FABRICATION OF HIGH SURFACE AREA, HIGH ASPECT RATIO MINI-CHANNELS AND THEIR APPLICATION IN LIQUID COOLING SYSTEMS
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.
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 INVENTIONEffective 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.
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.
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.
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 INVENTIONThe 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
In some embodiments of the present invention, fins with pin protrusions are utilized.
The fins and heat exchangers illustrated in
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.
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.
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.
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.
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.
In some embodiments, the fins 1150 can be stacked with wall features of the types shown in
The heat exchangers illustrated in
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.
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.
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.
Type: Application
Filed: Sep 30, 2009
Publication Date: Mar 31, 2011
Inventors: Madhav Datta (Milpitas, CA), Peng Zhou (El Cerrito, CA), Hae-won Choi (Albany, CA), Brandon Leong (Santa Clara, CA), Mark McMaster (Menlo Park, CA), Douglas E. Werner (Santa Clara, CA)
Application Number: 12/571,265
International Classification: F28F 9/00 (20060101); F28F 9/24 (20060101); B21D 53/02 (20060101);