U.S. patent application number 10/927800 was filed with the patent office on 2006-03-02 for pumped fluid cooling system and method.
This patent application is currently assigned to Cooligy, Inc.. Invention is credited to Kenneth Goodson, Mark Munch, Girish Upadhya, Douglas Werner.
Application Number | 20060042785 10/927800 |
Document ID | / |
Family ID | 35941406 |
Filed Date | 2006-03-02 |
United States Patent
Application |
20060042785 |
Kind Code |
A1 |
Werner; Douglas ; et
al. |
March 2, 2006 |
Pumped fluid cooling system and method
Abstract
The present invention is a pumped fluid cooling system and
method. The pumped fluid cooling system and method includes new
relative magnitudes of advection, convection and spreading
components of the resistance for a pumped fluid system. The pumped
fluid cooling system and method also includes adjusting the
chemical composition of the working fluid, specifically adjusting
the composition and viscosity as the sensitivity to the fluid heat
capacity per unit mas increases.
Inventors: |
Werner; Douglas; (Atherton,
CA) ; Goodson; Kenneth; (Belmont, CA) ; Munch;
Mark; (Los Altos, CA) ; Upadhya; Girish; (San
Jose, CA) |
Correspondence
Address: |
HAVERSTOCK & OWENS LLP
162 NORTH WOLFE ROAD
SUNNYVALE
CA
94086
US
|
Assignee: |
Cooligy, Inc.
|
Family ID: |
35941406 |
Appl. No.: |
10/927800 |
Filed: |
August 27, 2004 |
Current U.S.
Class: |
165/80.4 |
Current CPC
Class: |
F28F 3/12 20130101; F28F
9/0263 20130101; F28F 2260/02 20130101 |
Class at
Publication: |
165/080.4 |
International
Class: |
F28F 7/00 20060101
F28F007/00 |
Claims
1. A pumped fluid cooling system for cooling a device, the pumped
fluid cooling system comprising: a. a heat exchanger, the heat
exchanger including an interface layer coupled to the device for
cooling the device; and b. a fluid pumped through the interface
layer of the heat exchanger, the fluid having an inlet temperature
and an outlet temperature, wherein the pumped fluid cooling system
is configured such that the difference between the fluid outlet
temperature and the fluid inlet temperature is at least 30% of the
difference between a hottest temperature of the fluid in the heat
exchanger and the fluid inlet temperature.
2. The pumped fluid cooling system as claimed in claim 1 further
comprising a plurality of microchannels configured in a
predetermined pattern along the interface layer wherein the
plurality of microchannels have an internal feature size in the
range of 15-300 microns.
3. The pumped fluid cooling system as claimed in claim 2 wherein
the plurality of microchannels have a surface to volume ratio
greater than 1000 m.sup.-1.
4. The pumped fluid cooling system as claimed in claim 1 further
comprising a plurality of pillars configured in a predetermined
pattern along the interface layer wherein the plurality of pillars
have an internal feature size in the range of 15-300 microns.
5. The pumped fluid cooling system as claimed in claim 4 wherein
the plurality of pillars have a surface to volume ratio greater
than 1000 m.sup.-1.
6. The pumped fluid cooling system as claimed in claim 1 further
comprising a microporous structure disposed on the interface layer
wherein a plurality of pores in the microporous structure have an
internal feature size in the range of 15-300 microns.
7. The pumped fluid cooling system as claimed in claim 6 wherein
the plurality of pores of the microporous structure have a surface
to volume ratio greater than 1000 m.sup.-1.
8. The pumped fluid cooling system as claimed in claim 1 wherein a
first surface area of the interface layer that is coupled to the
device is less than or equal to 150% of a second surface area of
the device that is coupled to the interface layer.
9. The pumped fluid cooling system as claimed in claim 1 wherein
the viscosity of the fluid at its average temperature in the heat
exchanger is less than 150% of the viscosity of water.
10. The pumped fluid cooling system as claimed in claim 1 wherein
the heat capacity per unit mass of the fluid at its average
temperature in the heat exchanger is greater than 80% of the heat
capacity per unit mass of water.
11. The pumped fluid cooling system as claimed in claim 1 wherein
the fluid consists of at least 90% water by mass.
12. A method of efficiently cooling a device in a pumped fluid
cooling system, the method comprising: a. decreasing a spread
resistance between an interface layer of a heat exchanger and the
device; b. decreasing a convection resistance between a fluid and
the interface layer of the heat exchanger, wherein the fluid is
pumped through the interface layer, and further wherein the fluid
has an inlet temperature and an outlet temperature; c. increasing
an advection resistance; and d. adjusting the composition of the
fluid to increase the heat capacity per unit mass and decrease the
viscosity, wherein the difference between the fluid outlet
temperature and the fluid inlet temperature is at least 30% of the
difference between a hottest temperature of the fluid in the heat
exchanger and the fluid inlet temperature.
13. The method as claimed in claim 12 wherein the step of
decreasing the convention resistance includes configuring a
plurality of microchannels in a predetermined pattern along the
interface layer wherein the plurality of microchannels have an
internal feature size in the range of 15-300 microns.
14. The method as claimed in claim 13 wherein the plurality of
microchannels have a surface to volume ratio greater than 1000
m.sup.-1.
15. The method as claimed in claim 12 wherein the step of
decreasing the convection resistance includes configuring a
plurality of pillars in a predetermined pattern along the interface
layer wherein the plurality of pillars have an internal feature
size in the range of 15-300 microns.
16. The method as claimed in claim 15 wherein the plurality of
pillars have a surface to volume ratio greater than 1000
m.sup.-1.
17. The method as claimed in claim 12 wherein the step of
decreasing the convection resistance includes disposing a
microporous structure on the interface layer wherein a plurality of
pores in the microporous structure have an internal feature size in
the range of 15-300 microns.
