U.S. patent number 6,748,758 [Application Number 10/454,965] was granted by the patent office on 2004-06-15 for cooling device, method of manufacturing the same and portable equipment.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Katsumi Imada, Atsushi Komatsu.
United States Patent |
6,748,758 |
Imada , et al. |
June 15, 2004 |
**Please see images for:
( Certificate of Correction ) ** |
Cooling device, method of manufacturing the same and portable
equipment
Abstract
In a cooling device including a pump, a heat absorber, a heat
radiator, a flow channel that allows communication between
interiors thereof and forms a closed-loop circulating cycle
therebetween, and a liquid refrigerant that circulates in the flow
channel, a volume of a gas generated in the liquid refrigerant
owing to temperature change within an operating temperature range
of the liquid refrigerant is smaller than a volume of a sphere that
is inscribed in a cross-section of the flow channel. In this way,
even when the solubility changes due to rapid heating or cooling of
the liquid refrigerant, no gas is generated in the liquid
refrigerant. Thus, it is possible to provide a cooling device that
maintains an excellent cooling effect even after a long time
use.
Inventors: |
Imada; Katsumi (Nara,
JP), Komatsu; Atsushi (Osaka, JP) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (Osaka, JP)
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Family
ID: |
29774142 |
Appl.
No.: |
10/454,965 |
Filed: |
June 5, 2003 |
Foreign Application Priority Data
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Jun 26, 2002 [JP] |
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2002-186706 |
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Current U.S.
Class: |
62/259.2;
165/104.28; 257/E23.098; 62/118 |
Current CPC
Class: |
G06F
1/203 (20130101); H01L 23/473 (20130101); G06F
2200/203 (20130101); H01L 2924/0002 (20130101); H01L
2924/0002 (20130101); H01L 2924/00 (20130101) |
Current International
Class: |
G06F
1/20 (20060101); H01L 23/34 (20060101); H01L
23/473 (20060101); H05K 7/20 (20060101); H05K
5/02 (20060101); F25D 023/12 () |
Field of
Search: |
;62/118,259.2
;165/104.28,104.33 ;361/699 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2001-24372 |
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Jan 2001 |
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JP |
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2002-494102 |
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Apr 2002 |
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JP |
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2002-314279 |
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Oct 2002 |
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JP |
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Primary Examiner: Jones; Melvin
Attorney, Agent or Firm: Merchant & Gould, P.C.
Claims
What is claimed is:
1. A cooling device comprising: a pump; a heat absorber; a heat
radiator; a flow channel that allows communication between
interiors of the pump, the heat absorber and the heat radiator and
forms a closed-loop circulating cycle therebetween; and a liquid
refrigerant that circulates in the flow channel; wherein a volume
of a gas generated in the liquid refrigerant owing to temperature
change within an operating temperature range of the liquid
refrigerant is smaller than a volume of a sphere that is inscribed
in a cross-section of the flow channel.
2. The cooling device according to claim 1, wherein the liquid
refrigerant is a mixture of a material whose gas solubility changes
positively with respect to a temperature and a material whose gas
solubility changes negatively with respect to a temperature.
3. A portable piece of equipment comprising the cooling device
according to claim 1.
4. A cooling device comprising: a pump; a heat absorber; a heat
radiator; a flow channel that allows communication between
interiors of the pump, the heat absorber and the heat radiator and
forms a closed-loop circulating cycle therebetween; and a liquid
refrigerant that circulates in the flow channel; wherein a
difference between a product and an amount of a gas dissolved in
the liquid refrigerant in a state where no gas is generated is
smaller than a volume of a sphere that is inscribed in a minimal
cross-section of the flow channel, the product being a product of a
minimal solubility of the gas in the liquid refrigerant within an
operating temperature range of the liquid refrigerant and a total
capacity of the flow channel.
5. The cooling device according to claim 4, wherein the liquid
refrigerant a mixture of a material whose gas solubility changes
positively with respect to a temperature and a material whose gas
solubility changes negatively with respect to a temperature.
6. A portable piece of equipment comprising the cooling device
according to claim 4.
7. A method for manufacturing a cooling device comprising a pump, a
heat absorber, a heat radiator, a flow channel that allows
communication between interiors of the pump, the heat absorber and
the heat radiator and forms a closed-loop circulating cycle
therebetween, and a liquid refrigerant that circulates in the flow
channel; the method comprising: sealing the liquid refrigerant in
the flow channel while maintaining an atmosphere at a temperature
at which a gas solubility in the liquid refrigerant takes on a
minimal value within an operating temperature range of the liquid
refrigerant or is smaller than the minimal value.
8. The method for manufacturing a cooling device according to claim
7, wherein the liquid refrigerant is sealed in the flow channel
while maintaining the atmosphere at a temperature equal to or
higher than the temperature at which the gas solubility in the
liquid refrigerant takes on the minimal value within the operating
temperature range of the liquid refrigerant.
9. The method for manufacturing a cooling device according to claim
7, wherein the liquid refrigerant is sealed in the flow channel
under a decompressed atmosphere.
10. A method for manufacturing a cooling device comprising a pump,
a heat absorber, a heat radiator, a flow channel that allows
communication between interiors of the pump, the heat absorber and
the heat radiator and forms a closed-loop circulating cycle
therebetween, and a liquid refrigerant that circulates in the flow
channel; the method comprising: sealing the liquid refrigerant in
the flow channel under an atmosphere decompressed so that a gas
solubility in the liquid refrigerant at a temperature of an
atmosphere at the time of sealing the liquid refrigerant in the
flow channel is smaller than a minimal value of the gas solubility
under an atmospheric pressure within an operating temperature range
of the liquid refrigerant.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cooling device using a liquid
refrigerant and a method for manufacturing the cooling device. The
present invention also relates to portable equipment including the
cooling device.
2. Description of Related Art
A conventionally known cooling device using a refrigerant is
described by JP 2001-24372 A.
FIG. 17 is a schematic perspective view showing how elements of a
cooling device are arranged in a conventional notebook personal
computer (in the following, referred to as a "notebook PC") in
which the cooling device is incorporated.
