Thermal Expansion Compensation

Background of the Invention

[0100| 1. Field of the Invention

[01011 The subject invention, generally pertains to razed microchannel. heat exchangers and more specifically to a means for compensating for unequal thermal expansion in such heat exchangers.

[0i 02] 2. Description of Related Art

[0103] MicroChannel heat exchangers often comprise a slack of alternating tubes and serpentine fins brazed between two or more headers. The tubes convey an internal fluid between the headers, while the serpentine fin promote heat transfer between, the internal, fluid and an external fluid passing across the beat exchanger.

Summary of the Invention

[0104] 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 hea t exchanger.

[0105} 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-atmosp ^' here brazing process.

[0106] 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.

[0107] In some embodiments the present invention provides a microchannel. heat exchanger for conveying an interna! fluid in heat transfer relationship with an external fluid. The microchannel heat exchanger includ.es a first header defining an inlet for the intemal fluid to enter the microchannel heat exchanger, a second header, and a plurality of lubes 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 t ns interconnecting the plurality of tubes. The phtrality 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.

01081 to 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 front 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 phtrality 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 tabes 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 iios to the second plurality of tubes. The microchannei beat exchanger also includes an expansion relief feature existing beiween. the first header aad the second header, the expansion relief feature accommodating relative movement in the longitudinal direction between the first header and the third heiider hi response to a difference in longitudinal thermal expansion of the first plurality of tubes relative to the second plurality of tubes.

[0109J In some embodiments the present invention provides a microchannei heat exchanger for conveying an internal fluid in beat transfer relationship with an external fluid. The microchannei heat exchanger includes a. first header defining an inlet for the internal fluid to enter the microchannei heat exchanger, a second header, a third header adjacent to the first header, and a first plurali ty 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 microchannei 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 die third header. The microchannei 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 microchannei heat exchanger also includes a. second plurality of serpentine fins -interconnecting in the lateral direction the second pluralit of tubes. The microchannei 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 microchannei heat exchanger also includes an expansion relief feature existing between the first header and the second header. The expansion relief feature accommodates relat e 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 piuralst of tubes relative to the second plurality of tubes. The microchannei 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 tunes. The elongate member conveys substantially none of the internal fluid. The raicrochannel 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

[6110} Figure I is a front view of an example microchannel heat exchanger with an expansion relief feature.

[91 1 Figure 2 is an. enlarged cross-sectional view of the area identified by circle-2 of Figure i .

{01 12} figure 3 is a cross-sectional view taken along line 3-3 of Figure I .

[01131 Figure 4 is a cross-sectional view takes along line 4-4 of Figure I .

fw 11.41 Figure 5 is a cross-sectional view similar to Figure 4 but showing the cross section of an alternate elongate member,

[0115} Figure 6 is a front view of another example microchannel heat exchanger with aii expansion relief feature.

[0116} Figure 7 is a front view similar to Figure 6 but showing the expansion relief feature accommodating uneven, thermal expansion of the heat exchanger.

10117} Figure 8 is a front v ew of another example microchannel heat exchanger with an expansion relief feature.

[0118} Figure 9 is a front view of another example microchannel heat exchanger with an expansion relief feature.

[011 j Figure 10 is a front view of another example microchannel heat exchanger with an expansion relief feature.

10120} figure Ϊ 1 is a front view of another example microchannel heat exchanger with an expansion relief feature,

[0121} Figure 12 is a front view of another example microchannel heat exchanger with an expansion relief feature. Description of t e Preferred Km hod in tent

[0122} Figure 1, with additional reference fo Figures 2 - 5, illustrates one example of a microchatmel heat exchanger 10 that includes an expansion relief feature 12 for accommodating uneven thermal expansion in heat exchanger 10.

[0123} In the illustrated example, heat exchanger 10 comprises a first plurality of tubes 14a extending between a first heade 16 (manifold) and a second header 18, a second plurality of tubes 1 b extending between second header 18 and a tlrird header 20, a first plurality of serpentine fins 22a stacked and bonded (e.g., brazed) in an alternating arrangement with, the first plurality of tubes 1.4a, and a. second plurality of serpentine fin s 22 stacked and bonded in an alternating arrangement with the second plurality of tubes 14b. The term, "serpentine." means that the fin is wavy with peaks and valleys (e.g., sine wave, square wave, and various modifications thereof).

