US20130075069A1

US20130075069A1 - Brazed microchannel heat exchanger with thermal expansion compensation

Info

Publication number: US20130075069A1
Application number: US13/200,583
Authority: US
Inventors: Todd A. Michael
Original assignee: Trane International Inc
Current assignee: Trane International Inc
Priority date: 2011-09-26
Filing date: 2011-09-26
Publication date: 2013-03-28
Also published as: GB2509637A8; CN104053965A; CN104053965B; GB201406037D0; WO2013048922A2; WO2013048922A3; GB2509637A

Abstract

A brazed aluminum microchannel heat exchanger comprising a stack of alternating tubes and serpentine fins includes an expansion relief feature that accommodates uneven thermal expansion in the heat exchanger. The expansion relief feature provides the heat exchanger with sufficient structural support, at least during assembly, so that components of the heat exchanger can be firmly clamped in compression during a controlled-atmosphere brazing process. In some examples, the expansion relief feature is a gap or sliding engagement between adjacent headers of the heat exchanger. In addition or alternatively, the expansion relief feature comprises one or more slits cut into the serpentine fins after the brazing process, wherein each slit extends generally parallel to the tubes.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The subject invention generally pertains to brazed microchannel heat exchangers and more specifically to a means for compensating for unequal thermal expansion in such heat exchangers.
2. Description of Related Art
Microchannel heat exchangers often comprise a stack of alternating tubes and serpentine fins brazed between two or more headers. The tubes convey an internal fluid between the headers, while the serpentine fins promote heat transfer between the internal fluid and an external fluid passing across the heat exchanger.

SUMMARY OF THE INVENTION

It is an object of some embodiments of the invention to provide a brazed aluminum microchannel heat exchanger with an expansion relief feature that accommodates uneven thermal expansion in the heat exchanger.
Another object of some embodiments is to provide an expansion relief feature that has sufficient structural support, at least during assembly, so that components of the heat exchanger can be clamped in compression during a controlled-atmosphere brazing process.
Another object of some embodiments is to provide an expansion relief feature suitable for a heat exchanger comprising a stack of alternating tubes and serpentine fins.
In some embodiments the present invention provides a microchannel heat exchanger for conveying an internal fluid in heat transfer relationship with an external fluid. The microchannel heat exchanger includes a first header defining an inlet for the internal fluid to enter the microchannel heat exchanger, a second header, and a plurality of tubes each of which extend in a longitudinal direction between the first header and the second header. The plurality of tubes connect the first header in fluid communication with the second header to convey the internal fluid therebetween. The plurality of tubes include a first tube, a second tube and a third tube. The plurality of tubes are spaced apart from each other to define a plurality of spaces including a first space and a second space. The first space is between the first tube and the second tube, the second space is between the second tube and the third tube, and the second tube and the third tube are spaced apart over a separation distance. The microchannel heat exchanger also includes a plurality of serpentine fins interconnecting the plurality of tubes. The plurality of serpentine fins includes a first serpentine fin and a second serpentine fin. The first serpentine fin is contained in the first space between the first tube and the second tube. The second serpentine fin is contained in the second space between the second tube and the third tube. The second serpentine fin defines a slit extending in the longitudinal direction for a slit length that is greater than the separation distance between the second tube and the third tube.
In some embodiments the present invention provides a microchannel heat exchanger for conveying an internal fluid in heat transfer relationship with an external fluid. The microchannel heat exchanger includes a first header defining an inlet for the internal fluid to enter the microchannel heat exchanger, a second header, and a third header adjacent to the first header. The microchannel heat exchanger also includes a first plurality of tubes each of which extend in a longitudinal direction. The first plurality of tubes connect the first header in fluid communication with the second header to convey the internal fluid from the first header to the second header. The microchannel heat exchanger also includes a second plurality of tubes each of which extend in the longitudinal direction. The second plurality of tubes connect the second header in fluid communication with the third header to convey the internal fluid from the second header to the third header. The microchannel heat exchanger also includes a first plurality of serpentine fins interconnecting in a lateral direction the first plurality of tubes, wherein the lateral direction is generally perpendicular to the longitudinal direction. The microchannel heat exchanger also includes a second plurality of serpentine fins interconnecting in the lateral direction the second plurality of tubes. The microchannel heat exchanger also includes a braze material bonding the first header to the first plurality of tubes, bonding the second header to the first plurality of tubes, bonding the second plurality of tubes to the second header, bonding the second plurality of tubes to the third header, bonding the first plurality of serpentine fins to the first plurality of tubes, and bonding the second plurality of serpentine fins to the second plurality of tubes. The microchannel heat exchanger also includes an expansion relief feature existing between the first header and the second header, the expansion relief feature accommodating relative movement in the longitudinal direction between the first header and the third header in response to a difference in longitudinal thermal expansion of the first plurality of tubes relative to the second plurality of tubes.
In some embodiments the present invention provides a microchannel heat exchanger for conveying an internal fluid in heat transfer relationship with an external fluid. The microchannel heat exchanger includes a first header defining an inlet for the internal fluid to enter the microchannel heat exchanger, a second header, a third header adjacent to the first header, and a first plurality of tubes each of which extend in a longitudinal direction. The first plurality of tubes connect the first header in fluid communication with the second header to convey the internal fluid from the first header to the second header. The microchannel heat exchanger also includes a second plurality of tubes each of which extend in the longitudinal direction. The second plurality of tubes connect the second header in fluid communication with the third header to convey the internal fluid from the second header to the third header. The microchannel heat exchanger also includes a first plurality of serpentine fins interconnecting in a lateral direction the first plurality of tubes, wherein the lateral direction is generally perpendicular to the longitudinal direction. The microchannel heat exchanger also includes a second plurality of serpentine fins interconnecting in the lateral direction the second plurality of tubes. The microchannel heat exchanger also includes a braze material bonding the first header to the first plurality of tubes, bonding the second header to the first plurality of tubes, bonding the second plurality of tubes to the second header, bonding the second plurality of tubes to the third header, bonding the first plurality of serpentine fins to the first plurality of tubes, and bonding the second plurality of serpentine fins to the second plurality of tubes. The microchannel heat exchanger also includes an expansion relief feature existing between the first header and the second header. The expansion relief feature accommodates relative movement in the longitudinal direction between the first header and the third header in response to a difference in longitudinal thermal expansion of the first plurality of tubes relative to the second plurality of tubes. The microchannel heat exchanger also includes an elongate member interposed between the first plurality of tubes and the second plurality of tubes. The elongate member is elongated in the longitudinal direction. The elongate member is shorter than each of the first plurality of tubes. The elongate member conveys substantially none of the internal fluid. The microchannel heat exchanger also includes a first serpentine fin, and the braze material joins the first plurality of tubes to the elongate member. The microchannel heat exchanger also includes a second serpentine fin, and the braze material joins the second plurality of tubes to the elongate member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an example microchannel heat exchanger with an expansion relief feature.

