U.S. patent application number 11/198889 was filed with the patent office on 2006-03-23 for methods and apparatuses for electronics cooling.
Invention is credited to Lalit Chordia, John C. Davis, Stephan Fatschel, Brian Moyer, Robert Panella.
Application Number | 20060060333 11/198889 |
Document ID | / |
Family ID | 46123679 |
Filed Date | 2006-03-23 |
United States Patent
Application |
20060060333 |
Kind Code |
A1 |
Chordia; Lalit ; et
al. |
March 23, 2006 |
Methods and apparatuses for electronics cooling
Abstract
Methods and apparatuses for cooling a device are disclosed. The
device may be an electrical or electronic component that includes
an integrated circuit or embedded control. The apparatus employs a
fluid that near or above its critical pressure and at least one
heat exchanger. At least two configurations are disclosed: one with
a pump and another without a pump.
Inventors: |
Chordia; Lalit; (Pittsburgh,
PA) ; Davis; John C.; (Pittsburgh, PA) ;
Fatschel; Stephan; (Seven Fields, PA) ; Panella;
Robert; (New Kensignton, PA) ; Moyer; Brian;
(Pittsburgh, PA) |
Correspondence
Address: |
Thar Technologies, Inc.
730 William Pitt Way
Pittsburgh
PA
15238
US
|
Family ID: |
46123679 |
Appl. No.: |
11/198889 |
Filed: |
August 5, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10702396 |
Nov 5, 2003 |
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11198889 |
Aug 5, 2005 |
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60424142 |
Nov 5, 2002 |
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Current U.S.
Class: |
165/104.33 ;
257/E23.098 |
Current CPC
Class: |
F28F 2260/02 20130101;
H01L 2924/00 20130101; H01L 23/473 20130101; H01L 2924/0002
20130101; H01L 2924/0002 20130101; F25B 2309/061 20130101; F28D
15/0266 20130101; F28F 3/12 20130101 |
Class at
Publication: |
165/104.33 |
International
Class: |
F28D 15/00 20060101
F28D015/00 |
Claims
1. An apparatus for cooling a device comprising: (a) a fluid near
or above its critical pressure; (b) at least one heat exchanger;
(c) a pump for circulation of the fluid; and (d) a fluid connection
between the heat exchanger and the pump.
2. The apparatus as in claim 1, wherein the device is selected from
the group consisting of electrical or electronic components
comprising at least an integrated circuit or embedded control.
3. The apparatus as in claim 1, wherein the fluid is selected from
the group consisting of carbon dioxide, water, air, and a natural
hydrocarbon.
4. The apparatus as in claim 1, wherein the pump utilizes
electrical, electromechanical, mechanical or magnetic means of
fluid flow.
5. The apparatus as in claim 4, wherein the actuation of the pump
is selected from the group consisting of electrohydrodynamic,
magnetic and electromechanical actuations.
6. The apparatus as in claim 1, wherein the at least one heat
exchanger is of microchannel type.
7. The apparatus as in claim 1, wherein an absence of lubricants
increases performance of the apparatus.
8. The apparatus as in claim 1, further comprising control by
software, hardware or other method.
9. The apparatus as in claim 1, further comprising at least one
sensor to monitor and control temperature and temperature-related
phenomena.
10. The apparatus as in claim 1, wherein power is derived from a
public power network of the device.
11. The apparatus as in claim 1, wherein power is derived from an
independent source.
12. The apparatus as in claim 1, wherein the at least one heat
exchanger and the pump are contained in the apparatus package.
13. The apparatus as in claim 12, further comprising at least one
heat exchanger that is external to the apparatus package.
14. The apparatus as in claim 13, wherein the external heat
exchanger is connected to the apparatus by a fluidic
connection.
15. The apparatus as in any one of claims 12-14, wherein the heat
exchanger is integrated into a package of the device.
16. The apparatus as in claim 15, wherein the external heat
exchanger is in thermal contact with the device.
17. The apparatus as in claim 1, wherein the fluid comprises
thermally conductive nanoparticles to increase cooling
performance.
18. The apparatus as in claim 1, further comprising an additional
effect selected from the group consisting of electrohydrodynamic
and magnetic effect to increase cooling performance.
19. An apparatus for cooling a device comprising: (a) a fluid near
or above its critical pressure; (b) at least two heat exchangers;
and (c) a fluid connection between the heat exchangers.
20. The apparatus as in claim 19, wherein the device is selected
from the group consisting of electrical or electronic components
comprising at least an integrated circuit or embedded control.
21. The apparatus as in claim 19, wherein the fluid is selected
from the group consisting of carbon dioxide, water, air, and a
natural hydrocarbon.
22. The apparatus as in claim 19, wherein the at least one heat
exchanger is of microchannel type.
23. The apparatus as in claim 19, further comprising a control by
software, hardware or other method.
24. The apparatus as in claim 19, further comprising a sensor to
monitor and control temperature and temperature-related
phenomena.
25. The apparatus as in claim 19, wherein the at least one heat
exchanger is contained in the apparatus package.
26. The apparatus as in claim 25, further comprising at least one
heat exchanger external to the apparatus package.
