Heat Exchangers

Abstract

A heat exchanger 11 for use as a cross flow radiator for an engine cooling system has a heat exchanger matrix 12, header tanks 13, 14 and a side plate 16 arranged at the upper of a pair of opposite side edges 16, 17 of the matrix 12. The matrix 12 has tubes 18 which extend between tanks 13, 14 and cooling fins 19. A restrictor plate 21 arranged on side plate 16 restricts air flow past fin 19A. Restrictor plate 21 may have cut out gaps or castellations 22. This reduces heat transfer through the fins above the uppermost tube 18A allowing for a more even temperature distribution, which reduces stress from thermal expansion.

Description

FIELD OF INVENTION

The invention relates to heat exchangers; in particular to engine cooling system radiators.

BACKGROUND OF THE INVENTION

Heat exchangers, particularly those used as engine cooling system radiators, often have a generally rectangular heat exchanger matrix, an inlet header tank and an outlet header tank each at a respective one of one pair of opposite side edges of the matrix and a pair of side plates each arranged at an a respective one of the other pair of opposite side edges of the matrix. The matrix has a number of tubes extending in a parallel array between the tanks to provide a path for liquid coolant to flow from one tank to the other. Cooling fins are arranged between adjacent pairs of tubes and between each side plate and the adjacent tube such that in use air flows between adjacent pairs of tubes and between each side plate and its adjacent tube.

A problem with the heat exchangers described above is that the tubes which are adjacent the side plates may be overcooled since it is common to provide the same size and type of fins between these components as are used between adjacent pairs of tubes. The fins situated between a side plate and an adjacent tube can conduct heat away from one tube only while the fins situated between adjacent pairs of tubes have to conduct heat away from two tubes. This overcooling can be particularly noticeable if the heat exchanger is arranged with the tubes horizontal and the header tanks vertical (a so-called cross flow radiator). Where there is a relatively low rate of flow of liquid coolant and high air flow such as is encountered in a motor vehicle during gentle open road cruising, the hotter coolant tends to rise by convection to the upper tubes. The difference in temperature between the uppermost tube (i.e., the one adjacent the uppermost side plate) and the next tube down can lead to stress cracking of the tubes or tube to header tank joint with a subsequent loss of coolant.

SUMMARY OF THE INVENTION

According to the invention, there is provided a heat exchanger having a generally rectangular heat exchanger matrix, an inlet header tank and an outlet header tank each at a respective one of a pair of opposite side edges of the matrix and a pair of side plates each arranged at an a respective one of the other pair of opposite side edges of the matrix. The matrix has a plurality of tubes extending in a parallel array between the tanks to provide a path for liquid to flow from one tank to the other and cooling fins arranged between adjacent pairs of tubes and between each side plate and the adjacent tube such that, in use, air flows between adjacent pairs of tubes and between each side plate and the adjacent tube. The heat exchanger also has heat transfer restrictors to restrict the transfer of heat from the tube adjacent one of the side plates to the air flow between the one side plate and the tube.

In one embodiment, the heat transfer restrictor has a restrictor plate arranged on at least one of the side plates to restrict the flow of air between the one side plate and the adjacent tube.

In another embodiment, the restrictor plate has a blanking plate having cut out gaps or castellations. The blanking plate, in use, blocks the flow of air between the side plate and the adjacent tube over part of its length and allowing air to flow through the gaps over the remainder of its length. Alternatively, the restrictor plate has a blanking plate with perforations to restrict the flow of air between the side plate and the adjacent tube or a strip of constant width that extends the length of the side plate and over part of the gap between the side plate and the adjacent tube to leave a narrow slit for air to pass through. The restrictor plate may be attached to or form part of a cooling fan cowl.

An advantage of the present invention is that the heat transfer rate from the plurality of tubes is more uniform so that the temperatures differences are lessened. Consequently, the stresses on the radiator are less, thereby preventing cracking failures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example and with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of part of a vehicle heat exchanger according to the invention; and

FIG. 2 is a perspective view based on FIG. 1 but to a larger scale showing part of a conventional vehicle heat exchanger according to the prior art.

DETAILED DESCRIPTION

The vehicle heat exchanger 11 shown in FIG. 1 is a cross flow radiator for an engine cooling system. It has a generally rectangular heat exchanger matrix 12, an inlet header tank 13 and an outlet header tank 14, each at a respective one of one pair of opposite side edges 15 of the matrix 12. A side plate 16 is arranged at the upper of the other pair of opposite side edges 17 of the matrix 12, there being a corresponding side plate 16 arranged at the opposite, lower, side edge (not shown). The matrix 12 has a number of tubes 18 which extend in a parallel array between the tanks 13, 14 to provide a path for liquid coolant to flow from one tank to the other. Cooling fins 19 are arranged between adjacent pairs of the tubes 18 and between each side plate 16 and the adjacent tube such that in use air flows not only between adjacent pairs of tubes but also between each side plate and its adjacent tube. As is best seen in the conventional heat exchanger shown in FIG. 2, the fins 19 are in the form of a flat strip bent into a corrugated or serpentine formation with the crests bonded to the tubes to aid conduction. As a production expedient, the fins 19 are identical throughout the matrix 12 such that the fins 19A between each side plate 16 and its adjacent tube 18A are the as fins 19B as those between adjacent tubes 18A and 18B.

