U.S. patent application number 12/571265 was filed with the patent office on 2011-03-31 for fabrication of high surface area, high aspect ratio mini-channels and their application in liquid cooling systems.
Invention is credited to Hae-won Choi, Madhav Datta, Brandon Leong, Mark McMaster, Douglas E. Werner, Peng Zhou.
Application Number | 20110073292 12/571265 |
Document ID | / |
Family ID | 43778998 |
Filed Date | 2011-03-31 |
United States Patent
Application |
20110073292 |
Kind Code |
A1 |
Datta; Madhav ; et
al. |
March 31, 2011 |
FABRICATION OF HIGH SURFACE AREA, HIGH ASPECT RATIO MINI-CHANNELS
AND THEIR APPLICATION IN LIQUID COOLING SYSTEMS
Abstract
The present invention provides methods and apparatuses which
achieve high heat transfer in a fluid cooling system, and which do
so with a small pressure drop across the system. The present
invention teaches the use of wall features on the fins of a heat
exchanger to cool fluid in a fluid cooling system. The present
invention also discloses high aspect ratio, high surface area
structures applicable in micro-heat exchangers for fluid cooling
systems and cost effective methods for manufacturing the same.
Inventors: |
Datta; Madhav; (Milpitas,
CA) ; Zhou; Peng; (El Cerrito, CA) ; Choi;
Hae-won; (Albany, CA) ; Leong; Brandon; (Santa
Clara, CA) ; McMaster; Mark; (Menlo Park, CA)
; Werner; Douglas E.; (Santa Clara, CA) |
Family ID: |
43778998 |
Appl. No.: |
12/571265 |
Filed: |
September 30, 2009 |
Current U.S.
Class: |
165/157 ;
165/159; 29/890.03 |
Current CPC
Class: |
F28F 1/40 20130101; H01L
2924/0002 20130101; Y10T 29/4935 20150115; H01L 23/473 20130101;
F28F 2275/04 20130101; H01L 2924/0002 20130101; F28F 3/02 20130101;
F28F 2260/02 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
165/157 ;
165/159; 29/890.03 |
International
Class: |
F28F 9/00 20060101
F28F009/00; F28F 9/24 20060101 F28F009/24; B21D 53/02 20060101
B21D053/02 |
Claims
1. A stacked fin heat exchanger comprising: a. a cannister
comprising: i. a bottom section; ii. a lid; iii. at least one wall;
iv. an inlet conduit for allowing fluid into the cannister; and v.
an outlet conduit for allowing fluid out of the cannister, wherein
the bottom section, the lid and the at least one wall
substantially, hermetically seal the cannister from fluid entering
or exiting the cannister, except for the inlet conduit or the
outlet conduit; and b. a plurality of fins, each individual fin
with at least one wall feature, wherein the plurality of fins are
coupled to the bottom section of the cannister such that the
individual fins are stacked substantially parallel to one another,
forming channels having substantially vertical walls, wherein the
wall features enhance the surface area of the channels, wherein the
channels have a high surface area to volume aspect ratio, and
wherein fluid input into the cannister through the inlet conduit
flows through the channels and outputs the cannister through the
outlet conduit.
2. The stacked fin heat exchanger according to claim 1, wherein the
plurality of fins are coupled to the bottom section through
brazing.
3. The stacked fin heat exchanger according to claim 1, wherein the
plurality of fins are coupled to the bottom section through
soldering or diffusion bonding.
4. The stacked fin heat exchanger according to claim 2, wherein the
plurality of fins are coupled to the bottom section through
brazing.
5. The stacked fin heat exchanger according to claim 4, further
comprising: a. a brazing layer between the bottom section and the
plurality of fins, wherein the brazing layer is configured to bond
the plurality of fins to the bottom section when subjected to
heat.
6. The stacked fin heat exchanger according to claim 5, wherein the
brazing layer is an alloy comprising a portion of copper and a
portion of silver.
7. The stacked fin heat exchanger according to claim 5, wherein the
brazing layer is an alloy comprising a portion of copper, a portion
of nickel, a portion of tin, and a portion of phosphorous.
8. The stacked fin heat exchanger according to claim 4, further
comprising: a. a brazing layer between the at least one wall and
the lid, wherein the brazing layer is configured to bond the lid to
the at least one wall when subjected to heat.
9. The stacked fin heat exchanger according to claim 8, wherein the
brazing layer is an alloy comprising a portion of copper and a
portion of silver.
10. The stacked fin heat exchanger according to claim 8, wherein
the brazing layer is an alloy comprising a portion of copper, a
portion of nickel, a portion of tin, and a portion of
phosphorous.
11. The stacked fin heat exchanger according to claim 1, wherein
the bottom section is comprised of thermally conductive
material.
12. The stacked fin heat exchanger according to claim 1, wherein
the bottom section is comprised of copper.
13. The stacked fin heat exchanger according to claim 1, wherein
the bottom section is comprised of aluminum.
14. The stacked fin heat exchanger according to claim 1, wherein
the plurality of fins are configured to be self-aligning, and
wherein the plurality of fins are configured to be individually
stacked within the cannister while remaining upright and
substantially parallel to each other.
15. The stacked fin heat exchanger according to claim 14, wherein
the plurality of fins have an I-beam shape, wherein the individual
fins comprise a beam section with flanges on a top and a bottom of
the beam section, wherein the flanges extend substantially
perpendicular to the beam section, wherein the flanges of
adjacently stacked individual fins contact each other thereby
causing the plurality of fins to self-align.
16. The stacked fin heat exchanger according to claim 14, wherein
the plurality of fins have a T-beam shape, wherein the individual
fins comprise a beam section with flanges on a top of a beam
section and a footer on each bottom corner of the beam section,
wherein the flanges and footers extend substantially perpendicular
to and equidistantly from the beam section, wherein the flanges of
adjacently stacked individual fins contact each other and the
footers of adjacently stacked individual fins contact each other,
thereby causing the plurality of fins to self-align.
17. The stacked fin heat exchanger according to claim 14, wherein
each of the individual fins of the plurality of fins comprise a
beam section with footers on each corner of the beam section,
wherein the footers extend substantially perpendicular to and
equidistantly from the beam section, wherein the footers of
adjacently stacked individual fins contact each other, thereby
causing the plurality of fins to self-align.
