GB2031578A

GB2031578A - Heat exchanger assembly

Info

Publication number: GB2031578A
Application number: GB7929080A
Authority: GB
Inventors: Anton Schwarz
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-09-04
Filing date: 1979-08-21
Publication date: 1980-04-23
Also published as: FR2435013A1; IT7953551U1; GR63145B; CH642165A5; SE437074B; SE7907184L; GB2031578B; FR2435013B1; IT7953551V0

Abstract

In a heat exchange conduit assembly (e.g. in a convection air heater) wherein one end at least of a riser pipe 2 is connected, with the interposition of a sealing element 5, to a corresponding opening 4 in a header pipe 1 (conveying e.g. a heating medium), the connecting means comprises webs 6' with slots 13 therein in which are received the edges of opposed fins 3 projecting from the riser pipe 2, welds 12 being formed in said slots to secure the fins 3 to the webs. The webs 6' may as shown, be formed at the ends of a strip 7 embracing the pipe 1. Or the webs may comprise elements welded to the pipe 1 (e.g. Figure 4) or formed integrally with the pipe 1 (e.g. Figure 1). <IMAGE>

Description

SPECIFICATION Heating element The invention relates to a multi-part heating element or the like of light-metal, the parts of which are each formed buy a riser having at least two heat-exchange and air-conducting fins projecting at either side, the risers being in tight communication, at at least one of their ends, with openings in the wall of a heating-medium pipe extending transversely of the ribs, and a sealing element being interposed between each riser and each opening.

In recent times, such heating elements have been used very extensively since they can be produced from a few types of extruded sections. An aluminium alloy is preferably used as the material for the extruded sections. However, a problem associated with these heating elements is that of connecting, in a liquid-tight and gas-tight manner, the individual parts of the heating elements, which contain the risers for the heat-exchange medium, to the heatingmedium pipes.

For this purpose it has been proposed to weld or bond the risers directly to the heating-medium pipes. However, the provision of a tight welded or bonded connection between the pipes raises considerable problems since, in practice and particularly when the heating element starts up and cools down and because of great differences in the amount of heat in adjacent members, thermal stress and expansion occur which may have a deleterious effect upon the quality of the joint after the system has been operating for a fairly lengthy period. Furthermore, in the case of light-metal heating elements, the welding of the zones to be sealed off has never been seriously considered since, on the one hand, these zones are difficult to reach and, on the other hand, it is extremely difficult to effect sound welding of aluminum.A connection that can be made between the risers and the heating-medium pipes of a heating element involves pressing the heatingmedium pipes against the risers by means of one or more screw-bolts, with sealing rings interposed between the pipes and the risers, in which system the screw-bolts are supported in a thrust member which is secured in the fins of the riser. A disadvantage of this connection resides in the relatively high cost of assembly and in the fact that, because of the above-mentioned thermal stresses, gradual loosening of the clamping screws is observed. Measurements have shown that differences in the lengths of adjacent risers can reach as much as approximately 2 mm. This can lead to leakage at the pipe joint over brief periods. Such defects are difficult to localise and, in practice, cannot be avoided.

A further problem specific to heating elements made of light-metal alloys is that ringing, crackling and clicking sounds and noises can be heard during operation and particularly during start-up of the heating system. This has hitherto been through to result from the great and differing thermal expan sionswithin the heating element and has been regarded as a disadvantageous feature that could not be eliminated.

The Applicant has found that the undesirable noise occurring during operation occurs mainly at the joints between the risers on the one hand and the heating pipe on the other. This is due to the fact that the above-described clamping and screw connections permit slight displacements which are caused by thermal expansion and occur suddenly and induce vibrations in the fins of the parts of the heating element and of the risers.

In a proposal made by the Inventor, the abovedescribed disadvantages can be removed to a large extent by pressing the heating-medium pipe and the risers together to form a close joint between them, the compressive force being applied by weld points between the heating-medium pipe and the ribs of the riser.

Surprisingly, this has had the effect of largely eliminating the vibratory and crackling noises, hitherto apparently unavoidable, that occur when starting up and cooling down the heating element, said effect resulting from the stiffening and damping action of the weld points. In particular, reverse torsion in the risers is prevented.

In order to prevent disadvantageous deformation and heating up of the sealing faces when providing the weld points, the heating-medium pipe was produced with integral co-extensive projecting base strips, for example, and the welding was then carried out on these strips.

The object of the present invention was to improve the heating element particularly along the lines of making it easier to assemble and of using little raw material for its production.

According to the invention, this object is achieved in that the heating-medium pipe is pressed into the zone of inter-section of at least two fixing webs which are associated with the fins of each riser and which have slots which extend radially of the heating-medium pipe and in which the fins of each riser fit and are welded to the fixing webs.

This arrangement not only permits automatized assembly, since the openings of the heatingmedium pipe and the riser are centered, but also enables reliable and firm spot-welding to be carried out even when the wall-thicknesses of the fins of the riser are very small.

Advantage also accrues if the end-edges of the fins are disposed approximately in the plane of the associated ends of the risers and form an acute angle with the surface zones of the fixing webs that are to be welded.

An optimum cross-section for the passage of the air used for effecting convection heating is provided if the width of the fixing webs exceeds the diameter of the riser at most to only a slight extent, since the space between the heating-medium pipe and the air-conducting surfaces is unoccupied between the zones of intersection. This leads to greater efficiency.

