TECHNICAL FIELD

The present invention relates to a heat exchanger, in particular, to a heat exchanger for use in condensing boilers.

In other words, the heat exchanger, which is the main object of the present invention, is of advantageous, but not exclusive application in the realization of condensing boilers, to which the following description will make explicit reference without loss of generality.

BACKGROUND ART

In fact, as known, in Europe the construction industry is evolving towards the design and construction of homes with ever-lower energy needs for heating.

Individual States, prompted by the European Community through the issuance of binding Guidelines, ensure compliance by issuing laws, decrees and implementing regulations that encourage the production of housing with less energy consumption, encouraging or even requiring the use of condensing boilers.

The market for condensing boilers is developing so rapidly, generating a range of solutions to increasingly lower costs.

Currently on the market are condensing boilers with heat exchangers made of different materials and different technologies :

1. exchangers made of stainless steel using smooth straight or finned tubes;

2. exchangers made of stainless steel using smooth wound-coil tubes ;

3. exchangers made of aluminum using smooth straight or finned tubes;

4. exchangers made of aluminum using the die casting technique;

5. exchangers made of aluminum by sand casting.

All these solutions, except the last, were made to obtain modular products; in order to obtain different power ranges with the same basic components.

These solutions comprise the use of individual tubes, often finned with the addition of welded fins, always contained within containers in turn composed of several parts; all combined with the use of complex manifolds, in turn composed of several parts.

DISCLOSURE OF INVENTION

The present invention belongs to the heat exchangers referred to in paragraph ( 4 ) .

In fact, the solution to the present invention is based on the technology of aluminum die casting, the less expensive sand casting technology, to obtain a heat exchanger with a drastic reduction in the number of needed components and therefore with a significant reduction of costs.

Therefore, according to the present invention a heat exchanger is provided as claimed in claim 1, and a condensing boiler comprising the aforementioned heat exchanger as defined in claim 10.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, certain preferred embodiments are now described, purely by way of non limitative examples and with reference to the attached drawings in which:

- Figure 1 illustrates a three-dimensional view of a first embodiment of a heat exchanger according to the present invention inserted in a condensing boiler;

- Figure 2 shows an exploded diagram of condensing boilers in Figure 1; - Figure 3 shows an enlarged detail of the heat exchanger illustrated in figures 1, 2 taken from a first point of observation;

- Figure 4 shows the detail seen in Figure 3 by a second point of observation;

- Figure 5 shows a front view of the detail shown in Figures

3, 4;

- Figure 6 shows a plan view of the detail shown in Figures 3,

4, 5;

- Figure 7 shows a three dimensional view of a section of certain details comprised in the condensing boiler shown in Figure 1;

- Figure 8 shows a plurality of elements included within the heat exchanger shown in Figure 1;

- Figure 9 shows a three dimensional view of a second embodiment of a heat exchanger according to the present invention inserted within a condensing boiler; and

- Figure 10 shows an exploded view of the condensing boiler shown in Figure 9.

In Figure 1, indicated as a whole with 100, is shown a condensing boiler comprising a heat exchanger 10, made according to the teaching of the present invention, on which is mounted a burner 50 of a traditional type.

In Figure 2 is shown an exploded view of the condensing boiler 100 of Figure 1.

The heat exchanger 10 comprises, in turn, three essential parts:

- an element of direct exchange, the so-called main body 11;

- a series of elements of indirect exchange, called inserts 12, and

- a container 13 which, as will be seen, contains within it both the main body 11, and the inserts 12; it should be noted, also, that the container 13 is provided with a cold water inlet fitting 13a and a hot water outlet fitting 13b (Figures 1, 2) .

In this first embodiment the container 13 has an axially symmetric shape that allows it to withstand the internal pressure of the water with minimal mechanical stress.

In the condensing boiler 100, as known, there are two circulating fluids that exchange heat:

- exhaust gases produced in the burner 50, and

- heating circuit water flowing inside the heat exchanger 10.

The main body 11 forms the element of heat exchange between exhaust gas and water. Said main body 11 preferably, but not necessarily, is obtained in a single piece by only one aluminum die casting process.

The exhaust gases are generated during the combustion process, which takes place in a known way in the burner 50 by way of a process of combustion of the air/fuel gas forced within the burner 50 itself by a fan (not shown) .