27. The apparatus as in claim 26, wherein the external heat
exchanger is connected to the apparatus by a fluidic
connection.
28. The apparatus as in any one of claims 25-27, wherein the heat
exchanger is integrated into the package of the device.
29. The apparatus as in claim 28, wherein the external heat
exchanger is in thermal contact with the device.
30. The apparatus as in claim 19, wherein a density difference is
maintained between at least two heat exchangers.
31. The apparatus as in claim 19, wherein the fluid comprises
thermally conductive nanoparticles to increase cooling
performance.
32. The apparatus as in claim 19, further comprising an additional
effect selected from the group consisting of electrohydrodynamic
and magnetic effect to increase cooling performance.
33. A method of cooling a device, the method comprising: (a)
providing a fluid near or above its critical pressure; (b)
transferring heat from the device to the fluid; (c) transferring
heat from the fluid to an external environment; and (d) providing a
pump for fluid flow.
34. The method as in claim 33, wherein the device is selected from
the group consisting of electrical or electronic components
comprising at least an integrated circuit or embedded control.
35. The method as in claim 33, wherein the fluid is selected from
the group consisting of carbon dioxide, water, air, and a natural
hydrocarbon.
36. The method as in claim 33, wherein the pump utilizes an
electrical, electromechanical, mechanical or magnetic means for
fluid flow.
37. The method as in claim 33, wherein the actuation of the pump is
selected from the group consisting of electrohydrodynamic, magnetic
and electromechanical actuations.
38. The method as in claim 33, wherein an absence of lubricants
increases the performance of the apparatus.
39. The method as in claim 33, further providing a control by
software, hardware or other method.
40. The method as in claim 33, further providing at least one
sensor to monitor and control temperature and temperature-related
phenomena.
41. The method as in claim 33, further providing power from a
public power network of the device.
42. The method as in claim 33, further providing power from an
independent source.
43. The method as in claim 33, further adding thermally conductive
nanoparticles to the fluid to increase cooling performance.
44. The method as in claim 33, further adding an
electrohydrodynamic or magnetic effect to increase cooling
performance.
45. A method for cooling a device comprising (a) providing a fluid
near or above its critical pressure; (b) transferring heat from the
device to the fluid; and (c) transferring heat from the fluid to an
external environment.
46. The method as in claim 45, wherein the device is selected from
the group consisting of electrical or electronic components
comprising at least an integrated circuit or embedded control.
47. The method as in claim 45, wherein the fluid is selected from
the group consisting of carbon dioxide, water, air, and a natural
hydrocarbon.
48. The method as in claim 45, further providing a control by
software, hardware or other method.
49. The method as in claim 45, further providing at least one
sensor to monitor and control temperature and temperature-related
phenomena.
50. The method as in claim 45, further providing an addition of
thermally conductive nanoparticles to the fluid to increase cooling
performance.
51. The method as in claim 45, further providing an addition of an
electrohydrodynamic or magnetic effect to increase cooling
performance.
52. The method as in claim 33 or claim 45 wherein, nanomaterials
with high heat capacity are added to the fluid to reduce the fluid
flow rate.
53. The apparatus as in claim 1 or claim 19 wherein, nanomaterials
with high heat capacity are added to the fluid to reduce the fluid
flow rate.
54. The method as in claim 33 or claim 45 wherein the fluid is a
high thermal conducting fluid.
55. The apparatus as in claim 1 or claim 19 wherein the fluid is a
high thermal conducting fluid.
56. The method as in claim 39 or claim 48 wherein the control
software and hardware are integrated with the device.
57. The apparatus as in claim 8 or claim 23 wherein the control
software and hardware are integrated with the device.
58. A method of removing heat from a printed circuit boards
consisting of: (a) Impelling means to impel a fluid; (b) At least
one heat exchanger for transferring heat from the heat-transfer
fluid to an external environment; (c) At least one heat exchanger
for accepting heat to the heat-transfer fluid from within a printed
circuit board; (d) A closed loop connecting a-c.
59. An apparatus for removing heat from a printed circuit board
consisting of: (a) A mechanism to impel a fluid; (b) At least one
heat exchanger for rejecting heat; (c) At least one heat exchanger
that accepts heat laminated to a printed circuit board; (d) Fluid
connections among a-c.
60. The apparatus as in claim 59 wherein the heat-accepting heat
exchanger incorporates microchannels of a depth of less than 500
micro meters.
61. The apparatus as described in claim 59 wherein the heat
exchanger that accepts heat is formed from materials from the group
consisting of metallic, ceramic, polymeric or a combination
thereof.
62. The apparatus as described in claim 59 wherein the fluid is
chosen from the group consisting of water, carbon dioxide, ammonia,
sulfur dioxide, chlorofluorocarbon, hydrofluorocarbon, hydrocarbon
or combination thereof.
63. The apparatus as described in claim 59 wherein the impelling
means is a pump.
64. The apparatus as described in claim 59 wherein the impelling
means is a compressor.
65. The apparatus as described in claim 59 wherein heat is removed
from multiple sources on the printed circuit board.
66. The apparatus as described in claim 59 wherein the printed
circuit board has thermal vias.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/702,396, which itself claims priority to
U.S. provisional patent application Ser. No. 60/424,142 filed Nov.
