U.S. patent application number 12/474984 was filed with the patent office on 2010-12-02 for modified heat pipe for phase change cooling of electronic devices.
Invention is credited to Darvin Renne EDWARDS.
Application Number | 20100300654 12/474984 |
Document ID | / |
Family ID | 43218888 |
Filed Date | 2010-12-02 |
United States Patent
Application |
20100300654 |
Kind Code |
A1 |
EDWARDS; Darvin Renne |
December 2, 2010 |
MODIFIED HEAT PIPE FOR PHASE CHANGE COOLING OF ELECTRONIC
DEVICES
Abstract
Exemplary embodiments provide a heat pipe including a flexible
chamber that is capable of expanding, compressing and/or restoring.
In one embodiment, the heat pipe can include a hollow metal casing
including a pipe structure connected to an expandable chamber at
one end of the pipe structure. The other end of the pipe structure
can include an evaporating section for receiving heat and the
expandable chamber can include a condensing section for releasing
the heat. The expandable chamber can be configured to change in
volume to control one or both of a temperature and a pressure in
the hollow metal casing. The heat pipe can also include a capillary
system arranged at an inner surface of the hollow metal casing that
includes the pipe structure and the expandable chamber.
Inventors: |
EDWARDS; Darvin Renne;
(Garland, TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
US
|
Family ID: |
43218888 |
Appl. No.: |
12/474984 |
Filed: |
May 29, 2009 |
Current U.S.
Class: |
165/104.26 ;
165/104.33; 29/890.032 |
Current CPC
Class: |
F28D 15/0241 20130101;
Y10T 29/49353 20150115; H01L 2924/0002 20130101; H05K 7/20336
20130101; H01L 23/427 20130101; F28F 2265/12 20130101; H01L 2924/00
20130101; H01L 2924/0002 20130101 |
Class at
Publication: |
165/104.26 ;
29/890.032; 165/104.33 |
International
Class: |
F28D 15/02 20060101
F28D015/02; B21D 53/02 20060101 B21D053/02; F28D 15/00 20060101
F28D015/00 |
Claims
1. A heat pipe comprising: a hollow metal casing comprising a pipe
structure and an expandable chamber connected to a first end of the
pipe structure, wherein the expandable chamber is configured to
change in volume to control one or both of a temperature and a
pressure in the hollow metal casing; and a capillary system
disposed at an inner surface of the pipe structure and the
expandable chamber.
2. The heat pipe of claim 1, wherein the expandable chamber
comprises one or more flexible corrugations so that the volume of
the expandable chamber is changed by folding or unfolding the one
or more flexible corrugations.
3. The heat pipe of claim 1, wherein the expandable chamber
comprises a spring-type mechanism.
4. The heat pipe of claim 3, wherein the spring-type mechanism
comprises a non-linear expansion and a non-linear restoration.
5. The heat pipe of claim 1, wherein the expandable chamber
comprises a cross sectional shape comprising a circle, a square, a
rectangle, a triangle, or a polygon.
6. The heat pipe of claim 1, further comprising a heat sink cooled
heat pipe comprising the expandable chamber.
7. The heat pipe of claim 1, further comprising a heat source at a
second end of the pipe structure, wherein the second end of the
pipe structure comprises an evaporating section for receiving heat
from the heat source.
8. The heat pipe of claim 7, wherein the heat source comprises a
device within a cell phone, a MP3 device, a GPS device or a laptop
computer.
9. A heat pipe comprising: a pipe structure attached to an
electronic device for receiving heat from the electronic device;
and an expandable chamber connected to the pipe structure for
dissipating the received heat through a phase change of water that
flows through the pipe structure and the expandable chamber,
wherein the expandable chamber is configured to change in volume so
as to control one or both of a temperature and a pressure in the
pipe structure.
10. The heat pipe of claim 9, wherein the expandable chamber
comprises one or more flexible corrugations so that the volume of
the expandable chamber is changed by folding or unfolding the one
or more flexible corrugations.
