WO1979000944A1

WO1979000944A1 - A method for manufacturing a tube array for a heat exchanger

Info

Publication number: WO1979000944A1
Application number: PCT/SE1979/000094
Authority: WO
Inventors: H Eriksson
Original assignee: Elge Verken Ab; H Eriksson
Priority date: 1978-04-18
Filing date: 1979-04-18
Publication date: 1979-11-15
Also published as: SE7804395L; EP0015952A1; SE441628B

Abstract

A tube array for a tubular heat exchanger comprises (i) a cylindrical container (2) having an inlet opening (5) and an outlet opening (6) for a through-flowing fluid, (ii) a plurality of helically coiled tubes (9) which extend axially of the container and which are adapted for a through-flow of another fluid and (iii) a tube mounting member (11) at each end portion of the container for securing the respective ends of the helically coiled tubes (9) and for forming a header for the other fluid flowing through said tubes. Said mounting members have the shape of a tubular sleeve (11) the longitudinal axis of which extends coaxially with the longitudinal axis of the container and are provided with a plurality of tube mounting openings (10) over its peripheral surface in which the ends of the respective tubes (9) are adapted to be permanently secured A method for manufacturing such a tube array according to the invention is substantially distinguished by the step of securing a tubular sleeve (11) with one of its ends, which is closed, to either end of an elongated shaft (13), introducing a rotatable mandrel (16, 16a) into the opposite open end of both the sleeves (11), inserting one end of at least one of the tubes (9) into an associated opening (10) in one of the tubular sleeves (11) and then rotating the mandrels (16, 16a) and thus the sleeves (11) and the shaft (13) connected therewith while winding the tube (9) around the shaft in a helical path towards the other sleeve (11) so as to form a first tube layer around the shaft (l3), after which the other end of the tube (9) is inserted into an associated opening (10) in the other tubular sleeve (11) and finally the two tube ends are permanently secured in the respective sleeve (11), furthermore one or more layers of tubes (9), if desired, being wound helically in the same way between further openings in the tubular sleeves (11) located axially beyond the openings (10) for the tubes (9) in the first layer.

Description

A METHOD FOR MANUFACTURING A TUBE ARRAY FOR A

HEAT EXCHANGER

The present invention refers to a method for manufacturing a tube array for a tubular heat exchanger of the kind comprising a substantially cylindrical container, at one end having an inlet opening and at the other an outlet opening for a through-flowing fluid, a plurality of helically coiled tubes extending axially of the container and adapted for a through-flow of another fluid preferably in opposite direction to the first-mentioned fluid, and a tube mounting member at each end portion of the container for securing the respective ends of the helically coiled tubes and for forming a header for the other fluid flowing through said tubes, said mounting members having the shape of a tubular sleeve the longitudinal axis of which extends coaxially with the longitudinal axis of the container and has a plurality of tube mounting openings over its peripheral surface in which the respective tube ends are adapted to be permanently secured such as by soldering.

In a well-known heat exchanger of this kind each tube mounting member is constituted by a plane tube plate at right angles to the container axis, said plate forming together with the container end wall a header for the fluids flowing through the helically coiled tubes. For the reasons of manufacture and strength such a tube plate has a relatively great diameter and thickness, which makes the tube mounting member expensive to manufacture. In the manufacture of such a heat exchanger the helically coiling of the tubes is carried out as a separate operation before the tube ends are inserted and secured into the openings in the tube plates. Normally the winding is carried out such that the txibes are wound in superimposed layers, the first layer being wound around a separate elongated cylindrical core supported by a winding machine. After the winding of the tubes the tube ends are simultaneously inserted into associated openings in the tube plates, which is a work which requires time and precisio

In another known heat exchanger each mounting member is made as a thick-walled, part-spherical tube plate with its concave space turned outwards, the cup-shaped tube plates each being connected to a separate, corresponding cover portion for forming a header for the outlet and inlet, respectively, for the fluid flowing through the tubes. Also in said heat exchanger the coiling of the tubes must be carried out in a separate operation before the mounting of the tube plates. The coiling is carried out such that a first helically coiled tube layer is wound on a mandrel, after which said tube layer is removed from the mandrel and inserts into engagement with the internal surface of a cylindrical casing. After that, the next following layer is wound on a mandrel of smalle diameter than the preceding one, after which said tube layer is introduced concentrically in the preceding tube layer within the cylindrical casing. This procedure is repeated until a required number of tube layers has been obtained. Before the tube ends are inserted and secured into the cup-shaped tube places a centre core is mounted. Similar to the first-mentioned known heat exchanger, said design of the tube mounting means requires a pre-coiling of the tube array and a time-consuming simultaneous insertion of the tube ends into the cup-chaped tube plates, which normally are manufactured by stamping of a circular blank of relatively great thickness, which causes great material expenses.

