U.S. patent application number 10/258499 was filed with the patent office on 2003-07-03 for heat transport device.
Invention is credited to Hori, Kazuhito, Ishikawa, Hiroichi, Kitagawa, Koji, Tonosaki, Minehiro.
Application Number | 20030121644 10/258499 |
Document ID | / |
Family ID | 26610295 |
Filed Date | 2003-07-03 |
United States Patent
Application |
20030121644 |
Kind Code |
A1 |
Tonosaki, Minehiro ; et
al. |
July 3, 2003 |
Heat transport device
Abstract
A heat mass transport device, utilizing microchannels and
micropumps, achieving a thinner form and offers a higher thermal
conductance. The heat mass transport device (1) has a structure in
which the microchannels for passing through a coolant and the
micropumps for transporting the coolant form a single unit. For
example, a channel layer (2), in which the microchannels (2a) are
formed, and a pump layer (4), in which the micropumps (4a) are
formed, may be laminated in a multi-layer structure, or a large
number of single units in which a microchannel and a micropump are
combined, may be placed in an array. Moreover, the heat mass
transport device is made flexible, as the microchannels and
micropumps are formed on a resin substrate utilizing flexible
material.
Inventors: |
Tonosaki, Minehiro;
(Kanagawa, JP) ; Kitagawa, Koji; (Kanagawa,
JP) ; Ishikawa, Hiroichi; (Kanagawa, JP) ;
Hori, Kazuhito; (Kanagawa, JP) |
Correspondence
Address: |
SONNENSCHEIN NATH & ROSENTHAL
P.O. BOX 061080
WACKER DRIVE STATION
CHICAGO
IL
60606-1080
US
|
Family ID: |
26610295 |
Appl. No.: |
10/258499 |
Filed: |
October 25, 2002 |
PCT Filed: |
February 28, 2002 |
PCT NO: |
PCT/JP02/01853 |
Current U.S.
Class: |
165/104.25 ;
165/104.26; 165/46; 165/80.4; 257/E23.098 |
Current CPC
Class: |
F28F 2260/02 20130101;
H01L 23/473 20130101; H01L 2924/00 20130101; H01L 2924/0002
20130101; H01L 2924/0002 20130101 |
Class at
Publication: |
165/104.25 ;
165/80.4; 165/46; 165/104.26 |
International
Class: |
F28F 007/00; F28D
015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2001 |
JP |
P2001-054220 |
Feb 18, 2002 |
JP |
2002-039656 |
Claims
1. A heat mass transport device characterized by having a
microchannel for passing through a coolant, and a micropump for
passing through said coolant, wherein said microchannel and said
micropump are formed into a single unit, and said coolant
transports heat by circulating through said microchannel.
2. The heat mass transport device of claim 1, characterized by
having a channel layer, in which said microchannel is formed, and a
pump layer, in which said micropump is formed, wherein said heat
mass transport device comprises a multi-layer structure in which
said channel layer and said pump layer are laminated.
3. The heat mass transport device of claim 1, characterized by
comprising a unit structure in which said microchannel and said
micropump form a single unit, wherein said heat mass transport
device includes a plurality of said single unit structures.
4. The heat mass transport device of claim 1, characterized by
having said micropump formed by making a portion of said
microchannel narrower by constriction.
5. The heat mass transport device of claim 4, characterized by
having said microchannel and the said micropump formed in closed
loop form.
6. The heat mass transport device of claim 1, characterized by
having a constituting material for said microchannel and said
micropump formed of a flexible material.
7. The heat transport device of claim 2, characterized by having a
constituting material for said channel layer and said pump layer
formed of a flexible material.
8. The heat mass transport device of claim 3, characterized by
having a constituting material for said microchannel and said
micropump formed of a flexible material.
9. The heat mass transport device of claim 4, characterized by
having a constituting material for said microchannel and said
micropump formed of a flexible material.
Description
TECHNICAL FIELD
[0001] The present invention relates to a technology for reducing a
thickness of a heat mass transport device that uses microchannels
and micropumps.