In FIG. 17, numeral 101 denotes a housing of the notebook PC,
numeral 102 denotes a heat generator such as a central processing
unit (CPU), numeral 104 denotes a heat absorber, numeral 103
denotes a heat-transfer pad arranged between the heat generator 102
and the heat absorber 104, numeral 105 denotes a pump, and numeral
106 denotes a heat radiator. Numeral 107 denotes a display portion
of the notebook PC, and numeral 108 denotes a flow channel that
allows communication between the interiors of the heat absorber
104, the pump 105 and the heat radiator 106. Inside the flow
channel 108 is filled with a water-based or fluorocarbon-based
liquid refrigerant.
Next, the operation of this cooling device will be described.
When the notebook PC is used, the pump 105 is powered and activated
so as to send out the liquid refrigerant by pressure, whereby the
liquid refrigerant circulates through a closed-loop circulating
cycle from the pump 105, the heat absorber 104, the heat radiator
106 to the pump 105, which are connected via the flow channel 108.
Thus, the liquid refrigerant pushed out from the pump 105 absorbs
heat from the heat generator 102 in the heat absorber 104, moves to
the heat radiator 106 to radiate the heat and be cooled down again
and then returns to the pump 105. By repeating this operation, the
heat generated in the notebook PC is radiated outward.
When this cooling device is used for a long time, the liquid
refrigerant is heated and cooled, so that a gas (bubbles) is
generated in the device. In particular, considerable gas generation
occurs inside the heat absorber 104. Since the generated gas blocks
the flow channel in the heat absorber 104, a channel resistance
increases considerably, thus deteriorating flow rate
characteristics of the pump 105. As a result, the flow velocity of
the liquid refrigerant drops, causing a problem that a cooling
power deteriorates.
Furthermore, inside the heat absorber 104, the formation of a gas
layer between an inner wall of the heat absorber 104 and the liquid
refrigerant lowers heat conductivity. Consequently, there has been
a problem that lowering heat absorbing power of the heat absorber
104 deteriorates the cooling power of the cooling device.
In addition, since not only the liquid refrigerant but also the
generated gas flows into other devices, for example, the pump 105,
the performance of the pump 105 declines, leading to a problem that
the cooling power deteriorates.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve these problems
and to provide a cooling device that maintains an excellent cooling
effect even after a long time use, and a method for manufacturing
the cooling device. It is a further object of the present invention
to provide portable equipment that achieves an improvement in
performance owing to a stabilized cooling power.
In order to achieve the above-mentioned objects, the present
invention has the following configurations.
A first cooling device according to the present invention includes
a pump, a heat absorber, a heat radiator, a flow channel that
allows communication between interiors of the pump, the heat
absorber and the heat radiator and forms a closed-loop circulating
cycle therebetween, and a liquid refrigerant that circulates in the
flow channel. A volume of a gas generated in the liquid refrigerant
owing to temperature change within an operating temperature range
of the liquid refrigerant is smaller than a volume of a sphere that
is inscribed in a cross-section of the flow channel.
A second cooling device according to the present invention includes
a pump, a heat absorber, a heat radiator, a flow channel that
allows communication between interiors of the pump, the heat
absorber and the heat radiator and forms a closed-loop circulating
cycle therebetween, and a liquid refrigerant that circulates in the
flow channel. A difference between a product described below and an
amount of a gas dissolved in the liquid refrigerant in a state
where no gas is generated is smaller than a volume of a sphere that
is inscribed in a minimal cross-section of the flow channel. The
product is a product of a minimal solubility of the gas in the
liquid refrigerant within an operating temperature range of the
liquid refrigerant and a total capacity (volume) of the flow
channel.
A first method for manufacturing a cooling device according to the
present invention is a method for manufacturing a cooling device
including a pump, a heat absorber, a heat radiator, a flow channel
that allows communication between interiors of the pump, the heat
absorber and the heat radiator and forms a closed-loop circulating
cycle therebetween, and a liquid refrigerant that circulates in the
flow channel. The method includes sealing the liquid refrigerant in
the flow channel while maintaining an atmosphere at a temperature
at which a gas solubility in the liquid refrigerant takes on a
minimal value within an operating temperature range of the liquid
refrigerant or is smaller than the minimal value.
A second method for manufacturing a cooling device according to the
present invention is a method for manufacturing a cooling device
including a pump, a heat absorber, a heat radiator, a flow channel
that allows communication between interiors of the pump, the heat
absorber and the heat radiator and forms a closed-loop circulating
cycle therebetween, and a liquid refrigerant that circulates in the
flow channel. The method includes sealing the liquid refrigerant in
the flow channel under an atmosphere decompressed so that a gas
solubility in the liquid refrigerant at a temperature of an
atmosphere at the time of sealing the liquid refrigerant in the
flow channel is smaller than a minimal value of the gas solubility
under an atmospheric pressure within an operating temperature range
of the liquid refrigerant.
According to the first and second cooling devices and the first and
second manufacturing methods of the present invention described
above, even when the solubility changes due to rapid heating or
cooling of the liquid refrigerant, no gas is generated. Thus, it is
possible to prevent the cooling power from deteriorating due to the
deterioration in flow rate characteristics of the pump occurring
because the gas generated after a long time use blocks the flow
channel, the lowering of heat conductivity caused by adhesion of
the gas to the inner wall of the flow channel and the decline in
the pump performance occurring because the generated gas flows into
the pump. As a result, a cooling device that maintains an excellent
cooling efficiency even after a long time use can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic perspective view showing an example of a
notebook PC in which a cooling device in a first embodiment of the
present invention is incorporated.
FIG. 2 is a sectional view showing an example of a pump used in the
cooling device of the first embodiment of the present
invention.
FIG. 3A is an exploded perspective view showing an example of a
heat absorber used in the cooling device of the first embodiment of
the present invention.
FIG. 3B is a sectional view, taken along line 3B--3B in FIG. 3A and
seen from an arrow direction, showing the heat absorber used in the
cooling device of the first embodiment of the present
invention.
FIG. 4 is a plan sectional view showing an example of an inner flow
channel of a heat radiator used in the cooling device of the first
embodiment of the present invention.