5, 2002, and also claims priority to U.S. provisional patent
application 60/619,504 filed Oct. 15, 2004, teachings of which are
incorporated herein by reference.
BACKGROUND
[0002] 1. Field
[0003] Aspects of this disclosure generally relate to cooling
systems and methods that employ a fluid near or above its critical
pressure, and more particularly to a small-scale apparatus needed
to operate such a cycle. Typical target applications include, for
example, cooling of printed circuit boards, computers, computer
components, analytical and laboratory equipment, lasers, and remote
sensing equipment.
[0004] 2. Background
[0005] The cooling of such devices as computers, servers,
telecommunications switchgear and numerous other types of
electronic and medical gear has been an intense area of research
for quite some time. The need for increased performance, together
with ever increasing compactness, has led to greatly increased
levels of heat dissipation from these devices. Integrated circuits
work faster, more reliably, and with less current leakage if their
temperature is kept as low as possible. The heat emitted by these
circuits can overwhelm the cooling capacity of conventional
air-blown heat sinks, especially in the cases of thin-profile
apparatuses such as laptop computers and stacked server boards.
Another method of improving a heat sink is to construct it as a
thermoelectric cooler, known as a Peltier cooler, which enables the
temperature at the junction with the heat source to be
substantially below the temperature of the heat source itself.
Peltier coolers require more input power than can be dissipated and
are therefore an inefficient means of refrigeration. The attachment
of a heat pipe to an electronic component is another method of
removing heat from a target device. Typically, one end of the heat
pipe is exposed to a heat source while the other end is exposed to
a heat sink. Evaporation of a working fluid inside the heat pipe at
the exposed end allows for heat to be absorbed from the heat
source. In the absence of a pumping means to speed the rate of mass
transfer within the heat pipe, capacity is limited.
[0006] Microchannel heat exchangers through which a pumped fluid
flows can take the place of conventional air-blown heat sinks. In
such cases, the heat exchanger could be placed atop an integrated
circuit so as to coot it directly. Liquid coolant within the
microchannel heat exchanger would be impelled toward a secondary
heat-rejecting heat exchanger by pumping, capillary action,
thermo-syphoning, electrohydrodynamic or other means of fluid flow
and returned to the microchannel heat exchanger as coolant. The
small size of the channels allows for high pressure operation,
which widens the possibilities for heat-transfer fluids to use in
the system.
[0007] Alternatively, heat from integrated circuits can be drawn
from within the printed-circuit boards upon which they are mounted
by means of thin heat sinks that are laminated into the boards
themselves. Until now, these heat sinks have been passive
components that conduct heat to an external heat exchanger, which
is typically cooled by countercurrent air, such that they
supplement the function of a heat-sink that is mounted on top of an
integrated circuit. Examples are found in U.S. Pat. No. 6,288,906
and others which describe the use of conductive vertical posts, or
"thermal vias" to transport heat to metallic planes that are
typically located on the top or back side of a printed circuit
board. This metallic plane can serve a primary function as the
electrical ground for the board. Blish et at (U.S. Pat. No.
6,518,661) take this concept a step further by connecting internal
conductive planes first with one set of thermal vias that runs down
from the heat-generating elements, then with another set of thermal
vias that runs up to a air-blown heat sink that is mounted some
distance away from the integrated circuit. All of these inventions
are limited by the thermal conductivity of the transporting media,
which in turn is limited by the temperature difference that can be
achieved between the conductive media and cooling air. More
heat-removal capacity can be achieved if the heat conducting media
contained microchannels capable of transporting a coolant.
[0008] A key problem in bringing any microchannel structure to
commercial reality is in connecting fluid inlets and outlets in a
manner that is not so bulky as to defeat the design advantages of
the thin structure itself. In U.S. Pat. No. 5,099,910, Walpole and
Missaggia teach a means of installing one central inlet and two
outlets on one level of a two-level structure, with holes arranged
in such a way that fluid flows in opposite directions in adjacent
channels, thereby reducing the temperature gradient for fluid
entering and exiting the device. More elaborate manifolding systems
have appeared since, but most employ a similar two- or even
three-layer distribution system (U.S. patent application
2004/0104022, Kenny et at). As these manifolds become more
complicated, however, heat exchangers tend to grow in thickness,
and they would no longer be candidates for incorporation within
laminated printed circuit boards.
SUMMARY
[0009] An apparatus for cooling a device includes the following
components: a fluid that is near or above its critical pressure, a
heat exchanger, a pump for circulating the fluid, and a fluid
connection between the heat exchanger and the pump. The device may
be an electrical or electronic component that includes an
integrated circuit or embedded control. The fluid may be carbon
dioxide, water, air, or natural hydrocarbon. The pump may utilize
electrical, electromechanical, mechanical, or magnetic means of
fluid flow and the actuation of the pump may be
electrohydrodynamic, magnetic, or electromechanical actuation. The
heat exchanger is of microchannel type.
[0010] The disclosure further relates to the apparatus recited
above, where an absence of lubricants increases the performance of
the apparatus. Control may be provided by software, hardware, or
other method. A sensor may be used to monitor and control
temperature and temperature-related phenomena. Power may be derived
from a public power network of the device or an independent
source.