BACKGROUND ART
[0002] Heat pipes, heat sinks, and radiators are widely used as
heat releasing and cooling devices and basically heat exchange and
cooling is performed by repetitive cycles of returning back flows
of steam, fluid after heat release or the like.
[0003] By the way, technology commonly known as MEMS (micro
electromechanical system) technology is receiving increased
attention, as a result of recent advances in the electron device
technology and micromachining technology, for taking advantage of
the silicon process technology in order to develop devices having a
better thermal conductance in a smaller form factor. For example, a
device called microchannel is used as a cooling element for a
localized, high-density source of heat, the cooling being performed
by making a coolant fluid pass through each of a channel (path)
upon forming a plurality of microscopic fins, which are tens of
.mu.m (microns) wide and approximately 100 .mu.m deep, on a silicon
substrate. Furthermore, a closed microchannel, that includes a
forced oscillating plate for the fluid, achieves a nominal
thermal-conductance performance that far exceeds copper.
[0004] However, conventional devices faces a constant limitation in
terms of reducing thickness and compaction of heat releasing
devices and cooling devices, and, as a result, when attached to
sources of heat, these devices caused difficulty in making the
device sizes smaller.
[0005] For example, a heat pipe that is 1 mm thick, 10 mm wide, and
50 mm long has a limited capacity of only several Watts per square
centimeter and requires large areas for heat realizing or for
thermal conductance, and cannot be used in very small scale
devices.
[0006] Furthermore, some forms of a device having a pumping
mechanism (for example, a micropump) is required for forcibly
circulating a coolant in a device having a microchannel. When a
circulation path for the coolant is set up for each (device) by
installing a microchannel and a micropump independently, it would
be difficult to reduce the size of the space taken up by the entire
heat transporting system. This issue leads to a difficulty in
achieving a higher heat transporting density.
[0007] In view of that, the present invention addresses the problem
of achieving a smaller thickness and improving thermal conductance
with a heat mass transport device that relies on microchannels and
micropumps.
DISCLOSURE OF THE INVENTION
[0008] In order to address the issue described above, the present
invention includes a single-unit structure that includes microscale
channels for passing a coolant and microscale pumps for
transporting the coolant. For example, a unit structure may combine
a channel layer, that includes the microscale channels, and a pump
layer, that includes the microscale pumps, that are laminated in a
multi-layer structure; or the unit structure may combine a
microscale channel and a microscale pump in a single-unit.
[0009] Therefore, according to the present invention, it is
possible to make a device having smaller thickness by combining the
microscale channels and microscale pumps into a single unit in a
multi-layer structure or an arrangement of a single-unit structure.
Furthermore, thermal conductance can be easily enhanced by
increasing the number of microscale channels in the channel layer
and microscale pumps in the pump layer in the multi-layer structure
or by increasing the number of single-unit structures, each of
which includes a microscale channel and a microscale pump.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a diagram showing an example of a structure of the
heat transporting device of the present invention, with (A) showing
a multi-layer structure, (B) showing a top view of each layer, and
(C) showing a side view from a direction D.
[0011] FIG. 2(A) through FIG. 2(C) are diagrams showing a basic
structure of a bubble-driven pump.
[0012] FIG. 3(A) through FIG. 3(F) are diagrams showing a method of
forming microchannel and micropump flow paths.
[0013] FIG. 4(A) through FIG. 4(D) are diagrams showing a method of
forming a piezo driven pump.
[0014] FIG. 5(A) through FIG. 5(B) are simplified drawings of a
micropump array.
[0015] FIG. 6 is a simplified drawing of an example of structure of
a heat mass transport device, including a side view and the shape
of each portion.
[0016] FIG. 7 is a diagram showing an example of a structure of a
heat mass transport device constituted by repetitive arrangement of
a unitary structure.
[0017] FIG. 8 is a diagram showing an example of application of a
heat mass transport device of the present invention.
[0018] FIG. 9 is a diagram showing another example of application
of the heat mass transport device of the present invention.