FIG. 2 is an enlarged cross-sectional view of the area identified by circle-2 of FIG. 1.

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 1.

FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 1.

FIG. 5 is a cross-sectional view similar to FIG. 4 but showing the cross section of an alternate elongate member.

FIG. 6 is a front view of another example microchannel heat exchanger with an expansion relief feature.

FIG. 7 is a front view similar to FIG. 6 but showing the expansion relief feature accommodating uneven thermal expansion of the heat exchanger.

FIG. 8 is a front view of another example microchannel heat exchanger with an expansion relief feature.

FIG. 9 is a front view of another example microchannel heat exchanger with an expansion relief feature.

FIG. 10 is a front view of another example microchannel heat exchanger with an expansion relief feature.

FIG. 11 is a front view of another example microchannel heat exchanger with an expansion relief feature.

FIG. 12 is a front view of another example microchannel heat exchanger with an expansion relief feature.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1, with additional reference to FIGS. 2-5, illustrates one example of a microchannel heat exchanger 10 that includes an expansion relief feature 12 for accommodating uneven thermal expansion in heat exchanger 10.
In the illustrated example, heat exchanger 10 comprises a first plurality of tubes 14 a extending between a first header 16 (manifold) and a second header 18, a second plurality of tubes 14 b extending between second header 18 and a third header 20, a first plurality of serpentine fins 22 a stacked and bonded (e.g., brazed) in an alternating arrangement with the first plurality of tubes 14 a, and a second plurality of serpentine fins 22 b stacked and bonded in an alternating arrangement with the second plurality of tubes 14 b. The term, “serpentine,” means that the fin is wavy with peaks and valleys (e.g., sine wave, square wave, and various modifications thereof).
In the illustrated examples, the peaks and valleys of serpentine fins 22 are brazed or otherwise bonded to adjacent tubes 14, whereby fins 22 interconnect in a lateral direction 24 the plurality of tubes 14. Each fin 22 extends farther in a longitudinal direction 26 (parallel to tubes 14) than in lateral direction 24. The general expression, “the serpentine fins are stacked in an alternating arrangement with the tubes,” means that each fin 22 is contained within its own space 28 between two tubes and that the tubes do not pass through the fin. Thus, a serpentine fin 22 in one space 28 is separated from another serpentine fin 22 in another space 28, and heat exchanger 10 has a plurality of spaces 28, e.g., a first space, a second space, a third space, etcetera. Each space 28 is defined in lateral direction 24 by two adjacent tubes 14 that are spaced apart by a separation distance 30, and each space 28 is further defined in longitudinal direction 26 by a spaced-apart distance 32 between headers at opposite ends of tubes 14.
In this example, first header 16 has an inlet 34, and third header 20 has an outlet 36. An internal fluid 38 (e.g., refrigerant, water, glycol, etc.) enters first header 16 through inlet 34, and the first plurality of tubes 14 a convey fluid 38 to second header 18. The second plurality of tubes 14 b convey fluid 38 from second header 18 to third header 20, and outlet 36 releases fluid 38 out from within third header 20. Inlet 34 and outlet 36 can be connected to various elements of a system that incorporates heat exchanger 10. Such a system, for example, could be an air conditioner or heat pump where heat exchanger 10 functions as an evaporator or a condenser.
Fins 22 (i.e., fins 22 a and 22 b) are thermally conductive to promote heat transfer between internal fluid 38 flowing through tubes 14 (i.e., tubes 14 a and 14 b, which are also thermally conductive) and an external fluid (e.g., air) flowing across the external surfaces of fins 22 and tubes 14. A fan, blower or some other known means can be used for forcing air or some other external fluid across the external surfaces of heat exchanger 10.
Although the actual structure of heat exchanger 10 may vary, in some examples, tubes 14; fins 22; headers 16, 18 and 20; and an elongate member 40 (to be explained later) are made primarily of common aluminum (and/or alloys thereof) and are joined or bonded by a common braze material 42. In some examples, at least some of the aforementioned parts of heat exchanger 10 are coated (e.g., plated, clad, etc.) with a thin layer of braze material 42 (e.g., aluminum fin stock clad with braze alloy) so that after the parts are assembled in a desired arrangement, the entire assembly is heated in a controlled atmosphere (e.g., an extreme vacuum) until braze material 42 melts, flows and subsequently bonds the parts together. Tube-to-fin heat transfer is enhanced by providing tubes 14 with substantially flat surfaces 44, as shown in FIG. 3.
In the example shown in FIG. 1, expansion relief feature 12 is first header 16 being spaced apart from second header 20 to define a gap 46 therebetween. Gap 46 allows relative movement between headers 16 and 20 and thus allows tubes 14 a to expand more or less than tubes 14 b in longitudinal direction 26. Gap 46 might also accommodate differences in thermal expansion in a vertical direction (vertical as viewed in FIG. 1). A difference in thermal expansion in heat exchanger 10 can be caused by the temperature of internal fluid 38 increasing or decreasing as fluid 38 flows through heat exchanger 10.