11. The heat pipe of claim 9, wherein the expandable chamber
comprises a linear spring-type mechanism or a non-linear
spring-type mechanism so as to control one or both of the
temperature and the pressure in the pipe structure.
12. The heat pipe of claim 9, wherein the expandable chamber
comprises a cross sectional shape comprising a circle, a square, a
rectangle, a triangle, or a polygon.
13. The heat pipe of claim 9, further comprising a heat sink cooled
heat pipe comprising the expandable chamber.
14. The heat pipe of claim 9, wherein the electronic device
comprises a device within a cell phone, a MP3 device, a GPS device
or a laptop computer.
15. A method for forming a heat pipe comprising: providing a hollow
metal casing comprising a pipe structure, wherein a first end of
the pipe structure comprises an evaporating section for receiving
heat; placing an expandable chamber in the hollow metal casing and
connected at a second end of the pipe structure, wherein the
expandable chamber comprises a condensing section for releasing the
heat and is configured to change in volume to control one or both
of a temperature and a pressure in the hollow metal casing; and
arranging a capillary system at an inner surface of the pipe
structure and the expandable chamber.
16. The method of claim 15, wherein the volume of the expandable
chamber is changed by folding or unfolding one or more flexible
corrugations of the expandable chamber.
17. The method of claim 15, wherein the expandable chamber
comprises a linear spring-type mechanism or a non-linear
spring-type mechanism so as to control one or both of the
temperature and the pressure in the hollow metal casing.
18. A method for dissipating heat comprising: providing a hollow
metal casing comprising a pipe structure and an expandable chamber
connected at a first end of the pipe structure; wherein the
expandable chamber is configured to change in volume to control one
or both of a temperature and a pressure in the hollow metal casing;
packaging an electronic device at a second end of the pipe
structure; and flowing a fluid in the hollow metal casing to
receive heat transmitted from the electronic device and thereby
generating a vapor that is condensed in the expandable chamber to
release the heat.
19. The method of claim 18, further comprising controlling a vapor
pressure in the hollow metal casing by controlling an amount of the
fluid flowing in the hollow metal casing.
20. The method of claim 18, further comprising controlling a
boiling temperature of the fluid flowing in the hollow metal casing
by adjusting a spring constant of a spring-type expandable
chamber.
21. The method of claim 18, further comprising adjusting an amount
of the fluid flowing in the hollow metal casing such that the fluid
evaporates at a power for a maximum length of an operation of the
electronic device.
22. The method of claim 18, wherein the fluid flowing in the hollow
metal casing comprises water, alcohol, or combinations thereof.
Description
DESCRIPTION OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention generally relates to heat transfer components
and, more particularly, to heat pipes that include an expandable
chamber.
[0003] 2. Background of the Invention
[0004] The power density of components used in portable electronics
such as cellphones, MP3 players and global positioning systems
(GPSs) is increasing as more features are added to the equipment
and with the advent of new package technologies such as stacked
die, stacked packages, and through-silicon vias (TSV) packages.
Additionally, new battery technologies have increased the power
capacity, e.g., by about 10% per year. Due to these reasons, the
operating temperature of portable electronic devices has increased
dramatically. However, due to battery life concerns, these portable
electronic devices do not use miniature fans and heat sinks.
[0005] Conventional methods to release the increased heat generated
by these devices include the use of heat spreaders, which are
either integrated into the printed circuit board (PCB) or
distributed on top of the package. For example, the heat spreader
may be an external casing having high thermal conductivity, often
simply a copper plate, designed to cover an electronic device and
conduct heat to a dissipating surface. Heat is removed from the
dissipating surface through either conduction into the user's hand
or convection and radiation into the environment.
[0006] Other cooling schemes which have been explored include the
use of phase change materials to absorb heat generated from an
activity or operation such as a phone call. The absorbed heat is
then gradually released during the quiescent time between calls by
cooling down and changing phase. For example, a mass of paraffin or
low melting temperature salt might be encased around the component
to be cooled. As the component heats, the phase change material
melts, transforming the heat from a temperature rise to a phase
change event. The phase change material also is provided with
thermal conduction to heat dissipative surfaces such that when the
heating cycle such as a phone call completes, the phase change
material cools, changing back into a solid before the next heating
event.
