U.S. patent application number 11/458696 was filed with the patent office on 2008-01-24 for heat exchanger with angled secondary fins extending from primary fins.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Levi A. Campbell, Richard C. Chu, Michael J. Ellsworth, Madhusudan K. Iyengar, Roger R. Schmidt, Robert E. Simons.
Application Number | 20080017360 11/458696 |
Document ID | / |
Family ID | 38970340 |
Filed Date | 2008-01-24 |
United States Patent
Application |
20080017360 |
Kind Code |
A1 |
Campbell; Levi A. ; et
al. |
January 24, 2008 |
HEAT EXCHANGER WITH ANGLED SECONDARY FINS EXTENDING FROM PRIMARY
FINS
Abstract
A heat exchanger, method of fabrication and cooled electronics
system employing the heat exchanger are provided. The heat
exchanger, which in one embodiment cools air provided to heat
generating components of a computer system, is disposed at an angle
with respect to a direction of airflow. The heat exchanger includes
a plurality of primary fins oriented parallel, and at least one
plurality of secondary fins extending from at least one of a
leading edge and a trailing edge of the plurality of primary fins.
Each secondary fin extends from a respective primary fin at an
angle other than 0.degree. to facilitate airflow through the heat
exchanger. Additionally, the secondary fins are fixedly positioned
relative to and integral with the primary fins, thereby providing
an increased heat transfer surface area.
Inventors: |
Campbell; Levi A.;
(Poughkeepsie, NY) ; Chu; Richard C.; (Hopewell
Junction, NY) ; Ellsworth; Michael J.;
(Lagrangeville, NY) ; Iyengar; Madhusudan K.;
(Woodstock, NY) ; Schmidt; Roger R.;
(Poughkeepsie, NY) ; Simons; Robert E.;
(Poughkeepsie, NY) |
Correspondence
Address: |
HESLIN ROTHENBERG FARLEY & MESITI P.C.
5 COLUMBIA CIRCLE
ALBANY
NY
12203
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
Armonk
NY
|
Family ID: |
38970340 |
Appl. No.: |
11/458696 |
Filed: |
July 20, 2006 |
Current U.S.
Class: |
165/148 ;
165/153; 257/E23.098; 257/E23.103 |
Current CPC
Class: |
H01L 23/473 20130101;
Y10T 29/49377 20150115; F28F 1/30 20130101; Y10T 29/49359 20150115;
F28F 2009/228 20130101; G06F 1/20 20130101; H01L 2924/0002
20130101; Y10T 29/49378 20150115; F28F 1/32 20130101; Y10T 29/4938
20150115; F28D 2021/0031 20130101; F28D 2001/0266 20130101; F28F
1/126 20130101; H01L 2924/0002 20130101; Y10T 29/4935 20150115;
H01L 2924/00 20130101; H01L 23/3672 20130101; G06F 2200/201
20130101 |
Class at
Publication: |
165/148 ;
165/153 |
International
Class: |
F28D 1/04 20060101
F28D001/04 |
Claims
1. A heat exchanger comprising: a plurality of primary fins
oriented parallel; and at least one plurality of secondary fins
extending from at least one of a leading edge and a trailing edge
of the plurality of primary fins, each secondary fin extending from
a respective primary fin at an angle other than 0.degree. to
facilitate airflow through the heat exchanger.
2. The heat exchanger of claim 1, wherein at least the leading edge
of the plurality of primary fins is disposed at angle .alpha. with
respect to a direction of airflow, wherein angle
.alpha..noteq.0.degree., and wherein at least some secondary fins
of the at least one plurality of secondary fins extend from the
plurality of primary fins at an angle .beta. to the plurality of
primary fins, wherein .beta.=.alpha..
3. The heat exchanger of claim 1, wherein the heat exchanger
further comprises a first plurality of secondary fins and a second
plurality of secondary fins, wherein the first plurality of
secondary fins extend from the leading edge of the plurality of
primary fins and the second plurality of secondary fins extend from
the trailing edge of the plurality of primary fins, wherein the
first plurality of secondary fins extend from the plurality of
primary fins at an angle aligned to a direction of airflow on an
air inlet side of the heat exchanger, and wherein the second
plurality of secondary fins extend from the plurality of primary
fins at an angle aligned to a direction of airflow on an air outlet
side of the heat exchanger.
4. The heat exchanger of claim 1, wherein the at least one
plurality of secondary fins are fixedly positioned relative to and
integral with the plurality of primary fins and provide an
increased heat transfer surface area over the plurality of primary
fins alone.
5. The heat exchanger of claim 1, wherein the at least one
plurality of secondary fins comprises n secondary fins, and the
plurality of primary fins comprises m primary fins, wherein
n.ltoreq.m, and wherein the n secondary fins at least one of:
extend at the leading edge of the plurality of primary fins from at
most every other primary fin of the m primary fins; and extend at
the trailing edge of the plurality of primary fins from at most
every other primary fin of the m primary fins.
6. The heat exchanger of claim 1, wherein the at least one
plurality of secondary fins comprises at least one of: a first
plurality of secondary fins extending from the leading edge of the
plurality of primary fins at a first angle, wherein the first
plurality of secondary fins extend from all primary fins of the
plurality of primary fins; and a second plurality of secondary fins
extending from the trailing edge of the plurality of primary fins
at a second angle, wherein the second plurality of secondary fins
extend from all primary fins of the plurality of primary fins.