[0011] The disclosure further relates to the apparatus recited
above, where the heat exchanger and the pump are contained in the
apparatus package. A heat exchanger may be external to the
apparatus package. The external heat exchanger is connected to the
apparatus by a fluidic connection. The heat exchanger is integrated
into a package of the device. The external heat exchanger is in
thermal contact with the device.
[0012] Further aspects of the apparatus as recited include the
fluid comprising thermally conductive nanoparticles to increase
cooling performance and an additional effect of electrohydrodynamic
or magnetic effect may be used to increase cooling performance.
[0013] A method for cooling a device that consists of the
following: providing a fluid near or above its critical pressure,
transferring heat from the device to the fluid, transferring heat
from the fluid to an external environment, and providing a pump for
fluid flow. The details of the disclosure mentioned in the previous
paragraphs can also be applied to this method as well.
[0014] Another aspect of the invention comprises an apparatus for
cooling a device includes the following components: a fluid that is
near or above its critical pressure, two heat exchangers and a
fluid connection between the heat exchangers. The details of the
disclosure mentioned in the previous paragraphs can also be applied
to this apparatus as well. In addition, the apparatus provides for
a density difference to be maintained between the heat exchangers.
Additionally, nanomaterials with high heat capacity may be added to
the fluid to reduce the flow rate. Alternatively, the fluid may be
a highly conducting fluid.
[0015] A method for cooling a device that consists of the
following: providing a fluid near or above its critical pressure,
transferring heat from the device to the fluid and transferring
heat from the fluid to an external environment. The details of the
disclosure mentioned in the previous paragraphs can also be applied
to this method as well.
[0016] Additionally, a method is disclosed for removing heat from
printed circuit boards by means of a heat exchanger that is
laminated to the top or bottom sides of, or within, the structure
of the board. An apparatus for executing this method is further
disclosed. Said apparatus includes a thin heat-accepting heat
exchanger, though which at least one array of microchannels is
constructed. Said thin heat exchanger is capable of withstanding
internal pressure of up to 6,000 psi, which permits the use of a
wide variety of heat-transfer fluids, including such fluids as
water, carbon dioxide, hydrocarbons, chlorofluocarbons, fluorinated
hydrocarbons, ammonia and sulfur dioxide. The heat exchanger is
formed from the materials from the group consisting of metallic,
ceramic, polymeric or combination thereof.
[0017] An apparatus for cooling a device that includes a mechanism
to impel a heat-transfer fluid, which can be a pump or compressor;
at least one heat-rejecting heat exchanger; at least one
heat-accepting heat exchanger that is laminated to a printed
circuit board and which may be in contact with thermal vias that
extend to the heat emitting device on the board surface; and fluid
connections among these elements.
[0018] The printed circuit board itself may hold more than one heat
emitting device, many, if not all, of which are cooled by the
laminated heat acceptor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The drawings are provided to illustrate some of the
embodiments of the disclosure. It is envisioned that alternate
configurations of the embodiments of the present disclosure maybe
adopted without deviating from the disclosure as illustrated in
these drawings.
[0020] A detailed description of the disclosure follows with
reference to the following drawings:
[0021] FIG. 1 is a schematic representation of the microcooler for
electronics cooling that utilizes a pump.
[0022] FIG. 2 is a schematic representation of the microcooler for
electronics cooling that does not utilize a pump.
[0023] FIG. 3 presents an overall schematic of a pumped cooling
system as in FIG. 1, showing a typical printed circuit board
through which a microchannel heat exchanger is placed.
[0024] FIG. 4 shows a typical printed circuit board having a
central heat-emitting processor, along with peripheral
surface-mounted devices, and with a thin-plate microchannel heat
exchanger laminated within. A cross-sectional detail A shows a
pattern of microchannels emerging from the end of the board.
[0025] FIG. 5 describes the channel construction in cross-sectional
view.
[0026] FIG. 6 shows the positioning of a microchannel heat
exchanger, in cross-sectional view, within a printed circuit
board
[0027] FIG. 7 presents performance data for a thin microchannel
cooling system.
[0028] FIG. 8 depicts a typical server mother board, showing the
positions of heat-generating integrated circuits, with the route of
embedded microchannels shown in a shaded path.
DETAILED DESCRIPTION
Description
[0029] The present disclosure provides novel methods and
apparatuses for cooling using a fluid near or above its critical
pressure. The cooling methods herein relate to a sealed, closed
loop for circulation of a fluid. The cooling system is comprised of
at least one heat exchanger and may include a pump. All components
may be connected within a closed circuit and may be integrated into
one package or distributed throughout the device. The apparatus
provides a means of cooling devices, including, but not limited to,
electrical and electronic devices, and other devices and components
having at least an integrated circuit or embedded control. Examples
of such devices include electrical, electronic or optical elements
within an appliance or the appliance itself, with at least an
integrated circuit or embedded control that generates heat,
including computers, servers, telecommunications switchgear, radio
frequency devices, lasers and numerous other types of electronic
equipment, medical equipment, military hardware and many more items
that are generally compact in design.