[0007] A structure which is commonly used to conduct heat from a
heated component to the dissipative surface in computers is a heat
pipe. A heat pipe consists of a tube coated on the inside with a
wicking structure. The heat pipe is partially filled with water and
the pressure inside is reduced to tune the boiling point of the
water to a desired temperature which becomes the operating
temperature of the heat pipe. The heating end of the heat pipe is
attached to the hot component. The cooling end of the heat pipe is
attached to the heat dissipating surface, often a heat sink. When
the temperature of the heated end reaches the boiling point of the
water inside, the water absorbs the heat needed to vaporize, fills
the tube with vaporized water, which then re-condenses at the
cooled end of the heat pipe. The heat of vaporization is given up
during the condensing process. The now liquid water is pulled by
capillary action back to the hot end of the pipe.
SUMMARY OF THE INVENTION
[0008] Applicant has realized that new heat pipes and methods are
needed to have an increased cooling capacity so as to release the
increased heat generated by components used in, for example,
portable electronics with increased power density and/or increased
power capacity.
[0009] Conventional cooling devices, such as heat spreaders, have
low cooling capacity. For example, when heat spreaders are used,
the total power dissipation of the hand held system is about 3
watts due to the cooling capacity of the hand. Conventional heat
pipes use low volumes of phase change materials, such as water, and
have low stand alone cooling capacity. A common failing of
conventional heat pipes is dry-out of the water. That is, the water
boils away from the hot end of the pipe faster than it re-condenses
at the cold end.
[0010] Thus, there is a need to overcome these and other problems
of the prior art and to provide a new heat pipe construction to
minimize heat pipe dry-out, to provide more phase change working
fluid volume to handle higher power peaks, and to integrate the
heat sink onto the heat pipe in a compact structure intended for
portable electronic devices. The new heat pipe can have increased
stand alone cooling capacity as compared with conventional heat
transfer components used in the art.
[0011] In order to develop such heat pipe, the Applicant
incorporated an expandable chamber into a conventional heat pipe,
such as a conventional cylindrical heat pipe. In one embodiment,
the discovered expandable chamber can be connected to one end of a
pipe structure and can have flexible corrugations so that the
volume of the expandable chamber can increase or decrease. The
incorporation of the inventive expandable chamber can be used to
control internal pressure and boiling point of a working fluid or a
phase change material flowing within the heat pipe. The
incorporation of the inventive expandable chamber can allow for a
large quantity of the working fluid or the phase change material to
enable more peak power heat dissipation through its boiling.
[0012] Preliminary experiments and calculations have been performed
to analyze the inventive heat pipe having the expandable chamber.
For example, water, having a latent heat of vaporization of about
2300 J/gm, can be used as a working fluid or a phase change
material. As known, a watt represents about 1 J/sec. A phone call
that runs 3 watts for 8 minutes (i.e., 480 seconds) can therefore
represent 1440 joules. This energy is sufficient to boil only 0.6
gm of water.
[0013] In the case when 1 gm of water (i.e., 1 cc, or 1000
mm.sup.3) is used, the disclosed heat pipe can handle a 3 watt
power peak for 13 minutes by boiling alone. Water having the volume
of about 1000 mm.sup.3 (i.e., 1 gm) can be filled in an exemplary
heat pipe having a cross sectional area of about 100 mm.sup.2 with
an initial length of about 10 mm, which however can be extended to
be, e.g., about 40 mm to about 80 mm, which allows for a large
volume of vapor to fill the heat pipe. It should be noted that as
the vapor chamber expands, the internal pressure will also be
increasing, raising the boiling point of the working fluid. The
electronic system into which the exemplary vapor chamber will be
placed must allow for adequate cooling of the chamber to allow the
boiling temperature of the fluid to remain below the maximum
allowed operating temperature of the electronic device, which is
often 85.degree. C. or 105.degree. C.