7. The heat exchanger of claim 1, wherein the at least one
plurality of secondary fins are fixedly positioned relative to and
integral with the plurality of primary fins, and wherein the
plurality of primary fins comprise a plurality of primary folded
fins fabricated of a thermally conductive material, and wherein the
heat exchanger further comprises at least one fluid conduit
extending through and coupled to the plurality of primary folded
fins for carrying fluid through the heat exchanger, wherein heat is
transferred between the airflow and the fluid via the plurality of
primary folded fins and the at least one plurality of secondary
fins extending therefrom.
8. The heat exchanger of claim 1, wherein primary fins of the
plurality of primary fins each have at least a first surface area
and secondary fins of the at least one plurality of secondary fins
each have at most a second surface area, wherein the first surface
area is greater than the second surface area, and wherein the angle
that each secondary find extends from a respective primary fin is
selected to reduce pressure drop through the heat exchanger based
on anticipated orientation of the heat exchanger relative to a
direction of airflow on at least one of an air inlet side or an air
outlet side of the heat exchanger.
9. A cooled electronics system comprising: at least one heat
generating component; a housing containing the at least one heat
generating component; an air-moving device for moving air within
the housing containing the at least one heat generating component;
and an air-to-liquid heat exchanger disposed within the housing,
the air-to-liquid heat exchanger comprising: a plurality of primary
fins oriented parallel; and at least one plurality of secondary
fins extending from at least one of a leading edge and a trailing
edge of the plurality of primary fins, each secondary fin extending
from a respective primary fin at an angle other than 0.degree. to
facilitate airflow through the air-to-liquid heat exchanger,
wherein the airflow through the air-to-liquid heat exchanger is at
least partially established by the air-moving device.
10. The cooled electronics system of claim 9, wherein the housing
contains a computing environment and comprises a server frame, and
wherein the heat exchanger is disposed in a side-mounted sub-frame
of the server frame, the heat exchanger being disposed so that
airflow forms a closed airflow loop through the server frame and
the sub-frame and enters and exits the heat exchanger as part of
the closed airflow loop, and wherein the air-to-liquid heat
exchanger extracts heat from the air and transfers the heat to
fluid passing through at least one fluid conduit coupled to the
plurality of primary fins.
11. The cooled electronics system of claim 9, wherein at least the
leading edge of the plurality of primary fins is disposed at angle
.alpha. with respect to a direction of airflow, wherein angle
.alpha..noteq.0.degree., and wherein at least some secondary fins
of the at least one plurality of secondary fins extend from the
plurality of primary fins at an angle .beta. to the plurality of
primary fins, wherein .beta.=.alpha..
12. The cooled electronics system of claim 9, wherein the heat
exchanger further comprises a first plurality of secondary fins and
a second plurality of secondary fins, wherein the first plurality
of secondary fins extend from the leading edge of the plurality of
primary fins and the second plurality of secondary fins extend from
the trailing edge of the plurality of primary fins, wherein the
first plurality of secondary fins extend from the plurality of
primary fins at an angle relative to the primary fins aligned to a
direction of airflow on an air inlet side of the heat exchanger,
and wherein the second plurality of secondary fins extend from the
plurality of primary fins at an angle aligned to a direction of
airflow on an air outlet side of the heat exchanger, wherein the
air-to-liquid heat exchanger is disposed at an angle relative to at
least one of the direction of airflow on the air inlet side and the
direction of airflow on the air outlet side thereof.
13. The cooled electronics system of claim 9, wherein the at least
one plurality of secondary fins comprises n secondary fins, and the
plurality of primary fins comprises m primary fins, wherein
n.ltoreq.m, and wherein the n secondary fins at least one of:
extend at the leading edge of the plurality of primary fins from at
most every other primary fin of the m primary fins; and extend at
the trailing edge of the plurality of primary fins from at most
every other primary fin of the m primary fins.
14. The cooled electronics system of claim 9, wherein the at least
one plurality of secondary fins comprises at least one of: a first
plurality of secondary fins extending from the leading edge of the
plurality of primary fins at a first angle, wherein the first
plurality of secondary fins extend from all primary fins of the
plurality of primary fins; and a second plurality of secondary fins
extending from the trailing edge of the plurality of primary fins
at a second angle, wherein the second plurality of secondary fins
extend from all primary fins of the plurality of primary fins.
15. The cooled electronics system of claim 9, wherein the plurality
of primary fins comprise a plurality of primary folded fins
fabricated of a thermally conductive material, and wherein the
air-to-liquid heat exchanger further comprises at least one fluid
conduit extending through and coupled to the plurality of primary
folded fins for carrying fluid through the heat exchanger, wherein
heat is transferred between the airflow and the fluid via the
plurality of primary folded fins and the at least one plurality of
secondary fins extending therefrom.
16. The cooled electronics system of claim 9, wherein primary fins
of the plurality of primary fins each have at least a first surface
area and secondary fins of the at least one plurality of secondary
fins each have at most a second surface area, wherein the first
surface area is greater than the second surface area, and wherein
the angle that each secondary fin extends from a respective primary
fin is selected to reduce pressure drop through the air-to-liquid
heat exchanger based on orientation of the air-to-liquid heat
exchanger relative to direction of airflow on at least one of an
air inlet side or an air outlet side of the air-to-liquid heat
exchanger.