18. The stacked fin heat exchanger according to claim 1, wherein
the wall features are configured to affect the quality of fluid
flow between the channels.
19. The stacked fin heat exchanger according to claim 1, wherein
the at least one wall feature extends the entire length of the
individual fin.
20. The stacked fin heat exchanger according to claim 1, wherein
the at least one wall feature extends a partial length of the
individual fin.
21. The stacked fin heat exchanger according to claim 1, wherein
the individual fins have wall features substantially equally spaced
across the entire individual fin.
22. The stacked fin heat exchanger according to claim 1, wherein
the wall features have a diagonal configuration.
23. The stacked fin heat exchanger according to claim 1, wherein
the wall features have a sinusoidal configuration.
24. The stacked fin heat exchanger according to claim 1, wherein
the wall features have a zig-zag configuration.
25. The stacked fin heat exchanger according to claim 1, wherein
the wall features have a cross hatch pattern configuration.
26. The stacked fin heat exchanger according to claim 1, wherein
the wall features have a straight line configuration.
27. The stacked fin heat exchanger according to claim 1, wherein at
least one pair of adjacent individual fins from among the plurality
of fins are complimentary fins, the complimentary fins comprising:
a. a first fin with a first complimentary wall feature; and b. a
second fin with a second complimentary wall feature, wherein the
complimentary fins are configured such that the first complimentary
wall feature face the second complimentary wall feature when the
plurality of fins are coupled to the bottom section of the
cannister.
28. The stacked fin heat exchanger according to claim 27, wherein
at the first complimentary wall feature has a increasing gradient
diagonal configuration and the second complimentary wall feature
has a decreasing gradient diagonal configuration.
29. The stacked fin heat exchanger according to claim 1, wherein
the wall features are holes extending completely through the
individual fins.
30. The stacked fin heat exchanger according to claim 1, wherein
the individual fins have more than one wall feature, and wherein at
least one wall feature has a different shape than another wall
feature.
31. The stacked fin heat exchanger according to claim 1, wherein
the individual fins have at least one wall feature comprising
protrusions extending out of the individual fins.
32. The stacked fin heat exchanger according to claim 31, wherein
the protrusions are cylindrical pins.
33. The stacked fin heat exchanger according to claim 1, wherein
the individual fins have at least one wall feature comprising
protrusions extending out of the individual fins and at least one
wall feature comprising apertures cut into the individual fin.
34. The stacked fin heat exchanger according to claim 33, wherein
the apertures are holes extending completely through the individual
fins and wherein the protrusions are cylindrical pins.
35. The stacked fin heat exchanger according to claim 1, wherein a
filler material is positioned within the channels formed by the
plurality of fins.
36. The stacked fin heat exchanger according to claim 35, wherein
the filler material is a mesh material.
37. The stacked fin heat exchanger according to claim 36, wherein
the mesh material is comprised of a thermally conductive
material.
38. The stacked fin heat exchanger according to claim 35, wherein
the filler material is a open-cell metal foam material.
39. The stacked fin heat exchanger according to claim 1, wherein
the cannister further comprises a manifold layer coupled to the top
of the substantially vertical walls, wherein the manifold layer
comprises a substantially hermetic cavity with at least one
manifold aperture, wherein the inlet conduit is positioned on the
manifold layer such that fluid enters the manifold layer via the
inlet conduit and outputs from the manifold layer into the channels
through the at least one manifold aperture.
40. The stacked fin heat exchanger according to claim 39, wherein
the manifold layer further comprises a fluid flow divider
positioned in relation to the inlet conduit such that the fluid
flow divider at least partially divides fluid entering the
interface layer.
41. A method of manufacturing a heat exchanger with a mini-channel
fluid interface comprising the steps of: a. manufacturing an
interface housing cannister having a bottom section, a lid, at
least one wall section, an inlet conduit and an outlet conduit; b.
manufacturing a plurality of fins with wall features; c. coupling
the plurality of fins with the interface housing cannister, forming
channels having substantially vertical walls, wherein the wall
features enhance the surface area of the channels and wherein the
plurality of fins are molecularly bonded to the bottom section; and
d. sealing the interface housing cannister with the lid.
42. The method of manufacturing a heat exchanger with a
mini-channel fluid interface according to claim 41, wherein the
step of manufacturing a plurality of fins further comprises
manufacturing individual fins with a wall feature comprising: a.
cleaning a metal sheet to remove surface contaminants; b. applying
photoresist on both sides of the metal sheet; c. exposing and
developing the photoresist to form a patterned photoresist on the
metal sheet; d. exposing the photoresist patterned metal sheet to
an etchant to remove material from an exposed portion of the metal
sheet, thereby forming an etched metal sheet having a series of
tabbed fins with pattern, each patterned fin having one or more
tabs connected to an adjacent patterned fin on the etched metal
sheet; e. rinsing and drying the etched metal sheet; and f.
detaching individual patterned fins from the etched metal sheet by
breaking the tabs.
43. The method of manufacturing a heat exchanger with a
mini-channel fluid interface according to claim 41, wherein the
step of manufacturing individual fins further comprises etching at
least one self-aligning feature on the individual fins, forming a
plurality of self-aligning fins.
44. The method of manufacturing a heat exchanger with a
mini-channel fluid interface according to claim 43, further
comprising the step of stacking the plurality of self-aligning fins
along a width of the bottom surface of the interface housing
cannister such that the self-aligning features cause the plurality
of self-aligning fins to remain substantially parallel and
upright.
45. The method of manufacturing a heat exchanger with a
mini-channel fluid interface according to claim 41, wherein the
step of sealing the interface housing cannister further comprises:
a. placing brazing material between the plurality of fins and the
interface housing cannister, forming an assembled cannister bottom;
and b. heating the assembled cannister bottom with sufficient heat
to thermally couple the plurality of fins and the interface
housing.
46. The method of manufacturing a heat exchanger with a
mini-channel fluid interface according to claim 41, further
comprising placing a brazing material on a top of the at least one
wall of the interface housing cannister before sealing the
interface housing cannister with the lid.
