EP2499437B1

EP2499437B1 - Heat exchanger with improved thermal efficiency

Info

Publication number: EP2499437B1
Application number: EP10768981.2A
Authority: EP
Inventors: Mario Morini
Original assignee: Unical AG SpA
Current assignee: Unical AG SpA
Priority date: 2009-11-12
Filing date: 2010-10-27
Publication date: 2018-05-02
Anticipated expiration: 2030-10-27
Also published as: IT1396923B1; WO2011057895A8; WO2011057895A1; EP2499437A1; ITMI20091983A1

Description

Technical field

The present invention relates to a heat exchanger with improved thermal efficiency.

Background art

In the field of heat exchangers and the like, for boilers to be used for heating sanitary water or water for central heating systems, the use is known of heat exchangers that are constituted, generally, by a metal container body inside which a combustion chamber is provided, which accommodates one or more coiled ducts inside which the fluids to be heated circulate.
Usually, the combustible mixture, which is typically constituted by air and gas, is sent forcibly into the burner under the thrust of a fan and, after the combustion that occurs in an appropriate chamber, as a result of the thrust from the fan, the burned gases strike the duct by way of the spaces provided in the coiled duct, thus achieving the desired exchange of heat.
Such known types of heat exchangers are not devoid of drawbacks, among which the fact that the burned gases cannot manage to strike the coiled duct completely and therefore the heat exchange has an effective efficiency that is not satisfactory.
This drawback is even more pronounced when a plurality of coiled ducts are used in the same heat exchanger. The presence of a plurality of coiled ducts intertwined in each other and/or intercalated with each other, leads to evident fluidodynamic limits of the burned gases which should strike the ducts and to evident heat exchange limits between the outer duct and the inner duct.
EP 1 750 070 A1 discloses a condensation gas-burning boiler with a heat exchanger through which combustion fumes and water flow, for producing hot water. A finned tube through which water flows is arranged inside a cylindrical casing, whereby the finned tube coils about the longitudinal axis of the casing to form a helix comprising a succession of adjacent turns each located adjacent the cylindrical lateral wall of the casing. A central deflecting disk is arranged to direct the fumes radially perpendicular to the longitudinal axis between successive turns of the helix, and the tube is provided with an oval-section wall with parallel fins extending tangentially and radially thereto, such that the fumes flow first from the boiler radially outward between gaps of the tangential and parallel fins of the helix turns towards the casing lateral wall, then secondly in a direction parallel to the longitudinal axis at the lateral wall, then thirdly radially inwardly from the lateral wall again between gaps of the tangential and parallel fins of the helix turns, whereby the successive gaps between the tangential and parallel fins of the helix turns define compulsory fume paths.
EP 0 385 700 discloses a boiler installation comprising an outer casing, central catalytic burner tube, and extending around the burner tube, a heat-exchange unit comprising twin coils each in the form of an inner pipe provided with interior and exterior helical formations and an exterior pipe surrounding the inner pipe. Mains cold water is fed through the inner pipe and gets heat exchanged to it by heated water fed through the exterior pipe which is heated by the hot gases produced by the burner tube. The exterior pipe is provided with helical ribs for increasing the surface area exposed externally thereof.

Disclosure of the invention

The aim of the present invention is to provide a heat exchanger with improved thermal efficiency that solves the drawbacks of the known art by increasing the thermal efficiency of the heat exchanger when compared to a conventional heat exchanger of the same dimensions.
Within this aim, an object of the present invention consists of providing a heat exchanger that is structurally simple, easy to make and assemble, and at low cost.
In accordance with the invention, there is provided a heat exchanger as defined in the appended claims.

