WO2011041600A1

WO2011041600A1 - Fabrication of high surface area, high aspect ratio mini-channels and their application in liquid cooling systems

Info

Publication number: WO2011041600A1
Application number: PCT/US2010/050990
Authority: WO
Inventors: Madhav Datta; Peng Zhou; Brandon Leong; Mark Mcmaster; Douglas E. Werner
Original assignee: Cooligy Inc.; Choi, Hae-Won
Priority date: 2009-09-30
Filing date: 2010-09-30
Publication date: 2011-04-07
Also published as: US20110073292A1

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.

Description

FABRICATION OF HIGH SURFACE AREA, HIGH ASPECT RATIO MINI- CHANNELS AND THEIR APPLICATION IN LIQUID COOLING SYSTEMS

FIELD OF THE INVENTION:

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:

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.

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. Patent Number 7,017,654, which issued on March 28, 2006 and entitled "APPARATUS AND METHOD OF FORMP G CHANNELS IN A HEAT-EXCHANGP^G 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 INVENTION:

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. 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.

BRIEF DESCRIPTION OF THE DRAWINGS:

Figure 1 A illustrates a schematic view of a fluid cooling system utilizing the heat exchanger with mini-channels.

Figure IB. illustrates a schematic isometric view of a partially assembled heat exchanger according to some embodiments of the present invention. Figure 2 A illustrates a schematic view of a high aspect ratio plate with a mask for etching according to some embodiments of the present invention.

Figure 2B illustrates a schematic view of an I-Beam fin fabricated through etching according to some embodiments of the present invention.

Figure 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.

Figure 2D illustrates a schematic view of a T-Beam fin fabricated through etching according to some embodiments of the present invention.

Figure 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.

Figure 3A is an exploded schematic view illustrating the parts which comprise the heat exchanger according to some embodiments of the present invention.

Figure 3B is a partially exploded schematic view illustrating a partially assembled cannister and lid according to some embodiments of the present invention.

Figure 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.

Figure 4 illustrates an exemplary process for fabricating patterned fins by

photochemical etching.

Figure 5A illustrates a side view of a fin treated with a mask in preparation for the step of forming wall features on the fin.

Figure 5B illustrates a close-up side view of the surface of a fin treated with a fluid etchant, forming wall features on the fin.

Figure 5C illustrates a side view of a fin with wall features formed from etching.

Figure 6A illustrates an isometric view of an individual fin with rectangular wall features.

Figure 6B illustrates an isometric view of an individual fin with triangular wall features.

Figure 6C illustrates an isometric view of an individual fin with rounded wall features.

Figure 7A illustrates a schematic view of an example of a fin having angled wall features according to some embodiments of the present invention.

Figure 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. Figure 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.

Figure 7D illustrates a schematic view of an example of a fin having zig-zag wall features according to some embodiments of the present invention.

Figure 7E illustrates a schematic view of an example of a fin having sinusoidal wall features according to some embodiments of the present invention.

Figure 7F illustrates a schematic view of an example of a fin having Crosshatch wall features according to some embodiments of the present invention.

Figure 7G illustrates a schematic view of an example of adjacent complimentary fins having complimentary wall features according to some embodiments of the present invention.

Figure 7H illustrates a schematic view of an example of adjacent complimentary fins having complimentary wall features according to some embodiments of the present invention. Figure 8A illustrates a schematic view of an example of a fin having of pin wall features according to some embodiments of the present invention.

Figure 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.

Figure 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.

Figure 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.

Figure 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.

Figure 10A illustrates a schematic side view of a fin having pin wall features and vents passing therethrough.

Figure 10B illustrates a schematic side view of a stack of fins having pin wall features and vents passing therethrough.

Figure IOC illustrates a schematic isometric view of a heat exchanger with a stack of fins having pin wall features and vents passing therethrough. Figure 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.

Figure 11B illustrates a schematic isometric view of a heat exchanger with fins having apertures for reducing the path length of the fluid.

Figure 12 illustrates a schematic top view of a heat exchanger with a spine divider for reducing the path length of fluid.

Figure 13 illustrates a schematic top view of a heat exchanger with a spine divider and four quadrants for cooling multi-core integrated chips.

Figure 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:

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.