[0! 24j 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 1.0 has a plurality of spaces 28, e.g., a first space, a second space, third space, etcetera. Each space 28 is defined in lateral direction 24 by two adjacent tubes 14 that are spaced apart by 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.

[0125} In this example, first header 16 has an inlet 34, and third header 20 has an outlet 36. An. internal fluid 38 (e.g., . efrigerant, water, glycol, etc.) enters .first header 16 through inlet 34, and (he fi st pkiraliiy of tubes 1 a convey fluid 38 to second header 18. The second plurality of tubes 14b con vey 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. {01261 Fins 22 (i.e., tins 22a and 22b) are thermally conductive to promote heat transfer between internal fluid 38 flowing through tubes 14 (i.e., tubes 14a and 1 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 lao, blower or some other known me ns can be used for forcing air or some other externa! fluid across the external surfaces of heat exchanger 10.

{0127J Although the actual structure of heat exchanger 10 may vary, in some examples, tubes 14; fins 22; headers 1 6, 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 b 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 iogether. Tube-to- fin heat transfer is enhanced by providing tubes 1 with substantially flat surfaces 44, as shown in Figure 3.

0128| In the example shown in Figure 1 , expansion relief feature 12 is first header 36 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 iiibes 14a to expand more or less than tubes 14b 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 increasin or decreasing as fluid 38 flows through heat exchanger 1 .

[0129} To provide some structural support in the general area o gap 46 and expansion relief feature 12, heat exchanger 10 has elongate member 40 brazed or otherwise bonded between the two sets of tubes 14a and 14b. In examples where elongate member 40 is brazed, to tribes oo .l 4aoa and 14b, structural support i 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 Figures 4 and 5. Figure 4 shows an example elongate member 40a with a tubular cross-sectional area (similar to that of tube 14); however, elongate member 40a does not convey any internal fluid 38. figure 5 shows an example elongate member 40b 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,

[01301 In another example, show in Figures 6 and 7, a niicrochannel 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 Figure 6, Figure 7 shows tubes 14a being longer than tubes 14b due to a difference in thermal expansion of tubes 4a relative to tubes 14b,

01311 I» another example, shown in Figure 8, a mkrochannel heat exchanger 58 is similar to heat exchanger 10 of Figure 1 ; however, elongate member 40 is elimina ted in heat exchanger 58 b placing tubes 14 a closer to tubes 4b. instead of elongate member 40 and an intermediate serpentine fin 22c (Fig, 1), a lowermost tube 14a' is all that couples the lowermost fin 22a' to an uppermost .fin 22b'. 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 microehannei heat exchanger 62 of Figure 9, a slit 64 in an uppermost fin 22b" 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 22b' to produce fin 22b"', 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 i4a and 14b. 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.

[0132J Figure 10 shows an example microehannei 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 Figure 10, instead of two separate headers 1.6 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 74a and 74b. Fluid 38 enters chamber 72 a through inlet 34, and the first pluralit of tubes 14a convey Ouid 38 to header 1 8. The second plurality of tubes 1.4b con vey fluid 38 from header 18 to chamber 72b, and outlet 36 releases fluid 38 oat from within chamber 72b. Since fluid 38 makes two passes across the width of heat exchanger 70, it can be considered a two-pass heat exchanger. [0133| A single-pass version is shown in Figure I I. Irt 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 (aay number of slits, one or more) serve as the heat exchanger's expansion relief feature,

[0134] Any of the example heat exchangers shown in Figures 1 and 6 - 11 can be readily modified to provide any number of passes. Figure 12, for example, shows a microchannel heal 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 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 tabes 14 convey fluid 38 from second header 84 to third header 86 for a second pass, and the Sower 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.

[0135} If should be noted that when one heade 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.

|0136J 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: