EP0609189A1 - Finned tubes and relevant manufacturing method - Google Patents

Abstract

The fin tube consists of a tube (2) having plane surfaces and provided with fins (11) on the outside which are in the form of corrugated metal plates having external generatrices (7) and internal generatrices (8), as well as two edges located at the ends of the generatrices of the fins, and is characterised in that at least one of the edges (12) of the corrugated metal sheets is bevelled with respect to the plane of the said plane surfaces. <IMAGE>

Description

The present invention relates to finned tubes and, more particularly, to heat exchangers between two fluids without direct contact between these fluids, consisting of galvanized finned tubes, the fluid inside the tubes being either a liquid or a condensing gas. , in particular saturated water vapor, the fluid external to the tubes being a gas, in particular atmospheric air.

The invention also relates to the method of manufacturing these finned tubes.

The finned tubes considered here are made of galvanized steel and have an elongated section whose two opposite long sides have rectilinear surfaces. These tubes are normally straight, that is to say not curved, therefore having two opposite planar faces; these tubes are said to be flat. These flat faces are externally provided with sinuous fins constituted by corrugated thin sheets. There is one corrugated sheet per tube face. A fin tube can be formed by welding two profiled sheets provided with sinuous fins. Corrugated sheets can also be welded directly to a flat tube. After the finned tube has been produced, or even after the batteries have been formed, the assembly is galvanized by immersion in a hot-dip galvanizing bath.

The concept of heat exchanger where the winding fins are applied to flat tubes is already mentioned in US Pat. No. 2,063,757 to General Motors of December 29 1934. It is the heat exchanger which conventionally constitutes the radiators of motor vehicles.

Since then many patents relate to such types of exchangers. Each fin can extend over several flat tubes, as represented in FIG. 4 of patent EP-B 325 844 of Modine or on a single tube, as represented in FIG. 6 of the same patent.

In this patent, each fin is applied between two tubes, the valleys of the corrugation of the fin being connected to one tube, while the vertices of the corrugation are connected to the other tube. But there are also exchangers where each tube has its own fins, one on each side. This is the case of the heat exchanger described in US Pat. No. 4,256,177 to Modine.

FIG. 2 of this patent represents a fin tube typical of the known art to which our invention relates.

A very common industrial material is galvanized steel, which is inexpensive and relatively resistant to atmospheric corrosion.

The galvanization of flat tubes with sinuous fins poses a problem due to the retention by capillarity of too large quantities of zinc at the lower edge of the fins, when the tubes are removed from the galvanizing bath.

The tubes are removed in a horizontal position from the galvanizing baths, the walls of the fins being arranged vertically (vertical air channels in the fins). When a fin leaves the surface of the zinc bath, a strip of zinc (burr) remains attached to its lower edge, by capillary action, surface tension, or even a veil of zinc can block the lights between fins and tubes.

These zinc beads obstruct the passage of air in the channels of the fins and greatly increase the air pressure losses.

As for leveling the lower edge of the fins to remove the zinc burrs, it is a very expensive job. As for electrogalvanizing, it gives zinc thicknesses that are much too small, on the order of a micron, while we are looking for a thickness of at least 60 microns. It is the same with previously zinc-coated sheets, such as sheets of the Zenzimir process where the thickness of zinc can only reach a few tens of microns, less than 60 microns.

In addition, these zinc-coating processes do not allow the fins at the feet, that is to say at the contact between the sinuous sheet and the face of the tube, the right amount of zinc that gives full hot-dip galvanization. bath, with its zinc retention in the very acute angles formed between the sinuous sheet and the face of the tubes, ensuring excellent heat transfer (thermal bridge).

There are two known means for reducing, or even practically eliminating, the zinc beads at the ends of the fins.

One process consists in raising the temperature of the zinc bath by a hundred degrees and thus galvanizing around 550 ° C instead of 450 ° C. Zinc is much more fluid, less viscous, more wetting. Its viscosity and surface tension are lower. The zinc thicknesses are more regular, and in particular the zinc thicknesses at the lower edges of the parts at the outlet of the baths are negligible. But such installations are much more costly in investment; in fact, the tanks can no longer be made of steel, but must be made of ceramic. Energy consumption is also much higher, due to the significantly higher heat loss at 550 ° C than at 450 ° C.

Such installations are rarer throughout the world, or even nonexistent in less developed countries, where it can be interesting to manufacture the finned tubes, with machines easily transportable in these countries, and where it would be necessary to finish the work with a galvanization to be done in the vicinity of the place where the manufacturing was carried out. Finally, a higher temperature increasing the fluidity of the zinc gives a smaller thickness of zinc at a lower temperature, of the order of 40 to 50 microns instead of 60 to 70 microns commonly obtained at 450 ° C.

The other method giving less zinc burrs consists in adding more additives, in particular aluminum or lead, to the zinc in order to reduce its viscosity. As with high-temperature galvanizing, this results in a reduced thickness of zinc on the galvanized part. The process is also more expensive (cost of additives), and the conduct of galvanization (bath control) more difficult.