47. The method of manufacturing a heat exchanger with a
mini-channel fluid interface according to claim 41, further
comprising: a. coupling a manifold layer to the heat exchanger
between the interface layer and the lid, wherein the inlet conduit
is located in the manifold layer, and wherein the manifold layer
includes an aperture for allowing fluid to flow from the inlet
conduit, through the manifold layer and into the interface
layer.
48. The method of manufacturing a heat exchanger with a
mini-channel fluid interface according to claim 41, further
comprising manufacturing a lid with an integrally formed manifold
layer integrated within the lid.
49. The method of manufacturing a heat exchanger with a
mini-channel fluid interface according to claim 41, wherein the
step of manufacturing a plurality of fins further comprises
manufacturing individual fins with a wall feature using a
mechanical method that includes cold rolling, laser cutting,
stamping, or wet etching.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the field of heat exchangers. More
particularly, this invention relates to a method of fabricating
heat exchangers having high surface area, high aspect ratio
minichannels and/or high aspect ratio microchannels, and their
application in fluid cooling systems.
BACKGROUND OF THE INVENTION
[0002] Effective heat transfer in a fluid cooling system has a
flowing fluid in contact with as much surface area as possible of
the material that is thermally coupled to extract heat from the
device to be cooled. Fabrication of a reliable and efficient High
Surface to Volume Ratio Material (HSVRM) structure is therefore
extremely critical for developing an effective heat exchanger.
[0003] The use of silicon microchannels is one heat collector
structure in fluid cooling systems previously proposed by the
assignee of the present invention. For example, see U.S. Pat. No.
7,017,654, which issued on Mar. 28, 2006 and entitled "APPARATUS
AND METHOD OF FORMING CHANNELS IN A HEAT-EXCHANGING DEVICE", which
is hereby incorporated in its entirety by reference.
[0004] High aspect ratio channels are fabricated by anisotropic
etching of silicon, which has found widespread use in
micromachining and MEMS. However, silicon has a low thermal
conductivity relative to many other materials, and especially
relative to true metals.
[0005] Methods for fabrication and designs for micro-heat
exchangers from higher conductivity materials exist in the prior
art, but either use expensive fabrication technologies or involve
complicated structures without specifying economically feasible
fabrication methods.
SUMMARY OF THE INVENTION
[0006] The present invention provides methods and apparatuses which
achieve high heat transfer in a fluid cooling system, and which do
so with a relatively small pressure drop across the system.
[0007] The present invention discloses high aspect ratio, high
surface area structures applicable in micro-heat-exchangers for
fluid cooling systems and cost effective methods for manufacturing
the same.
[0008] In some embodiments of the present invention, fins used to
construct mini-channels are fabricated with self-aligning features.
The self-aligning features allow the fins to be stacked within a
heat exchanger cannister without bonding each fin, such that the
cannister only needs to be heated once to bond the entire heat
exchanger.
[0009] In some embodiments of the present invention, methods of
fabricating fins are utilized which are especially commercially
practical. In some embodiments, fins are fabricated with wall
features to mix fluid passing through a mini-channel. In other
embodiments, fins are fabricated with one or more passages,
conduits or vents passing therethrough to reduce pressure drop in a
heat exchanger. In yet other embodiments, fins are fabricated
having both wall features and passages therethrough.
[0010] In some embodiments of the present invention, methods are
employed to reduce pressure drop in a heat exchanger. In some
embodiments, a unique geometry is provided to divert fluid flow
paths in order to reduce pressure drop. In other embodiments, a
manifold layer is used to divert fluid flow paths in order to
minimize pressure drop.
[0011] It is an object of the present invention to provide a heat
exchanger which effectively transfers heat from the heat exchanger
to a fluid, which subsequently cools the fluid and which reuses the
cool fluid in a closed loop system. It is also an object of the
present invention to fabricate a commercially feasible heat
exchanger capable of doing the same.
[0012] In some aspects of the present invention, the coupling of
the microchannel fins to the spacers is provided by the use of a
brazing material. The brazing material is placed in contact with
the microchannel fins and the structure and heated to above the
melting temperature of the brazing material. In another aspect of
the present invention, the step of coupling the microchannel fins
to the structure is provided by thermal fusing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1A illustrates a schematic view of a fluid cooling
system utilizing the heat exchanger with mini-channels.
[0014] FIG. 1B. illustrates a schematic isometric view of a
partially assembled heat exchanger according to some embodiments of
the present invention.
[0015] FIG. 2A illustrates a schematic view of a high aspect ratio
plate with a mask for etching according to some embodiments of the
present invention.
[0016] FIG. 2B illustrates a schematic view of an I-Beam fin
fabricated through etching according to some embodiments of the
present invention.
[0017] FIG. 2C illustrates a schematic view of a stack of I-Beam
fins to be used in a heat-exchanger according to some embodiments
of the present invention.
[0018] FIG. 2D illustrates a schematic view of a T-Beam fin
fabricated through etching according to some embodiments of the
present invention.
[0019] FIG. 2E illustrates a schematic view of a stack of T-Beam
fins to be used in a heat-exchanger according to some embodiments
of the present invention.
[0020] FIG. 3A is an exploded schematic view illustrating the parts
which comprise the heat exchanger according to some embodiments of
the present invention.
[0021] FIG. 3B is a partially exploded schematic view illustrating
a partially assembled cannister and lid according to some
embodiments of the present invention.
[0022] FIG. 3C illustrates a schematic view of a fully assembled
heat exchanger positioned above a heat-producing surface according
to some embodiments of the present invention.
[0023] FIG. 4 illustrates an exemplary process for fabricating
patterned fins by photochemical etching.
[0024] FIG. 5A illustrates a side view of a fin treated with a mask
in preparation for the step of forming wall features on the
fin.
[0025] FIG. 5B illustrates a close-up side view of the surface of a
fin treated with a fluid etchant, forming wall features on the
fin.
[0026] FIG. 5C illustrates a side view of a fin with wall features
formed from etching.
[0027] FIG. 6A illustrates an isometric view of an individual fin
with rectangular wall features.
[0028] FIG. 6B illustrates an isometric view of an individual fin
with triangular wall features.
[0029] FIG. 6C illustrates an isometric view of an individual fin
with rounded wall features.
