Technical field of the invention The present invention relates to a gas cooling assembly, intended in particular but not exclusively to be incorporated in a tube bundle heat exchanger or in a process air cooler, what is known as a "gas cooler". The invention is suitable for application, for example, in any one of the following technical fields: petrochemical, energy recovery, naval, railway, aeronautical, energy production.

Prior art

A gas cooling assembly of a conventional type comprises a plurality or a bundle of rectilinear metal tubes, which extend parallel to a given direction and are spaced from one another in a given volume. The tubes convey a cooling liquid (or "service fluid") within them and are supported by a pack of parallel metal sheets, spaced from one another in transverse planes perpendicular to the direction of the tubes. Each sheet has a flat portion extending transversely or perpendicularly to the direction of the tubes and forms a plurality of through holes, one for each tube. The holes each have an annular cylindrical collar which tightly accommodates a short length of the outer surface of one of the tubes.

An intersecting flow is provided between the service cooling fluid, which flows inside the tubes, and a stream of the process fluid, for example air or nitrogen, which is made to pass around the tubes and between the pairs of parallel metal sheets. The process fluid is thereby cooled by convection. The metal sheets are provided with slits for the purpose of increasing the turbulence of the flow of the aeriform fluid (gas) and increasing the heat exchange.

The object of the collars provided by the holes is to increase the surface area for heat exchange, by conduction, between the sheet plates and the tubes.

In the methods for use which have been common to date, use is made of metal tubes that are dimensioned in such a way as to be inserted with a certain radial play through the axially aligned holes in the sheets. For the purpose of improving the contact between the tubes and the sheets, the tubes are made to expand plastically, with an ogive-shaped forming tool being made to pass forcedly inside said tubes and radially expanding the tubes so as to bring the outer surfaces thereof into contact with the cavities of the collars. This method involves high operating costs and does not ensure that the contact between the tubes and the collars is continuous along the entire inner circumference of the collars. The radial expansion of the metal tubes is difficult to precisely control and it is difficult to confirm when expansion has occurred.

Summary of the invention

It is an object of the present invention to ensure continuous contact between the collars of the sheets and the tubular ducts adapted to convey the cooling fluid within them, while at the same time dealing with the problem of reducing the production costs.

This and other objects and advantages, which will be explained in more detail hereinbelow, are achieved according to the invention by a gas cooling assembly as defined in claim 1. Preferred embodiments of the invention are indicated in the dependent claims. In summary, the invention proposes a gas cooling assembly which comprises a pack of metal sheets and a bundle of tubular ducts. Each tubular duct is formed by the mechanical coupling of a plurality of modular annular elements of plastic material. Each annular element is locked on a cylindrical collar provided by one of the holes in one of the metal sheets and provides a tubular projection, by means of which the annular element is mechanically connected to an adjacent annular element.

Brief description of the drawings

A number of preferred but not limiting embodiments of a gas cooling assembly according to the present invention will now be described; reference is made to the appended drawings, in which:

Figure 1 is a schematic and partial perspective view of a gas cooling assembly; Figure 2 is a schematic view, in axial cross section, of a tubular duct with metal sheets which are part of a gas cooling assembly according to one embodiment of the present invention;

Figure 3 is a partial view, on an enlarged scale, of a detail of Figure 2;

Figure 4 is a schematic view, in axial cross section, of an annular element suitable for forming a length of the tubular duct shown in Figure 2 and of a sheet portion associated with this element;

Figure 5 is a schematic view, in axial cross section, of an annular element according to another embodiment of the present invention, with an associated sheet portion;

Figure 6 is a schematic view, in axial cross section, of a tubular duct formed by elements of the type shown in Figure 5;

Figures 7 to 1 1 are views, similar to Figure 2, of further embodiments of tubular ducts according to the present invention; and

Figure 12 is a schematic perspective view of part of a sheet according to a further embodiment of the invention.

For explanatory purposes, in some drawings not all proportions have been respected.