18. The method as claimed in claim 17 wherein the plurality of
pores of the microporous structure have a surface to volume ratio
greater than 1000 m.sup.-1.
19. The method as claimed in claim 12 wherein the step of
decreasing the spread resistance includes reducing a first surface
area of the interface layer that is coupled to the device such that
the first surface area is less than or equal to 150% of a second
surface area of the device that is coupled to the interface
layer.
20. The method as claimed in claim 12 wherein the step of adjusting
the composition of the fluid includes decreasing the viscosity of
the fluid at its average temperature in the heat exchanger, such
that the viscosity is less than 150% of the viscosity of water.
21. The method as claimed in claim 12 wherein the step of adjusting
the composition of the fluid includes increasing the heat capacity
per unit mass of the fluid at its average temperature in the heat
exchanger, such that the heat capacity per unit mass is greater
than 80% of the heat capacity per unit mass of water.
22. The method as claimed in claim 12 wherein the fluid consists of
at least 90% water by mass.
23. A pumped fluid cooling system for cooling a device, the pumped
fluid cooling system comprising: a. means for decreasing a spread
resistance between an interface layer of a heat exchanger and the
device; b. means for decreasing a convection resistance between a
fluid and the interface layer of the heat exchanger, wherein the
fluid is pumped through the interface layer, and further wherein
the fluid has an inlet temperature and an outlet temperature, c.
means for increasing an advection resistance; and d. means for
adjusting the composition of the fluid to increase the heat
capacity per unit mass and decrease the viscosity, wherein the
difference between the fluid outlet temperature and the fluid inlet
temperature is at least 30% of the difference between a hottest
temperature of the fluid in the heat exchanger and the fluid inlet
temperature.
24. The pumped fluid cooling system as claimed in claim 23 wherein
the means for decreasing the convention resistance includes means
for configuring a plurality of microchannels in a predetermined
pattern along the interface layer wherein the plurality of
microchannels have an internal feature size in the range of 15-300
microns.
25. The pumped fluid cooling system as claimed in claim 24 wherein
the plurality of microchannels have a surface to volume ratio
greater than 1000 m.sup.-1.
26. The pumped fluid cooling system as claimed in claim 23 wherein
the means for decreasing the convection resistance includes means
for configuring a plurality of pillars in a predetermined pattern
along the interface layer wherein the plurality of pillars have an
internal feature size in the range of 15-300 microns.
27. The pumped fluid cooling system as claimed in claim 26 wherein
the plurality of pillars have a surface to volume ratio greater
than 1000 m.sup.-1.
28. The pumped fluid cooling system as claimed in claim 23 wherein
the means for decreasing the convection resistance includes means
for disposing a microporous structure on the interface layer
wherein a plurality of pores in the microporous structure have an
internal feature size in the range of 15-300 microns.
29. The pumped fluid cooling system as claimed in claim 28 wherein
the plurality of pores of the microporous structure have a surface
to volume ratio greater than 1000 m.sup.-1.
30. The pumped fluid cooling system as claimed in claim 23 wherein
the means for decreasing the spread resistance includes means for
reducing a first surface area of the interface layer that is
coupled to the device such that the first surface area is less than
or equal to 150% of a second surface area of the device that is
coupled to the interface layer.
31. The pumped fluid cooling system as claimed in claim 23 wherein
the means for adjusting the composition of the fluid includes means
for decreasing the viscosity of the fluid at its average
temperature in the heat exchanger, such that the viscosity is less
than 150% of the viscosity of water.
32. The pumped fluid cooling system as claimed in claim 23 wherein
the means for adjusting the composition of the fluid includes means
for increasing the heat capacity per unit mass of the fluid at its
average temperature in the heat exchanger, such that the heat
capacity per unit mass is greater than 80% of the heat capacity per
unit mass of water.
33. The pumped fluid cooling system as claimed in claim 23 wherein
the fluid consists of at least 90% water by mass.
34. An apparatus for cooling an integrated circuit, the apparatus
comprising: a. a heat exchanger including an interface layer
coupled to the integrated circuit, wherein a first surface area of
the interface layer that is coupled to the integrated circuit is
less than or equal to 150% of a second surface area of the
integrated circuit that is coupled to the interface layer, such
that a spread resistance between the interface layer and the
integrated circuit is decreased; b. a plurality of microchannels
configured in a predetermined pattern along the interface layer
wherein the plurality of microchannels have an internal feature
size in the range of 15-300 microns and a surface to volume ration
greater than 1000 m.sup.-1, such that a convection resistance is
decreased; and c. a fluid pumped through the heat exchanger, such
that a flowrate of the fluid increases an advection resistance,
wherein the fluid consists of at least 90% water by mass.
35. The apparatus as claimed in claim 34 wherein the viscosity of
the fluid at its average temperature in the heat exchanger is less
than 150% of the viscosity of water.
36. The apparatus as claimed in claim 34 wherein the heat capacity
per unit mass of the fluid at its average temperature in the heat
exchanger is greater than 80% of the heat capacity per unit mass of
water.
37. A pumped fluid cooling system for cooling a device, the pumped
fluid cooling system comprising: a. a spread resistance, wherein
the spread resistance is decrease when a heat exchanger including
an interface layer is coupled to the device, further wherein a
first surface area of the interface layer that is coupled to the
device is less than or equal to 150% of a second surface area of
the device that is coupled to the interface layer; b. a convection
resistance, wherein the convection resistance is decreased when a
plurality of microchannels is configured in a predetermined pattern
along the interface layer, and further wherein the plurality of
microchannels have an internal feature size in the range of 15-300
microns and a surface to volume ration greater than 10000 m.sup.-1;
and c. an advection resistance, wherein the advection resistance is
increased when a fluid is pumped through the heat exchanger, such
that a flowrate of the fluid decreases, wherein the fluid consists
of at least 90% water by mass.
