Abstract:
A heat exchanger for a gas boiler for producing hot water is provided with a casing extending along a first axis and through which combustion fumes flow; a tube forming a plurality of turns along which water flows arranged inside the casing so as to form gaps between adjacent turns; a disk for guiding said fumes trough the gaps; and teeth integrally made with the tube for spacing adjacent turns apart and forming said gaps.

Description:
[0001]    The present invention relates to a heat exchanger. 
         [0002]    More specifically, the present invention relates to a heat exchanger for a gas boiler for producing hot water. 
       BACKGROUND OF THE INVENTION 
       [0003]    A gas boiler for producing hot water normally comprises a gas burner, and at least one heat exchanger through which combustion fumes and water flow. Some types of gas boilers, known as condensation boilers, condense the steam in the combustion fumes and transfer the latent heat in the fumes to the water. Condensation boilers are further divided into a first type, equipped with a first exchanger close to the burner, and a second exchanger for simply condensing the fumes; and a second type, equipped with only one heat exchanger which provides solely for thermal exchange along a first portion, and for both thermal exchange and fume condensation along a second portion. Condensation or dual-function exchangers of the above type normally comprise a casing extending along a first axis and through which combustion fumes flow; and a tube along which water flows, and which extends along a second axis and coils about the first axis to form a succession of turns. The combustion fumes flow over and between the turns to transfer heat to the water flowing along the tube. 
         [0004]    EP 0 678 186 discloses a heat exchanger for a gas boiler for producing hot water. The heat exchanger comprises a casing extending along a first axis and through which combustion fumes flow; a tube forming a plurality of tube sections along which water flows; said tube sections being arranged inside said casing so as to forms gaps between adjacent tube sections; guiding means for guiding said fumes trough said gaps; and bosses for spacing adjacent tube sections. 
         [0005]    Each tube section is provided with a cross section delimited by two parallel, opposite, flat walls. Bosses protrude from one of said flat walls for abutting a flat wall without bosses of an adjacent tube section and forming the above mentioned gaps between adjacent tube sections. 
         [0006]    Even though the above described heat exchanger is provided with integrally made spacers, a rather expensive and time-consuming hydro-forming process is needed to form bosses in tube sections. The hydro-forming process is performed by a press that squeezes the tube sections between dies in order to form the flat walls and, at the same time, forms the bosses by injecting inside the tube sections a fluid under high pressure. It follows that hydro-forming process lacks flexibility because a modification of the distributions pitch or the height of the bosses requires different dies. 
         [0007]    In addition to that, the process is not extremely accurate and small gaps cannot be formed by embossed tube sections. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an object of the present invention to provide a heat exchanger for a gas boiler for producing hot water, which overcomes the drawbacks of the prior art. 
         [0009]    According to the present invention, there is provided a heat exchanger for a gas boiler for producing hot water; characterised in that said spacing means are teeth integrally made with said tube. 
         [0010]    Replacing bosses with teeth has the advantage of not requiring hydro-forming process and increasing the accuracy. 
         [0011]    The present invention also relates to a method of producing a heat exchanger. 
         [0012]    According to the present invention, there is provided a method of producing a heat exchanger, as claimed in the attached Claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    A number of non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
           [0014]      FIG. 1  shows a schematic front view, with parts in section and parts removed for clarity, of a gas boiler equipped with a heat exchanger in accordance with the present invention; 
           [0015]      FIG. 2  shows a larger-scale section of a detail of the  FIG. 1  heat exchanger; 
           [0016]      FIG. 3  shows a view in perspective of a tube used to produce the  FIG. 1  exchanger; and 
           [0017]      FIGS. 4 and 5  shows variations of the  FIG. 3  tube. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Number  1  in  FIG. 1  indicates as a whole a gas boiler. Boiler  1  is a wall-mounted condensation boiler, i.e. in which the vapour in the combustion fumes is condensed, and comprises an outer structure  2  in which are housed a burner  3 ; a heat exchanger  4 ; a gas supply conduit  5 ; a pipe  6  for supplying an air-gas mixture to burner  3 ; a combustion gas exhaust pipe  7 ; a fan  8  connected to supply pipe  6 , and which performs the dual function of supplying the air-gas mixture to burner  3 , and expelling the combustion fumes; and a water circuit  9 . Burner  3  is connected to pipe  6 , is cylindrical in shape, and comprises a lateral wall with holes (not shown) for emitting the air-gas mixture and feeding the flame. Burner  3  is housed inside exchanger  4  which, in fact, also acts as a combustion chamber. Heat exchanger  4  is substantially cylindrical in shape, extends along a substantially horizontal axis A 1 , and comprises a casing  10 , through which the combustion products flow; a tube  11 , along which water flows; and a disk  12  for directing the fumes along a given path inside exchanger  4 . Casing  10  comprises a cylindrical lateral wall  13  about axis A 1 ; an annular wall  14  connected to lateral wall  13 , to supply pipe  6 , and to burner  3 ; and an annular wall  15  connected to lateral wall  13  and to exhaust pipe  7 . Burner  3  extends, coaxially with exchanger  4 , inside of exchanger  4  for a given length. Tube  11  coils about axis A 1  to form a helix  16  comprising a succession of adjacent turns  17 , each located close to lateral wall  13 , and has two opposite ends with known fittings (not shown) for connecting tube  11  to water circuit  9  outside exchanger  4 . Disk  12  is shaped so as to fit with the shape of the coiled tube  11 . 