Brief description of the drawings

Further characteristics and advantages of the invention will become better apparent from the description of a preferred, but not exclusive, embodiment of a heat exchanger with improved thermal efficiency, according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 shows a longitudinal sectional view of a heat exchanger with improved thermal efficiency, according to the invention;
Figure 2 is a side elevation view of the coiled duct of the heat exchanger shown in Figure 1;
Figure 3 is a plan view of the coiled duct of the heat exchanger shown in Figure 1;
Figure 4 is a partial plan view of a first variation of the coiled duct shown in Figure 3;
Figure 5 is a sectional view of the coiled duct shown in Figure 4, taken along the line V-V;
Figure 6 is a partial plan view of a second variation of the coiled duct shown in Figure 3;
Figure 7 is a sectional view of the coiled duct shown in Figure 4, taken along the line VII-VII;

Ways of carrying out the invention

With reference to the figures, the heat exchanger with improved thermal efficiency, generally indicated with the reference numeral 1, comprises a container body 2, cylindrical with a circular end face, inside which a coiled duct 3 is accommodated which externally delimits a chamber 4 for the combustion of a combustible mixture 5 for heating the fluid or fluids to be heated 6, which circulate in the coiled duct 3, with the burned gases 7 produced by the combustion of the combustible mixture 5 by means of a burner cylinder 16 with a perforated surface 17.
By way of fan means, not shown, the burned gases 7, produced by the combustion of the combustible mixture 5 and defining a flow of hot fluid, are sent forcibly onto the coiled duct 3 thus striking its outer surface in order to heat the fluid to be heated 6.
More precisely, the coiled duct 3 runs from an inlet mouth 8 to an outlet mouth 9, both outside the container body 2 and positioned, respectively, in the lower portion and in the upper portion of the container body 2.
According to the invention, a plurality of fins 30 is provided which are defined on the outer surface of the coiled duct 3 and which run substantially along the entire longitudinal length of the coiled duct 3 in order to guide the hot fluid 7 along the coiled duct 3 with consequent increasing of the heat exchange between the hot fluid 7 and the fluid to be heated 6.
Advantageously, the coiled duct 3 is substantially circular in transverse cross-section and the fins 30 run radially with respect to the circular transverse cross-section of the coiled duct 3, the whole being made in a single piece and without welds.
In order to be able to simultaneously or selectively heat a plurality of fluids 6 such as, for example, water intended for the sanitary plumbing system of a building or for the central heating system of the same building, the coiled duct 3 is divided internally, along a transverse cross-section, into a plurality of channels which are substantially parallel and independent of each other, each channel being crossed by a respective fluid to be heated 6.
More specifically, the coiled duct 3 is divided internally, along a transverse cross-section, into a main channel 31, which is coaxial to the coiled duct 3, and into a plurality of parallel secondary channels 32, which are mutually independent and radially external to the main channel 31.
In this way, it is possible to obtain five channels of which one, the main channel 31, is crossed by a first fluid to be heated 6 and four, the secondary channels 32, having a transverse cross-section that is substantially equal to one quarter of the transverse cross-section of the region outside the main channel 31, i.e. equal to one quarter of the circular rim, are crossed by a second fluid to be heated 6.
In a first possible variation of the coiled duct 3, the fins 30 can trace a helical path with respect to the axis of the coiled duct 3.
In a second possible variation of the coiled duct 3, the coiled duct 3 can be divided into four channels 33 each of which is defined by a circular sector of the circular transverse cross-section of the coiled duct 3, for example, equal to one quarter of the circular transverse cross-section of the coiled duct 3.
With a helicoid fin structure of the coiled duct 3, the coiled duct 3 can be arranged in proximity to, or even almost in direct contact with, substantially along all of its length, the outer walls 10 of the container body 2 and an element 11 for conveying the burned gases 7 in order to direct them to a discharge collection tank 20 and subsequently to a discharge tube 12 outside the container body 2.
At the upper face 13 of the container body 2, an air intake 14 is provided for forcibly injecting the combustible mixture 5, which can be for example a mixture of air and gas, by way of the above mentioned external fan means which consist, for example, in a fan outside the container body 2 which is not shown.
The combustible mixture 5 is then sent into an intake chamber 15 which is annular in shape, is also defined at the upper face 13, and is connected with the burner cylinder 16.
In more detail, the intake chamber 15 is connected directly with the burner cylinder 16 which is defined by a permeable surface 17 and is cylindrical with a circular end face where the flame burns.
