US20100139902A1

US20100139902A1 - Plastic heat exchanger

Info

Publication number: US20100139902A1
Application number: US12/329,225
Authority: US
Inventors: Bobbye K. Baylis; Paul D. Daly; Ian R. McLean
Original assignee: Mahle International GmbH
Current assignee: Mahle International GmbH
Priority date: 2008-12-05
Filing date: 2008-12-05
Publication date: 2010-06-10
Also published as: ATE545836T1; EP2204628A1; EP2204628B1

Abstract

The invention relates to a plastic heat exchanger (1), in particular for automotive applications, having an inlet tank (2) which has an inlet (5) for a first fluid and surrounds an inlet chamber (6), having an outlet tank (3) which has an outlet (7) for the first fluid and surrounds an outlet chamber (8), having multiple plastic tubes (4) which are tightly connected to the inlet tank (2) and to the outlet tank (3) and connect the inlet chamber (6) to the outlet chamber (8) so they communicate with one another and around which a second fluid flows during operation.

To improve the heat transfer, at least some of the plastic tubes (4) have at least one longitudinal section (9) in which ring-shaped areas (13) having variable cross sections follow one another in the longitudinal direction of the tube.

Description

The present invention relates to a plastic heat exchanger, in particular for automotive applications.
A heat exchanger usually has an inlet tank that has an inlet for a first fluid and surrounds an inlet chamber. Furthermore, an outlet tank is also provided that has an outlet for the first fluid and surrounds an outlet chamber. The plastic heat exchanger also has several plastic tubes which are tightly connected to the inlet tank and to the outlet tank. The plastic tubes connect the inlet chamber to the outlet chamber so they communicate, and a second fluid flows around them during operation of the plastic heat exchanger.
Plastic heat exchangers are characterized by a lightweight design and low manufacturing cost in comparison with traditional metal heat exchangers. However, the plastic tubes have a reduced coefficient of thermal conductivity in comparison with metal tubes. To be able to achieve a heat transfer comparable to that of a metal heat exchanger, a plastic heat exchanger must be designed with larger dimensions.
The present invention relates to the problem of providing an improved embodiment for a plastic heat exchanger, which is characterized in particular by the fact that it allows an improved heat exchange which can be utilized in particular to design the plastic heat exchanger to be smaller and/or more compact.
According to the invention, the solution of this problem is achieved by the subject matter of the independent claim. Advantageous embodiments are the subject matter of the dependent claims.
The invention is based on the general idea of furnishing at least some of the plastic tubes in at least one longitudinal section with ring-shaped areas having varying cross sections following one after the other in the longitudinal direction of the tube. In said longitudinal sections, the ring-shaped areas create turbulence during operation of the heat exchanger due to the varying cross sections, this turbulence leading to crosscurrents and/or to a transverse mixing of the first fluid flowing in the plastic tubes. The heat exchange between the respective plastic tube and the first fluid can be improved significantly in this way. Subsequently, the ability to transfer heat between the first fluid and the second fluid can be increased throughout the entire heat exchanger, so that the heat exchanger can be designed to be more compact, i.e., smaller on the whole, while achieving the same performance. It is noteworthy here that the plastic tubes need not be provided with varying cross sections over their entire length but instead over only longitudinal sections or partial sections of the plastic tubes, which may turn out to be comparatively short in comparison with the total length of the respective plastic tubes.
The longitudinal sections in which the ring-shaped areas with varying cross sections follow one another may be designed, for example, in the manner of bellows or in the manner of a corrugated tube. In this way, a plurality of such ring-shaped areas with a varying cross section can be implemented in a comparatively small longitudinal section to produce the desired disturbance in interfacial flow.
With the plastic tubes, the longitudinal sections having the varying ring areas can be manufactured by forming by upsetting so that this is performed during the manufacture of the plastic tubes in particular. Extrusion of plastic tubes may be extruded especially economically, for example. In a state in which they have not yet completely hardened, the plastic may then be formed by upsetting especially easily to form said longitudinal sections.
According to an especially advantageous embodiment, the plastic tubes may each have an inlet section connected to the inlet tank, an outlet section connected to the outlet tank and a central section connecting the inlet section to the outlet section. The wall thickness of the plastic tubes in the central section is smaller than that in the inlet section and/or than that in the outlet section. To be able to join the plastic tubes to the inlet tank and/or to the outlet tank, a minimum wall thickness is necessary. In this embodiment, however, the plastic tubes have this minimum wall thickness only in the inlet section and in the outlet section. In the central section in between, the wall thickness is reduced. In this way, the heat transfer through the plastic tubes and thus between the two fluids can be improved.
Additional important features and advantages of the invention are derived from the dependant claims, the drawings and the respective description of the figures on the basis of the drawings.
It is self-evident that the features mentioned above and those yet to be explained below may be used not only in the particular combination given but also in other combinations or alone without going beyond the scope of the present invention.
Preferred exemplary embodiments of the invention are depicted in the drawings and are explained in greater detail in the following description, where the same reference numerals refer to the same or similar or functionally identical components.