Detailed description of the invention

Referring first of all to Figure 1, a gas cooling assembly, denoted as a whole by 10, comprises a bundle of rectilinear tubular ducts 20 which are accommodated and supported by a pack of metal sheets or plates of metal sheet 30. According to a known arrangement, the ducts 20 extend parallel to a given direction x and are spaced from one another in a given volume to convey a cooling liquid, for example water, within them. The metal sheets 30 are spaced in planes (yz) transverse or perpendicular to the direction x, referred to here as the axial direction. Throughout the present description and in the claims, the terms and the expressions which indicate positions and orientations, such as "axial", "longitudinal", "radial" or "transverse", refer to the axis x.

The general arrangement of an assembly shown schematically in Figure 1 is to be considered as known on the whole. As a consequence, in the following text of the present description a detailed description will be given only of the elements of specific significance and interest for the purposes of carrying out the present invention. For the construction of parts and elements which are not shown in detail, reference can therefore be made to a cooling assembly of the known type. In particular, the metal sheets 30 can be sheets of a conventional type.

Each metal sheet has a plurality of through holes 31, one for each duct 20. In the example shown in Figure 1 , the holes 31 are circular. In other embodiments, the holes can have a non-circular shape (as shown in Figure 12, a more detailed description of which is provided hereinbelow), for example an oval or elliptical or elongated shape. Around the holes 31, the metal sheets form flat plate portions 32, these extending transversely with respect to the axial or longitudinal direction x. In a manner known per se, each hole 31 has an axially extending annular collar 33, which can engage with circumferential continuity a length of an outer surface of one of the ducts 10.

Conveniently, the metal sheets 30 form a multitude of through slits 34 distributed between the holes 31 for the purpose of increasing the turbulence of the flow of an aeriform process fluid (for example air or nitrogen) which is made to flow around the ducts 20, in accordance with an intersecting flow scheme. The service cooling fluid, which flows inside the ducts 20, produces convective cooling of the process fluid which is made to pass around the ducts 20 and between the parallel metal sheets, in a flow direction perpendicular to the direction x (for example in the direction z). The slits 34, or other apertures of differing shape, can be used to increase the heat exchange between the two fluids, but are not essential for the implementation of the present invention.

Each tubular duct 20 comprises a plurality of modular annular elements 21 (Figures 2 and 3) of plastic material, these being aligned consecutively in an axial direction and being mechanically coupled to one another in sequence. In a preferred embodiment, shown in Figures 2 and 3, the annular elements 21 are mechanically locked to the collars of the metal sheets 30. In this embodiment, each annular element 21 forms a peripheral annular pocket 23 and a tubular connecting projection 24, which is radially on the inside with respect to the annular pocket 23 and is axially offset with respect thereto. The annular pocket 23 has a first abutment surface 23a, which is located at the bottom of the pocket and faces in a first axial direction, towards the right with reference to the example shown in Figure 3.

The annular pocket 23 is delimited by a radially outermost and axially extended edge 25, by an axially extended annular length 26 and by a radial or transverse wall 28, which connects the outer edge 25 to the annular length 26. The wall 28 has a second abutment surface 28a, which faces in a second axial direction, towards the left in the example shown in Figure 3, opposite to the first axial direction in which the first abutment surface 23a (at the bottom of the pocket 23) faces. The annular length 26 has a radially inner seat 26a which is substantially cylindrical (Figures 2, 3 and 4) or slightly frustoconical (Figures 5 and 6).

The tubular connecting projection 24 has a cylindrical radially inner cavity 24a, which can make up a length of the duct for conveying the cooling fluid, and a radially outer surface 24b, which is substantially cylindrical (Figures 2, 3 and 4) or preferably slightly frustoconical and tapered towards the second axial direction (Figures 5 and 6). For the purpose of improving the seal, the radially outer surface 24b of each annular element 21 is fitted with radial interference in the seat 26a of the annular length 26 of a consecutively adjacent annular element 21.