17. A method of fabricating a heat exchanger, the method
comprising: forming a plurality of primary fins oriented parallel,
the plurality of primary fins having a leading edge and a trailing
edge relative to an anticipated direction of airflow into the heat
exchanger, wherein the heat exchanger is to be disposed at an angle
with respect to the direction of airflow; and wherein the forming
includes forming at least one plurality of secondary fins extending
from at least one of the leading edge and the trailing edge of the
plurality of primary fins, each secondary fin extending from a
respective primary fin at an angle other than 0.degree., wherein
the angle that at least some secondary fins extend from the
respective primary fins is selected to reduce pressure drop through
the heat exchanger based on anticipated orientation of the heat
exchanger relative to the direction of airflow on at least one of
an air inlet side or an air outlet side of the heat exchanger.
18. The method of claim 17, wherein at least the leading edge of
the plurality of primary fins is to be disposed at an angle .alpha.
with respect to the direction of airflow, wherein angle
.alpha..noteq.0.degree., and wherein at least some secondary fins
of the at least one plurality of secondary fins are formed to
extend from the plurality of primary fins at an angle .beta. to the
plurality of primary fins, wherein .beta.=.alpha..
19. The method of claim 17, wherein the at least one plurality of
secondary fins comprises n secondary fins, and the plurality of
primary fins comprises m primary fins, wherein n.ltoreq.m, and
wherein the n secondary fins are formed to at least one of: extend
at the leading edge of the plurality of primary fins from at most
every other primary fin of the m primary fins; and extend at the
trailing edge of the plurality of primary fins from at most every
other primary fin of the m primary fins.
20. The method of claim 17, wherein forming the at least one
plurality of secondary fins comprises forming at least one of: a
first plurality of secondary fins extending from the leading edge
of the plurality of primary fins at a first angle, wherein the
first plurality of secondary fins extend from all primary fins of
the plurality of primary fins; and a second plurality of secondary
fins extending from the trailing edge of the plurality of primary
fins at a second angle, wherein the second plurality of secondary
fins extend from all primary fins of the plurality of primary fins.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application contains subject matter related to the
subject matter of the following co-pending application, which is
assigned to the same assignee as this application and which is
hereby incorporated herein by reference in its entirety:
[0002] "Heat Exchanger with Angled Fin", Campbell et al., Ser. No.
11/420,237, filed May 25, 2006.
TECHNICAL FIELD
[0003] The present invention relates generally to heat transfer
mechanisms, and more particularly, to cooling of heat generating
components used in computing system environments. Still more
particularly, the present invention relates to cooling of heat
generating components used in large computing environments, such as
rack or blade mounted computer server units.
BACKGROUND OF THE INVENTION
[0004] As is well known, as circuit density of electronic devices
increases in order to achieve faster and faster processing speeds,
there is a corresponding increasing demand for the removal of heat
generated by these devices. The increased heat load arises both
because the devices are packaged more closely together and because
the circuits themselves are operated at increasingly higher clock
frequencies. Nonetheless, it is also known that thermal runaway
conditions and excessive heat generated by circuits is a leading
cause of failure of electronic devices. Furthermore, it is
anticipated that the demand for heat removal from these devices
will increase indefinitely.
[0005] Accordingly, there is a large and significant need to
provide useful cooling mechanisms for electronic components,
individually and at all levels of packaging, including for example,
rack-mounted or blade-mounted electronic components of various
large computer systems today.
SUMMARY OF THE INVENTION
[0006] Briefly summarized, provided herein in one aspect is a heat
exchanger which includes: a plurality of primary fins oriented
parallel; and at least one plurality of secondary fins extending
from at least one of a leading edge and a trailing edge of the
plurality of primary fins. Each secondary fin extends from a
respective primary fin at an angle other than 0.degree. to
facilitate airflow through the heat exchanger.
[0007] In another aspect, a cooled electronics system is provided
which includes: at least one heat generating component; a housing
containing the at least one heat generating component; an
air-moving device for moving air within the housing containing the
at least one heat generating component; and an air-to-liquid heat
exchanger disposed within the housing. The air-to-liquid heat
exchanger includes a plurality of primary fins oriented parallel
and at least one plurality of secondary fins extending from at
least one of a leading edge and a trailing edge of the plurality of
primary fins. Each secondary fin extends from a respective primary
fin at an angle other than 0.degree. to facilitate airflow through
the air-to-liquid heat exchanger, wherein the airflow through the
air-to-liquid heat exchanger is at least partially established by
the air-moving device.
[0008] In a further aspect, a method of fabricating a heat
exchanger is provided. The method includes: forming a plurality of
primary fins oriented parallel, the plurality of primary fins
having a leading edge and a trailing edge relative to an
anticipated direction of airflow through the heat exchanger,
wherein the heat exchanger is to be disposed at an angle with
respect to the direction of airflow; and wherein the forming
includes forming at least one plurality of secondary fins extending
from at least one of the leading edge and the trailing edge of the
plurality of primary fins, each secondary fin extending from a
respective primary fin at an angle other than 0.degree., wherein
the angle that at least some secondary fins extend from the
respective primary fins is selected to reduce pressure drop through
the heat exchanger based on anticipated orientation of the heat
exchanger relative to the direction of airflow on at least one of
an air inlet side or an air outlet side of the heat exchanger.
