US20070272396A1

US20070272396A1 - Heat Exchanger With Angled Fin

Info

Publication number: US20070272396A1
Application number: US11/420,237
Authority: US
Inventors: Levi A Campbell; Richard C. Chu; Michael J. Ellsworth; Madhusudan K. Iyengar; Roger R. Schmidt; Robert E. Simons
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 2006-05-25
Filing date: 2006-05-25
Publication date: 2007-11-29

Abstract

An angled finned heat exchanger and associated method is provided. The heat exchanger cools the air provided to the electronic components and is disposed at an angle with respect to direction of air flow. The heat exchanger comprises a plurality of fins that are at an angle with respect to frontal area of the heat exchanger. In alternate embodiments, the angle of the fin is optimized to minimize air pressure loss and/or drop. Some suggested methods of fabrication of the fins are also provided.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to cooling of electronic packages used in computing system environments and more particularly to cooling of electronic components used in large computing environments such as those including servers.
2. Description of Background
The industry trend has been to continuously increase the number of electronic components inside computing system environments. A computing system environment can simply comprise a single personal computer or a complex network of large computers in processing communication with one another. Increasing the components inside a simple computing system environment does create a few problems, but such an increase in complex computing system environments that include large computer complexes lead to many challenges. This is because in large and complex environments, any simple problem is magnified so that seemingly isolated issues start to affect one another, and have to be resolved in consideration with one another.
One such particular challenge when designing any computing system environment is the issue of heat dissipation. Heat dissipation poses a challenge at both the module and system level. Increased air flow rates are needed to effectively cool modules and to limit the temperature of the air that is exhausted into the computing environment and ultimately the data center level. Prior art continues to struggle to achieve an acceptable solution for the heat dissipation problem.
One such concept was presented in U.S. Pat. No. 6,775,137. In that patent an air and liquid heat removal enclosure system was provided with an enclosure scheme within which a stack(s) of electronic drawers was packaged. Air was then circulated within the enclosure to cool the electronics and was ultimately passed across one or more air-to-liquid finned-tube heat exchanger(s). The heat exchangers were mounted to the side of the electronics frame in a first embodiment, and in front and/or back of the electronics in a second embodiment to transfer the total system heat load to water which then exited the frame.
While that patent solved many of the heat dissipation issues related to prior art, it did not address the air pressure drop through the angled heat exchangers, a problem especially in the case of side mounted sub-frame design.
Heat exchangers are typically designed to accept an air flow normal to its frontal area as shown in the prior art conventional heat exchanger design of FIGS. 1 a through c. Forcing the air to enter through a heat exchanger at an oblique angle to the upstream air flow, results as illustrated in FIG. 2, in a substantial loss in air pressure. This pressure loss adversely affects the system air flow rate impairing dissipation of heat from the system. Consequently, an apparatus and method is desired that can still provide the benefit associated with the angled heat exchanger design but also addresses the pressure drop concerns discussed above.

SUMMARY OF THE INVENTION

The shortcomings of the prior art are overcome and additional advantages are provided through the provision of an angled finned heat exchanger and incorporated method. The heat exchanger cools the air provided to the electronic components and is disposed at an angle with respect to direction of air flow. The heat exchanger comprises a plurality of fins that are at an angle with respect to frontal area of the heat exchanger. In alternate embodiments, the angle of the fin is optimized to minimize air pressure loss and/or drop. Some suggested methods of fabrication of the fins are also provided.
Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features, refer to the description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIGS. 1 a though c are prior art depictions illustrating a flat tube and folded fin heat exchanger;

FIG. 2 is a sectional cut schematic representation of the a heat exchanger as provided in the sidecar application of FIG. 3;

FIG. 3 is a top view illustration of a horizontal air flow rack level heat removal system used in conjunction with the embodiments of the present invention;

FIGS. 4 a and 4 b are sectional cut schematic representations showing an angled finned heat exchanger as per one embodiment of the present invention;

FIGS. 5 a and 5 b are sectional cut schematic representation of an angled finned heat exchanger demonstrating an angle of attack;

FIG. 6 is a graphical depiction of the relationship between angle of attack and air pressure drop;

FIGS. 7 and 8 provide an alternate embodiment of the present invention; and

FIGS. 9 and 10 are a first and second manner of fabricating the angled fins of embodiments depicted by FIGS. 4 a and 4 b.

