US20150285569A1

US20150285569A1 - Heat exchanger with dimpled manifold

Info

Publication number: US20150285569A1
Application number: US14/244,959
Authority: US
Inventors: Judd W. Glenn
Original assignee: Mahle International GmbH
Current assignee: Mahle International GmbH
Priority date: 2014-04-04
Filing date: 2014-04-04
Publication date: 2015-10-08

Abstract

A heat exchanger for containing pressurized refrigerant includes a manifold, a first opening, and a dimple. The manifold is configured to receive and fixedly attach a plurality of tubes. The manifold defines the first opening which is configured to receive a first tube. The manifold also defines the dimple which is located proximate to the first opening. The dimple is configured to reduce stress on the first tube imparted thereon by the manifold when the first tube is fixedly attached to the manifold. Multiple dimples may be distributed about the manifold to reduce stress imparted on each of the tubes by the manifold.

Description

TECHNICAL FIELD OF INVENTION

This disclosure generally relates to a heat exchanger for containing pressurized refrigerant, and more particularly relates to adding dimples to the manifold of the heat exchanger to reduce stress on refrigerant tubes attached to the manifold.

BACKGROUND OF INVENTION

It has been observed that burst pressure test failures of heat exchangers such as air conditioning condensers often occur in a refrigerant tube or cross tube proximate to where the tube is joined (e.g. brazed) to a manifold. Increasing the thickness of material used to form the tube is undesirable as doing so undesirable increases cost and weight of the condenser.

SUMMARY OF THE INVENTION

Described herein is a heat exchanger assembly with a manifold equipped with dimples that reduce stress imparted to refrigerant tubes attached to the manifold.
In accordance with one embodiment, a heat exchanger for containing pressurized refrigerant is provided. The heat exchanger includes a manifold, a first opening, and a dimple. The manifold is configured to receive and fixedly attach a plurality of tubes. The manifold defines the first opening which is configured to receive a first tube. The manifold also defines the dimple which is located proximate to the first opening. The dimple is configured to reduce stress on the first tube imparted thereon by the manifold when the first tube is fixedly attached to the manifold.
In another embodiment, a manifold for a heat exchanger for containing pressurized refrigerant is provided. The manifold includes or defines a first opening and a dimple. The first opening is configured to receive and fixedly attach a first tube. The dimple is located proximate to the first opening. The dimple is configured to reduce stress on the first tube imparted thereon by the manifold when the first tube is fixedly attached to the manifold.
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 view of a heat exchanger in accordance with one embodiment; and