In a still further known heat exchanger the tube mounting members are made as an annular tube chamber located in each end portion of a container and forming a header. These annular headers are connected through branch pipes to an inlet at one end of the container and an outlet at the other end thereof. The manufacture of such an annular chamber is complicated, however, and is usually carried out by joining to annular halves by an extensive soldering operation of the securing of the tubes in one of that annular halve The very coiling of the tubes also is carried out in this case as a separate operation before the mounting of the tubes and is in principle made in the same way as in the above mentioned heat exchanger with plane tube plates. An object of the present invention is to provide an improved heat exchanger which allows a simplified manufacture of the heat exchanger as a whole and particularly an improved tube mounting member for such a heat exchanger.

In accordance with the present invention, this object as well as other objects obvious to those skilled in the art are obtained by securing a tubular sleeve with one of its ends, which is closed, to either end of an elongated shaft ,introducing a rotatable mandrel into the opposite open end of both the sleeves and brought into driving engagement with the sleeve, inserting one end of at least one of the tubes into an associated opening in one of the tubular sleeves and then rotating the mandrels and thus the sleeves and the shaft connected therewith while winding the tube around the shaft in a helical path towards the other sleeve so as to form a first tube layer around the shaft, after which the other end of the tube is inserted into an associated opening in the other tubular sleeve and finally permanently securing the two tube ends in the respective sleeve, furthermore one or more tube layers, if desired, being wound helically in the same way between further openings in the tubular sleeves located axially beytnd the openings for the first tube layer.

An essential advantage of the invention is that the assembly of the tube array in principle can be made in one single continuous working operation, i.e. the tubes can be secured in the tube mounting members and wound helically around a central shaft. Thus the tube mounting members made as tube sleeves actively co-operate in the very winding phase of the tubes in that they are brought to rotate as a unit with the shaft mounted between the tube sleeve by means of the mandrels, which are adapted to be introduced into said sleeves, 'when inserting the tube ends into the openings in the tubular sleeves the ends of the tubes are upset against the driving mandrels introduced into said tubular sleeves, said mandrels thus also serving as a stop member defining the insertion depth of the tube ends into the tubular sleeves. By way of example, the method according to the invention will be further described below with reference to the accompanying drawings, in which fig. 1 is a partially sectioned side elevation of view of a tube heat exchanger manufactured according to the invention and fig. 2 is a fragmentary side view of two tubular sleeves according to the invention with rotatable driving mandrels inserted therein.

The heat exchanger generally designated 1 in Fig. 1 comprises an external cylindrical container 2 with dome-shaped end portions 3 and 4. The end portion 3 is provided with an inlet 5 for a first fluid flowing through the container, while the other end portion 4 is provided with an outlet 6 for the same fluid. The container 2 accommodates a cylindrical internal casing 7, which in its turn envelopes the portion of a tube array 8 which contains helically coiled tubes 9. The tubes 9 are preferably constituted by copper tubes having a substantially oval cress-sectional shape and another fluid is adapted to flow through said tubes in a direction preferably opposite the direction of flow of the first-mentioned fluid through the container 2.

Either end of each tube 9 is inserted into and secured by soldering into an associated opening 1C in a tube mounting member 11, which has the form of a cylindrical tubular sleeve which forms a header for the through-flowing other fluid. The heat exchanger comprises one such tubular sleeve 11 at either end of the container 2. Since the tubular sleeves 11 are of similar design only one of them will be described in detail below.

Each tubular sleeve 11 is manufactured preferably from a cylindrical copper tube blank, in a pressing operation being provided with a corrugated or wave-shaped wall surface as seen in a longitudinal section of the sleeve.