[0030] In its basic operation, the apparatus causes a cooling fluid
to circulate between a heat acceptor, where heat is absorbed from
the device being cooled, and a heat rejecter, where the absorbed
heat is discharged from the apparatus, thereby cooling the fluid so
that it can re-circulate to the heat accepter. The fluid flows
through small channels of less than 1 millimeter in length, width
or diameter. Because of frictional forces within these channels,
the fluid must be impelled in some manner. The present disclosure
describes two methods of impelling the fluid--one by means of a
pump, the other by utilizing density differences and thereby doing
without a pump. The heat rejecter in this apparatus is a type of
heat exchanger that causes heat from the apparatus' fluid to
transfer to an ambient fluid, typically air. The heat accepter in
this apparatus is a heat exchanger than is in direct or indirect
contact with the device.
[0031] According to the present disclosure, a pump may be used in
the system to circulate a fluid around the closed circuit and
through at least one or more heat exchangers for accepting and
rejecting heat. The pump may be used for circulation of the fluid
through the loop. Many types of pumps can be used for the purpose.
The pump can be electrical in nature, meaning that the driving
force is strictly electrical in nature and does not involve
mechanical moving parts. Specific examples of electrical pumps
include electrohydrodydnamic (EHD). In EHD pumps, an electric field
is applied to a dielectric fluid, inducing an electric charge in
the fluid and dragging fluid along with it as the electric field is
made to travel down the flow path. The effect can be enhanced with
the use of small particles in the fluid, which can become charged
and move with the field, dragging fluid along with them and thus
actuating a pumping effect. If the electric field were made static,
i.e., it does not travel along the flow path, then the electric
pump might take the form of electrokinetic pumps, such as
electro-osmotic pumps.
[0032] Alternatively, the pump can be mechanical in nature, wherein
the immediate driving force that impels the fluid is mechanical,
such as the action of a reciprocating piston or a rotating-vane
impeller. The force that drives a mechanical pump can itself be
electrical in nature, such as an electric motor, in which case the
combination of pump and motor can be described as actuated by
electromechanical means.
[0033] A further means of fluid flow is magnetic in nature, as in
the case of pumping element that moves in response to a changing
magnetic field. An example is a piston impeller that moves back and
forth with the changing direction of a magnet field. The magnetic
field may result from electrical current flowing through a coil. As
the current reverses direction, so does the magnetic field and the
impeller. Such pumps can be described as magnetically actuated,
because the means for actuating the driving element is
magnetic.
[0034] The present disclosure also includes a method and apparatus
for cooling without the use of a pump. In such case, the heat
absorbed from the heat exchangers alters the characteristics of the
fluid. Such an alteration--a change in density or viscosity--drives
the flow of the fluid between the heat exchangers.
[0035] The present disclosure exploits some of the properties of a
fluid near or above its critical pressure, which enable a reduction
in the size of such components as heat exchangers and a pump. These
reductions also allow for the process to use less energy. The said
fluid is may be carbon dioxide, water, air or a natural
hydrocarbon.
[0036] Heat transfer can be further improved with the addition of
additives to fluid, such as thermally conductive nanoparticles.
Such additives improve the heat transfer characteristics of the
fluid, such as thermal conductivity. Nanoparticles may also provide
a mechanism for inducing fluid flow in EHD devices. In addition,
additives can be added to increase the heat capacity of the fluid
which helps in reducing the flow rate of the fluid required to
cooling certain heat load.
[0037] Another way to improve heat transfer is to limit or
eliminate lubricants that might be contained in the fluid. Such
lubricants would normally leak from the pump or be added to the
fluid to increase the mechanical performance of the system. Such
lubricants may coat the heat transfer area effectively reducing the
heat transfer efficiencies. In a preferred embodiment of this
disclosure, the pump--if used at all--is operated without the aid
of lubricants and lubricants in the fluid are avoided.
[0038] All of the components and interconnections of the apparatus
may be connected and sealed into one package. The entire package is
contacted with the external surface of a device element and heat is
transferred between the device element and the apparatus. In some
cases, the components of the cooling apparatus may also be
distributed across more than one device element rather than sealed
into a single package. For example, a single heat-rejecting heat
exchanger might serve all sub-assemblies of an apparatus in a
device, not just one of them.
[0039] In one preferred embodiment, FIG. 1 shows a schematic of the
cycle components of the present disclosure. As detailed and labeled
in the diagram, the apparatus is comprised of a pump 13 and heat
exchangers for heat rejection 14 and heat acceptance 11 in a closed
loop with all components connected. Said apparatus has a regulating
means and sensors to monitor and control performance and
environmental conditions. For example, a sensor can relay
temperature information to a control mechanism or software that in
turn causes the pump to increase (or decrease) speed so as to vary
the rate of fluid flow, and by consequence, the rate of heat
dissipated by the apparatus. If the temperature is too high, fluid
flow is increased; if the temperature is too low, fluid flow is
decreased. Any method of control can be integrated into the cooling
device. Power to said apparatus may be derived from the public net
of the device or from an independent source. A public net is a
circuit contained within the device that derives electric power
from a power source that is also contained within the device. It
supplies power to all components of the device, hence its
description as "public" within the device itself. Such internal
power sources typically rectify power that is available from
commercial nets. The apparatus as disclosed herein may derive power
internally from the public net, or it may be supplied by a separate
electrical connection to an independent, commercial net.
