GB2156064A

GB2156064A - Helically-finned heat exchange tube

Info

Publication number: GB2156064A
Application number: GB08507067A
Authority: GB
Inventors: Wolfgang Weber; Karl Hermann Becker
Original assignee: TERMOTEC
Current assignee: TERMOTEC
Priority date: 1984-03-20
Filing date: 1985-03-19
Publication date: 1985-10-02
Also published as: GB2156064B; FI81669B; GB8507067D0; FI81669C; MX161117A; FI851082A0; NL8500812A; FI851082L

Abstract

A spiral-finned tube comprises a tube shell 1 to which spiral finning 2 has been applied. The finning has a substantially flat-rectangular cross-section and the contact of the edges of the finning with the tube shell is reinforced by a shielded arc welding seam 3. The seam is applied at the base of the finning and connects the finning with the tube shell across the entire width of the finning. <IMAGE>

Description

SPECIFICATION Spiral-finned tubes This invention relates to spiral-finned tubes and is especially concerned with a spiralfinned tube of the type which comprises a tube-shell, to which spirally wound fins with basically a flat rectangular cross section are applied, the contact of the flat sides of the fins with the carrying tube-shell being intensified by welding.

In general, spiral-finned tubes are employed for heating and cooling purposes, these tubes being equipped with screw-like spirally wound fins, which provide an extended heat transfer.

Spiral-finned tubes are widely employed as heating or cooling tubes for heat exchangers or the like.

Normal spiral-finned tubes are made of finning, which has a rectangular profile, which is wound on to the respective tube-shell and only connected thereto by a stiff contact between the two elements and as such ensures the heat transfer. In practice, it has been found that with finned tubes which consist of a finning which is applied only under pressure, the actual contact between tube-shell and finning material takes place only in relatively limited areas and can result in undesirably high temperature drops. Therefore, measures have been devised to improve the heat transfer of finned tubes. As an example, Lprofile material is used for the finning because the short side of the profile is connected to the surface of the tube-shell, so that the contacting area is enlarged. Still, this does not change the fact that only relatively limited areas come into direct contact.Alternatively, a dove-tail-like profile has been used for the fins where the ends of the profile are being grooved into the tube-shell; this results in a drastically higher manufacturing cost combined with still unsolved manufacturing problems and does not result in a completely successful heat transfer between fins and tube shell.

Furthermore, it is known to apply the fins to the tube-shell by means of an HF-contact welding procedure. This procedure requires relatively intensive high-frequency energy in order to effect the welding procedure. Also the application of the HF-energy does provide certain problems in directing the energy locally to the welding area because the areas which have just been welded tend to cause short-circuiting of the areas about to be welded. It has been shown as a disadvantage that under these circumstances a welding seam which was created by this procedure is not guaranteed to be without interruptions, as the HF-contact welding consists of a multiplicity of small welded areas and may contain pores or bag-like areas which are not really welded.This not only reduces the actually achieved heat transfer compared with the opti mally possible ratio, but also the pores or "bags" which are positioned between the flat side of the fins and the tube-shell offer contact areas for a possible split corrosion so that the life span of HF-welded spiral-finned tubes is reduced.

The invention therefore seeks to provide a spiral-finned tube with fins which are stable and completely connected with the tube-shell, so that not only the required efficient heat transfer is achieved but also a mechanically stable and highly chargeable finned tube is created which is distinguished by a very low corrosion susceptibility.

This aim is achieved by providing a spiralfinned tube in which the fins are connected with the tube-shell by a continuously welded seam which is positioned at one side of the fin at low height and connects, that is welds, the fins in their total width porefree with the tube-shell. Test-prove to be suitable for this procedure is a shielded arc welding seam, e.g.

a CO2-welding seam which connects the fins and tube-shell.

Individual preferred characteristics of the invention will now be described on the basis of a manufacturing example with reference to the drawing.