FIG. 5 is a graph schematically showing a solubility curve of the
air with respect to the temperature of a liquid refrigerant used in
the cooling device of the first embodiment of the present invention
(downwardly-sloping characteristics).
FIG. 6 is a graph schematically showing a solubility curve of the
air with respect to the temperature of another liquid refrigerant
used in the cooling device of the first embodiment of the present
invention (upwardly-sloping characteristics).
FIG. 7 is a graph schematically showing a solubility curve of the
air with respect to the temperature of still another liquid
refrigerant used in the cooling device of the first embodiment of
the present invention (substantially horizontal
characteristics).
FIG. 8 is a graph schematically showing a solubility curve of the
air with respect to the temperature of still another liquid
refrigerant used in the cooling device of the first embodiment of
the present invention (downwardly convex characteristics).
FIG. 9 is a schematic perspective view showing an example of a
notebook PC in which a cooling device obtained by a method for
manufacturing a cooling device in a second embodiment of the
present invention is incorporated.
FIG. 10 is a schematic view showing an example of a sealing device
used for sealing a liquid refrigerant into the cooling device in
the method for manufacturing a cooling device according to the
second embodiment of the present invention.
FIG. 11 is a graph schematically showing an example of
downwardly-sloping solubility characteristics of the liquid
refrigerant used in the cooling device in the method for
manufacturing a cooling device according to the second embodiment
of the present invention.
FIG. 12 is a graph schematically showing an example of
upwardly-convex solubility characteristics of the liquid
refrigerant used in the cooling device in the method for
manufacturing a cooling device according to the second embodiment
of the present invention.
FIG. 13 is a graph schematically showing an example of
upwardly-sloping solubility characteristics of the liquid
refrigerant used in the cooling device in the method for
manufacturing a cooling device according to the second embodiment
of the present invention.
FIG. 14 is a graph schematically showing an example of
downwardly-convex solubility characteristics of the liquid
refrigerant used in the cooling device in the method for
manufacturing a cooling device according to the second embodiment
of the present invention.
FIG. 15 is a schematic view showing an example of a sealing device
used for sealing a liquid refrigerant into a cooling device in a
method for manufacturing a cooling device according to a third
embodiment of the present invention.
FIG. 16 is a graph schematically showing an example of solubility
characteristics of the liquid refrigerant used in the cooling
device in the method for manufacturing a cooling device according
to the third embodiment of the present invention.
FIG. 17 is a schematic perspective view showing a notebook PC in
which a conventional cooling device is incorporated.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, the present invention will be described in detail by
way of preferred embodiments.
First Embodiment
The following is a description of a first embodiment of the present
invention, with reference to the accompanying drawings.
FIG. 1 is a schematic perspective view showing an example of a
notebook PC in which a cooling device of the first embodiment of
the present invention is incorporated. FIG. 2 is a sectional view
showing an example of a pump used in the cooling device of the
first embodiment of the present invention. FIG. 3A is an exploded
perspective view showing an example of a heat absorber used in the
cooling device of the first embodiment of the present invention.
FIG. 3B is a sectional view, taken along line 3B--3B in FIG. 3A and
seen from an arrow direction, showing the heat absorber used in the
cooling device of the first embodiment of the present invention.
FIG. 4 is a plan sectional view showing an example of an inner flow
channel of a heat radiator used in the cooling device of the first
embodiment of the present invention.
In FIG. 1, numeral 1 denotes a pump, numeral 2 denotes a heat
absorber, numeral 3 denotes a heat radiator, and numeral 4 denotes
a flow channel that allows communication between the interiors of
the pump 1, the heat absorber 2 and the heat radiator 3 and forms a
closed-loop circulating cycle from the pump 1 through the heat
absorber 2, the heat radiator 3 to the pump 1. Numeral 5 denotes a
housing of the notebook PC, numeral 6 denotes a heat generator such
as a CPU, numeral 6a denotes a heat-transfer pad arranged between
the heat generator 6 and the heat absorber 2, and numeral 7 denotes
a display portion of the notebook PC. Inside the flow channel 4
forming the closed-loop circulating cycle from the pump 1, the heat
absorber 2, the heat radiator 3 to the pump 1 is filled with a
liquid refrigerant. The liquid refrigerant is out of contact with
an outside air. The heat absorber 2 closely contacts the heat
generator 6 such as the CPU via the heat-transfer pad 6a, whereby
the heat from the heat generator 6 is transferred to the heat
absorber 2 efficiently. The heat of the heat generator 6 is
absorbed in the heat absorber 2 and further transmitted to the
liquid refrigerant in the heat absorber 2. The heated liquid
refrigerant is carried by a force of the pump 1, thereby carrying
the heat to the heat radiator 3, which is formed on a back surface
of the display portion 7, and exhausting the heat from the heat
radiator 3 into the air. The resultant liquid refrigerant that has
been cooled down is carried again to the heat absorber 2, and then
the above-described operations are repeated.
In FIG. 2, which shows a schematic structure of the pump 1, numeral
11 denotes a first casing, numeral 12 denotes a second casing,
numeral 13 denotes a third casing, numeral 14 denotes an impeller,
numeral 15 denotes a bearing, numeral 16 denotes a rotor, numeral
17 denotes a stator, numeral 18 denotes a suction port, and numeral
19 denotes a discharge port. The impeller 14 is held rotatably by
the bearing 15 in a space 20 formed by the first casing 11 and the
second casing 12. The suction port 18 is provided along the axis of
rotation of the impeller 14, whereas the discharge port 19 is
provided in a radial direction of the impeller 14. Both of the
suction port 18 and the discharge port 19 are connected to the
space 20. The rotor 16 formed of a permanent magnet is provided on
a periphery of the impeller 14. The stator 17 formed of a coil is
held in a space formed by the second casing 12 and the third casing
13 so as to face the rotor 16. This pump is a general centrifugal
pump that forms a liquid refrigerant flow utilizing a centrifugal
force. By passing an electric current through the coil of the
stator 17, an electromagnetic force is generated in the rotor 16,
so that a rotary driving force is generated therein. This rotates
the impeller 14 to which the rotor 16 is attached. The liquid
refrigerant flowing from the suction port 18 into the space 20 is
rotated by the rotation of the impeller 14. This generates a
centrifugal force to discharge the liquid refrigerant vigorously
from the discharge port 19. In this manner, this miniature pump
allows the liquid refrigerant to flow in directions indicated by
arrows 10.
