EP0607839B1 - Heat exchange tube, process for making and use of such a tube - Google Patents

Description

The invention relates to a heat exchange tube according to the preamble of claim 1. Such a tube is known, for example, from EP-A-0 495 453. The invention also relates to a method for producing and using such a tube. The heat exchange tube is, for example, a heat exchange tube for spray evaporation in a tube bundle heat exchanger (see FIG. 1). In spray evaporators, the medium to be evaporated is applied or sprayed onto the pipes in the jacket space. The advantage is that the free volume between the tubes does not have to be filled with liquid. In this way, the filling quantity of such apparatus can be minimized. The type of spraying must ensure that the pipes are always adequately covered with liquid. In order to meet this requirement, these systems are operated with a liquid overflow which is up to a factor of 10 higher than the amount of liquid required for the evaporation process. However, the heat transfer coefficient of the evaporation is considerably reduced by the excess liquid. To compensate for this reduction, the tube bundle heat exchanger must be oversized. For the circulation of the quantities of liquid which are necessary for evaporation and for the liquid overflow, the pump must be chosen to be large enough. This requires a high energy consumption of the pump, which is about a factor of 2 above the energy consumption than if only the amount of liquid required for evaporation has to be pumped.

Tubes are known from the area of absorption heat pumps, which have V-shaped grooves on the outer side to improve the distribution of the liquid in the axial direction of the tube. Such tubes have been developed for use in expellers (brochure "F-tube" from Furukawa Electric Co., Ltd.).

The invention has for its object to design a heat exchange tube of the type mentioned so that in addition to good distribution of the liquid on the surface, good evaporation properties are guaranteed at the same time.

The object is achieved by the features of claim 1.

It was found that with the described embodiment of the surface a complete wetting of the surface can be achieved even with very small amounts of liquid. In conjunction with the significantly improved evaporation properties, the number of tubes used and the amount of liquid required in the circuit can be minimized, especially in shell-and-tube heat exchangers. Another advantage is that the overall system, in which the shell-and-tube heat exchanger is integrated, can be made smaller and more compact.

According to a special embodiment of the invention, the distribution channels run parallel to one another, in particular two groups of parallel distribution channels intersect at an angle β.

According to alternative embodiments, the distribution channels are spaced apart from one another — preferably the spacing is a 3 3 × t — or adjoin one another directly.

The distribution channels are preferably substantially V-shaped, the depth T = 0.3 to 1.5 mm and the Opening angle α = 30 to 90 °. (The depth T is measured from the top edge of the channel walls.)

The distribution channels have the task of distributing liquid that is dripped or sprayed on the outer surface and supplying it to the channels underneath. For this purpose, the distribution channels can have corresponding openings in addition to the overflows. The shape of the openings can vary. So the openings can be hole-like, i.e. the flanks of the channels are pierced, while the ridges and the bottom of the channels pass through. On the other hand, the openings can be slit-like, i.e. the ridges run through and the bottom of the channel is broken, or conversely the ridges are broken and the bottom of the channel is continuous. For certain applications, the simultaneous arrangement of different types of openings on a heat exchange tube can be advantageous.

It is crucial that the dimensions of the openings are chosen so that only a part of the liquid leaves the channel at each opening, but the majority is passed along the channel. The driving forces for the liquid distribution are the inertial forces, the capillary forces and (in the case of inclined or vertically oriented surfaces) gravity. With the crossed version, the liquid is redistributed at each crossing point, so that the distribution effect is considerably better than with the parallel channels.

Teilung t =

0,40 bis 1,5 mm,

Höhe h =

0,5 x t bis 2 x t,

Kanalwanddicke s =

0,2 x t bis 0,8 x t.

It is recommended that the parallel channels have the following dimensions:

Division t =

0.40 to 1.5 mm,

Height h =

0.5 xt to 2 xt,

Channel wall thickness s =

0.2 xt to 0.8 x t.

The channels and distribution channels run helically, in particular the distribution channels run at an angle of inclination γ to the pipe longitudinal axis, 0 ° <γ ≤60 ° and 120 ° ≤ γ <180 °. In particular to further improve the evaporation properties, the inner surface of the heat exchange tube is structured or finned.

It is proposed to produce the pipe according to the invention by the following methods:

According to a first proposal, helical circumferential channels are first produced in that the material of the channel walls is obtained by displacing material out of the tube wall of a smooth tube to the outside by means of a rolling process (cf. the usual rolling method for producing finned tubes, for example according to US Pat. No. 3,327,512) , and then the distribution channels are produced by pressing in the channel walls by means of a rolling process with appropriately shaped toothed disks, pressure rollers or the like (cf. for example DE-OS 1.501.656).

According to a second proposal, first helically circumferential channels in the tube wall of a smooth tube are produced by a drawing process with a stationary or rotating drawing die, and then the distribution channels are produced by pressing the channel walls in with a rolling process with appropriately shaped toothed disks, spinning rollers or the like.

According to a third proposal, spiral channels are first produced in that the material of the channel walls is obtained by displacing material from the tube wall of a smooth tube to the outside by means of a rolling process and the distribution channels are then produced by a drawing process with a stationary or rotating drawing die.

