Fluid heater and related manufacturing method

Abstract

The heating device (1) for fluid consists of a tube (2) made of steel on which a polyimide insulating layer (4) is wrapped, an electrical resistance (5) consisting of a metal sheet with some etched tracks (15', 15'', 15'''). An adhesive layer made of silicone is wrapped around the resistance on which another insulating polyimide layer (7) is wrapped. Lastly, a small heat shrinkable plastic tube (8) is wrapped onto the outer surface, which, with a final heating operation, is shrunk and therefore all the layers are tightened on the metal tube. A variant of the device (1) provides for wrapping another adhesive layer (3) directly on the outer surface of the tube (2) before the first insulating layer (4).

Description

Field of the invention

[0001] The invention relates to the field of heaters for fluids contained in tubes with small diameters.Background art

[0002] In numerous applications of the art, heating devices are used for fluids contained or flowing in tubes with small or very small flow rates, such as for heating liquids for washing the windows of motor vehicles or also for applications in scientific and electromedical equipment, for example.

[0003] Some important features, which are needed in small heating devices, include heating speed, effectiveness, and efficiency. Furthermore, aspects relating to the safety of the device need to be addressed, such as the capacity to prevent undesired overheating, for example. It is also important for the heating devices to have small dimensions, in particular they need to be very thin in a radial direction, and manufacturable at a low cost, when applied to widely consumed products, and they also need to be light-weight and manageable. A further important feature, which is desired in such heating devices, is the creation and maintaining of a homogenous temperature in specific zones of a tube where a fluid flows.

[0004] The manufacturing of a tubular heating device for fluids being capable of combining all of the aforesaid aspects is not simple.

[0005] Therefore, the need is felt for a fluid heating which has better performance and technical features than the known heaters, and with a low manufacturing cost.

[0006] KR 2020 0001576 U discloses a heating device for heating fluids comprising a tube having a predefined length and having a longitudinal axis X, covered by a plurality of layers of materials enveloping the tube, wherein the plurality of layers comprises, considering a sectional view on a plane transversal to said axis X, a first electrically insulating layer wrapped around the tube; an electrical resistance, the electrical resistance enveloping the first electrically insulating layer, a second electrically insulating layer wrapped around the electrical resistance, said layers being arranged in sequence and in the order listed, starting from an outer surface of the tube.Summary of the invention

[0007] Therefore, it is an object of the present invention to manufacture a heating device for fluids flowing in tubes, which is reliable, compact, offers a uniform temperature distribution, can be better manageable, and has a low production cost. This objective is achieved by a heating device for heating fluids according to claim 1.

[0008] According to another aspect of the invention, the aforesaid objective is achieved by a method of manufacturing the heating device having the features in claim 10.

[0009] By virtue of the invention, there is the advantage of having a highly compact heating device, particularly adapted to produce heat with a very low electricity consumption, which can be mounted about tubes having a small diameter in which a fluid flows, with a small flow rate and capable of reaching the working temperature very quickly. The device of the invention is particularly advantageous for heating medical, sanitary, edible fluids or industrial fluids, in particular for heating medical, sanitary, edible, and industrial liquids.

[0010] Advantageous variants can easily be obtained by virtue of the composition of the elements thereof, where the heating device operates with an electrical resistance with a PTC effect.

[0011] The small thicknesses of the layers composing the device contribute to a small mass, which ensures very quick response times with low thermal inertia.

[0012] The small volume in a diametral direction optimizes the introduction of the device into existing systems or apparatuses, or however an easy adaptation thereof to such systems or apparatuses.

[0013] The flexibility of the layers also allows the application thereof to tubular shapes with a non-circular section, e.g., elliptical or composite.

[0014] The plurality of tracks of the electrical resistance allows homogenizing the heat distribution over the whole heating device.

[0015] Since the electrical resistance is placed outside the tube, it does not causes flow rate losses along the hydraulic circuit, since it does not reduce the fluid passage section.

[0016] The dependent claims describe particular embodiments of the invention and also form an integral part of this description, where same reference numerals correspond to same elements.Brief description of the drawings

[0017] Further features and advantages of the present invention will become more apparent in the light of the detailed description of preferred, but not exclusive embodiments of a fluid heating device, shown by way of a non-limiting example, with the aid of the accompanying drawings, in which: Fig. 1 shows an overall axonometric view of a heating device according to the invention; Fig. 2 shows a section along an axial plane of the heating device in Fig. 1; Fig. 2a shows an enlarged detail of the structural element in Fig. 2; Fig. 3 shows the view of an electrical heating resistance deployed on a plane and belonging to the heating device in Fig. 1; Fig. 4 shows an axonometric view of the partially mounted heating device in Fig. 1; Fig. 5 shows an axonometric view of the heating device in fig. 1, on which further components are mounted; Fig. 6 shows a structural element used in the production cycle of the heating device; Fig. 6a shows an enlarged detail of the structural element in Fig. 6; Fig. 7 shows a partial subset of the device of the invention in an intermediate step of the manufacturing process; Fig. 8 shows a partial subset of the device of the invention in an intermediate step of the manufacturing process following that in Fig. 7.