According to a prefered embodiment of the heat exchanger the openings 10 in the tubular sleeve 11 are stamped in sets in axially spaced radial planes 12 through the tubular sleeve 11, said openings 10 being formed in such way that the ends of the tubes 9 will be oriented obliquely inwardly to the center axis of the header formed by said tubular sleeve and away from a plane disposed at right angles to the container shaft A and within the inner end of the respective tubular sleeve 11. Owing thereto, very good flow-characteristics are obtained at the tubular sleeve 11 serving as inlet header as well as the similar tubular sleeve 11 serving as outlet header. In the embodiment according to Fig. 1 each tubular sleeve has six axially spaced sets of openings 10, evenly distributed around the periphery of the sleeve wall. Each such set may comprise e.g. 7-15 openings 10. Furthermore, the openings 10 in the various radial planes 12 are arranged in straight rows parallel to the axis of the tubular sleeve 11 for providing open passages between the rows so as to facilitate the work with soldering the ends of the tubes to the sleeves 11.

The two tubular sleeves 11 are arranged in mutual concentric relationship and mutually connected or releasably coupled together by means of a central elongated shaft 13 in the form of e.g. a steel tube. The inner end of the sleeves is closed by an end wall 14 , which on its inside is provided with suitable coupling means 15 for driving co-operation with a mandrel l6, i6a, Which is to be inserted into the tubular sleeve for a purpose to be further described below.

As is evident from fig. 1 the tube array 9 of the heat exchanger preferably comprises a plurality of superimposed and in different radial layers helically coiled tubes 9, between each layer being layed a plurality of circumferεntially distributed andaxially extending wire or band-shaped spacing elements 17, which keep the tube layers spaced a distance suitable from a view-point of flow. Between the inner tube layer and the tube shaft 13 and between the outer tube layer and the surrounding inner casing 7 are also arranged a plurality of circumferentially distributed and axially extending spacing elements which also can be made of wires or bands 17 or still better ridges or protuberances formed on the outer surface of the tubular shaft 13 and the inner surface of the inner casing 7 , respectively. Common to said inner and outer spacing elements is that they have half the thickness or height of the wires laid between the tube layers for making the flow conditions uniform around the exterior of the tubes 9.

In order to improve the flow conditions of the first-mentioned fluid flowing exteriorly of the helically coiled tubes and hence the heat exchange with the other fluid the tubes have substantially oval cross-sectional shapes with an axis ratio of about 7:12.

The inner casing 7 surrounding the tube array 8 has at one end a plurality of holes 18 for removal of air between the inner casing and the cylindrical container portion 2 when test pressurizing or starting the heat exchanger for thus preventing eventual rupture or deformation of the thin-walled inner casing 7.

The preferred embodiment of the heat exchanger according to the present invention is manufactured and assembled in the following way.

The tube mounting members 11 are manufactured by cutting cylindrical copper tube blanks of standard diameter into suit^¬ able lengths and inserting said blanks into a form press, in which the cylindrical wall of each tube blank is givena corrugated or wave-like shape in longitudinal section. The tube mounting openings 10 are then made by stamping and one end of the tubular sleeve 11 is provided with an end wall 14, the inner surface of which is formed with suitable coupling means 15. The closed ends of the tubular sleeves 11 are rigidly secured to or releasably coupled together through a central tubular shaft 13, the two sleeves 11 and the shaft 13 thus forming a continuous unit.

After that, one of the tubular sleeves 11 is slid onto a rotatably driven mandrel 16 (see fig. 2), at its outer end having complementary coupling means to the coupling means 15 of the tubular sleeve for co-operation therev/ith but not illustrated in the drawing Into the other tubular sleeve 11 is inserted another mandrel 16a, which also has coupling means for co-operation with the coupling means 15 of the other tubular sleeve 11 and which when rotating the first mandrel 16 is brought to rotate together therewith. After mounting of the unit consisting of the two tubular sleeves 11 and the shaft 13 between the mandrels 16, 16a the winding of the tubes 9 is started. This is carried out in such a way that one end of one or possibly more tubes 9 from a supply roll are inserted each into an opening in the set of openings 10 which lie in the radial plane 12 closest to the inner end wall 14of the tubular sleeve. The end of the tube or tubes 9 is inserted into engagement with the mandrel iβ and l6a, respectively, which has substantially the same diameter as the inner diameter of the tubular sleeve 11, thereby deforming the tube ends slightly so as to secure them in the respective opening 10 while extending a predetermined distance into the tubular sleeve. The driving mandrel 16 then is brought to rotate the entire unit, the tube or tubes 9 being helically coiled in a first layer around the shaft 13, on which, if desired, thin axially extending spacing elements of wire or band shape have been previously applied. It is to be noted that the tubes 9 at their bending point for the helical coiling are slightly flattened so as to obtain a slightly oval cross-sectional shape, whereby the flow conditions for the surrounding first fluid are improved.