In the exemplary embodiment shown in Figures 2 and 3, it is preferable that each annular element has a radially inner annular step 27a, which connects the inner cavity 24a with the seat 26a, and a radially outer annular step 27b, which joins the radially outer surface 24b of the tubular connecting projection 24 with a radially outer surface 26b of the annular length 26. Optionally, in the portion next to the abutment wall 28a, the annular length 26 may have an opening 26c that can facilitate the insertion and the reciprocal positioning between the seat 26a and the tubular connecting projection 24 of the adjacent annular element 21. The surface 26b is substantially cylindrical or frustoconical. Each collar 33 may advantageously be mounted with radial interference on the radially outer surface 26b of the annular length 26, thereby establishing continuous 360° circumferential contact between the metal sheet and the tubular duct 20.

In one embodiment, the radially outer surface 24b of the tubular projection 24 has an axial length equal to the axial length of the radially outer surface 26b of the annular length 26. In the assembled state, the free end of the connecting portion 24 abuts against the inner annular step 27a, while a (radially inner) part of the abutment surface 28a of the wall 28 abuts against the radially outer annular step 27b. As a result of this configuration, there are no empty spaces or interruptions between the inner cavities 24a of the consecutive annular elements 21, whereby the inner cavities 24a together form a continuous and smooth duct.

According to a preferred embodiment, the annular elements 21 are firstly coupled to each metal sheet 30 on the collars 33. What is thereby obtained is a series of units 22 each comprising a sheet provided with a plurality of annular elements 21. One of these units 22 is shown in Figure 4.

Figure 5 shows a further embodiment of the annular elements 21, in which both the annular length 26 and the tubular connecting projection 24 have tapered profiles in place of the cylindrical or ribbed profiles of the element 21 as shown in Figure 4.

Each annular element 21 is mechanically coupled so as to make the annular collar penetrate into the annular pocket 23. The free end 33a of the collar can abut against the bottom 23a of the pocket 23, while the collar 33 continuously engages the annular length 26 of the annular element 22.

Advantageously, the collar 33 and the annular length 26 are manufactured in such a way that the collar is forcedly coupled with radial interference against the radially outer surface 26b of the annular length 26. For this purpose, the radially outer surface 26b and/or the collar 33 can be extended along cylindrical or conical axial surfaces. Then, a number of units 22 such as those shown in Figures 4 and 5 can be consecutively coupled to one another, by inserting the connecting portions 24 into the seats 26a of the annular lengths of consecutively adjacent annular elements. This realises a plurality of continuous ducts, which are formed by the juxtaposition of the inner cavities 24a of consecutive annular elements 21 (Figures 2 and 6).

According to the embodiment shown in Figures 2 and 3, in the assembled state the abutment surfaces 28a of the walls 28 abut against the flat portions 32 of the sheets 30, while the free ends of the collars 33 abut against the bottom surfaces 23a of the pockets 23. In this arrangement, relative movements between the duct 20 and the sheets 30 are prevented.

As plastic materials suitable for the annular elements 21, mention can be made both of a generic polymer and of PBT (polybutylene terephthalate), for example Pocan B1505 and Pibiter TQ 8.5. The indication of these materials is not to be considered as limiting.

The walls of the annular elements 21 can have a thickness which varies depending on the requirements. Promising experimental results have been obtained with thicknesses of the order of approximately 1 mm for the annular length 26 and the connecting portion 24.

In an alternative embodiment as shown in Figure 7, the seat 26a of the annular length 26 and the radially outer surface 24b of the tubular connecting projection 24 are not positioned in contact along the entire lengths thereof, thereby creating a narrow annular gap between two adjacent elements 21.

