Heat exchange applications employ at least one flowing medium, liquid or gaseous or a mixture of both flowing through a conduit. Efficiency of thermal transfer depends partly on relative velocity of the medium. One way of improving efficiency is to increase axial velocity of the medium. In order to increase axial velocity, the discharge rate of the medium must be increased, which is generally not desired. Another way of improving efficiency is to add a transversal velocity component to the medium. Due to such a transversal velocity component the flow velocity of the medium is increased near the walls of the conduit, whereby the heat transfer is improved. By optimizing the transversal velocity, considering the required heat transfer, the total discharge rate of the medium can be reduced considerably. Turbulator inserts are commonly used as passive elements in such heat exchange applications to add or increase a transversal velocity component of a medium, or in other words to curl or swirl the medium so as to benefit from aforementioned increase in efficiency.

Different embodiments of such turbulator inserts are known.

EP-B-0 181 711 discloses a turbulator insert for waste gases made from a single flat sheet, loosely inserted into a flue and maintained by the biasing effect of an end section. FR-A-2 320 520 discloses a turbulator insert made from a single flat sheet, maintained by an end section which is out of the straight and engages a cavity. US-B-6 530 422 discloses a heat exchanger tube, for petrochemical applications, with a turbulator directly cast with the tube, or at least part of it.

In applications where density of the flowing medium combined with high axial flow velocity impart considerable tractive forces onto the turbulator insert, secure fastening is required.

A common solution to securely fastening a turbulator insert within a conduit, such as a tube or a pipe, is to provide at least one opening in, or a cut through, the conduit at a convenient location. The turbulator insert can then be securely fastened inside the conduit by soldering or welding before restoring the conduit. Another solution is to produce at least one recess onto the conduit wall such as to deform the inner wall of the conduit. The turbulator insert can then engage this deformation by means of a retainer ring or similar support structure having little radial clearance from the inner conduit wall.

While such known embodiments present the advantage of increasing efficiency of thermal transfer and are suitable for insertion into heat exchanger conduits they also present a disadvantage related to their fixation method inside heat exchanger conduits. Known fastening or fixation methods for turbulators are either relatively straightforward but do not provide sufficient firmness or they provide sufficient firmness but require relatively elaborate measures.

;, Object of the invention The object of the present invention is to provide a simplified method for securely fastening a turbulator insert within a conduit. This object is achieved by a method as claimed in claim 1.

General description of the invention In order to overcome the abovementioned problems, the present invention proposes a method for fastening a turbulator insert within a conduit, in particular in a blast furnace cooling system. The method comprises the steps of providing a conduit; providing a turbulator insert suitable for insertion into the conduit; and inserting the turbulator insert into a region of the conduit to form a work assem- bly comprising the conduit and the turbulator insert. According to an important aspect of the invention, the method comprises the further step of fastening the

turbulator insert within the conduit by bending the work assembly at the region containing the turbulator insert.

The turbulator insert is simply inserted in the conduit and fastened therein by bending. Once the conduit is bent, the turbulator insert is trapped therein.

The bending of the conduit is an easy and effective method for fixing the turbulator insert in the conduit, in particular if compared to other methods, such as e. g. welding. More importantly, through the bending of both the turbulator insert and the conduit, the turbulator insert is securely fixed in the conduit. The turbulator insert is prevented from moving in the conduit, even if quite consider- able forces are exerted on the turbulator insert by the cooling medium. A particularly easy, fast and secure method for fixing a turbulator insert in a conduit is thereby provided by the above method.

Preferably an essentially straight portion of the turbulator insert is inserted into an essentially straight portion of the conduit, so as to allow for an easy insertion of the turbulator insert into the conduit.

The region of the conduit is advantageously predetermined to be bent. By inserting the turbulator insert in a region of the conduit that is e. g. to be trans- formed into a pipe elbow or knee bend, the turbulator insert can be fixed at the same time. A separate step for fixing the turbulator insert in the conduit is no longer necessary. By thereby saving a manufacturing step, manufacturing time and costs can be reduced.

