US20150000880A1

US20150000880A1 - Heat exchanger with varied louver angles

Info

Publication number: US20150000880A1
Application number: US14/486,130
Authority: US
Inventors: Debashis Gosh; Scott B. Lipa
Original assignee: Delphi Technologies Inc
Current assignee: Mahle International GmbH
Priority date: 2008-08-06
Filing date: 2014-09-15
Publication date: 2015-01-01

Abstract

A heat exchanger assembly includes spaced apart tubes and a fin. The fin extends between and in thermal contact with adjacent tubes. The fin defines a planar portion between adjacent tubes. The planar portion defines a louver. The louver defines an axis about which the louver is rotated relative to the planar portion when the louver is formed. A middle portion of the louver is rotated about the axis to a first angle. A top portion of the louver is rotated about the axis to a second angle greater than the first angle such that the louver angle is varied along the axis. The louver may be characterized along the axis by a continuous transition of angle from the first angle to the second angle. A bottom portion of the louver may be rotated about the axis to a third angle greater than the first angle.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application and claims the benefit under 35 U.S.C. §120 of U.S. patent application Ser. No. 13/834,355 filed 15, Mar. 2013 and titled SPLIT MINI-LOUVERED FINS, which is a continuation-in-part application U.S. patent application Ser. No. 12/221,705 filed 06, Aug. 2008 and titled LOUVERED AIR CENTER FOR COMPACT HEAT EXCHANGER, now abandoned, the entire disclosure of both is hereby incorporated herein by reference.

TECHNICAL FIELD OF INVENTION

This disclosure generally relates to a heat exchanger assembly, and more particularly relates to a louvered fin where an angle of each louver is varied such that the angle of the louver varies along the length or axis of the louver.

BACKGROUND OF INVENTION

Air cooled heat exchanger assemblies are used in automobiles to transfer heat from various working fluids such as engine coolant, engine lubricating oil, air conditioning refrigerant, and transmission oil. A typical air cooled heat exchanger assembly includes a plurality of fluid conveying tubes hydraulically connecting an inlet header to an outlet header, and corrugated louvered fins disposed in a zig-zag pattern between adjacent fluid tubes. Louvers are provided to increase the heat transfer efficiency of the heat exchanger assembly.

SUMMARY OF THE INVENTION

In accordance with one embodiment, a heat exchanger assembly is provided. The assembly includes a plurality of parallel spaced apart tubes and a fin. The tubes are configured to convey coolant within the tubes. The fin extends between and in thermal contact with adjacent tubes. The fin defines a planar portion between the adjacent tubes. The planar portion defines a louver. The louver defines an axis about which the louver is rotated relative to the planar portion when the louver is formed. A middle portion of the louver is rotated about the axis to a first angle. A top portion of the louver is rotated about the axis to a second angle greater than the first angle such that the louver angle is varied along the axis.
In another embodiment, the louver is characterized along the axis by a continuous transition of angle from the first angle to the second angle.
In yet another embodiment, a bottom portion of the louver is rotated about the axis to a third angle greater than the first angle.
Further features and advantages will appear more clearly on a reading of the following detailed description of the preferred embodiment, which is given by way of non-limiting example only and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

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

FIG. 1 is a perspective front view of a heat exchanger assembly equipped with fins in accordance with one embodiment;

FIG. 2 is a perspective view of a known fin;

FIG. 3 is a close-up view of the known fin of FIG. 2;

FIGS. 4A, 4B, and 4C show a louver configuration for a fin of the assembly of FIG. 1 in accordance with one embodiment;

FIG. 5A, 5B, and 5C show a louver configuration for a fin of the assembly of FIG. 1 in accordance with one embodiment; and