The burner cylinder 16, besides being connected at one end with the intake chamber 15 in order to introduce the combustible mixture 5 into the combustion chamber 4, has the opposite end closed by a thermally insulating disk 18.
Advantageously, the conveyance element 11 can comprise a cylindrical hollow body with a circular end face, which is delimited in an upper region by the thermally insulating disk 18 and is connected, in proximity to the thermally insulating disk 18, with the discharge tube 12.
Conveniently, the conveyance element 11 is accommodated in the container body 2 on the opposite side with respect to the burner cylinder 16 and has a lower opening which faces the lower end face 19 of the container body 2 for the transit of the burned gases 7 from the combustion chamber 4 to the discharge collection tank 20.
Moreover, the discharge collection tank 20 is arranged at the lower end face 19 of the container body 2 and is adapted to collect the liquids 21 produced by the condensation of the burned gases 7 in contact with the coiled duct 3.
The discharge collection tank 20 is provided with an outward discharge connector 22 for the outflow of the liquids 21 from the container body 2 and with a discharge connector 23 for the outflow of the exhaust gases 7 by way of the outward discharge tube 12.
In a possible variation of the heat exchanger 1, the overall geometry of the heat exchanger 1 or some components can change, such as, for example, the discharge tube 12 which can be accommodated inside the container body 2. In any case, the coiled duct 3 remains unchanged.
Operation of the heat exchanger according to the present invention is as follows.
In particular, it is necessary to emphasise that the heat exchange between the fluid to be heated 6 and the burned gases 7, which in the drawings occurs in counter-current, is favoured by the presence of the fins 30.
The combustible mixture 5, under the thrust of the fan means, is sent into the intake chamber 15 through the air intake 14 to then descend in the direction of the axis, i.e. parallel to the axis 25 of the heat exchanger 1, in the burner cylinder 16.
The combustion occurs through the permeable surface 17 of the burner cylinder 16 and the burned gases 7 are directed into the combustion chamber 4.
Due to the thrust generated by the fan means, the burned gases 7 are pushed towards the coiled duct 3 and guided into the helicoid grooves defined between one fin 30 and the next, thus completely striking the outer surface of the coiled duct 3 and yielding heat to it.
The burned gases 7, again due to the thrust generated by the fan means, are pushed further downwards because they are compelled by their being guided into the helicoid grooves defined between one fin 30 and the next, and are then conveyed by the conveyance element 11 towards the lower end face 19 of the container body 2.
More specifically, the geometry of the coiled duct 3, by being contained between the walls of the container body 2 and of the conveyance element 11, forces the burned gases 7 to cross the helicoid grooves defined between the fins 30 thus considerably increasing the thermal efficiency.
As mentioned above, any condensation 21 is collected on the bottom of the container body 2 in the discharge collection tank 20 and is then discharged by way of the connector 22, and the burned gases 7 flow outside by way of the discharge connector 23 and the discharge tube 12.
In this manner, the calorific power possessed by the burned gases 7 is yielded to the fluids to be heated 6.
More precisely, this yield occurs thanks to the inner walls 34 or 35 of the coiled duct 3 which divide the channels 31, 32 and 33. In fact, the material from which the coiled duct 3 is made, for example aluminum or alloys thereof, through the inner walls 34 and 35 bring the heat yielded to the fins 30 right to the centre of the coiled duct 3.
Therefore, if one or more of the channels 31, 32 and 33 are not crossed by any fluid to be heated, then the heat exchange between the burned gases 7 and the fluid to be heated 6 which crosses at least one of the channels 31, 32 and 33 occurs in any case.
In practice it has been found that the heat exchanger with improved thermal efficiency, according to the present invention, fully achieves the intended aim and object in that the presence of the fins, specifically with helicoid twisting, on the outer surface of the coiled duct allows to guide the hot fluid, thus making it completely strike the outer surface of the coiled duct so as to optimise the heat exchange.
A further advantage of the heat exchanger with improved thermal efficiency, according to the present invention, consists in that it is structurally simple, easy to make and at low cost.
The heat exchanger with improved thermal efficiency, thus conceived, is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.
Moreover, all the details may be substituted by other, technically equivalent elements.
In practice the materials employed, provided they are compatible with the specific use, and the dimensions and the contingent shapes, may be any according to requirements and to the state of the art.
The disclosures in Italian Patent Application No. MI2009A001983 from which this application claims priority are incorporated herein by reference.
Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