[0014] In one experiment, the larger volume of water can absorb
excess heat energy as the temperature of related electronic devices
goes above 65.degree. C. Water boils at 65.degree. C. at a pressure
of -3.8 psi. In the example where the cross sectional area of the
expandable chamber is about 100 mm.sup.2 (i.e., about 0.155
in.sup.2.), the expandable chamber may have spring-type mechanism
to produce a weight of about 1.58 lbs against the atmospheric
pressure of about 14 psi in order to obtain the pressure of about
3.8 psi required to boil water at 65.degree. C.
[0015] In this manner, the inventive heat pipe can provide an
increased cooling capacity by allowing a higher volume of working
fluid, the water. The expanding chamber can act to maintain a lower
pressure as the water boils while at the same time can perform the
function of a heat sink to re-condense the water. Conventional heat
pipes allow only minimal change in volume and have fixed physical
dimensions that are dependent on only the thermal expansion
constants of the materials. As a result, large volume of working
fluids, such as water, cannot be used to absorb excess heat energy
in conventional heat pipes.
[0016] Additionally, the disclosed heat pipe having an expandable
chamber connected to a pipe structure can provide flexibility in
assembly. For example, the pipe portion can be bent around curves
to fit the contours of related electronic systems and the
expandable structure portion can be flattened to fit any flat-like
volume.
[0017] Further, the inventive heat pipe having expandable chambers
can be very compact to enable cooling, e.g., in cell phones or
other handheld applications and can be an enabler for high density
stacked die components.
[0018] The technical advances represented by the invention, as well
as the aspects thereof will become apparent from the following
description of the preferred embodiments of the invention, when
considered in conjunction with the accompanying drawings and the
novel features set forth in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate several
embodiments of the invention and together with the description,
serve to explain the principles of the invention. In the
figures:
[0020] FIG. 1 depicts an exemplary heat pipe including an
expandable chamber in accordance with the present teachings;
[0021] FIG. 1A depicts a cross sectional view of the exemplary
expandable chamber of FIG. 1 in accordance with the present
teachings; and
[0022] FIG. 2 depicts the exemplary heat pipe of FIG. 1 in an
exemplary working state in accordance with the present
teachings.
[0023] It should be noted that some details of the FIGS. have been
simplified and are drawn to facilitate understanding of the
inventive embodiments rather than to maintain strict structural
accuracy, detail, and scale.
DESCRIPTION OF THE EMBODIMENTS
[0024] The Applicant has realized that a new heat pipe needs to be
provided. In an exemplary embodiment, the inventive heat pipe can
include an expandable chamber that can accommodate an increased
volume of water, as compared to a conventional heat pipe. The
increased volume of water can be used as the phase change material
to control and improve heat dissipation. The increased volume of
water can be used because the expandable chamber can increase one
or more of its dimensions, for example, in an accordion-like
manner. In contrast, conventional heat pipes have fixed physical
dimensions. Applicants recognize that conventional heat pipes can
change dimensions due to thermal expansion. However, the change in
dimension due to thermal expansion is not sufficient to accommodate
a larger volume of water to increase heat dissipation.
[0025] Reference will now be made in detail to the present
embodiments (exemplary embodiments) of the invention, examples of
which are illustrated in the accompanying drawings. Wherever
possible, the same reference numbers will be used throughout the
drawings to refer to the same or like parts.
[0026] In the following description, reference is made to the
accompanying drawings that form a part thereof, and in which is
shown by way of illustration specific exemplary embodiments in
which the invention may be practiced. These embodiments are
described in sufficient detail to enable those skilled in the art
to practice the invention and it is to be understood that other
embodiments may be utilized and that changes may be made without
departing from the scope of the invention. The following
description is, therefore, merely exemplary.