[0040] The apparatus attaches to the packaging of the integrated
circuit and at least one heat exchanger is near or in contact with
said device. The heat accepting exchanger 11 of the system faces
toward said packaging of the device and is directly in thermal
contact with it. Heat exchanger 11 may be located in any position
relative to the device, for example above or below the heat source
15, and it may have any suitable configuration. The heat rejecting
exchanger 14 faces away from said device. Heat exchanger 14 may be
located in any position relative to the device and may have any
suitable configuration. A fan that is directed toward heat
exchanger 14 may be used to discharge heat from the closed
loop.
[0041] The heat exchanger, or exchangers, used in the apparatus are
preferably of a microchannel type, in which case the channel
dimensions are less than 1 millimeter in cross-sectional length,
width or diameter. The smaller the channel dimension, the larger
the wall surface area can be, and hence, the more area there is for
heat transfer. Within limits determined by the manufacturability of
the channels and the increase in pressure drop, and with it power
to drive the pump, channels should be as small as possible.
[0042] The heat exchanger may be integrated into the device,
typically as part of the device "package," i.e., components,
adhesives and sealants that hold the device together as a single
unit. For example, the heat rejecter may be mounted atop an
integrated circuit, with a fan, and continuously blow heat away
from the device package. The heat accepter, meanwhile, by be
contained within the device package in the form of a microchannel
heat exchanger that is in direct contact with the integrated
circuit itself, or more likely, in direct contact with a heat sink
that is itself in contact with the integrated circuit.
[0043] The pump can be selected from commercially available models
such as Thar Technologies' P-10, P-50 or P-200 Series pumps, or can
be designed to suit the specific cooling application.
[0044] In another preferred embodiment, there is a heat exchanger
in addition to the one or more heat exchangers within the single
unit packaging of the apparatus. Said additional heat exchanger is
external to the apparatus but still is connected to the loop of the
components within the single apparatus. Piping connects said
external heat exchanger to the components within the apparatus
packaging, providing a means for fluid flow between components of
the cooling apparatus. The external heat exchanger faces away from
the device. A fan may be attached to an external heat-rejecting
heat exchanger is used to discharge heat from the closed loop.
[0045] In electronic devices such as microcomputers, the heat
dissipated from an integrated circuit can range from 25 to 1,000
watts, and more typically between 50 and 200 watts. The area
available for contact by the heat accepter against such an
integrated circuit can rage from between 0.1 square inches and
nearly 4.0 square inches. This combination of heat dissipation and
area available calls for heat acceptors that are capable of
removing as much as 1,000 watts per square inch, but typically in a
range of 50 to 300 watts per square inch. The flow rate for a fluid
above the critical point that is removing heat at this rate can be
measured in milliliters per minute. For carbon dioxide, the rate is
between 200 and 1,000 milliliters per minute.
[0046] In another preferred embodiment, FIG. 2 shows a schematic of
the cycle components of the present disclosure in which case the
pump is omitted. As detailed and labeled in FIG. 2, the apparatus
is comprised of at least one or more heat exchangers for heat
rejection 14 and heat acceptance 11 in a closed, connected loop.
Said apparatus has a regulating means and sensors to monitor
performance and environmental conditions. In contrast to the pumped
apparatus, described above, the sensor output might be used to
control the speed of a fan that blows cooling air against the heat
rejecter. The temperature difference between components 14 and 11
causes a density gradient that drives fluid flow between them. Low
viscosity of the fluid around the critical point also reduces the
resistance of the fluid to flow.
[0047] The apparatus attaches to the packaging of the integrated
circuit and at least one heat exchanger is near or in contact with
said packaging. The heat-accepting heat exchanger 15 of the system
faces toward said packaging of the device and is directly in
contact with it. The heat-rejecting heat exchanger 14 faces away
from said packaging. A fan attached to the heat-rejecting heat
exchanger 14 is used to discharge heat from the closed loop.
[0048] The heat exchanger, or exchangers, used in the apparatus are
preferably of a microchannel type, in which case the channel
dimensions are less than 1 millimeter in cross-sectional length,
width or diameter. The smaller the channel dimension, the larger
the wall surface area can be, and hence, the more area there is for
heat transfer. Within limits determined by the manufacturability of
the channels and the increase in pressure drop, and with it power
to drive the pump, channels should be as small as possible.
[0049] The heat exchanger may be integrated into the device,
typically as part of the device "package," i.e., components,
adhesives and sealants that hold the device together as a single
unit. For example, the heat rejector may be mounted atop an
integrated circuit, with a fan, and continuously blow heat away
from the device package. The heat accepter, meanwhile, by be
contained within the device package in the form of a microchannel
heat exchanger that is in direct contact with the integrated
circuit itself, or more likely, in direct contact with a heat sink
that is itself in contact with the integrated circuit.