Although an example of a centrifugal pump as the pump 1 has been
illustrated in the above description, a diaphragm type pump or a
pump utilizing a piezoelectric effect also may be used. It is
needless to say that effects of the present invention can be
obtained regardless of the type of pump.
In FIGS. 3A and 3B showing the heat absorber 2, numeral 21 denotes
a lid, numeral 22 denotes a heat absorber case, numeral 23a denotes
an inflow port, numeral 23b denotes an outflow port, and numeral 24
denotes a flow channel. On one surface of the heat absorber case
22, the flow channel 24 is formed like a groove connecting the
inflow port 23a and the outflow port 23b. The surface of the case
22 with a bottom on which the flow channel 24 is formed is sealed
by the lid 21 via a sealing layer (not shown). A lateral surface of
the case 22 is provided with the inflow port 23a and the outflow
port 23b, which are an inlet and an outlet for the liquid
refrigerant, respectively. The inflow port 23a and the outflow port
23b are connected to the discharge port 19 of the pump 1 and an
inflow port of the heat radiator 3, respectively, via the flow
channel 4. The liquid refrigerant is sent by pressure from the
inflow port 23a via the flow channel 24 inside the case 22 to the
outflow port 23b. When passing through the flow channel 24 in the
heat absorber case 22, the liquid refrigerant absorbs the heat from
the heat generator 6.
In FIG. 4 illustrating the heat radiator 3, numeral 31 denotes a
flow channel, numeral 32a denotes an inflow port, numeral 32b
denotes an outflow port, and numeral 33 denotes a case. The flow
channel 31 is a single long tube that is formed by bonding and
cutting resin sheets, metal sheets or the like and connects a
passage between the inflow port 32a and the outflow port 32b. The
liquid refrigerant flows in this flow channel 31, whereby the heat
of the liquid refrigerant is transferred to the case 33. Then, the
case 33 radiates the heat into the surrounding atmosphere, thereby
achieving a heat radiating effect. In this figure, arrows indicate
a flowing direction of the liquid refrigerant.
Next, a principle by which a gas (bubbles) is generated in the
liquid refrigerant will be explained. In general, the solubility (a
saturated solubility) of a gas in a liquid varies according to the
temperature of the liquid. In the present embodiment, a case where
a liquid whose solubility decreases as the temperature rises is
used as the liquid refrigerant will be described for example.
The liquid refrigerant that has flowed into the heat absorber 2 is
heated rapidly by the heat generated from the heat generator 6.
This causes the solubility of the gas (i.e., the air) in the liquid
refrigerant to drop sharply, and eventually the amount of dissolved
gas exceeds the solubility. Consequently, the gas that has been
dissolved in the refrigerant suddenly turns into bubbles. This is a
mechanism of gas generation.
Furthermore, there are three crucial influences of the gas
generation on the cooling device. First, owing to the gas
generation, the flow channel in the heat absorber 2 is blocked, so
that the liquid refrigerant cannot be circulated. Second, a layer
of the gas is formed between the inner wall of the heat absorber 2
and the liquid refrigerant, thus lowering heat conductivity. Third,
since not only the liquid refrigerant but also the generated gas
flows into other devices, for example, the pump 1, the pump
performance declines, thus deteriorating the cooling power.
Among the above, the most crucial problem is the first influence
described above, that is, the flow channel in the heat absorber 2
is blocked, so that the liquid refrigerant cannot be circulated.
This raises the temperature of the heat generator 6 such as a CPU,
so that a circuit portion of portable equipment such as a notebook
PC is likely to suffer from great damage.
In the process of generating the gas, first, the gas generated in
the heat absorber 2 adheres to the inner wall of the heat absorber
2. The liquid refrigerant flowing into the heat absorber 2 is
heated sequentially in the heat absorber 2, thus generating the gas
further. Accordingly, the gas adhering to the inner wall grows.
This substantially narrows a part of the flow channel of the heat
absorber 2, so that a pressure loss of the flow channel increases
greatly. In the cooling device mounted on the portable equipment
such as a notebook PC, a miniature pump whose flow rate and head
difference are relatively small is used as the pump 1. Therefore,
such an increase in the pressure loss of the flow channel has a
particularly large influence, so that the flow rate lowers
considerably, making it impossible to circulate the liquid
refrigerant.
In order to prevent such a problem, it is appropriate to regulate
the amount (volume) of gas generated in the liquid refrigerant. In
other words, the volume of the gas generated in the liquid
refrigerant owing to a temperature change in the liquid refrigerant
has to be smaller than the volume of a sphere that is inscribed in
a cross-section of the flow channel forming the closed-loop
circulating cycle. It is particularly preferable that the
above-mentioned "cross-section" is a cross-section at a position
where a cross-sectional area is minimal. When this condition is
satisfied, the gas does not block the flow channel completely.
Also, the pressure loss of the flow channel does not increase
greatly. As a result, the flow rate of the liquid refrigerant can
be secured.
The above-mentioned condition refers to the "sphere" because the
gas is present as a sphere in the liquid refrigerant owing to a
surface tension of the liquid refrigerant. Further, the "flow
channel forming the closed-loop circulating cycle" includes not
only the flow channel 4 in FIG. 1 but also the flow channels in the
pump 1, the heat absorber 2 and the heat radiator 3. The reason why
the above-mentioned condition refers to "is inscribed" in the flow
channel is as follows. The gas that adheres to the inner wall of
the flow channel grows first while maintaining its spherical shape.
When the flow channel does not have a circular cross-sectional
shape, the gas grows along a flowing direction of the liquid
refrigerant after it grows to be inscribed in the flow channel. In
this way, although the gas does not occupy the flow channel
completely, it greatly reduces an effective cross-sectional area of
the flow channel, so that the pressure loss of the flow channel
increases considerably as in the case where the flow channel has a
circular cross-sectional shape. Thus, it is more suitable to
consider the relationship between the volume of the generated gas
and "the volume of a sphere that is inscribed in a cross-section of
the flow channel" rather than "the volume of a sphere whose
projected area is equivalent to the cross-sectional area of the
flow channel."