[0030] FIG. 7A illustrates a schematic view of an example of a fin
having angled wall features according to some embodiments of the
present invention.
[0031] FIG. 7B illustrates a schematic view of an example of a fin
having angled wall features and straight wall features according to
some embodiments of the present invention.
[0032] FIG. 7C illustrates a schematic view of an example of a fin
having angled wall features and an empty center according to some
embodiments of the present invention.
[0033] FIG. 7D illustrates a schematic view of an example of a fin
having zig-zag wall features according to some embodiments of the
present invention.
[0034] FIG. 7E illustrates a schematic view of an example of a fin
having sinusoidal wall features according to some embodiments of
the present invention.
[0035] FIG. 7F illustrates a schematic view of an example of a fin
having crosshatch wall features according to some embodiments of
the present invention.
[0036] FIG. 7G illustrates a schematic view of an example of
adjacent complimentary fins having complimentary wall features
according to some embodiments of the present invention.
[0037] FIG. 7H illustrates a schematic view of an example of
adjacent complimentary fins having complimentary wall features
according to some embodiments of the present invention.
[0038] FIG. 8A illustrates a schematic view of an example of a fin
having of pin wall features according to some embodiments of the
present invention.
[0039] FIG. 8B is a schematic side view of a heat exchanger with
fins having pin wall features forming a structured pseudo foam
according to some embodiments of the present invention.
[0040] FIG. 9A illustrates a schematic side view of a high aspect
ratio, high surface area heat exchanger using mini-channels and a
metal mesh between the mini-channels according to some embodiments
of the present invention.
[0041] FIG. 9B illustrates a schematic side view of a high surface
area heat exchanger using a stack of metal mesh layers according to
some embodiments of the present invention.
[0042] FIG. 9C illustrates a schematic side view of a high surface
area heat exchanger using an open-cell metal foam insert according
to some embodiments of the present invention.
[0043] FIG. 10A illustrates a schematic side view of a fin having
pin wall features and vents passing therethrough.
[0044] FIG. 10B illustrates a schematic side view of a stack of
fins having pin wall features and vents passing therethrough.
[0045] FIG. 10C illustrates a schematic isometric view of a heat
exchanger with a stack of fins having pin wall features and vents
passing therethrough.
[0046] FIG. 11A illustrates a schematic isometric view of fins
having conduits and a fin without a conduit used in heat exchangers
according to some embodiments of the present invention.
[0047] FIG. 11B illustrates a schematic isometric view of a heat
exchanger with fins having apertures for reducing the path length
of the fluid.
[0048] FIG. 12 illustrates a schematic top view of a heat exchanger
with a spine divider for reducing the path length of fluid.
[0049] FIG. 13 illustrates a schematic top view of a heat exchanger
with a spine divider and four quadrants for cooling multi-core
integrated chips.
[0050] FIG. 14 illustrates a schematic isometric view of a heat
exchanger with a manifold layer for dividing the fluid for separate
fluid paths.
DETAILED DESCRIPTION OF THE INVENTION
[0051] Those of ordinary skill in the art will realize that the
following detailed description of the present invention is
illustrative only and is not intended to limit the claimed
invention. Other embodiments of the present invention will readily
suggest themselves to such skilled persons having the benefit of
this disclosure. It will be appreciated that in the development of
any such actual implementation, numerous implementation-specific
decisions must be made in order to achieve the developer's specific
goals. Reference will now be made in detail to implementations of
the present invention as illustrated in the accompanying drawings.
The same reference indicators will be used throughout the drawings
and the following detailed description to refer to the same or like
parts.
[0052] FIG. 1A illustrates a schematic view of a fluid cooling
system 199 according to some embodiments of the present invention.
The fluid cooling system 199 utilizes a heat exchanger 100 with
internal mini-channels 150. As shown by directional arrows, fluid
is pumped through the heat exchanger 100 and to a heat rejecter 140
by a pump 110, which is controlled by control module 120. The heat
exchanger 100 with high aspect ratio fins 150 transfers heat from a
surface (not shown) to the fluid pumped through the fins of the
heat exchanger. Heat exchange in such a fluid cooling system is
improved by configuring the flowing fluid to be in contact with as
much surface area as possible of the material that is designed to
extract the heat from the surface. The fabrication of a heat
exchanger with high surface area structures is therefore
advantageous for developing an effective heat-exchanger. However,
it is desired that the fabrication process be low cost in order to
be competitive in consumer electronics markets. Therefore, it is an
object of the invention to provide a low-cost fabrication process
for producing heat exchangers which effectively cools a surface.
For the purpose of this disclosure the term heat exchanger and the
term cannister are synonymous and may be used interchangeably.
[0053] In some embodiments of the present invention the heat
exchanger is comprised of copper. In other embodiments of the
present invention, the heat exchanger is comprised of aluminum.
Furthermore, although specific examples of suitable construction
materials are given, it will readily apparent to those having
ordinary skill in the art that a number of materials are suitable
for use in constructing the heat exchanger.
[0054] FIG. 1B illustrates a schematic isometric view of a
partially assembled heat exchanger 100 according to some
embodiments of the present invention. The heat exchanger 100
comprises a cannister 101, a thermal interface section 102, a block
of mini-channels 105 and conduits 103 and 104. The heat exchanger
100 is positioned on a surface (not shown) such that the interface
section 102 is positioned directly on top of a heat-producing
portion of the surface. The heat exchanger 100 is thermally coupled
to the heat-producing portion of the surface in order to transfer
heat to the fluid flowing through the heat exchanger 100. A Thermal
Interface Material (TIM) is used to couple the heat exchanger 100
to the surface. For example, thermal grease may be used to couple
the heat exchanger 100 to the surface.
[0055] In some embodiments of the present invention the block of
channels 105 are positioned lengthwise in the cannister 101. In
some embodiments of the present invention, the individual fins 150
comprising the block of channels 105 are spaced very close
together, but do not touch one another. The size of the channels
are preferably on the order of millimeters or micrometers. Some
methods of producing closely spaced stacks of metal fins are known,
but are not economically feasible. The present invention provides
inexpensive methods of making high aspect ratio mini-channels.