The container 13 contains, together with the main body 11, the water in the hydraulic system and collects the exhaust gases from the burner 50.

The exhaust gases, after having exchanged heat with the water, in a manner that will be seen more fully below, are discharged from an outlet 13c (Figures 1, 2) , and sent to a chimney (not shown) . Since, as mentioned above, the boiler 100 is of a condensation type, before discharge into the atmosphere, certain elements such as water vapor contained in the exhaust gases are condensed. The condensate produced, in turn, is removed from the heat exchanger 10 with well known systems (see below) . As shown particularly in Figures 3, 4, the main body 11 comprises a combustion chamber 14 substantially cylindrical and at least partially finned. From the bottom of the combustion chamber 14 a series of channels 15 downwardly branch off for the passage of exhaust gases ending at a terminal flange 16 parallel to the bottom of the combustion chamber 14. The flow of exhaust gases in the channels 15 takes place according to a first direction identified by an arrow (Fl) . In this case, the direction (Fl) is vertical.

As shown particularly in Figure 6, each channel 15 is defined by a pair of vertical baffles 17a, 17b, substantially parallel to each other, which in plan-view drawing and in the case of the embodiment shown in Figures 1-8, are "chords", parallel to each other, of a circumference (CIR) that encloses the main body 11. In the same way each pair of vertical baffles 17b, 17a also defines a duct 18 closed at the top and at the bottom by parallel walls, respectively, at the bottom of the combustion chamber 14 and the end flange 16.

Therefore, the exhaust gas channels 15 alternate with water ducts 18 to be heated. Note also that while the channels 15 of the exhaust gases do not communicate with each other but each with the output 13c of the container 13, the water ducts 18 are in hydraulic communication with each other (see below) .

More specifically, as shown in more detail in Figures 3, 4, in the main body 11 are obtained from a single piece, always with the same casting process, some horizontal baffles 19, parallel to the end flange 16 and to the bottom end of the combustion chamber 14. These horizontal baffles 19 will not, of course, interrupt the flow of exhaust gases according to the arrow (Fl). As will be better seen below, in the main body 11 are provided also two vertical baffles 20, which define, together with horizontal baffles 19 and the inner wall (SUPI) of the container 13 (see also Figures 6, 7) , areas 21a, 21b, 21c, 21d within which occurs the passage of water which is forced to flow through said areas 21a, 21b, 21c, 21d in directions perpendicular to the channels 15 crossed through by exhaust gases (see below). In other words, the water flows through the areas 21a, 21b, 21c, 21d in the directions (F2), substantially horizontal and perpendicular to the abovementioned direction (Fl) of the exhaust gases.

As shown particularly in Figures 3, 4 both the horizontal baffles 19 and the vertical baffles 20 are provided with seals 19a, respectively, 20a, which, when the main body 11 is mounted within the container 13, rest upon the inner surface (SUPI) of the container 13 thereof defining the regions in which there can be no passage of water between an area 21a, 21b, 21c, 21d and the other.

As shown particularly in Figures 3, 4, corresponding to each horizontal baffle 19, and upon an ideal substantially cylindrical outer surface (SUPE) (Figure 2) of the main body 11 recesses 22a, 22b (Figure 3), 22c (Figure 4) are obtained aimed at allowing the passage of water from the area 21a farthest from the combustion chamber 14 to the next 21b closest to the combustion chamber 14, to finally reach the area 21d that surrounds and embraces the combustion chamber 14 itself. Evidently, the seals 19a, 20a, serve to ensure that the flow of water between one area 21a, 21b, 21c, 21d and the other, takes place by exclusively using the recesses 22a, 22b, 22c.

In other words, it is as if the zones 21a, 21b, 21c, 21d constitute a sort of overlapping "planes" jointed together, two by two, by the recesses 22a, 22b, 22c, which, therefore, represent a sort of "stairs" between one "plane" and the other. This is to allow the flow of water from the cold water inlet fitting 13a towards the outlet fitting 13b (Figure 1, after undergoing the desired heating during the outflow from ducts 18 and into a cavity (INT) defined on one hand, by said inner surface (SUPI) of the container 13, and, on the other, from the recesses 22a, 22b, 22c and spaces (SP1) (SP2) , SP3) (SP ) , (SP5) (Figure 7) left empty from the channels 15, which, not always in use, rest upon the inner surface (SUPI) of the container 13 (Figure 7).

