EP0925856B1 - Method for manufacturing an evaporation tube - Google Patents

Description

The invention relates to a method for producing a Heat exchange tube, especially for the evaporation of liquids from pure substances or mixtures on the outside of the pipe, according to the preamble of claim 1 (see e.g. DE-A-28 08 080).

The invention thus relates to a method for producing channel-like structures on the outside of pipes with Ribs formed on the outside from the tube wall. These structures serve to intensify the heat transfer during evaporation of liquids from pure substances and mixtures the outside of the pipe.

Evaporation occurs in many areas of refrigeration and air conditioning technology as well as in process and energy technology. In the Tube heat exchangers are often used in technology which liquids of pure substances or mixtures on the Vaporizing the outside of the pipe and doing so on the inside of the pipe cool the flowing medium. Such devices are considered flooded Called evaporator.

By intensifying the heat transfer on the outside of the pipe and the inside of the tube can be the size of the evaporator greatly reduce. This will increase the manufacturing costs of such apparatus. In addition, the necessary one drops Filling quantity of refrigerant, which is mainly used today chlorine-free safety refrigerants don't negligible share of the total plant costs can make out. With toxic or flammable refrigerants the risk potential can be reduced by reducing the filling quantity decrease. The usual pipes with channel-like Structures on the outside of the pipe are about a factor of three more powerful than smooth pipes of the same diameter.

State of the art:

The present invention relates to a method for Manufacture of tubes with a textured outside, whereby the structure to enlarge the outer surface and the Heat transfer coefficients in the evaporation of liquids serves on the outside of the pipe. To increase the heat transfer coefficient the process of evaporation of bubble boiling intensified. It is known that education from bubbles to germ sites. These are germs mostly small gas or vapor inclusions on the surface. When the growing bubble has reached a certain size, it comes off the surface. If in the course of the bladder detachment the germ site is flooded with flowing liquid will, may the inclusion of gas or vapor by liquid repressed. In this case the germ site is inactivated. This can be done by a suitable design of the Avoid germination. For this it is necessary that the opening the germ site is smaller than the cavity underneath, such as. with undercut structures.

It is state of the art to base such structures of integrally rolled finned tubes where the fins are formed from the tube wall by rolling. Under integrally rolled finned tubes are understood to be finned tubes, where the ribs are made of a wall material Smooth tube were formed. For the use of such finned tubes it is in many cases in shell and tube heat exchangers necessary that the outer diameter of the tube in the finned Area is not larger than the outside diameter of the non-ribbed End and intermediate pieces of the pipe.

Various methods are known with which the between adjacent ribs are closed in such a way that connections between channels and environment in the form remain from pores or slits. Through this, the transport of liquid and steam. In particular, be such essentially closed channels by bending or Folding the ribs (US-PS 3,696,861, US-PS 5,054,548) by Splitting and compressing the ribs (DE-PS 2,758,526, US-PS 4,577,381), by notching and complete compression of the ribs (US-PS 4,660,630, EP-PS 0.713.072) or by notches and unilaterally offset upsetting of the ribs (US Pat. No. 4,216,826).

It is to further increase the heat transfer performance necessary, the outer tube surface and number of channels by increasing the number of fins per tube length. To at small rib spacing at the same time a structure with high Porosity (= relative volumetric void fraction of the channels) to produce, a reduction in the rib thickness is required. As a result, the above-mentioned processes reach their limits the manufacturing stability:

With decreasing distances between adjacent ribs the tools for folding or bending the rib (US-PS 3,696,861, US-PS 5,054,548) are always designed to be more delicate. Due to unavoidable, within technical tolerance limits lying fluctuations in the dimensions of the Smooth pipe (e.g. in the wall thickness) step along the pipe Changes in the forces acting in the finning process on when processing the rib asymmetrically (bending or folding) undesirable irregularities in the slot width or lead in the pore pattern. With a finer structure these irregularities are becoming increasingly serious.

With thin ribs, there is a central splitting of the rib, as in DE-PS 2,758,526 and US-PS 4,577,381 is proposed, no longer economically feasible under manufacturing conditions.

Experience shows that thin ribs during the upsetting process bend or collapse if the process as in the US-PS 4,660,630 and EP-PS 0.713.072 described becomes). It cannot create a high porosity structure become.