FIG. 6 is a sectional end view of a pair of louvers of a fin of the assembly of FIG. 1 in accordance with one embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a non-limiting example of a heat exchanger assembly, hereafter referred to as the assembly 20. The assembly 20 includes a first manifold 22 and a second manifold 24 spaced apart from and in a substantially parallel relationship with the first manifold 22. The first manifold 22 and the second manifold 24 are configured to receive a plurality of parallel spaced apart tubes 28 configured to convey, for example, coolant through the tubes 28 between the first manifold 22 and the second manifold 24. The tubes 28 are typically inserted into slots 26 of the first manifold 22 and the second manifold 24 and sealed to the manifolds by, for example, brazing, as will be recognized by those in the art. A plurality of corrugated fins 32 is disposed between and in thermal contact with adjacent instances of the tubes 28 for increased heat transfer efficiency between the fluid in the tubes 28 and the airflow 30 through the assembly 20, which may be urged by a fan (not shown). The tubes 28 and the corrugated fins 32 between the tubes 28 generally cooperate to define a core 34 of the assembly 20. Spaces between adjacent planar portions of the corrugated fins 32 and the tubes 28 cooperate to define a plurality of channels 36 that direct the airflow 30 through the core 34.
FIGS. 2 and 3 illustrate a prior art corrugated louvered fin, hereafter the fin 250, equipped with single louvers 252 along a planar portion 254 of the fin 250. The fin 250 is formed from a thin strip of heat conductive material into radiused portions 256 and planar portions 254 that are alternately continuously arranged to define a corrugation. Each of the planar portions 254 includes a leading edge 258 oriented into the oncoming direction of the airflow 30, an opposite trailing edge 260 spaced from the leading edge 258, and a plurality of louvers 252 therebetween. Each louver 252 is defined by a louver segment 262 oriented at a predetermined angle relative to the planar portion 254 between a pair of slits 264. On opposite ends of the louver segment 262 is a juncture 266 that transitions the louver segment 262 to the planar portion 254. Each louvers 252 is generally formed by pivoting the louver segments 262 about the junctures 266 (i.e. an axis that extends between the junctures 266) such that the louver segments 262 are oblique or angled relative to the planar portion 254. The pivoting of the louver segment 262 about the juncture 266 defines a twisted transition that connects the single louver 252 to the planar portion 254. The louver 252 defines a front edge 268 oriented toward the direction of airflow 30 and an opposite rear edge 270. The front edges 268 of the louvers 252 are substantially parallel with each other and may be parallel with the leading edge 258 of the planar portion 254. That is, the angle of the louver segments 262 is relatively constant along the length of the louver segments 262 or relatively constant along the axis that extends between the junctures 266.
It was discovered that the amount of heat transferred from a heat exchanger assembly (e.g. the assembly 20) could be increased if the angle of the louvers was varied along the axis of the louver as opposed to keeping the angle fixed as shown in FIGS. 2 and 3. In particular, the heat transfer was increased if the angle relative to the planar portion of the end portions of a louver segment was increased relative to the middle portion of the louver segment. U.S. Pat. No. 6,672,376 issued Jan. 6, 2004 to Shembekar et al. shows louvers with an abrupt twist in the middle of each louver. U.S. Pat. No. 5,730,214 issued Mar. 24, 1998 to Beamer et al. shows flat louvers with angles set in accordance with the location of the louver on a fin relative to the direction of airflow. As will become apparent in the description that follows, the assembly 20 described herein is equipped with louvers characterized by a louver angle that varies along the length or axis of the louver. It will also be apparent that the louvers described herein are not comparable to the louvers shown by Shembekar or Beamer.
FIGS. 4A, 4B, and 4C illustrate a non-limiting example of a portion of a fin 32 suitable for use in the assembly 20 of FIG. 1. As shown in FIG. 1, the fin 32 extends between and is in thermal contact with adjacent tubes 28. The fin 32 defines a planar portion 40 (FIG. 4A, 4B, and 4C) between the adjacent tubes. The planar portion 40 includes or defines a plurality of louvers, hereafter the louver 42. Each louver defines an axis 44 about which the louver 42 is rotated relative to the planar portion 40 when the louver 42 is formed. Each louver includes or defines a middle portion 46 shown in cross section in FIG. 4C, and a top portion 48 shown in cross section in FIG. 4B. That is, Figs. 4B and 4C show a perspective where the axis 44 is normal or perpendicular to the page on which FIGS. 4B and 4C are shown.
As mentioned above, it was discovered that heat transfer of the assembly 20 could be improved if the middle portion 46 and the top portion 48 had different angles relative to the planar portion 40. Preferably, the middle portion 46 of the louver 42 is rotated about the axis 44 to a first angle 50, and the top portion 48 of the louver 42 is rotated about the axis 44 to a second angle 52 that is greater than the first angle 50. By this configuration, the angle of the louver 42 is varied along the axis 44.
In one embodiment the angle of the louver 42 at any point along the axis 44 may be continuously varied along the axis 44 so that the transition from the top portion 48 to the middle portion 46 is a smooth transition. That is, the louver 42 may be characterized along the axis 44 by a continuous or smooth transition of angle from the first angle 50 to the second angle 52. This does not preclude having the angle be fixed for a portion of the length of the axis 44. For example, the middle portion 46 may be defined to be the middle third of the louver 42, and that middle third may all be at the same angle (e.g. the first angle 50) and not continuously varied through that middle third.
It may also be advantageous if a bottom portion 54 of the louver 42 is rotated about the axis 44 to a third angle 56 greater than the first angle 50. Such a configuration would cause an end view or side view of the louver 42 to have the appearance of an hour glass shape (FIG. 6), even though the actual width of the louver 42 is substantially constant. In one embodiment, the third angle 56 is substantially equal to the second angle 52. As used herein, substantially equal means within the tolerance of manufacturing, e.g. +/−3 degrees of angle. Also, the shape of the louver 42 may be symmetrical about the middle portion 46. Furthermore, like the embodiment described above, the louver 42 may be configured so that the louver 42 is characterized along the axis 44 by a continuous transition of angle from the second angle 52 to the first angle 50, and from the first angle 50 to the third angle 56.
FIGS. 5A, 5B, and 5C illustrate another non-limiting example of a portion of a fin 32 of the assembly 20. The louvers in this example are sometimes referred to as split louvers where a first louver 60 defines or is oriented about a first axis 64 offset from the planar portion 40 in first direction 68, and a second louver 62 defines or is oriented about a second axis 66 offset from the planar portion 40 in a second direction 70 opposite the first direction 68. While not subscribing to any particular theory, the split louvered fins have been observed to increase heat transfer efficiency relative to the single louver arrangement shown in FIGS. 4A-C. It is believe that the increase is due to allowing greater louver penetration into the channels 36 defined by each pair of planar portions to increase the distance that the airflow 30 has to travel through the core 34 and thereby increase the number of boundary layer interruptions that the airflow 30 has to encounter, while minimizing the pressure drop. As with the previous example, each louver includes or defines a middle portion 72 at a first angle 50 relative to the planar portion 40 as shown in cross section in FIG. 5C, and a top portion 74 at a second angle 52 relative to the planar portion 40 as shown in cross section in FIG. 5B. That is, FIGS. 5B and 5C show a perspective where the first axis 64 and the second axis 66 are normal or perpendicular to the page on which FIGS. 5B and 5C are shown. As with the prior example shown in FIGS. 4A-C, the second angle 52 is preferably greater than the first angle 50.
By way of example and not limitation, if the distance between adjacent tubes is 5.5 mm, a suitable length of the middle portion (46, 72) is 2.6 mm, and a suitable length of the top portion (48, 74) and the bottom portion (54, 78) is 1.0 mm. For this size louver, a suitable value for the first angle 50 is 23 degrees, and a suitable angle for the second angle 52 and/or the third angle is 35 degrees. It is recognized that other angles may be optimum for different dimensioned fins. It is also recognized that each louver of a plurality of louvers may have an optimum angle. For example, the louvers near the middle of the fin may advantageously have a greater angle than louvers near the leading edge and the trailing edge of the fin 32.
FIG. 6 illustrates a non-limiting example of the fin 32 that includes or defines a first planar portion 40A adjacent to a second planar portion 40B. The fin 32 is also configured to define a radiused portion 76 so the first planar portion 40A is parallel to the second planar portion 40B. By having a large enough radius, adjacent planar portions can be parallel. However, if the radius is too large, the density of the fins may be undesirably reduced Having adjacent planar portions in a parallel orientation is advantageous as airflow through the channels 36 defined by the adjacent planar portions is more uniform from top to bottom. If the radius was smaller, as is in vogue today, the adjacent planar portions could not be parallel, so airflow inside the channel near the radiused portion would be more restricted than in the part of the channel that was away from the radiused portion. Also, the relatively large fin tip radius of a radiused portion 76 as compared to the distance between the two adjacent planer portions of adjacent louvers allows for maximizing the second angle 52 and the third angle 56 relative to the first angle 50. This significantly enhances airflow between the louver passages at the top and bottom of the fin, and thus improving the resulting heat transfer. A concomitant benefit realized with the variable louver angle fin combined with large tip radius is that the first few (2-3) louvers in the second half of the fin, i.e. the fins after the mid-section (i.e. the first planer portion 40A) which are typically starved of airflow and heat transfer in conventional fin, have improved heat transfer due to improved airflow.
Accordingly, a heat exchanger assembly (the assembly 10) is provided. The twisting of each louver (42, 60, 62) helps to optimize the angle of the louver for local airflow conditions. That is, different airflow rates may exist at the middle portion as compared to the top or bottom portion, so varying the angle of the louver along the length of the louver helps to improve heat transfer from the fin 32 to the airflow 30.
While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.