[0019] FIG. 10 is a diagram showing an example of application of a
micropump array.
[0020] FIG. 11 is a conceptual drawing showing a structure having a
microchannel formed in closed loop.
[0021] FIG. 12, along with FIG. 13 and FIG. 14, shows an example of
a closed-loop structure and FIG. 12 shows a simplified view from
the top.
[0022] FIG. 13 shows enlarged views of portions of a microchannel
and a micropump in a heat mass transport device.
[0023] FIG. 14 is a diagram showing a key portion of a
micropump.
[0024] FIG. 15 is a perspective view showing an example of an
embodiment of the present invention in which each of a plurality of
heat sources has a heat mass transport device, which are connected
to each other.
BEST MODES FOR CARRYING OUT THE INVENTION
[0025] The present invention relates to a thin heat mass transport
device that relies on microscale channels (microchannels) for
passing through a coolant and microscale pumps (micropumps) for
transporting the coolant and may be widely used for device cooling
and heat exchange.
[0026] In addition, the heat mass transport device of the present
invention has the microscale channel and the microscale pump
combined into a single unit in following forms:
[0027] 1. A form in which a channel layer and a pump layer are
laminated, and the laminated layers may be formed into a
multi-layer structure;
[0028] 2. A channel and a pump are formed into a single unit to
form a unit structure, and a plurality of unit structures is placed
next to each other.
[0029] First, FIG. 1 shows an example of the form 1. This example
has a structure in which a channel layer, on which the
microchannels are formed, and a pump layer, on which the micropumps
are formed, are superposed. This structure is used as a heat mass
transport device 1 (for example, a cooling or heat removal device)
for a heat source HG. FIG. 1(A) shows its side view.
[0030] The heat mass transport device 1 has a multi-layer structure
that includes a microchannel layer 2, a microvia and throughhole
layer 3, and a micropump layer 4, and the layers are attached by
fusion bond or the like.
[0031] FIG. 1(B) shows top views of each layer. In addition, FIG.
1(C) shows a side view of the heat mass transport device 1 seen
from the direction of arrow D. Out of the three layers, the
microchannel layer 2 is in direct contact with the heat source HG,
and a plurality of microchannels 2a, 2a, . . . are formed in
parallel to each other. Heat is transmitted from the heat source HG
to each channel, as a coolant (for example but not limited to freon
materials like FC72 or FC75, or water, air, or ethanol) flows
through each channel.
[0032] The microvia and throughhole layer 3 is formed over the
microchannel layer 2 and includes throughholes 3a, 3a, . . . ,
shown with black circles, and via holes 3b, 3b, . . . , shown with
white circles, which are formed in a substrate made of a
heat-insulating material. It should be noted that the throughholes
3a are formed towards both ends in a longer direction of the heat
mass transport device 1 (or along the directions of formation of
the microchannels), thereby connecting the flow paths of the
microchannels and the micropumps. In addition, each of the via
holes 3b is used for supplying heat required for driving a
micropump, and a material having preferable thermal conductance,
such as copper, is embedded in the holes.
[0033] A plurality of micropumps 4a, 4a, . . . is formed in the
micropump layer 4. In the present example, a bubble-driven thermal
pump (micropumps that are driven solely by thermal effect) is used
as each micropump.
[0034] FIG. 2A through FIG. 2C are descriptive diagrams of its
basic structure and the micropump 4a is formed with a structure
having a constricted portion in its flow path.
[0035] In addition, heater 5 is placed before a flow outlet in FIG.
2A and, as shown in FIG. 2B, bubble 6 is generated upon application
of heat by such heater. By making use of a pumping effect resulting
from vibration of this bubble, fluid is pumped out as shown in FIG.
2C.
[0036] It is well known that a maximum pressure generated in such a
micropump can be well described by the Laplace Equation determined
by surface tension, as well as the maximum radius and the minimum
radius of the flow path. There is however a problem in which, if a
heater is used as shown in FIG. 2A through FIG. 2C, an external
power supply is needed, thus efficiency is affected. In view of
this, it is desirable to make use of heat from the heat source HG,
instead of such a heater, as shown in FIG. 1. In the present
example, heat is transmitted directly from the microchannels 2a to
the micropumps 4a through the via holes 3b.
