EP1790931A2 - Coaxial or pipe in pipe assembly, in particular for a heat exchanger - Google Patents

Abstract

The arrangement has a low pressure side arranged in a radial direction near a central longitudinal axis than a high pressure side. A free flow section of the high pressure side is altogether smaller than a free flow section of the low pressure side. Inflow openings are provided for two mediums, where the inflow openings are arranged on different sides of the arrangement. An outer tube (5) of the arrangement is divided maximally into sixteen partial channels, where an inner tube (3) exhibits a small wall thickness.

Description

The invention relates to a coaxial tube or a tube-in-tube arrangement according to the preamble of claim 1.

From the EP 1 202 016 A2 is a one-piece heat exchanger tube with a multi-chamber profile known, according to which a plurality of outer channels are provided around a central channel. The outer channels are divided by intermediate walls which extend in the radial direction. On the wall of the central channel projections are provided which extend into the central channel. These projections serve to reduce the cross-sectional area and thus increase the flow velocity. The cross-sectional area of the central channel is significantly smaller than the sum of the cross-sectional areas of the outer channels. The ribs / projections may also be helical, wherein constant, changing or alternating gradients may be provided. The inner channel is used as a high pressure side, the outer channels as a low pressure side.

Spiral-shaped webs, which separate the outer channels from each other, and the provision of turbulence elements on the webs are from the DE 199 44 951 A1 in turn, in turn, the inner channel, the high pressure side and the outer channels form the low pressure side. The cross-sectional area of the inner channel is smaller than the sum of the cross-sectional areas of the outside of the inner channel disposed outer channels.

An example of a use of a two-part coaxial tube system, consisting of an outer tube and an inner tube inserted into the outer tube, for an air conditioning system, in particular a motor vehicle air conditioning system, is known from US Pat DE 199 44 951 A1 known.

From the US 6,098,704 B2 a tube-in-tube arrangement is known, wherein both the outer tube and the inner tube has a plurality of equidistant spaced around the circumference, radially inwardly pointing ribs.

Based on this prior art, it is an object of the invention to provide an improved coaxial tube available. This object is achieved by a coaxial tube or a tube-in-tube arrangement with the features of claim 1. Advantageous embodiments are the subject of the dependent claims.

According to the invention, a coaxial tube or a tube-in-tube arrangement for the separate line of at least two media, which is preferably refrigerant, is provided, whose pressure level differs, wherein in the coaxial tube or the tube-in-tube arrangement the Low pressure side is arranged in the radial direction closer to the central longitudinal axis than the high pressure side. The twisted arrangement, the inner tube may be formed with a smaller wall thickness, which reduces the total weight, the material requirements and thus the cost of the coaxial tube or the tube-in-tube arrangement. Furthermore, the dimensions can be slightly reduced, which also reduces the heat input from the outside into the system and thus the performance can be increased.

The term "pipe" is to be interpreted in the following very broad and refers not only to round cross-sections, but in particular also oval, rounded rectangular or any other cross-sections. The tube may also be two tubes arranged inside one another which do not have any have direct connections (tube-in-tube arrangement). In this case, however, positioning elements for the inner tube may be provided in the outer tube, such as provided on the outer and / or inner tube, radially inwardly or outwardly projecting ribs to optionally ensure a coaxial arrangement. The arrangement of the inner tube or of the inner region in the outer tube is preferably coaxial, but does not have to be, so that eccentric arrangements are also possible. Likewise, several inner tubes may be provided, which are connected by means of several sleeves. The inner tube may also be soldered or otherwise connected to the outer tube in the contact regions.

The free flow cross section of the high pressure side is preferably smaller overall than the free flow cross section of the low pressure side. The free flow cross sections differ in such a way that the free flow cross section of the. High pressure side is preferably at most half as large and preferably at least a quarter as large, more preferably about one-third +/- 10% is as large as the free flow area of the low pressure side. These cross-sectional ratios result in a very good heat exchange between the two media.

The outer diameter of the outer tube is preferably 10 to 18 mm, in particular 12 to 16 mm. The inner diameter of the inner tube is preferably 6 to 12 mm, in particular 8 to 10 mm. The width of the ribs between the inner and outer tubes is preferably 0.3 to 0.8 mm, particularly preferably 0.4 to 0.7 mm.

Preferably, the inlet openings of the two media are arranged on different sides of the coaxial tube or the tube-in-tube arrangement, so that the coaxial tube or the tube-in-tube arrangement is flowed through in countercurrent operation.

The outer tube is preferably subdivided into at least six, in particular at least ten, in particular preferably at least twelve subchannels and a maximum of twenty, preferably a maximum of sixteen subchannels.