[0009] Further, 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] 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:
[0011] FIGS. 1A-1C depict a conventional flat tube and folded fin
heat exchanger;
[0012] FIG. 2 is a partial cross-sectional representation of a heat
exchanger disposed at an angle relative to a direction of airflow,
for example, in the electronics frame sidecar application of FIG.
3;
[0013] FIG. 3 is a partial cross-sectional plan view of a
horizontal closed-loop airflow heat removal system for an
electronics frame with a side-mounted cooling system (cooling
connections to the heat exchanger not shown), to be implemented in
conjunction with one of the various heat exchanger embodiments
disclosed herein, in accordance with an aspect of the present
invention;
[0014] FIG. 4A is a cross-sectional plan view representation of one
embodiment of an angled fin heat exchanger, in accordance with an
aspect of the present invention;
[0015] FIG. 4B is a cross-sectional plan view representation of the
heat exchanger of FIG. 4A shown disposed within an airflow conduit,
in accordance with an aspect of the present invention;
[0016] FIG. 5A is a cross-sectional plan view representation of an
alternate embodiment of an angled fin heat exchanger, which
demonstrates an angle of attack, in accordance with an aspect of
the present invention;
[0017] FIG. 5B is a cross-sectional plan view representation of the
angled fin heat exchanger of FIG. 5A, shown disposed at an angle
within an airflow conduit, in accordance with an aspect of the
present invention;
[0018] FIG. 6 is a graphical depiction of the relationship between
angle of attack and air pressure drop through an angled fin heat
exchanger such as depicted in FIGS. 4A-5B, in accordance with an
aspect of the present invention;
[0019] FIGS. 7A & 7B depict an alternate embodiment of an
angled fin heat exchanger, in accordance with an aspect of the
present invention;
[0020] FIGS. 8A & 8B depict a further alternate embodiment of
an angled fin heat exchanger, in accordance with an aspect of the
present invention;
[0021] FIG. 9 depicts a first fabrication embodiment for forming
folded primary fins for an angled fin heat exchanger, in accordance
with an aspect of the present invention;
[0022] FIGS. 10A & 10B depict an alternate embodiment for
forming primary fins for an angled fin heat exchanger, in
accordance with an aspect of the present invention;
[0023] FIGS. 11 & 11A depict an alternate embodiment of a heat
exchanger having angled secondary fins extending from primary fins,
in accordance with an aspect of the present invention;
[0024] FIG. 12 depicts an alternate embodiment of a heat exchanger
with angled secondary extending from primary fins, in accordance
with an aspect of the present invention;
[0025] FIGS. 13 & 13A depict a further embodiment of a heat
exchanger with angled secondary fins extending from primary fins,
in accordance with an aspect of the present invention;
[0026] FIG. 14 depicts still another embodiment of a heat exchanger
with angled secondary fins extending from primary fins, in
accordance with an aspect of the present invention;
[0027] FIG. 15A is a conventional heat exchanger schematic showing
a direction of airflow on an air inlet and an air outlet side of
the heat exchanger assuming, for example, angled disposition of the
heat exchanger relative to the direction of airflow;
[0028] FIG. 15B is a schematic of one embodiment of a heat
exchanger with angled secondary fins extending from primary fins,
and assuming the same direction of airflow as shown in FIG. 15A, in
accordance with an aspect of the present invention;
[0029] FIG. 15C is an alternate embodiment of a heat exchanger with
angled secondary fins extending from primary fins, again assuming
the same direction of airflow as shown in FIG. 15A, in accordance
with an aspect of the present invention; and
[0030] FIG. 16 is a graph of relative performance of the three heat
exchangers of FIGS. 15A-15C, showing relative heat transfer,
pumping power and coefficient of performance of the heat
exchangers, and illustrating the benefits of the heat exchanger
embodiments of FIGS. 15B & 15C, in accordance with an aspect of
the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0031] As used herein, "electronics system" comprises one or more
heat generating components of a computer system or other
electronics system requiring cooling. By way of example, an
electronics system may comprise a mainframe server in one
implementation. The term "electronics rack" includes any housing,
frame, rack, blade server system, etc., having a heat generating
component of a computer system or electronics system, and may be,
for example, a stand alone computer processor having high, mid or
low end processing capability. In one embodiment, an electronics
rack may comprise multiple electronics drawers, each comprising an
electronics system with one or more heat generating components
requiring cooling. Each heat generating component may comprise an
electronics device, such as an electronics component, an integrated
circuit chip, a single-chip electronics module, a multi-chip
electronics module, etc.
[0032] A "heat exchanger" means any heat exchange mechanism through
which coolant can circulate; and includes, one or more discrete
heat exchange devices coupled either in series or in parallel. A
heat exchange device may comprise, for example, one or more coolant
flow paths, formed of thermally conductive fluid conduit (such as
copper, brass or other tubing) in thermal or mechanical contact
with a plurality of air-cooled primary fins (formed of a thermally
conductive material, such as copper). Unless otherwise specified,
size, configuration and construction of the heat exchangers
described herein below can vary without departing from the scope of
the present invention.