As again shown in Figures 3, 4 water preferably flows in directions (F2) substantially perpendicular to the direction

(Fl) of exhaust gas flow, with paths in parallel or in series within each area 21a, 21b, 21c, 21d, as needed.

In fact, the ducts 18 as a whole provides an essentially horizontal labyrinth path for the water, except for the vertical passages consisting in transit recesses 22a, 22b, 22c from one area 21a, 21b, 21c, 21d to the other.

In Figure 3 can be seen a solution having the area 21a divided into four ducts 18 flowed by water in parallel in one direction, followed by three ducts 18 flowed in parallel in the opposite direction.

The area 21b, immediately above the area 21a is divided into ducts 18 initially flowed in parallel and then in series. Finally, the area 21c, below the combustion chamber 14, comprises a plurality of ducts 18 flowed by water only in series .

This division of the various areas 21a, 21b, 21c, 21d has been made with the purpose of having higher speed of the water, and therefore lower heat contributions per unit mass of water in transit, m order to minimize the risk of boiling the water itself. In fact, especially in areas close to the combustion chamber 14, due to the large amount of heat that is transferred there from the exhaust gases, there is the danger that the water could come to a boil.

To avoid this problem the solution adopted is particularly shown in Figures 5, 7.

In fact, in at least some of the ducts 18 flowed in parallel by the water and at a plane perpendicular to the direction of water flow, partition elements 30 are provided with an adequate number of calibrated circular holes 31 (or calibrated slots) whose dimensions are determined so as to obtain water flows evenly distributed among the single ducts 18 affected by the flow of water in the same direction.

The partition element 30 with relative calibrated circular holes 31 can be obtained as a single piece with the main body 11 during the same die casting operation.

In fact, in the absence of said perforated partition elements 30 there would be preferential flows in some ducts 18 rather than in others being part of the same "block" of channels in parallel, resulting in a deterioration of the overall heat exchange between exhaust gas and water in transit.

For example, if one refers to the first four ducts 18 (Figure 3, bottom left) of the area 21a, in the absence of these perforated partition elements 30 it would result that the two ducts 18 that are closer to the cold water inlet fitting 13a would be extremely favored over the other two remaining ducts 18 which are more distant from said fitting 13a, reaching even to trigger a re-circulation of water between the more outer duct 18 and the adjoining one, with the result of penalizing the exchange of heat towards these last channels 18 maintained at a higher than average temperature.

Consequently, the usefulness/need to ensure, as far as possible, uniformity of the speed of water flow in various ducts 18 through the use of the abovementioned perforated partition elements 30.

As shown in Figures 2, 3, at the level of the combustion chamber 14 there are two through holes 35, 36 for the passage of the spark plug 37 and for a detecting device 38, and a window 39 to display the combustion chamber 14.

The main body 11 is held in position with respect to the container 13 by an appropriate number of screws (not shown) that fix it to the latter.

In this way it is possible to dismount the burner 50 from the heat exchanger 10 having the certainty that the heat exchanger 10 itself still remains assembled. Preferably, but not necessarily, the inner surfaces of channels 15 flowed by the exhaust gases are corrugated for increasing the exchange surface at the side of the exhaust gases for a given size of each single channel 15. In addition, in channels 15 flowed by the exhaust gases is placed a plurality of pairs of inserts 12 having corrugated walls in turn to form a gap, measured in the direction of flow of exhaust gases, of uniform thickness, and small enough to require each smaller portion of the exhaust gases to touch the walls of the channels 15 themselves and release heat by convection .

Each insert 12 presents dimensions and shapes so as to enable a proper coupling with the respective channel 15. Moreover, as shown in Figure 2, a first insert 12 of each pair is inserted in the respective channel 15 from above, while an identical second insert 12, which completes the pair, is inserted in the same channel 15 from below.

Each insert 12 presents upon its surface an adequate number of protruding fins 41 (Figure 8), compared to the corrugated surface of the adjacent channel 15 in which it is inserted in order to come into contact with the corresponding corrugated area of the channel 15 and transmit by conduction the heat collected from the exhaust gases.