Schematically in the drawings:

FIG. 1 shows a highly simplified basic diagram like a schematic for a plastic heat exchanger,

FIGS. 2 through 6 each show a greatly simplified longitudinal section through a plastic tube in the area of a longitudinal section having varying cross sections in various embodiments,

FIGS. 7 through 9 each show a highly simplified longitudinal section through a plastic tube in various embodiments,

FIGS. 10 through 14 each show a simplified longitudinal section through a plastic tube, each having at least one longitudinal section having varying cross sections, shown in various embodiments.

According to FIG. 1, a plastic heat exchanger 1 comprises an inlet tank 2, an outlet tank 3 and multiple plastic tubes 4. In the simplified diagram in FIG. 1, only four such plastic tubes 4 are shown. It should be obvious that significantly more of such plastic tubes 4 or several groups of such plastic tubes 4 may be used here. The heat exchanger 1 is especially suitable for automotive applications. For example, it may be used as the main radiator in an engine coolant circuit to cool the coolant of the engine coolant circuit with an air flow. Likewise, the heat exchanger 1 may be assigned to an air conditioning system or to an oil circuit of the motor vehicle.
In a primary application the heat exchanger 1 may be used as a charge air cooler on a turbo charge engine application. The inlet tank 2 has an inlet 5 for a first fluid, which may be a gas or a liquid. The inlet tank 2 surrounds an inlet chamber 6. The outlet tank 3 has an outlet 7 through which the first fluid can be escape. The outlet tank 3 surrounds an outlet chamber 8. The plastic tubes 4 are tightly connected to the inlet tank 2 on the one hand and to the outlet tank 3 on the other hand. For example, the inlet tank 2 and the outlet tank 3 may also be made of plastic. Then the plastic tubes 4 are expediently tightly connected to the respective tank 2, 3 by means of welded joints. The plastic tubes 4 implement a communicating connection between the inlet chamber 6 and the outlet chamber 8. This means that the first fluid can flow out of the inlet chamber 6 through the plastic tubes 4 into the outlet chamber 8 during operation of the heat exchanger 1. The plastic tubes 4 have a second fluid flowing around them during operation of the heat exchanger 1, the second fluid optionally being a gas or a liquid.
At least some of the plastic tubes 4, preferably all the plastic tubes 4, each have at least one longitudinal section 9, which is characterized in that ring-shaped areas with a varying flow-through cross sections follow one another in the longitudinal direction of the tube. The plastic tubes 4 preferably have a circular cross section and are each designed to be straight in the example in FIG. 1. Essentially, however, other round cross sections and/or a curved design are also conceivable.
Accordingly, the longitudinal direction of the tube is either straight or curved. In the example shown in FIG. 1, the longitudinal sections 9 are positioned along the individual plastic tubes 4 in such a way that they are arranged offset from one another in the longitudinal direction of the tube with neighboring plastic tubes 4. In this way the individual plastic tubes 4 can be packed and/or arranged more densely side by side so that the heat exchanger 1 can be designed to be more compact as a whole. In particular, neighboring tubes 4 can therefore be arranged relatively close to one another with regard to their longitudinal middle axes 17 so that distance 18 can be minimized. For example, an offset 10 between the longitudinal sections 9 of neighboring plastic tubes 4 is designed to be slightly larger, e.g., 10-20% larger than length 11 of the longitudinal sections 9.