[0037] Therefore, in the present example, the coolant circulates
between the microchannel layer 2 and the micropump layer 4 and the
throughholes 3a between the two layers, and, as a result, a cooling
system is formed, in which heat is transported by the coolant from
the heat source HG through the various microchannels.
[0038] An example of a method of forming the microchannel layer and
the micropump layer are shown in FIG. 3A through FIG. 3F. A
substrate 7, made of a plastic material, is prepared (FIG. 3A), and
stop layers 8, 8 (or surface modifying layers) are formed on both
sides thereof by an ion implanting method (PBII treatment), as
shown in FIG. 3B. Then, mask patterning is performed as shown in
FIG. 3C. A photoresist resin, metal, ceramic material or the like
may be used as a mask MP. After a subsequent formation of an
opening 9 is performed by dry etching method such as O.sub.2
(oxygen) beam etching, a portion of the substrate is removed
through this opening by a chemical etching method using, for
example, limonene (d-C.sub.10H.sub.16), as shown in FIG. 3E. In
other words, a path 10 for a channel or pump flow path is formed,
as shown in FIG. 3F, by dissolution with immersion in an etching
solvent bath.
[0039] In addition, flexible microchannels and micropumps can be
formed by using a flexible material (for example, a resin material
used for polymer films, flexible substrates an the like) as
substrates for the channel layer and the pump layer. In other
words, the various devices may be formed on film layers. As a
result, it would be possible to bend the heat mass transport device
or have the heat mass transport device conform to a prescribed
contour in a wide range of applications. This is especially
effective in devices with limited space for their arrangement as a
result of downsizing or thinner shape.
[0040] Although a structure relying on bubble-driven pumps is
presented in the above-mentioned example, there is no limitation
thereto, thus apiezoelectric driven pump (or piezo-driven)
micropump may also be used.
[0041] FIG. 4A through FIG. 4D show an example of an overview of a
method of forming such a pump.
[0042] Firstly, as shown in FIG. 4A, ion implanted layers 12, 12
are formed on each of both sides of a substrate 11, and thin films
13, 13 are deposited on top thereof. Then, after an opening 14 is
formed by ion beam etching, as shown in FIG. 4B, a tapered circular
hole 15 (or, more accurately, a truncated-cone-shaped hole with a
bottom) is formed by limonene etching, as shown in FIG. 4C. FIG. 4C
shows the circular hole 15 viewed from bottom. Next, as shown in
FIG. 4D, a piezoelectric body 16 (or a piezoelectric thin film) is
fixed (or formed) in the circular hole 15, and a piezo-driven pump
18a is formed by attaching driver electrodes 17, 17. The
piezo-driven pump 18a may be able to pump the coolant by driving
the piezoelectric body 16 with external signals so as to make the
thin film 13 vibrate. In other words, the coolant is pumped out
along a path facing the pump.
[0043] FIG. 5A through FIG. 5B show a micropump array 18 having a
plurality of piezo-driven pumps 18a, 18a, . . . on a substrate.
FIG. 5A shows a view from the holes for the piezoelectric bodies,
while FIG. 5B shows a side view. It is to be noted that reference
numerals 19, 19 . . . here refer to the respective coolant
paths.
[0044] FIG. 6 shows an example of a structure of the heat mass
transport device 20 using the micropump array 18 described
above.
[0045] The microchannel layer 2 is attached to the heat source HG,
and a microvia layer 21 (a layer in which only via holes 21a, 21a,
. . . are formed) is provided on top of the channel layer. In
addition, flat plate fluid pipes 22 and 23, using, for example,
flexible substrates, are placed. It is to be noted that, although
the various layers are not shown to be laminated in FIG. 6 for the
sake of illustration, an actual configuration comprises a structure
having laminated a layer including the microchannel layer 2 and the
flat plate fluid pipe 23 and a layer including the micropump layer
24 and the flat plate fluid pipe 22, thus configuring a thin-type
heat mass transport device 20. These flat plate fluid pipes are
flow paths for the coolant (FC75 or the like) and also function as
heat releasing portions.