         [0019]    Exchanger  4  comprises three spacers  18  for keeping turns  17  a given distance from lateral wall  13 . Each spacer  18  comprises a straight portion  19  parallel to axis A 1 , and from which project fingers  20  for clamping the helix  16 . 
         [0020]    With reference to  FIG. 2 , tube  11 , disk  12 , and spacers  18  define, inside casing  11 , a region B 1  housing burner  3 ; a region B 2  communicating directly with exhaust pipe  7 ; and three regions B 3 , each extending between two spacers  18 , turns  17 , and lateral wall  13 . Combustion of the air-gas mixture takes place in region B 1 ; and the resulting fumes, being prevented by disk  12  from flowing directly to region B 2 , flow between turns  17 , in a direction D 1  substantially perpendicular to axis A 1 , to regions B 3 , along which they flow in a direction D 2  substantially parallel to axis A 1 . On reaching regions B 3 , the fumes flow between turns  17  in direction D 3  opposite to D 1  to region B 2  and then along exhaust pipe  7 . 
         [0021]    Tube  11  is preferably made of aluminium or aluminium-based alloy. With reference to  FIG. 3 , tube  11  is an extruded tube, which extends along an axis A 2 , and comprises a wall  21  with an oval cross-section (major axis X and a minor axis Y) and a longitudinal rib  22  shown partially in dotted lines in  FIG. 3 . Wall  21  has an outer surface  21   a  and an inner surface  21   b  and a constant thickness. Rib  22  protrudes from the outer surface  21   a  at the intersection of outer surface  21   a  and minor axis Y and has two lateral faces  23  substantially parallel to minor axis Y and a distal face  24  substantially parallel to major axis X. In other words, rib  22  protrudes from the area of the cross section having the largest radius. 
         [0022]    After extrusion, rib  22  is partially machined in order to separate teeth  25 , which, in the best embodiment, are equally distributed along the length of the tube  11 . Each tooth  25  has a cross-section corresponding to the cross-section of rib  22 . 
         [0023]    In an alternative embodiment, not shown, the cross-section of teeth  25  is modified by reducing the height of the teeth  25  by machining. 
         [0024]    As an example of the sizes of the teeth  25  and of the tube  11 , tube  11  may have an axis Y 20 mm high and teeth 0,8 mm high per 1,1 mm wide. The ratio between the height of the tube  11  and the eight of the teeth  25  is roughly about 23. 
         [0025]    Once the rib  22  is machined, tube  11  is coiled about axis A 1 , so that axis A 2  of tube  14  also assumes a helical shape. Tube  11  is coiled with a constant pitch and radius, so that each turn  17  faces an adjacent turn  17 . This operation actually comprises calendering tube  11 , with the minor axis Y of the section of tube  11  maintained substantially parallel to axis A 1 . The three spacers  18  are then fitted to helix  16 , and arranged 120 degrees apart, so as to compress turns  17  along axis  1 . 
         [0026]    Then, teeth  25  of a given turn  17  comes into contact with the outer surface  21   a  of the adjacent turn  17  so as to form a gap between the two adjacent turns  17 . 
         [0027]    With reference, to  FIG. 2 , the fumes flow from region B 1  to regions B 3  in direction D 1  towards wall  13 , then flow in direction D 2  between turns  17  and wall  13 , flow between turns  17  in direction D 3  from regions B 3  to region B 2 , and are finally expelled by exhaust pipe  7 . The successive gaps therefore define compulsory fume paths. 
         [0028]    With reference to the  FIG. 4  variation, tube  11  is provided with four fins  26 ,  27 ,  28 , and  29  tangent to wall  21  and parallel to each other and to major axis X. Fins  26  and  27  are located on the same side of tube  11 , whereas fins  28  and  29  are located on the opposite side. Then, fin  26  is coplanar to fin  28  and fin  27  is coplanar to fin  29 . Fins  26 ,  27 ,  28  and  29  have a surface  26   a ,  27   a ,  28   a , and  29   a , which is tangent to outer surface  21   a  of wall  21  so that surfaces  26   a  and  28   a  form a single surface from which teeth  25  protrude. Surfaces  27   a  and  29   a  form a single surface without any protruding teeth  25 . Once tube  11  is coiled in a helix  16  and clamped by spacers  18 , teeth abut against the single surface formed by surfaces  27   a  and  29   a.    
         [0029]    With reference to the  FIG. 5  variation, tube  11  is provided with fins  26  and  27 , fins  28  and  29  being omitted. 
         [0030]    Many other variations in shape of tube  11  cross-section and arrangement of the fins are possible without departing from the essence of the present invention. 
         [0031]    Exchanger  4  as described above may also be used in condensation boilers comprising a main exchanger, and in which exchanger  4  provides solely for condensing the fumes, as opposed to acting as a combustion chamber as in the example described. 
         [0032]    Exchanger  4  as described above has numerous advantages, by combining straightforward construction as a result of teeth  25  formed directly by the tube  11  extrusion process and extremely flexible machining operation. 
         [0033]    Even though the embodiment disclosed in the detailed description refers to a tube  11  coiled in a helix  16  to form a plurality of turns, the invention is not limited to this embodiment and turns  17  should be intended more generally as adjacent tube sections.