[0018] The same reference numerals and letters in the figures identify the same elements or components.Detailed description of preferred embodiments of the invention

[0019] The heating device, or simply heater, of the invention, indicated by reference numeral 1 as a whole, comprises a tube 2 defining a longitudinal central axis X, in particular a longitudinal central axis of symmetry X and having a preferably circular section on a plane transversal to the axis X.

[0020] The tube can also have a different cross-section shape from the circular one, e.g., elliptical or polygonal or any other section commonly used in tubes. Preferably, the tube 2 is made of metal, preferably of stainless steel or a plastic or ceramic material, with a thin wall thickness. The thickness of the wall of the tube 2 is preferably between 70 and 110 µm (micrometers), preferably of about 90 µm. Depending on the uses and type of fluid to be heated, the material can have different wall thicknesses, as a function of the design and use requirements.

[0021] The length of the tube 2 can be selected based on the use thereof and on the amount of heat to be supplied to the fluid. The tube 2 can have a limited axial length and be wrapped around another tube (not shown) of greater length where the fluid flows or connected to the other tube in a known manner. In this case, the choice of the material of tube 2 depends on the heat transmission capacity existing with the material of the longer tube where the fluid flows.

[0022] A first adhesive layer 3 (preferably made of silicone or an acrylic material) is wrapped around the outer surface of the tube 2, being for example in the form of a film having a thickness of about 50 µm and preferably square or rectangular in plan when deployed on a plane, or more generally polygonal, as well as the other layers composing the heating device 1. A first electrically insulating layer 4, or first insulating layer, is wrapped directly around the adhesive layer 3, preferably comprising or consisting of polyimide, e.g., "Kapton ®< " or a material comprising or consisting of poly-oxy diphenylene-pyromellitimide), and preferably having a thickness of about 25 µm. Other materials for this insulating layer can be selected from polyimides, polyesters, silicones, polyamides, fluoropolymers, polyetherimides and polyesterimides.

[0023] A heating layer consisting of an electrical heating resistance 5 (or electrical resistor), in the shape of a flexible metal sheet and with a thickness preferably of about 50 µm, is directly wrapped around the insulating layer 4.

[0024] The electrical resistance 5 is adapted to generate heat when it is electrically powered.

[0025] In a particularly advantageous embodiment, the electrical resistance 5 is made of a material having a PTC (Positive Temperature Coefficient) feature or is coupled to a layer with PTC effect, which allows controlling the passage of electricity in the electrical resistance 5 and thus interrupting the heating when the predetermined design temperature is reached.

[0026] A second adhesive layer 6, preferably made of silicone or acrylic material, preferably having the same thickness as the first adhesive layer 3, is wrapped directly around the electrical resistance 5. A second electrically insulating layer 7 or second insulating layer, preferably made of polyimide (such as "Kapton ®< ", for example), or other, preferably having the same thickness as the first insulating layer 4, is wrapped around the second adhesive layer 6. It can also be made of the same materials listed for the first insulating layer.

[0027] A small tube 8 made of a plastic material is directly wrapped around the second insulating layer 7, which has the property of shrinking when heated, e.g., the material commercially known as thermoshrink PEEK. The heating device 1, after undergoing the final heating which causes the tube 8 to shrink, takes a compact shape which contributes to keeping all the layers 3, 4, 5, 6, 7, 8 tightened together, in particular sealed, around the tube 2, giving the heating device 1 its final shape. It is possible to use a final fixing system for the layers, which is different from the small heat shrinkable tube 8.

[0028] In a variant of the heating device, it is also possible to avoid inserting the first adhesive layer 3 and / or the second adhesive layer 6, with the same additional constitutive elements, without departing from the scope of the invention.

[0029] Advantageously, if it is necessary, for example, to control the interruption of the electrical circuit, a temperature sensor 9, with a related electrical circuit 16, is conveniently fixed to the second insulating layer 7 before the small tube 8, wrapped around the tube, is shrunk by heating and when the small tube is shrunk, it also tightens the sensor 9 firmly along with the layers. Thereby, the temperature of the heater can be measured with precision during operation.

[0030] In a particularly advantageous variant of the heater (not shown in the figures), the temperature sensor 9 is positioned so that after completing the winding of the layers, the sensor is positioned in a hole made on the underlying insulating layers. Thereby, at the end of the assembly operations, the sensor 9 is fixed in direct contact with the tube 2, and a particularly precise measurement of the tube 2 wall is obtained.