When staggered upsetting according to US Pat. No. 4,216,826, incline thin ribs to dodge to one side. So that is this process is extremely difficult to control with thin ribs and therefore unsuitable for large series production.

The invention has for its object that between neighboring Ribs of an integrally rolled finned tube Channels with material from the top of the Ribs to close essentially, the closing of the channels take place with the least possible material expenditure should. The thinner the covers of the channels, the smaller are weight and therefore material costs of the pipe. For transportation of liquid and vapor between the channel and the environment have pore-like or slit-like openings in the lids of the Channels are formed. At the same time, the goal is on the To create a structure with high porosity on the outside of the tube. A high porosity leads to a large specific Contact area between the pipe and the surrounding medium and increased thus the active heat transfer surface for the evaporation process. This gain in space helps to increase the effective heat transfer coefficients related to the envelope surface at. The structure is also said to be of high uniformity Pore size or slot width along the tube axis exhibit. To ensure that the pipe can be easily inserted into the To ensure the tube sheet of a tube bundle heat exchanger, without changing the structure, the outside of the Pipe should be as smooth as possible.

The object is achieved in that the projections after the first upsetting step the first part of the Form manhole cover and that at least one further upsetting step carried out by means of a gearwheel-like swaging disk is so that the manhole cover is gradually joined together is formed by cantilevers.

The material of the rib is used for sectioned upsetting within limited, defined by the swage plate Areas from the upper region of the rib on both sides in the axial direction repressed. The displaced material forms over the Channel cantilevers that are used to cover a lid to form. After the first processing step, the lid is only in the areas to the side of the machined sections of the Rib tip formed. In the subsequent processing steps are not compressed in the first compression step Sections of the rib tip partially or completely compressed expanding the covered areas of the canal. Last can the outer surface of the tube through a smoothing disc constant diameter can be smoothed.

With a finer external structure, i.e. with thinning ones Ribs, the reduction in the stability of the rib represents increasing the greatest difficulty of the task Rib sags while deforming the entire upper one Rib area under the pressure load from the tool in instead of forming a lid over the canal. It it is cheaper to split the deformation into partial steps. DE-PS 2,808,080 already points to this. In the above Property right is suggested, not the entire rib in to deform in one operation, but the tool for Arrange the deformation so that only one side of the rib a working step is deformed (see Fig. 2 of DE-PS 2808080). With this procedure, however, the rib becomes like this deformed to thicken the upper areas of the rib, as shown in Fig. 17 of DE-PS 2,808,080. It will so no thin covers formed over the channel and the the desired high porosity cannot be achieved.

It is also proposed in DE-PS 2,808,080, the ribs through to deform a single, suitable tool like a gear, so that after further machining steps grooves in the axial direction of the tube are formed. That with the gear-like Deformation of displaced material does not serve to cover to form over the channels between the ribs.

Further advantageous variants of the method according to the invention are the subject of claims 2 to 11.

With a suitable tool design, in particular the first upsetting step produced cantilevers up to the middle of the Project channel so that cantilevers from adjacent ribs meet and form a bridge over the canal. Due to increasing material solidification, they are sufficient Overhangs formed in the subsequent upsetting steps become less far across the channel. In this way it is possible to create a surface structure in which the channels are connected to the environment via pores. Hit the cantilevers after the first machining step not together, one arises in the following steps Surface structure with slit-like openings.

Fig. 1

eine Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens,

Fig. 2

schematisch zwei Stauchscheiben mit schräg zur Scheibenachse verlaufenden Zähnen,

Fig. 3a - 3c

schematisch die Durchführung der einzelnen Stauchschritte,

Fig. 4a - 4c

eine Draufsicht auf die Rohroberfläche bei beabstandeten Auskragungen und

Fig. 5a - 5c

eine Draufsicht auf die Rohroberfläche bei sich berührenden Auskragungen.

The invention is explained in more detail using the following exemplary embodiments. It shows:

Fig. 1

a device for carrying out the method according to the invention,

Fig. 2

schematically two upsetting disks with teeth running obliquely to the disk axis,

3a-3c

schematically the implementation of the individual upsetting steps,

4a-4c

a plan view of the pipe surface with spaced projections and

5a-5c

a plan view of the pipe surface in contact with projections.

