EP3048407A1 - Heat exchanger - Google Patents

Abstract

The invention relates to a heat exchanger with at least one of a flow medium from an inlet to an outlet cross-section through which an inner and an outer side having flow channel, which has on the inside of structural elements to increase the heat transfer. It is proposed that the structural elements (11) are variably arranged and / or formed in the flow direction (P), such that the flow channel (10) has a variable heat transfer on the inside, in particular a heat transfer increasing in the flow direction (P).

Description

The invention relates to a heat exchanger according to the preamble of claim 1 - known by the EP 0 677 715 A1 the applicant.

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 a heat exchanger with turbulence inserts is known, 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 be 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 substantially evenly distributed 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, especially in the flow direction is increasing. With this design measure, the heat transfer coefficient on the inside of the flow channel is variable, in particular, 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, 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, d. H. be formed without structural elements, since - as mentioned - already in this area due to the high temperature difference and the low 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. Advantageously, the structural elements are formed as swirl-generating indentations in the wall of the flow channel, as so-called winglets, as they are known for exhaust gas heat exchanger according to the aforementioned prior art. The arrangement and design of the winglets in the flow channel can be made variable according to the invention: thus, the distance of 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 gas heat exchangers require on the one hand a high power density and on the other hand a low exhaust back pressure, so that the required EGR rates (proportion of the recirculated exhaust gas in the total exhaust gas flow) can be achieved to achieve the emission requirements. The reduced pressure drop resulting from the invention thus has a particularly advantageous effect when used as an exhaust gas heat exchanger. In addition, 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 that is variable in the direction of flow, ie. 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.

It is advantageous if at the upstream and at the downstream end of a flow channel, a smooth area, without structural elements, is left as a separation point.

It is advantageous if, when used as a heat exchanger, the flow channels are designed as exhaust gas flows through and can be umströmbare exhaust gas from a coolant.

It is advantageous if the structural elements, in particular the inner ribs have a rib density, which is variable in the flow direction, in particular in the flow direction (P) is increasing.

It is advantageous if the rib density increases in stages.

It is advantageous if the rib ridge has a variable longitudinal pitch (t ₁ , t ₂ , t ₃ , t ₄ , t ₅ ... t _x ).

It is advantageous if the smallest longitudinal pitch t _{x has} a limit value t _x > 0.3 H, where H is the channel height.

It is advantageous if the rib ridge has a variable angle of attack (α ₁ , α ₂ , α ₃ ... α _x ), wherein the angle of attack is preferably in the range of 0 <α <30 °.

It is advantageous if the rib ridge has a variable transverse distribution (q ₁ , q ₂ , q ₃ ... Q _x ).

It is advantageous if the transverse pitch q has a range of 8> q> 1 mm, preferably 5> q> 2 mm.

It is advantageous if the inner rib has a longitudinal swivel with variable pitch (t ₁ , t ₂ , t ₃ , t ₄ ).

It is advantageous if the pitch t of the inner rib has a range of 10 <t <50 mm.

It is advantageous if the flow channels are formed as tubes, in particular as a tube of a tube bundle.

It is advantageous if the flow channels are formed as disks, in particular as disks of a disk package.

It is advantageous if a use of the heat exchanger is provided as a charge air cooler for cooling combustion air for an internal combustion engine of a motor vehicle.

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 tube 1 is traversed by a hot exhaust gas of an internal combustion engine, not shown, and is part of a Abgaswärmeübertragers not shown. The tube 1 has a smooth inner side or inner wall 1a and an outer or outer wall 1b, which is cooled by a preferably liquid coolant. The hot exhaust gas gives its heat over the Pipe 1 to the coolant. During the flow 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 flow direction 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 of the invention with five different variants, namely the arrangement of structural elements with variable density. Fig. 3a shows in a first variant, 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 V-shaped arranged structural elements embossed from the tube wall 7, so-called winglets, are arranged. 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 provide for an improvement of the heat transfer (heat transfer coefficient α). The smooth-walled region 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 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 third variant 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 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 increases due to the increasing spreading of the winglets in the flow direction, continuously or in small steps. The angle β is advantageously in a range of 20 ° <β <50 °.

Fig. 3e shows a fifth variant 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.

For all tubes, a smooth area without structural elements is preferably left at the beginning of the tube and at the tube end so that a clean separation point can be produced when the tubes are cut to length.

