EP2146173B1

EP2146173B1 - Plastic heat exchanger

Info

Publication number: EP2146173B1
Application number: EP08160592.5A
Authority: EP
Inventors: Paul D. Daly; Roy Haworth; Ian R. Mclean; Bobbye Kaye Whitenton Baylis
Original assignee: Mahle International GmbH
Current assignee: Mahle International GmbH
Priority date: 2008-07-17
Filing date: 2008-07-17
Publication date: 2015-09-09
Anticipated expiration: 2028-07-17
Also published as: EP2146173A1

Description

This invention generally relates to a heat exchanger for use in a motor vehicle. More particularly, this invention relates to a plastic heat exchanger.
A heat exchanger according to the preamble of claim 1 is known from US 2005/0247442 A1 .
A heat exchanger is adapted for transferring heat from one fluid to another fluid wherein the fluids are not physically in contact. One example application of a specific example of a heat exchanger is an intercooler which is adapted for cooling the charge air exiting the compressor of an air charging device such as a turbocharger. An intercooler is desired to cool and to reduce the volume of the charge air so that more air can be introduced into the cylinders of an engine. The hot charge air is directed through a plurality of tubes over which cooling air flows.
A conventional heat exchanger for automotive appliances includes a plurality of tubes that span between manifolds or tanks on each end. The tanks typically comprise an open internal volume in communication with an open end of the plurality of tubes. The tanks include an inlet to provide for a single inlet or outlet for air flow through the heat exchanger. The tubes are typically formed from metals such as aluminium, copper or brass that are welded or brazed to end plates. The end plates are in turn attached to the tanks to provide the desired inlet and outlet for the heat exchanger.
Disadvantageously, metal tube construction and fabrication provide a relatively heavy and cumbersome device. Further, the use of metal tubes limits the configuration of the heat exchanger. The constraints on devices installed within vehicles are becoming more demanding as related to cost, weight and flexibility of design. Therefore it has been considered to produce a heat exchanger from plastic whereby the weight of the heat exchanger can be reduced whilst offering improved design flexibility. A disadvantage of using plastic as a material for the heat exchanger is that the heat transfer from plastic to air is relatively low compared to the heat transfer between metal and air. Therefore the efficiency of a plastic heat exchanger is lower than that of an equivalent metal heat exchanger.
Accordingly, it is desirable to design a plastic heat exchanger with an improved heat transfer between the cooling medium and the medium to be cooled.
A plastic heat exchanger assembly according to the present invention includes the features of claim 1. A baffle is arranged in the heat exchanger which extends across the flow path of the air flowing over plastic tubes. The baffle includes openings which allow the air to flow through the baffle and over the plastic tubes. The baffle introduces turbulence into the air flow and disrupts the boundary layer on the outside of the tube walls. By disrupting this boundary layer the heat transfer between the fluid inside the tubes and the air flowing over the tubes can be improved. The baffle can also serve as a support for the tubes.
These features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
Figure 1 is a schematic view of an example heat exchanger assembly.
Figure 2 is a schematic view of an heat exchanger baffle.
Figures 3A-3D are schematic views of example shapes for openings in the heat exchanger baffle.
Figure 4 is a schematic view of an example square tube, not according to the invention.
Figure 5 is a schematic view of an example twisted square tube.
Figure 6 is a schematic cross-section of the twisted square tube.
Referring to Figure 1, a heat exchanger assembly 10 includes a first end plate 12 and a second end plate 14. Extending between the end first end plate 12 and the second end plate 14 are a plurality of plastic tubes 16. The plastic tubes 16 are secured to the end plates 12, 14 to provide the desired seal between the end plates 12, 14 and the ends of the tubes 16. This can be achieved by laser welding or another suitable method.
A first tank 18 is attached to the first end plate 12 and a second tank 20 is attached to the second end plate 14. The first tank 18 includes an inlet opening 30 providing an inlet for a cooling fluid 50 and the second tank 20 includes an outlet opening 32 providing an outlet for the cooling fluid 50. The cooling fluid 50 follows a path through the first tank 18, the plastic tubes 16 and the second tank 20.
The air which is to be cooled (or charge air) flows over the plastic tubes 16 in a direction indicated with arrows 22 perpendicular to the fluid flowing through the tubes 16. As the charge air flows over the plastic tubes 16 heat is transferred through the plastic tubes 16 to the cooling fluid 50 inside the tubes 16. In order to improve the heat transfer between the fluid 50 inside the plastic tubes 16 and the air flow over the plastic tubes 16 a deflector or baffle 24 is introduced into the heat exchanger 10. The baffle 24 extends between the endplates 12, 14 of the heat exchanger 10. The baffle 24 has preferably a concertina form, in particular a zigzag form as shown or a wave form. The concertina form extends through multiple rows of tubes 16. The concertina form provides for the baffle 24 to be angled relative to both charge air flow 22 and the plastic tubes 16. The specific angle of the baffle parts is provided to disrupt air flow 22, but not generate back pressure or reduce desired air flow.
Referring to Figure 2, a portion of the baffle 24 is shown with first openings 26 or oval shaped openings 26 which each accommodate a corresponding one of the plurality of plastic tubes 16. The plastic tubes 16 have a circular cross section. It is however also possible for the tubes 16 to have a non-circular cross section, e.g. oval or square, in order to increase the surface area of the tube and therefore improve the heat transfer between the cooling fluid and the charger air.
Between the oval shaped openings 26, second openings 28 or turbulence generating openings 28 are provided in the baffle 24. The turbulence generating openings 28 allow the air flowing over the plastic tubes 16 in the direction 22 to flow past the baffle 24 and, in doing so, the air flow is disturbed. The disturbed air creates turbulence that disrupts the boundary layer flow on the outer surface of the plastic tubes 16. Through disturbing the boundary layer flow the heat transfer between the plastic tubes 16 and the charge air flowing over the plastic tubes 16 can be increased.
The area of the baffle 24 with turbulence generating openings 28 is large enough that no considerable back pressure is created within the heat exchanger 10 which would significantly reduce the air flow volume through the heat exchanger 10 and consequently adversely affect the cooling efficiency. The example baffle 24 can be a mesh e.g. a wire mesh whereby the plastic tubes 16 are inserted through openings in the wire mesh and openings adjacent to the plastic tubes serve as the turbulence generating openings.
Alternate example shapes of the openings 28 are shown in Figures 3A-3D. Figure 3A illustrates a star shaped cross-section 34. Figure 3B illustrates a triangle shaped tube cross-section 36. Figure 3C illustrates a cross shaped cross-section 38. Figure 3D illustrates a pentagon shaped cross-section 40. Other shapes which produce a large turbulence of the air flowing past the baffle 24 can also be used. It is particularly preferable for the shape to have a large edge length to surface area ratio.
Referring back to Figure 1, the baffle 24 can be used as a support for the plastic tubes 16 at the same time as providing the turbulence producing effect. This simplifies the manufacture in that the tubes 16 can be maintained together in a block using the baffle 24 as a support whilst the endplates 12, 14 are being attached. The example baffle 24 is shown to have five folds. It would however also be possible for the baffle 24 to be longer or shorter and to have more or less folds dependent on the size or shape of the heat exchanger 10. The baffle 24 can also be used as a conductor to conduct heat from the charge air to the cooling fluid. The baffle 24 can be made from any suitable material including metal, plastic or card.
Due to the low heat transfer between air and plastic it is preferable to have a liquid as the cooling fluid flowing through the plastic tubes 16. It is however possible in applications where no cooling liquid is available to have the charge air flowing through the plastic tubes 16 and the cooling air flowing in the direction of the arrows 22 over the plastic tubes 16. In the case where the charge air is flowing through the plastic tubes 16 it is advantageous to create turbulence within the plastic tubes 16. This can be achieved by producing non-circular shaped twisted tubes.
Referring to Figures 4-6, a plastic tube 42 with a square cross section can be produced e.g. by extrusion. By then twisting the square tube 42 along its length and about the axis 52 a twisted tube 44 is provided. The twisted tube 44 provides that the cross-sectional shape is twisted about the axis 52 at least once along a length between the endplates. The twisted tube 44 generates an internal air flow that follows the twists in the corners 48 (Figure 6). Much of the airflow will try to continue straight down a middle flow area 46 of the twisted tube 44 and creates turbulence where it interfaces with the air 48 from the corners which is twisting.
The heat exchanger 10 is preferably adapted to provide an intercooler for cooling charge air. The heat exchanger 10 may alternatively be adapted to provide a cooler for cooling batteries of an electric vehicle or a cooler for cooling a fuel cell, e.g. for cooling a fuel cell, of a vehicle, in particular a fuel cell vehicle. In general, the heat exchanger 10 can be adapted to provide a cooler for cooling fluids, i.e. liquids and/or gases, in a vehicle, in particular in an electric vehicle.
An electric vehicle uses at least one electric motor for generating drive power. It may also have an internal combustion engine (hybrid vehicle) or may not (pure electric vehicle). A fuel cell vehicle is a kind of an electric vehicle provided with at least one fuel cell for generating electric power to power at least one electric motor and/or to charge at least one battery of the electric vehicle.