DESCRIPTION OF THE INVENTION

FIG. 3 is a top view illustration of a closed horizontal air flow rack level heat removal system 300, used to house one or more computers or computing environments (such as servers). It should be noted that while the workings of the present invention will be described below in conjunction with a computing environment such as the one provided in conjunction with FIG. 3, this is only done for ease of understanding. The workings of the present invention can be equally applicable to any heat exchangers used in any other electrical device or in other similar environments and its use should not be particularly limited to computers and computing environments per se.
Referring back to FIG. 3, the frame assembly 310 is comprised of a front 320, housing a front cover 322; and a back 330, housing a back cover 332. In the embodiment provided in conjunction with FIG. 3, a side mounted cooling sub-frame 340, interchangeably referenced hereinafter as side car 340, is also provided. The side mounted sub-frame 340 houses a heat exchanger 350 that is disposed, as illustrated in the figure, at an oblique angle. It should be noted that while the depiction of FIG. 3 illustrates a side mounted sub-frame arrangement, the heat exchanger in question can be placed in any other angled arrangements as will be discussed below in detail and still benefit from the workings of the present invention as will be disclosed.
In FIG. 3, the heat generating electronics and other such related components (not individually shown), are placed in the electronics frame 360. In a preferred embodiment, as illustrated, the electronics and the associated frame 360 are placed adjacent to the side mounted sub-frame 340 housing the heat exchanger 350 such as to directly and immediately benefit from the ensuing cooling effects. This is because the placement of the heat exchanger 350 and other the components allows for a closed loop air flow with the direction of generalized air flow path being illustrated in FIG. 3 and referenced by use of arrows and reference numerals 390.
The angled heat exchanger design is to provide for cooling rack-mounted modular electronic units in an attempt to address some of the defects existing in the prior art by combining the air cooling approach with an air-to-water heat exchanger fixed within the server cabinet. In this regard, the oblique heat exchanger 350 design of FIG. 3, is designed to minimize overall system floor space while maintaining a given thermal performance. This is because of the change in design of many such servers. Traditionally, in many large server applications, processors along with their associated electronics are packaged in removable drawer configurations stacked within a rack or frame or in fixed locations within the rack or frame. The desire to increase the number of components while maintaining the same or slightly larger footprints has lead to a scenario where the heat exchanger is housed in very narrow areas, sometimes necessitating the heat exchanger 350 to be rotated as shown in FIG. 3.
Before a detailed discussion of the workings of the present invention is provided, however, the problem with using a traditional heat exchanger placed in an oblique angle needs to be further explored. Referring back to the prior art schematic illustration of a heat exchanger as provided by FIG. 2, this concept becomes more clear. As illustrated by the sectional cut schematic of FIG. 2, the heat exchanger 250 is placed at an oblique angle θ with respect to the horizontal axis as referenced by numerals 280. Air flows into the heat exchanger 250 as depicted by arrows 290 though fins 205.
The sectional cut view of the heat exchanger 250 illustrates the orientation of the fins 205. As can be observed, the air flows through the oblique angled fins 205 and is forced to change direction upon exiting the heat exchanger 250 again in substantially the same orientation as it entered the heat exchanger 250. This temporary changing of direction leads to the increased pressure drop in the air flow as discussed previously, ultimately causing less than optimal thermal management results.
This concept becomes more evident by examining the prior art illustration of FIGS. 1 a through 1 c. FIGS. 1 a though 1 c illustrate the basic core structure of a heat exchanger (hx) such as the widely known compact copper/brass heat exchanger currently being used in the industry. It should be noted that in the figures, the manifolds at the ends of the brass tubes are not shown. FIG. 1 b is a cross sectional front view illustration of a folded copper fin as referenced as 105. The flat brass tubes are also illustrated and referenced as 170.
FIG. 1 a is a sectional cut illustration of the heat exchanger of FIG. 1 b, cut across the lines A-A. It is important to understand the basic air side flow structure as seen in the sectional cut A-A of FIG. 1 a. For ease of understanding, a perspective view is also provided in FIG. 1 c where the liquid flow though tubes 170 and air flow through the fins 105 is shown and referenced respectively by arrows 195 and 190.