[0056] A first method of making high aspect ratio mini-channels
involves stacking individual high aspect ratio fins 150 having
self-aligning features to form channels between successively
stacked fins 150. FIGS. 2A-2C illustrates the process of creating a
block of mini-channels from individual high aspect ratio fins 150.
First, high aspect ratio plates 149 are formed into high aspect
ratio fins. In some embodiments of the present invention, separator
patterns are built into high aspect ratio plates 149 through
wet-etching or by mechanical means. The separator features serve as
self-aligning features. According to the wet-etching embodiment,
masks 148 are placed on high aspect ratio plates 149 and etched to
create desired patterns. FIG. 2A illustrates a high aspect ratio
plate 149 with a mask 148. The high aspect ratio plate 149
undergoes wet-etching to remove material from the plate. The end
result of the etching process is a fin 150 with channels 151 and
spacer elements 152. As shown in FIG. 2B, the fin 150 is the shape
of an I-Beam. The spacer elements 152 allow a number of fins 150 to
be stacked together without the danger that the stack will
collapse. Furthermore, since the depth of the channels is known
based on the etching parameters, the spacing between successively
stacked fins 150 is uniform. This offers a manufacturer of
mini-channel heat exchangers the ability to precisely control the
width of the mini-channels depending on the desired application.
FIG. 2C illustrates a stack of fins 150 to be used in a
heat-exchanger.
[0057] Any method of producing the fins 150 may be used, however,
etching the fins 150 has distinct advantages over machining a work
piece to the same parameters. First, the etching process results in
work pieces with extremely straight, clean surfaces. Any machining
process will have the problems of deformation of the pieces and
contamination of the pieces with dirt, oil, grease, cutting fluid,
etc. Additionally, etching the work pieces is much less expensive
than machine processes. Furthermore, the etching process allows the
mini-channels to be produced with extremely fine features.
[0058] FIGS. 2D and 2E illustrate another embodiment of the present
invention which utilizes a fin 150 in a T-shape with full length
spacers 152 on the upper part of the fin and footers 153 at the
lower corners of the fin 150. In FIG. 2E, the fin 150 is stacked in
the same manner as in FIG. 2C, except that fluid present in the
channels in FIG. 2E are in direct contact with the bottom surface
of a heat exchanger (not shown). Although in preferred embodiments
of the present invention, the fins 150 are constructed with a
conductive material, the embodiment described in FIG. 2E having
minimum thickness of the bottom plate in contact with the heat
producing source provides minimum resistance to heat transfer.
Therefore, the channels shown in FIG. 2E are more effective than
the channels shown in FIG. 2C in transferring heat from a heat
producing source (not shown) to a fluid medium in a fluid cooling
system.
[0059] In some embodiments of the present invention, a brazing
process is utilized to individually bond fins 150 and other pieces
together to construct a heat exchanger. Exemplary brazing processes
include, but are not limited to, vacuum brazing, inert atmosphere
brazing, and reducing atmosphere brazing. However, it is desirable
to provide a method for the fabrication of a heat exchanger in
which the parts only need to be heated once in order to braze all
the parts. By eliminating multiple brazing steps, the process
becomes less expensive and less time-consuming. Therefore, it is
desirable to use self-aligning fins which are able to stay in place
while preparing the rest of the parts for heating.
[0060] FIG. 3A illustrates an exploded view of the parts which
comprise the heat exchanger 100 according to some embodiments of
the present invention. The bottom part of a cannister 320 is
selected to be placed on a heat producing surface (not shown). The
bottom part of the cannister 320 includes a thermal interface
section 335 comprising a section of the floor of the bottom part of
the cannister 320 which has a high thermal conductivity.
Preferably, a layer of a brazing substance 330 is positioned within
the bottom part of the cannister 320 to thermally couple a stack of
fins 351 to the thermal interface section 335. In some embodiments
of the present invention, CuSil is used as a brazing substance 330.
In other embodiments, the brazing substance has a portion of
copper, a portion of nickle, a portion of tin, and a portion of
phosphorous. An example of a brazing substance that includes
copper, nickel, tin, and phosphorous is CuproBraze.TM. which has
approximately 67% copper, approximately 7% nickel, approximately 9%
tin, and approximately 7% phosphorous. In some embodiments, the
brazing material is in the form of a paste, a foil, or a wire.
Next, individual fins 350 are stacked up on top of the brazing
substance 330, along the width of the bottom part of the cannister
320, forming mini-channels. In some embodiments of the present
invention, a second brazing substance 360 is lined on the top edge
of the bottom part of the cannister 320 for brazing the lid 370 to
the bottom part of the cannister 320. In some embodiments of the
present invention, CuSil is used as a second brazing substance 360.
In other embodiments, the second brazing substance has a portion of
copper, a portion of nickle, a portion of tin, and a portion of
phosphorous, such as CuproBraze.TM.. In some embodiments, the
second brazing material is in the form of a paste, a foil, or a
wire. Finally, the lid 370 is coupled to the top of the bottom part
of the cannister 320.
[0061] FIG. 3B illustrates a partially assembled cannister 380
comprising a bottom part of a cannister 321 and lid 370. As shown,
the fins 350 are positioned in the bottom part of a cannister 321
forming a block of mini-channels 390. After the lid 370 is attached
to the bottom part of the cannister 321, the pieces are subjected
to heat to bond the parts.
[0062] FIG. 3C illustrates a fully assembled heat exchanger 300
according to some embodiments of the present invention. Again, for
the purpose of this disclosure the term heat exchanger and the term
cannister are synonymous and may be used interchangeably. The heat
exchanger 300 is positioned over a heat producing surface 319. As
shown, the heat producing surface 319 is an integrated chip.
However, the heat exchanger 300 according to the present invention
can be used to cool any heat-producing surface 319. In some
embodiments of the present invention, a Thermal Interface Material
(TIM) 330 such as thermal grease is placed between the
heat-exchanger 300 and the heat-producing surface 319. The
embodiments illustrated in FIGS. 3A-3C are fabricated such that the
heat exchanger is only heated once to braze all the pieces
together.
[0063] The above methods of fabricating heat exchanger
mini-channels offer economically feasible solutions over machining
mini-channels mechanically. Utilizing high aspect ratio
mini-channels increases the heat transfer rate in fluid cooling
heat exchangers. It is also an object of the present invention to
provide plates with wall features to further enhance the heat
transfer rates in these systems.