The production of an integrally rolled finned tube 1 with spiraling on the outside of the pipe Ribs 2 of the rib pitch t, forming channels 3 with duct cover 3a are deformed by a Rolling process (cf. US-PS 1,865,575 and US-PS 3,327,512) by means of the device shown in Fig. 1.

A device is used which consists of n = 3 tool holders 4, in each of which a rolling tool 5 and two gear-type compression disks 6/7 and a smoothing disk 8 of constant diameter are integrated (only one tool holder 4 is shown in FIG. 1 but for example four or more tool holders 4 are used). The tool holder 4 are each offset by α = 360 ° / n on the circumference of the finned tube. The tool holder 4 can be adjusted radially. They are in turn arranged in a stationary roller head (not shown) (according to another variant, the tube is only advanced axially when the roller head is rotating).
The smooth pipe 1 ′ entering the device in the direction of the arrow is set in rotation by the driven rolling tools 5 arranged on the circumference, the axes of the rolling tools 5 running obliquely to the pipe axis in order to be able to produce helical ribs 2. The rolling tools 5 consist, in a manner known per se, of a plurality of rolling disks 9 arranged side by side, the diameter of which increases in the direction of the arrow. The centrally arranged rolling tools 5 form the helically surrounding ribs 2 from the tube wall of the smooth tube 1 ', the tube wall in the forming area under the roller tools 5 being supported here by a profiled rolling mandrel 10. This results in ribs 11 running around the inside of the tube 1 in a helical manner.

After shaping the ribs 2 with the rib height H be partially open channels 3 through the following three upsetting steps generated:

In a first upsetting step, the ribs 2 are covered by the Teeth 6a of a first upsetting disk 6 in sections on the circumference compressed by the radial compression depth X (see Fig. 3a / 4a / 5a), the outer diameter of the first compression washer 6 smaller than the diameter of the last roller 9. Overhangs 12a are formed.

In a second compression step, those that have not yet been compressed are removed Sections 15a of the ribs 2 through the teeth 7a of the second compression plate 7 partially deformed (see Fig. 3b / 4b / 5b), the radial compression depth Y being at least as large is like the radial compression depth X in the first compression step. There are further overhangs 12b, and the cover 3a of the Channel 3 is enlarged.

The upsetting disks 6, 7 preferably have 10 to 30 teeth 6a, 7a per cm circumference, in particular 14 to 25 teeth 6a, 7a per cm circumference. The teeth 6a, 7a run parallel or obliquely at the angle α or β (as shown in Fig. 2) to the respective disc axis.

Finally, the pipe surface is smoothed by a smoothing disc 8, which after the second upsetting step not yet upset portions 15b of the ribs 2 smoothed and the final pores 13 or slot 14 train through which the channels 3 in connection with the environment stand. After the smoothing process, the outside of the Tube 16 no more surveys, as in Fig. 3c / 4c / 5c is shown.

4a / 4b / 4c show the case that the overhangs Do not touch 12a / 12b of adjacent ribs 2, i.e. a slot 14 of width B 'remains between them. This slot width B 'can be up to 20% of the open channel width B.

5a / 5b / 5c finally relate to the case where the Touch projections 12a of adjacent ribs 2.

Numerical example:

A smooth copper tube 1 'is made by a rolling process helical circumferential ribs 2 are formed, wherein the rib pitch is t = 0.41 mm. In the next processing step the rib tip is through the first compression washer 6 with diameter D = 35.0 mm compressed in sections.

Arranged evenly on the circumference of the upsetting disk 6 255 teeth 6a run at an angle α of 40 ° diagonally to the disc axis. The second upsetting disk 7 has the same diameter D as the first upsetting disk 6 and the same number Z of teeth 7a. The teeth 7a of the second Swage plate 7 also run obliquely to the plate axis, however, their orientation is the orientation of the teeth 6a first upsetting disk 6 opposite, so that the prints of teeth 6a and 7a cross on the tube (see Fig. 1 / 4b / 5b). To get a regular picture on the pipe surface too must generate the angle β that the teeth 7a with the disc axis include, calculated using the following formula: β = arctan (π. D / (Z. t) - tan α). In the present case results β to 12.0 °.