In FIG. 2, tube 18A is cooled by fins 19A and 19B. Fin 19B is shared between tubes 18A and 18B. Tube 18B is cooled by fins 19B and 19C. Both 19B and 19C are shared between two tubes: 18A and 18B share fin 19B and 18B and 18C share fin 19C. Because tube 18A has one fin that is not shared, fin 19A, and one fin that is shared, fin, 19B, it receives preferential cooling compared to tube 18B in which its two adjacent fins are shared fins. Consequently tube 18A, which is an edge tube, runs cooler than interior tubes, such as tubes 18B and 18C. The drawback of unequal heat transfer rates is that the edge tube 18A runs colder than its adjacent tube 18B so that the different expansion rates create stresses that can result in structural failure.

In the heat exchanger shown in FIG. 1, a restrictor plate 21, according to an aspect of the present invention, is arranged on the upper side plate 16 to restrict the flow of air past edge fin 19A, i.e., the fin between side plate 16 and uppermost tube 18A. Restrictor plate 21 is shown as being attached to side plate 16 (e.g. by adhesives, riveting or by welding). However, in an alternative embodiment, restrictor plate 21 is formed as part of side plate 16. In yet another alternative embodiment, restrictor plate 21 is part of or attached to a fan cowl of any known type, e.g. as shown in EP0108479B1. The restrictor plate 21 is a rectangular blanking plate which blocks the flow of air which would pass through the space between the side plate 16 and the uppermost tube 18A. As shown in FIG. 1, restrictor 21 has cut-out gaps.

Other forms of openings can be arranged in the restrictor plate 21, e.g. circular holes or perforations. Alternatively, there are no openings as such but instead the restrictor plate 21 is a plain rectangular strip of constant width that extends horizontally the length of the side plate 16 and vertically over part of the gap between the side plate and the adjacent tube to leave a narrow slit for air to pass through. Alternatively, the restrictor plate is arranged on the downstream (relative to the airflow) side of the side plate 16. In yet another alternative, a restrictor plate is placed on both sides, e.g. forming the sides of a channel section. Indeed, other heat transfer restrictors may be provided to restrict the transfer of heat from the tube adjacent the side plate to the air flow between the side plate and the tube. For example, the fins 19 may be reduced in number or in length to reduce their ability to transfer heat from the tube to the airflow.

Although restrictor plate 21 and its variations and equivalents have been described in relation to the top side plate of a cross flow radiator, a flow restrictor can also be used on the lower side plate or on the side plates of a vertical flow radiator. However, the problem of thermal expansion is usually much less concern in these areas. Other heat exchangers may also benefit, e.g. air conditioning condensers.

Claims

1. A heat exchanger, comprising:

a generally rectangular heat exchanger matrix;

an inlet header tank at one edge of said matrix;

an outlet header tank at a second edge of said matrix, said second edge being opposite from said first edge;

first and second side plates on third and fourth edges of the matrix;

a plurality of tubes extending in a parallel array between said inlet and outlet header tanks to provide a path for liquid to flow between said tanks;

a plurality of interior cooling fins arranged between adjacent pairs of tubes;

an edge cooling fin arranged between said first side plate and said first side plate's adjacent tube; and

a restrictor placed in adjacent said edge cooling fin.

2. The heat exchanger of claim 1, further comprising:

a second edge cooling fin arranged between said second side plate and said second side plate's adjacent tube; and

a second restrictor placed adjacent said second edge cooling fin.

3. The heat exchanger of claim 1 wherein said restrictor is a plate with cut-outs.

4. The heat exchanger of claim 1 wherein said restrictor is a plate which occludes a portion of said edge fin.

5. The heat exchanger of claim 3 wherein said restrictor is of nearly constant width.

6. The heat exchanger of claim 1 wherein said restrictor occludes an upstream side of said edge fin.

7. The heat exchanger of claim 1 wherein said restrictor occludes a downstream side of said edge fin.

8. The heat exchanger of claim 1 wherein said restrictor occludes an upstream side of said edge fin, said heat exchanger further comprising:

a second restrictor occluding a downstream side of said edge fin.

9. The heat exchanger of claim 1 wherein the restrictor is part of a cooling fan cowl.

10. The heat exchanger of claim 1 wherein said restrictor is attached to said first plate.

11. The heat exchanger of claim 10 wherein said restrictor is attached to said first plate by at least one of: welding, gluing, crimping, and riveting.

12. The heat exchanger of claim 10 wherein the heat exchanger is a cross-flow radiator.

13. A cross-flow radiator, comprising:

a generally rectangular heat exchanger matrix;

an inlet header tank at one edge of said matrix;

an outlet header tank at a second edge of said matrix, said second edge being opposite from said first edge;

first and second side plates on third and fourth edges of the matrix;

a plurality of tubes extending between said inlet and outlet header tanks to provide a path for liquid to flow between said tanks;

a cooling fin arranged between said first side plate and said first side plate's adjacent tube; and

a restrictor plate placed adjacent said cooling fin.

14. The radiator of claim 13 wherein said restrictor plate is attached to said first side plate occluding an upstream side of said cooling fin.

15. The radiator of claim 13 wherein said restrictor plate is attached to said first side plate occluding a downstream side of said cooling fin.

16. The radiator of claim 13 wherein said restrictor plate is part of a cooling fan cowl.

17. The radiator of claim 13 wherein said restrictor plate has perforations so that only a portion of the cross-sectional area of said cooling fin is occluded.

18. The radiator of claim 13 wherein said restrictor plate is narrower than the cooling fin width so that a portion of said cooling fin cross-sectional area is occluded.

19. The radiator of claim 13 wherein said cooling fin is an edge cooling fin and along its length has a first number of waves, the radiator further comprising: a plurality of interior fins having a second number of waves along their length, wherein said second number of waves is greater than said first number of waves.