[0033] One example of coolant passing through the thermally
conductive fluid conduit of the heat exchanger is water. However,
the concepts disclosed herein are readily adapted to use with other
types of coolant. For example, the coolant may comprise a brine, a
fluorocarbon liquid, a liquid metal, or other similar coolant, or a
refrigerant, while still maintaining the advantages and unique
features of the present invention.
[0034] As explained briefly above, advances in semiconductor
technology have led to an exponential increase in microprocessor
performance over the past several years. This has led to a steep
increase in consumed rack power within the air-cooled data center
equipment, representing a significant thermal design and cooling
challenge. Increasing heat load and local heat flux in mid-range
and high-volume server packages has become a significant factor in
the implementation of new CMOS technology. Current air-cooled heat
sinks, even those employing vapor-chamber heat spreaders, are
reaching the limit of their extendibility to the new hotter
microprocessors.
[0035] Data center equipment can house several hundred, and
sometimes several thousand, microprocessors. Facility level air
cooling of these data center systems is typically carried out using
large air conditioning units that supply chilled air to the front
of the server racks by an under-floor or overhead ducting system.
These air cooling options have limitations with respect to the
maximum heat flux they can support, which is typically in the
50-200 Watts per square foot range. Data center heat fluxes,
especially in localized regions can far exceed these values, and
can be as high as 500 Watts per square foot, when current high
performance, high power server racks (20-35 kW/rack) are
brick-walled to form high density clusters. The efficient cooling
of such computer systems is one focus of the present invention.
However, the concepts disclosed herein are equally applicable to
other computing environments, including personal computers and
laptops.
[0036] Disclosed herein are various heat exchanger embodiments
referred to as "angled fin heat exchangers" and "heat exchangers
with angled secondary fins extending from primary fins". Angled fin
heat exchangers are described below with reference to FIGS. 4A-10,
while heat exchangers with angled secondary fins extending from
primary fins are described below with reference to FIGS. 11-16.
Before discussing these novel heat exchanger embodiments, however,
various drawbacks to traditional heat exchangers placed at oblique
angles are described with reference to FIGS. 1A-3.
[0037] FIGS. 1A-1C illustrate a core heat exchange mechanism of a
heat exchanger such as the widely known compact copper/brass heat
exchanger currently used in the computer industry. It should be
noted that in the figures, the manifolds at the ends of the brass
tubes are not shown.
[0038] FIG. 1B is a cross-sectional front view illustration of a
folded copper fin 105. Flat brass tubes 170 are also
illustrated.
[0039] FIG. 1A is a cross-sectional illustration of the heat
exchanger of FIG. 1B, cut across lines 1A-1A. The basic air side
flow structure of FIG. 1A is significant for understanding aspects
of the present invention. For ease of understanding, a perspective
view of the heat exchanger is also provided at FIG. 1C, wherein
liquid flows through coolant conduits or tubes 170 and air flows
through the fins 105 as illustrated and referenced respectively by
arrows 195 and 190. As understood from these figures, air is
essentially channeled orthogonal to the frontal area or leading
edge of the heat exchanger. Consequently, for a heat exchanger
disposed at an angle relative to airflow direction, the air must
turn going into and out of the fin structure, potentially resulting
in a significant increase in pressure drop. In fact, pressure drop
can be as much as ten times higher at the same volume of airflow
through a heat exchanger in an airflow orientation normal to the
front face of the heat exchanger.
[0040] FIG. 2 illustrates disposition of a heat exchanger 250 at an
oblique angle .theta. with respect to a horizontal axis 280 of an
airway conduit. Air flows through fins 205 of heat exchanger 250 as
depicted by arrow 290. Forcing air to enter through the heat
exchanger at an oblique angle to the upstream airflow results in
substantial loss in air pressure. This pressure loss adversely
affects the system airflow rate, thereby impairing dissipation of
heat from the system.
[0041] FIG. 3 is a plan view illustration of a closed, horizontal
airflow rack level heat removal system 300, used to house one or
more computers or computing environments (such as servers). It
should be noted again that while the workings of heat exchangers in
accordance with aspects of the present invention are described
below in conjunction with a computing environment such as the one
illustrated in FIG. 3, this is only done for ease of understanding.
The workings of the present invention can be equally applicable to
any heat exchanger used in any other computing environment or
electrical device, or in other similar environments and its use is
not particularly limited to computers and computing environments
per se.
[0042] As shown in FIG. 3, a frame assembly 310 includes a front
320, housing a front cover 322; and a back 330, housing a back
cover 332. In the embodiment illustrated, 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. As noted above, while FIG. 3 illustrates a side
mounted sub-frame arrangement, the heat exchanger in question could
reside in any other angled arrangement as discussed herein and
still benefit from the workings of the present invention.
[0043] In FIG. 3, the heat generating electronics and other such
related components (not individually shown), are disposed in the
electronics frame 360. In the embodiment illustrated, the
electronics and the associated frame 360 are disposed adjacent to
the side mounted sub-frame 340 housing the heat exchanger 350 so as
to directly and immediately benefit from the ensuing cooling
effects. This is because the placement of the heat exchanger 350
and the other components allows for a closed loop airflow with the
direction of the generalized airflow path being illustrated in FIG.