38. The pumped fluid cooling system as claimed in claim 37 wherein
the fluid is water.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of
cooling systems. More specifically, the present invention relates
to the field of pumped fluid cooling systems.
BACKGROUND OF THE INVENTION
[0002] In current pumped fluid cooling systems as depicted in FIG.
1, the total "temperature budget," or the difference between the
peak device temperature (T.sub.Device, peak) and the temperature of
the cold fluid inlet (T.sub.fluid inlet) is consumed by the total
heat power (q(W)) flowing through four separate resistances.
[0003] FIG. 1 illustrates such a resistance model for an exemplary
pumped fluid cooling system. The device/attach resistances
(R.sub.Device and attach) dissipate a significant amount of q(W).
However, the device/attach resistances are not related to the
present invention and need no further explanation. The spreading
resistance (R.sub.spread) accounts for spreading the heat from a
small device into a larger heat exchanger (hx). The R.sub.spread
increases with the ratio of the hx to device area. The convection
resistance (R.sub.convention) accounts for conducting the heat into
the fluid from the hx walls. It is equal to 1/hA, where h is the
convection coefficient and A is the total wetted surface area
within the hx. This resistance increases strongly with increasing
values of the minimum feature size of the hydraulic diameter
(d).
[0004] Still referring to FIG. 1, the advection resistance
(R.sub.advection) accounts for the heating of the fluid as it
transverses the hx, and is approximately equal to C/mc, where m is
the mass flowrate and c is the specific heat capacity per unit mass
and C is a constant near 0.5. Traditional heat exchangers use
relatively large dimensions ranging in size from two times to four
times the size of the area of the device being cooled. These
dimensions result in relatively large values of R.sub.spread.
Traditional heat exchangers also have large internal features,
usually 0.3 mm or larger. These dimensions result in relatively
large values of R.sub.convection. These relatively large values of
R.sub.spread and R.sub.convection result in an inefficient pumped
fluid system.
[0005] Referring now to FIG. 2, a resistance model of a current
pumped fluid system 20 of the prior art is illustrated. As stated
earlier, current pumped fluid systems 20 utilize heat exchangers
that are two to four times the size of the device being cooled.
This current design therefore includes a large spreading resistance
22, which continues to increase as the surface area ratio of
(hx/device being cooled) increases. Furthermore, current pumped
fluid systems 20 have large hydraulic diameters (d). Referring back
to the R.sub.convection formula 1/hA, as the hx d increases the
total wetted surface area A decreases, thus according to 1/hA,
causing a relatively large convection resistance 24.
[0006] Because the current pumped fluid systems 20 have large
values of d (and very small values of A), a great deal of the
temperature budget is used in this part of the resistance chain. To
stay within the total temperature budget at this point requires the
current pumped fluid system 20 to have a very small advection
resistance 26. Therefore, referring back to the R.sub.advection
formula C/cm, the R.sub.advection may be reduced significantly by
creating very large mass flow rates m. Of course, this puts large
demands on the pump requirements for a pumped fluid system 20.
[0007] It should also be noted that pumped fluid cooling systems of
the prior art require specific fluids to operate effectively with
the system, e.g., to avoid freezing at low temperatures. Such
fluids include those with high concentrations of ethylene glycol or
propylene glycol, or similar substances. The characteristics of
such fluids include a low heat capacity and a high viscosity and do
not function well in a system having a reduced flowrate.
SUMMARY OF THE INVENTION
[0008] The present invention is a pumped fluid cooling system and
method. The pumped fluid cooling system and method includes new
relative magnitudes of advection, convection and spreading
components of the resistance for a pumped fluid system. The pumped
fluid cooling system and method also includes adjusting the
chemical composition of the working fluid, specifically adjusting
the composition and viscosity as the sensitivity to the fluid heat
capacity per unit mass increases.
[0009] In one aspect of the present invention, a pumped fluid
cooling system for cooling a device comprises a heat exchanger, the
heat exchanger including an interface layer coupled to the device
for cooling the device and a fluid pumped through the interface
layer of the heat exchanger, the fluid having an inlet temperature
and an outlet temperature, wherein the pumped fluid cooling system
is configured such that the difference between the fluid outlet
temperature and the fluid inlet temperature is at least 30% of the
difference between a hottest temperature of the fluid in the heat
exchanger and the fluid inlet temperature.
[0010] The pumped fluid cooling system further comprises a
plurality of microchannels configured in a predetermined pattern
along the interface layer wherein the plurality of microchannels
have an internal feature size in the range of 15-300 microns. The
plurality of microchannels have a surface to volume ratio greater
than 1000 m.sup.-1. The pumped fluid cooling system further
comprises a plurality of pillars configured in a predetermined
pattern along the interface layer wherein the plurality of pillars
have an internal feature size in the range of 15-300 microns. The
plurality of pillars have a surface to volume ratio greater than
1000 m.sup.-1.
[0011] The pumped fluid cooling system further comprises a
microporous structure disposed on the interface layer wherein a
plurality of pores in the microporous structure have an internal
feature size in the range of 15-300 microns. The plurality of pores
of the microporous structure have a surface to volume ratio greater
than 1000 m.sup.-1. A first surface area of the interface layer
that is coupled to the device is less than or equal to 150% of a
second surface area of the device that is coupled to the interface
layer. The viscosity of the fluid at its average temperature in the
heat exchanger is less than 150% of the viscosity of water. The
heat capacity per unit mass of the fluid at its average temperature
in the heat exchanger is greater than 80% of the heat capacity per
unit mass of water. The fluid consists of at least 90% water by
mass.