When reaching the opposite tubular sleeve 11, the tube or tubes 9 are cut and inserted in a corrεponding manner into associated openings 10 in the first radial set of openings. The next tube layer is coiled in the same way, the spacing wires 17 first being applied onto the preceding tube layer. In the continued winding operation all the openings 10 in the first radial set are connected to the adjacent radial set of openings 10. If desired, the winding can be carried out alternately, i.e. the tubes 9 are coiled alternately to the left and to the right. When all tubes 9 have been coiled the tube ends are fixed by soldering along the passages which have been formed between the tube rows in the axial direction of the tubular sleeves. After soldering the obtained tube array 8 is mounted into the inner casing 7 which then is mounted in the container 2 in a suitable way. From the above-stated description it is evident that the present invention suggest a tubular heat exchanger which,as far as material and manufacture is concerned, implies great savings when compared with the previously applied methods in the present field. The new design of the headers of the heat exchanger also has implied improved flow conditions for the fluid flowing through the helically coiled tubes 9.

The present invention is not limited to the above-described embodiment but can be varied within the scope of the accompanying claims.

Claims

C l a i m s

1. A method for manufacturing a tube array for a tubular heat exchanger of the kind comprising a substantially cylindrical container, at one end having an inlet opening and at the other an outlet opening for a through-flowing fluid, a plurality of helically coiled tubes extending axially of the container and adapted for a through-flow of another fluid preferably in opposite direction to the first-mentioned fluid, and a tube mounting member at each end portion of the container for securing the respective ends of the helically coiled tubes and for forming a header fjr the other fluid flowing through said tubes , said mounting members having the shape of a tubular sleeve, the longitudinal axis cf which extends coaxially with the longitudinal axis of the container and has a plurality of tube mounting openings over its peripheral surface on which the respective tube ends are adapted to be permanently. secured such as by soldering, characterized by securing a tubular sleeve with one of its ends, which is closed, to either end of an elongated shaft, introducing a rotatable mandrel into the opposite cpen end of both the sleeves and brought into driving engagement with the sleeve, inserting one end of at least one of the tubes into an associated opening in one of the tubular sleeves and then rotating the mandrels and thus the sleeves and the shaft connected therewith while winding the tube around the shaft in a helical path towards the other sleeve so as to form a first tube layer around the shaft, after which the other end of the tube is inserted into an associated opening in the other tubular sleeve and finally permanently securing the two tube ends in the respective sleeve, furthermore one or more tube layers, if desired, being wound helically in the same way between further openings in the tubular sleeves located axially beyond the openings for the first tube layer.

2. A method according to claim 1, characterized in that before- the coiling of each tube layer wire or band-like spacing elements (17) are applied axially to the coiling shaft (13) and on top of the preceding tube layer or the coiling shaft (13), respectively.

3. A method according to claim 1 or 2, characterized in that as tube (9) is utilized a copper tube with circular cross-sectional shape, said tube at the bending point for the helically coiling at the sametime being flattened to a substantially oval cross-sectional profile.

4. A method according to any of claims 1-3, characterized in that the tubular sleeve (11) in a pressing operation is given a wave-like wall shape in longitudinal section.

5. A method according to any of claims 1-4, characterized in that the ends of the tubes (9) inserted into the openings (10)in the tubular sleeves are upset against the mandrel (16, 16a) inserted in the respective sleeve, said mandrels thus serving as a stop means determining the insertion depth of the tube ends into the tubular sleeve (11).