US20160377350A1

US20160377350A1 - Optimized plate fin heat exchanger for improved compliance to improve thermal life

Info

Publication number: US20160377350A1
Application number: US14/754,235
Authority: US
Inventors: Joseph Jensen; David Asher Berukhim; Yung Oey
Original assignee: Honeywell International Inc
Current assignee: Honeywell International Inc
Priority date: 2015-06-29
Filing date: 2015-06-29
Publication date: 2016-12-29

Abstract

A heat exchanger includes a hot passage; a cold passage adjacent the hot passage; a pair of tube sheets, with one tube sheet on each opposing side of one of the hot passage and the cold passage; a fin in one of the hot passage and the cold passage; wherein the fin includes a first distal portion, a second distal portion, and an intermediate portion between the first and second distal portions; wherein the fin is configured to provide, at only the first distal portion and the second distal portion, improved flexibility in three degrees of freedom of movement within one of the hot passage and the cold passage.

Description

BACKGROUND OF THE INVENTION

The present invention generally relates to heat exchangers and, more particularly, apparatus and methods for minimizing strain in heat exchangers to achieve a longer useful life or enabling the heat exchanger to tolerate a more severe operating environment.
Plate-fin heat exchangers are brazed to form a core that is a monolithic structure where the each tube sheet layer is locked into close synchronicity with its two neighboring tube plate. Each of the internal tube sheets is connected to a neighboring tube sheet via the hot side fins and to the other neighboring tube sheet via the cold side fins. With this rigid, non-compliant construction, heat exchangers can exhibit a significant strain when the heat exchanger has a temperature difference placed on the unit, especially when the operationally temperature difference is large. This strain can lead to conditions where, with repeated exposure, the tube sheet cracks, thus negatively impacting the performance of the system and the useful life of the heat exchanger. A typical situation where this issue may occur is with bleed air pre-coolers that are found on most commercial (large and small) and military environmental control/bleed air systems. Any heat exchanger that is repeatedly exposed to rapid and large temperature differences may exhibit this issue.
As can be seen, there is a need for improved apparatus and methods for reducing strain in heat exchangers.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a heat exchanger comprises a hot passage; a cold passage adjacent the hot passage; a pair of tube sheets, with one tube sheet on each opposing side of one of the hot passage and the cold passage; a fin in one of the hot passage and the cold passage; wherein the fin includes a first distal portion, a second distal portion, and an intermediate portion between the first and second distal portions; wherein the fin is configured to provide, at only the first distal portion and the second distal portion, three degrees of freedom of movement within one of the hot passage and the cold passage.
In another aspect of the present invention, a plate fin heat exchanger comprises a hot passage; a cold passage adjacent the hot passage; a pair of tube sheets on opposing sides of the cold passage; a fin in the cold passage; wherein the fin includes a first distal portion, a second distal portion, and an intermediate portion between the first and second distal portions; wherein the fin, at only the first distal portion and the second distal portion, is separated laterally into a first lateral portion and a second lateral portion.
In a further aspect of the present invention, a plate fin heat exchanger comprises a plurality of cold passages; a plurality of fins in the cold passages; a plurality of hot passages; a plurality of tube sheets; wherein the cold passages, hot passages and tube sheets are positioned in an recurring pattern of cold passage, tube sheet, hot passage, and tube sheet; wherein one of the plurality of fins has a distal portion with a divided configuration to provide three degrees of freedom of movement of the fin at the distal portion.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heat exchanger according to an embodiment of the present invention;

FIG. 2 is a close up view of a portion of the heat exchanger of FIG. 1;

FIG. 3 is a close up perspective view of a portion of a heat exchanger according to another embodiment of the present invention;

FIG. 4 is a plan view of a portion of a heat exchanger according to a further embodiment of the present invention;