[0012] In another aspect of the present invention, a method of
efficiently cooling a device in a pumped fluid cooling system
comprises decreasing a spread resistance between an interface layer
of a heat exchanger and the device, decreasing a convection
resistance between a fluid and the interface layer of the heat
exchanger, wherein the fluid is pumped through the interface layer,
and further wherein the fluid has an inlet temperature and an
outlet temperature, increasing an advection resistance and
adjusting the composition of the fluid to increase the heat
capacity per unit mass and decrease the viscosity, wherein the
difference between the fluid outlet temperature and the fluid inlet
temperature is at least 30% of the difference between a hottest
temperature of the fluid in the heat exchanger and the fluid inlet
temperature.
[0013] The step of decreasing the convention resistance includes
configuring a plurality of microchannels in a predetermined pattern
along the interface layer wherein the plurality of microchannels
have an internal feature size in the range of 15-300 microns. The
plurality of microchannels have a surface to volume ratio greater
than 1000 m.sup.-1. The step of decreasing the convection
resistance includes configuring a plurality of pillars in a
predetermined pattern along the interface layer wherein the
plurality of pillars have an internal feature size in the range of
15-300 microns. The plurality of pillars have a surface to volume
ratio greater than 1000 m.sup.-1.
[0014] The step of decreasing the convection resistance includes
disposing a microporous structure on the interface layer wherein a
plurality of pores in the microporous structure have an internal
feature size in the range of 15-300 microns. The plurality of pores
of the microporous structure have a surface to volume ratio greater
than 1000 m.sup.-1. The step of decreasing the spread resistance
includes reducing a first surface area of the interface layer that
is coupled to the device such that the first surface area is less
than or equal to 150% of a second surface area of the device that
is coupled to the interface layer. The step of adjusting the
composition of the fluid includes decreasing the viscosity of the
fluid at its average temperature in the heat exchanger, such that
the viscosity is less than 150% of the viscosity of water. The step
of adjusting the composition of the fluid includes increasing the
heat capacity per unit mass of the fluid at its average temperature
in the heat exchanger, such that the heat capacity per unit mass is
greater than 80% of the heat capacity per unit mass of water. The
fluid consists of at least 90% water by mass.
[0015] In yet another aspect of the present invention, a pumped
fluid cooling system for cooling a device comprises means for
decreasing a spread resistance between an interface layer of a heat
exchanger and the device, means for decreasing a convection
resistance between a fluid and the interface layer of the heat
exchanger, wherein the fluid is pumped through the interface layer,
and further wherein the fluid has an inlet temperature and an
outlet temperature, means for increasing an advection resistance
and means for adjusting the composition of the fluid to increase
the heat capacity per unit mass and decrease the viscosity, wherein
the difference between the fluid outlet temperature and the fluid
inlet temperature is at least 30% of the difference between a
hottest temperature of the fluid in the heat exchanger and the
fluid inlet temperature.
[0016] The means for decreasing the convention resistance includes
means for configuring a plurality of microchannels in a
predetermined pattern along the interface layer wherein the
plurality of microchannels have an internal feature size in the
range of 15-300 microns. The plurality of microchannels have a
surface to volume ratio greater than 1000 m.sup.-1. The means for
decreasing the convection resistance includes means for configuring
a plurality of pillars in a predetermined pattern along the
interface layer wherein the plurality of pillars have an internal
feature size in the range of 15-300 microns. The plurality of
pillars have a surface to volume ratio greater than 1000
m.sup.-1.
[0017] The means for decreasing the convection resistance includes
means for disposing a microporous structure on the interface layer
wherein a plurality of pores in the microporous structure have an
internal feature size in the range of 15-300 microns. The plurality
of pores of the microporous structure have a surface to volume
ratio greater than 1000 m.sup.-1. The means for decreasing the
spread resistance includes means for reducing a first surface area
of the interface layer that is coupled to the device such that the
first surface area is less than or equal to 150% of a second
surface area of the device that is coupled to the interface
layer.
[0018] The means for adjusting the composition of the fluid
includes means for decreasing the viscosity of the fluid at its
average temperature in the heat exchanger, such that the viscosity
is less than 150% of the viscosity of water. The means for
adjusting the composition of the fluid includes means for
increasing the heat capacity per unit mass of the fluid at its
average temperature in the heat exchanger, such that the heat
capacity per unit mass is greater than 80% of the heat capacity per
unit mass of water. The fluid consists of at least 90% water by
mass.
[0019] In yet another aspect of the present invention, an apparatus
for cooling an integrated circuit comprises a heat exchanger
including an interface layer coupled to the integrated circuit,
wherein a first surface area of the interface layer that is coupled
to the integrated circuit is less than or equal to 150% of a second
surface area of the integrated circuit that is coupled to the
interface layer, such that a spread resistance between the
interface layer and the integrated circuit is decreased, a
plurality of microchannels configured in a predetermined pattern
along the interface layer wherein the plurality of microchannels
have an internal feature size in the range of 15-300 microns and a
surface to volume ration greater than 1000 m.sup.-1, such that a
convection resistance is decreased and a fluid pumped through the
heat exchanger, such that a flowrate of the fluid increases an
advection resistance, wherein the fluid consists of at least 90%
water by mass. The viscosity of the fluid at its average
temperature in the heat exchanger is less than 150% of the
viscosity of water. The heat capacity per unit mass of the fluid at
its average temperature in the heat exchanger is greater than 80%
of the heat capacity per unit mass of water.