Advantages of the manufacturing process:

With the manufacturing process mentioned, heat exchanger tubes can with a highly porous surface structure become. In the present case, an evaporator tube was used such a surface based on integrally rolled Ribs with a thickness of the order of 0.1 mm. Despite the small rib thickness, the channels were successful between the ribs with thin lids emerging from the top Area of the rib were shaped to essentially occlude without the ribs buckling to the side or in itself slumped together.

It also proves advantageous that with the proposed Manufacturing process pore shape and pore size by the relative arrangement of the two upsetting disks 6 and 7 to each other can be changed in a targeted manner. So it is possible the structure of the pipe surface the operating conditions (used Medium, pressure, power density, etc.) optimal adapt.

Claims (12)

1. Method for the manufacture of a heat exchange pipe (1), in particular for evaporation of fluids comprising pure substances or mixtures on the pipe exterior, having integral ribs (2), that is, ribs shaped from the pipe wall, running round helically on the pipe exterior, which are deformed to form channels (3) located between the ribs (2), in which method the following process steps are carried out:

   a) on the exterior of a plain pipe (1'), helically extending ribs (2) are formed by obtaining the material for the ribs through displacement of the material from the pipe wall by means of a rolling operation and the resulting ribbed pipe (1) is caused to rotate by the rolling forces and/or is advanced corresponding to the helical ribs (2) being formed, the ribs (2) being shaped with an increasing height from the otherwise undeformed plain pipe (1'),

   b) the pipe wall is supported in the deformation region by a rolling mandrel (10) lying in the pipe,

   c) after being shaped, the ribs (2) are subjected to a compression operation to create partially open channels (3) lying between them, the ribs (2) being compressed in a first compression step circumferentially in sections by means of a toothed wheel-like compression disc (6), the outer diameter of which is smaller than the diameter of the last rolling disc, by the radial compression depth X, so that rib material is displaced on either side axially to form projections (12a),

      characterised in that

   after the first compression step, the projections (12a) form the first part of the channel cover (3a) and

   at least one further compression step is carried out using a toothed wheel-like compression disc (7), wherein the as yet uncompressed portions of the ribs are partly or completely compressed, so that the channel cover (3a) is formed progressively by abutting of projections (12a, 12b).
2. Method according to claim 1, characterised in that the radial compression depth Y in the second compression step is at least the same magnitude as the radial compression depth X in the first compression step.
3. Method according to claim 1 or 2, characterised in that, as further and last compression step, continuous smoothing of the pipe (1) by means of a smoothing wheel (8) of constant diameter is carried out.
4. Method according to one or more of claims 1 to 3, characterised in that the radial compression depth X in the first compression step is from 10 to 50% of the rib height H.
5. Method according to one or more of claims 1 to 4, characterised in that the ribs (2) are so compressed in the first compression step that between the projections (12a) of adjacent ribs (2) there remains a slot (14) of width B'.
6. Method according to claim 5, characterised in that the slot width B' amounts to up to 20% of the open channel width B.
7. Method according to one or more of claims 1 to 4, characterised in that the ribs (2) are so compressed in the first compression step that the projections (12a) of adjacent ribs (2) touch each other.
8. Method according to one or more of claims 1 to 7, characterised in that a compression disc (6, 7) having from 10 to 30 teeth (6a, 7a) per cm of compression disc circumference is used.
9. Method according to claim 8, characterised in that a compression disc (6, 7) having from 14 to 25 teeth (6a, 7a) per cm of compression disc circumference is used.
10. Method according to claim 8 or 9, characterised in that the teeth (6a, 7a) of the compression discs (6, 7) used run parallel to the disc axis.
11. Method according to claim 8 or 9, characterised in that the teeth (6a, 7a) of the compression discs (6, 7) used run obliquely at an angle α and at an angle β respectively to the disc axis.
12. Method according to claim 11, characterised in that, when using compression discs (6, 7) of the same diameter D and the same number Z of teeth (6a, 7a), the angles α and β are matched to one another according to the following formula: β = arctan (π . D/(Z . t)- tan α) t being the pitch of the ribs (2).

Images