FIGS. 5A-5B are schematic top views of a heat exchanger depicting two variations of compliant fin separation according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Various inventive features are described below that can each be used independently of one another or in combination with other features.
Broadly, embodiments of the present invention generally provides a heat exchanger that can minimize the locking of a tube sheet to its two neighboring tube sheets. In embodiments, the heat exchanger can include a hot circuit usually at high pressure and a cold circuit at relatively low pressure. This is the case for bleed air pre-coolers found on commercial and military aircraft. Tube sheets that surround a hot passage can be brazed to the hot side fin to provide for pressure containment of the high pressure fluid. However, the tube sheets that surround the cold side passage are not connected or otherwise affixed, in certain locations, to one another. This is possible due to the low pressure of the fluid in this passage.
FIG. 1 depicts a heat exchanger 10 according to an embodiment of the present invention. The heat exchanger 10 can be of a plate fin construction and receive, at a cold inlet face 17, a cold flow 11, such as a fan air flow in the context of an aircraft, and which exits at a cold outlet face (not shown). The heat exchanger 10 can also receive, at a hot inlet face 18, a hot flow 12, such as a bleed air flow in the context of an aircraft, and which exits at a hot outlet face (not shown).
A core of the heat exchanger 10 can include a plurality of cold passages 13 that can receive the cold flow 11 at the cold inlet face 17 of the heat exchanger 10. The cold passages 13 can include a plurality of main or primary cold passages 13 a that may be generally located in a center area of the core. The cold passages 13 can further include outer or distal cold passages 13 b at one side of the main cold passages 13 a, in addition to outer or distal cold passages 13 c at an opposite side of the main cold passages 13 a. The outer passages 13 b, 13 c can be at the far ends/side areas of the core.
The outer cold passages 13 b can include a distal portion or area 13 b-1 and a distal portion or area 13 b-2 at opposed corners of the heat exchanger 10 where the cold passages 13 meet hot passages 14 as described below. Between the distal portions 13 b-1, 13 b-2 can be an intermediate portion 13 b-5. Similarly, the outer cold passages 13 c can include a distal portion or area 13 c-1 and a distal portion or area 13 c-2 at opposed corners of the heat exchanger 10 where the cold passages 13 meet the hot passages 14. Between the distal portions 13 c-1, 13 c-2 can be an intermediate portion 13 c-5.
FIG. 2 is a close up view of the distal portion or area 13 b-2 of the cold passages 13. The distal portion 13 b-2 can be defined by an area having a length 13 b-3 and a height 13 b-4. The other distal portions 13 b-1, 13 c-1, and 13 c-2 can be similarly defined, and the widths and lengths can be different or the same from one another and with different detailed modification of the fin geometry.
In embodiments of the distal portion 13 b-2, the height 13 b-4 can be measured in numbers of cold passages 13 b. For example, the number of cold passages 13 b in height 13 b-4 can be from about 4 to about 8 passages specifically and from 2 to 10 as a general range, as an example. The number of passages that form the passages 13 b can depend on the thermal stresses that are induced upon the core with the operational conditions.
In embodiments of the distal portion 13 b-2, the ratio of the length 13 b-3 to the height 13 b-4 may be from about 0.5 to about 1.0 specifically and from 0.2 to 2.0 as a general range.
In embodiments, the length 13 b-3 may be from about 0.5 to about 1.5 inches specifically and from 0.2 to 2 inches as a general range.
In embodiments, the ratio of the height 13 b-4 to the overall height of the cold inlet face may be from about 5% to about 10% specifically and from 3% to 18% as a general range, though this number is dependent upon the cold inlet face width which can vary greatly for the heat exchanger.
The foregoing ratios may be the same or different among the other distal portions 13 b-1, 13 c-1, and 13 c-2.
Referring back to FIG. 1, the core of the heat exchanger 10 can additionally include a plurality of hot passages 14 that can receive the hot flow 12 at the hot inlet face 18 of the heat exchanger 10. The hot passages 14 can include a plurality of main or intermediate hot passages 14 a. The hot passages 14 can further include outer or distal hot passages 14 b at one side of the main hot passages 14 a, in addition to outer or distal hot passages 14 c at an opposite side of the main hot passages 14 a.
Further, the core of the heat exchanger 10 can include a plurality of tube sheets 15 that, in an embodiment, can form a recurring pattern of cold passage 13, tube sheet 15, hot passage 14, and tube sheet 15 (FIG. 2). Therefore, any one tube sheet (such as tube sheet 15-1) has two immediately adjacent or neighboring tube sheets (such as tube sheets 15-2, 15-3). And, one tube sheet can be on each of the opposed sides of the any one tube sheet.
