Heat exchanger and a method for its fabrication

Abstract: Heat exchanger including progressively angled or over their length slightly spirally wound tubes (1, 2) extending between two tube plates (4). The tubes (1 and 2) are arranged in two concentric circles and the tubes of the different circles are given differing progression so that the same tube length can be used in the different concentric circles of the tubes. The tubes (1, 2) are corrugated over their length and the rings of tubes are in close contact with each other. In the end of the tubes the tube plates (4) are achieved by widening the ends of the pipe so that they come in contact with each other, whereafter the ends are soldered to each other. The tube bundle is surrounded by a tight fitting shell (3) and wide surrounding connections (5, 6) allowing the heat exchanger to be easily coupled in series parallel etc.

Description: This invention is related to heat exchangers of the kind that include pipes or tubes that are arranged helically extending between two tube plates, and with one fluid streaming inside the pipes and another outside the pipes. The tube package or heat exchanger core is surrounded by the shell. The helical or spiral arrangements as is for instance shown in the US patents 1,655,086 and 2,081,043 and EP-A-0 342 959, provide a resilience to the core tubes and reduce the thermally caused tension between core and shell. However these heat exchangers become very spacious. The object of the invention is to provide a heat exchanger with an angular progression for the tubes between tube plates that is space efficient. This object is achieved by the tubes being arranged in concentric circles with the tubes of adjacent circles in contact with each other and the tubes being corrugated in their length direction. Preferably over their entire length but for the ends. This will improve flow on the outside of the tubes so much that that they within each ring can be arranged very close to each other providing a very space efficient heat exchanger. The corrugations will also improve turbulence in and outside of the tubes and will also improve heat transfer. The heat exchangers with helical tubes extending between tubeplates are however also expensive to fabricate due to the great number of fabrication steps and amount of manual labor for each heat exhanger,for instance for the mounting of the neccesary distance elements, the invented heat exchanger is however easy to fabricate since no distance elements are needed with the tubes in different rings supporting each other. Preferably the invented heat exchanger is fabricated by arrangeing straight tubes ring- or cylinderwise and then turning each entire cylinder or ring of tubes in one simultaneous motion. Preferably the heat exchanger is constituted by several concentric rings of tubes, that can be turned in the same direction or in different directions. Preferably each ring is turned separately beginning with the innermost ring. In order to have tubes with identical length and thus identical inner flow resistance the inner tube circles have a greater progression or turning angle than the outer ones. When the rings of tubes arc turned the diameter of the tube circles tend to diminish and a good grip is therefor achieved for the inner circle on a center core tube and for the outer circles on the inner ones. In this way a very compact packing of the tubes in the heat exchanger can be achieved in a simple manner and it should perhaps also be mentioned that this package will even hold together of its own accord when released from the machine that turns the tube circles. When the tube package or core has been fabricated the ends of the bundle are machined to the desired shape (normally flat). The tubes are then in their ends expanded so that no space will be left between them and the tubes can then be welded or soldered to each other so that a tube plate is achieved. Expansion and soldering can be carried out ringwise or simultaneous or in a close timed sequence. In fabrication the tubes can be located on two rings of axially directed pins each tube ring at a turn and when each tube in a ring is in place it is turned and given its intended angular progression at the same time as the length is correspondingly reduced and then the next circular set of pins is used to set up the next layer etc. The locating of the tubes can be done by hand or by a simple robot. The demands on precision in fabrication is reduced in relation to the known art and the invention will thus provide a cost and space efficient heat exchanger. Further advantages of the invention are apparent from the following description of preferred embodiments shown in the drawings. Fig 1 shows schematically a heat exchanger in accordance with the invention, fig 2 the tube plate end of a tube bundle, fig 3 shows schematically a coupling scheme of heat exchangers in accordance with the invention used in a device at a municipal heating network and figs 4 and 5 shows the compact actual arrangement of the device, and fig 6 shows an embodiment of the tube as used in the invention. The heat exchanger shown in fig 1 and 2 includes two concentric circles of corrugated tubes, where the inner tubes have been designated by 1 and the outer by 2. The tubes 1 and 2 are