Preferably, the turbulator insert comprises a turbulating part and an exten- sion part. By providing the turbulator insert with a turbulating part and an extension part, only the extension part of the turbulator needs to be suitable for bending in the conduit. The turbulating part, on the other hand, can be located in an unbent part of the conduit, thereby not compromising the turbulating effect of the turbulating insert on the cooling medium. Furthermore, depending on where, with respect to the bend, the turbulating effect is to be achieved, the turbulating part can be either upstream or downstream of the extension part in a flow direction of the cooling medium.

According to an embodiment of the invention, the step of providing a tur- bulator insert comprises the steps of: - providing a flat sheet having an upper surface and an opposite lower sur- face, a downstream edge and an opposite upstream edge, a first side edge and an opposite second side edge; - making at least one incision in the sheet; - transforming part of the sheet at the incision so as to form a vane on the upper surface of the sheet; and - transforming the sheet into an essentially cylindrical body by bringing the first side edge in proximity to the second side edge, wherein the vane is formed in the turbulating part of the turbulator insert.

This method provides a simple, fast and cheap way of producing turbulator inserts, wherein the vanes can be arranged so as to impart a swirling motion to the medium, without having an excessive flow restriction or resistance.

Preferably, the incision is such as to describe an open contour on the sheet, the open contour being complemented by a base line so as to define a vane area., The base line provides a connection between the vane area and the sheet.

The base line of the vane area can be directed towards the upstream edge of the sheet. The base line of the vane area can also be directed towards one of the side edges of the sheet. Alternatively, the base line of the vane can be arranged at an angle with respect to the direction of flow of the medium, thereby imparting a swirling motion to the medium.

Advantageously, the incision extends from the downstream edge into the flat sheet and in a direction generally towards the upstream edge. The incision is normally perpendicular to the downstream edge. Providing an incision from the downstream edge of the flat sheet is particularly easy and quick, thereby further simplyifing the production method It is however not excluded to provide the incision in other parts of the sheet.

The vane can have a first free corner and a second free corner, the first free corner being moved further away from its original position than the second free corner. Such a vane has a surface imparting, on its own, a swirling motion to the medium.

A plurality of vanes are preferably provided in the flat sheet so as to be offset in the direction of flow a medium in order to impart a swirling motion to the medium and to improve turbulation.

According to another embodiment of the invention, the turbulator insert is provided by connecting an extension part to a turbulating part. The turbulating part of the turbulator insert can e. g. be a turbulator readily available on the market. By complementing such a turbulator with an extension part, such a turbulator can also be fixed in the conduit according to the present invention.

The extension part is preferably essentially cylindrical. An essentially cy- lindrical extension part is particularly well suited for providing a good fixing means when being bent within a conduit. Such an essentially cylindrical extension part also minimises flow restriction.

The method can comprise bending the work assembly at a region contain- ing only the extension part of the turbulator insert. As long as the extension part of the turbulator insert is suitable for bending, it does not matter whether the turbulating part is.

The conduit and the turbulator insert can each be made of metal or plastic material. It will be understood that the material should be chosen depending on the intended use. The material can e. g. be steel, preferably stainless steel, or copper. Any other suitable material which has the properties of being resistant to thermal fatigue, corrosion resistant, machineable, thermally conductive and of sufficient strength can also be used.

After bending of the conduit at the region containing the turbulator insert, the conduit can be installed in a cooling stave for a blast furnace cooling system. The present invention therefore also relates to a cooling stave comprising a cooling conduit with a turbulator insert fastened therein in accordance with the method as described above.

Detailed description with respect to the figures The present invention will be more apparent from the following description of not limiting embodiments with reference to the attached drawings, wherein Fig. 1 : is a longitudinal sectional view of a turbulator insert according to a first embodiment suitable for fastening within a conduit according to the present invention; Fig. 2: is a longitudinal sectional view of the turbulator insert of Fig. 1 coaxially inserted into a conduit; Fig. 3: is a longitudinal sectional view of the turbulator insert of Fig. 1 fastened within the conduit by means of a bend according to the present invention; Fig. 4A: is a perspective view of a first step for manufacturing the turbulator insert of Fig. 1; Fig. 4B: is a perspective view of a second step for manufacturing the turbulator insert of Fig. 1 ; Fig. 4C: is a perspective view of a third step for manufacturing the turbulator insert of Fig. 1; Fig. 4D: is a perspective view of a first step for manufacturing an alternative turbulator insert; Fig. 4E: is a perspective view of a second step for manufacturing an alternative turbulator insert; Fig. 4F: is a perspective view of a third step for manufacturing an alternative turbulator insert; Fig. 4G: is a perspective view of a first step for manufacturing another alternative turbulator insert; Fig. 4H: is a perspective view of a second step for manufacturing another alternative turbulator insert; Fig. 41 : is a perspective view of a third step for manufacturing another alternative turbulator insert;