The object of the invention is to allow hot-dip galvanizing of flat tubes with sinuous fins, free of zinc beads or burrs at the lower edges of the fins (in the position for withdrawing from the galvanizing bath), in standard (conventional) baths of hot-dip galvanizing, that is to say in baths at 445 to 460 ° C, without special additives, baths as they are commonly found throughout the world.

The galvanization of flat tubes with sinuous fins according to the invention does not require either special galvanizing baths or special galvanizing techniques. To this end, a galvanized fin tube according to the invention consists of a tube having flat surfaces and provided externally with fins, in the form of thin corrugated sheets having external generators and internal generators as well as two edges, one upper and lower, located at the ends of the generatrices of the fins, of which at least one of the two, the lower edge, is bevelled at an angle α relative to the longitudinal plane of the plane faces of the tube.

The invention therefore consists in bevelling one of the ends of the sinuous fins and in constituting each finned tube so that the fins of the tubes have all their beveled parts on the same side, which is the lower side during galvanization.

Similarly, if the galvanization takes place by battery of flat tubes with sinuous fins, rather than tube by tube, all the tubes of the same battery are arranged so that they present the bevelled part of their fins on the same side, which will be the bottom side during galvanization.

• la figure 1 représente une vue en perspective d'un tube plat à ailettes sinueuses selon l'art connu;
• la figure la est une vue de dessous, illustrant les sections de passage d'air entre les ailettes selon la figure 1 après galvanisation;
• la figure 2 représente une vue en perspective d'un tube plat à ailettes sinueuses galvanisé selon l'invention;
• la figure 2a est une vue de dessous, illustrant les sections de passage d'air entre les ailettes galvanisées selon la figure 2;
• la figure 3 représente une coupe transversale dans le tube d'échange de chaleur à ailettes sinueuses selon l'invention;
• la figure 3a est une vue en coupe selon la ligne AA dans la figure 3;
• la figure 4 représente le profil de l'arête de découpe de l'outil (poinçon) de biseautage de la tôle plane des ailettes non encore ondulée.

An exemplary embodiment of the invention will be described below with reference to the accompanying drawings in which:

• Figure 1 shows a perspective view of a flat tube with sinuous fins according to the known art;
• Figure la is a bottom view, illustrating the air passage sections between the fins according to Figure 1 after galvanization;
• Figure 2 shows a perspective view of a flat tube with sinuous fins galvanized according to the invention;
• Figure 2a is a bottom view illustrating the air passage sections between the galvanized fins according to Figure 2;
• FIG. 3 represents a cross section in the heat exchange tube with sinuous fins according to the invention;
• Figure 3a is a sectional view along line AA in Figure 3;
• Figure 4 shows the profile of the cutting edge of the tool (punch) for bevelling the flat sheet of the fins not yet wavy.

In Figure 1 there is shown an assembly of a fin tube 1 according to the known technique. The flat tube is composed of two profiled sheets 2 constituting the half-tubes connected to the ends 4 by welding over the entire length of the tube ensuring sealing. The flat section of a half-tube 2 is provided with a corrugated sheet forming the sinuous fins 3 with external generators 7 and internal generators 8. These fins 3 are welded on the outside and plane side of the half-tube 2 by their generatrix internal 8. During galvanizing, this assembly 1 is immersed and removed in a position as shown in FIG. 3, that is to say the flat tube 2, in a horizontal position, and the fins 3 with the generators 7 and 8, in a vertical position.

FIG. 1a, representing a front view of the lower side of the fins 3, shows the formation of zinc beads 6 after solidification, leaving only a heavily obstructed passage 9, or even completely blocked for cooling air. These zinc beads 6 result from hot-dip galvanizing in a normal bath, that is to say at a temperature of 445 to 460 ° C., without additives.

FIG. 2 shows an assembly 10 produced according to the invention with a flat tube 2 consisting of two welded half-tubes, one outer side of which is provided with sinuous fins 11. According to the invention, one of the edges of these fins 11 has a bevelled part 12 on the same side, which is the lower side during galvanizing.

The angle α of the bevel is such that the zinc flows along the inclined edge 12 without further forming beads or burrs there. The only place where a zinc retention could appear is the lower point 13 of the undulations of the fin in contact with the tube, which does not in any way obstruct the passage of air, because this extra thickness is very local, punctual , and because the bevel clearly enlarges the orifices of the air channels between sinuous fins and tubes.

In addition, the zinc beads 5 situated at the foot of the fins, along the internal generatrices 8, resulting from the galvanization produce a very favorable thermal bridge between the tube 2 and its fins 11.

Preferably the bevel is presented, seen in section, transversely to the tubes, in rectilinear form with an angle α of 30 ° between the bevelled edge seen in section and the face of the tube (see FIG. 3). This angle α, preferably constant, can be between 15 and 60 °. But this angle can also vary along the bevel.