In the core of the heat exchanger 10, a fin may be disposed in one or more cold passages 13. Differently configured fins may be disposed in different cold passages 13. In an embodiment, a fin 17 having a main or base configuration can be disposed in one or more of the main cold passages 13 a. In an embodiment, a fin 16 having an outer or dual configuration can be disposed in one or more of the outer cold passages 13 b, 13 c.
For example, the fin 17 may have a wave or sinusoidal configuration over its entire cross section—from a first distal portion at a first end of the fin 17 and to a second distal portion at a second send of the fin 17 (FIG. 2). In other words, the fin may have such configuration from the cold inlet face 17 to a cold outlet face (not shown) where the cold flow exits, and also have such configuration from the hot inlet face 18 to a hot outlet face (not shown) where the hot flow exits.
In contrast, and as an example, the fin 16 may have a wave or sinusoidal configuration 16 c but only over its cross section in the intermediate portion (e.g., 13 b-5). At one or both of its first and second distal portions, respectively located at its first and second distal ends, the fin 16 may have a divided wave or sinusoidal configuration. In other words, the fin may be separated laterally through its cross section at one or both of its distal portions or ends, but not in its intermediate portion. Thereby, the fin 16, at one or both of its distal portions/ends can have a first lateral portion 16 a and a second lateral portion 16 b (FIGS. 2-3).
In embodiments, the fin may be laterally separated at its cross-sectional mid-point (FIGS. 2-3) or at other points along the fin. In embodiments, the lateral separation may be less (FIG. 5A) than the entire distance (FIG. 5B) between the cold inlet face and the cold outlet face, and it may be in multiple segments between the cold inlet face and the cold outlet face. In embodiments, the distal portions of the fin 16 may or may not have the same lateral separation, if any at all.
As depicted in FIG. 3, with the first lateral portion 16 a separated from the second lateral portion 16 b, such first and second lateral portions can have three degrees of freedom of movement without confinement from attachment to neighboring fins, i.e., movement in an x, y, and z direction. In embodiments, the three degrees of freedom of movement may be increased over the movement that may already exist. For example, in the “x” direction, the movement may be increased by about 0.1% to about 2%. In the “y” direction, the movement may be increased by about 2% to about 20%. In the “z” direction, the movement may be increased by about 0.1% to about 2%.
FIG. 4 is an alternative embodiment of the first and second lateral portions, but in the context of distal portion 13 b-1′ which correlates to 13 b-1 in FIG. 2. This embodiment is otherwise the same as the embodiment depicted in FIG. 2. This embodiment could be applied to 13 b-2, 13 c-1 or 13 c-2. In FIG. 4, a fin 16′ includes an intermediate portion 16 c′ which is generally of a wave or sinusoidal configuration (or could be in other configurations, such as plain or offset fin). A first lateral portion 16 a′ and a second lateral portion 16 b′ are two wave or sinusoidal configurations (whereas 16 a and 16 b of FIG. 2 are portions of a single wave or sinusoidal configuration). In other words, the lateral portion 16 a′ is a wave or sinusoidal configuration stacked on the lateral portion 16 b′ which is a separate wave or sinusoidal configuration.
In yet another embodiment, a splitter plate may be disposed laterally through a fin, keeping fin 16 a′ and 16 b′ separated. To relieve stress, portions of the fin at its distal ends may be unbrazed to the fins or otherwise disconnected from the plate. Or, the plate may be eliminated at the distal ends of the fin.
If the disconnection of the complete cold side fin causes other issues (such as pressure containment), the fins could be modified in select locations such as near the hot-hot, hot-cold and cold-hot corners, for −2 inches into the core and −2 inches away from the bar (FIG. 5A). It is possible the amount/area of disconnection would vary depending on what corner is being modified.
For embodiments, preliminary structural analysis and investigation of strain range reduction associated with this invention is 17% on a typical commercial transport pre-cooler for the worst transient maneuver if applied to the whole heat exchanger. The strain reduction is 8% if the cold side fin cut were applied only to the top and bottom six cold side passages with the passages in the center of the core unmodified. This is a significant strain decrease and would result in a much more increase in estimated pre-cooler useful life than the 17% due to the associated strain reduction. This analysis is preliminary in nature and was conducted without reflecting the reduction in the stackwise conduction due to the fin cut at the mid-plane. The structural analysis was conducted with a complete disconnection of the fins in the three directions at the mid-plane.
It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.