[0020] In yet another aspect of the present invention, a pumped
fluid cooling system for cooling a device comprises a spread
resistance, wherein the spread resistance is decrease when a heat
exchanger including an interface layer is coupled to the device,
further wherein a first surface area of the interface layer that is
coupled to the device is less than or equal to 150% of a second
surface area of the device that is coupled to the interface layer,
a convection resistance, wherein the convection resistance is
decreased when a plurality of microchannels is configured in a
predetermined pattern along the interface layer, and further
wherein the plurality of microchannels have an internal feature
size in the range of 15-300 microns and a surface to volume ration
greater than 1000 m.sup.-1 and an advection resistance, wherein the
advection resistance is increased when a fluid is pumped through
the heat exchanger, such that a flowrate of the fluid decreases,
wherein the fluid consists of at least 90% water by mass. The
pumped fluid cooling system as claimed in claim 37 wherein the
fluid is water.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a graphical representation illustrating an
exemplary temperature budget resistance model.
[0022] FIG. 2 is a graphical representation illustrating a
temperature budget resistance model according to the prior art.
[0023] FIG. 3 is a graphical representation illustrating a
temperature budget resistance model according to an embodiment of
the present invention.
[0024] FIG. 4A is a graphical representation illustrating a top
view of a manifold layer of a heat exchanger in accordance with the
present invention.
[0025] FIG. 4B is a graphical representation illustrating an
exploded view of a heat exchanger with a manifold layer in
accordance with the present invention.
[0026] FIG. 5 is a graphical representation illustrating a
perspective view of an interface layer having a micro-pin layer and
a foam layer in accordance with the present invention.
[0027] FIG. 6 is a flowchart illustrating a method of efficiently
cooling a device in a pumped fluid cooling system in accordance
with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0028] FIG. 3 is a graphical representation of the preferred
embodiment of the present invention. The preferred embodiment of
the present invention includes new relative magnitudes of the
advection 36, convection 34, and spreading 32 components of the
resistance for a pumped fluidic system (PFS) 30, which enable lower
pump flowrates and, consequently, pumps that are smaller and
consume less power. The new relative magnitudes of these
resistances are enabled by a micro hx as described below with
feature sizes in the range of 15-300 microns. Still referring to
FIG. 3, this micro hx of the PFS 30 of the preferred embodiment of
the present invention allows for a smaller spread resistance 32 and
smaller convection resistance 34, thereby conserving the
temperature budget. This conservation allows for a higher advection
36 component.
[0029] Referring back to the advection formula once again, C/mc
where m is the flowrate, reducing the flowrate m will cause the
advection 36 component to increase. This increase in the advection
36 component may continue until the total temperature budget is
spent. Therefore, in effect, the decrease spreading 32 and
convection 34 components allow for a micro hx having a smaller
flowrate m and higher advection 36 component, thereby resulting in
less work for the pump, and thus a more efficient PFS 30.
[0030] The micro hx of the present invention decreases the
spreading 32 component by reducing the size of the cooling surface
of the micro hx such that it is less than or equal to 150% of the
size of the surface of the device that is being cooled by the micro
hx. The convection 34 component is again equal to 1/hA, where h is
the convection coefficient and A is the total wetted surface area
of the micro hx. This convection 34 component is decreased as the
wetted surface area in the micro hx is greatly increased relative
to current pumped fluidic systems. The wetted surface area of the
micro hx is increased by incorporating pillars, foam and/or
channels having internal feature sizes in the range of 15-300
microns and surface to volume ratios greater than 1000 m.sup.-1.
The structure of the micro hx is explained in greater detail
below.
[0031] In order to better understand the description of the
preferred embodiment of the present invention described above, it
is necessary to also understand the structure and operation of a
micro hx according to an embodiment of the present invention.
However, it should be understood that the description of the heat
exchanger below represents but one design applicable to the present
invention, and it has been contemplated that the system and method
of the present invention may be applied to any heat exchanger
having the requisite dimensions of the preferred embodiment of the
present invention.
[0032] Generally, a heat exchanger captures thermal energy
generated from a heat source by passing fluid through selective
areas of the interface layer which is preferably coupled to the
heat source. In particular, the fluid is directed to specific areas
in the interface layer to cool the hot spots and areas around the
hot spots to generally create temperature uniformity across the
heat source while maintaining a small pressure drop within the heat
exchanger. As discussed in the different embodiments below, the
heat exchanger utilizes a plurality of apertures, channels and/or
fingers in the manifold layer as well as conduits in the
intermediate layer to direct and circulate fluid to and from
selected hot spot areas in the interface layer. Alternatively, the
heat exchanger includes several ports which are specifically
disposed in predetermined locations to directly deliver fluid to
and remove fluid from the hot spots to effectively cool the heat
source.
[0033] FIG. 4A illustrates a top view of an exemplary manifold
layer 106 of the present invention. In particular, as shown in FIG.
4B, the manifold layer 106 includes four sides as well as a top
surface 130 and a bottom surface 132. However, the top surface 130
is removed in FIG. 4A to adequately illustrate and describe the
workings of the manifold layer 106. As shown in FIG. 4A, the
manifold layer 106 has a series of channels or passages 116, 118,
120, 122 as well as ports 108, 109 formed therein. The fingers 118,
120 extend completely through the body of the manifold layer 106 in
the Z-direction, as shown in FIG. 4B. Alternatively, the fingers
118 and 120 extend partially through the manifold layer 106 in the
Z-direction and have apertures as shown in FIG. 4A. In addition,
passages 116 and 122 extend partially through the manifold layer
106. The remaining areas between the inlet and outlet passages 116,
120, designated as 107, extend from the top surface 130 to the
bottom surface 132 and form the body of the manifold layer 106.
[0034] As shown in FIG. 4A, the fluid enters the manifold layer 106
via the inlet port 108 and flows along the inlet channel 116 to
several fingers 118 which branch out from the channel 116 in
several X and Y directions to apply fluid to selected regions in
the interface layer 102. The fingers 118 are preferably arranged in
different predetermined directions to deliver fluid to the
locations in the interface layer 102 corresponding to the areas at
and near the hot spots in the heat source. These locations in the
interface layer 102 are hereinafter referred to as interface hot
spot regions. The fingers are configured to cool stationary
interface hot spot regions as well as temporally varying interface
hot spot regions. As shown in FIG. 4A, the channels 116, 122 and
fingers 118, 120 are disposed in the X and Y directions in the
manifold layer 106 and extend in the Z direction to allow
circulation between the manifold layer 106 and the interface layer
102. Thus, the various directions of the channels 116, 122 and
fingers 118, 120 allow delivery of fluid to cool hot spots in the
heat source 99 and/or minimize pressure drop within the heat
exchanger 100.