In FIG. 3, the position of the assembly of the finned tube 10 according to the invention has been shown, before immersion in a bath 14 filled with zinc 15 at a temperature of approximately 450 ° C.

The invention also covers a method of manufacturing finned tube 10 according to the invention and more particularly the production of beveled fins.

As shown in Figure 4, the bevels 12 are produced by cutting 16 in the sheet 17 of the fins before the shaping (corrugation) of this sheet, that is to say by cutting the strip flat. The cutting tool has a cutting edge with a sinuous profile. The profile of the cutting edge 16 must judiciously correspond to the profile of the corrugations of the fins so that the bevel is in cross section in rectilinear form. In particular, the cut is triangular if the profile of the fins is triangular. It is sinusoidal if it is sinusoidal. Otherwise, the bevelled edge of the fins seen in cross section is curved, even wavy, which is however acceptable and meets the aims of the invention provided that the angles between the local tangents to the sinuous beveled edge and the face of the tube are sharp enough to allow easy flow of zinc.

• · en ce qui concerne les ailettes:
  • a) découpe sinueuse à plat d'un côté du feuillard 17 constituant les ailettes, destinée à former le futur biseau;
  • b) ondulation du feuillard, en correspondance (synchronisme) avec la sinuosité de la découpe 16 précédente du biseau 12.
• · en ce qui concerne le tube:
  • découpe et mise en forme des tôles des demi-tubes 2;
  • soudage des ailettes 11 sur le côté extérieur des demi-tubes 2;
  • assemblage par soudage en 4 des demi-tubes 2 pour constituer les tubes entiers à ailettes 10;
  • assemblage des ensembles de tubes à ailettes en batteries;
  • galvanisation des batteries de tubes à ailettes, les génératrices des ailettes ondulées étant disposées verticalement, biseaux 12 situés en bas, comme représenté à la figure 3.

All the manufacturing operations for galvanized batteries of flat tubes with sinuous fins normally take place according to the following process:

• · With regard to the fins:
  • a) sinuous cut flat on one side of the strip 17 constituting the fins, intended to form the future bevel;
  • b) undulation of the strip, in correspondence (synchronism) with the sinuosity of the previous cut 16 of the bevel 12.
• · With regard to the tube:
  • cutting and shaping of the sheets of the half-tubes 2;
  • welding of the fins 11 on the outside of the half-tubes 2;
  • assembly by welding in 4 of the half-tubes 2 to constitute the whole finned tubes 10;
  • assembling sets of finned tubes into batteries;
  • galvanizing the batteries of finned tubes, the generators of the corrugated fins being arranged vertically, bevels 12 located at the bottom, as shown in FIG. 3.

Another advantage of the bevelling of the fins is the possibility of dip painting of the galvanized batteries of flat tubes with sinuous fins, without formation of paint beads at the lower edges (in the position of withdrawal of the paint bath) of the fins.

Claims (9)

Finned tube consisting of a tube (2) having flat surfaces and externally provided with fins (11), in the form of corrugated sheets having external generators (7) and internal generators (8) as well as two edges located at the ends of the generatrices of the fins, characterized in that at least one of the edges (12) of the corrugated sheets is bevelled relative to the plane of said plane surfaces. Finned tube according to claim 1, characterized in that the fins of the tube have all their bevelled edges (12) on the same side, which is the lower side during an immersion treatment operation (in a liquid or pasty product) . Finned tube according to claim 1 or 2, characterized in that the bevelled edge (12) is presented, seen in section, transversely to the tube in rectilinear form with a constant angle (α) between 15 and 60 ° between the bevelled edge seen in section and the flat face of the tube (2). Finned tube according to claim 3, characterized in that the bevel (12) has an angle (α) of 30 °. Finned tube according to claim 1 or 2, characterized in that the bevelled edge (12) is presented, seen in section, transversely to the tube in curvilinear form, the angles between the local tangents to the beveled edge seen in section and the flat face of the tube being between 15 and 60 °. Method of manufacturing a finned tube according to claims 1 to 5, characterized by the following steps: - sinuous cut flat on one side of the strip constituting the fins; - corrugation of the strip in correspondence with the sinuous cut; - cutting and shaping of the sheets constituting the half-tubes; - welding of the corrugated sheet fins on the outside of the half-tubes; - assembly by welding of the half-tubes to constitute an entire tube with fins. A method according to claim 6, characterized by the additional step of assembling sets of finned tubes into batteries. Method according to claim 6 or 7 for the manufacture of finned tubes, characterized in that a complete immersion of the set of finned tubes is carried out in a bath of liquid or pasty products, the external and internal generators of the corrugated sheets being arranged vertically with the beveled edge down. Method according to claim 6 or 7 for the manufacture of galvanized fin tubes, characterized in that a complete immersion of all the fin tubes is carried out in a zinc bath at a temperature between 445 and 460 ° C, without adding more additives, the external and internal generators of the corrugated sheets being arranged vertically with the bevelled edge downwards.

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