3, as referenced by use of arrows and reference numeral 390. More
particularly, heat exchanger 350 enables heat to be transferred
from the hot exhaust air exiting the servers within electronics
frame 360 to chilled water passing through the heat exchanger from
a chilled liquid source (not shown) disposed, for example, outside
system 300. By angling the heat exchanger as shown in FIG. 3,
airflow through the heat exchanger necessarily makes two turns when
passing through the fin core; that is, a first turn as the airflow
enters the fin core, and a second turn as the airflow exits the fin
core.
[0044] The angled heat exchanger design provides for cooling
rack-mounted modular electronic units, and addresses some of the
defects existing in the prior art by combining an 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 that the heat exchanger 350 be angled as
shown in FIG. 3.
[0045] As an alternate electronics system implementation to that
illustrated in FIG. 3, a closed loop liquid system (not shown)
including cold plates, direct liquid impingement modules, or other
high performance liquid cooling structures on the microprocessors
can be employed, along with an approximately five (5) inch
side-attached drawer containing an air-moving device, liquid pump,
and heat exchanger. The heat exchanger in this configuration is
also typically angled relative to the airflow pathway through the
side-attached drawer in a manner analogous to that depicted in FIG.
3, and the same high-flow resistance occurs in this geometry as
well. Thus, disclosed herein are various heat exchanger designs
which alleviate the high pressure drop associated with these angled
flow configurations.
[0046] FIGS. 4A & 4B are 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. 4B illustrates a similar sectional view as provided by prior
art FIG. 2 previously discussed. Direction of airflow is shown by
arrow 490. The heat exchanger, referenced here as 450, is tilted at
an angle .theta. with respect to the horizontal axis and the
direction of airflow. In the embodiment shown specifically in FIG.
4A, however, the fins 405 (e.g., folded fins) form an oblique angle
.phi., with respect to the normal of the frontal area of the heat
exchanger.
[0047] As illustrated in FIG. 4B, by making the value of angle
.phi. equal to 90-.theta., the airflow channels formed by the
angled folded fins 405 become parallel to the direction of airflow
when the heat exchanger is angled by .theta.. It is noted that air
no longer turns as was the case in FIGS. 1 & 2, but the channel
flow length is significantly longer than that of the normal channel
configuration. Since the pressure drop within the channel itself is
proportional to the channel flow length, the pressure is also
significantly higher. For example, for a heat exchanger angle
.theta. 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.
[0048] 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 .psi.. Angle .psi. is defined as
the angle between the upstream airflow direction and the folded
fins/channels and is related to the heat exchanger angle .theta.
and fin angle .phi. as shown in FIGS. 5A & 5B. (Direction of
airflow provided by arrows and associated reference numerals
590).
[0049] As illustrated, FIG. 5A is a depiction of the orientation of
angle .phi., while FIG. 5B illustrates the relationship between
angle .psi. with respect to angle .theta., angle .phi. and the
horizontal axis. FIG. 5B, especially, illustrates a sectional cut
schematic representation of the heat exchanger 405 with angled
folded fins 405 having an optimum fin angle of attack .psi. which
is defined as 90-(.theta.+.phi.).
[0050] For example, an attack angle of zero degrees represents the
"no air turning" configuration shown and discussed above in
conjunction with the embodiment of FIGS. 4A & 4B. On the other
hand, an attack angle of (90-.theta.) represents the conventional
heat exchanger configuration of .phi. being equal to zero as was
discussed in conjunction with embodiments of FIGS. 1 & 2.
[0051] As the angle of attack increases from a value of zero, 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.
[0052] FIG. 6 is a graphical depiction of the computational fluid
dynamics (CFD) calculations performed to establish the relationship
between angled fin air side pressure drop and various attack
angles. As illustrated, the air pressure drop that was calculated
in inches of water is represented by the vertical axis, while the
value of the attack angle is plotted on the horizontal axis.
[0053] Note that angle .theta., 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 0.058
inches of water and this value actually decreases to less than 0.04
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 the heat
exchanger and its location in the frame (i.e., side car, or more
generally, airflow conduit).
[0054] FIGS. 7A-8B depict an alternate embodiment of an angled fin
heat exchanger, in accordance with aspects of the present
invention, having a tubular structure and fins provided at an
oblique angle with respect to its frontal area. FIGS. 7A & 7B
depict cross sectional views of the structure, which are disposed
in different orientations.
[0055] FIG. 7A is a cross-sectional illustration wherein a section
of the active core region with the fins at an angle .phi. (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. In one implementation, the tube 710 is
disposed to run horizontally with respect to gravity. FIG. 7B shows
the same heat exchanger section positioned at an angle .theta.
(722) with respect to the direction of airflow 760.
[0056] FIGS. 8A & 8B illustrate other details about the fins,
particularly as discussed with reference to the embodiment of FIGS.
7A & 7B. FIG. 8A provides a top down illustrations of
unmodified fins 820, while FIG. 8B provides a similar illustration
with respect to modified fins 825, as will be discussed in more
detail below. Both the modified and unmodified fins 825 and 820 can
be disposed on a structure, similar to the tubular structure 710 of
FIGS. 7A & 7B.