[0031] Optionally, a cable 10 can be provided for transmitting the data on the working temperature of the heating device 1 during use, detected by the sensor 9, which is brought out of one end of the small tube 8 and which can thus be connected to a possible electrical or electronic circuit to control the use of the heating device 1.

[0032] The current supply needed for the electrical resistance 5 is obtained by means of the two cables 11 and 12 which are fixed, in a known manner, e.g., by brazing, to the terminals 13, 14 of the electrical resistance 5 and they cause the current to arrive from batteries or accumulators specifically provided, but the electrical supply can be achieved using other known means.

[0033] The electrical resistance 5 is made by etching the tracks 15', 15", 15‴ from a flexible sheet of current-conducting metal, such as copper, for example. Preferably, the tracks 15', 15", 15‴ are three in number, joined parallel to one another to the ends forming the terminals 13, 14. However, it is also possible to obtain the electrical resistance 5 with a greater number than three tracks without departing from the scope of the invention. The electrical cables 11 and 12 are connected, at the other respective end thereof, to the electrical source, not shown, and to the possible electronic control circuit in a manner well known to those skilled in the art, based on the applications for which the heating device is designed.

[0034] Now we shall describe a first preferred method of manufacturing the heating device of the invention, with particular reference to the figures.

[0035] The method includes coupling the metal sheet, in the shape of leaf, e.g., of copper, to an insulating material sheet 4, preferably by hot pressing. Then, with the two layers coupled, the metal part is etched to obtain the electrical resistances 5 seen in Fig. 6, one of which is enlarged in Fig. 6a. Photoengraving process of the known type can be used, such as application of photosensitive layer, photo impression, etching by means of acids and removal of a photosensitive layer, for example. Finally, the sheet 17, or substrate, on which several etched electrical resistances 5 arranged, for example, according to a matrix are obtained, is cut into pieces 20, preferably having a substantially quadrangular shape, e.g., substantially rectangular, with the desired dimensions for wrapping them around the tubes 2 to obtain the heating devices 1.

[0036] An advantageous variant of the invention provides that the dimensions of each piece 20 are such that the longer side of the rectangle is selected to be substantially double the length of the circumference of the tube 2. The electrical resistance 5 is arranged on one part of the piece 20, corresponding to about half of the surface thereof, while the part on which there is the circuit or connection 16 corresponds to the other half of the surface of the piece 20.

[0037] A layer 3 of adhesive material is laid over the outer surface of the tube 2.

[0038] The piece 20 is then wrapped around the tube 2, with the face on which the electrical resistance 5 is fixed facing outside, and by virtue of the length thereof, two windings are made around the tube 2. Alternatively, the step of etching the electrical resistances 5 can be carried out from the single thin sheet of electrical conductor material or metal sheet, without previously gluing it onto a layer of insulating material. In this case, all the electrical resistances 5 and connections 16, after etching, are transferred and glued onto a thin sheet 4 of insulating material. In this case, the next step consists in cutting the insulating material sheet 4 into pieces 20, or strips, preferably having a substantially quadrangular shape, in plan, preferably rectangular or square, as shown in Fig. 6a.

[0039] The piece 20 is then wrapped around the tube 2 arranging the face on which the electrical resistance 5 is fixed outwards, and also in this case two windings are made around the tube 2, as explained above. Advantageously, in addition to the electrical heating resistances 5, in all variants of the method, other circuits can also be obtained from the metal sheet, intended to be arranged on each of the pieces 20, e.g., for connecting other types of sensor.

[0040] Generally, but not necessarily, all the pieces 20 are made with the same dimensions, which are sufficient to allow two complete windings around the tube 2, so that the electrical resistance 5 and the temperature sensor 9, at the end of the winding, are arranged in the position which causes the temperature sensor 9 to take the position on the surface of the electrical resistance 5 where the maximum temperature is generated during operation.

[0041] In the next stage, the temperature sensor 9 is fixed to the circuit 16 by welding or brazing, and the two terminals 13, 14 of the electrical resistance 5 are welded to the electrical conductors 11 and 12, preferably and advantageously by laser welding.

[0042] After the winding, and in any case after applying the temperature sensor 9, if provided, a small tube 8 made of a heat shrinkable material is wrapped, which, after being heated above a certain temperature, tightens all the underlying layers, e.g., it is a material comprising or consisting of PEEK (polyether ether ketone), such as thermoshrink PEEK, or a similar product serving the same purposes.