In the example of FIG. 1, all the longitudinal sections 9 are designed to be the same length. They are shorter than total length 12 of the individual plastic tubes 4. For example, the length 11 of longitudinal sections 9 is in a range between and including 5% and 10% of the total length 12 of the respective plastic tube 4. In the example in FIG. 1, each plastic tube 4 is also provided with only one single such longitudinal section 9.
According to FIGS. 2 through 6, the respective longitudinal section 9 may preferably be designed in the manner of bellows or a corrugated tube. The ring-shaped areas here are indicated by curly brackets and are labeled as 13 in FIGS. 2 through 6. These ring-shaped areas 13 in the longitudinal direction of the tube, indicated by an arrow 14 in FIGS. 2 through 6, discernibly have varying cross sections. The sequence of varying cross sections ensures a disturbance in the interfacial layer and creates turbulence to improve the mixing effect in the first fluid. The ring-shaped areas 13 may have a corrugated profile according to FIG. 2 or may have a saw-toothed profile according to FIG. 3 or may have a rectangular profile according to FIG. 4. Likewise, a stepped profile according to FIG. 5 is also conceivable. FIG. 6 shows a special embodiment in which the ring-shaped areas 13 each have ring bulges 15, one of which protrudes inward and the others protrude outward. The different ring bulges 15 develop directly into one another, forming a sinusoidal profile. It is clear that essentially only outwardly protruding ring bulges 15 or only inwardly protruding ring bulges 15 may be provided. The ring bulges 15 connect tube areas 16 in the longitudinal direction of the tube. These tube areas 16 may essentially have constant cross sections. The varying cross sections within the respective area 13 are then implemented by the bulges 15. In FIG. 6, however, the successively following tube areas 16 are provided with stepped cross sections as in the embodiment shown in FIG. 5. In the embodiments in FIGS. 2 through 4, increasing and decreasing cross sections follow one another, so that on the average there is a constant cross section, but FIGS. 5 and 6 show decreasing cross sections in the direction of flow. In particular the respective longitudinal section 9 therefore has a decreasing average cross section in its longitudinal direction and/or in the direction of flow of the first fluid.
The ring-shaped areas 13 having varying cross sections and/or the longitudinal sections 9 may be implemented by forming the plastic tube 4 by upsetting, for example. Such forming by upsetting may be implemented in a particularly favorable manner during the production of the plastic tubes 4, e.g., during an extrusion operation.
According to FIGS. 1 and 7 to 9, the plastic tubes 4 may each have an inlet section 19, an outlet section 20 and a central section 21. Whereas the inlet section 19 is connected to the inlet tank 2, the outlet section 20 is connected to the outlet tank 3. FIGS. 7 to 9 show the plastic tubes 4 without the tanks 2, 3 and for a simplified diagram also without the longitudinal sections 9. The central section 21 connects the inlet section 19 to the outlet section 20, and transitional sections 22 may also be provided which can be assigned to the central section 21. It is likewise possible to assign the one transitional section to the inlet section 19 and the other transitional section 22 to the outlet section 20. For the embodiments illustrated in FIGS. 7 to 14, it is important that wall thickness 23 of the central section 21 is smaller than wall thickness 24 of the inlet section 19 and is smaller than wall thickness 25 of the outlet section 20. The wall thicknesses 24, 25 of the inlet section 19 and of the outlet section 20 are the same size. They are as small as possible but must