[0027] Exemplary embodiments provide a heat pipe including a
flexible vapor chamber that is capable of expanding, compressing
and/or restoring. In one embodiment, the heat pipe can include a
hollow metal casing including a pipe structure connected to an
expandable chamber at one end of the pipe structure. The other end
of the pipe structure can include an evaporating section for
receiving heat and the expandable chamber can include a condensing
section for releasing the heat. The heat pipe can also include a
capillary system arranged at an inner surface of the hollow metal
casing that includes the pipe structure and the expandable chamber.
In an exemplary embodiment, the expandable chamber can be, for
example, a spring type vapor chamber that increases or decreased in
volume to control the heat pipe internal pressure and the boiling
point of a working fluid, such as water, alcohol or their
combinations, continuously flowing in the heat pipe. A larger
quantity of water can then enable more heat dissipation through
boiling.
[0028] In various embodiments, the expandable chamber can include,
for example, corrugations that are flexible so that the volume of
expandable chamber can increase or decrease. In various
embodiments, the expandable chamber can include a cross sectional
shape, such as, for example, a circle, a square, a rectangle, a
triangle, or a polygon. Such cross sectional shapes can be, for
example, shaped into folds to form corrugations along a main axis
direction of the expandable chamber. In this case, the volume of
the expandable chamber can thus be changed by folding or unfolding
the corrugations.
[0029] In various embodiments, the expandable chamber can be
expandable and restorable relative to an equilibrium state. In
various embodiments, the expandable chamber can include a
spring-type mechanism that further includes a linear or non-linear
expansion and a linear or non-linear restoration. In various
embodiments, the expandable chamber may or may not include a
thermal expansion depending on the materials used for the
chamber.
[0030] FIG. 1 depicts an exemplary heat pipe 100 in accordance with
the present teachings. It should be readily apparent to one of
ordinary skill in the art that the heat pipe 100 depicted in FIG. 1
represents a generalized schematic illustration and that other
components can be added or existing components can be removed or
modified.
[0031] As shown, the heat pipe 100 can include a metal casing 102.
The metal casing 102 can include a pipe structure 124, e.g., having
a cylindrical configuration, and an expandable chamber 116
connected at one end of the pipe structure 124. As used herein, the
term "expandable chamber" refers to a chamber that can increase one
or more of its dimensions because of the structural configuration
of the chamber. In an exemplary embodiment, the structural
configuration of the expandable chamber can be accordion-like. The
other end of the pipe structure 124 can include an evaporating
section 112 (also referred to herein as a heating section, or a
heat absorbing section) which is connected to the electronic
component 180 for receiving heat during a heat pipe operation,
while the expandable chamber 116 can include a condensing section
(also referred to herein as a cooling section, or a heat emitting
section) for releasing the heat. Other embodiments can also include
a condensing section covering a portion of the pipe structure 124,
in addition to the covering of a portion or a whole of the
expandable chamber 116. An adiabatic section 114 can be arranged
between the evaporating section 112 and the condensing section.
[0032] Inside the metal casing 102 that includes the pipe structure
124 and the expandable chamber 116, the heat pipe 100 can further
include a capillary system 104 and a vapor channel 106.
[0033] The metal casing 102 can be a hollow metal casing made of
highly thermally conductive materials, such as copper, copper
alloys, aluminum, or copper clad stainless steel. A working fluid,
e.g., a volatile medium such as water or alcohol, can be contained
in the metal casing 102. The capillary system 104 can include,
e.g., a capillary wick structure known to one of ordinary skill in
the art, and can be arranged in the inner surface of both the pipe
structure 124 and the expandable chamber 116. In various
embodiments, the capillary system 104 can include a wick material
including, for example, braided Cu or sintered powdered Cu.
[0034] The vapor channel 106 can be surrounded by an inner surface
of the capillary system 104 so as to guide the working fluid to
flow therein during operation. The vapor channel 106 can be defined
along an axial direction of the pipe structure 124 and extended
into the expandable chamber 116. The vapor channel 106 can be
located at a center of both the metal casing 102 and the expandable
chamber 116.