By way of the use of inserts 12 a significant improvement is obtained in the exhaust gas/water heat exchange acting upon two levels:

- on one hand, the amount of heat is increased transmitted by conduction between the inserts 12, which heat up, and the surfaces of the ducts 18 on which the projecting wings 41 are lying;

- on the other, heat transfer parameters are also improved by convection between the exhaust gases themselves in transit, that due to the shape of the fins 41 themselves, are pushed towards the walls of the ducts 18.

Now described is the path of the fluids involved in the heat exchange .

The cold water enters the boiler 100 through the inlet fitting 13a housed on the container 13 in the most distant area 21a from the combustion chamber 1, the water then flows in parallel a first part of the ducts 18 of said area 21a, passing onto the next block of ducts 18 in the same area through a space (of the type (SP) ) cleared by the end of the channel 15 of the exhaust gas and the inner surface (SUPI) of the container 13; flows in parallel along these latter ducts 18 of the same area 21a in the opposite direction to the previous; the water then passes through the following area 21b through the recess 22a (Figure 3) housed in the horizontal baffles 19 that separates the two adjacent areas 21a, 21b; once all paths of this area 21b are flowed through, the water rises to the next area 21c, positioned at the bottom of the combustion chamber 13, by way of the recess 22c (Figure 4) correspondingly obtained in the first duct 18 of said area 21c affected by the flow of water.

The water flows, therefore, in all the ducts 18 of the area 22c positioned in series with each other, and finally back, through the appropriate recess 22b (Figure 3), in the annular area 21d placed outside of the combustion chamber 14 until the hot water outlet fitting 13b is reached.

As shown particularly in Figure 7, a mixture of air/gas fuel enters the combustion chamber 14 exiting from the burner 50, feeds the combustion process previously activated and is transformed into combustion products.

The exhaust gases, in turn, give off heat to the finned walls of the combustion chamber 14 and are forwarded into the gaps existing between the corrugated walls of the channels 15 of the heat exchanger 10 and the corresponding inserts 12 further exchanging heat to reach the dew-point temperature equivalent to the atmospheric pressure and then condensing the vapor fraction contained therein; finally the exhaust gases exit from the gaps of the channels 15 collecting in a compartment 42 (Figure 7) below the main body 11 to be sent, finally, outside the boiler 100 by way of the outlet 13c, while the condensation that has formed in the compartment 42 is evacuated through an appropriate duct (not shown) .

According to a further embodiment of the present invention illustrated in Figures 9, 10 it is provided, however, a boiler 100* with a container 13* essentially of rectangular shaped perimeter (PR), with the walls adequately reinforced and stiffened with an adequate number of fixing points with screws (not shown) so as to withstand the internal pressure of the water (in this case, the channels 15* and the ducts 18* are parallel to the underside of the perimeter (PR). Therefore, the channels 15* and the ducts 18* can be in a way considered "chords" of the perimeter (PR) of the container 13*.

Incidentally, the present invention can be applied to main bodies having perimeters (PR) of any shape (circular, elliptical, square, rectangular, etc.).

As shown in Figure 10, the inner surface of the container 13* is free of recesses and sealing gaskets, needed to contain the water and to divert the flow of water inside, are assembled on the main body 11* substantially in the same way seen for the first embodiment illustrated in Figures 1-8.

The main advantages of the boiler, and of the respective heat exchanger, objects of the present invention, are as follows:

- ease of assembly of the condensing boiler consisting of only three major devices, namely a burner, a boiler main body and a container;

ease of implementation of the main body of the heat exchanger by way of simple aluminum die casting;

- ease of implementation of the container by way of simple aluminum die casting or in a plastic material;

- possibility to obtain, in a single piece, the partition elements with calibrated holes during the die casting process relative to the main body;

- possibility to delete unwanted recirculation of water within the heat exchanger, while minimizing the risk of boiling water in the heat exchanger itself;

- possibility to obtain an optimal exhaust gas/ water heat exchange by adopting a substantially vertical flow, from top to bottom, of exhaust gas combined with a substantially horizontal flow of water to be heated; and possibility to obtain an optimal heat exchange by adopting inserts in the exhaust gas passage channels, inserts that present upon their surfaces an adequate number of protruding fins.