[0050] In another preferred embodiment, there is a heat exchanger
in addition to the one or more heat exchangers within the single
unit packaging of the apparatus. Said additional heat exchanger is
external to the apparatus but still is connected to the loop of the
components within the single cooling apparatus. Piping connects
said external heat exchanger to the other components within the
apparatus, providing a means for fluid flow between said components
of the cooling apparatus. The external heat exchanger faces away
from the device packaging. A fan attached to the heat-rejecting
heat exchanger is used to discharge heat from the closed loop.
[0051] There is a plurality of advantages that may be inferred from
the present disclosure arising from the various features of the
apparatus, systems and methods described herein. It will be noted
that other embodiments of each of the apparatuses, systems and
methods of the present disclosure may not include all of the
features described yet still benefit from at least some of the
inferred advantages of such features. Those of ordinary skill in
the art may readily devise their own implementations of an
apparatus, system and method that incorporate one or more of the
features of the present disclosure and fall within the spirit and
scope of the disclosure.
EXAMPLE 1
[0052] In the case of carbon dioxide, the fluid would be maintained
at a pressure above 1,070 pounds per sq. in. (absolute). Heat
capacity is typically between 0.4 and 1.0 Btu per pound-.degree. R,
except near the critical point, at which it can jump up to 30 Btu
per pound-.degree. R, Thermal conductivity increases by a factor of
almost four around the critical temperature. These conditions
promote efficient heat acceptance and rejection when heat is
exchanged against ambient air. The pressure difference between the
heat rejecter and heat accepter is that which corresponds to the
pressure drop of the apparatus, and can be as low as a few pounds
per square inch. This difference is small enough to be overcome
with a small pump.
EXAMPLE 2
[0053] In the case of a pumpless scheme, as shown in FIG. 2, flow
is assured by a density gradient, aided by the low viscosity of the
fluid near or above the critical point. In the case of carbon
dioxide. Density at the critical temperature is 0.63 g/ml at a
pressure of 1,100 pounds per sq. inch and drops quickly to half of
this density with only a 5.degree. F. temperature rise. Viscosity,
meanwhile, remains low, ranging from 0.047 centipoise at the
critical temperature to 0.023 centipoise at 93.degree. F., both
conditions at 1,100 psi.
[0054] Referring to FIG. 3, the microchannel cooling system 1
includes a mechanism 13 to impel a fluid, a microchannel heat
exchanger 11 that accepts heat picked up from a target device,
another heat exchanger 14 that rejects heat picked up by the heat
exchanger that accepts heat and the associated piping 16, controls
and valves. The cooling apparatus may be used for refrigerating or
cooling a target device. In the case of refrigeration to
sub-ambient temperatures, the system's fluid impeller 13 could be
compressor and there would also be a fluid expansion device 15 that
constricts fluid flow in such a way that higher pressure is
maintained between the compressor outlet and through the heat
exchanger 11 that rejects heat, while lower pressure is maintained
from the inlet of the heat exchanger 11 that rejects heat to the
inlet of the compressor. Such expansion devices may take any of
several forms known to the art of refrigeration, and in particular
to this invention may take the form of fixed- or variable-width
orifices, as well as capillary tubes of sufficient length to
provide adequate pressure drop. In the case of cooling to ambient
temperatures, a pump may be used without the need for a
fluid-expansion constrictor. The fluid may be any of several types
common to heat transfer, including but not limited to water,
ammonia, sulfur dioxide, chlorofluorocarbon, hydrofluorocarbon,
hydrocarbon, carbon dioxide, or a combination thereof. The fluid
used in the system may be in liquid or gaseous state, as well as in
a supercritical state.
[0055] One embodiment of the current invention is shown in FIG. 4,
a printed circuit board 2 that includes a heat-emitting microchip
21, circuit line traces (not shown) mounted on its surface and a
tab for electrical connections 22 along one edge. Additional tabs
23 and A1 are meant for insertion into connectors (not shown) to
the heat exchanger A4 that resides within the structure of the
laminated board between regular circuit-board laminations A3. At
the outer edge of these tabs can be seen the microchannels A2 of
the heat exchanger A4. Also seen in Detail A is part of one of the
surface mounted devices, shown as A5. The heat exchanger A4 can
reside at any layer position, be it top, bottom or laminated
between the top and bottom (as shown). Also, the connection tabs 23
can be relocated to any other position along the edges of the
printed circuit board, or they can be replaced entirely by
connections that are placed on the top or bottom surface of the
board. FIG. 3 merely represents one example of a board
configuration. What is common to all configurations, however, is
the heat exchanger that accepts heat has a thin profile that is
preferably, less than 1.0 millimeters and more preferably less than
10 mils, which is similar to the thickness of copper-clad laminates
that make up most of the printed circuit board structure. The heat
exchanger that accepts heat may be formed of materials from the
group consisting of metallic, ceramic, polymeric or a combination
thereof
[0056] FIG. 5 shows a cross section of the heat exchanger that
accepts heat. The heat exchanger 3 consists of a substrate 31 onto
which the microchannels 32 are formed and a top layer 33 that bonds
to the unpatterned areas of the substrate to form a capping layer
above the microchannels. Channels can be straight or meandering.