To provide some structural support in the general area of gap 46 and expansion relief feature 12, heat exchanger 10 has elongate member 40 brazed or otherwise bonded between the two sets of tubes 14 a and 14 b. In examples where elongate member 40 is brazed to tubes oo14 aoa and 14 b, structural support in the area of expansion relief feature 12 is particularly important during the brazing process. Elongate member 40 can be of various cross-sectional areas, such as those shown in FIGS. 4 and 5. FIG. 4 shows an example elongate member 40 a with a tubular cross-sectional area (similar to that of tube 14); however, elongate member 40 a does not convey any internal fluid 38. FIG. 5 shows an example elongate member 40 b as a solid bar with a generally rectangular cross-sectional area. In some examples, elongate member 40 is shorter than tubes 14 because there may be no need for elongate member 40 to contact any of the headers.
In another example, shown in FIGS. 6 and 7, a microchannel heat exchanger 48 includes a first header 50, second header 52, and a third header 54. The first and third headers 50 and 54 are in sliding abutment with each other to provide an expansion relief feature 56 therebetween. In comparison to FIG. 6, FIG. 7 shows tubes 14 a being longer than tubes 14 b due to a difference in thermal expansion of tubes 14 a relative to tubes 14 b.
In another example, shown in FIG. 8, a microchannel heat exchanger 58 is similar to heat exchanger 10 of FIG. 1; however, elongate member 40 is eliminated in heat exchanger 58 by placing tubes 14 a closer to tubes 14 b. Instead of elongate member 40 and an intermediate serpentine fin 22 c (FIG. 1), a lowermost tube 14 a′ is all that couples the lowermost fin 22 a′ to an uppermost fin 22 b′. Heat exchanger 58 still includes an expansion relief feature 60 similar or identical to expansion relief features 12 and 56. In some examples, as shown in a microchannel heat exchanger 62 of FIG. 9, a slit 64 in an uppermost fin 22 b″ is added to expansion relief feature 60 (FIG. 8) to create a more flexible expansion relief feature 60′. In some cases, slit 64 is created by sawing into fin 22 b′ to produce fin 22 b″. To provide heat exchanger 62 with sufficient flexibility at feature 60′, slit 64 has a length 66 in longitudinal direction 26 that is greater than a separation distance 68 between tubes 14 a and 14 b. Length 66 of slit 64 preferably is more than ten times as great as separation distance 68. In some examples, length 66 is about 30 times as great as separation distance 68.
FIG. 10 shows an example microchannel heat exchanger 70 wherein one or more slits 64 in a plurality of serpentine fins 22 is sufficient in itself to provide heat exchanger 70 with an expansion relief feature (slits 64). In some examples, fins 22 are the same as others mentioned herein, except for slits 64 being cut into them. In the example of FIG. 10, instead of two separate headers 16 and 20, the two are combined in a single header 72 with a block-off 74 or plug that divides header 72 into two chambers 74 a and 74 b. Fluid 38 enters chamber 72 a through inlet 34, and the first plurality of tubes 14 a convey fluid 38 to header 18. The second plurality of tubes 14 b convey fluid 38 from header 18 to chamber 72 b, and outlet 36 releases fluid 38 out from within chamber 72 b. Since fluid 38 makes two passes across the width of heat exchanger 70, it can be considered a two-pass heat exchanger.
A single-pass version is shown in FIG. 11. In this example, a heat exchanger 76 includes a single chamber inlet header 78 without block-off 74 and a single chamber outlet header 80. Tubes 14 convey fluid 38 in a single pass from inlet header 78 to outlet header 80. Slits 64 (any number of slits, one or more) serve as the heat exchanger's expansion relief feature.
Any of the example heat exchangers shown in FIGS. 1 and 6-11 can be readily modified to provide any number of passes. FIG. 12, for example, shows a microchannel heat exchanger 80 that includes a first header 82, a second header 84, a third header 86 and a fourth header 88 that makes heat exchanger 80 a three-pass heat exchanger. The upper four tubes 14 convey fluid 38 from first header 82 to second header 84 for a first pass, the middle four tubes 14 convey fluid 38 from second header 84 to third header 86 for a second pass, and the lower four tubes 14 convey fluid 38 from third header 86 to fourth header 88 for a third pass. One or more expansion relief features are provided by a slit 64′, a gap 90 (or sliding engagement) between headers 82 and 86, slit 64, a gap 92 (or sliding engagement) between headers 84 and 88, and/or various combinations thereof. Example slit 64′ has frayed/jagged edges 94 to promote heat transfer in that area. Such frayed/jagged edges can be the result of cutting burrs from a conventional sawing process.
It should be noted that when one header is stated as being “adjacent” to another header, that means the two headers are in proximity with each other but not necessarily in contact with each other.
Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those of ordinary skill in the art. The scope of the invention, therefore, is to be determined by reference to the following claims:

Claims

1. A microchannel heat exchanger for conveying an internal fluid in heat transfer relationship with an external fluid, the microchannel heat exchanger comprising:

a first header defining an inlet for the internal fluid to enter the microchannel heat exchanger;

a second header;

a plurality of tubes each of which extend in a longitudinal direction between the first header and the second header, the plurality of tubes connecting the first header in fluid communication with the second header to convey the internal fluid therebetween, the plurality of tubes includes a first tube, a second tube and a third tube, the plurality of tubes being spaced apart from each other to define a plurality of spaces including a first space and a second space, the first space being between the first tube and the second tube, the second space being between the second tube and the third tube, and the second tube and the third tube being spaced apart over a separation distance; and

a plurality of serpentine fins interconnecting the plurality of tubes, the plurality of serpentine fins including a first serpentine fin and a second serpentine fin, the first serpentine fin being contained in the first space between the first tube and the second tube, the second serpentine fin being contained in the second space between the second tube and the third tube, the second serpentine fin defining a slit extending in the longitudinal direction for a slit length that is greater than the separation distance between the second tube and the third tube.

2. The microchannel heat exchanger of claim 1, wherein the slit length is more than ten times as great as the separation distance between the second tube and the third tube.

3. The microchannel heat exchanger of claim 1, wherein the slit length is shorter than a spaced-apart distance between the first header and the second header.