[0064] In some embodiments of the present invention, fins or plates
with wall features increase the overall surface area of the
mini-channel which allows more fluid to interact with the thermally
conductive material. By increasing the liquid-to-plate interaction,
more fluid is heated by the plates and the fluid is heated more
evenly. The wall features also provide a means to mix the fluid,
resulting in an even more homogeneously heated fluid. Obtaining
more homogeneously heated fluid results in better overall
performance of the heat exchanger. In some embodiments of the
present invention, the wall features allow laminar flow mixing of
the cooling fluid. In other embodiments of the present invention,
the wall features cause turbulent flow therethrough.
[0065] The wall features on the fins are created by a variety of
mechanical methods including, but not limited to cold rolling,
laser cutting, stamping, etc, or by photochemical etching.
Preferably, the wall features are fabricated using a wet etching
process, thus achieving economic feasibility. FIG. 4 illustrates an
exemplary process for fabricating patterned fins by photochemical
etching. At the step 400, a metal sheet is cleaned to remove grease
and other surface contaminants. At the step 402, photoresist is
applied to both sides of the cleaned metal sheet. At the step 404,
the metal sheet with photoresist is exposed and patterned such that
the photoresist forms a series of tabbed fins with desired
patterns. At the step 406, the metal sheet patterned with
photoresist is exposed to an etchant, thereby forming an etched
metal sheet including the series of tabbed fins with desired
patterns. Each patterned fin is separated from an adjacent fin on
the etched metal sheet by one or more etched tabs in the etched
metal sheet. At the step 408 the etched metal sheet is rinsed and
dried. At the step 410, individual patterned fins are detached from
the etched metal sheet by breaking the tabs.
[0066] FIG. 5A illustrates a side view of a fin 550 prepared to be
etched with wall features (not shown) according to some embodiments
of the present invention. The fin 550 is masked with masks 560.
Once masked, the fin 550 is exposed to an etchant. FIG. 5B
illustrates a side view close-up of the etching process. As the
surface 551 of the fin 550 is exposed to an etchant, fin material
is removed in multiple directions (as indicated by the directional
arrows). Finally, FIG. 5C illustrates the fin 550 after being
exposed to the etchant with the masks 560 removed.
[0067] Furthermore, depending on the desired effect and the method
used to form wall features on the fins, the cross section of the
fin's groove will range in shape and will react differently to
fluid flowing over its surface. FIGS. 6A-6C illustrate isometric
views of fins 650, 660, 670, all with wall features according to
some embodiments of the present invention. FIG. 6A illustrates a
isometric view of a fin 650 with a substantially
rectangularly-shaped grooves 651 as a wall feature. In some
embodiments of the present invention, the grooves 651 are disposed
on both sides of the fin 650. FIG. 6B illustrates a isometric view
of a fin 660 with substantially triangularly-shaped grooves 661.
The grooves 661 shown in FIG. 6B are disposed on both sides of fin
660. FIG. 6C illustrates a isometric view of a fin 670 with
substantially rounded grooves 671. Furthermore, the grooves 671
shown in FIG. 6C are disposed on both sides of fin 670. Although
the grooves 651, 661 and 671 are shown as straight uni-directional
grooves, it will be clear to those having ordinary skill in the
relevant art, that a number of different configurations are
possible for the orientation of the groove, depending on a number
of design and implementation goals.
[0068] FIGS. 7A-7F illustrate examples of the wall features on the
fins according to some embodiments of the present invention. The
wall features in FIGS. 7A-7F are channels formed into the fins
751-760. Preferably, a wet-etching technique is used to create the
wall features, although any other process can equally be used.
Further, it is clear to those skilled in the art that, although
channels are illustrated, the wall features can be protrusions.
FIG. 7A illustrates an example of a fin 751 having diagonal wall
features according to some embodiments of the present invention.
FIG. 7B illustrates an example of a fin 752 having angled wall
features and straight wall features according to some embodiments
of the present invention. FIG. 7C illustrates an example of a fin
754 having angled wall features and a channel-less center according
to some embodiments of the present invention. FIG. 7D illustrates
an example of a fin 756 having zig-zag wall features according to
some embodiments of the present invention. FIG. 7E illustrates an
example of a fin 758 having sinusoidal wall features according to
some embodiments of the present invention. FIG. 7F illustrates an
example of a fin 760 having crosshatch wall features according to
some embodiments of the present invention.
[0069] FIGS. 7G and 7H illustrate adjacent fins 770 and 780 having
complementary wall features according to some embodiments of the
present invention. FIG. 7G illustrates an isometric view of fin 770
and fin 780 laid down on its side to show detail. As shown, fin 770
as diagonal wall features 771 that slope from the upper left side
of the fin 770 to the bottom right side of the fin 770 (decreasing
gradient diagonal configuration). Fin 780 has diagonal wall
features 781 that, when the fin 780 is stood upright, slope from
the lower left side of the fin 780 to the upper right side of the
fin 780 (increasing gradient diagonal configuration). FIG. 7H
illustrates an isometric view of fins 770 and 780 orientated such
that a channel 775 is formed between them. The slope of the wall
features 771 and 781 crisscross to encourage turbulent flow within
the channel 775 as the channel 775 is flooded with a fluid (not
shown).
[0070] In some embodiments of the present invention, fins with pin
protrusions are utilized. FIGS. 8A and 8B illustrate an example of
pin wall features according to some embodiments of the present
invention. In some embodiments, the fins with pin protrusions have
vent features. These vent features will be described more
thoroughly in the discussion of FIGS. 10A-10C below.
