EP1899670B1 - Heat exchanger - Google Patents

Description

The invention relates to a heat exchanger according to the preamble of claim 1 - known by the US 4,314,587 ,

It is known to arrange in the flow channels of heat exchangers to increase the heat transfer structure elements which generate vortex and a turbulent flow. Such structural elements are known in various embodiments, for. B. as corrugated inner ribs, turbulence inserts, rib ribs or as formed from the wall of the flow channel vortex generator, which protrude into the flow. By the EP 0 677 715 A1 , the applicant has been known a heat exchanger with turbulence inserts, which have paired up, forming an angle to the flow direction tabs. The known heat exchanger is used in particular for cooling exhaust gas, wherein a liquid cooling or air cooling is provided. The V-shaped tabs with opening V in the flow direction on the one hand produce a turbulent flow and prevent by their vortex formation, a deposit of soot, which is contained in the exhaust gas.

Further developments of the V-shaped arranged structural elements were by the DE 195 40 683 A1 , the DE 196 54 367 A1 as well as the DE 196 54 368 A1 the applicant for exhaust heat exchanger known. Here, the V-shaped arranged structural elements are formed by non-cutting deformation of the wall of the exhaust pipes. The V-shaped arranged structural elements, Also referred to as so-called winglets can thus economically, ie introduced at low cost in the exhaust pipes.

How through the EP 1 061 319 A1 and the DE 101 27 084 A1 become known to the applicant, similar structural elements for other types of heat exchangers, for. B. air-cooled coolant cooler used. All known structural elements have in common that they are distributed substantially uniformly over the entire length of the respective flow channels, be it exhaust pipes or coolant flat pipes. On the one hand, the desired increased heat transfer is achieved by the structural elements, on the other hand, this advantage is paid for with an increased pressure drop on the exhaust gas or coolant side. In particular, in exhaust gas heat exchangers, which are arranged in the exhaust gas recirculation of an internal combustion engine, an increased pressure drop is not desirable because of the associated increased exhaust backpressure. On the other hand, an increased power density is required in particular for exhaust gas heat exchanger of motor vehicles.

It is an object of the present invention to improve a heat exchanger of the type mentioned in that an optimum between power density and pressure drop is achieved.

This object is solved by the features of claim 1. According to the invention, it is provided that the density of the structural elements is variable, and increases in the flow direction. With this design measure, the heat transfer coefficient on the inside of the flow channel is variable, and the heat transfer increases in the flow direction, while it is comparatively low or minimal in the inlet region of the flow. The invention is based on the recognition that the heat dissipation in the inlet region of the flow channel-for example, to a cooling medium flowing around the flow channel-is greater than in the downstream region of the flow channel due to the high temperature difference prevailing there, and that a forming on the inner wall of the flow channel, in the flow direction growing temperature boundary layer in the inlet region is still relatively thin. In this respect, structural elements for increasing the heat transfer on the inside of the flow channel in favor of a reduced pressure drop in this area can be dispensed with in the inlet region. The density of the structural elements is adapted to the conditions prevailing locally in the flow channel with respect to temperature difference and temperature boundary layer. With the arrangement of the structural elements according to the invention, the advantage is achieved that the pressure drop in the flow channel is reduced at high power density.

Advantageous embodiments of the invention will become apparent from the dependent claims. Preferably, the inlet region of the flow channel initially smooth-walled, ie be formed without structural elements, since - as mentioned - already in this area due to the high temperature difference and the small boundary layer thickness, a high power density is achieved. With decreasing temperature difference and increasing boundary layer thickness then structural elements with increasing density or with the heat transfer increasingly increasing effect are arranged downstream in the flow channel. According to the invention, the structural elements are formed as swirl-generating indentations in the wall of the flow channel, as so-called winglets, as are known for exhaust gas heat exchangers according to the aforementioned prior art. The arrangement and design of the winglets in the flow channel is inventively made variable: so the distance between the winglets in the flow direction can increase continuously or gradually, as well as the height of the winglets, which extends into the flow. For manufacturing reasons, it is advantageous if the distances each amount to a multiple of the smallest distance. Further, the angle included by the V-shaped winglets can be increased continuously or stepwise in the flow direction, thereby also increasing the heat transfer, but also the pressure drop.