[0043] In an advantageous and alternative embodiment of the method, the first adhesive material layer 3 is applied to the face of the electrically insulating layer 4 opposite to that on which the electrical resistance 5 and the temperature sensor 9 are fixed and only at the surface half where the electrical resistance 5 is positioned. In this case, an aggregation is prepared (i.e., a preassembled component is formed), including the adhesive layer 3, with the electrically insulating layer 4 and the electrical resistance 5 on top, and then the adhesive layer 3 is arranged first in contact with the outer surface of the tube 2, and the aggregation consisting of the three elements is rolled up: also in this case, two windings are made around the tube 2 because of the dimension of the larger side of the piece 20.

[0044] When the first adhesive layer 3 is also used, the adhesion of the electrically insulating layer 4 to the surface of the tube 2 is increased.

[0045] In a further advantageous variant of the method of the invention, a second adhesive layer is wrapped around the electrical resistance 5 after this is wrapped around the tube 2 according to the methods explained above. This variant can be obtained by extending the adhesive layer 3 over the whole surface of the electrically insulating layer 4 opposite to the surface where the heating resistance 5 and the circuit 16 are glued.

[0046] The first 3 and second 6 adhesive layers may also not be used together, in a variant of the invention, or only one of the two or none of the two can be used. If both adhesive layers 3 and 6 are obtained together, this can be done by gluing only one adhesive layer or adhesive sheet which covers the whole surface of the piece 20 on the side opposite to the side where the electrical resistance 5 and the circuit 16 are glued, or this can be done by gluing two different pieces 3 and 6 onto the same side. From the above explanation, it is apparent to those skilled in the art that, since the length of the piece 20 is preferably defined as double the length of the circumference of the outer surface of the tube 2, at the end of the process of winding the layers 3, 4, 5 about the tube 2, the final structure of the heating device 1, seen in a cross-section to the axis of the tube 2, and from the outer surface of the tube 2, contains the first adhesive layer 3, the electrically insulating layer 4, the electrical resistance 5, the second adhesive layer 6 (which, in a variant shown above, is a part of the same adhesive layer 3), the second electrically insulating layer 7 (which, in a variant already shown above, is a part of the same electrically insulating layer 4), and the heat shrinkable material layer 8. Fig. 2a shows the distribution of the layers in this particular preferred variant of the invention.

[0047] If the first 3 and / or second 6 adhesive layers are missing, the cross-section structure of the heating device 1 would be correspondingly different, as those skilled in the art can easily understand.

Examples

Embodiment Construction

[0019]The heating device, or simply heater, of the invention, indicated by reference numeral 1 as a whole, comprises a tube 2 defining a longitudinal central axis X, in particular a longitudinal central axis of symmetry X and having a preferably circular section on a plane transversal to the axis X.

[0020]The tube can also have a different cross-section shape from the circular one, e.g., elliptical or polygonal or any other section commonly used in tubes. Preferably, the tube 2 is made of metal, preferably of stainless steel or a plastic or ceramic material, with a thin wall thickness. The thickness of the wall of the tube 2 is preferably between 70 and 110 µm (micrometers), preferably of about 90 µm. Depending on the uses and type of fluid to be heated, the material can have different wall thicknesses, as a function of the design and use requirements.

[0021]The length of the tube 2 can be selected based on the use thereof and on the amount of heat to be supplied to the fluid. The tub...

Field of the invention

[0001] The invention relates to the field of heaters for fluids contained in tubes with small diameters.Background art

[0002] In numerous applications of the art, heating devices are used for fluids contained or flowing in tubes with small or very small flow rates, such as for heating liquids for washing the windows of motor vehicles or also for applications in scientific and electromedical equipment, for example.

[0003] Some important features, which are needed in small heating devices, include heating speed, effectiveness, and efficiency. Furthermore, aspects relating to the safety of the device need to be addressed, such as the capacity to prevent undesired overheating, for example. It is also important for the heating devices to have small dimensions, in particular they need to be very thin in a radial direction, and manufacturable at a low cost, when applied to widely consumed products, and they also need to be light-weight and manageable. A further important feature, which is desired in such heating devices, is the creation and maintaining of a homogenous temperature in specific zones of a tube where a fluid flows.

[0004] The manufacturing of a tubular heating device for fluids being capable of combining all of the aforesaid aspects is not simple.

[0005] Therefore, the need is felt for a fluid heating which has better performance and technical features than the known heaters, and with a low manufacturing cost.

[0006] KR 2020 0001576 U discloses a heating device for heating fluids comprising a tube having a predefined length and having a longitudinal axis X, covered by a plurality of layers of materials enveloping the tube, wherein the plurality of layers comprises, considering a sectional view on a plane transversal to said axis X, a first electrically insulating layer wrapped around the tube; an electrical resistance, the electrical resistance enveloping the first electrically insulating layer, a second electrically insulating layer wrapped around the electrical resistance, said layers being arranged in sequence and in the order listed, starting from an outer surface of the tube.Summary of the invention

[0007] Therefore, it is an object of the present invention to manufacture a heating device for fluids flowing in tubes, which is reliable, compact, offers a uniform temperature distribution, can be better manageable, and has a low production cost. This objective is achieved by a heating device for heating fluids according to claim 1.