Figure 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.

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.

Figure IB 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 maybe used to couple the heat exchanger 100 to the surface.

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. Figures 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. Figure 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 Figure 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. Figure 2C illustrates a stack of fins 150 to be used in a heat-exchanger.

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.

Figures 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 Figure 2E, the fin 150 is stacked in the same manner as in Figure 2C, except that fluid present in the channels in Figure 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 Figure 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 Figure 2E are more effective than the channels shown in Figure 2C in transferring heat from a heat producing source (not shown) to a fluid medium in a fluid cooling system.

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.

Figure 3 A 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™ 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™. 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.

Figure 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.

Figure 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 Figures 3A-3C are fabricated such that the heat exchanger is only heated once to braze all the pieces together.

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. Figure 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. Figure 5 A 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. Figure 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, figure 5C illustrates the fin 550 after being exposed to the etchant with the masks 560 removed.

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. Figures 6A-6C illustrate isometric views of fins

650, 660, 670 , all with wall features according to some embodiments of the present invention. Figure 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. Figure 6B illustrates a isometric view of a fin 660 with substantially triangularly-shaped grooves 661. The grooves 661 shown in Figure 6B are disposed on both sides of fin 660. Figure 6C illustrates a isometric view of a fin 670 with substantially rounded grooves 671. Furthermore, the grooves 671 shown in Figure 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.

Figures 7A-7F illustrate examples of the wall features on the fins according to some embodiments of the present invention. The wall features in Figures 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. Figure 7A illustrates an example of a fin 751 having diagonal wall features according to some embodiments of the present invention. Figure 7B illustrates an example of a fin 752 having angled wall features and straight wall features according to some embodiments of the present invention. Figure 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. Figure 7D illustrates an example of a fin 756 having zig-zag wall features according to some

embodiments of the present invention. Figure 7E illustrates an example of a fin 758 having sinusoidal wall features according to some embodiments of the present invention. Figure 7F illustrates an example of a fin 760 having Crosshatch wall features according to some embodiments of the present invention.

Figure 7G and 7H illustrate adjacent fins 770 and 780 having complementary wall features according to some embodiments of the present invention. Figure 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).

Figure 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).

In some embodiments of the present invention, fins with pin protrusions are utilized. Figures 8 A 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 Figures 1 OA- IOC below.

Figure 8 A 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. Figure 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™. 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™. 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.

The fins and heat exchangers illustrated in Figures 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. Figure 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. Figure 9B illustrates a side view of a high surface area heat exchanger 902 using a stack of metal mesh layers 960. Figure 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.

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. Patent No. 6,988,534 B2, which issued on January 24, 2006 and entitled "Method and Apparatus for Flexible Fluid Delivery for Cooling Desired Hot Spots in a Heat-Producing Device", U.S. Patent No. 6,986,382, which issued on January 17, 2006 and entitled "Interwoven Manifolds for Pressure Drop Reduction in Heat Exchangers", U.S. Patent No. 7,000,684, which issued on February 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 No.: 10/698,180, filed on October 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. Figures 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.

Figures 1 OA- IOC illustrate a pin- vent fin wall structure for dividing fluid flow in a heat exchanger according to some embodiments of the present invention. Figure 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.

Figure 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.

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.

Figure IOC 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.

Figures 1 1 A and 1 IB illustrates another embodiment of the present invention used to alleviate pressure drop in a heat exchanger 1 100 by diverting fluid through holes in mini- channels. Figure 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 (Figure 1 IB, 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 1 153, effective heat exchange occurs.

Figure 1 IB 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.

Fluid is pumped into a reservoir 1115 in the heat exchanger 1 100 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 Figures 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.

Figure 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.

Figure 13 illustrates an alternative embodiment of a heat exchanger with a spine 1351 and four quadrants I, Π, ΠΙ, 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, ΙΠ, 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, ΙΠ, and IV is positioned above a separate heat source (not shown).

Alternatively, each quadrant I, Π, ΠΙ and TV 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.

The heat exchangers illustrated in Figures 1 1-13 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.

Figure 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.

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

CLAIMS What is claimed is:

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.

The stacked fin heat exchanger according to claim 2, wherein the plurality of fins 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 comer 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.

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. 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

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.

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.