in their ends widend as is shown for some tubes 1¹ and 2¹ in dashed lines so that they contact each other and they are soldered to each other, constituting a tube plate. In each end of the heat exchanger a distributing/collecting connection 5 is arranged over the two plates 4 transporting the medium that is to be led through the tubes to and from these. The tubes or rather the bundle of tubes are further surrounded over a greater part of their length by a shell 3. The shell 3 is in its ends provided with connections 6 surrounding the shell and in turn provided with connections 7 for the medium that is to stream around the tubes inside the shell. As is apparent from fig 1 the shell 3 extends a short distance into the connections 6. In this way the entering/leaving medium will be distributed around the tube bundle more efficiently than if the shell only had extended to the connections 6. This in turn reduces the risk of internal heat differences and thereby caused tensions. In fig 1 only one tube of each circle of tubes have been shown in order clearly to depict the angular progression or helical shape of the tubes. The tubes are not only helical in different directions but also the pitch is somewhat different for each circle. In the shown example the inner tube 1 has been turned more than the outer one in order to secure that the tube lengths of the tubes 1 and 2 can coincide so that the flow resistances inside the tubes are the same. The arrangement of the tubes will secure a good turbulence around the tubes and since tubes will enter on one location in one tube plate and come out at another location in the other tube plate possible laminations in the entrance flow will effectively be broken up, also enhancing performance. Since it would be difficult to provide tubes in the centre with a sufficient turning in order to achieve the necessary resilience and length of the tubes a blind tube 8 is located in the centre. The only object of this is to fill up a certain space in the heat exchanger and it can be connected either via a tube plate to the inner medium or being provided with openings towards the outer medium surrounding the tubes. The blind tube 8 is however only fastened to one tube plate so that the possible movements of the heat exchanger core are not hindered by this tube. The heat exchanger tubes 1 and 2 are when fabricated turned ringwise. The tubes are corrugated lengthwise (see fig 6) or perhaps one should say profiled crosswise by being compressed laterally in alternating directions (preferably by 90°), giving an alternating flattening of the tubes. This improves the turbulence inside the tubes and contributes to an increased heat exchange. The flow conditions outside the tubes will be improved by this and in particular the flow resistance for the outer medium will be reduced. When turning each ring of the heat exchanger tubes a stable shape will be achieved for each ring and if one starts with the inner ring this will contract and grip efficiently around the centre blind tube and the consecutive outer ring of tubes 2 will be contracted and press against the inner ring of tubes 1. Tools turning the tubes or rather the rings of tubes will while turned move axially the same distance whereas the turning angle will differ. The tools used can however with very small alterations be used for several different tubes of heat exchangers and lengths of heat exchangers. Preferably the different rings are turned in alternating directions. By turning the rings separately the total torque that has to be applied is kept at a low level and the tools can be made simpler. Since the different rings of tubes in a heat exchanger core are only to be given such an angular progression that the same length is achieved despite different diameter the machinery for turning the rings of tubes can be controlled so as to turn each ring until a preset intended final length of the core is reached. In this way one does not have to calculate the progression angle but instead the final length controles the degree of progression for each ring of tubes. A ring of tubes turned in the above indicated way will even without an inner core be stable so if one so wishes the different rings could be fabricated separately and then brought together. Since the ring of tubes contract on turning the ends of the tubes will have a larger diameter than the tube bundle and therefor before soldering the tubes to each other the ends of the tube bundle is compressed to the diameter of the bundle so that a close fitting, by pass preventing shell can be used. With the shown construction of the shell 3 and the connections 6, the connection 6 can be used to by-pass the heat exchanger with yet another heat exchanger since a flow across and through the connections 6 past the tubes will have very little influence on the efficiency of the heat exchangers. This will in turn faciliate the building of very compact heat exchanger centrals, as they for instance are used in individual houses in a municipal heating net work, and this will be shown in figs 3, 4 and 5, and described below. The bellowlike dashed part 9 between the shell 3 and the connection 5 further improves the resilience so that the heat exchanger can cope even better with possible heat tensions that can result