Claims

A heat exchanger comprising:
a plurality of plastic cooling tubes (16) extending between a first end plate (12) and a second end plate (14), a baffle (24) arranged in the heat exchanger (10)
characterized in that
- the battle extends between the first end plate (12) and the second end plate (14), the baffle (24) comprising a plurality of first openings (26) for receiving a respective plastic cooling tube (16) and a plurality of second openings (28) arranged between the first openings (26),

- the plastic tubes (16) have a non-circular cross section,

- the tubes (16) furthermore have a twisted form along their length.
The heat exchanger according to claim 1, wherein the baffle (24) has one or more folds or waves to form a concertina shape.
The heat exchanger according to claim 1 or 2, wherein the second openings (28) in the baffle (24) are circular.
The heat exchanger according to any one of the claims 1 to 3, wherein the baffle (24) is made from plastic, metal or card.
The heat exchanger according to any one of the claims 1 to 4, wherein the first end plate (12) is included into a first tank (18); the second end plate (14) is included into a second tank (20); the plastic tubes (16) being in communication on distal ends with each of the first tank (18) and the second tank (20).
The heat exchanger according to any one of the claims 1 to 5, wherein the heat exchanger (10) is adapted for providing at least one of the following:
an intercooler for cooling charge air, a cooler for cooling batteries of an electric vehicle,

a cooler for cooling a fuel cell, a cooler for cooling a fuel cell in a vehicle, in particular a fuel cell vehicle, a cooler for cooling liquid and/or gaseous fluids in a vehicle, in particular in an electric vehicle and/or in a fuel cell vehicle.