Claims

We claim:

1. A heat exchanger, comprising

a hot passage;

a cold passage adjacent the hot passage;

a pair of tube sheets, with one tube sheet on each opposing side of one of the hot passage and the cold passage;

a fin in one of the hot passage and the cold passage;

wherein the fin includes a first distal portion, a second distal portion, and an intermediate portion between the first and second distal portions;

wherein the fin is configured to provide, at only the first distal portion and the second distal portion, three degrees of freedom of movement within one of the hot passage and the cold passage.

2. The heat exchanger of claim 1, further comprising a plurality of tube sheets, whereby any one tube sheet has two immediately adjacent tube sheets, whereby one tube sheet of the two immediately adjacent tube sheets is on each side of the any one tube sheet.

3. The heat exchanger of claim 1, wherein the pair of tube sheets are on opposing sides of the cold passage, and the pair of tube sheets are not affixed to one another at certain locations.

4. The heat exchanger of claim 1, wherein the fin has a sinusoidal configuration.

5. The heat exchanger of claim 1, wherein one of the first distal portion and the second distal portion has a divided sinusoidal configuration.

6. The heat exchanger of claim 1, wherein one of the first distal portion and the second distal portion is separated laterally through its cross section.

7. The heat exchanger of claim 1, wherein the fin is laterally separated at its cross-sectional mid-point.

8. A plate fin heat exchanger, comprising a hot passage;

a cold passage adjacent the hot passage;

a pair of tube sheets on opposing sides of the cold passage;

a fin in the cold passage;

wherein the fin, at only the first distal portion and the second distal portion, is separated laterally into a first lateral portion and a second lateral portion.

9. The heat exchanger of claim 8, further comprising:

a plurality of cold passages,

wherein the plurality of cold passages include outer cold passages, and

wherein the cold passage with the fin therein is one of the outer cold passages.

10. The heat exchanger of claim 9, wherein the plurality of outer cold passages includes a distal area defined by an area having a length and height.

11. The heat exchanger of claim 10, wherein a ratio of the length to the height is from about 0.5 to about 1.0.

12. The heat exchanger of claim 10, further comprising a cold inlet face, and

wherein a ratio of the height of the distal area to an overall height of the cold inlet face is from about 3% to about 11%.

13. The heat exchanger of claim 9, wherein the plurality of outer cold passages includes from about 4 to about 8 cold passages.

14. The heat exchanger of claim 8, wherein:

the cold passage includes a cold passage distal portion located at a corner where the cold passage meets the hot passage, and

one of the first and second distal portions of the fin is located at the cold passage distal portion.

15. A plate fin heat exchanger, comprising

a plurality of cold passages;

a plurality of fins in the cold passages;

a plurality of hot passages;

a plurality of tube sheets;

wherein the cold passages, hot passages and tube sheets are positioned in an recurring pattern of cold passage, tube sheet, hot passage, and tube sheet;

wherein one of the plurality of fins has a distal portion with a divided configuration to provide three degrees of freedom of movement of the fin at the distal portion.

16. The heat exchanger of claim 15, wherein the divided configuration is a lateral separation through a cross section of the distal portion.

17. The heat exchanger of claim 16, wherein the lateral separation is at a mid-point of the cross section.

18. The heat exchanger of claim 16, wherein the lateral separation is less than an entire distance between a cold inlet face and a cold outlet face.