As discussed briefly in conjunction with FIG. 2 and better understood by referring to FIGS. 1 a and 1 c, air is essentially channeled orthogonal to the frontal area of the heat exchanger. Consequently, the air must turn significantly going into and out of the fin structure resulting in a large increase in the pressure drop that can be as much as ten times higher than the same volume air flow through the heat exchanger in a narrow air flow orientation.
To remedy this problem, while maintaining the much desired side car configuration discussed, a first embodiment of the present invention is provided as illustrated in FIGS. 4 a and b.
FIGS. 4 a and b provides for a sectional cut schematic representation of a heat exchanger, such as a copper/brass heat exchanger currently being used by the industry. As can be seen, FIG. 4 b provides for a similar sectional cut as provided by prior art FIG. 2 previously discussed. Direction or air flow is provided by arrows 490. The heat exchanger, referenced here as 450, is still tilted at an angle θ with respect to the horizontal axis. In the embodiment shown specifically in FIG. 4 a, however, the fins (preferably folded fins) referenced as 405 form an oblique angle φ, with respect to the normal of the frontal area.
As illustrated in FIG. 4 b, by making the value of angle φ equal to 90−θ, the air flow channels formed by the angled folded fins 405 will become parallel to the direction of air flow when the heat exchanger is angled by θ. It should be noted that air no longer has to turn as was the case in FIGS. 1 and 2, but the channel flow length which is proportional to the pressure drop within the channel itself is significantly longer than the normal channel configuration. For example, for a heat exchanger angle θ of 15 degrees which is representative for the side car application with this type of heat exchanger, the angled channel flow length is almost four times that of the normal channel flow length.
The pressure drop through the heat exchanger in an oblique orientation is primarily a function of the degree of air turning and the channel flow length. The degree of air turning is represented by an angle of attack ψ. Angle ψ is defined as the angle between the upstream air flow direction and the folded fins/channels and is related to the heat exchanger angle θ and fin angle φ as shown in FIGS. 5 a and 5 b. (Direction of air flow provided by arrows and associated reference numerals 590).
As illustrated FIG. 5 a is a depiction of the orientation of angle ψ, while FIG. 5 b illustrates the relationship between angle ψ with respect to angle θ, angle φ and the horizontal axis. FIG. 5 b, especially illustrates a sectional cut schematic representation of the heat exchanger 405 with angled folded fins 405 having an optimum fin angle of attack ψ which is defined as 90−(θ+φ).
For example, an attack angle of zero degrees represents the “no air turning: configuration as was shown and discussed in conjunction with the embodiment of FIG. 4. On the other hand, an attack angle of (90−θ) represents the conventional heat exchanger configuration of φ being equal to zero as was discussed in conjunction with embodiments of FIGS. 1 and 2.
As the angle of attack increases from a value of zero, however, the air turning contribution to pressure drop increases but the channel pressure drop decreases because of the decreasing channel flow length. A computational fluid dynamics analysis was undertaken to demonstrate that there is an optimum attack angle, and thus an optimum fin angle, for which pressure drop is a minimum. The results of the analysis are provided in FIG. 6.
FIG. 6 provides for a graphical depiction of the experimental data taken to establish the relationship between angled fin air side pressure drop and various attack angles. As illustrated, the air pressure drop that was measured in inches of water is represented by the vertical axis, while the value of the attack angle is plotted on the horizontal axis.
Note that angle φ, for this graph has been consistently kept at a value of 16.54 degrees as illustrated. At a zero attack angle, as shown, the air pressure drop value is 0.06 inches of water and this value actually decreases to less than 0.02 inches of water at around a 15 degree angle of attack and then from that point on the air pressure drop value increases. It should be noted that the example provided in the graph depicted in FIG. 6 is only to aid understanding and the results can vary depending on the variables used. In other words, there is no single unique fin angle since the pressure drop is also a function of the heat exchanger depth and the fin spacing. The optimal angle of attack is dependent on heat exchanger depth, fin spacing and orientation of heat exchanger and its location in the frame (i.e. sidecar).