This subdivision allows optimal strength properties of the tube, combined with a large heat transfer area for the medium flowing in the outer region.

The wall thickness of the outer wall is preferably greater than the wall thickness of the wall between the outer tube and the inner tube. Due to the greater pressure difference from the outer tube to the environment than from the outer tube to the inner region, the wall thickness to the inner tube can be made smaller, so that a material saving is possible. Is - as in conventional coaxial tubes - the maximum pressure in the inner tube provided, the outer tube, however, must also be able to withstand the corresponding pressure, which is why it should have a corresponding wall thickness and therefore designed in conventional coaxial tubes according to the inner tube, making the coaxial tube heavier and thus more expensive than a coaxial tube according to the invention. Incidentally, an improvement in the heat transfer performance can be achieved by the thinner wall.

The width of the ribs or webs, which divide the individual sub-channels of the outer tube, is preferably smaller than the wall thickness of the wall of the outer tube, which can also save material.

Preferably, the width of the webs, which divide the individual sub-channels of the outer tube, greater than or equal to the wall thickness of the wall between the outer tube and the inner tube.

In the interior of the inner tube, at least one turbulence generator is preferably provided, which is preferably an inner tube coil. Likewise, at least one inner rib and / or at least one chord, which in this case also means a web extending in the radial direction from one to the other side of the inner wall, may be provided in the inner tube.

At least one of the turbulence generators and / or at least one of the inner ribs and / or at least one of the webs and / or at least one of the ribs between the inner and outer tubes is preferably inclined with respect to arranged the pipe axis. However, the slope can also change over the total length of the tube, as well as the direction of rotation.

Preferably, at least one of the turbulence generators and / or at least one of the inner ribs and / or at least one of the webs and / or at least one of the ribs between the inner and outer tubes is formed obliquely with respect to the tube longitudinal axis with such a pitch that a 360 ° rotation over a tube length of 15 to 35 mm, in particular from 20 to 25 mm, takes place.

Furthermore, it may prove advantageous if the length of at least one of the turbulence generators and / or at least one of the inner ribs and / or at least one of the webs and / or at least one of the ribs between the inner and outer tube is 0.3 times to 0, 5 times, preferably equal to 0.4 times the tube length. It is also conceivable, however, for the length of at least one of the aforementioned devices to correspond essentially to the tube length.

In order in particular to keep the low-pressure-side pressure loss as low as possible, the inflow of the low-pressure medium is preferably carried out substantially coaxially, for which purpose the corresponding connecting piece is designed accordingly.

A coaxial tube according to the invention or a tube-in-tube arrangement according to the invention can be used in particular for heat exchangers, preferably for motor vehicle air conditioners, particularly preferably for high-pressure air conditioning systems (such as in R744 air conditioners) of motor vehicles, however, other applications are also possible. Particularly preferred is the use as a so-called inner heat exchanger or internal heat exchanger. In particular, in the latter use and in the use of R744, the refrigerant used usually behaves, even if it is at least partially in the gaseous state, due to the usually very high density similar to a fluid. In particular, this makes it possible, for example, by use a turbulence generator to increase the heat transfer between the channels.

Particularly when used as an inner heat exchanger in a refrigerant circuit, the proposed application of high or low pressure may prove to be particularly advantageous. Thus, the high pressure usually has a higher temperature than the low pressure, so that particularly good additional heat energy can be dissipated from the high-pressure side refrigerant to the environment.

Fig. 1

einen Schnitt durch ein Koaxialrohr gemäß dem ersten Ausführungsbeispiel,

Fig. 2

eine schematische Darstellung eines Wärmeaustauschers mit einem anderen Koaxialrohr,

Fig. 3

einen Längsschnitt durch einen Endbereich eines Koaxialrohrs mit Anschlussstück, wobei im Koaxialrohr ein schematisch angedeuteter Turbulenzerzeuger gemäß einer Variante des ersten Ausführungsbeispiels dargestellt ist, und

Fig. 4

einen Schnitt durch ein Koaxialrohr gemäß dem zweiten Ausführungsbeispiel.

In the following, the present invention with reference to two embodiments with variants, partially explained with reference to the drawings. Show it:

Fig. 1

a section through a coaxial tube according to the first embodiment,

Fig. 2

a schematic representation of a heat exchanger with another coaxial tube,

Fig. 3

a longitudinal section through an end portion of a coaxial tube with fitting, wherein in the coaxial tube a schematically indicated turbulence generator according to a variant of the first embodiment is shown, and

Fig. 4

a section through a coaxial tube according to the second embodiment.