In the above-described condition, "the volume of the gas generated
in the liquid refrigerant" is influenced by a condition of an
atmosphere when the liquid refrigerant is sealed in the flow
channel of the cooling device and a temperature change to which the
liquid refrigerant is subjected during an operation of the cooling
device thereafter.
Now, the following is an exemplary case where a liquid having
solubility characteristics shown by a downwardly-sloping solubility
curve of the gas (the air) in which a solubility decreases as the
temperature rises as in FIG. 5 (such characteristics will be
expressed as "the solubility changes negatively with respect to the
temperature") is used as the liquid refrigerant. When the range of
temperature change to which the liquid refrigerant is subjected
inside the cooling device is expressed by an "operating temperature
range Trange," a temperature at which the solubility is minimal
within this temperature range (in the example of FIG. 5, an upper
limit temperature within the operating temperature range, namely,
the highest operating temperature) is expressed by T1, and the
solubility of the air at the temperature T1 is expressed by D1.
Further, the temperature at which the liquid refrigerant is sealed
into the cooling device is expressed by T2, and the solubility of
the air at the temperature T2 is expressed by D2. When a total
capacity of the flow channel forming the closed-loop circulating
cycle is expressed by V, the amount (volume) of gas Vair generated
in the liquid refrigerant is calculated by Formula (1) below.
The generated gas is present as a sphere in the liquid refrigerant
owing to the surface tension of the liquid refrigerant. Therefore,
the generated gas amount Vair and the area of the cross-section of
the gas (circle) (namely, the projected area of the sphere) Sair
have a relationship of Formula (2) below. ##EQU1##
When the area of a circle that is inscribed in the flow channel at
the position where the cross-sectional area of the flow channel in
the cooling device is minimal is expressed by Schannel, the above
condition can be given by Formula (3) below.
Alternatively, when the amount of gas dissolved in the liquid
refrigerant in a state where no gas is generated is expressed by
V0, the above condition also can be given by Formula (4) below.
where Vchannel is the volume of the sphere that is inscribed in the
flow channel at the position where the cross-sectional area of the
flow channel in the cooling device is minimal. Vchannel and the
above-mentioned area Schannel have a relationship of Formula (5)
below. ##EQU2##
When Formula (3) or (4) is satisfied, the gas generated in the flow
channel does not block the flow channel. Also, the pressure loss of
the flow channel does not increase greatly. As a result, the flow
rate of the liquid refrigerant can be secured.
FIG. 6 shows an upwardly-sloping solubility curve in which the air
solubility increases as the temperature rises within the operating
temperature range Trange (such characteristics will be expressed as
"the solubility changes positively with respect to the
temperature"). When using a liquid refrigerant having such
solubility characteristics, it is appropriate to adopt the
above-listed Formulae (1) to (5) by using the temperature T1 at
which the solubility is minimal within the operating temperature
range Trange (namely, the lowest operating temperature) and the
solubility D1 of the air at the temperature T1, as shown by FIG.
6.
FIG. 7 shows a solubility curve in which a decrease in the air
solubility as the temperature rises within the operating
temperature range Trange is so small that the curve can be
considered substantially horizontal. When using a liquid
refrigerant having such solubility characteristics, as in the case
of FIG. 5, it is appropriate to adopt the above-listed Formulae (1)
to (5) by using the temperature T1 at which the solubility is
minimal within the operating temperature range Trange (namely, the
highest operating temperature) and the solubility D1 of the air at
the temperature T1. In the liquid refrigerant whose solubility
curve is substantially horizontal, since D1.apprxeq.D2, Formula (1)
yields Vair.apprxeq.0, and Formula (2) yields Sair.apprxeq.0.
Accordingly, Formula (3) results in Formula (6) below.
As becomes clear from the above, when such a liquid refrigerant is
used, it is possible to achieve a cooling device in which the
generation of the gas is extremely small and a high cooling effect
can be obtained stably.
FIG. 8 shows a solubility curve of the air that is downwardly
convex within the operating temperature range Trange. When using a
liquid refrigerant having such solubility characteristics, as shown
by FIG. 8, it is appropriate to adopt the above-listed Formulae (1)
to (5) by using the temperature T1 at which the solubility is
minimal within the operating temperature range Trange and the
solubility D1 of the air at the temperature T1.
Furthermore, when using a liquid refrigerant having such solubility
characteristics as indicated by a solubility curve of the air that
is upwardly convex within the operating temperature range though
not shown, it is appropriate to adopt the above-listed Formulae (1)
to (5) by using the temperature T1 at which the solubility is
minimal within the operating temperature range (namely, a
temperature with smaller solubility out of the lowest operating
temperature and the highest operating temperature) and the
solubility D1 of the air at the temperature T1.
As described above, even when the solubility changes due to rapid
heating or cooling of the liquid refrigerant, little gas is
generated in the cooling device described in the present
embodiment. Thus, it is possible to prevent the cooling power from
deteriorating due to the deterioration in flow rate characteristics
of the pump occurring because the gas generated after a long time
use blocks the flow channel, the lowering heat conductivity caused
by adhesion of the gas to the inner wall of the flow channel and
the decline in the pump performance occurring because the generated
gas flows into the pump.
In addition, since the gas in the present invention is the air
containing usually nitrogen, oxygen, carbon dioxide etc., it is
sufficient to consider the nitrogen and the oxygen that are major
components when dealing with the solubility curve.
Various solubility characteristics of the liquid refrigerants
described in the present embodiment may be achieved by using a
single material as a liquid refrigerant or mixing a material whose
solubility curve slopes downward and a material whose solubility
curve slopes upward. For example, the material whose solubility
curve slopes downward typically is water, hexane or methanol, and
the material whose solubility curve slopes upward typically is
acetone, octane, carbon tetrachloride or benzene. Moreover, not
only two but also three of the above may be mixed. In those cases,
needless to say, similar effects can be obtained by satisfying the
above-mentioned condition.