Fig. 5 : is a longitudinal sectional view of a cooling stave for blast furnace cooling system comprising the fastened turbulator insert of Fig. 1; Fig. 6: is a longitudinal sectional view of an alternative turbulator insert suitable for fastening within a conduit according to the present invention; Fig. 7: is a longitudinal sectional view of the turbulator insert of Fig. 6 coaxially inserted into a conduit; Fig. 8: is a longitudinal sectional view of the turbulator insert of Fig. 6 fastened within the conduit by means of a bend according to the present invention; Description of preferred embodiments Fig. 1 shows a turbulator insert 10 of essentially cylindrical shape suitable for insertion into a conduit according to a first embodiment of the invention. The turbulator insert 10 comprises a turbulating part 12, which comprises turbulating means, and an extension part 14 of cylindrical or tubular shape. The turbulating part 12 is on a downstream side 16 of the turbulator insert, with respect to flow direction of a heat exchange medium. The extension part 14 is on an upstream side 18 of the turbulator insert 10.

Fig. 2 shows the turbulator insert 10 coaxially inserted into a straight region of a conduit 20. The region of conduit 20 and the turbulator insert 10 inserted therein form a work assembly, which is subsequently bent into a pipe elbow or knee bend. The outer diameter of the turbulator insert 10 is chosen to differ from the inner diameter of the region of conduit 20 such as to provide only the minimally required amount of radial clearance necessary for insertion into the region of conduit 20.

Fig. 3 shows the turbulator insert 10 after transformation of the originally straight section of the work assembly into a pipe elbow or knee bend 20'. The transformation operation is carried out by bending the work assembly, e. g. using a conventional tube-bending device. The originally straight extension part 14 of the turbulator insert 10 has adopted the arcuate shape of the surrounding

region of conduit 20'through the transformation operation. The turbulating part 12 comprising the turbulating means is located at the preferred location of turbulating the medium. The turbulating part 12 has not undergone substantial deformation through the transformation.

Preferably a transformation method avoiding formation of buckles on the turbulator insert extension part 14 and loosening of the extension part 14 exterior from the conduit interior during the process is chosen. Such methods generally employ a granulate material, e. g. sand, inserted into the inner cavity of the work assembly and maintained under pressure. Such methods also generally employ characteristic heating and bending schemes known for bending double or composite pipes.

The turbulator insert 10 is, as a result of the described method, perma- nently and securely fastened or fixed within the conduit 20'without requiring further steps such as cutting or welding of the conduit 20 or 20'. It will be appreciated that, if the region of the conduit 20 containing the turbulator insert 10 is predetermined to be bent after insertion of the turbulator insert 10, extra steps required for securely fastening a turbulator insert are not necessary. This is the case for example if a knee bend in the conduit is required at the region of the extension part 14 of the turbulator insert 10.

Fig. 4A, Fig. 4B, Fig. 4C show the steps for manufacturing a turbulator insert 10 according to the first embodiment of the invention. In Fig. 4A, a flat, generally rectangular sheet 30 is provided. This sheet 30 has an upper surface 32, an opposite lower surface 34, a downstream edge 36 and an opposite upstream edge 38, a first side edge 40 and an opposite second side edge 42. The sheet 30 is made from steel, preferably stainless steel, or copper. Any other suitable material, such as e. g. plastic material, which has the properties of being resistant to thermal fatigue, corrosion resistant, machineable, thermally conductive and of sufficient strength can be used.

In Fig. 4B, the flat sheet 30 is provided with incisions 44,44', 44", e. g. by means of cutting or punching. These incisions 44,44', 44"are essentially

straight, perpendicular to and starting at the downstream edge 36 of the sheet 30.

