The present invention relates to a heat exchanger.
More specifically, the present invention relates to a heat exchanger for a gas boiler for producing hot water.
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.
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.
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.
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.
In addition to that, the process is not extremely accurate and small gaps cannot be formed by embossed tube sections.
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.
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.
Replacing bosses with teeth has the advantage of not requiring hydro-forming process and increasing the accuracy.
The present invention also relates to a method of producing a heat exchanger.
According to the present invention, there is provided a method of producing a heat exchanger, as claimed in the attached Claims.
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:
Number 1 in
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 A1, and from which project fingers 20 for clamping the helix 16.
With reference to
Tube 11 is preferably made of aluminium or aluminium-based alloy. With reference to
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.
In an alternative embodiment, not shown, the cross-section of teeth 25 is modified by reducing the height of the teeth 25 by machining.
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.
Once the rib 22 is machined, tube 11 is coiled about axis A1, so that axis A2 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 A1. The three spacers 18 are then fitted to helix 16, and arranged 120 degrees apart, so as to compress turns 17 along axis 1.
Then, teeth 25 of a given turn 17 comes into contact with the outer surface 21a of the adjacent turn 17 so as to form a gap between the two adjacent turns 17.
With reference, to
With reference to the
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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.
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.
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.
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.