FIGS. 7 and 8 as will be discussed below provide an alternate embodiment of the present invention, having a tubular structure and fin heat exchanger with fins provided at an oblique angle with respect to its frontal area. FIGS. 7 a and 7 b provide cross sectional views of the structure of such an alternate embodiment but disposed in different orientations.
FIG. 7 a provides for a cross sectional illustration where a section of the active core region with the fins at an angle φ (702), is provided with respect to the heat exchanger frontal area. In a preferred embodiment, the tubular structure is a round tube 710 as referenced in the figures. The tube 710 is preferably disposed to run horizontally with respect to gravity. FIG. 7 b shows the same heat exchanger section positioned at an angle θ (722) with respect to the direction of air flow 760.
FIGS. 8 a and 8 b provide illustrations and other details about the fins particularly as discussed with reference to the embodiment discussed in conjunction with FIGS. 7 a and 7 b. FIG. 8 a provides a top down illustrations of unmodified fins 820, while FIG. 5 b provides similar illustration with respect to modified fins 825 as will be discussed in more details below. Both the modified and unmodified fins 825 and 820 can be disposed on a structure, similar to the tubular structure 710 of FIGS. 7 a and 7 b.
FIG. 8 a illustrates an unmodified fin(s) 820 with a staggered array of holes 830 punched into it to fit over the associated structure (which in this embodiment can be a tube bank) according to the embodiment as illustrated in FIGS. 7 a and 7 b. As illustrated in the figure, “D” referenced as 851 is the tube hole diameter. Px referenced as 852 is the tube hole pitch in the x-direction in this embodiment which in this case is further defined by the direction of heat exchanger. Similarly, Py 853 is the tube hole pitch in the y-direction (in the direction of heat exchanger depth or thickness). Finally “t” is the fin width 854 which can be equal to heat exchanger depth or thickness in the illustrated embodiment of FIG. 8 a.
FIG. 8 b is a top down illustration of one embodiment of the present invention showing fin modifications. The fin modification, as illustrated in embodiment of FIG. 5 b, is designed to ensure that the fin remain in complete circumferential contact with the tubes for the best heat transfer effectiveness. In this embodiment, the fins are referenced as 825 and holes as 835. Dx, as illustrated and referenced by numerals 770, is the minor diameter of tube hole in an angled fin. Dy, as referenced as 77, is a major diameter of tube hole in an angled fin. Px_af 772 and Py_af 773 are respectively the tube hole pitch in x and y-direction for the angled fin. Finally “t_af” 774 is the angled fin width. If “s” is thought of as the spacing between fins along tube axis in an unmodified fin configuration (FIG. 8 a), then the following set of equations can be provided that relate the modified fin to the unmodified version.
$Dx = D$ $Dy = \frac{D}{\sin (θ + ψ)}$ $Px_af = Px$ $Py_af = \frac{Py}{\sin (θ + ψ)}$ $t_af = \frac{t}{\sin (θ + ψ)}$ $s_af = \frac{s}{\sin (θ + ψ)}$
The problem of optimizing the value of different angles including the angle of attack has now been explored and the attention can be turned to methods of manufacturing such an optimal folded fins with optimal angles. As will be appreciated by those skilled in the art, a variety of different embodiments can be used to achieve such fabrication goals. For ease of understanding, however, a couple of such methodologies will be explored below. As suggested, however, such methods are only provided as examples and should not be restrictive and limiting as with regards to the teaching of the present invention. A first and second method of fabricating a folded finned heat exchanger with an optimal angle is illustrated in FIGS. 9 and 10.
FIG. 9 is a schematic illustration of a first method of manufacturing folded fins with oblique angle channels by slicing wide fin stock at a desired angle, as shown and achieving angled fins 905. In other words, manufacturing starts with a very wide (deep) folded fin. The wide folded fins are then subsequently cut to a useable width but at a desired (and previously selected) angle with respect to the fins.
FIGS. 10 a and b, by contrast, depicts a second embodiment for manufacturing of the angled fins. FIG. 10 a provides for a schematic illustration of a manufacturing fold fin with oblique angled channels by stamping with oblique angled gear tooth gears 1900. In other words, the folded fins 1905 are stamped using gears 1900 with teeth, shown at 1910 in FIG. 10 b, at an oblique angle to the gear axis.
FIGS. 10 a and 10 b are particularly provided in regard to existing manufacturing techniques so that each method can be easily adopted without much necessity to change the fabrication process steps. This allows for fabrication flexibility and cost effectiveness in manufacturing of the fins.
While the preferred embodiment to the invention has been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.