A heat exchanger (1) with improved thermal efficiency, comprising a containment body (2) crossed by a forced flow of hot fluid (7) and at least one coiled duct (3) crossed internally by at least one fluid to be heated (6), said at least one coiled duct (3) being accommodated inside said containment body (2) and being struck by said hot fluid (7) in order to heat said at least one fluid to be heated (6), the heat exchanger (1) further comprising a plurality of fins (30), which are provided on the outer surface of said at least one coiled duct (3) and run substantially along the entire longitudinal length of said at least one coiled duct (3) in order to guide said hot fluid (7) along said at least one coiled duct (3) so as to increase the heat exchange between said at least one hot fluid (7) and said fluid to be heated (6), said fins (30) tracing a helical path with respect to the axis of said at least one coiled duct (3), characterized in that said at least one coiled duct (3) is arranged in proximity to, or even almost in direct contact with, substantially along all of its length, the outer walls (10) of said container body (2) and an element (11) for conveying the burned gases (7) in order to direct them to a discharge collection tank (20) and subsequently to a discharge tube (12) outside the container body (2), wherein the geometry of said at least one coiled duct (3), by being contained between the walls of the container body (2) and of the conveyance element (11) forces the burned gases (7) to cross the helicoid grooves defined between the fins (30) for increasing the thermal efficiency.
The heat exchanger (1) according to claim 1, characterized in that said at least one coiled duct (3) substantially has a circular transverse cross-section and in that said fins (30) run radially with respect to said circular transverse cross-section.
The heat exchanger (1) according to one or more of the preceding claims, characterized in that said at least one coiled duct (3) is divided internally, along a transverse cross-section, into a plurality of channels (33) which are substantially parallel and independent of each other, each channel being crossed by a respective fluid to be heated (6).
The heat exchanger according to claim 3, characterized in that each one of said channels (33) is formed by a circular sector of the circular transverse cross-section of said at least one coiled duct (3).
The heat exchanger (1) according to one or more of the preceding claims, characterized in that it comprises four of said channels (33) having a transverse cross-section that is substantially equal to one quarter of the circular transverse cross-section of said at least one coiled duct (3).
The heat exchanger (1) according to one or more of claims 1 and 2, characterized in that said at least one coiled duct (3) is divided internally, along a transverse cross-section, into a main channel (31), which is coaxial to said at least one coiled duct (3), and into a plurality of parallel secondary channels (32), which are mutually independent and radially external to said main channel (31), said main channel (31) and said secondary channels (32) being crossed respectively by a first fluid to be heated (6) and by a second fluid to be heated (6).
The heat exchanger (1) according to claim 6, characterized in that each one of said secondary channels (32) is formed by an annular sector of said at least one coiled duct (3).
The heat exchanger (1) according to one or more of claims 6 and 7, characterized in that it comprises four of said secondary channels (32) having a transverse cross-section that is substantially equal to one quarter of the transverse cross-section of the region outside said main channel (31) of said at least one coiled duct (3).