[0035] The arrangement as well as the dimensions of the fingers
118, 120 are determined in light of the hot spots in the heat
source 99 that are desired to be cooled. The locations of the hot
spots as well as the amount of heat produced near or at each hot
spot are used to configure the manifold layer 106 such that the
fingers 118, 120 are placed above or proximal to the interface hot
spot regions in the interface layer 102. The manifold layer 106
allows one phase and/or two-phase fluid to circulate to the
interface layer 102 without allowing a substantial pressure drop
from occurring within the heat exchanger 100. The fluid delivery to
the interface hot spot regions creates a uniform temperature at the
interface hot spot region as well as areas in the heat source
adjacent to the interface hot spot regions.
[0036] The dimensions as well as the number of channels 116 and
fingers 118 depend on a number of factors. In one embodiment, the
inlet and outlet fingers 118, 120 have the same width dimensions.
Alternatively, the inlet and outlet fingers 118, 120 have different
width dimensions. The width dimensions of the fingers 118, 120 are
within the range of and including 0.25-1.00 millimeters. In one
embodiment, the inlet and outlet fingers 118, 120 have the same
length and depth dimensions. Alternatively, the inlet and outlet
fingers 118, 120 have different length and depth dimensions. In
another embodiment, the inlet and outlet fingers 118, 120 have
varying width dimensions along the length of the fingers. The
length dimensions of the inlet and outlet fingers 118, 120 are
within the range of and including 0.5 millimeters to three times
the size of the heat source length. In addition, the fingers 118,
120 have a height or depth dimension within the range and including
0.25-1.00 millimeters. In addition, less than 10 or more than 30
fingers per centimeter are disposed in the manifold layer 106.
However, it is apparent to one skilled in the art that between 10
and 30 fingers per centimeter in the manifold layer is also
contemplated.
[0037] It is contemplated within the present invention to tailor
the geometries of the fingers 118, 120 and channels 116, 122 to be
in non-periodic arrangement to aid in optimizing hot spot cooling
of the heat source. In order to achieve a uniform temperature
across the heat source 99, the spatial distribution of the heat
transfer to the fluid is matched with the spatial distribution of
the heat generation. As the fluid flows along the interface layer
102, its temperature increases and as it begins to transform to
vapor under two-phase conditions. Thus, the fluid undergoes a
significant expansion which results in a large increase in
velocity. Generally, the efficiency of the heat transfer from the
interface layer to the fluid is improved for high velocity flow.
Therefore, it is possible to tailor the efficiency of the heat
transfer to the fluid by adjusting the cross-sectional dimensions
of the fluid delivery and removal fingers 118, 120 and channels
116, 122 in the heat exchanger 100. This effect will also be
realized in single phase flow.
[0038] For example, a particular finger can be designed for a heat
source where there is higher heat generation near the inlet. In
addition, it may be advantageous to design a larger cross section
for the regions of the fingers 118, 120 and channels 116, 122 where
a mixture of fluid and vapor is expected. Although not shown, a
finger can be designed to start out with a small cross sectional
area at the inlet to cause high velocity flow of fluid. The
particular finger or channel can also be configured to expand to a
larger cross-section at a downstream outlet to cause a lower
velocity flow. This design of the finger or channel allows the heat
exchanger to minimize pressure drop and optimize hot spot cooling
in areas where the fluid increases in volume, acceleration and
velocity due to transformation from liquid to vapor in two-phase
flow.
[0039] In addition, the fingers 118, 120 and channels 116, 122 can
be designed to widen and then narrow again along their length to
increase the velocity of the fluid at different places in the
microchannel heat exchanger 100. Alternatively, it may be
appropriate to vary the finger and channel dimensions from large to
small and back again many times over in order to tailor the heat
transfer efficiency to the expected heat dissipation distribution
across the heat source 99. It should be noted that the above
discussion of the varying dimensions of the fingers and channels
also apply to the other embodiments discussed and is not limited to
this embodiment.
[0040] Alternatively, as shown in FIG. 4A, the manifold layer 106
includes one or more apertures 119 in the inlet fingers 118. In a
three tier heat exchanger 100, the fluid flowing along the fingers
118 flows down the apertures 119 to the intermediate layer 104. In
addition, as shown in FIG. 4A. the manifold layer 106 includes
apertures 121 in the outlet fingers 120. In the three tier heat
exchanger 100, the fluid flowing from the intermediate layer 104
flows up the apertures 121 into the outlet fingers 120.
[0041] The inlet and outlet fingers 118, 120 are open channels
which do not have apertures. The bottom surface 103 of the manifold
layer 106 abuts against the top surface of the intermediate layer
104 in the three tier exchanger 100 or abuts against the interface
layer 102 in the two tier exchanger. Thus, in the three-tier heat
exchanger 100, fluid flows freely to and from the intermediate
layer 104 and the manifold layer 106. The fluid is directed to and
from the appropriate interface hot spot region by conduits 105 the
intermediate layer 104. It is apparent to one skilled in the art
that the conduits 105 are directly aligned with the fingers, as
described below or positioned elsewhere in the three tier
system.
