GB2072316A

GB2072316A - Heat exchanger

Info

Publication number: GB2072316A
Application number: GB8103306A
Authority: GB
Original assignee: Runtal Holding Co SA
Current assignee: Runtal Holding Co SA
Priority date: 1980-02-07
Filing date: 1981-02-03
Publication date: 1981-09-30
Also published as: FR2475708A1; CH644444A5; ES265380U; BE887413A; DE3026731C2; ES265380Y; DK151159C; IT8119541A0; DE3026731A1; FR2475708B1; GB2072316B; DK53481A; IE810228L; IT1135326B; IE50686B1; DK151159B; CA1132531A

Abstract

In a heat exchanger co-planar, parallel flat tubes (1) are connected at a distance inboard from their ends to manifolds (2) for the supply and return flow of a fluid medium. The flat tubes (1) have very small internal clear widths and the ratio of the internal cross-sectional area to the outer peripheral length of each tube (1) is less than or equal to 2.5. The fluid medium flows with correspondingly greater velocity through the flat tube. A smaller thermal inertia and a better heat transfer results. The tubes (1) are closed at their inwardly bent edges by a welding seam. Outwardly pressed wall regions of the manifold (2) surround bores therein and are connected by welding to the tubes (1), the welding taking place from the inside of the manifold. The manifold (2) consists of at least two parts which are secured together by welding. <IMAGE>

Description

SPECIFICATION Heat exchanger The invention concerns a heat-exchanger having flat tubes arranged mutually in parallel and connected at a distance from their ends to forward and return flow manifolds.

Heat-exchangers of this type are known in numerous different embodiments, the differences being manifested particularly in the construction of the connections of the parallel flat tubes to the manifolds in order to enable the heat-exchangers to be produced in a rational manner by welding either manually or by machine, for example by means of a projection-welding machine that produces a plurality of simultaneous weld connections.

In the utilisation of heat-exchangers as heater bodies in a central heating plant, hot water flows through the heating body at a velocity which depends amongst other things, on the selected dimensions of the tubes. The thermal inertia of the heater body and its heat dissipation depend on the flow rate of the hot water.

For reasons of manufacturing technique, in known heat-exchangers flat tubes have been used which have hitherto been made with a relatively large ratio of water content to heat surface of the flat tube or in other words, the ratio of the inner cross-sectional area to the circumference of the tube is relatively large.

A task of the present invention is to provide a heat-exchanger which, in the interests of better energy utilisation and energy saving has a lower thermal inertia and better heat dissipation or transfer due to a greater velocity of flow of the heating medium and which, by virtue of constructional simplifications, may be manufactured in an economic manner.

According to the present invention, this task is achieved in that, for each flat tube, the ratio of the internal cross-sectional area (e.g. in mm2) to the external circumferential length of the tube (e.g. in mm) is smaller than or equal to 2.5 (mm).

Because of the small clear width the flat tubes may be produced in an advantageous manner. The flat tubes made in long tubular lengths are cut to the desired size and expediently closed at the front ends by providing the mutually opposite longitudinal sides of the tube with respective terminal zones that are bent inwardly towards the middle and connected together by means of a welding seam.

In another expedient embodiment, the flat tubes are closed at their front ends by means of a welding seam that connects a terminal zone formed on one longitudinal side of the tube bent inwardly towards the oppositely lying longitudinal side of the flat tube, the latter being circumferentially shortened by the extent of the said terminal zone.

Further details will become clear from the following description and drawings, in which various embodiments of the invention are shown purely by way of example and in which: Figure 1 is a front elevational view of the heatexchanger, Figure 2 is a vertical section along line I-I of Figure 1, on an enlarged scale, Figure 3 is a vertical section like Figure 2, but in a different embodiment of the connection and wall-opening, Figure 4 is a horizontal section through a flat tube and a manifold along the line Il-Il in Figure 1, on another enlarged scale, Figure 5 is a horizontal section like Figure 4 but showing a different embodiment of the flat tube and manifold; and Figure 6 is a vertical section through a further embodiment of the heat-exchanger with flat tubes on both sides of the manifold, on a larger scale.