In the present embodiment, the total capacity V of the flow channel
refers to a capacity of an entire flow channel through which the
liquid refrigerant circulates. Thus, capacities of the flow channel
24 of the heat absorber 2, the flow channel 31 of the heat radiator
3 and the space 20 of the pump 1 are included in the total capacity
V.
In the cooling device of the present embodiment, elements other
than the pump 1, the heat absorber 2 and the heat radiator 3 may be
connected to the flow channel 4. For example, a tank that stores
the liquid refrigerant may be connected to the flow channel 4 in
order to adjust the amount of the liquid refrigerant appropriately.
In this case, since the liquid refrigerant in the tank does not
circulate, it is not heated or cooled. Accordingly, a capacity of
this tank is not included in the above-described total capacity V
of the flow channel.
Second Embodiment
The following is a description of a second embodiment of the
present invention, with reference to the accompanying drawings.
FIG. 9 is a schematic perspective view showing an example of a
notebook PC in which a cooling device obtained by a method for
manufacturing a cooling device in the second embodiment of the
present invention is incorporated. FIG. 10 is a schematic view
showing an example of a sealing device used for sealing a liquid
refrigerant into the cooling device in the method for manufacturing
a cooling device according to the second embodiment of the present
invention. FIG. 11 is a graph schematically showing an example of
the solubility characteristics of the liquid refrigerant used in
the cooling device in the method for manufacturing a cooling device
according to the second embodiment of the present invention.
In FIG. 9, numeral 1 denotes a pump, numeral 2 denotes a heat
absorber, numeral 3 denotes a heat radiator, and numeral 4 denotes
a flow channel that allows communication between the interiors of
the pump 1, the heat absorber 2 and the heat radiator 3 and forms a
closed-loop circulating cycle from the pump 1, the heat absorber 2,
the heat radiator 3 to the pump 1. Numeral 5 denotes a housing of
the notebook PC, numeral 6 denotes a heat generator such as a CPU,
numeral 6a denotes a heat-transfer pad arranged between the heat
generator 6 and the heat absorber 2, and numeral 7 denotes a
display portion of the notebook PC. Inside the flow channel 4
forming the closed-loop circulating cycle from the pump 1, the heat
absorber 2, the heat radiator 3 to the pump 1 is filled with a
liquid refrigerant. The liquid refrigerant is out of contact with
an outside air. The heat absorber 2 closely contacts the heat
generator 6 such as the CPU via the heat-transfer pad 6a, whereby
the heat from the heat generator 6 is transferred to the heat
absorber 2 efficiently. The heat of the heat generator 6 is
absorbed in the heat absorber 2 and further transmitted to the
liquid refrigerant in the heat absorber 2. The heated liquid
refrigerant is carried by the action of the pump 1, thereby
carrying the heat to the heat radiator 3, which is formed on a back
surface of the display portion 7, and exhausting the heat from the
heat radiator 3 into the surrounding atmosphere. The resultant
liquid refrigerant that has been cooled down is carried again to
the heat absorber 2, and then the above-described operations are
repeated.
Since the pump 1, the heat absorber 2 and the heat radiator 3 have
structures similar to those described in the first embodiment, the
description thereof will be omitted here.
The method of the present embodiment for sealing a liquid
refrigerant into the cooling device of FIG. 9 constituted by the
pump 1, the heat absorber 2, the heat radiator 3 and the flow
channel 4 that allows communication therebetween will be described
referring to FIG. 10.
In FIG. 10, numeral 40 denotes a container that encloses the
cooling device in order to seal a liquid refrigerant, numeral 41
denotes a sealing port that is provided in, for example, the heat
radiator 3 and introduces and seals a liquid refrigerant into the
cooling device, and numeral 42 denotes a control valve-cum-sealer
that passes a liquid refrigerant introduced by a differential
pressure with respect to atmospheric pressure by decompressing the
interior of the container 40 while decompressing the interior of
the cooling device at the same time and, when the cooling device is
filled with the liquid refrigerant, seals the sealing port 41 by
heat or a similar effect. Numeral 43 denotes a decompressor for
decompressing the interior of the container 40 and the cooling
device, numeral 44 denotes a pipe for introducing a liquid
refrigerant into the cooling device, and numeral 45 denotes a
liquid refrigerant. Numeral 46a denotes a first heater for
adjusting the temperature of an atmosphere inside the container 40,
and numeral 46b denotes a second heater for adjusting the
temperature of the liquid refrigerant 45. If necessary, the first
heater 46a and/or the second heater 46b may be replaced by a
cooler.
The following is a description of a method for manufacturing a
cooling device using the liquid refrigerant sealing device with the
above-described configuration. The cooling device disposed inside
the container 40 is connected to the liquid refrigerant 45 via the
sealing port 41, the control valve-cum-sealer 42 and the pipe 44.
Since the liquid refrigerant 45 is under atmospheric pressure, it
flows into and fills the cooling device when the interior of the
container 40 and the cooling device are decompressed at the same
time by the decompressor 43.
At this time, it is necessary to maintain the temperature of the
atmosphere inside the cooling device and that of the liquid
refrigerant 45 at a predetermined temperature in the present
embodiment.
This will be described with an exemplary case in which the used
liquid refrigerant has downwardly-sloping solubility
characteristics as shown in FIG. 11. Within the operating
temperature range Trange, the solubility of the gas (air) in this
liquid refrigerant is minimal on a high temperature side of the
operating temperature range Trange (namely, the highest operating
temperature T1). Thus, the liquid refrigerant is sealed while
maintaining the temperature inside the container 40 and that of the
liquid refrigerant 45 at a temperature equal to or higher than this
highest operating temperature T1. In this manner, even when the
liquid refrigerant is heated rapidly inside the heat absorber 2
during an operation of the cooling device after the sealing, no air
bubbles are generated because the amount of the air dissolved in
the liquid refrigerant is smaller than the solubility at that
temperature. Thus, it is possible to prevent the cooling power from
deteriorating due to the deterioration in flow rate characteristics
of the pump occurring because the gas generated after a long time
use blocks the flow channel in the heat absorber, the lowering heat
conductivity caused by adhesion of the gas to the inner wall of the
flow channel in the heat absorber and the decline in the pump
performance occurring because the generated gas flows into the
pump.