[0057] FIG. 8A illustrates an unmodified fin(s) 820 with a
staggered array of holes 830 punched out to fit over the associated
structure (which in this embodiment can be a tube bank) according
to the embodiment illustrated in FIGS. 7A & 7B. As illustrated
in the figure, "D" (referenced as 851) is a tube hole diameter. Px
(referenced as 852) is the tube hole pitch in the x-direction,
which in this case is further defined by the direction of the heat
exchanger. Similarly, Py (853) is the tube hole pitch in the
y-direction (i.e., in the direction of heat exchanger depth or
thickness). Finally "t" is the fin depth 854, which can be equal to
the heat exchanger depth or thickness in the illustrated embodiment
of FIG. 8A.
[0058] FIG. 8B is a top down illustration of one embodiment of the
present invention showing fin modifications. The fin modification,
as illustrated in FIG. 8B, is designed to ensure that the fins
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 (referenced by numerals 870)
is the minor diameter of the tube hole in an angled fin. Dy
(referenced as 871) is a major diameter of the tube hole in an
angled fin. Px_af 872 and Py_af 873 are respectively the tube hole
pitch in x- and y-directions for the angled fin. Finally t_af 874
is the angled fin depth. If "s" is thought of as the spacing
between fins along tube axis in an unmodified fin configuration
(FIG. 8A), then the following set of equations relate the modified
fin version to the unmodified version.
Dx = D ##EQU00001## Dy = D sin ( .theta. + .psi. ) ##EQU00001.2##
Px_af = Px ##EQU00001.3## Py_af = Py sin ( .theta. + .psi. )
##EQU00001.4## t_af = t sin ( .theta. + .psi. ) ##EQU00001.5## s_af
= s sin ( .theta. + .psi. ) ##EQU00001.6##
[0059] The problem of optimizing the value of different angles
including the angle of attack has now been explored, and attention
is 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 & 10.
[0060] 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.
[0061] FIGS. 10A & 10B, by contrast, depict a second embodiment
for manufacturing of the angled fins. FIG. 10A provides for a
schematic illustration of a manufacturing fold fin with oblique
angled channels by stamping with oblique angled gear tooth gears
1000. In other words, the folded fins 1005 are stamped using gears
1000 with teeth, shown at 1010 in FIG. 10B, at an oblique angle to
the gear axis.
[0062] FIGS. 10A & 10B 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.
[0063] FIGS. 11 & 11A depict one embodiment of a heat exchanger
with angled secondary fins extending from primary fins, in
accordance with an aspect of the present invention. This heat
exchanger, generally denoted 1100, includes a plurality of primary
fins 1110 oriented parallel to each other and separated by
coolant-carrying conduits 1115 as shown in FIG. 11. A first
plurality of secondary fins 1120a extend from a leading edge 1111
of the plurality of primary fins 1110 and a second plurality of
secondary fins 1120b extend from a trailing edge 1112 of the
plurality of primary fins 1110. These pluralities of secondary
fins, 1120a, 1120b, each extend from the plurality of primary fins
at an angle other than 0.degree. to facilitate airflow through the
heat exchanger.
[0064] In the embodiment illustrated, air flows in a direction
1130a at an air inlet side of the heat exchanger and in a direction
1130b at an air outlet side of the heat exchanger, which in this
example is the same direction as the direction of airflow on the
air inlet side. Thus, the secondary fins on the leading edge of the
primary fins are angled to extend in the direction of airflow, and
the secondary fins at the trailing edge of the primary fins are
also angled to extend in the direction of airflow. The secondary
fins 1120a at the leading edge of the primary fins receive and
direct the airflow 1130a into the air passageways or channels 1140
defined by the primary fins 1110, which in the embodiment
illustrated are defined by a folded fin construction. After flowing
across the primary fins, the airflow is then redirected by the
secondary fins 1120b at the trailing edge of the primary fins to
align to the direction of airflow 1130b on the outlet side of the
heat exchanger.
[0065] As shown in the figures, secondary fins 1120a, 1120b
function as airflow direction fins or vanes which are integrally
formed with the plurality of primary fins 1110. Thus, in addition
to guiding the airflow into and out of the fin core, the secondary
fins also provide greater heat transfer surface area compared with
the primary fins alone. In the exemplary embodiment, each primary
fin of the plurality of primary fins has a first, similar heat
transfer surface area, and each secondary fin of the plurality of
secondary fins has a second, similar heat transfer surface area,
wherein the first surface area is greater than the second surface
area. Although the height of each secondary fin is (in one example)
the same or similar to the height of each primary fin, the distance
that each secondary fin extends from the primary fin can vary
between implementations, for example, dependent upon size
restrictions imposed by the airway conduit within which the heat
exchanger is to be placed. As best shown in FIG. 11A, in one
embodiment, secondary fins 1120a extend at the leading edge of
every other primary fin, and secondary fins 1120b extend at the
trailing edge of every other primary fin 1110. In alternate
implementations, the secondary fins could extend, for example, from
every third, fourth, fifth, etc., primary fin, provided that a
sufficient number of secondary fins extend from the primary fins to
facilitate redirection of the airflow through the heat exchanger,
and thereby reduce the pressure drop across the heat exchanger for
a given implementation.