[0042] Although FIG. 4B shows the three tier heat exchanger 100
with the manifold layer, the heat exchanger 100 is alternatively a
two layer structure which includes the manifold layer 106 and the
interface layer 102, whereby fluid passes directly between the
manifold layer 106 and interface layer 102 without passing through
the interface layer 104. It is apparent to one skilled in the art
that the configuration of the manifold, intermediate and interface
layers shown are for exemplary purposes and is thereby not limited
to the configuration shown.
[0043] As shown in FIG. 4B, the intermediate layer 104 includes a
plurality of conduits 105 which extend therethrough. The inflow
conduits 105 direct fluid entering from the manifold layer 106 to
the designated interface hot spot regions in the interface layer
102. Similarly, the apertures 105 also channel fluid flow from the
interface layer 102 to the exit fluid port(s) 109. Thus, the
intermediate layer 104 also provides fluid delivery from the
interface layer 102 to the exit fluid port 109 where the exit fluid
port 108 is in communication with the manifold layer 106.
[0044] The conduits 105 are positioned in the interface layer 104
in a predetermined pattern based on a number of factors including,
but not limited to, the locations of the interface hot spot
regions, the amount of fluid flow needed in the interface hot spot
region to adequately cool the heat source 99 and the temperature of
the fluid. The conduits have a width dimension of 100 microns,
although other width dimensions are contemplated up to several
millimeters. In addition, the conduits 105 have other dimensions
dependent on at least the above mentioned factors. It is apparent
to one skilled in the art that each conduit 105 in the intermediate
layer 104 has the same shape and/or dimension, although it is not
necessary. For instance, like the fingers described above, the
conduits alternatively have a varying length and/or width
dimension. Additionally, the conduits 105 may have a constant depth
or height dimension through the intermediate layer 104.
Alternatively, the conduits 105 have a varying depth dimension,
such as a trapezoidal or a nozzle-shape, through the intermediate
layer 104.
[0045] The intermediate layer 104 is horizontally positioned within
the heat exchanger 100 with the conduits 105 positioned vertically.
Alternatively, the intermediate layer 104 is positioned in any
other direction within the heat exchanger 100 including, but not
limited to, diagonal and curved forms. Alternatively, the conduits
105 are positioned within the intermediate layer 104 in a
horizontally, diagonally, curved or any other direction. In
addition, the intermediate layer 104 preferably extends
horizontally along the entire length of the heat exchanger 100,
whereby the intermediate layer 104 completely separates the
interface layer 102 from the manifold layer 106 to force the fluid
to be channeled through the conduits 105. Alternatively, a portion
of the heat exchanger 100 does not include the intermediate layer
104 between the manifold layer 106 and the interface layer 102,
whereby fluid is free to flow therebetween. Further, the
intermediate layer 104 alternatively extends vertically between the
manifold layer 106 and the interface layer 102 to form separate,
distinct intermediate layer regions. Alternatively, the
intermediate layer 104 does not fully extend from the manifold
layer 106 to interface layer 102.
[0046] FIG. 4B illustrates a perspective view of the interface
layer 102 in accordance with the present invention. As shown in
FIG. 4B, the interface layer 102 includes a bottom surface 103 and
a plurality of microchannel walls 110, whereby the area in between
the microchannel walls 110 channels or directs fluid along a fluid
flow path. The bottom surface 103 is flat and has a high thermal
conductivity to allow sufficient heat transfer from the heat source
99. Alternatively, the bottom surface 103 includes troughs and/or
crests designed to collect or repel fluid from a particular
location. The microchannel walls 110 are preferably configured in a
parallel configuration, as shown in FIG. 4B, whereby fluid flows
between the microchannel walls 110 along a fluid path.
Alternatively, the microchannel walls 110 have non-parallel
configurations.
[0047] It is apparent to one skilled in the art that the
microchannel walls 110 are alternatively configured in any other
appropriate configuration depending on the factors discussed above.
In addition, the microchannel walls 110 have dimensions which
minimize the pressure drop or differential within the interface
layer 102. It is also apparent that any other features, besides
microchannel walls 110 are also contemplated, including, but not
limited to, pillars 203 (FIG. 5), roughed surfaces, and a
micro-porous structure, such as sintered metal and silicon foam 213
(FIG. 5) or a combination. An alternative interface layer 202
incorporating both pillars 203 and foam microporous 213 inserts is
depicted in FIG. 5. However, for exemplary purposes, the parallel
microchannel walls 110 shown in FIG. 4B is used to describe the
interface layer 102 in the present invention.
[0048] Referring back to the assembly in FIG. 4B, the top surface
of the manifold layer 106 is cut away to illustrate the channels
116, 122 and fingers 118, 120 within the body of the manifold layer
106. The locations in the heat source 99 that produce more heat are
hereby designated as hot spots, whereby the locations in the heat
source 99 which produce less heat are hereby designated as warm
spots. As shown in FIG. 4B, the heat source 99 is shown to have a
hot spot region, namely at location A, and a warm spot region,
namely at location B. The areas of the interface layer 102 which
abut the hot and warm spots are accordingly designated interface
hot spot regions. As shown in FIG. 4B, the interface layer 102
includes interface hot spot region A, which is positioned above
location A and interface hot spot region B, which is positioned
above location B.
[0049] As shown in FIGS. 4A and 4B, fluid initially enters the heat
exchanger 100 through one inlet port 108. The fluid then flows to
one inlet channel 116. Alternatively, the heat exchanger 100
includes more than one inlet channel 116. As shown in FIGS. 4A and
4B, fluid flowing along the inlet channel 116 from the inlet port
108 initially branches out to finger 118D. In addition, the fluid
which continues along the rest of the inlet channel 116 flows to
individual fingers 118B and 118C and so on.