Claims

1. A heat exchanger comprising:

a plurality of fins angled with respect to a frontal area of said heat exchanger; and at least said frontal area being disposed at an angle with respect to direction of air flow.

2. The heat exchanger of claim 1, wherein said heat exchanger is disposed at an angle θ with respect to the air flow direction.

3. The heat exchanger of claim 2, wherein the fins are angled at an angle φ and value of φ is equal to 90−θ.

4. The heat exchanger of claim 3, wherein any necessary turning of air flow is measured by an angle ψ defined by relationship ψ=90−(θ+φ).

5. The heat exchanger of claim 1, wherein said heat exchanger comprises of a tubular structure placed horizontally with respect to gravity, said tubular structure being in thermal communication with said fins, such that said fins remain in complete circumferential contact with said heat exchanger.

6. The heat exchanger of claim 1, wherein fin angle is optimized to minimize air pressure drop.

7. The heat exchanger of claim 1, wherein said fins are folded fins.

8. The heat exchanger of claim 7, wherein said folded fins are made out of copper.

9. The heat exchanger of claim 7, wherein said folded fins have attached brass tubing for carrying fluids for fluid cooling.

10. The heat exchanger of claim 8, wherein said folded fins have attached brass tubing for carrying fluids for fluid cooling.

11. The heat exchanger of claim 1, wherein said heat exchanger is used in conjunction with a computing environment.

12. The heat exchanger of claim 11, wherein said heat exchanger is used in a server frame.

13. The heat exchanger of claim 12, wherein said heat exchanger is used in a side mounted sub-frame of a frame assembly housing a computing environment.

14. The heat exchanger of claim 12, wherein said heat exchanger is disposed such that air flow forms a closed loop and enters, exits and enters said heat exchanger as part of said closed air flow loop.

15. A method of cooling electronic components using a heat exchanger disposed at an angle with respect to direction of air flow comprising forming a plurality of angled fins provided such that are formed at an angle with respect to frontal area of said heat exchanger.

16. The method of claim 15, wherein said heat exchanger is disposed at an angle θ with respect to the air flow direction and said fins are angled at an angle φ and value of φ is equal to 90−θ.

17. The method of claim 16, wherein fin angle is optimized to minimize air pressure drop.

18. The method of claim 16, wherein said fins are formed by steps of: cutting a plurality of wide strips and recutting said wide strips to a desired width and at a preselected oblique angle.

19. The method of claim 16, wherein said fins are fabricated by stamping folded fins using gears with teeth at an oblique angle to gear axis to achieve desired fin angle.

20. The method of claim 16, wherein said fins are used in a computing environment.