Technical Field The present invention relates to a tube for conveying exhaust gases in heat exchange devices, particularly boilers for generating hot water or steam. Background Art

Conventional heat exchange devices are known that have tubes designed to convey exhaust gases generated by combustion in adapted furnaces inserted within a vessel that contains the fluid to be heated.

Many types of conventional tubes are provided internally with variously shaped fms in contact with the wall of the tube, and a high transfer of heat from the exhaust gases to the fluid to be heated is thus provided because the fins collect heat from the exhaust gases in the central region, where they are hottest, and transfer it to the wall of the tubes, which is struck by the fluid to be heated at the outer surface.

Heat exchange devices are known, such as for example certain types of boilers for generating hot water, or boilers for generating steam, in which the exhaust gas conveyance tubes operate in high temperature conditions, with the consequent onset of problems linked to the strength of the materials. Disclosure of the Invention

The aim of the present invention is to devise an exhaust gas conveyance tube that can ensure, in addition to high-level heat exchange characteristics, also absolute assurance of operating in safe conditions.

This aim is achieved by a tube for conveying exhaust gases in a heat exchange device, particularly a boiler for generating steam, according to the invention, which comprises internally fms in contact with the wall of said tube, characterized in that the fms arranged proximate to the exhaust gas inlet end are made of steel, while the fins arranged proximate to the exhaust gas exit end are made of aluminum. Brief Description of the Drawings

Further characteristics and advantages of the tube according to the invention will become better apparent from the description of two preferred but not exclusive embodiments thereof, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a sectional view of the tube, taken along a longitudinal plane; Figures 2 and 3 are respectively sectional views taken along the line

II-II and along the line III-III of Figure 1;

Figure 4 is a sectional view, taken along a longitudinal plane, of a tube according to another embodiment. Ways of carrying out the Invention With reference to the Figures 1 to 3, the reference numeral 1 generally designates a tube according to the invention, designed to be crossed by the exhaust gases in the direction of the arrow of Figure 1.

A turbulator 2 is provided, in a known manner, at the exhaust gas inlet end, and inside the tube fins are provided in contact with the wall of said tube, which according to an important feature of the invention are divided into two groups.

The fins, generally designated by the reference numeral 3, of the first group, located proximate to the exhaust gas inlet end, are made of steel, while the fins of the second group, generally designated by the reference numeral 4, located proximate to the exhaust gas exit end, are made of aluminum, and between the two groups of fins there is an interruption portion determined by the presence of a spacer 5.

In the embodiment of Figure 4 there are again two groups of fins 3 and 4, respectively made of steel and aluminum as in the first described embodiment, and the two groups of fins are arranged without discontinuity. The presence of the steel fins proximate to the exhaust gas inlet end of the tube, where the exhaust gases have a temperature that is too high to allow the use of aluminum fins, ensures the necessary safety while maintaining high heat exchange efficiency, albeit not at an optimum level; this level is reached by means of the aluminum fins inserted proximate to the exhaust gas exit end, where the temperature of the exhaust gases is reduced enough to allow installation of such fins without concerns.

Thus, a good compromise situation has been provided between the need to ensure high heat exchange efficiency to the tube according to the invention and the primary need to operate in conditions of absolute safety.

The tube according to the invention is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; all the details may further be replaced with other technically equivalent elements. The disclosures in Italian Patent Application No. MI2009A000404 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.