According to a further advantageous embodiment of the invention, the inventive arrangement of structural elements with variable density, in particular for exhaust gas heat exchanger of internal combustion engines for motor vehicles is advantageously used. Exhaust heat exchangers require one hand a high power density and on the other hand a low exhaust back pressure, so that the required EGR rates (proportion of recirculated exhaust gas in the total exhaust gas flow) can be achieved to achieve the emissions regulations. The reduced pressure drop resulting from the invention thus has a particularly advantageous effect when used as an exhaust gas heat exchanger. In addition, there is also an advantageous application in intercoolers for internal combustion engines and generally in gas flow channels.

In a further advantageous embodiment of the invention, ribs, in particular rib ribs are arranged as structural elements on the inside of the flow channel, which increase the heat transfer. According to the invention, the rib elements have a density which is variable in the flow direction, i. H. preferably gradually increases in the flow direction, which in turn can be dispensed with in the inlet area entirely on a Innenberippung. The change in density can advantageously be achieved in the case of a rib ridge by means of a variable longitudinal or transverse distribution or by a variable angle of attack for the flow. This also achieves the advantage of a reduced pressure drop. In addition to changing the rib density, further measures could be taken to increase the heat transfer, e.g. As the arrangement of gills or windows in the flanks of the corrugated fins, also with the aim to make the heat transfer in the flow direction variable. The measures according to the invention are particularly advantageous in the inlet region of the respective flow channel, d. H. in the area of the flow, where there are still transient conditions with respect to the temperature difference and the thickness of the boundary layer. These parameters reach a near stationary state downstream, where variable density of the structural elements no longer brings any significant advantages.

Fig. 1

ein Temperaturprofil im Eintrittsbereich eines Strömungskanals,

Fig. 2

die Abhängigkeit der Wärmeübergangszahl α von der Länge des Strömungskanals,

Fig. 3a - 3e

die erfindungsgemäße Anordnung von Strukturelementen mit variabler Dichte in einem Strömungskanal,

Fig. 4

ein zweites Ausführungsbeispiel der Erfindung mit Innenrippen unterschiedlicher Rippendichte,

Fig. 5

ein drittes Ausführungsbeispiel der Erfindung für eine Stegrippe mit variabler Längsteilung,

Fig. 6

ein viertes Ausführungsbeispiel der Erfindung für eine Stegrippe mit variablem Anstellwinkel,

Fig. 7

ein fünftes Ausführungsbeispiel der Erfindung für eine Stegrippe mit variabler Querteilung und

Fig. 8

ein sechstes Ausführungsbeispiel der Erfindung für eine gewellte Innenrippe mit variabler Wellenlänge (Teilung).

Embodiments of the invention are illustrated in the drawings and will be explained in more detail below. Show it

Fig. 1

a temperature profile in the inlet region of a flow channel,

Fig. 2

the dependence of the heat transfer coefficient α on the length of the flow channel,

Fig. 3a - 3e

the arrangement according to the invention of structural elements with variable density in a flow channel,

Fig. 4

A second embodiment of the invention with inner ribs of different fin density,

Fig. 5

A third embodiment of the invention for a rib with variable longitudinal pitch,

Fig. 6

A fourth exemplary embodiment of the invention for a rib with a variable angle of attack,

Fig. 7

a fifth embodiment of the invention for a rib with variable transverse distribution and

Fig. 8

a sixth embodiment of the invention for a wavy inner rib with variable wavelength (pitch).

Fig. 1 shows a pipe 1 designed as a flow channel 2, which has an inlet cross-section 3 and is flowed through by a flow medium according to the arrow P. Preferably, the pipe 1 is traversed by a hot exhaust gas of an internal combustion engine, not shown, and is part of a Abgäswärmeübertragers, not shown. The tube 1 has a smooth inner side or inner wall 1a and an outer wall or outer wall 1b, which is cooled by a preferably liquid coolant. Thus, the hot exhaust gas releases its heat via the pipe 1 to the coolant. When flowing through the flow channel 2, a temperature boundary layer 4 forms on the inner wall 1a, which increases in its thickness d from the inlet cross-section 3 in the direction of flow of the arrow P. The temperature profile in this boundary layer 4 is represented by a temperature profile 5. The temperature in the temperature boundary layer thus rises from a temperature Ta on the inner wall 1a to a temperature level Ti in the interior of the flow channel (core flow), which corresponds to the exhaust gas inlet temperature. Due to the growing temperature boundary layer 4, the heat transfer conditions in the inlet region of the tube 1 deteriorate.