[0035] As shown in FIG. 1, the metal casing 102, the capillary
system 104 and the vapor channel 106 can have a conformable shape
according to the shape of the pipe structure 124 and the expandable
chamber 116. For example, portions of the metal casing 102, the
capillary system 104 and the vapor channel 106 that are associated
with the pipe structure 124 can have, e.g., a cylindrical shape
corresponding to the shape of the pipe structure, while portions
associated with the expandable chamber 116 can have expandable
shapes corresponding to the shape of the expandable chamber 116 as
illustrated in FIG. 1A. For example, FIG. 1A depicts a cross
sectional view of the expandable chamber 116 of the heat pipe 100
of FIG. 1 in accordance with the present teachings.
[0036] The expandable chamber 116 that includes corresponding
portions of the casing 102, the capillary structure 104 and/or the
vapor channel 106 can exhibit an expansion and/or contraction
action from its equilibrium state (also referred to herein as a
rest state), for example, expanding in one or more axial directions
of length, width, height, and/or volume; and can experience a
partial or full restoration to its equilibrium state after the
expansion and/or contraction.
[0037] For comparison, the device 100 of FIG. 1 shows an exemplary
expandable chamber 116 in an equilibrium or rest state having an
exemplary length L.sub.0 in accordance with the present teachings.
From this equilibrium state, the chamber 116 can be expanded, for
example, along a length wise direction 150 or can be compressed
along a length wise direction 155. The expandable chamber 116 can
also be restored along direction 155 after the expansion. For
example, FIG. 2 depicts the exemplary heat pipe 100 of FIG. 1 in an
exemplary working state, wherein the expandable chamber is an
expanded chamber 116a in a length wise direction to have an
expanded length L.sub.Expanded, where L.sub.Expanded is greater
than L.sub.D.
[0038] To accomplish the expansion, expandable chamber 116 can
include, for example, flexible corrugations having various cross
sections shaped into folds. The volume of expandable chamber 116
can then be increased (see 116a) from its rest state by unfolding
the folds. In the illustrated example of FIG. 2, the expanded
chamber 116a can have a circular cross section 132 unfolded at 134
to increase the volume of the chamber. Such expanded chamber 116a
can be capable of partially or fully restoring to its equilibrium
state having a restored length close or equal to L.sub.0 (see FIG.
1), wherein the exemplary circular cross section 132 of the
flexible corrugations can be folded at 134.
[0039] In an exemplary embodiment, the expandable chamber 116 can
have a spring-type mechanism, wherein the force (e.g., provide by
the water vapor) required to expand the expandable chamber has a
linear or non-linear relationship with the distance that the
chamber has been stretched or compressed away from the equilibrium
state. That is, the spring-type mechanism can include a linear or
non-linear expansion and compression from equilibrium state and/or
a linear or non-linear restoration to its equilibrium state.
[0040] In one embodiment, the expandable chamber 116 can have a
force constant or a spring constant which is a function of the
number of folds in the expandable chamber, the depth of the folds,
the angle of the bends at the top and bottom of the folds, and the
material of the chamber, all of which can be adjusted to control
the heat pipe operation. The spring constant can be adjusted
depending on the area and compressed length of the expandable
chamber 116 to maintain a predetermined boiling temperature for the
water inside the chamber. For example, water at one-quarter of
normal pressure can boil at about 65.degree. C., while water at
one-tenth of normal pressure can boil at about 45.degree. C. One of
ordinary skill in the art will understand that by adjusting the
spring constant of the expandable chamber 116, the boiling point
can be tuned to give the best thermal performance for the
electronic system. One of ordinary skill in the art will also
understand that the spring constant of expandable chamber 116 can
be adjusted in a variety of ways including, but not limited to,
adjusting the thickness and/or cross sectional shape of the walls
of the expandable chamber, changing the material composition of the
walls of the expandable chamber, changing the number of folds in
the expandable chamber, changing the depth of the folds, or other
adjustments. In various embodiments, a separate spring may be
inserted in the expandable chamber to accommodate the controlled
boiling pressure or to stop the expansion at a fixed length.