In addition, deposition of particles of dust and dirt is reduced. The heating element is virtually completely quiet, since the considerable resilience of the heating-medium pipe as regards bending enables thermal expansion to be taken up without generating crackling noises.

It is of further advantage as regards providing a permanently tight joint if the floors of the slots are designed as stops for the fins of the riser, a sealing means, resiliently deformable to a predetermined extent, being arranged between the riser and the heating-medium pipe.

According to a further feature, the fixing webs are formed integrally with the heating-medium pipe in the zone of inter-section.

In a preferred arrangement, the fixing webs are formed by the limbs of a substantially U-shaped bowed member which embraces the heatingmedium pipe.

Further details of the invention will now be described by reference to examples of forms of construction and to the attached drawings, wherein: Figure 1 illustrates, in cross-section, part of the zone of intersection of a heating-medium pipe and a riser of a heating element of light-metal, Figure la is a diagrammatic plan view of part of the pipe connection of Figure 1, immediately prior to welding, Figure 2 is a cross-section through part of a modified form of the Figure 1 arrangement, and Figure 2a is the corresponding plan view, Figure 3 is a diagrammatic illustration of a multipart heating member during start-up, and Figure 4 shows a further form of the connection between the heating-medium pipe and the riser.

Figures 1 and 1a illustrate a part of a heating element made of light-metal extruded sections. Each part of the heating element consists of a riser 2, which is provided with fins 3 projecting transversely of the longitudinal axis of a heating-medium pipe 1.

These fins 3 are extended in the shape of a T to form air-conducting surfaces 8. The end of the riser 2 is tightly connected to an opening 4 in the wall of the heating-medium pipe 1. For this purpose, the heating-medium pipe has, in the zone of intersection, two fixing webs 6 which are associated with the fins 3 and in which are cut slots 13 extending radially of the heat-medium pipe 1.

The fins 3 of the riser are inserted into these slots 13, and the floors 14 of the slots 13 form stops for the end edges 15 of the fins 3, so that a sealing means 5, arranged between the openings, is compressed to a predetermined extent. Thus, no damage can be caused to the sealing means 5 during assembly. The fixing webs 6 are connected to the fins 3 of the riser 2 at a distance from the sealing means 5 by means of spot welds 12. The surface zone of the fixing webs 6 that lies below the end-edges 15 of the fins 3 forms an acute angle a with the end-edges 15, so that fused material occurring during the welding of the fins 3 forms a stable spot weld 12. The thickness of the fins 3 can therefore be relatively small.As shown in Figure 1 a, the fixing webs 6 are formed by an extruded section which includes the heatingmedium pipe 1, and these webs are bevelled off between the zones of intersection of the risers 2 and the heating-medium pipe 1. Thus the total space between the heating-medium pipe 1 and the airconducting surfaces 8 is kept practically the same as the cross-section for the passage of the heated air.

Figures 2 and 2a illustrate a modified form of the heating element. Here, the fixing webs 6' are formed by the limbs of a substantially U-shaped bowed element 7 which embraces the heating-medium pipe 1. Figure 3 shows a multi-part heating element at the commencement of the heating process. The various parts 9 of the heating element which contain the risers 2 are united at their two ends by way of heating-medium pipes 1 which are fed for example from one side. The arrows 10 indicate the thermal expansion of the parts of the heating element that occurs during start-up, whereas the dot-dash line in the heating-medium pipes 1 indicate the curvature caused by said thermal expansion. Because of the joint between the risers and the heating-medium pipes as proposed in the invention, the pipes can very readily yield under these bending loads without any undesirable noise being caused. This is due to the fact that the intimate force-locking joint between the heating-medium pipe and the riser precludes relative displacement without reducing the resilience, under bending load, of the heating-medium pipe.

Figure 4 illustrates a further possible form of the invention wherein the fixing webs 6" are in turn connected by welding to the heating-medium pipe 1.

This connection can be made prior to final assembly of the heating element, and there is therefore no danger of damage occurring to the sealing means 5.

Claims

1. A multi-part heating element or the like of light-metal, the parts of which are each formed by a riser having at least two heat-exchange and airconducting fins projecting at either side, the risers being in tight communication, at at least one of their ends, with openings in the wall of a heating-medium pipe extending transversely of the ribs, and a sealing element being interposed between each riser and each opening, wherein the heating-medium pipe is pressed into the zones of intersection of at least two fixing webs which are associated with the fins of each riser, which have slots which extend radially of the heating-medium pipe and in which the fins of each riser fit and are welded to the fixing webs.

2. A heating element according to claim 1, wherein the end-edges of the fins are disposed substantially in the plane of the associated ends of the risers and form an acute angle (a) with the surface zones of the fixing webs that are to be welded.

3. A heating element according to claim 1, wherein the width (b) of the fixing webs exceeds the diameter of the riser to at most only a slight extent.

4. A heating element according to any one of claims 1 to 3, wherein the floors of the slots consitute stops for the fins of the riser, the sealing means, arranged between the riser and the heating-medium pipe being resiliently or plastically deformed to a predetermined extent.

5. A heating element according to any one of claims 1 to 4, wherein the fixing webs are formed integrally with the heating-medium pipe in their zone of intersection.

6. A heating element according to any one of claims 1 to 4, wherein the fixing webs are formed as the limbs of a substantially U-shaped bowed member embracing the heating-medium pipe.

7. A heating element according to any one of claims 1 to 4, wherein the fixing webs are welded to the heating-medium pipe.

8. A multi-part heating element or the like substantially as hereinbefore described with reference to the accompanying drawings.