Fig. 2 shows a diagram in which the heat transfer coefficient α is plotted as a relative size over the length I of a smooth-walled flow channel, ie from the inlet cross-section (reference numeral 3 in Fig. 1 ) in the flow direction of the flow medium. The length I is plotted in millimeters. The heat transfer coefficient α is set in the inlet cross-section, ie at 1 = 100 (100%). With increasing length, ie in the flow direction in the flow channel 2 (FIG. Fig. 1 ), the heat transfer coefficient α decreases to about 0.8 (80%) of the value at the inlet cross section. This is primarily due to the formation of the temperature boundary layer 4 according to Fig. 1 due.

Fig. 3a, 3b, 3c, 3d and 3e show a first embodiment with five different variants, namely the arrangement of structural elements with variable density. Fig. 3a shows in a first variant, which does not belong to the invention a schematically illustrated flow channel 6, preferably an exhaust pipe of a Abgaswärmeübertragers not shown, wherein the exhaust pipe 6 is traversed according to the arrow P. The outside of the exhaust pipe 6 is - what is not shown, but from the above-mentioned prior art is known - preferably lapped by a liquid coolant - but is also possible air cooling. The exhaust pipe 6 is formed as a stainless steel tube, consisting of two halves welded together, with a rectangular cross-section. The exhaust pipe 6 has an inlet region 6a, which is smooth-walled over a length L. Downstream of the smooth-walled region 6a, a region 6b adjoins, in which are arranged V-shaped structural elements 7, so-called winglets, embossed from the tube wall. The winglet pairs 7 are arranged in the section 6b at the same distance and in the same formation. The transition from the smooth-walled region 6a to the winglets 7 occupied area 6b thus takes place in the form of a "step". As mentioned above, despite the lack of structural elements, a sufficiently large heat transfer or heat transfer is achieved in the smooth-walled region 6a, since the temperature difference is still sufficiently large and the temperature boundary layer is relatively small. At the point where these conditions no longer apply, structural elements 7 are arranged, which for a. Improvement of the heat transfer (heat transfer coefficient α) provide. The smooth-walled Area 6a - this also applies to the following variants 3b, 3c, 3d, 3e-may have a length of up to 100 mm.

In a second variant, which does not belong to the invention according to Fig. 3b a rectangular tube 8 is shown in longitudinal section, which also has a smooth-walled inlet region 8a and a channel height H. Downstream of this smooth-walled region 8a winglet pairs 9 are arranged with equal distances a in the flow direction, but with different heights h: projecting into the flow cross-section of the exhaust pipe 8 heights h of the winglet pairs 9 grow continuously in the flow direction P. Thus, the heat transfer in This pipe section has been successively increased. At the same time, the pressure drop increases. The transition from smooth to not smooth is thus continuous. In a preferred embodiment, a range of 0.05 ≦ h / H ≦ 0.4 is selected for the ratio h / H.

In a variant according to the invention according to Fig. 3c are in a tube 10 winglet pairs 11 with decreasing in the flow direction P distances a ₁ , a ₂ , a ₃ arranged. Thus, the heat transfer, starting from the smooth inlet region 10a, successively increased, since the density of the structural elements or winglets 11 is greater. For reasons of simplified production, the distances a ₁ , a ₂ , a _{3 can} each be a multiple of the minimum distance a _x . The latter is advantageously in a range of 5 <a _x <50 mm and preferably in a range of 8 <a _x <30 mm.

Fig. 3d shows a fourth variant, which does not belong to the invention for the arrangement of structural elements with different density in an exhaust pipe 12, which is permeable according to the arrow P of exhaust gas. The smooth-walled entry region 12a is shorter in comparison to the previous embodiments. This is followed by winglet pairs 13 with equal distances in the flow direction, but with different angles β (angle with respect to flow direction P). The winglets of the upstream winglet pair 12 are aligned almost parallel (β≈0), while the angle β formed by the winglets of the downstream winglet pair 13 is about 45 degrees. The intervening winglet pairs 13 have corresponding intermediate values, so that the heat transfer coefficient for the Inner wall of the exhaust pipe 13 due to the increasing spreading of the winglets in the flow direction grows, continuously or in small steps. The angle β is advantageously in a range of 20 ° <β <50 °

Fig. 3e shows another variant of the invention with an exhaust pipe 30, a smooth-walled portion 30a and adjoining rows of parallel winglets 31, which each form an angle β with the flow direction P. The rows have in the flow direction P decreasing distances a ₁ , a ₂ , a ₃ , wherein the angle β of the winglets 31 from row to row changes the sign.