[0008] According to another aspect of the invention, the aforesaid objective is achieved by a method of manufacturing the heating device having the features in claim 10.

[0009] By virtue of the invention, there is the advantage of having a highly compact heating device, particularly adapted to produce heat with a very low electricity consumption, which can be mounted about tubes having a small diameter in which a fluid flows, with a small flow rate and capable of reaching the working temperature very quickly. The device of the invention is particularly advantageous for heating medical, sanitary, edible fluids or industrial fluids, in particular for heating medical, sanitary, edible, and industrial liquids.

[0010] Advantageous variants can easily be obtained by virtue of the composition of the elements thereof, where the heating device operates with an electrical resistance with a PTC effect.

[0011] The small thicknesses of the layers composing the device contribute to a small mass, which ensures very quick response times with low thermal inertia.

[0012] The small volume in a diametral direction optimizes the introduction of the device into existing systems or apparatuses, or however an easy adaptation thereof to such systems or apparatuses.

[0013] The flexibility of the layers also allows the application thereof to tubular shapes with a non-circular section, e.g., elliptical or composite.

[0014] The plurality of tracks of the electrical resistance allows homogenizing the heat distribution over the whole heating device.

[0015] Since the electrical resistance is placed outside the tube, it does not causes flow rate losses along the hydraulic circuit, since it does not reduce the fluid passage section.

[0016] The dependent claims describe particular embodiments of the invention and also form an integral part of this description, where same reference numerals correspond to same elements.Brief description of the drawings

[0017] Further features and advantages of the present invention will become more apparent in the light of the detailed description of preferred, but not exclusive embodiments of a fluid heating device, shown by way of a non-limiting example, with the aid of the accompanying drawings, in which: Fig. 1 shows an overall axonometric view of a heating device according to the invention; Fig. 2 shows a section along an axial plane of the heating device in Fig. 1; Fig. 2a shows an enlarged detail of the structural element in Fig. 2; Fig. 3 shows the view of an electrical heating resistance deployed on a plane and belonging to the heating device in Fig. 1; Fig. 4 shows an axonometric view of the partially mounted heating device in Fig. 1; Fig. 5 shows an axonometric view of the heating device in fig. 1, on which further components are mounted; Fig. 6 shows a structural element used in the production cycle of the heating device; Fig. 6a shows an enlarged detail of the structural element in Fig. 6; Fig. 7 shows a partial subset of the device of the invention in an intermediate step of the manufacturing process; Fig. 8 shows a partial subset of the device of the invention in an intermediate step of the manufacturing process following that in Fig. 7.

[0018] The same reference numerals and letters in the figures identify the same elements or components.Detailed description of preferred embodiments of the invention

[0019] The heating device, or simply heater, of the invention, indicated by reference numeral 1 as a whole, comprises a tube 2 defining a longitudinal central axis X, in particular a longitudinal central axis of symmetry X and having a preferably circular section on a plane transversal to the axis X.

[0020] The tube can also have a different cross-section shape from the circular one, e.g., elliptical or polygonal or any other section commonly used in tubes. Preferably, the tube 2 is made of metal, preferably of stainless steel or a plastic or ceramic material, with a thin wall thickness. The thickness of the wall of the tube 2 is preferably between 70 and 110 µm (micrometers), preferably of about 90 µm. Depending on the uses and type of fluid to be heated, the material can have different wall thicknesses, as a function of the design and use requirements.

[0021] The length of the tube 2 can be selected based on the use thereof and on the amount of heat to be supplied to the fluid. The tube 2 can have a limited axial length and be wrapped around another tube (not shown) of greater length where the fluid flows or connected to the other tube in a known manner. In this case, the choice of the material of tube 2 depends on the heat transmission capacity existing with the material of the longer tube where the fluid flows.

[0022] A first adhesive layer 3 (preferably made of silicone or an acrylic material) is wrapped around the outer surface of the tube 2, being for example in the form of a film having a thickness of about 50 µm and preferably square or rectangular in plan when deployed on a plane, or more generally polygonal, as well as the other layers composing the heating device 1. A first electrically insulating layer 4, or first insulating layer, is wrapped directly around the adhesive layer 3, preferably comprising or consisting of polyimide, e.g., "Kapton ®< " or a material comprising or consisting of poly-oxy diphenylene-pyromellitimide), and preferably having a thickness of about 25 µm. Other materials for this insulating layer can be selected from polyimides, polyesters, silicones, polyamides, fluoropolymers, polyetherimides and polyesterimides.