FIG. 2 is a cut-away perspective view of the heat exchanger of FIG. 1 in accordance with one embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a non-limiting example of a heat exchanger 20 for containing pressurized refrigerant within the heat exchanger. In this example a condenser for an automotive air-conditioning system is shown, but the teachings presented herein are applicable to any heat exchanger assembly, even assemblies used to contain coolant at relatively low pressures compared to pressures experienced in air-conditioning systems.
The heat exchanger 20 includes a manifold 22 and a manifold 24 configured to receive and fixedly attach a plurality of tubes 28. The tubes 28 may define a single passageway through each tube, or may be of the micro-channel configuration shown that defines a plurality of ports or passageways arranged parallel to each other and separated by webs between each port. The tubes 28 are typically attached or joined to the manifolds 22, 24 by way of, for example, brazing to form a brazed joint 26, as will be recognized by those in the art. The tubes 28 and the manifolds 22, 24 are preferably made of the same material, aluminum for example, so stress due to thermal expansion mismatch is minimized. The heat exchanger may also include fins 32 thermally coupled to the tubes 28 to increase heat transfer between the heat exchanger and air flow flowing therethrough. While not specifically shown, it is understood that the manifolds 22, 24 would include some sort of inlet/outlet coupling so that refrigerant or coolant can be delivered to, and removed from, the heat exchanger 20.
FIG. 2 illustrates details of a non-limiting example of the manifolds 22, 24. The manifold 22, 24 includes or defines a first opening 34 configured to receive a first tube 36. As used herein, the modifier ‘first’ is only used to distinguish the tube and opening from other tubes and openings for the purpose of explanation, and is not intended to imply any particular importance of the first opening and the first tube 36 relative to other openings or tubes. As suggested above, the first tube 36 may be joined to the manifold 22, 24 by a brazed joint 26. However, the heat exchanger is not limited joining by way of brazing as other means of joining a tube to a manifold are contemplated.
As noted above, it has been observed that burst test failures often occur in the vicinity of the brazed joint 26. Finite element analysis of the heat exchanger suggests that the tubes 28 are being stressed by the manifold 22, 24, and that the highest stress concentration is at or near the brazed joint. Burst test failures often appear through the webs, especially the webs nearest the edges of the tubes 28. It was also observed that the top and bottom tubes of the heat exchangers tested were more susceptible to burst test failure than tubes more centrally located on the heat exchanger.
Applicants discovered that forming a dimple 40 (i.e. a depression, bump, deformation) into the manifold 22, 24 at a location proximate to the first opening 34 helped to reduce stress on the tubes 28 (e.g. the first tube 36) imparted thereon by the manifold 22, 24 when the first tube 36 is fixedly attached to the manifold 22, 24. Further analysis indicated that each of the tubes 28 may benefit from dimples located above and below (directions determined with respect to FIGS. 1 and 2) each of the tubes 28. While not subscribing to any particular theory, it is believed that adding a dimple or other deformation near the openings in the manifold creates a load path between the manifold and adjacent tubes that is less direct and therefore less stiff or more flexible.
It is believed that the dimples provide two benefits. The first is to create a less stiff zone where elastic deformation can take place near maximum burst pressures which will redirect the load around the area of the brazed joint 26. The second supposed benefit is that internal pressure will attempt to flatten the inward formed dimple, which will put a compressive stress into the adjacent tubes directly countering the tensile loads that lead to tube failure. The combined effects believe to be responsible for an observed increase in the burst pressure rating of the heat exchanger 20. Alternatively, the dimples will allow for a lower strength tubes and manifolds (i.e. thinner wall thickness) to be used, which can improve performance and reduce cost of the heat exchanger 20.
It is noted that although the dimples are in the manifold, the stress reduction is manifest on the tubes. That is, it is an indirect method of stress reduction as interactions with other components is typically not a consideration when adding a stress reduction feature, and most other stress reducing features are for the improvement in strength of the part onto which the feature is imparted. In general, such features intended to minimize hoop stresses when designing pressure vessels. The dimple 40 may increase stress in the manifold itself adjacent to the dimple. However, the tubes 28 preferably have a minimum wall thickness so as to be able to pass refrigerant with the lowest pressure drop. Since the tubes 28 typically are also the more expensive and numerous component of the heat exchanger 20, it is economically advantageous to add cost to the manifolds 22, 24 by adding dimples instead of increasing the cost of the tubes 28.
Continuing to refer to FIGS. 1 and 2, the heat exchanger 20 defines a manifold axis 42 parallel to the manifold 22. Also defined is a tube axis parallel 44 to the first tube 36 and substantially perpendicular to the manifold axis 42. As used herein, substantially perpendicular means that the axis are as perpendicular as is possible taking in to account normal variation experienced during manufacturing of the heat exchanger 20.
In one embodiment, the dimple 40 is advantageously located a radial offset angle 46 about the manifold axis 42 that is less than ninety degrees (90°) from the tube axis 44. The further the dimple 40 is moved around the manifold 22, 24 away from the first opening 34, the less stress reduction is expected to be provided by the dimple 40. In one example evaluated, the dimple had a radial offset angle 46 of about forty degrees (40°). Alternatively, another way to describe a preferred location of the dimple 40 is when the radial offset angle 46 is such that a center 48 of the dimple 40 is substantially aligned with a tube edge 50 relative to the manifold and in the direction of the manifold axis 42 axis.
In another embodiment of the heat exchanger 20, the manifold 22, 24 further defines a second opening 54 that is configured to receive a second tube 56 spaced apart from the first tube 26. In this example, the dimple 40 is preferably located substantially equidistant (e.g. within manufacturing tolerances) from the first opening 34 and the second opening 54. By locating the dimple equidistant from the first opening 34 and the second opening 54, the stress relief provided to the first tube 36 and the second tube 56 by the dimple 40 is equalized. Alternatively, the single dimple illustrated could be replaced by a pair of dimples arranged along the manifold axis 42 if the distance between the first tube 36 and the second tube 56 is sufficiently great to accommodate two dimples.
A variety of dimple shapes are contemplated. An improvement over a circular dimple appear to be an oval shaped dimple that is wider than it is high using the orientation shown in FIG. 2. That is, the dimple defines a height 62 characterized as a distance along the manifold axis 42, and a width 64 characterized as a distance perpendicular to the height 42. In this instance the height is less than the width. Another shape contemplated is an asymmetrical oval that with a height that decreases along a direction toward the tube axis 44.
Accordingly, a heat exchanger 20 and a manifold 22, 24 for the heat exchanger are provided. The manifold 22, 24 is equipped with or includes one or more duplications of the dimple 40 in order to reduce stress imparted on the tubes 28 by the manifold 22, 24. For example, some manifolds may be circular tubes, while some manifolds may be ‘D’ shaped. As such, various shapes of dimples are contemplated, and the shape selected would likely be optimized for each configuration of the heat exchanger 20 based on the shape of the manifold and/or the tube.
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 for containing pressurized refrigerant, said heat exchanger comprising:

a manifold configured to receive and fixedly attach a plurality of tubes, wherein the manifold defines

a first opening configured to receive a first tube, and

a dimple located proximate to the first opening, wherein the dimple is configured to reduce stress on the first tube imparted thereon by the manifold when the first tube is fixedly attached to the manifold.

2. The heat exchanger in accordance with claim 1, wherein the heat exchanger defines a manifold axis parallel to the manifold, and a tube axis parallel to the first tube and substantially perpendicular to the manifold axis, wherein the dimple is located a radial offset angle about the manifold axis that is less than ninety degrees from the tube axis.

3. The heat exchanger in accordance with claim 2, wherein the radial offset angle is such that a center of the dimple is substantially aligned with a tube edge relative to the manifold axis.

4. The heat exchanger in accordance with claim 1, wherein the manifold further defines a second opening is configured to receive a second tube spaced apart from the first tube, wherein the dimple is located substantially equidistant from the first opening and the second opening.

5. The heat exchanger in accordance with claim 1, wherein the dimple defines a height characterized as a distance along the manifold axis, and a width characterized as a distance perpendicular to the height, wherein the height is less than the width.

6. A manifold for a heat exchanger for containing pressurized refrigerant, said manifold comprising:

a first opening configured to receive and fixedly attach a first tube, and