In aiien pipes is preferably left at the beginning of the pipe and at the pipe end a smooth area without structural elements, so that at a lengthening of the tube a clean separation point can be produced.

Fig. 4 shows a further embodiment, which does not belong to the invention, for a flow channel 14 which is according to the arrow P flows of a flow medium - this may be, for example, a liquid coolant or even charge air. The outside of the flow channel 14, 14 can be cooled by a gaseous or liquid cooling medium. The flow channel 14 has a smooth-walled inlet region 14a, which is adjoined in the flow direction P by a first region 14b provided with internal ribs 15 and by another ribbed region 14c thereon. The regions 14b and 14c have a different fin density - in the illustrated embodiment, the rib density in the downstream region 14c is twice as large as in the upstream region 14b, since between the continuous ribs 15 further ribs 16 are arranged. Thus, an increase of the heat transfer is also achieved, in stages from 14a to 14b to 14c.

Fig. 5 shows as a further embodiment, which does not belong to the invention, a gas flow channel in which a Stegrippe 17 with variable longitudinal pitch t ₁ , t ₂ , t ₃ , t ₄ , t _{5 is} arranged. In the drawing, t ₁ > t ₂ > t ₃ > t ₄ > t ₅ , ie the heat transfer increases from t ₁ to t ₅ , ie in the flow direction P too. Web ribs are used in particular for intercoolers and are preferably soldered to the pipes. In an advantageous embodiment, the ratio of the smallest pitch t _x to the channel height H has a limit of 0.3 <t _x / H.

Fig. 6 Also shows an embodiment, which does not belong to the invention, a gas flow channel in which a Stegrippe 18 with variable angles of attack α ₁ , α ₂ , α ₃ ... α _{x is} arranged. Advantageous angles of attack are in the range of 0 <α <30 °.

Fig. 7 shows as an embodiment, which does not belong to the invention, a gas flow channel in which a ridge rib 19 with variable transverse pitch q ₁ , q ₂ , q ₃ ... q _{6 is} arranged, the heat transfer with decreasing transverse division of q ₁ in the direction q _6. ie in the flow direction P increases. Advantageous areas for the transverse division q are 8>q> 1 mm and preferably 5>q> 2 mm.

Fig. 8 shows in a gas flow channel a corrugated in the flow direction P (deep waved) inner fin 20 with variable pitch t ₁ , t ₂ , t ₃ , t ₄ - the heat transfer increases here in the direction of decreasing pitch t. Advantageous ranges for the pitch t are 10 <t <50 mm.

In a modification of the illustrated embodiments, a variation of the heat transfer in the flow channel can also be achieved by further means known from the prior art, for example by arranging gills or windows in the ribs. In addition, other forms of structural elements for vortex generation or to increase the heat transfer can be selected. The application of the invention is not limited to exhaust gas heat exchangers, but also extends to intercoolers whose tubes are flowed through by hot charge air, and generally to gas flow channels, which may be formed as tubes of a tube heat exchanger or as slices of Scheibenwärmeübertragers.

Claims (25)