[0023] A heating layer consisting of an electrical heating resistance 5 (or electrical resistor), in the shape of a flexible metal sheet and with a thickness preferably of about 50 µm, is directly wrapped around the insulating layer 4.

[0024] The electrical resistance 5 is adapted to generate heat when it is electrically powered.

[0025] In a particularly advantageous embodiment, the electrical resistance 5 is made of a material having a PTC (Positive Temperature Coefficient) feature or is coupled to a layer with PTC effect, which allows controlling the passage of electricity in the electrical resistance 5 and thus interrupting the heating when the predetermined design temperature is reached.

[0026] A second adhesive layer 6, preferably made of silicone or acrylic material, preferably having the same thickness as the first adhesive layer 3, is wrapped directly around the electrical resistance 5. A second electrically insulating layer 7 or second insulating layer, preferably made of polyimide (such as "Kapton ®< ", for example), or other, preferably having the same thickness as the first insulating layer 4, is wrapped around the second adhesive layer 6. It can also be made of the same materials listed for the first insulating layer.

[0027] A small tube 8 made of a plastic material is directly wrapped around the second insulating layer 7, which has the property of shrinking when heated, e.g., the material commercially known as thermoshrink PEEK. The heating device 1, after undergoing the final heating which causes the tube 8 to shrink, takes a compact shape which contributes to keeping all the layers 3, 4, 5, 6, 7, 8 tightened together, in particular sealed, around the tube 2, giving the heating device 1 its final shape. It is possible to use a final fixing system for the layers, which is different from the small heat shrinkable tube 8.

[0028] In a variant of the heating device, it is also possible to avoid inserting the first adhesive layer 3 and / or the second adhesive layer 6, with the same additional constitutive elements, without departing from the scope of the invention.

[0029] Advantageously, if it is necessary, for example, to control the interruption of the electrical circuit, a temperature sensor 9, with a related electrical circuit 16, is conveniently fixed to the second insulating layer 7 before the small tube 8, wrapped around the tube, is shrunk by heating and when the small tube is shrunk, it also tightens the sensor 9 firmly along with the layers. Thereby, the temperature of the heater can be measured with precision during operation.

[0030] In a particularly advantageous variant of the heater (not shown in the figures), the temperature sensor 9 is positioned so that after completing the winding of the layers, the sensor is positioned in a hole made on the underlying insulating layers. Thereby, at the end of the assembly operations, the sensor 9 is fixed in direct contact with the tube 2, and a particularly precise measurement of the tube 2 wall is obtained.

[0031] Optionally, a cable 10 can be provided for transmitting the data on the working temperature of the heating device 1 during use, detected by the sensor 9, which is brought out of one end of the small tube 8 and which can thus be connected to a possible electrical or electronic circuit to control the use of the heating device 1.

[0032] The current supply needed for the electrical resistance 5 is obtained by means of the two cables 11 and 12 which are fixed, in a known manner, e.g., by brazing, to the terminals 13, 14 of the electrical resistance 5 and they cause the current to arrive from batteries or accumulators specifically provided, but the electrical supply can be achieved using other known means.

[0033] The electrical resistance 5 is made by etching the tracks 15', 15", 15‴ from a flexible sheet of current-conducting metal, such as copper, for example. Preferably, the tracks 15', 15", 15‴ are three in number, joined parallel to one another to the ends forming the terminals 13, 14. However, it is also possible to obtain the electrical resistance 5 with a greater number than three tracks without departing from the scope of the invention. The electrical cables 11 and 12 are connected, at the other respective end thereof, to the electrical source, not shown, and to the possible electronic control circuit in a manner well known to those skilled in the art, based on the applications for which the heating device is designed.

[0034] Now we shall describe a first preferred method of manufacturing the heating device of the invention, with particular reference to the figures.

[0035] The method includes coupling the metal sheet, in the shape of leaf, e.g., of copper, to an insulating material sheet 4, preferably by hot pressing. Then, with the two layers coupled, the metal part is etched to obtain the electrical resistances 5 seen in Fig. 6, one of which is enlarged in Fig. 6a. Photoengraving process of the known type can be used, such as application of photosensitive layer, photo impression, etching by means of acids and removal of a photosensitive layer, for example. Finally, the sheet 17, or substrate, on which several etched electrical resistances 5 arranged, for example, according to a matrix are obtained, is cut into pieces 20, preferably having a substantially quadrangular shape, e.g., substantially rectangular, with the desired dimensions for wrapping them around the tubes 2 to obtain the heating devices 1.