The drawing shows a partially cut tube-shell (1) on which a continuous fin (2) has been wound spirally under press tension. Still during this winding operation, the foot areas of the fin (2) which have just been applied on to the tube-shell (1) are simultaneously being welded from the still free end of the tube to the outer surface of the tube-shell (1). During the application of the welding seam according to the shielded arc e.g. CO2-welding procedure, welding material coming from the electrode material is being applied into the welding seam (3) which yields a complete filling of the welding seam and achieves a porefree connection to the fin as well as the tube-shell (1).During this procedure the electrode of the applied method of welding is not directed straight into the middle of the angle which is formed by the outside of the tube-shell (1) and the flank of the fin (2), but is directed against the flank of the fin, suitably in a direction making an angle of less than 45 with the tube-shell, and somewhat above the apex of the angle. This has the effect that on the one hand the tube-shell itself is included in the welding seam but on the other hand only areas on the surface of the tube-shell are being effected by the welding seam. With respect to the fin, the result is that the fins in practice are being caught by the welding seam over their total width.This results from a corresponding alignment of the electrode and during the actual welding procedure in a welding operation results in a continuous through welding seam (3) which only rela tiveiy insignificantly penetrates into the tube shell (1), so that at least the inner shell of the tube is not affected by the welding seam. On the other hand a complete through-welding through the fin is achieved so that the fin is bound to the tube-shell (1) over its total width by the welding seam (3). In the moment of the welding, a basically liquid welding seam is being created which, without any deforming problems of the tube shell (1), eliminates completely the existence or creation of welding bags, split-like openings, pores or the like, which could lead to corrosion.By this means, the desired object is reached of creating a large-sized direct contact between the finning and the tube-shell which furthermore eliminates the danger of split corrosion.

Similar to the known high frequency contact welding, the invention is based on a continuous welding procedure, where the welding point progresses at any given position simultaneously with the speed of winding. In contrast to the high-frequency welding procedure, the welding procedure, on which the invention is based, does not need high-frequency energy carrying electrodes or the like.

The actual point of welding is clearly defined by the applied welding electrode. However, the speed of winding, as in the known highfrequency contact welding, has to be adjusted to the welding performance.

As necessary during manufacturing, it can be expedient to apply the inert gas, e.g. CO2, used not only at the side of the welding and therefore the front side of the just applied fin but also by an additional connection on the opposite side of the fin.

We have found that in all described cases the required result will be achieved, that is the achievement of a safe connection which results in excellent heat transfer ability and therefore eliminates effectively temperature drops within the connection area. Furthermore, the mechanical stability as well as the chemical resistance is increased by the complete elimination of corrosion susceptible points within the connecting area between finning and tube-shell.

Claims

1. A spiral-finned tube comprising a tube shell to which spiral finning has been applied, the finning having a substantially flat-rectangular cross-section and the contact of the edges of the finning with the tube shell being reinforced by a welding seam, applied at the base of the finning, which seam connects the finning with the tube shell across the entire width of the finning in the substantial absence of pores within the seam.

2. A spiral-finned tube according to claim :1, wherein the welding seam is applied by shielded-arc welding.

3. A spiral-finned tube according to claim 2, wherein the welding seam is applied by carbon dioxide welding.

4. A spiral-finned tube according to claim 2 or 3, wherein the welding electrode is directed against the flank of the finning.

5. A spiral-finned tube according to any one of the preceding claims, wherein the welding seam is applied simultaneously with applying the finning to the tube shell.

6. A method of making a spiral finned tube comprising spirally winding finning of substantially flat-rectangular cross-section on a tube shell and simultaneously reinforcing the contact edges of the finning with the tube shell by applying a welding seam at the base of the finning so that the seam connects the finning with the tube shell across the entire width of the finning in the substantial absence of pores within the seam.

7. A spiral-finned tube substantially as shown in the drawing and described herein with reference thereto.

8. A method of making a spiral-finned tube substantially as described herewith with reference to the drawing.