The incisions 44,44', 44"are such as to describe open contours on the sheet 30, which are complemented by base lines 46,46', 46"46"'so as to form vane areas 48,48', 48", 48"'in the sheet 30. The vane areas 48,48', 48", 48"' are then transformed, generally by bending, into vanes 50,50', 50", 50"'. This can be achieved e. g. by bending upwards (with respect to upper surface 32 and lower surface 34), only one corner of the vane areas 48,48', 48", 48"'. The thickness of the sheet 30 is chosen such that the vanes 50,50', 50", 50"'resist operational stress of the turbulator insert without being deformed.

In Fig. 4C, the flat sheet 30 is shown with all of the vane areas 48,48', 48", 48"'transformed into vanes 50,50', 50", 50"'. The sheet 30 is then transformed, e. g. by bending or coiling, as shown by arrow 52, into a generally cylindrical body, wherein the first side edge 40 and the second side edge 42 meet. In order to maintain the shape of the turbulator insert, first side edge 40 can be welded to the second side edge 42.

Fig. 4D, Fig. 4E, Fig. 4F show the steps for manufacturing an alternative turbulator insert. It may be noted that the same reference numerals identify similar or identical parts with respect to Fig. 4A, Fig. 4B and Fig. 4C.

In Fig. 4E, the flat sheet 30 is provided with incisions 44,44', 44", e. g. by means of cutting or punching. In this alternative turbulator insert, the incisions 44,44', 44"are essentially U-shaped and describe open contours on the sheet 30, which are complemented by base lines 46,46', 26"so as to form vane areas 28,28', 28"in the sheet 30. The vane areas 48,48', 48"are then transformed, generally by bending, into vanes 50,50', 50". With respect to a direction of flow of the medium, the base lines 46,46', 46"are arranged at an angle. Furthermore, the incisions 44,44', 44"are offset in a direction of flow of the medium. These measures ensure that a swirl motion is imparted to the medium.

Fig. 4G, Fig. 4H, Fig. 41 show the steps for manufacturing a further alterna- tive turbulator insert. It may be noted that the same reference numerals identify similar or identical parts with respect to Fig. 4A, Fig. 4B and Fig. 4C.

In Fig. 4H, the flat sheet 30 is provided with incisions 44,44', 44", e. g. by means of cutting or punching. In this alternative turbulator insert, these incisions 44,44', 44"are essentially trapezium-shaped and describe open contours on the sheet 30, which are complemented by base lines 46,46', 46"so as to form vane areas 48,48', 48"in the sheet 30. The base lines 46,46', 46"are the longer base of the trapezium. The vane areas 48,48', 48"are then transformed, generally by bending, into vanes 50,50', 50". With respect to a direction of flow of the medium, the base lines 46,46', 46"are arranged at an angle. These measures ensure that a swirling motion is imparted to the medium.

Fig. 5 shows a cooling stave 60 of a blast furnace cooling system contain- ing a cooling plate 62 and a conduit 20"with a turbulator insert 10 therein. The cooling stave 60 has been manufactured while taking advantage of the method for fastening the turbulator insert 10 according to the present invention.

It will be understood that the fastening method is, although preferred, not limited to a turbulator insert 10 manufactured accoring to the method described above.

Fig. 6 shows an alternative turbulator insert 10'suitable for fastening ac- cording to the method of the present invention. The turbulator insert 10'com- prises a downstream turbulating part 12'comprising turbulating means and an upstream extension part 14'of tubular shape. The turbulating means comprises a helical shape attached to a support structure, which in turn is firmly attached to the upstream extension part 14'.

Fig. 7 shows the alternative turbulator insert 10'inserted into a straight re- gion of conduit 20. The turbulator insert 10'and the region of conduit containing the turbulator insert 10'form a work assembly, which is subsequently trans- formed.

Fig. 8 shows the alternative turbulator insert 10'fastened within the conduit 20'by transformation of the work assembly into a permanent bend according to the present invention.

It will be appreciated that the above method allows fastening of turbulator elements unsuitable for bending if connected to an extension part, which is suitable for bending.