Claims

We claim:

1. A heat exchanger assembly comprising:

a plurality of parallel spaced apart tubes configured to convey coolant therethrough; and

a fin extended between and in thermal contact with adjacent tubes, wherein the fin defines a planar portion between the adjacent tubes, the planar portion defines a louver, the louver defines an axis about which the louver is rotated relative to the planar portion when the louver is formed, and a middle portion of the louver is rotated about the axis to a first angle, wherein

a top portion of the louver is rotated about the axis to a second angle greater than the first angle such that the louver angle is varied along the axis.

2. The assembly in accordance with claim 1, wherein the louver is characterized along the axis by a continuous transition of angle from the first angle to the second angle.

3. The assembly in accordance with claim 1, wherein a bottom portion of the louver is rotated about the axis to a third angle greater than the first angle.

4. The assembly in accordance with claim 3, wherein the third angle is substantially equal to the second angle.

5. The assembly in accordance with claim 3, wherein the louver is characterized along the axis by a continuous transition of angle from the second angle to the first angle, and from the first angle to the third angle.

6. The assembly in accordance with claim 5, wherein the third angle is substantially equal to the second angle.

7. The assembly in accordance with claim 1, wherein a first louver defines a first axis offset from the planar portion in first direction, and a second louver defines a second axis offset from the planar portion in a second direction opposite the first direction.

8. The assembly in accordance with claim 1, wherein the fin includes a first planar portion adjacent to a second planar portion, and the fin is configured to define a radiused portion so the first planar portion is parallel to the second planar portion.