1. A heat exchanger, having at least one flow duct which can be flowed through by a flow medium from an inlet cross section to an outlet cross section and which has an inside and an outside, and which has, on the inside, structural elements for increasing the heat transfer, wherein the structural elements (7, 9, 11, 13, 15, 16, 17, 18, 19, 20, 31) are arranged and/or embodied variably in the direction of flow (P) such that, on the inside, the flow duct (6, 8, 10, 12, 14, 30) has variable heat transfer, increasing in the direction of flow (P), wherein the density of the structural elements (11; 15, 16; 19; 31) is variable and increasing in the direction of flow (P), the structural elements being embodied as eddy generators, referred to as winglets (7, 9, 11, 13, 31), characterised in that the winglets (11, 31) are arranged in rows and form, with the direction of flow (P), an angle (•), wherein the angle (•) has an identical or opposed sign for adjacent winglets, and the winglets (11, 31) are arranged in rows transverse with respect to the direction of flow (P), and in that the rows have a spacing (a₁, a₂, a₃...a_x) which is variable and decreasing in the direction of flow.
2. The heat exchanger as claimed in claim 1, characterised in that the structural elements (9, 11, 13, 15, 16, 17, 18, 19, 20, 31) have a flow resistance with respect to the flow medium and are arranged and/or embodied such that the pressure drop in the flow duct (8, 10, 12, 14) is variable, in particular being minimal in the inlet region (6a, 8a, 10a, 12a, 14a, 30a).
3. The heat exchanger as claimed in claim 1 or 2, characterised in that the flow duct (6, 8, 10, 12, 14, 30) has, starting from the inlet cross section, a smooth-walled section (6a, 8a, 10a, 12a, 14a, 30a) without structural elements.
4. The heat exchanger as claimed in claim 3, characterised in that the smooth-walled section (6a, 8a, 10a, 12a, 14a, 30a) has a length L in the direction of flow (P), where L • 100 mm.
5. The heat exchanger as claimed in one of claims 1 to 4, characterised in that the structural elements are embodied as internal ribbing, internal ribs (15, 16, 20), web ribs (17, 18, 19) and/or turbulence inlays and are, in particular, soldered into the flow ducts.
6. The heat exchanger as claimed in one of claims 1 to 5, characterised in that the winglets (13, 31) form, with the direction of flow (P), an angle (•) which is variable, in particular increasing in the direction of flow (P).
7. The heat exchanger as claimed in claim 6, characterised in that the angle • has a range of 20° < • < 50°.
8. The heat exchanger as claimed in one of the preceding claims, characterised in that the winglets (9) have a height (h) which projects into the flow and which increases variably, in particular in the direction of flow (P).
9. The heat exchanger as claimed in claim 8, characterised in that the flow duct (8) has a height H and the ratio of h/H has a range of 0.05 • h/H • 0.4.
10. The heat exchanger as claimed in one of the preceding claims, characterised in that the smallest spacing a_x has a range of 5 < a_x < 50 mm, in particular a range of 8 < a_x < 30 mm.
11. The heat exchanger as claimed in one of the preceding claims, characterised in that the spacing (a₁, a₂, a₃ ...) of the rows is an (integral) multiple of the smallest spacing a_x.
12. The heat exchanger as claimed in one of claims 1 to 11, characterised in that a smooth region (without structural elements) is left as a dividing point at the upstream and downstream ends of a flow duct.
13. A use of the heat exchanger as claimed in one of claims 1 to 4 or 6 to 12 as an exhaust gas heat exchanger, wherein the flow ducts are embodied as exhaust pipes (6, 8, 10, 12, 30) through which exhaust gas can flow and around which a coolant can flow.
14. The heat exchanger as claimed in claim 5, characterised in that the structural elements, in particular the internal ribs (15, 16), have a rib density which is variable in the direction of flow, in particular increasing in the direction of flow (P) .
15. The heat exchanger as claimed in claim 14, characterised in that the rib density increases in stages (14b, 14c).
16. The heat exchanger as claimed in claim 5, characterised in that the web rib (17) has a variable longitudinal pitch (t₁, t₂, t₃, t₄, t₅, ... t_x).
17. The heat exchanger as claimed in claim 16, characterised in that the smallest longitudinal pitch t_x has a limiting value t_x > 0.3 H, where H is the duct height.
18. The heat exchanger as claimed in claim 5, characterised in that the web rib (18) has a variable angle of incidence (•₁, •₂, •₃ ... •_x) wherein the angle of incidence is preferably in the range of 0 < • <30°.
19. The heat exchanger as claimed in claim 5, characterised in that the web rib (19) has a variable transverse pitch (q₁, q₂, q₃ ... q_x).
20. The heat exchanger as claimed in claim 19, characterised in that the transverse pitch q has a range of 8 > q > 1 mm, preferably 5 > q > 2 mm.
21. The heat exchanger as claimed in claim 5, characterised in that the internal rib (20) has a longitudinal corrugation with variable pitch (t₁, t₂, t₃, t₄).
22. The heat exchanger as claimed in claim 21, characterised in that the pitch t of the internal rib (20) has a range of 10 < t < 50 mm.
23. The heat exchanger as claimed in one of the preceding claims, characterised in that the flow ducts are embodied as pipes, in particular as pipes of a pipe bundle.
24. The heat exchanger as claimed in one of claims 1 to 22, characterised in that the flow ducts are embodied as disks, in particular as disks of a disk package.
25. A use of the heat exchanger as claimed in one of claims 14 to 24 as the charge air cooler for cooling combustion air for an internal combustion engine of a motor vehicle.

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