[0046] The pump layer 24, which includes the above-mentioned
micropump array 18, has a function of drawing in the coolant from
the flat plate fluid pipe 22 and sending the coolant out against
the flat plate fluid pipe 23.
[0047] In the present configuration, a forced circulation system
for the coolant is formed by placing the micropump layer 24 in the
coolant path utilizing the microchannel layer 2 and the flat plate
fluid pipes 22 and 23, so that heat from the heat source HG is
transmitted through the microchannel layer 2 into the flat plate
fluid pipes and released by the flat plate fluid pipes as well as
the microvia layer 21.
[0048] In addition, although in the description above, only a basic
example, combining each one of the microchannel layer and the
micropump layer, has been described, a device having a multi-layer
structure can easily be formed by laminating a plurality of
layers.
[0049] Next, a structure for the form 2 mentioned above will be
described.
[0050] In the present form, there is a unit (unit) structure in
which a microchannel and a micropump are combined into one body, so
that a it is possible to obtain a so-called multi-structure or
expandability by arranging such structures in parallel or ordered
in a regular fashion.
[0051] FIG. 7 shows a heat mass transport device 25 having such
configuration having a unit structure in which a micropump 27 is
placed over a microchannel 26 (simplified into a long narrow
rectangular parallelepiped in the drawing). It is to be noted that,
because the present example utilizes bubble-driven micropumps, a
via hole 28 is provided between such pump and the microchannel 26
for supplying heat to the micropump. Such a portion is not
necessary if piezo-driven micropumps as described above are used
instead. Conversely, a wiring substrate (for example, a flexible
substrate) would be necessary between the piezoelectric driver
electrodes.
[0052] It is to be noted that, one of the heat transport units,
which includes the microchannel 26 and the micropump 27, is shown
to be shifted upward in FIG. 7 in order to schematically illustrate
with arrows the flow of the coolant through such unit. Upon
arranging the heat transport units having such structure in
parallel to each other, it is possible to make attempts at
realizing a multi-unit heat transport path.
[0053] In addition, for the sake of representation on the drawing,
although a substrate material for the heat transport unit is
omitted, each channel, pump and the like may be formed on a
flexible substrate utuilizing a flexible material.
[0054] Although FIG. 7 showing a combined configuration in which a
microchannel and a micropump are laminated, there is no limitation
thereto, so that it is possible to adopt a unit structure in which
a single or a plurality of micropumps are formed at a portion of
the coolant path formed by a microchannel. For example, the pump
portion and the channel portion may form a flow path for the
coolant on a single plane surface by forming a loop on a thin and
flat substrate (flexible substrate). Such a structure will be
described later in detail.
[0055] Furthermore, although the present form 2 and the
above-mentioned form 1 may be used independently, the two forms may
be combined to accommodate a wider range of forms, according to the
application.
[0056] FIG. 8 shows an example of application of the heat mass
transport device of the present invention, in which a heat mass
transport device 29 in film sheet form is arranged spread over an
exothermic body 30 and a heat realizing plate 31. As shown through
an enlarged cross-section structure thereof within the large
circular frame in the figure, the heat mass transport device 29 in
this case has a multi-layer structure in which the microchannel
layers 2 and the micropump layers 4 or layers that include the
micropump layers 4 as well as the via hole and throughhole layers
are interlaminated and, because a flexible material (e.g., a
polymer material) is used as a substrate for each layer, it is
user-friendly in terms of flexibility and there is also an
advantage of having an ability to withstand deformation under a
bending stress. At this event, because the thickness of each layer
is of magnitude of tens of .mu.m to 100 .mu.m, a total film
thickness of the multi-layer structure does not become
significantly large. For example, as the total thickness may be
kept within 1 mm or less, it is possible to achieve a thin enough
embodiment.