They may be formed by any of several methods known to the art of
image transference onto surfaces. The path followed by the channels
might follow a pattern that is transferred from a drawing or
photograph, as in the cases of photolithography and embossing.
[0057] FIG. 6 shows a cross-sectional view of a printed circuit
board 4. The heat exchanger 41 that accepts heat is positioned with
its microchannels passing under an integrated circuit 42 that is
mounted on top of the board. The heat exchanger forms one of the
lamination layers that make up the entire board 4. In the
embodiment shown in FIG. 6, the heat exchanger 41 is separated from
the integrated circuit 42 by at least one layer of epoxy lamination
43, though which an array of thermal vias 44 facilitates direct
contact with the heat-emitting device that is mounted on top of the
board, which can be an integrated circuit, through vertical,
thermal conductors.
[0058] The heat exchanger that accepts heat may be positioned
within a printed circuit board as any layer in the lamination
process. Furthermore, it may be added to the top or bottom sides of
a printed circuit board. Thermal vias contribute greatly to the
transference of heat from the heat-emitting devices to the heat
exchanger that accepts heat within the board. Thermal vias, as
shown in FIG. 6, may be present in the printed circuit board but
are not a required condition.
[0059] The cooling system of the present invention is capable of
withstanding internal pressures that might be encountered with
heat-transfer fluids undergoing evaporation as they absorb heat, or
might be encountered as a result of a pressure differential that
develops between the inlet and the outlet of the microchannel
array. Included in this group of fluids are such environmentally
benign materials as water and carbon dioxide.
EXAMPLE 3
[0060] A heat exchanger that accepts heat measuring 100.times.100
millimeters square and 0.010 inches in thickness is constructed
with an array of 80 microchannels running through the center of the
lamination, from one side to the opposite side, and laminated into
a printed circuit board configuration of layers with FR-4 epoxy
insulation. The channels measured nominally 200 microns wide by 100
microns deep and were separated by a distance of nominally 100
microns. In the center of the board was a heat source measuring
27.times.27 millimeters. The microchannel heat exchanger that
accepts heat was separated from direct contact with the heat source
by the distance of one layer of FR-4 but was in indirect contact
with the heat source through a square array of 81 thermal vias.
[0061] Heat emitted by the heater was from 15-55 watts. Into this
heat exchanger was passed carbon dioxide at 84 bar and 37.degree.
C. inlet temperature, and at flowrates ranging between 0.18 and
1.70 gm per sec. As shown in FIG. 7, the temperature at the center
of the heat source can be controlled to under 90.degree. C., which
corresponds to a temperature difference between the center junction
of the hot chip and the fluid flowing though microchannels
(represented as the y-axis of FIG. 7) of about 53.degree. C., at a
CO.sub.2 flow rate as low as approximately 0.65 gm/sec, given a
heating rate of 40 watts. Pressure drop at this flow rate is
approximately 20 psi.
[0062] A single run of microchannels in the heat exchanger that
accepts heat may serve more than one integrated circuit on a
printed circuit board, however. FIG. 8 shows a layout of chips on a
printed circuit board 6. The board 6 holds an assortment of
integrated circuits. The integrated circuits 62 that are above the
path of the microchannels are cooled. The other integrated circuits
63 may not be directly cooled by the single run of microchannels;
however, more than one run of microchannels is possible, such that
chips 63 are also cooled. Given the heat-removal capability of just
one such bundle of microchannels, as demonstrated in the example,
it is possible to remove most of the heat dissipated by
surface-mounted devices on a printed circuit board.
[0063] The heat exchanger that accepts heat is connected to the
rest of the cooling system first by connectors that either deliver
and distribute fluid to the microchannels at one end of the channel
array and then gather the fluid at the discharge end. Connectors
lead into pipes or tubes that direct flow to other system
components: a pump or compressor to impel the fluid throughout the
system; a heat exchanger that rejects heat for purposes of
expelling heat to the environment; and in the case of sub-ambient
refrigeration, an expansion device to relieve the pressure of the
heat-transfer fluid and drive its temperature lower with little
change in enthalpy. The heat-rejecter need not be of a microchannel
design and typically uses blown air as a medium for cooling the
heat-exchange fluid. The location of the pump or compressor depends
on the thermodynamic conditions desired at different points in the
loop.
[0064] The connector is joined to the heat exchanger that accepts
heat in any suitable manner, including but not limited to clamping
or soldering. One way to expose the microchannels outward of a
printed circuit board is by means of connection tabs 61 and 64
(inlet and outlet). These are positioned at opposite edges of the
heat exchanger that accepts heat because the single run of
microchannels is spread directly across the printed circuit board.
It is also possible to direct the microchannels in a broad
90-degree sweep across the board, such that the connection tabs are
on adjacent edges. Alternatively, the microchannels could be turned
around by 180 degrees and exit along the same edge as the inlet.
Connecting through tabs on edges of the heat exchanger that accepts
heat is just one method for passing fluid to and from the heat
exchanger that accepts heat. Edge connection tabs do have the
advantage of taking up only a small amount of space and allow
installation onto boards that are typically placed in slots on
mounting racks. Connection tabs can also be mounted on the
surface.
* * * * *