have a minimum wall thickness to be able to establish the connection to the respective tank 2, 3 in a sufficiently stable manner that will be reliable during mass production. The inlet section 19 and the outlet section 20 thus expediently have this minimum wall thickness 24 and/or 25, which is required for the respective joining technique. In contrast with that, the central section 21 has a much smaller wall thickness 23. For example, the smaller wall thickness 23 is in a range from 30% up to and including 40% of the wall thickness 24 of the inlet section 19 or the wall thickness 25 of the outlet section 20. The preferred embodiment shown here is the one in which the wall thickness 23 in the central section 21 is approximately half as large as the wall thicknesses 24, 25 of the inlet section 19 and/or of the outlet section 20.
According to FIG. 7, the reduced wall thickness 23 of the central section 21 can be implemented by reducing only an outside cross section 26 on the respective plastic tube 4. As an alternative, it is also possible according to FIG. 8 to enlarge only an inside cross section 27 of the plastic tube 4 to implement the reduced wall thickness 23 of the central section 21. It is likewise possible according to FIG. 9 to produce the reduced wall thickness 23 of the central section 21 by reducing the outside cross section 26 on the one hand and widening the inside cross section 27 on the other hand.
The respective longitudinal section 9 may then be arranged in the inlet section 19. Alternatively, the respective longitudinal section 9 may be arranged in the outlet section 20. It is likewise possible to arrange the respective longitudinal section 9 in the central section 21. Furthermore, the respective longitudinal section 9 may be arranged in one of the transitional areas 22, e.g., at the transition 22 between the inlet section 19 and the central section 21 or at the transition 22 between the central section 21 and the outlet section 20. In addition, essentially an embodiment in which the respective longitudinal section 9 is arranged in the central section 21 is conceivable, a greater wall thickness being implemented here in the central section 21, e.g., for simplified implementation of this longitudinal section 9. This greater wall thickness in the central section 21 is labeled as 23′ in the variant illustrated in FIG. 13. It is larger in particular than either upstream or downstream from the longitudinal section 9 within the central section 21. At its maximum it is as large as the wall thicknesses 24, 25 of the inlet section 19 and/or of the outlet section 20.
The inlet section 19 preferably amounts to max. 20% of the total length 12 or max. 10% of the total length 12 of the respective plastic tube 4. The outlet section 20 comprises max. 20% or max. 10% of the total length 12 of the respective plastic tube 4.
FIG. 10 shows an embodiment in which, within the respective plastic tube 4, there are two such longitudinal sections 9. These two longitudinal sections 9 are arranged at a distance from one another in the longitudinal direction of the tube. Said distance 28 may be, for example, five times greater than outside diameter 29 or inside diameter 30 of the tube 4. In the embodiment shown in FIG. 10, the first longitudinal section 9 shown at the left may be a distance 32 away from the inlet 31 of the respective plastic tube 4, said distance being from 50% up to and including 60% of the total length 12 of the tube 4, for example. The length 11 of the longitudinal sections 9 preferably amounts to 5% up to and including 10% of the total length 12 of the respective tube 4. An outside cross section and/or outside diameter 33 in the largest cross section of the respective longitudinal section 9 and/or the respective inside cross section or inside diameter 34 may be from 1.4 up to and including 2.0 times larger than the outside diameter 29 and/or the inside diameter 30 of the tube 4.
