GB2096757A - Double-wall heat exchanger - Google Patents

Abstract

In a double-wall or coaxial heat exchanger made of high grade steel and consisting of an inner pipe (14) and an outer pipe (16), first connection sockets (20) are soldered into the ends of the inner pipe and the end segments (35) of the outer pipe are tapered in a direction towards the pipe end down to the diameter of the inner pipe by means of calender cuts (30) to which the ends (26) of the outer pipe are soldered. Second connection sockets (28) discharge radially into the annular space (18) between the inner pipe and the outer pipe. In the area of the soldered connection, the inner pipe, the outer pipe and the first connecting sockets are preferably cylindrical segments. The inner pipe may be tightly encompassed by a jacket pipe (Figs. 3 and 4, not shown) and in the inner pipe or in the jacket pipe, at least one longitudinally-extending conduit is provided, so as to discharge the penetrating liquid in the case of corrosion. <IMAGE>

Description

SPECIFICATION Double-wall heat exchanger The invention relates to a double-wall or coaxial heat exchanger having an inner pipe, an outer pipe which encompasses the inner pipe spaced at a distance therefrom, thus forming an annular space therebetween, with first connection sockets discharging in an axial direction into the inner pipe ends, and second connection sockets discharging generally radially into the end sections of the annular space.

Such heat exchangers are known and are preferably presently made of copper, because this material has a high degree of heat conductivity, on the one hand, and a relatively easy workability, on the other hand. At the end of these known coaxial heat exchangers, fittings are inserted which are provided with the first, as well as the second connecting sockets, and with which the inner pipe and the outer pipe are coupled in a truncated manner.

One disadvantage of a heat exchanger made of copper in that the material is not electrolytically neutral, so that such a heat exchanger has only limited usefulness. For example, it cannot be connected to galvanized pipes. Also, when using copper, a limited stress compressability exists. In addition, only a limited permissible number of mediums can be used.

With aggressive waters, in the foods or beverage industry, in laundries and in many other fields of use, the use of heat exchangers made of copper is not possible or is possible only in a very limited way.

It is therefore desirable to use heat exchangers which are preferably made of fine or high grade steel, because this material is electrolytically neutral, can be subjected to higher stresses or compressive loads and can also be used with aggresive flow mediums. Therefore, high grade steel heat exchangers are very versatile in their use and they simplify storage.

Special mediums are very often used as the heat transferring flow medium which are commercially available under the trademarks "Frigen" or "TKL", for example. Due to the legal regulations as they exist, for example, in Germany and the U.S.A., care has to be taken that these mediums are not brought into contact with water for consumption, for example, drinking water.

Therefore, the heat exchanger structure must be such that the inner space of the inner pipe cannot communicate act with the annular space between the outer and inner pipe, due to corrosion. When making heat exchangers from high quality steel, this danger is not quite eliminated because welding seams may start leaking due to corrosion, for example, whereby the danger in heat exchangers made of high quality or alloy steel require particular care, because due to the high resistancy of the steel against aggressive flow medium, the weld seams would be subjected to higher aggressive effects in such heat exchangers.

The use of fittings with the associated connecting sockets used in heat exchangers made of copper would be disadvantageous in coaxial heat exchangers made of high grade steel, because the manufacturing of such fittings made of high grade steel would Incur prohibitive costs which would have a disadvantageous effect on the total price of the heat exchanger. A further disadvantage is that if the corrosion phenomenon takes place at the weld seam which welds the inner pipe to the fitting, it could corrode so that the flow medium which is present in the inner pipe and in the annular space between the inner pipe and the outer pipe would come into contact with each other which, for the aforementioned reasons, should be prevented under all circumstances.

It is therefore an object of the invention to provide a coaxial heat exchanger which is useful for many applications, affords simple storage, can resist aggressive flow mediums, affords means which prevent the different flow mediums on both sides of the heat exchanger from coming into contact with each other, and which is of a construction which can be made economically.

This object of the invention is obtained by the provision of a heat exchanger of the aforementioned type which is made of high grade steel and which is characterized in that the first connection socket are soldered into the ends of the inner pipe, and the end sections of the outer pipe, outside of the second connection sockets, are tapered by forming calender cuts or beads on the outer side of the pipe in the direction of'the pipe end, and they taper to match the outside diameter of the inner pipe and are soldered to the inner pipe.

This construction is advantageous in that the very expensive fittings at both ends of the coaxial heat exchanger can be eliminated while, at the same time, a very reliable separation of the two flow mediums is assured. If the soldered connection between the outer pipe and the inner pipe would start to leak, the flow medium in the annular space can only discharge to the outside of the first connection socket, still separated from the flow medium in the inner pipe. Similarly, if the soldered connection between the inner pipe and the first connecting socket begins to leak, the flow medium in the inner pipe can discharge between the first connecting socket and the inner pipe, but it is still separated from the annular space between the inner pipe and the outer pipe.

In addition, the soldered connection permits a substantial saving in man hours. This is advantageous relative to the costs of the heat exchanger.

In a particular advantageous embodiment, the outer pipe and inner pipe are provided with cylindrical segments in the area of their soldered connections. This results in a particularly reliable solder connection.