[0050] In FIG. 4B, fluid is supplied to interface hot spot region A
by flowing to the finger 118A, whereby fluid preferably flows down
through finger 118A to the intermediate layer 104. The fluid then
flows through the inlet conduit 105A, positioned below the finger
118A, to the interface layer 102, whereby the fluid undergoes
thermal exchange with the heat source 99. The fluid travels along
the microchannels 110 as shown in FIG. 4B, although the fluid may
travel in any other direction along the interface layer 102. The
heated liquid then travels upward through the conduit 105B to the
outlet finger 120A. Similarly, fluid flows down in the Z-direction
through fingers 118E and 118F to the intermediate layer 104. The
fluid then flows through the inlet conduit 105C down in the
Z-direction to the interface layer 102. The heated fluid then
travels upward in the Z-direction from the interface layer 102
through the outlet conduit 105D to the outlet fingers 120E and
120F. The heat exchanger 100 removes the heated fluid in the
manifold layer 106 via the outlet fingers 120, whereby the outlet
fingers 120 are in communication with the outlet channel 122. The
outlet channel 122 allows fluid to flow out of the heat exchanger
through one outlet port 109.
[0051] The inflow and outflow conduits 105 are also positioned
directly or nearly directly above the appropriate interface hot
spot regions to directly apply fluid to hot spots in the heat
source 99. In addition, each outlet finger 120 is preferably
configured to be positioned closest to a respective inlet finger
119 for a particular interface hot spot region to minimize pressure
drop therebetween. Thus, fluid enters the interface layer 102 via
the inlet finger 118A and travels the least amount of distance
along the bottom surface 103 of the interface layer 102 before it
exits the interface layer 102 to the outlet finger 120A. It is
apparent that the amount of distance which the fluid travels along
the bottom surface 103 adequately removes heat generated from the
heat source 99 without generating an unnecessary amount of pressure
drop. In addition, as shown in FIGS. 4A and 4B, the comers in the
fingers 118, 120 are curved to reduce pressure drop of the fluid
flowing along the fingers 118.
[0052] It is apparent to one skilled in the art that the
configuration of the manifold layer 106 shown in FIGS. 4A and 4B is
only for exemplary purposes. The configuration of the channels 116
and fingers 118 in the manifold layer 106 depend on a number of
factors, including but not limited to, the locations of the
interface hot spot regions, amount of flow to and from the
interface hot spot regions as well as the amount of heat produced
by the heat source in the interface hot spot regions. Any other
configuration of channels 116 and fingers 118 is contemplated.
[0053] Referring to FIG. 4B, the preferred embodiment of the
present invention includes microchannels 110 in the interface layer
102. In order to achieve the desired decrease in convection
resistance as described previously, the internal feature size of
the microchannels 110 are in the range of 15-300 microns, and the
surface to volume ratios of the microchannels are greater than 1000
m.sup.-1. Of course, the present invention contemplates further
embodiments contemplating microchannels not entirely within the
stated ranges.
[0054] Referring now to FIG. 5, further embodiments also
contemplate utilizing alternatives to the microchannels 110 (FIG.
4B) of the preferred embodiment such as pillars 203, roughed
surfaces or a micro-porous structure, such as sintered metal and
silicon foam 213. Furthermore, any of these alternatives could be
used instead of the microchannels 110, or they could be used in
combination as an alternative interface layer 202. Furthermore,
these alternatives may be used in any conceivable combination with
the microchannels 110. Of course, any alternative listed above or
combination thereof has internal features sizes and a surface to
volume ration that conforms to those set out in the preferred
embodiment of the present invention.
[0055] Also critical in achieving the desired relative resistance
levels is the fluid composition used in the pumped fluid system on
the preferred embodiment of the present invention. Specifically,
the heat capacity and viscosity become important when the desired
relative resistance levels are achieved. Using micro dimensions as
those described in the preferred embodiment can dramatically
increase the pumping pressure drop. Using low fluid flowrates makes
the performance highly sensitive to the fluid heat capacity per
unit mass, which governs its heat absorbing properties.
[0056] Therefore, in order for the system to operate properly with
the desired relative resistance levels, fluid with very high heat
capacity per unit mass (enabling high absorption) and low viscosity
(enabling low pressure drop in a micro hx) are required.
Preferably, a fluid at its average temperature in the heat
exchanger, having a viscosity, greater than 150% of the viscosity
of water and a heat capacity greater than 80% of water is required.
Also in the preferred embodiment of the present invention, the
fluid consists of at least 90% of water by mass.
[0057] FIG. 6 depicts a method of efficiently cooling a device in a
pumped fluid cooling system 400 of the preferred embodiment of the
present invention. The method 400 starts in step 410, by decreasing
the relative spread resistance in a pumped fluid system. This is
achieved by limited the size of the cooling surface of the micro hx
relative to the surface of the device being cooled. Preferably, to
equal to or less than 150% of the surface of the device being
cooled. In step 420, the relative convection resistance of the
pumped fluid system is decreased by increasing the total wetted
surface area in the micro hx. This is accomplished by reducing the
internal feature sizes of the micochannels in the micro hx,
preferably to a size in the range of 15-300 microns, with a surface
to volume ratio of 1000 m.sup.-1.
[0058] Still referring to FIG. 6, in step 430 the relative
advection resistance for the pumped fluid system is increased. This
is preferably done by decreasing the flowrate m, where the
advection resistance equals C/mc, where C is a constant near 0.5
and c is the specific heat capacity per unit mass. The last step in
this method 400 is step 440, by adjusting the fluid composition in
the pumped fluid system such that the fluid has a relatively high
heat capacity and a low viscosity. Preferably, the viscosity of the
fluid at its average temperature in the heat exchanger is less than
150% of the viscosity of water and the heat capacity per unit mass
of the fluid at its average temperature in the heat exchanger is
greater than 80% of the heat capacity per unit mass of water. This
is preferably achieved by adjusting the fluid such that it consists
of at least 90% water by mass.
[0059] 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 of the present invention could be
implemented in several different ways and have several different
appearances.
* * * * *