FIG. 11 shows an embodiment in which the respective longitudinal section 9 is implemented inside the central section 21. Here again, the different wall thicknesses 23, 24, 25 are discernible. Also within the longitudinal section 9 here, the largest outside diameter 33 and the largest inside diameter 34 are 1.4 to 2.0 times greater than the outside diameter 29 and the inside diameter 30 of the plastic tube 4, respectively, in the central section 21 or than in the inlet section 19 or in the outlet section 20 here.
FIG. 12 shows a variant in which the longitudinal section 9 is incorporated into the outlet section 20, i.e., in an area of the plastic tube 4 which has a greater wall thickness 25. The central section 21 which has the smaller wall thickness 23 is shown here in a shortened form for the sake of a clearer illustration. In this embodiment, it comprises, for example, an area including 30% up to and including 40% of the total length 12 of the respective plastic tube 4. However, as stated, the inlet section 19 comprises an area of 10% up to and including 20% of the total length 12. The length 32 of the inlet section 19 and the length 28 of the central section 21 are not shown to scale in FIG. 12.
The reduced wall thickness 23 in the central section 21 improves not only the heat transfer between the two fluids but at the same time it also leads to substantial weight savings for the heat exchanger 1. In addition, manufacturing costs can be reduced because substantially less plastic material is needed.
FIG. 13 now shows an embodiment in which a section 35 having a greater wall thickness 23′ is provided within the central section 21, which is characterized by reduced wall thickness 23. This wall thickness may be between the wall thickness 23 of the other central section 21 and between the wall thicknesses 24 and 25 of the inlet section 19 or of the outlet section 20, respectively. Production of the respective longitudinal section 9, which is characterized by varying cross sections, can be simplified in this way. For example, said section 35 is provided at the end of the central section 21 so that the central section 21 develops into the transitional section 22 into the end section 20 via this longitudinal section 35. Likewise, the central section 21 may also develop directly into the end section 20 via this section 35. The central section 21 extends from the inlet section 19 and/or from the transitional section 22 on the inlet end up to the beginning of the section 35 containing the longitudinal section 9 for a length 36, which is shown in a shortened form here and may be, for example, in a range from 40% up to and including 60% of the total length 12 of the plastic tube 4. FIG. 13 also shows the inside diameter 30 of the plastic tube 4 in the inlet section 19.
FIG. 14 shows an embodiment in which the longitudinal section 9 is arranged in the transitional section 22 on the outlet end. In this way the longitudinal section 9 has an increasing wall thickness according to the transitional section 22 from the central section 21 to the outlet section 20. For example, the length 32 of the inlet section 19 is again in a range from 10% up to and including 20% of the total length 12 of the plastic tube 4. The length 11 of the longitudinal section 9 corresponds here to the length of the transitional section 22 on the outlet end and is, for example, in a range from 5% up to and including 10% of the total length 12. A length 37 of the outlet section 20 is expediently in a range from 10% up to and including 20% of the total length 12. In addition, the outside diameter 29 of the tube 4 in the inlet section 19 is also indicated in FIG. 14.