According to the first embodiment, a heat exchanger 1, of which only a cross-section is shown in Fig. 1, but which may be formed in principle, as shown in Fig. 2 with an enlarged, shown another cross-section provided. This heat exchanger 1 serves the heat exchange of a first medium and a second medium. Here, the first medium flows through the inner region 2 of an inner tube 3 and the second medium through the outer region 4 which between an outer tube 5 and the inner tube 3 is formed. Here, the inner tube 3 and the outer tube 5 together with them in the radial direction in the longitudinal direction continuously extending ribs 6 are integrally extruded as a coaxial tube 7 made of an aluminum alloy.

The outer diameter of the coaxial tube 7 is present 16 mm, the wall thickness of the outer tube 5 0.8 mm, the wall thickness of the inner tube 3 0.6 mm, the rib width 0.7 mm and the inner diameter 11 mm. There are fourteen ribs 6, so also fourteen spaced apart formed outer channels provided, which are distributed due to the corresponding width of the individual ribs 6 at equidistant intervals around the inner tube 3. The free cross-sectional area of the inner tube 3 is about 95 mm ² , the sum of the free cross-sectional areas of the outer channels is about 35 mm ² , that is about 60% smaller than that of the inner tube. 3

To initiate the cooling and the medium to be cooled in the coaxial tube 7, 7 connecting components 8 (see Fig. 2) are provided at both ends of the coaxial tube, via which the media, which by the inner region 2 and the outer region 4 present in the Countercurrent flow, separately from each other or be derived.

On the coaxially extruded coaxial tube 7, a higher pressure is applied to the outer tube 5 (high pressure side) than to the inner tube 3 (low pressure side). The operating pressure on low pressure side (low pressure p _N ) is according to the present embodiment about 130 bar, the corresponding bursting pressure 264 bar, and the operating pressure on the high pressure side (high pressure p _H ) is about 160 bar, the corresponding bursting pressure 352 bar. The mentioned pressure values refer in particular to the use of CO ₂ (R744) as refrigerant.

Because the low-pressure side is arranged inside, an improved flow of the low-pressure refrigerant can be realized via the corresponding connection piece 8; in particular, as shown in FIG. 3, a deflection-free flow of the low-pressure refrigerant is provided in the direction of the longitudinal axis of the inner tube, whereby the pressure loss can be reduced and thereby the cooling capacity can be improved. The flow of the high-pressure refrigerant takes place in the radial direction with respect to the longitudinal axis of the coaxial tube. 1

According to a variant of the first embodiment, which is shown in Fig. 3, a turbulence generator 11 in the form of a helix (round tube helix) is provided in the interior of the inner tube 3, which can be arranged in the coaxial tube bend with the same. Apart from the helix, the embodiment corresponds exactly to that of the first embodiment. The pitch of the helix in this case corresponds approximately to twice the inner diameter of the inner tube 3, that is about 22 mm, and is constant over the entire length of the coaxial tube. The helix deflects the refrigerant flowing in the inner tube, so that no laminar flow is formed in the wall region, resulting in improved mixing and improved heat exchange.

According to further variants, the pitch of the helix changes over the length of the coaxial tube and / or changes the direction of rotation of the turning, wherein multiple changes can be provided.

Fig. 4 shows a second embodiment of a coaxial tube, wherein in the inner tube 3 both four evenly distributed over the circumference inner ribs 21 are provided with a length of about half the radius and two perpendicular to each other and at a gap to the inner ribs 21 webs 22 which the Divide the interior into four separate areas. These internals in the inner tube 3 enlarge the heat transfer surface and therefore improve the heat exchange.

According to a first variant of the second embodiment, the coaxial tube is extruded turned, i. the ribs, inner ribs and webs run helically, in this case with a constant pitch.

According to a second variant of the second embodiment, the coaxial tube is in turn rotated extruded, but changed with changing Rotational speed, so that the pitch of the ribs, inner ribs and webs changed over the length of the coaxial tube.

According to a further variant of the second embodiment, two tendons are provided opposite one another in the inner tube of the coaxial tube instead of the webs extending in the radial direction.

A third embodiment provides a tube-in-tube arrangement as a coaxial tube, wherein the outer tube ribs and the inner tube inner ribs and webs, and the outer tube is soldered at the end of the ribs to the inner tube, resulting in a configuration according to the second embodiment ,

A first variant of the third embodiment provides that the two tubes are extruded rotated in different directions, i. that the flow paths of the refrigerant flowing in the interior are rotated on the one hand in countercurrent operation and on the other hand in different directions, whereby the heat exchange is improved.

According to a second variant, the rotations of the two tubes have mutually different slopes over the length, so that, for example, a smaller pitch can be provided in the inflow area and a larger pitch in the outflow area.