According to an alternative embodiment as shown in Figure 8, the outer edge 25 can be axially offset with respect to the annular length 26, in such a way as to leave the radially outer surface 26b of the annular length 26 uncovered. In this variant, the collar 33 is forcedly mounted on the surface 26b of an annular element 21 , and the free end of the collar remains held in a pocket 23 located by the outer edge 25 of the adjacent annular element 21. Optimum results in terms of sealing against the fluid and in terms of speed of assembly have been obtained with modular annular elements 21 locked mechanically to the collars of the sheets 30, as shown in Figures 2, 3 and 6. Figures 9, 10 and 1 1 show further alternative embodiments, in which circumferentially continuous contact between the collars 33 and the corresponding tubular duct 20 is made by moulding the annular elements 21 on the collars 33 of the metal sheets 30. In Figure 9, holes 35 have been formed in the sheets 30 in the proximity of the annular collar 33, on which the annular length 26 of the annular element 21 is moulded. According to the embodiment shown in Figure 10, the collar 33 is integrated entirely in the annular length 26, together with a part of the flat plate portion 32 around the collar 33. In the embodiment shown in Figure 1 1 , the connecting portions 24 have elevations 24c, for example annular elevations or bumps, which can engage with a snap fit into corresponding annular depressions or rounded recesses 24d formed in the outer surface 26b of the annular length 26. Elevations and depressions of this type can also be provided in all the other embodiments of the annular element 21.

Around the holes 31, the metal sheets form flat plate portions 32, these extending transversely with respect to the axial or longitudinal direction x. In a manner known per se, each hole 31 has an axially extending annular collar 33, which can engage with circumferential continuity a length of an outer surface of one of the ducts 20.

Figure 12 shows a flat plate portion 32 included in a metal sheet 30, according to a further embodiment of the through holes 31. In contrast to the embodiments shown in the preceding figures, the contour of the holes 31 and of the corresponding protruding collars 33 is not circular, but rather has a substantially elliptical shape. This shape makes it possible, with the same area of the hole 31, to maximise the surface area for heat exchange between the flow of the gaseous stream and the flow of the service fluid, in particular along a direction perpendicular to the greater axis of the elliptical contour of the hole 31.

The arrangement shown in Figure 12 does not have to be considered to be preclusive with respect to different shapes of the hole 31 which contribute to maximising the surface area for heat exchange between the flow of the gaseous stream and the flow of the service fluid along a preferred direction.

It will be understood that a gas cooling assembly can be assembled without the use of the machinery which is commonly used for expanding the metal tubes. The coupling between collars and annular elements, which are manufactured with a certified degree of dimensional precision, can ensure that the desired coupling precision is achieved. As a consequence, there are no discontinuities along the interface between the inner surface of the collar and the outer surface of the duct.

The invention makes it possible to design gas coolers having tubular ducts with non- circular cross sections. It is known that the conventional technology which provides for the expansion of metal tubes is associated with the formation of ducts having a circular cross section. Since the present invention does away with the conventional step of radial expansion of metal tubes, it is possible to provide metal sheets having non-circular holes, in particular holes with an oval or elliptical or elongated shape, as shown for example in Figure 9. A duct having a cross section which is elongated in a direction matching that of the flow of the process fluid makes it possible to increase the efficiency of the heat exchanger.

Although a duct made of polymer material has a thermal, conductivity which is smaller than that of a metal tube, the heat exchange produced by the surfaces of the sheets which are hit by the gaseous flow is much greater with respect to the heat exchange which takes place at the interface between the tubes and the metal sheets. Therefore, the lesser heat conduction owing to the ducts made of plastic can be compensated for by slightly increasing the number of metal sheets or by modifying the shape of the cross section of the tubes/rings, this no longer necessarily being circular. In this way, the overall thermal efficiency of an exchanger produced with tubular ducts formed by joining modular annular elements of plastic material according to the present invention will in theory be comparable with that of a conventional exchanger with metal tubes. In practice, the continuity of contact between collars and tubular ducts will ensure a more efficient heat exchange. Various aspects and Embodiments of the gas cooling assembly have been described. It will be understood that each embodiment can be combined with any other embodiment. Moreover, the invention is not limited to the embodiments described, but instead can be varied within the scope defined by the appended claims.