4. The microchannel heat exchanger of claim 1, wherein the plurality of serpentine fins define a plurality of slits similar to the slit defined by the second serpentine fin.

5. The microchannel heat exchanger of claim 1, further comprising a braze material bonding the second serpentine fin to the first tube and the second tube.

6. The microchannel heat exchanger of claim 1, wherein the plurality of tubes include a plurality of substantially flat surfaces attached to the plurality of serpentine fins.

7. A microchannel heat exchanger for conveying an internal fluid in heat transfer relationship with an external fluid, the microchannel heat exchanger comprising:

a second header;

a third header adjacent to the first header;

a first plurality of tubes each of which extend in a longitudinal direction, the first plurality of tubes connecting the first header in fluid communication with the second header to convey the internal fluid from the first header to the second header;

a second plurality of tubes each of which extend in the longitudinal direction, the second plurality of tubes connecting the second header in fluid communication with the third header to convey the internal fluid from the second header to the third header;

a first plurality of serpentine fins interconnecting in a lateral direction the first plurality of tubes, wherein the lateral direction is generally perpendicular to the longitudinal direction;

a second plurality of serpentine fins interconnecting in the lateral direction the second plurality of tubes;

a braze material bonding the first header to the first plurality of tubes, bonding the second header to the first plurality of tubes, bonding the second plurality of tubes to the second header, bonding the second plurality of tubes to the third header, bonding the first plurality of serpentine fins to the first plurality of tubes, and bonding the second plurality of serpentine fins to the second plurality of tubes; and

an expansion relief feature existing between the first header and the second header, the expansion relief feature accommodating relative movement in the longitudinal direction between the first header and the third header in response to a difference in longitudinal thermal expansion of the first plurality of tubes relative to the second plurality of tubes.

8. The microchannel heat exchanger of claim 7, wherein the expansion relief feature is the first header being in sliding abutment with the second header.

9. The microchannel heat exchanger of claim 7, wherein the expansion relief feature is the first header being spaced apart from the second header to define a gap therebetween.

10. The microchannel heat exchanger of claim 7, further comprising a serpentine fin interposed between the first plurality of tubes and the second plurality of tubes, the serpentine fin defining a slit extending in the longitudinal direction for a slit length greater than a separation distance between the first plurality of tubes and the second plurality of tubes.

11. The microchannel heat exchanger of claim 7, further comprising:

an elongate member interposed between the first plurality of tubes and the second plurality of tubes, the elongate member being elongated in the longitudinal direction, the elongate member being distinguishable from each of the first plurality of tubes by virtue of at least one of length and cross-sectional area;

a first serpentine fin and the braze material joining the first plurality of tubes to the elongate member; and

a second serpentine fin and the braze material joining the second plurality of tubes to the elongate member.

12. The microchannel heat exchanger of claim 11, wherein the elongate member is tubular but conveys substantially none of the internal fluid.

13. The microchannel heat exchanger of claim 11, wherein the elongate member is a solid bar.

14. The microchannel heat exchanger of claim 11, wherein the elongate member is shorter than each of the first plurality of tubes.

15. The microchannel heat exchanger of claim 7, wherein the plurality of tubes include a plurality of substantially flat surfaces attached to the plurality of serpentine fins.

16. A microchannel heat exchanger for conveying an internal fluid in heat transfer relationship with an external fluid, the microchannel heat exchanger comprising:

a second header;

a third header adjacent to the first header;

a braze material bonding the first header to the first plurality of tubes, bonding the second header to the first plurality of tubes, bonding the second plurality of tubes to the second header, bonding the second plurality of tubes to the third header, bonding the first plurality of serpentine fins to the first plurality of tubes, and bonding the second plurality of serpentine fins to the second plurality of tubes;

an expansion relief feature existing between the first header and the second header, the expansion relief feature accommodating relative movement in the longitudinal direction between the first header and the third header in response to a difference in longitudinal thermal expansion of the first plurality of tubes relative to the second plurality of tubes;

an elongate member interposed between the first plurality of tubes and the second plurality of tubes, the elongate member being elongated in the longitudinal direction, the elongate member being shorter than each of the first plurality of tubes, the elongate member conveying substantially none of the internal fluid;

17. The microchannel heat exchanger of claim 16, wherein the expansion relief feature is the first header being in sliding abutment with the second header.

18. The microchannel heat exchanger of claim 16, wherein the expansion relief feature is the first header being spaced apart from the second header to define a gap therebetween.

19. The microchannel heat exchanger of claim 16, wherein the elongate member is tubular.

20. The microchannel heat exchanger of claim 16, wherein the elongate member is a solid bar.