In a further advantageous embodiment, the inner pipe is sheathed by a jacket pipe and the inner pipe or the jacket pipe is provided with at least one molded longitudinal conduit. Thereby, even when corrosion damage occurs in the inner pipe or the jacket pipe, the possibility of a liquid exchanger occurring between the two flow paths is still prevented. At the point of corrosion damage, the liquid collects between the inner pipe and the jacket pipe and is discharged through the longitudinal conduit which, at the same time, calls attention to the damage.

Other objects and the features of the present invention will become apparent from the following detailed description when taken in connection with the accompanying drawings which disclose several embodiments of the invention. It is to be understood that the drawings are designed for the purpose of illustration only and are not intended as a definition of the limits of the invention.

In the drawings, wherein similar reference characers denote similar elements throughout the several views; Fig. 1 is a side elevational view, in part section, of an end area of a coaxial heat exchanger made of high grade steel, embodying the present invention; Fig. 2 is an end view of the heat exchanger taken in the direction of arrow II in Fig. 1, but with the first connecting socket omitted for the purpose of clarity; Fig. 3 is an enlarged, sectional view of the end section of another embodiment of a coaxial heat exchanger, taken along line Ill-Ill of Fig. 4: and Fig. 4 is an end view taken in the direction of arrow VI in Fig. 3.

Referring now in detail to the drawings, the heat exchanger 10 shown in Figs. 1 and 2 consists of two end sections 12, only one of which is shown in the drawings, which serve to connect the connection lines. The heat exchanger itself is provided with an inner pipe 14 and an outer pipe 1 6 encompassing the inner pipe and spaced at a distance therefrom, so that between the inner pipe and the outer pipe, an annular space 18 is formed.

In this case, a first connection socket or pipe connection 20 formed as a pipe elbow is inserted with its cylindrical end segment 22 into a sieevelike, cylindrical expansion at the end 24 of inner pipe 14 and is soldered along the cylindrical connection faces to inner pipe 14.

Outer pipe 16 is welded in its end section 12 at a certain distance from its end 26 to an approximately radially-disposed connecting socket 28. In the area between the second connecting socket or pipe connection 28 and the end 26 of the outer pipe, there is provided a so-called "calender cut," bead or fold 30, 32 on two diametrically-opposite locations of the outer pipe which, in the direction of the end of the outer pipe, expands in width, so that outer pipe 1 6 conically tapers in the direction of end 26, but with the last segment 34 of outer pipe 1 6 being cylindrical and having an inner diameter complementing or matched to the outer diameter of the cylindrical expansion 24 of inner pipe 14, at which segment outer pipe 16 is soldered to inner pipe 14.

As can be clearly seen in Fig. 1, if the solder connection leaks, the flow medium within inner pipe 14 can only discharge to the outside without coming into contact witht he flow medium in annular space 1 8. The same is true for the medium which is in the annular space 1 8 which could discharge through a leaky solder connection to the outside, but which cannot come into contact with the flow medium in the inner pipe 14.

An expensive connecting piece is therefore completely eliminated and the heat exchanger is constructed with simple elements and can be made very economically.

In the embodiment in accordance with Figs. 3 and 4, a double-wall inner pipe is provided, i.e., inner pipe 14 is encompassed in a tight fitting relationship by a jacket pipe 35. When corrosion damage occurs at the separating wall formed by inner pipe 14 and jacket pipe 35 which separates the two flow paths, the flow medium would enter between the inner pipe 14 and the jacket pipe 35.

Therein it would collect in a longitudinal conduit 36 and discharge at its end. The liquid discharge would, in turn, call attention to the damage, so that rapid relief may be provided, for example, by replacing the heat exchanger.

When the longitudinal conduit 36 is indented into the inner pipe 14, the connecting socket must also be provided with a corresponding conduit in the area of the connection. However, the possibility exists of pressing or molding a longitudinal conduit 36 into jacket pipe 35. Finally, the possibility also exists that instead of one individual longitudinal conduit 36, a plurality of longitudinal conduits is provided.

Thus, while only several embodiments of the present invention have been shown and described, it will be obvious that many changes and modifications may be made thereunto, without departing from the spirit and scope of the invention.

Claims (5)

1. In a coaxial heat exchanger of the type having an inner pipe, an outer pipe which encompasses the inner pipe spaced at a distance therefrom so as to form an annular space therebetween, first connection sockets discharging in an axial direction into the inner pipe ends, and second connection sockets discharging into the annular space of the end sections in a generally radial direction to the end sections, the improvement comprising: said heat exchanger being made of steel, said first sockets being soldered into opposite ends of said inner pipe, and the end sections of the outer pipe disposed outwardly of the second connection sockets being tapered downwardly in the direction of the pipe end to substantially assume the outer diameter of the inner pipe, by the provision of calender cuts, and being soldered to opposite ends of said inner pipe.

2. The heat exchanger according to Claim 1, wherein said outer pipe and said inner pipe are provided with cylindrical segments in the area in which they are soldered.

3. The heat exchanger according to Claim 1 or 2, wherein said inner pipe is sheathed by a jacket pipe and wherein at least one of said inner pipe and said jacket pipe is provided with at least one longitudinal conduit.

4. The heat exchanger according to Claim 1 or 2, wherein said calender cuts on said end segment of the outer pipe are disposed at two diametrically-opposed positions and extend in the longitudinal direction of said outer pipe.

5. A coaxial heat exchanger substantially as herein described with reference to, and as illustrated in, Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.