[0057] In addition, FIG. 9 shows another example of application in
which an exothermic body 33 and a radiator 34 are attached
separately onto a heat mass transport device 32 in film sheet form
including a microchannel layer and a micropump layer. In addition,
even in this case, as a material of considerable flexibility is
used as a substrate for each layer, it is possible to easily cope
with bending and the like, in the flow paths for the coolant. For
example, in a portable computer apparatus or the like having two
chassis coupled by using hinges, the heat mass transport device 32
may be placed against an exothermic body, such as a CPU (central
processing unit), while the radiator 34 may be placed in another
chassis separated from the exothermic body, thus the present heat
mass transport device makes it possible to realize a heat releasing
structure and a cooling structure that thermally connects the
exothermic body with the radiator.
[0058] It is to be noted that the heat mass transport device is
especially effective in removing heat from or cooling an exothermic
body having a high thermal density and, in addition to a
multi-layer structure utilizing the laminated structure of form 1
or a multi-unit structure utilizing a unit structure of form 2 that
have been described earlier, other structures, are possible in
which, for example, as shown in FIG. 10, flexible pumps 35, 35, . .
. , which are film-shaped micropump layers (although the example
shows the micropump array 18 having piezo-driven micropumps,
bubble-driven pumps may also be used), may be placed on the
radiator 34 to enhance heat spreading efficiency, thus a wide range
of applications are expected as it is possible to conceptualize
embodiments resulting from combination of each type. Although being
it difficult to describe all possible applications, for example, a
heat releasing device to be used in conjunction with a high
temperature exothermic motor, or in a device for cooling a
removable cartridge disk (whose temperature rises during rotation)
in a compact hard disk drive system.
[0059] Furthermore, embodiments are possible for the microchannels,
which form the flow paths for the coolant, having an open structure
or a closed structure.
[0060] FIG. 11 shows a conceptual drawing of closed loop
configuration resulting from forming a microchannel in closed loop
form (endless loop shape).
[0061] A closed loop 36 in the figure shows a circulation path for
the microchannel, and a portion represented with a symbol `P`
within the path represents a micropump.
[0062] Although this micropump may be bubble-driven or
piezo-driven, the former, which does not require a power supply,
would be more desirable. In addition, in this case, the micropump
may be formed by making a portion of the microchannel narrower by
contriction. In other words, a circulation path may be formed with
a microchannel and a micropump formed by making a portion of the
microchannel narrower by constriction, in a closed loop, thus heat
transport efficiency can be increased using a structure having a
plurality of such flow paths disposed on a single plane.
[0063] Although the micropump P is placed near the heat source HG,
represented by a square frame drawn with broken lines in the
figure, when temperature distribution is not uniform in this heat
source HG, and the temperature is locally higher at, for example, a
point "Hs," the coolant would flow from the pump toward the point
"Hs" (in a direction shown by an arrow Y), if the pump is a
bubble-driven micropump. As a result, the coolant circulates
through the path by being cooled by a means of heat spreading or a
means of cooling by, for example, a heat spreading plate placed
away from the heat source HG, and returning back to the
micropump.
[0064] It is to be noted that water or ethanol is a preferred
coolant for filling the flow paths, considering user-friendliness
and safety and, for example, the coolant would be heated and
vaporized near the pump, which is a narrow portion of the
microchannel, return back into the fluid phase by subsequent
cooling, and circulate back to the heat source in repeating
cycles.
[0065] In addition, although heat is applied on the narrow portion
of the channel of the bubble-driven pump at a position slightly
dislocated from its central position, as shown in FIG. 2A through
FIG. 2C, it is also known that a similar pumping effect could be
obtained by heating a portion of the channel away from the narrow
portion. Therefore, another structure is possible in which a
portion of the channel having a constant diameter, and not
necessarily the narrow portion of the channel, would be heated. In
such case, the flow of the coolant would be determined by the
relative positions of the portion that is narrow and the portion
that is heated and the coolant flows from the portion that is
narrow to the portion that is heated.