[0041] In various embodiments, although the chamber 116/116a in a
direction perpendicular to the main direction of the pipe structure
124 is shown having a round cross sectional shape in FIG. 1, one of
ordinary skill in the art will understand that other regular or
irregular cross sectional shapes can be used including, but not
limited to, square, rectangle, triangle, or polygon. For example, a
square expansion chamber can be constructed in order to provide
better filling area and form factor concerns in electronic devices
connected thereto, such as a cell phone or other hand held device
including, for example, a MP3 player, a GPS (global positioning
system) device, and/or a laptop.
[0042] As disclosed, the incorporation of the expandable chamber
116 can provide many advantages to the disclosed heat pipe 100. For
example, as compared with a conventional heat pipe, the disclosed
heat pipe can utilize an increased volume of working fluid (e.g.,
water or alcohol) to fill the heat pipe 100. In this case, more
boiling of water can take place to provide more working capacity of
the heat pipe. In another example, the pressure in the heat pipe
100 can be controlled and maintained at a desired level due to the
addition of the expandable chamber in the heat pipe, as more and
more water can be boiled in the heat pipe. In a further example,
various cross sectional expandable/compressible shapes can be used
to make the expandable chamber act as a heat sink element. For
example, the expandable chamber can have a square cross section and
can be constructed to provide better filling area and form factor
concerns in electronic devices. The disclosed heat pipe can
therefore be used as a heat sink cooled heat pipe that absorbs and
dissipates heat from the electronic devices, e.g., using direct,
radiant, or convective thermal contact. Further more, the disclosed
heat pipe can provide flexibility in assembly. For example, the
disclosed heat pipe can be bent around curves to fit the contours
of any system, such as a video game system (not shown), while the
pipe structure part of the heat pipe can be flattened to fit any
flat-like surface of, e.g., the video game system. The compliance
of the disclosed heat pipe can improve application flexibility.
[0043] Referring back to FIG. 1, the heat pipe 100 including the
expandable chamber 116 can be made of a material with good heat
conductivity. The expandable chamber 116 can provide control of the
heat pipe internal pressure and/or the boiling point, and can
therefore be used as, e.g., a vapor chamber to store the vapor
therein; a pressure chamber to control the pressure therein; or a
temperature chamber to expel the heat therein.
[0044] In operation, the working fluid such as water can be
volatilized by heat transmitted or applied, e.g., from electronic
components 180 at 120 of the heat pipe, to the evaporating section
112 (i.e., the heating section, or heat absorbing section), causing
the water to boil at a preset temperature. The boiling temperature
(or the boiling point) can be preset depending on features of the
expandable chamber 116, for example, depending on the spring
constant of an exemplary spring-type expandable vapor chamber. In
various embodiments, the spring constant of the expandable pressure
chamber can be adjusted such that the boiling temperature of the
working fluid at "dry out" or a "complete evaporation" state is
less than the maximum allowed case temperature, such as about
100.degree. C.
[0045] As the water boils, the water vapor can occupy more space
than liquid water along the pipe structure 124 and the expandable
chamber 116 until the vapor fills pipe structure 124 and expandable
chamber 116, which causes the pressure of the heat pipe 100 and the
boiling temperature of the water to increase. When the water vapor
fills the expandable chamber 116 of the heat pipe 100, the vapor
chamber 116 can be expanded or unfolded, e.g., in a length
direction 150 of FIG. 1, and the vapor can condense on the vapor
chamber walls. The temperature of the expandable chamber 116 can
then be decreased and heat can be released from the expandable
chamber 116. The chamber 116 can be restored (or folded) to the
equilibrium state to have a length close or equal to L.sub.0 shown
in FIG. 1, when releasing heat. Such vapor condensation and the
heat releasing process can generate an under-pressure in the
expandable chamber 116, which further conveys more vapor from the
heat absorbing section 112 to the heat emitting section, i.e., the
expandable chamber 116. Because of the capillary action of the
capillary system 104, the condensed medium (e.g., water) can be
pumped out of the expandable chamber and can continuously flow back
to the heat absorbing section 112 of the heat pipe 100.
