that the heat exchanger of the invention presents numerous advantages, and in particular:

• it can be used in all appliances in contact with liquids or gases intended for foods or fluids for the human body,
• it has a high thermal efficiency due to the large heat transfer area,
• it has a multiplicity of uses,
• it can be formed in various shapes, lengths and thermal and electrical capacities,
• it enables the thermal fuse to be easily and quickly replaced,
• it can be considered intrinsically safe against overtemperatures.

Claims

1. A heat exchanger characterised by consisting of an armoured resistance element (2) about which a tube (8) is wound for passage of the fluid to be heated.

2. A heat exchanger as claimed in claim 1, characterised in that the tube (8) is wound spirally.

3. A heat exchanger as claimed in claim 1, characterised in that the armoured resistance element (2) is of U-shape.

4. A heat exchanger as claimed in claim 1, characterised in that the tube (8) is provided at its ends with connectors (10) of gas type.

5. A heat exchanger as claimed in claim 1, characterised in that the tube is welded to the resistance element by brazing.

6. A heat exchanger as claimed in claim 1, characterised in that a sleeve (18) for housing a thermal sensor is secured to the tube surface.

7. A heat exchanger as claimed in claim 1, characterised by comprising at least one bracket (14) for fixing to a support structure and for mounting a thermostat/thermostats and/or thermal sensors.

8. A heat exchanger as claimed in claim 1, characterised in that the armoured resistance element (2) internally houses a thermal fuse (22).

9. A heat exchanger as claimed in claim 8, characterised in that the thermal fuse (22) is housed in a hollow sleeve (20) inserted into the end of the resistance element.

10. A heat exchanger as claimed in claim 9, characterised in that the hollow sleeve (20) is separated from the magnesium oxide (30) insulating the resistive spiral (26) by a resin seal (28).

Drawing