The heat-exchanger according to Figure 1 has five co-planar somewhat spaced-apart flat tubes 1 arranged horizontally and mutually in parallel which are connected on their rear side at a distance (inboard) from their ends to vertical manifolds for the forward (supply) and return flow of a fluid medium therethrough. Each of these flat pipes 1 is connected to the same manifold pipe 2 via two couplings 3 of which one coupling is disposed near the upper edge of the flat tube while the other coupling is disposed near the lower edge of the flat tube so that the flat pipes may be vented and emptied without difficulty.

Each of the manifolds 2 has a coupling 4 to which are connected the supply and discharge ducts for a heating medium when the heat-exchanger serves as a heater body.

From the vertical sections through the fiat tube 1 shown in Figures 2 and 3, it may be seen that the width of the internal cross-sectional area 5 is relatively small in relation to its length. The clear width of the tube amounts to 3-5 mm for a height of the flat tube of about 70 mm, measured on the outside. The tube has a plate (wall) thickness of 1.25 mm to at most 2.00 mm. In such an extremely flat tube the ratio of the internal cross-sectional area to the external peripheral length of the tube is less than or equal to 2.5 (times the unit of length). Calculated over the length of the tube, the same value is true for the ratio of the volume of water in the tube to the external heating surface area of the tube.In comparison with the greater tube cross-sections of known heat-exchangers, a small value here signifies that the heating surface area related to the same value of water is greater and consequently the heat transfer or dissipation of the heating body is better. Since furthermore the flat tube contains less water which flows through at a greater velocity, the thermal inertia of the heating body is markedly lower. The dimensioning of the flat tubes accordingly allows various advantages regarding the improved exploitation of energy to be achieved.

The flat tubes manufactured in longer lengths are cut according to need and are closed at their front ends which can be carried out in a very advantageous manner in the case of very flat pipes. Figure 4 shows an embodiment wherein the flat pipes are closed at their front ends by providing the mutually opposite longitudinal sides of the pipe with respective terminal zones 6 which are bent inwardly towards the centre, with a welding seam 7 securing the terminal zones 6 together.

In the embodiment according to Figure 5, each of the flat tubes is closed at its front end by a welding seam 9 that connects a respective terminal zone 8 of one, inwardly bent longitudinal side of the tube with the oppositely lying longitudinal side of the flat tube, the latter being shortened by the extent of the said terminal zone 8. Since the flat tubes are illustrated in Figures 4 and 5, on an enlarged scale, while in Figures 2 and 3 they are shown in their approximate natural size, it is evident that the very flat tubes may be closed by one welding seam wherein at the somewhat slotted narrow sides of the tubes a somewhat thicker weld point at the ends of the welding seam suffices for the complete closure welding of the tube.Consequently, with relatively low manufacturing expenditure, it thus becomes possible to achieve a heat-exchanger construction which is preferable on aesthetic grounds, and which has manifolds on the rear side thereof at a position somewhat inwardly from the ends of the flat tubes.

A construction with manifolds arranged at and welded to the ends of the flat tubes requires more labour input and is less satisfactory from an aesthetic consideration due to the thickening at both ends required by the larger manifold.

Wall openings or bores 10 are formed in the manifolds 2 in order to connect them to the flat tubes 1 as shown in Figures 2 and 3; the region 11 of the wall surrounding the wall opening is pressed outwardly either in a step-like manner according to Figure 2 or, as shown in Figure 3, in some other manner a wall region 12 is pressed outwardly in a funnel-shaped configuration. The flat tubes 1 have wall openings or bores 13 of smaller diameter disposed coaxially with each of the wall openings or bores 10. A wall region 14 of the flat tube 1 surrounding the smaller diameter wall openings 13 is welded to the outwardly pressed wall region 11 according to Figure 2, or 12 according to Figure 3. A welding seam 1 5 shown only in Figures 4 and 5 is not shown in Figures 2 and 3 for the sake of clarity.A small clearance remains between the flat tubes 1 and the manifold 2 after the welding of the outwardly pressed wall section 11 or 12, which clearance enables any weld connection that may be found to be leaky subsequently to be made completely leakproof by laying a ring around the connection and brazing it.