[0036] An advantageous variant of the invention provides that the dimensions of each piece 20 are such that the longer side of the rectangle is selected to be substantially double the length of the circumference of the tube 2. The electrical resistance 5 is arranged on one part of the piece 20, corresponding to about half of the surface thereof, while the part on which there is the circuit or connection 16 corresponds to the other half of the surface of the piece 20.

[0037] A layer 3 of adhesive material is laid over the outer surface of the tube 2.

[0038] The piece 20 is then wrapped around the tube 2, with the face on which the electrical resistance 5 is fixed facing outside, and by virtue of the length thereof, two windings are made around the tube 2. Alternatively, the step of etching the electrical resistances 5 can be carried out from the single thin sheet of electrical conductor material or metal sheet, without previously gluing it onto a layer of insulating material. In this case, all the electrical resistances 5 and connections 16, after etching, are transferred and glued onto a thin sheet 4 of insulating material. In this case, the next step consists in cutting the insulating material sheet 4 into pieces 20, or strips, preferably having a substantially quadrangular shape, in plan, preferably rectangular or square, as shown in Fig. 6a.

[0039] The piece 20 is then wrapped around the tube 2 arranging the face on which the electrical resistance 5 is fixed outwards, and also in this case two windings are made around the tube 2, as explained above. Advantageously, in addition to the electrical heating resistances 5, in all variants of the method, other circuits can also be obtained from the metal sheet, intended to be arranged on each of the pieces 20, e.g., for connecting other types of sensor.

[0040] Generally, but not necessarily, all the pieces 20 are made with the same dimensions, which are sufficient to allow two complete windings around the tube 2, so that the electrical resistance 5 and the temperature sensor 9, at the end of the winding, are arranged in the position which causes the temperature sensor 9 to take the position on the surface of the electrical resistance 5 where the maximum temperature is generated during operation.

[0041] In the next stage, the temperature sensor 9 is fixed to the circuit 16 by welding or brazing, and the two terminals 13, 14 of the electrical resistance 5 are welded to the electrical conductors 11 and 12, preferably and advantageously by laser welding.

[0042] After the winding, and in any case after applying the temperature sensor 9, if provided, a small tube 8 made of a heat shrinkable material is wrapped, which, after being heated above a certain temperature, tightens all the underlying layers, e.g., it is a material comprising or consisting of PEEK (polyether ether ketone), such as thermoshrink PEEK, or a similar product serving the same purposes.

[0043] In an advantageous and alternative embodiment of the method, the first adhesive material layer 3 is applied to the face of the electrically insulating layer 4 opposite to that on which the electrical resistance 5 and the temperature sensor 9 are fixed and only at the surface half where the electrical resistance 5 is positioned. In this case, an aggregation is prepared (i.e., a preassembled component is formed), including the adhesive layer 3, with the electrically insulating layer 4 and the electrical resistance 5 on top, and then the adhesive layer 3 is arranged first in contact with the outer surface of the tube 2, and the aggregation consisting of the three elements is rolled up: also in this case, two windings are made around the tube 2 because of the dimension of the larger side of the piece 20.

[0044] When the first adhesive layer 3 is also used, the adhesion of the electrically insulating layer 4 to the surface of the tube 2 is increased.

[0045] In a further advantageous variant of the method of the invention, a second adhesive layer is wrapped around the electrical resistance 5 after this is wrapped around the tube 2 according to the methods explained above. This variant can be obtained by extending the adhesive layer 3 over the whole surface of the electrically insulating layer 4 opposite to the surface where the heating resistance 5 and the circuit 16 are glued.

[0046] The first 3 and second 6 adhesive layers may also not be used together, in a variant of the invention, or only one of the two or none of the two can be used. If both adhesive layers 3 and 6 are obtained together, this can be done by gluing only one adhesive layer or adhesive sheet which covers the whole surface of the piece 20 on the side opposite to the side where the electrical resistance 5 and the circuit 16 are glued, or this can be done by gluing two different pieces 3 and 6 onto the same side. From the above explanation, it is apparent to those skilled in the art that, since the length of the piece 20 is preferably defined as double the length of the circumference of the outer surface of the tube 2, at the end of the process of winding the layers 3, 4, 5 about the tube 2, the final structure of the heating device 1, seen in a cross-section to the axis of the tube 2, and from the outer surface of the tube 2, contains the first adhesive layer 3, the electrically insulating layer 4, the electrical resistance 5, the second adhesive layer 6 (which, in a variant shown above, is a part of the same adhesive layer 3), the second electrically insulating layer 7 (which, in a variant already shown above, is a part of the same electrically insulating layer 4), and the heat shrinkable material layer 8. Fig. 2a shows the distribution of the layers in this particular preferred variant of the invention.