[0066] It should be noted that while the micropump is placed at a
single location in the circulation path in FIG. 11, a structure
having a plurality of pumps is also possible.
[0067] FIG. 12 through FIG. 14 show examples of closed loop
structures as described above.
[0068] In FIG. 12, an exothermic body 37, such as a CPU, is placed
on a substrate, and a film-shaped heat mass transport device 38 is
pasted on this exothermic body.
[0069] The heat mass transport device 38 has a plurality of closed
loop microchannels, which do not intersect with each other, formed
thereon by forming microscale grooves on a substrate material
utilizing a flexible material like a polymer material. In addition,
it has a configuration in which a side of this substrate on which
the grooves are formed is coated with a cover material (film
material). In FIG. 12 and FIG. 13, a group of closed curves 39
represent circulation paths laid out like tracks for the coolant
(e.g., water).
[0070] In FIG. 12, a portion of the heat mass transport device 38
is in contact with a high temperature section 37a of the exothermic
body 37, and a micropump is formed on each circulation path in an
area inside a frame 40, shown with dotted lines. Also, although not
shown in this figure, heat spreading plate(s), heat removal
plate(s), and heat conducting plate(s) are placed on the right hand
side of a vertical line T in this figure and a portion of the heat
mass transport device (right hand portion) is in contact
therewith.
[0071] FIG. 13 and FIG. 14 show outlines of cross-sectional
structures of the heat mass transport device.
[0072] Each of the circulation paths, represented by a group of
closed curves 39, is made of a microchannel 41, formed as a groove
having a prescribed depth and a constant width, and a micropump 42,
formed as a narrower portion (a portion with a smaller width or a
shallower depth) in this channel.
[0073] FIG. 13 shows enlarged views of the microchannel and the
micropump, which are schematically shown as made of a transparent
material. In addition, FIG. 14 shows only key portions of the
micropump (grooves formed on the substrate).
[0074] For example, a pump 42a is formed by making a portion of the
channel narrower, and the channel is formed having a constant width
except for this narrower portion.
[0075] It is to be noted that, although a groove in the substrate
having a constant width (w) and a constant depth (d), except for
the pump portion, is simple to manufacture, in some cases, it is
possible to make a design so that the cross-sectional area of the
groove may be different by continuously changing according to a
position over the flow path or gradual change.
[0076] In addition, as mentioned above, because the coolant is
moved toward the source of heat in the bubble-driven pump, the
coolant moves in a counter-clockwise direction in FIG. 12, for
example, if a hot spot exists on the left hand side of the pump
portion, which is highlighted with a round frame 40. For example, a
CPU or the like does not have a uniform temperature distribution
across its surface, and there may be a localized spot with higher
temperature. The pump portion (the narrow portion of the channel)
should be deliberately positioned away from the spot with higher
temperature. As a result, an additional heat source for
facilitating a pumping effect would not need to be installed
separately.
[0077] However, in the present example, the coolant, by repeating
the cycle of being transported by the micropump upon been heated by
the exothermic body, moving through the circulation path, being
cooled by the radiator, and returning back to the pump, the coolant
is able to efficiently transport heat from the exothermic body to
the radiator.
[0078] Moreover, because the heat mass transport device 38 is
formed into an extremely thin sheet, an even more efficient heat
transfer is possible by superposing a plurality of sheets in many
layers and also occupying a small disposing space.
[0079] Furthermore, because the circulation paths for the coolant
can be formed with a relatively high degree of freedom by forming
each microchannel and micropump in a closed-loop flow path, there
is a high degree of freedom of design. In the example described
above, although portions made of concentric semicircles each, are
connected with a pair of straight paths to form flow paths that
look like a "track field", the present invention is not limited to
such shape and can accommodate a flow path that crosses across a
plurality of heat sources and also regardless of existence of
branches.
[0080] FIG. 15 shows an example in which a flow path that connects
a plurality of heat mass transport device, which are installed for
each of a plurality of heat sources, and the heat mass transport
device are connected with branching flow paths.