[0071] FIG. 8A illustrates an example of a fin 850 having pin
protrusion wall features according to some embodiments of the
present invention. As shown, the fin 850 has a number of right face
protrusions 860 and left face protrusions 865. In some embodiments,
the right face protrusions and the left face protrusions are
slightly staggered, so that when two fins 850 are pushed together
they are self-aligning and stack much like the fins with built in
separators as described above. FIG. 8B illustrates a heat exchanger
801 according to some embodiments of the present invention with
fins 850. As shown, a layer of brazing material 830 is laid on the
bottom surface of the cannister 800. In some embodiments, the
brazing material 830 is CuSil. In other embodiments, the brazing
material 830 has a portion of copper, a portion of nickle, a
portion of tin, and a portion of phosphorous, such as
CuproBraze.TM.. In some embodiments, the brazing material 830 is in
the form of a paste, a foil, or a wire. The fins 850 with wall
features 860 and 865 are then stacked to create a series of
structured pseudo-foam conduits 870. Next, a brazing material 880
is placed around the top of cannister 800 and a lid 890 is placed
over the cannister 800. In some embodiments, the brazing material
880 is CuSil. In other embodiments, the brazing material 880 has a
portion of copper, a portion of nickle, a portion of tin, and a
portion of phosphorous, such as CuproBraze.TM.. In some
embodiments, the brazing material 880 is in the form of a paste, a
foil, or a wire. Once constructed, the heat exchanger 801 is heated
in a furnace to braze the pieces together. As explained above, it
is desirable to braze the heat exchanger only once in order to
conserve time and money.
[0072] The fins and heat exchangers illustrated in FIGS. 7A-8B
provide an efficient way to provide a large surface area for heat
transfer in a mini-channel heat exchanger. Another method of
providing a greater surface area is through the use of porous
structures between or in the place of mini-channels. FIG. 9A
illustrates a side view of a high aspect ratio, high surface area
heat exchanger 900 using mini-channels 950 and a metal mesh 960
between the mini-channels 950. FIG. 9B illustrates a side view of a
high surface area heat exchanger 902 using a stack of metal mesh
layers 960. FIG. 9C illustrates a side view of a high surface area
heat exchanger 904 using an open-cell metal foam insert 980.
Preferably, the pore diameter of the open-cell metal foam insert
980 ranges from one micron to one millimeter.
[0073] In some cases, the use of high surface area, high aspect
ratio mini-channels in the heat exchanger causes a large pressure
drop between the inlet conduit and the outlet conduit of the heat
exchanger. This high pressure drop results in additional technical
challenges for the other components within the system, including
the pumps, other heat exchangers, and the heat rejector.
[0074] It is an object of this invention to decrease the pressure
drop across the heat exchanger. Methods of decreasing pressure drop
in heat exchanger apparatuses have previously been disclosed by the
applicant in U.S. Pat. No. 6,988,534 B2, which issued on Jan. 24,
2006 and entitled "Method and Apparatus for Flexible Fluid Delivery
for Cooling Desired Hot Spots in a Heat-Producing Device", U.S.
Pat. No. 6,986,382, which issued on Jan. 17, 2006 and entitled
"Interwoven Manifolds for Pressure Drop Reduction in Heat
Exchangers", U.S. Pat. No. 7,000,684, which issued on Feb. 21, 2006
and entitled "Method and Apparatus for Effective Vertical Fluid
Delivery for Cooling a Heat Producing Device", and Co-Pending U.S.
patent application Ser. No. 10/698,180, filed on Oct. 30, 2003 and
entitled "Optimal Spreader System, Device and Method for Fluid
Cooled Micro-scaled Heat Exchange", which are all incorporated
herein in their entirety. Other novel means for the reduction of
pressure drop are disclosed below.
[0075] FIGS. 10A-14 illustrate novel methods and apparatuses for
reducing pressure drop in the heat exchangers described herein
according to some embodiments of the present invention. In all of
the following examples, a reduction in pressure drop is achieved
through dividing the fluid by providing alternate paths of fluid
flow.
[0076] FIGS. 10A-10C illustrate a pin-vent fin wall structure for
dividing fluid flow in a heat exchanger according to some
embodiments of the present invention. FIG. 10A illustrates a side
view of a single fin 1050 with pin protrusions 1060 along its
surface. The fin 1050 also has vents 1070 which completely pass
through the surface of the fin 1050. Preferably, the pin
protrusions 1060 and the vents 1070 are formed on the fin 1050
through a wet-etching process.
[0077] FIG. 10B illustrates an end view of a stack of fins 1050
with pin protrusions 1060 and vents 1070 (indicated with dashed
lines) passing therethrough. As shown, the fins 1050 are
self-aligning in a similar way to the fins illustrated above.
Therefore, a heat exchanger (not shown) can be fabricated using
fins 1050 without the requirement that the fins 1050 be bonded to
the cannister (not shown) individually, thus saving cost by
eliminating steps in the fabrication process.
[0078] The narrow passages created between the fins 1050 when they
are stacked together can result in a pressure drop over the length
of the fin 1050. Including the vents 1070 in the fins 1050 gives
the fluid an alternate path to flow, thereby reducing the pressure
drop across the system.
[0079] FIG. 10C illustrates a isometric view of the stack of fins
1050 having pin protrusions 1060 and vents 1070. Fluid is pumped
between the fins 1050 and the fins 1050 absorb heat from the
heating source. Fluid is mixed by the pin protrusions 1060 to
achieve a more homogeneously mixed fluid. Furthermore, fluid
traverses between rows of fins 1050 through the vents 1070 to
further mix fluid and to alleviate the pressure in the heat
exchanger.
[0080] FIGS. 11A and 11B illustrates another embodiment of the
present invention used to alleviate pressure drop in a heat
exchanger 1100 by diverting fluid through holes in mini-channels.
FIG. 11A illustrates a schematic isometric view of a plurality of
fins 1150 and a fin 1152 used in heat exchangers according to some
embodiments of the present invention. The fins 1150 have apertures
(indicated with dashed lines 1151) to divide the fluid flow and one
fin 1152 does not include an aperture and is used to block the
passage of fluid. The fins 1150 are included in a heat exchanger
(FIG. 11B, element 1100) and form a series of channels 1153.
Preferably the fins 1150 are made of a material with a high thermal
conductivity so that when fluid flows through the channels 1153,
effective heat exchange occurs.
[0081] FIG. 11B illustrates a schematic isometric view of a heat
exchanger 1100 utilizing the fins with conduits 1150 (indicated
with dashed lines 1151) and the fin 1152. Each fin 1150 and fin
1152 extend substantially across the heat exchanger 1100 in the
X-direction. However, some amount of space exists between the walls
of the heat exchanger 1100 and the ends of the fins 1150 and fin
1152 so that fluid exits the channels in the X-direction.