[0047] If the first 3 and / or second 6 adhesive layers are missing, the cross-section structure of the heating device 1 would be correspondingly different, as those skilled in the art can easily understand.

Examples

Embodiment Construction

[0019]The heating device, or simply heater, of the invention, indicated by reference numeral 1 as a whole, comprises a tube 2 defining a longitudinal central axis X, in particular a longitudinal central axis of symmetry X and having a preferably circular section on a plane transversal to the axis X.

[0020]The tube can also have a different cross-section shape from the circular one, e.g., elliptical or polygonal or any other section commonly used in tubes. Preferably, the tube 2 is made of metal, preferably of stainless steel or a plastic or ceramic material, with a thin wall thickness. The thickness of the wall of the tube 2 is preferably between 70 and 110 µm (micrometers), preferably of about 90 µm. Depending on the uses and type of fluid to be heated, the material can have different wall thicknesses, as a function of the design and use requirements.

[0021]The length of the tube 2 can be selected based on the use thereof and on the amount of heat to be supplied to the fluid. The tub...

Claims

1. A heating device (1) for heating fluids comprising a tube (2) having a predefined length and having a longitudinal axis X, covered by a plurality of layers of materials enveloping the tube (2), wherein the plurality of layers comprises, considering a sectional view on a plane transversal to said axis X, a first electrically insulating layer (4) wrapped around the tube (2); an electrical resistance (5) made of a metal sheet etched so as to form three or more electrical conductor tracks (15', 15", 15‴) connected together at two respective ends at two respective terminals (13, 14), the electrical resistance (5) enveloping the first electrically insulating layer (4), a second electrically insulating layer (7) wrapped around the electrical resistance (5), a layer (8) made of heat-shrinkable material enveloping the second insulating layer (7), said layers being arranged in sequence and in the order listed, starting from an outer surface of the tube (2).

2. A heating device (1) according to claim 1, wherein there is provided a temperature sensor (9), fixed to the second electrically insulating layer (7) or directly on the outer surface of the tube (2), capable to detect the temperature in the heating device (1) during operation.

3. A heating device (1) according to one of claims 1 or 2, wherein there is also provided a first adhesive layer (6), disposed directly around the electrical resistance (5) and below the second electrically insulating layer (7).

4. A heating device (1) according to one of claims 1 to 3, wherein there is provided also a second adhesive layer (3) disposed directly around the external surface of tube (2), between the tube (2) and the first insulating layer (4).

5. A heating device (1) according to one of claims 3 or 4, wherein the first and / or second adhesive layers (6, 3) are made of a silicone or acrylic material.

6. A heating device (1) according to one of the preceding claims, wherein the first and second electrically insulating layers (4, 7) are made of a material selected from polyimides or polyesters or silicones or polyamides or fluoropolymers or polyetherimides or polyesterimides.

7. A heating device (1) according to claim 6, wherein the first (4) and second (7) electrically insulating layers are made of Kapton®.

8. A heating device (1) according to one of the preceding claims, wherein the heating device is made of a material with a PTC characteristic.

9. A heating device (1) according to one of the preceding claims, wherein the heat-shrinkable material layer (8) is disposed on the second electrically insulating layer (7).

10. A method of manufacturing a heating device (1) according to one of claims 1 to 8, wherein there is provided a plurality of tubes (2) of predetermined length and comprising the following stages: a) - gluing an electricity conducting metal sheet to an electrically insulating material layer (4), b) - etching the metal sheet to obtain a plurality of electrical resistances (5), c) - cutting the first electrically insulating material layer (4) into a plurality of pieces (20), preferably quadrangular, so that at least an electrical resistance (5) is glued on each of the first electrically insulating layer (4), d) - wrapping one of said plurality of pieces (20) around the outer surface of a tube (2) of said plurality of tubes wherein the first electrically insulating layer (4) faces the tube (2) and the electrical resistance (5) faces towards the exterior side; e) - wrapping a second electrically insulating layer (7) above the electrical resistance (5); f) - disposing a small tube (8) made of a heat-shrinkable plastic material around the second electrically insulating layer (7), g) - heating the small tube (8) so as to cause the shrinking thereof so as to take a shrinked shape capable of keeping tightly gripped said first electrically insulating layer (4), said electrical resistance ( 5), said second electrically insulating layer (7) about said tube (2).

11. A method according to claim 10, wherein there is provided disposing a second adhesive layer (3), before step d), directly around the outer surface of said tube (2).

12. A method according to claim 11, wherein there is provided disposing a first adhesive layer (6) above said electrical resistance (5), before step e).

13. Use of the heating device (1) according to any one of claims 1 to 9 for heating sanitary fluids or edible fluids or industrial fluids or medical fluids or technical fluids.

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