The connection of the flat tubes 1 with the manifolds 2 by means of the welding seam 1 5 takes place from the inside of the manifolds as may be seen from Figures 4 and 5. To enable this to be done, each manifold 2 consists of at least two parts extending over the length of the pipe and in particular, according to Figure 4, from a part 20 which is U-shaped in cross-section and a cover like part 21. These parts are connected together after making all the weld connections with all the flat tubes by means of welding seams 22 running along the whole length of the manifold. In the embodiment according to Figure 5, two similar U-section parts 23 and 24 of the manifold 2 are connected together by two welding seams 25.Naturally, many other possibilities of configuration exist in relation to these manifold parts, in particular in order to facilitate the assembly of the parts, one part may be formed with an edge which has been pressed slightly inwardly in a step-like manner and which engages over the other parts in the manner of a cover.

With a manifold consisting of at least two parts and using the above described methods, a heatexchanger according to Figure 6 may also be made without difficulty, this heat-exchanger having flat tubes on the opposite side of the manifold. In this heat-exchanger, for each of the two parts of the manifold 2, firstly the connections to the respective mutually superposedly arranged flat tubes are made by welding and subsequently the two parts of the manifold are welded together. A multiply bent convector plate 30 is arranged in the space between the flat tubes arranged on the two oppositely lying sides of the manifold as shown in Figure 6. Such a convector plate may also be rigidly arranged on the rear side of flat tubes arranged on only one side of the manifold.

Claims

1. A heat-exchanger comprising flat tubes arranged parallel with each other and connected at a distance inwardly from their ends to manifolds for the foward and return flow of a fluid medium, the ratio of the internal cross-sectional area of each flat tube to its outer circumferential length being less than or equal to 2.5.

2. A heat-exchanger according to claim 1, wherein the front ends of the flat tubes are closed by means of terminal zones formed on mutually opposite longitudinal sides of the tubes, which zones are bent towards the centre and welded together by a welding seam.

3. A heat-exchanger according to claim 1, wherein the flat tubes are closed at their front ends by means of a welding seam that connects a terminal zone formed on one longitudinal side of the tube bent inwardly towards the oppositely lying longitudinal side of the flat tube, the latter being circumferentially shorted by the extent of the said terminal zone.

4. A heat-exchanger comprising spaced-apart flat tubes connected to manifolds in a plane parallel to the manifolds, each manifold consisting of at least two parts extending over the length of the manifold: at each connection of a said tube to a manifold, a respective external wall region of the flat tube surrounding a respective wall opening in the flat tube is welded rigidly, from the inside, to an external wall region of one part of the manifold, said external wall region of said one manifold part surrounding a coaxial wall opening in the manifold and the parts of the manifold being connected together by welding seams extending over the length of the manifold.

5. A heat-exchanger according to claim 4, wherein one of the welded-together wall regions of the manifold and of the flat tube, preferably that of the manifold, is pressed outwardly towards the other tube and there is a gap between the flat tube and the manifold.

6. A heat-exchanger according to Claim 4, wherein one part of the parts of the manifold extending over the length of the manifold is formed with a U-shaped cross-section and is complemented to form a rectangular cross-section manifold by being connected by means of longitudinal welding seams with the other manifold part which latter is constructed as a cover or as another U-section part.

7. A heat-exchanger substantially as herein described with reference to and as shown in Figures 1 and 2 or Figure 3 or Figures 1 and 4 or Figure 5 or Figure 6 of the accompanying drawings.