[0082] Fluid is pumped into a reservoir 1115 in the heat exchanger
1100 through conduit 1105 where it encounters the first of a series
of fins 1150 with an aperture (not labeled). A portion of the fluid
is forced through the aperture and some portion of fluid is pushed
along the face of the fin 1150 towards each wall of the heat
exchanger 1100, effectively dividing the fluid flow path by some
amount. As such the pressure drop is reduced because the fluid only
needs to be pushed along half the length of the fins 1150.
Furthermore, since the system pressure is used to push the fluid in
two directions, the velocity of fluid traveling through the
channels 1153 is reduced. Therefore, the fluid moves at a slower
pace through a shorter fluid path causing a more effective heat
exchange between the fluid and the channel walls.
[0083] As fluid progresses through the series of fins 1150, the
channels 1153 formed by the fins 1150 become at least partially
flooded and effectuate heat exchange with the fluid. Heated fluid
is forced out of the channels 1153 and forced into a reservoir
1120, and out of a conduit 1110.
[0084] In some embodiments, the fins 1150 can be stacked with wall
features of the types shown in FIGS. 7A-7E. One or more apertures
are introduced between the wall features. In some embodiments, only
one aperture exists on the fins 1150. In other embodiments,
multiple apertures exist along the fin 1150. In some embodiments
having multiple apertures, the number of apertures on each fin
vary. In other embodiment having multiple apertures, each fin has
the same number of apertures. As shown, the apertures are circular,
however, the shape of the apertures can be selected from any shape.
As shown, the apertures are lined up, each centered on the fin
1150. In other embodiments, the apertures are staggered on the fins
1150. In alternate embodiments, the conduits 1105 and 1110 are
situated either on the sides of the heat exchanger 1100, on the
bottom of the heat exchanger 1100, or in a combination of the top,
bottom or sides.
[0085] FIG. 12 illustrates a top view of an alternative
configuration for reducing the path length that fluid travels in a
mini-channel heat exchanger 1200, thereby reducing pressure drop.
The heat exchanger 1200 includes an intake conduit 1205 leading to
reservoir 1215, an output conduit 1210 drawing from reservoir 1220,
walls 1252, fins 1250, and a vertical spine 1251. Fluid is pumped
into the heat exchanger 1200 via the input conduit 1205 into the
reservoir 1215. The fluid is split by the spine 1251. The spine
1251 also effectuates heat transfer from the heat source (not
shown) to the fluid. In some embodiments, the spine 1251 can be
configured with wall features. The spine 1251 forces the fluid into
mini-channels 1253 formed by the fins 1250. The walls of the
mini-channels 1253 transfer heat from the heat source (not shown)
to the fluid. The heated fluid is then forced out of the channels
1253, into the reservoir 1220 and out of the output conduit
1210.
[0086] FIG. 13 illustrates an alternative embodiment of a heat
exchanger with a spine 1351 and four quadrants I, II, III, and IV
of heat exchange. Fluid is pumped into reservoir 1315 via input
conduit 1305. The spine 1351 divides the fluid into the four
quadrants I, II, III, and IV. Each quadrant is separated with walls
1352 and contains mini-channels 1353 formed by fins 1350. Heat
exchange occurs in the mini-channels 1353 and the heated fluid
recombines in the reservoir 1320 and is pumped out of the output
conduit 1310. In some embodiments, each quadrant I, II, III, and IV
is positioned above a separate heat source (not shown).
Alternatively, each quadrant I, II, III and IV is positioned above
a specific zone of a single heat source (not shown). Preferably,
the heat exchanger 1300 is used to cool the multiple heat zones
associated with multi-core integrated chips.
[0087] The heat exchangers illustrated in FIGS. 11-13 all divide
the fluid path internally, within the heat exchanger itself. In
other embodiments, a manifold layer is positioned on top of the
thermal interface section of the heat exchanger and is used to
divide the fluid into separate fluid paths.
[0088] FIG. 14 illustrates a cut-out isometric view of a heat
exchanger 1400 with a manifold layer 1470 and an interface layer
1460. The interface layer 1460 includes thermally conductive
mini-channels 1465. The manifold layer 1470 sits on top of the
interface layer 1460 and supplies the interface layer 1460 with
fluid for fluid cooling. As shown, fluid (not shown) is pumped into
the manifold layer 1470 of the heat exchanger 1400 via inlet
conduit 1405. A wall 1415 is preferentially included to impede the
fluid flow and cause fluid to pool in the manifold layer 1470. The
pooled fluid drains through a narrow slit 1420 and into the
interface layer 1460. Draining fluid contacts the interface layer
1460 and is forced out both sides of the mini-channels 1465. As
such, the fluid only interfaces with one-half the length of a
mini-channel 1465, effectively reducing pressure drop in the heat
exchanger 1400. Although a single slit 1420 is shown as the conduit
between the manifold level 1470 and the interface level 1460, it
will be readily apparent to those ordinarily skilled in the art
that multiple slits or openings in multiple locations and
configurations are equally conceived.
[0089] The heat exchanger of the present invention effectively
transfers heat from a surface through a conductive cannister,
through mini-channel walls and into a fluid flowing therethrough.
The present invention also discloses providing the fins used in the
mini-channels with wall features to mix fluid and provide
alternative fluid paths to reduce pressure drop. The present
invention also discloses alternative methods of reducing pressure
drop including providing unique geometries to divert fluid flow and
providing the heat exchanger with a manifold layer. The present
invention also discloses cost-effective methods of fabricating the
heat exchanger, mini-channels, fins with wall features and
manifolds.
[0090] The present invention has been described in terms of
specific embodiments incorporating details to facilitate the
understanding of the principles of construction and operation of
the invention. Such reference herein to specific embodiments and
details thereof is not intended to limit the scope of the claims
appended hereto. It will be apparent to those skilled in the art
that modifications can be made in the embodiment chosen for
illustration without departing from the spirit and scope of the
invention. Specifically, it will be apparent to one of ordinary
skill in the art that the device and method of the present
invention could be implemented in several different ways and have
several different appearances.
* * * * *