The following is a description of a case in which the used liquid
refrigerant has upwardly-convex solubility characteristics as shown
in FIG. 12. Within the operating temperature range Trange, the
solubility of the gas (air) in this liquid refrigerant is minimal
on a high temperature side or a low temperature side of the
operating temperature range Trange. Here, the description is
directed to the case in which the solubility is minimal on the low
temperature side (namely, the lowest operating temperature T1)
within the operating temperature range Trange. The liquid
refrigerant is sealed while maintaining the temperature inside the
container 40 and that of the liquid refrigerant 45 at a temperature
equal to or lower than this lowest operating temperature T1. In
this manner, even when the liquid refrigerant is heated rapidly
inside the heat absorber 2 or the liquid refrigerant is cooled
inside the heat radiator 3 during the operation of the cooling
device after the sealing, little air bubble is generated because
the amount of the air dissolved in the liquid refrigerant is
smaller than the solubility at that temperature. Thus, it is
possible to prevent the cooling power from deteriorating due to the
deterioration in flow rate characteristics of the pump occurring
because the gas generated after a long time use blocks the flow
channels in the heat absorber and the heat radiator, the lowering
heat conductivity caused by adhesion of the gas to the inner walls
of the flow channels in the heat absorber and the heat radiator and
the decline in the pump performance occurring because the generated
gas flows into the pump. Incidentally, in the case where the liquid
refrigerant has upwardly-convex solubility characteristics and the
air solubility is minimal on the high temperature side of the
operating temperature range Trange, it is appropriate that the
liquid refrigerant is sealed while maintaining the temperature
inside the container 40 and that of the liquid refrigerant 45 at a
temperature higher than this temperature on the higher side (the
highest operating temperature T1).
The following is a description of a case in which the used liquid
refrigerant has upwardly-sloping solubility characteristics as
shown in FIG. 13. Within the operating temperature range Trange,
the solubility of the gas (air) in this liquid refrigerant is
minimal on a low temperature side of the operating temperature
range Trange (namely, the lowest operating temperature T1). The
liquid refrigerant is sealed while maintaining the temperature
inside the container 40 and that of the liquid refrigerant 45 at a
temperature equal to or lower than this lowest operating
temperature T1. In this manner, even when the liquid refrigerant is
heated rapidly inside the heat absorber 2 or the liquid refrigerant
is cooled inside the heat radiator 3 during the operation of the
cooling device after the sealing, little air bubble is generated
because the amount of the air dissolved in the liquid refrigerant
is smaller than the solubility at that temperature. Thus, it is
possible to prevent the cooling power from deteriorating due to the
deterioration in flow rate characteristics of the pump occurring
because the gas generated after a long time use blocks the flow
channels in the heat absorber and the heat radiator, the lowering
heat conductivity caused by adhesion of the gas to the inner walls
of the flow channels in the heat absorber and the heat radiator and
the decline in the pump performance occurring because the generated
gas flows into the pump.
The following is a description of a case in which the used liquid
refrigerant has downwardly-convex solubility characteristics as
shown in FIG. 14. Within the operating temperature range Trange,
the solubility of the gas (air) in this liquid refrigerant is
minimal at a temperature T1 between the high temperature side and
the low temperature side of the operating temperature range Trange.
The liquid refrigerant is sealed while maintaining the temperature
inside the container 40 and that of the liquid refrigerant 45 at
this temperature T1. In this manner, even when the liquid
refrigerant is heated rapidly inside the heat absorber 2 or the
liquid refrigerant is cooled inside the heat radiator 3 during the
operation of the cooling device after the sealing, little air
bubble is generated because the amount of the air dissolved in the
liquid refrigerant is smaller than the solubility at that
temperature. Thus, it is possible to prevent the cooling power from
deteriorating due to the deterioration in flow rate characteristics
of the pump occurring because the gas generated after a long time
use blocks the flow channels in the heat absorber and the heat
radiator, the lowering heat conductivity caused by adhesion of the
gas to the inner walls of the flow channels in the heat absorber
and the heat radiator and the decline in the pump performance
occurring because the generated gas flows into the pump.
The above description has been directed to the cases of using the
liquid refrigerants having downwardly-sloping, upwardly-convex,
upwardly-sloping and downwardly-convex solubility curves of the
air, respectively. As described above, the present embodiment is
applicable to any cases of downwardly-sloping, upwardly-convex,
upwardly-sloping and downwardly-convex solubility curves. It is
possible to obtain the above-mentioned effects by setting the
temperature of the atmosphere at the time of sealing the liquid
refrigerant to a temperature at which the solubility is minimal
within the operating temperature range Trange when the solubility
curve is downwardly convex within the operating temperature range
Trange of the liquid refrigerant and to a temperature at which the
solubility is smaller than the minimal value of the solubility
within the operating temperature range Trange (usually, this
temperature is outside the operating temperature range Trange) when
the solubility curve slopes downward, is upwardly convex or slopes
upward within the operating temperature range Trange of the liquid
refrigerant.
Third Embodiment
The following is a description of a third embodiment of the present
invention, with reference to the accompanying drawings.
FIG. 15 is a schematic view showing an example of a sealing device
used for sealing a liquid refrigerant into a cooling device in a
method for manufacturing a cooling device according to the third
embodiment of the present invention. FIG. 16 is a graph
schematically showing an example of solubility characteristics of
the liquid refrigerant used in the cooling device in the method for
manufacturing a cooling device according to the third embodiment of
the present invention.
Since the cooling device and a notebook PC in which this cooling
device is incorporated in the present embodiment have schematic
configurations similar to those described in the second embodiment,
the description thereof will be omitted here.
The method of the present embodiment for sealing the liquid
refrigerant into the cooling device constituted by the pump 1, the
heat absorber 2, the heat radiator 3 and the flow channel 4 that
allows communication therebetween will be described referring to
FIG. 15.