According to a fourth proposal, helical circumferential channels are first produced in the tube wall of a smooth tube by a drawing process with a stationary or rotating drawing die, and then the distribution channels are produced by a drawing process with a stationary or rotating drawing die.

The heat exchange tube according to the invention is preferably used for spray evaporation in a tube-bundle heat exchanger with horizontally or inclined heat exchange tubes.

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

• Fig. 2 ein erstes erfindungsgemäßes Wärmeaustauschrohr mit parallel verlaufenden Verteilungsrinnen,
• Fig. 3 eine weitere Ausführungsform eines erfindungsgemäßen Wärmeaustauschrohr mit parallelen Verteilungsrinnen,
• Fig. 4 ein erfindungsgemäßes Wärmeaustauschrohr mit zwei sich kreuzenden Verteilungsrinnen,
• Fig. 5 schematisch die Oberflächenbeschaffenheit eines erfindungsgemäßen Wärmeaustauschrohres mit sich kreuzenden Verteilungsrinnen,
• Fig. 6 unterschiedliche Ausführungsformen der Öffnungen in den Flanken der Verteilungsrinnen, und
• Fig. 7 schematisch ein Wärmeaustauschrohr mit schraubenlinienförmig umlaufenden Kanälen und Verteilungsrinnen.

It shows

• 2 shows a first heat exchange tube according to the invention with parallel distribution channels,
• 3 shows a further embodiment of a heat exchange tube according to the invention with parallel distribution channels,
• 4 shows a heat exchange tube according to the invention with two intersecting distribution channels,
• 5 schematically shows the surface condition of a heat exchange tube according to the invention with intersecting distribution channels,
• Fig. 6 different embodiments of the openings in the flanks of the distribution channels, and
• Fig. 7 schematically shows a heat exchange tube with helically circumferential channels and distribution channels.

A metallic heat exchange tube 1 according to FIGS. 2 to 4 has a first medium 2 on one side and a second medium 3 to be evaporated on the other side. On this other side, the tube 1 has channels 4 (with channel walls 5) which are parallel to one another and whose dimensions of pitch t, height h and wall thickness s are also entered. The channels 4 are crossed by distribution channels 6 for the second medium 3, which are formed by laterally displaced material of the channel walls 5. The channels 6 are essentially V-shaped. The depth of the channels 6 calculated from the upper edge of the channel walls 5 is denoted by T, the opening angle of which is denoted by α (here the V-shaped channels 6 are drawn with a tapering channel bottom. Normally, however, the channel bottom will be widened). In order to be able to distribute the dripped or sprayed on second medium 3 into the channels 4, the channels 6 are provided with overflows 7 and / or openings 8. Depending on the deformation of the channel walls 5, the overflows 7 and / or openings 8 are designed differently (cf. in particular FIG. 6).

In the case of FIGS. 2 and 4, only overflows 7 are present, the material of adjacent channel walls 5 that is displaced touches.

In the case of FIG. 3, slot-like openings 8 have formed.

In the case of FIG. 2, the channels 6 are spaced from one another, so that when the second medium 3 evaporates, the steam (see arrow “steam”) can escape through the remaining intermediate spaces 9.

The distance a is calculated between the bottom of adjacent channels 6.

In the case of FIG. 3, in which the channels 6 connect directly to one another, the openings 8 serve at the same time for the liquid to enter and to exit the steam (see arrows "liquid" and "steam").

4 shows the situation schematically with two intersecting channels 6.

5 shows the surface condition of a heat exchange tube 1 according to the invention with intersecting distribution channels 6 (intersection angle β / intersection points K). To simplify the illustration of overflows 7 and openings 8 has been omitted. The remaining gaps 9 for the steam outlet are highlighted.

6 shows various possibilities for the formation of the overflows 7 and openings 8 (cf. view according to section plane A - A through the channel bottom according to FIG. 2). According to Fig. 6a, the openings 8 are hole-like, i.e. the flanks 10 of the channels 6 are pierced, whereby combs 11 and channel bottom 12 each pass through. According to FIG. 6b, the combs 11 run through, but the channel bottom 12 is broken through, in the case of FIG. 6c the reverse is the case.

FIG. 7 schematically shows a heat exchange tube 1 with channels 4 (or channel walls 5) and distribution channels 6 that run helically on the outer surface and distribution channels 6. The angle of inclination of the distribution channels 6 to the pipe longitudinal axis is designated by γ. The distance a between the channel base 12 of adjacent channels 6 is also entered. The channels 6 have been drawn in a simplified manner without overflows 7 or openings 8.

In particular, steel, aluminum and aluminum alloys, copper and copper alloys, stainless steels and titanium come into consideration as materials for the heat exchange tube 1.

In particular, ammonia and safety refrigerants, such as R22, R134a etc., are available as the medium 3 to be evaporated.

Numerical example:

Structured heat exchange tubes 1 were made of steel with the following dimensions: Outside diameter of the pipe D _R = 19 mm Division of channels 4 t = 0.63 mm Channel height 4 h = 1.0 mm Thickness of the channel walls 5 s = 0.25 mm crosswise distribution channels 6 with a pitch angle γ = 30 ° (ie crossing angle β = 120 °) Depth of channels 6 T = 0.5 mm Channel opening angle 6 α = 90 °.