Claims (20)

Coaxial pipe or tube-in-tube arrangement for the separate conduction of at least two media whose pressure level is different, characterized in that in the coaxial tube (7) or the tube-in-tube arrangement, the low-pressure side in a radial direction closer to the central longitudinal axis as the high pressure side is arranged. Coaxial tube or tube-in-tube arrangement according to claim 1, characterized in that; that the free flow cross section of the high pressure side is smaller overall than the free flow cross section of the low pressure side. Coaxial tube or tube-in-tube arrangement according to claim 2, characterized in that the free flow cross section of the high pressure side is at most half as large and a minimum of a quarter so large, in particular one third +/- 10% is as large as the free Flow cross section of the low pressure side. Coaxial tube or tube-in-tube arrangement according to one of the preceding claims, characterized in that the outer diameter of the outer tube is 10 to 18 mm, in particular 12 to 16 mm. Coaxial tube or tube-in-tube arrangement according to one of the preceding claims, characterized in that the inner diameter of the inner tube is 6 to 12 mm, in particular 8 to 10 mm. Coaxial tube or tube-in-tube arrangement according to one of the preceding claims, characterized in that the width of ribs (7) or webs between the inner and outer tubes (3 and 5) 0.3 to 0.8 mm, in particular 0 , 4 to 0.7 mm. Coaxial tube or tube-in-tube arrangement according to one of the preceding claims, characterized in that the inflow openings of the two media are arranged on different sides of the coaxial tube or the tube-in-tube arrangement. Coaxial tube or tube-in-tube arrangement according to one of the preceding claims, characterized in that the outer tube is subdivided into at least six, in particular at least ten, in particular at least twelve sub-channels and a maximum of twenty, preferably a maximum of sixteen sub-channels. Coaxial tube or tube-in-tube arrangement according to one of the preceding claims, characterized in that the wall thickness of the outer wall is greater than the wall thickness of the wall between the outer tube and the inner tube. Coaxial tube or tube-in-tube arrangement according to one of the preceding claims, characterized in that the width of the ribs or webs which divide the individual sub-channels of the outer tube is smaller than the wall thickness of the wall of the outer tube. Coaxial pipe or pipe-in-pipe assembly according to one of the preceding claims, characterized in that the width of the ribs or webs which subdivide the individual subchannels of the outer tube is greater than or equal to the wall thickness of the wall between the outer tube and inner tube. Coaxial tube or tube-in-tube arrangement according to one of the preceding claims, characterized in that in the interior of the Inner tube (3) at least one turbulence generator (11) provided and / or at least one inner rib (21) and / or at least one web (22) is formed. Coaxial tube or tube-in-tube arrangement according to claim 12, characterized in that at least one of the turbulence generator (11) and / or at least one of the inner ribs (21) and / or at least one of the webs (22) and / or at least one of Ribs (7) between the inner and outer tubes (3 and 5) is arranged obliquely with respect to the tube longitudinal axis. Coaxial tube or tube-in-tube arrangement according to claim 13, characterized in that at least one of the turbulence generator (11) and / or at least one of the inner ribs (21) and / or at least one of the webs (22) and / or at least one of Ribs (7) between the inner and outer tubes (3 and 5) is formed obliquely with respect to the tube longitudinal axis with such a slope that a 360 ° rotation over a tube length of 15 to 35 mm, in particular from 20 to 25 mm occurs. Coaxial tube or tube-in-tube arrangement according to one of the preceding claims, characterized in that the length of at least one of the turbulence generators (11) and / or at least one of the inner ribs (21) and / or at least one of the webs (22) and / or at least one of the ribs (7) between the inner and outer tubes (3 and 5) corresponds to 0.3 times to 0.5 times, preferably 0.4 times, the tube length. Coaxial tube type heat exchanger characterized by at least one coaxial tube or tube-in-tube arrangement according to any one of claims 1 to 15. Heat exchanger according to claim 16, characterized in that at least one connecting piece (8) is provided for introducing at least one medium, which is an introduction of the medium in coaxial Direction to the coaxial tube (1) or to the tube-in-tube arrangement provides. Air conditioning system, in particular for a motor vehicle, characterized by at least one coaxial tube or a tube-in-tube arrangement according to one of claims 1 to 15, which is designed in particular as an internal heat exchanger. Use of a coaxial tube or a tube-in-tube arrangement according to one of claims 1 to 15, a heat exchanger according to claim 16 or 17 or an air conditioner according to claim 18, wherein at least one of the media is a refrigerant, in particular R744 and / or R134a , Use of a coaxial tube or a tube-in-tube arrangement according to one of claims 1 to 15 or 19 or a heat exchanger according to claim 16 or 17 in a refrigerant circuit, in particular as an internal heat exchanger.

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