Claims

1. A plastic heat exchanger, in particular for automotive applications,

having an inlet tank (2) which has an inlet (5) for a first fluid and surrounds an inlet chamber (6),

having an outlet tank (3) which has an outlet (7) for the first fluid and surrounds an outlet chamber (8),

having multiple plastic tubes (4) which are tightly connected to the inlet tank (2) and to the outlet tank (3) and connect the inlet chamber (6) to the outlet chamber (8) so they communicate with one another and around which a second fluid flows during operation,

wherein at least some of the plastic tubes (4) each have at least one longitudinal section (9), in which ring-areas (13) having varying cross sections follow one another in the longitudinal direction of the tube.

2. The plastic heat exchanger according to claim 1, wherein the respective longitudinal section (9) is designed in the manner of bellows or in the manner of a corrugated tube.

3. The plastic heat exchanger according to claim 1, wherein the respective longitudinal section (9) is designed by forming the plastic tube (4) by upsetting during production of the plastic tube (4) in particular.

4. The plastic heat exchanger according to claim 1, wherein the ring-shaped areas (13) have a corrugated profile or a sawtooth profile or a rectangular profile or a stepped profile or a combination thereof in the longitudinal direction of the tube.

5. The plastic heat exchanger according to claim 1, wherein

the ring-shaped areas (13) have ring bulges (15) all of which protrude inward or all of which protrude outward or one of which protrudes inward and the others of which protrude outward,

the ring bulges (15) connect tube areas (16) having constant or stepped cross sections to one another in the longitudinal direction of the tube.

6. The plastic heat exchanger according to claim 1, wherein the plastic tubes (4) each have an inlet section (19) connected to the inlet tank (2), an outlet section (20) connected to the outlet tank (3) and a central section (21) connecting the inlet section (19) to the outlet section (20), the wall thickness (23) thereof being smaller than the wall thicknesses (24, 25) of the inlet section (19) and of the outlet section (20).

7. The plastic heat exchanger according to claim 6, wherein the wall thickness (23) of the central section (21) is from 30% up to and including 70% of the wall thickness (24) of the inlet section (19) or the wall thickness (25) of the outlet section (20), such that the wall thickness (23) of the central section (21) amounts to in particular approx. 50% of the wall thickness (24) of the inlet section (19) or the wall thickness (25) of the outlet section (20).

8. The plastic heat exchanger according to claim 6, wherein the reduced wall thickness (23) of the central section (21) is implemented exclusively by reducing the outside cross section (26) of the plastic tube (4).

9. The plastic heat exchanger according to claim 6, wherein the reduced wall thickness (23) of the central section (21) is implemented exclusively by widening the inside cross section (27) of the outlet tube (4).

10. The plastic heat exchanger according to claim 6, wherein the reduced wall thickness (23) of the central section (21) is implemented by reducing the outside cross section (26) of the plastic tube (4) and by widening the inside cross section (27) of the plastic tube (4).

11. The plastic heat exchanger according to claim 6, wherein the respective longitudinal section (9) is situated in the inlet section (19).

12. The plastic heat exchanger according to claim 6, wherein the respective longitudinal section (9) is situated in the outlet section (20).

13. The plastic heat exchanger according to claim 6, wherein the respective longitudinal section (9) is situated in the central section (21).

14. The plastic heat exchanger according to claim 6, wherein the respective longitudinal section (9) is situated at the transition (22) between the inlet section (19) and the central section (21).

15. The plastic heat exchanger according to claim 6, wherein the respective longitudinal section (9) is situated at the transition (22) between the central section (21) and the outlet section (20).

16. The plastic heat exchanger according to claim 6, wherein the respective longitudinal section (9) is situated in the central section (21) such that the central section (21 ) has a greater wall thickness (23′) in the area of the longitudinal section (9) than upstream or downstream thereof.

17. The plastic heat exchanger according to claim 6, wherein the inlet section (19) comprises max. 20% or max. 10% of the total length (12) of the respective plastic tube (4).

18. The plastic heat exchanger according to claim 6, wherein the outlet section (20) comprises max. 20% or max. 10% of the total length (12) of the respective plastic tube (4).

19. The plastic heat exchanger according to claim 1, wherein at least two such longitudinal sections (9) are arranged in the respective plastic tube (4) with a distance between them in the longitudinal direction of the tube.

20. The plastic heat exchanger according to claim 19, wherein the longitudinal sections (9) within the respective plastic tube (4) are a distance (28) apart from one another, said distance being at least five times greater than the inside diameter (30) of the plastic tube (4).

21. The plastic heat exchanger according to claim 1, wherein the respective longitudinal section (9) extends from 5% up to and including 10% of the total length (12) of the respective plastic tube (4).

22. The plastic heat exchanger according to claim 1, wherein the longitudinal sections (9) are arranged so they are offset relative to one another in the longitudinal direction of the tube in the case of neighboring plastic tubes (4).

23. The plastic heat exchanger according to claim 1, wherein the inlet tank (2) is made of plastic and is welded to the plastic tubes (4).

24. The plastic heat exchanger according to claim 1, wherein the outlet tank (3) is made of plastic and is welded to the plastic tubes (4).