[0081] In the present example, each of the circuit substrate 43 and
44 has a plurality of ICs (integrated circuits) and among these
ICs, those that generate high volumes of heat are to be considered
exothermic bodies (heat sources). For example, among the ICs 43a,
43a, . . . on the substrate 43, a heat transport apparatus (device)
45 is installed on an IC 43a1, and a heat mass transport device 46
is attached to an IC 43a2.
[0082] Furthermore, out of the ICs 44a, 44a, . . . on the other
substrate 44, a heat mass transport device 47 is installed on an IC
44a1, and a heat spreading portion (or a heat sink) 48 is also
provided on the substrate 44.
[0083] The heat mass transport device 45 through 47 have a basic
structure consisting of loop-shaped flow paths that includes planer
channels and pump portions (bubble-driven) formed on the surface of
their substrate. Therefore, a plurality of flow paths are formed on
a same plane, and the pumps are driven by heat from the ICs, which
are exothermic bodies.
[0084] For example, as shown in this figure, the Heat mass
transport device 46 exchanges heat with the heat spreading section
48 through two flow sections 46A and 46A, which are made of a
plurality of microchannels. In other words, a portion of the Heat
mass transport device 46 is pasted on a surface of the IC 43a2,
which is an exothermic portion, and the coolant (i.e., water),
heated by the exothermic portion, passes through one of the flow
paths 46A, releases heat at the heat spreading section 48, and then
returns to the portion pasted to the surface of the IC 43a2.
[0085] Furthermore, some portions of the flow paths, connected to
the heat spreading section 48, branch out and connect to the seat
mass transport devices 45 and 47. In other words, out of the flow
path sections 47A and 47B, which connect the heat mass transport
device 47 and the heat spreading section 48, the flow path section
47A branches off in a T-shape in a middle and extends toward the
substrate 43 and connects with the flow paths 45A, 45A, which
extend from the heat mass transport device 45 toward the substrate
44. Therefore, heat exchange takes place between the various heat
mass transport devices and the heat spreading section 48 through
the microchannels formed in these flow path sections (in other
words, the coolant, heated at portions of the substrate where the
ICs are mounted, flows through the various flow path portions to
arrive at the heat spreading portion, releases heat at the heat
spreading portion, and then returns to portions of the substrate
where the various ICs are mounted.)
[0086] In this way, a high degree of freedom is available in terms
of the flow path layout and shapes, even in the presence of a
plurality of exothermic portions. Furthermore, highly flexible heat
mass transport devices, that can be bent easily, may be created by
using a flexible resin material for the substrate, and thin and
flat heat mass transport devices can be pasted onto the exothermic
bodies. Moreover, it is also possible to use a configuration having
a lamination of a plurality of sheet-shaped devices having a
plurality of flow paths on a same plane.
[0087] As clearly demonstrated by the descriptions above, according
to inventions in claims 1 through 3, as the overall arrangement
space, area occupied by the heat mass transport device and the like
can be reduced by combining microchannels and pumps into a single
unit, it is possible to make device thinner. Furthermore, thermal
conductance can be easily increased by increasing the number of
channels and pumps if adopting a multi-layer structure like the
invention in claim 2, or by increasing the number of unit
structures including the channel and pump if adopting a combined
structure like the invention in the scope of claim 3.
[0088] According to an invention in claim 4, the structure becomes
simpler as a microscale pump is formed by making a portion of the
microchannel path narrower.
[0089] According to an invention in claim 5, as it is possible to
perform heat transport by circulating a coolant through closed-loop
flow paths made of microchannel and microscale pump, heat-removal
and cooling efficiency can be increased by disposing a large number
of such closed loops.
[0090] According to inventions in claim 6 through 9, the
user-friendliness of the heat mass transport device is enhanced
significantly as a substrate is formed with flexible material, so
that it is possible to make a device that is flexible with respect
to a bending stress and could easily accommodate curved flow
paths.
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