Fig. 4 shows a further embodiment of 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 charge air. The outside of the flow channel 14 can be cooled by a gaseous or liquid cooling medium. The flow channel 14 has a smooth-walled inlet region 14a, at which, in the flow direction P, a first region 14b provided with internal ribs 15 and, at the same time, another ribbed region 14c connects. 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 third embodiment of 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. 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 shows a fourth embodiment of the invention, a gas flow channel in which a rib ridge 18 with variable angles of attack α ₁ , a ₂ , α ₃ ... α _{x is} arranged. Advantageous angles of attack are in the range of 0 <α <30 °.

Fig. 7 shows a fifth embodiment of the invention, a gas flow channel in which a rib ridge 19 with variable transverse pitch q ₁ , q ₂ , q ₃ ... q _{6 is} arranged, wherein the heat transfer with decreasing transverse division of q ₁ in the direction q ₆ , ie 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 also by further from the

Prior art known means can be achieved, for example by placing 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 (15)

Heat exchanger with at least one of a flow medium from an inlet to an outlet cross-section through, an inner and an outer having flow channel, which on the inside of structural elements to increase the heat transfer, characterized in that the structural elements (7, 9, 11, 13, 15, 16, 17, 18, 19, 20, 31) in the flow direction (P) are variably arranged and / or formed, such that the flow channel (6, 8, 10, 12, 14, 30) on the inside a variable, in particular in the flow direction (P) increasing heat transfer. Heat exchanger according to claim 1, characterized in that the density of the structural elements (11; 15, 16; 19; 31) is variable, in particular in the flow direction (P) increasing. Heat exchanger according to claim 1 or 2, characterized in that the structural elements (9, 11, 13, 15, 16, 17, 18, 19, 20, 31) have a flow resistance to the flow medium and are arranged and / or formed such that the pressure drop in the flow channel (8, 10, 12, 14) variable, in particular in the inlet region (6a, 8a, 10a, 12a, 14a, 30a) is minimal. Heat exchanger according to claim 1, 2 or 3, characterized in that the flow channel (6, 8, 10, 12, 14, 30), starting from the inlet cross section, a smooth-walled portion (6a, 8a, 10a, 12a, 14a, 30a) without Has structural elements. Heat exchanger according to claim 4, characterized in that the smooth-walled portion (6a, 8a, 10a, 12a, 14a, 30a) in the flow direction (P) has a length L, wherein L ≤ 100 mm. Heat exchanger according to one of claims 1 to 5, characterized in that the structural elements as vortex generators, so-called winglets (7, 9, 11, 13, 31) are formed. Heat exchanger according to claim 6, characterized in that the winglets (11, 31) are arranged in rows and with the flow direction (P) form an angle β, wherein the angle β for adjacent winglets has the same or opposite sign. Heat exchanger according to one of claims 1 to 5, characterized in that the structural elements as Innenberippung, inner ribs (15, 16, 20), rib ribs (17, 18, 19) and / or turbulence inserts are formed and in particular soldered into the flow channels. Heat exchanger according to claim 6 or 7, characterized in that the winglets (13, 31) with the flow direction (P) form an angle β, which is variable, in particular in the flow direction (P) is increasing. Heat exchanger according to claim 9, characterized in that the angle β has a range of 20 ° <β <50 °. Heat exchanger according to claim 6 or 7, characterized in that the winglets (9) have a projecting into the flow height (h), which is variable, in particular in the flow direction (P) is increasing. Heat exchanger according to claim 11, characterized in that the flow channel (8) has a height H and the ratio of h / H has a range of 0.05 ≤ h / H ≤ 0.4. Heat exchanger according to claim 5, 7 or 8, characterized in that winglets (11, 31) are arranged in rows transversely to the flow direction (P) and that the rows have a variable in flow direction, in particular decreasing distance (α ₁ , a ₂ , a ₃ ... a _x ). Heat exchanger according to claim 13, characterized in that the smallest distance a _{x has} a range of 5 <a _x <50 mm, in particular a range of 8 <a _x <30 mm. Heat exchanger according to claim 13, characterized in that the distance (a ₁ , a ₂ , a ₃ ...) of the rows is an (integer) multiple of the smallest distance a _x .

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