[0066] Further, although shown with a first plurality of secondary
fins 1120a and a second plurality of secondary fins 1120b,
dependent on the implementation, secondary fins may be employed
only on the leading edge 1111 or the trailing edge 1112 of the
plurality of primary fins 1110. Further, the angle that the
secondary fins form on the leading edge and the angle that the
secondary fins form on the trailing edge may be different and
unrelated depending, for example, on the configuration of the
airway passage within which the heat exchanger is to be placed.
[0067] FIG. 12 depicts an alternate embodiment of a heat exchanger
with angled secondary fins extending from primary fins, in
accordance with an aspect of the present invention. This heat
exchanger, generally denoted 1200, again includes a plurality of
primary fins 1210 oriented parallel, and a first plurality of
secondary fins 1220a extending from a leading edge 1211 thereof and
a second plurality of secondary fins 1220b extending from a
trailing edge 1212 thereof. A coolant conduit or tube 1215 extends
through the plurality of primary fins 1210 and is in physical
contact therewith as shown for the transfer of heat between air
passing through the heat exchanger and water flowing through the
conduit. In the example illustrated, the first plurality and second
plurality of secondary fins are each shown extending from every
other primary fin on the leading and trailing edges, respectively,
of the primary fins. The angle at which the first plurality of
secondary fins 1220a extend is aligned to a direction of airflow
1230a on an air inlet side of the heat exchanger, while the angle
at which the second plurality of secondary fins 1220b on the
trailing edge 1212 extend aligned to a direction of airflow on an
air outlet side of the heat exchanger 1230b.
[0068] FIGS. 13 & 13A depict a heat exchanger with angled
secondary fins extending from primary fins analogous to that
depicted in FIGS. 11 & 11A, only with the secondary fins (1120a
or 1120b) extending at the leading edge 1111 and at the trailing
edge 1112 from each primary fin 1110. Similarly, FIG. 14 is
analogous to the heat exchanger with angled secondary fins
extending from primary fins of FIG. 12, only with the secondary
fins 1220a, 1220b extending from each primary fin 1210 at the
leading edge 1211 and the trailing edge 1212, respectively.
[0069] FIG. 15A is a cross-sectional plan view representation of a
heat exchanger having only primary fins and illustrating a
direction of airflow into and from the heat exchanger at an angle
to the primary fins. Thus, in FIG. 15A, the air undergoes a turn
through angle .alpha. as it enters the heat exchanger fins, and
then turns again at angle .alpha. as the air leaves the primary
fins. Thus, the total turning angle of the air is 2a.
[0070] FIGS. 15B & 15C illustrate heat exchangers with angled
secondary fins extending from primary fins, in accordance with
aspects of the present invention. In FIG. 15B, the secondary fins
extend from every other primary fin, while in FIG. 15C, the
secondary fins extend from every primary fin. The integral
secondary fins (and primary fins) are formed at an angle .beta. to
the primary fin at the trailing edge of the primary fins, and at an
angle 180.degree.+.beta. to the primary fins at the leading edge of
the primary fins. Thus, in this case, the airflow turns by a total
of 2 (.alpha.-.beta.) as it enters and exits the heat exchanger.
The value of .beta. is greater than zero, and can be as high as
.alpha., thus allowing 2 (.alpha.-.beta.) to be in the range of
less than 2.alpha. to zero. Therefore, employing a heat exchanger
such as illustrated in FIGS. 15B & 15C reduces the turning
angle for the airflow in configurations where the heat exchanger is
placed at an angle to the airflow, thus reducing the pressure drop
associated with turning at the inlet and outlet of the heat
exchanger, while also providing additional fin surface area for
heat transfer. As noted above, angle .beta. can be the same or
different at the leading and trailing edges of the primary
fins.
[0071] A thermal and hydraulic analysis was carried out for a
section of fins representative of a heat exchanger core. The fins
were oriented at an angle to the airflow so that the airflow was
forced to turn upon entering and leaving the heat exchanger. Three
cases were considered. A conventional heat exchanger such as
depicted in FIGS. 1A-1C was analyzed for a baseline (Case 1). In a
second case (Case 2), a heat exchanger with angled secondary fins
extending from every primary fin was analyzed, while in a third
case (Case 3), a heat exchanger with angled secondary fins
extending from every other primary fin was analyzed. The fins were
assumed to be 5 mm tall, and made of copper, while the flow
velocity was assumed to be 3 m/s, and the temperature difference
between the inlet air and the base of the fins was 25.degree. C.
FIG. 16 displays the results of the analysis, showing that the heat
exchangers of Cases 2 & 3 yield a 22-44% increase in heat
transfer, a 30-34% reduction in pumping power (via a pressure drop
decrease), and an overall coefficient of performance (COP), defined
as the ratio of heat transfer rate to pumping power consumed for
cooling, superior to the conventional state of the art baseline
Case 1 by a factor of approximately 2.0.
[0072] Although preferred embodiments have been depicted and
described in detail herein, it will be apparent to those skilled in
the relevant art that various modifications, additions,
substitutions and the like can be made without departing from the
spirit of the invention, and that these are therefore considered to
be within the scope of the invention as defined in the following
claims.
* * * * *