between the tube bundle and the heat exchanger shell and the connections of this. At the use of tubes with angular progression as is above described the axial tensions between the tubes and the shell are efficiently eliminated. Within the frame of the invention one can also allow the blind tube to be fully free floating without being connected either to one or the other of the tube plates. At turning of the concentric circles of tubes these do not need to be guided over their length but at the turning of a circle of tubes a more or less automatic straightening of the bundle is achieved. In order to connect the rings of tubes to a tube plate mandrels of a suitable shape are pressed into the tubes. This can be done in one step or in consecutive steps for instance one step for each ring to a configuration as shown at 1¹ and 2¹ in fig 2. The tubes are widened over a sufficient stretch to allow for the solder to give a good connection. This soldering can be carried out by a robot. Since copper is the most commonly used material this shapening of the tube ends will not constitute any problem. In case the different rings of tubes are angled or turned separately and then mounted together of course also the shapeing of the ends can take place before the different layers of tubes are mounted together, but preferably it can be carried out on the tube core as a unit. The mandrels used to widen the tubes are preferably prismatically chamfered or diminishing towards their front end in order to give a soft shapening of the tubes. The turning of the tubes as well as the shapeing of their ends can be carried out by hydraulic, mechanical or other means. In figs 3-5 an embodiment of a heating device based on the invention is shown for the use in the separate houses in a municipal heating network. The exchanger device mainly is constituted of four heat exchangers as described above. Two of these heat exchangers 20, 21 are coupled in series and with an opposed flow direction for both of them for the heating of the water in the heating system of the house. The other two heat exchangers 22 and 23 are used to heat the hot water going to taps in the houses. An additional connection allows circulation of the hot water in the house, securing that hot water is swiftly obtained at each tap in the house. As is obvious from fig 3 the use of the heat exchangers as described above and in accordance with the invention give a rather simple total layout of the device. In figs 4 and 5 is further shown how really compact this device becomes when the heat exchangers are placed close to each other. The resulting device is compact and provided only with a minimum of outlets and inlets simplifying the mounting thereof and also reducing the risk of mistakes. From the above example it is apparent how easily the heat exchanger according to the invention can be coupled in parallel or series in adaption to different capacity requirements etc.

Claims: Heat exchanger with tubes (1, 2) that are arranged helically between tube plates (4), characterized in that the tubes (1, 2) are arranged in concentric circles with the tubes (1, 2) of adjacent circles in contact with each other and the tubes being corrugated in their length direction. Heat exchanger in accordance with claim 1, characterized in that the tubes (1, 2) in the different circles are wound in alternating directions. Heat exchanger in accordance with claims 1 or 2 characterized in that the tubes (1, 2) are close to adjacent tubes in the same circle of tubes. Heat exchanger according to any of the claims 1-3, characterized in that the ends of the tubes (1' ,2') are shaped so that their walls border closely to each other without any greater space between them and that they are soldered together so that the tube plates (4) are constituted by ends of the tubes themselves. Method for fabrication of a heat exchanger in accordance with claim 1 including tubes (1, 2) that are arranged helically between tube plates (4) and that are arranged in circles and in contact with each other and corrugated in their length direction characterized in that each circle of tubes (1, 2) is turned separately to its intended angular progression. Method according to claim 4, characterized in that the concentric circles of tubes (1,2) are turned in consecutive steps beginning with the innermost circle. Method according to claim 5 or 6, characterized in that the tubes (1,2) in the different circles are turned over different angles so that tubes with the same length can be used in all the circles. Method according to any of the claims 5-7, characterized in that the tubes (1,2) of consecutive circles are turned in alternating directions. Method according to any of the claims 5-8, characterized in that before turning of the inner circle of tubes (1) a central blind tube (8) is arranged. Method according to any of the claims 5-9, characterized in that after the turning of the circles of tubes (1,2) the ends of the circles are compressed radially, reducing the distance between the tubes and conforming the ends of the tube circles with the tube bundles general diameter which is diminished when the circles are turned.

Inventors: ERIKSSON RUNE, ERIKSSON, RUNE
Applicants: ELGE AB
Application year: 1990
Main classification: F28D7
IPC codes: F28D7