Excellent results were achieved when these heat exchanger tubes 1 were used in a shell-and-tube heat exchanger for the spray evaporation of ammonia.

Claims (20)

1. Heat exchanger tube (1) for transferring heat from a first medium (2) on the inner surface thereof to a second medium (3), which is to be evaporated, on the outer surface thereof, wherein this outer surface is provided with integral aligned distribution troughs (6) for distributing the liquid phase of the second medium (3),
   with the following features:

   a) the distribution troughs (6) intersect channels (4) which lie below them with the spacing (t),

   b) the distribution troughs (6) are formed by laterally displaced material from the channel walls (5), the depth (T) of the distribution troughs (6) being approximately between 30 and 90% of the channel height h,

   c) the distribution troughs (6) communicate with the channels (4) by way of overflows (7) and/or openings (8) in the distribution troughs (6),

   characterised by the following features:

   d) the distribution troughs (6) and the channels (4) run round helically; and

   e) the displaced material from adjacent channel walls (5) touches at least in part.
2. Heat exchanger tube as claimed in Claim 1, characterised in that the distribution troughs (6) extend parallel to one another.
3. Heat exchanger tube as claimed in Claim 2, characterised in that two groups of parallel distribution troughs (6) intersect at an angle β.
4. Heat exchanger tube as claimed in Claim 2 or 3, characterised in that the distribution troughs (6) are spaced from one another.
5. Heat exchanger tube as claimed in Claim 4, characterised in that the distance between the distribution troughs (6) is a ≤ 3 x t.
6. Heat exchanger tube as claimed in Claim 2 or 3, characterised in that the distribution troughs (6) immediately adjoin one another.
7. Heat exchanger tube as claimed in one or more of Claims 1 to 6, characterised in that the distribution troughs (6) are of V-shaped construction, wherein the depth T = 0.3 to 1.5 mm and the aperture angle α = 30 to 90°.
8. Heat exchanger tube as claimed in one or more of Claims 1 to 7, characterised in that the openings (8) are constructed as holes.
9. Heat exchanger tube as claimed in one or more of Claims 1 to 7, characterised in that the openings (8) are constructed as slots.
10. Heat exchanger tube as claimed in Claims 8 or 9, characterised in that different types of openings (8) are disposed simultaneously on a heat exchanger tube (1).
11. Heat exchanger tube as claimed in one or more of Claims 1 to 10, characterised in that the parallel channels (4) have the following dimensions: spacing t = 0.40 to 1.5 mm, height h = 0.5 x t to 2 x t, channel wall thickness s = 0.2 x t to 0.8 x t.
12. Heat exchanger tube as claimed in one or more of Claims 1 to 11, characterised in that the distribution troughs (6) extend at an angle of elevation γ to the longitudinal axis of the tube, wherein 0° < γ ≤ 60° or 120° ≤ γ < 180°.
13. Heat exchanger tube as claimed in one or more of Claims 1 to 12, characterised in that the inner surface of the heat exchanger tube is structured or ribbed.
14. Method of producing a heat exchanger tube as claimed in one or more of Claims 1 to 13, characterised in that first of all channels (4) which run round helically are formed, the material for the channel walls (5) being obtained by displacing material outwards from the tube wall of a smooth tube by means of a rolling operation, and that the distribution troughs (6) are then produced by impressing the channel walls (5) by a rolling operation with correspondingly shaped toothed discs, pressure rollers or the like.
15. Method of producing a heat exchanger tube as claimed in one or more of Claims 1 to 13, characterised in that first of all channels (4) which run round helically are produced in the tube wall of a smooth tube by a drawing operation with a stationary or rotating drawing die and then the distribution troughs (6) are produced by impressing the channel walls (5) by a rolling operation with correspondingly shaped toothed discs, pressure rollers or the like.
16. Method of producing a heat exchanger tube as claimed in one or more of Claims 1 to 13, characterised in that first of all channels (4) which run round helically are formed, the material for the channel walls (5) being obtained by displacing material outwards from the tube wall of a smooth tube by means of a rolling operation, and that then the distribution troughs (6) are produced by a drawing operation with a stationary or rotating drawing die.
17. Method of producing a heat exchanger tube as claimed in one of Claims 1 to 13, characterised in that first of all channels (4) which run round helically are produced in the tube wall of a smooth tube by a drawing operation with a stationary or rotating drawing die and that then the distribution troughs (6) are produced by a drawing operation with a stationary or rotating drawing die.
18. Use of a heat exchanger tube as claimed in one or more of Claims 1 to 13, for spray vaporisation in a multi-tube heat exchanger.
19. Use of a heat exchanger tube as claimed in one or more of Claims 1 to 13 in a multi-tube heat exchanger with horizontally disposed heat exchanger tubes for the purpose according to Claim 18.
20. Use of a heat exchanger tube as claimed in one or more of Claims 1 to 13 in a multi-tube heat exchanger with inclined heat exchanger tubes for the purpose according to Claim 18.

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