[0046] Various embodiments can also include a method for forming
the disclosed heat pipe. For example, the heat pipe can be formed
having a hollow metal casing that includes a pipe structure. In
various embodiments, hollow metal casings and pipe structures that
are known to one of ordinary skill in the art can be used for the
disclosed heat pipe. The pipe structure can include an evaporating
section for receiving heat at one end. An expandable chamber can be
connected at the other end of the pipe structure in the hollow
metal casing. Such expandable chamber can include a condensing
section for releasing the heat that is received from the
evaporating section of the pipe structure. A capillary system can
then be arranged at an inner surface of the hollow metal casing to
include the pipe structure and the expandable chamber.
[0047] The disclosed heat pipe 100 can be used in various
applications. For example, the heat pipe 100 can be a vapor chamber
cooler to allow water to be used to provide phase change cooling of
a portable electronic device in a small, compact, passive
(self-powered), and self-contained component.
[0048] In an exemplary embodiment, electronic devices can be
packaged with the disclosed heat pipe to enable a high level of
power to be dissipated. That is, the disclosed heat pipe can be an
enabler for high power stacked components. For example, at 120 as
shown in FIG. 1, a package stack of electronic devices 180 can be
attached to the pipe structure 124 to dissipate the heat generated
by the electronic device, such as a cell phone. In this case, the
quantity of water can be adjusted such that water dries out or
completely evaporates at the maximum power for the maximum length
of the cell phone call or other operation.
[0049] The use of the disclosed heat pipe can also provide many
advantages to the attached electronic devices. For example, more
heat storage capacity can be provided as compared with conventional
phase change solutions, e.g., using paraffin or salts. This is
because the use of water can provide a 10 times higher heat of
vaporization. In addition, the disclosed heat pipe can allow a
higher working volume of water as compared with a conventional heat
pipe due to use of the expandable chamber, which allows more heat
to be absorbed in phase change and more heat dissipation through
boiling. Further, the disclosed heat pipe having expandable chamber
can be used as heat sink cooled heat pipe. Furthermore, the
disclosed heat pipe can be very compact to enable cooling in, e.g.,
cell phones or other handheld applications. Even further, the
disclosed heat pipe device can be an enabler for high density
stacked die components.
[0050] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the invention are approximations,
the numerical values set forth in the specific examples are
reported as precisely as possible. Any numerical value, however,
inherently contains certain errors necessarily resulting from the
standard deviation found in their respective testing measurements.
Moreover, all ranges disclosed herein are to be understood to
encompass any and all sub-ranges subsumed therein. For example, a
range of "less than 10" can include any and all sub-ranges between
(and including) the minimum value of zero and the maximum value of
10, that is, any and all sub-ranges having a minimum value of equal
to or greater than zero and a maximum value of equal to or less
than 10, e.g., 1 to 5. In certain cases, the numerical values as
stated for the parameter can take on negative values. In this case,
the example value of range stated as "less than 10" can assume
values as defined earlier plus negative values, e.g. -1, -1.2,
-1.89, -2, -2.5, -3, -10, -20, -30, etc.
[0051] While the invention has been illustrated with respect to one
or more implementations, alterations and/or modifications can be
made to the illustrated examples without departing from the spirit
and scope of the appended claims. In addition, while a particular
feature of the invention may have been disclosed with respect to
only one of several implementations, such feature may be combined
with one or more other features of the other implementations as may
be desired and advantageous for any given or particular function.
Furthermore, to the extent that the terms "including", "includes",
"having", "has", "with", or variants thereof are used in either the
detailed description and the claims, such terms are intended to be
inclusive in a manner similar to the term "comprising." As used
herein, the term "one or more of" with respect to a listing of
items such as, for example, A and B, means A alone, B alone, or A
and B. The term "at least one of" is used to mean one or more of
the listed items can be selected.
[0052] Other embodiments of the invention will be apparent to those
skilled in the art from consideration of the specification and
practice of the invention disclosed herein. It is intended that the
specification and examples be considered as exemplary only, with a
true scope and spirit of the invention being indicated by the
following claims.
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