In FIG. 15, numeral 40a denotes a first container that encloses the
cooling device in order to seal a liquid refrigerant, numeral 40b
denotes a second container that encloses a liquid refrigerant,
numeral 41 denotes a sealing port that is provided in, for example,
the heat radiator 3 and introduces and seals a liquid refrigerant
into the cooling device, and numeral 42 denotes a control
valve-cum-sealer that passes a liquid refrigerant introduced by a
differential pressure with respect to atmospheric pressure by
decompressing the interior of the first container 40a while
decompressing the interior of the cooling device at the same time
and, when the cooling device is filled with the liquid refrigerant,
seals the sealing port 41 with heat or a similar effect. Numeral 43
denotes a decompressor for decompressing the interior of the first
container 40a, the second container 40b and the cooling device
independently at a predetermined pressure, numeral 44 denotes a
pipe for introducing the liquid refrigerant into the cooling
device, and numeral 45 denotes a liquid refrigerant.
The following is a description of a method for manufacturing the
cooling device using the liquid refrigerant sealing device with the
above-described configuration. The cooling device disposed inside
the first container 40a is connected to the liquid refrigerant 45
via the sealing port 41, the control valve-cum-sealer 42 and the
pipe 44. The decompressor 43 is used to decompress and control
individually the interior of the first container 40a, the cooling
device and the second container 40b at the same time. The pressure
inside the first container 40a and the pressure inside the cooling
device are set lower than the pressure inside the second container
40b, whereby the liquid refrigerant 45 flows into and fills the
cooling device.
At this time, it is necessary to set the pressure inside the second
container 40b at a pressure equal to or lower than a predetermined
pressure in the present embodiment.
This will be described with an exemplary case in which the used
liquid refrigerant has downwardly-sloping solubility
characteristics as shown in FIG. 16. In FIG. 16, a dotted line
indicates a solubility curve under atmospheric pressure, whereas a
solid line indicates a solubility curve under an atmosphere that is
decompressed to lower than the atmospheric pressure. Many liquids
have a solubility that lowers with a decrease in the pressure of an
atmosphere as shown in FIG. 16 (in other words, as the pressure of
the atmosphere lowers, the solubility curve shifts in a direction
indicated by an arrow 50 in FIG. 16). The solubility of the gas
(air) in this liquid refrigerant is minimal on a high temperature
side of the operating temperature range Trange (namely, the highest
operating temperature T1). Under atmospheric pressure, at the
highest operating temperature T1, the solubility reaches a minimal
value of D4 within the operating temperature range Trange. As the
interior of the second container 40b is decompressed more and more
(in other words, the solubility curve is shifted in the arrow 50
direction in FIG. 16), a solubility D3 at a temperature T2 of the
atmosphere at the time of sealing the liquid refrigerant eventually
reaches a point below the above-mentioned minimal value D4 of the
solubility within the operating temperature range Trange under
atmospheric pressure (D3<D4). In the present embodiment, the
liquid refrigerant is sealed in the cooling device while
decompressing the interior of the second container 40b so that
D3<D4 is satisfied. In this manner, the amount of gas dissolved
in the liquid refrigerant at the time of sealing can be set much
smaller than the minimal solubility D4 within the operating
temperature range Trange of the liquid refrigerant during an
operation of the cooling device. Therefore, even when the liquid
refrigerant is heated rapidly inside the heat absorber 2 during the
operation of the cooling device after the sealing, little air
bubble is generated because the amount of the air dissolved in the
liquid refrigerant is smaller than the solubility at that
temperature. Thus, it is possible to prevent the cooling power from
deteriorating due to the deterioration in flow rate characteristics
of the pump occurring because the gas generated after a long time
use blocks the flow channel in the heat absorber, the lowering heat
conductivity caused by adhesion of the gas to the inner wall of the
heat absorber and the decline in the pump performance occurring
because the generated gas flows into the pump.
Furthermore, in addition to the decompressing process of the
present embodiment at the time of sealing the liquid refrigerant,
the interior of the first container 40a and the liquid refrigerant
45 may be heated or cooled as described in the second embodiment,
thereby obtaining effects similar to those described in the second
and third embodiments.
Although the above description has been directed to the case of
using the liquid refrigerant whose solubility curve of the air
slopes downward, the present embodiment is not limited to the
above. For example, the solubility curve also may slope upward, be
downwardly convex or upwardly convex. In any cases, the liquid
refrigerant is sealed under an atmosphere decompressed so that the
solubility at the temperature of the atmosphere at the time of
sealing the liquid refrigerant is smaller than the minimal value of
the solubility under atmospheric pressure within the operating
temperature range of the liquid refrigerant, thereby obtaining
effects similar to the above.
Although the notebook personal computer has been illustrated as
portable equipment in the first to third embodiments described
above, there is no particular limitation to this. The portable
equipment also may be a miniature easily-portable electronic device
such as a PDA (personal digital assistance) or a cellular
phone.
Although the CPU has been illustrated as an object to be cooled
down to which the heat absorber 2 is attached in the first to third
embodiments described above, the present invention is not limited
to this but can be applied, for example, to a cooling device of a
semiconductor element.
Additionally, in the first to third embodiments described above,
the "operating temperature range" of the liquid refrigerant refers
to a range of temperature change to which the liquid refrigerant
actually is subjected (or designed temperature change to which the
liquid refrigerant is expected to be subjected) when the liquid
refrigerant circulates in the flow channel inside the cooling
device. The upper limit of this "operating temperature range"
mostly varies according to a temperature of heat generated from the
heat generator 6 that the heat absorber 2 closely contacts. The
lower limit thereof generally coincides with the temperature of the
liquid refrigerant after being cooled down by the heat radiator 3.
When the cooling device is used for a notebook PC, in general, the
upper limit of the operating temperature range of the liquid
refrigerant is 95.degree. C. or 65.degree. C., whereas the lower
limit thereof is 0.degree. C. It is needless to say, however, that
the operating temperature range of the liquid refrigerant in the
present invention is not limited to the above.
The invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. The
embodiments disclosed in this application are to be considered in
all respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description, all changes that come within the meaning and
range of equivalency of the claims are intended to be embraced
therein.
* * * * *