U.S. patent application number 12/481560 was filed with the patent office on 2009-12-10 for active multiphase heat transportation system.
This patent application is currently assigned to Dynalene Inc.. Invention is credited to Satish Chandra Mohapatra.
Application Number | 20090301691 12/481560 |
Document ID | / |
Family ID | 41399222 |
Filed Date | 2009-12-10 |
United States Patent
Application |
20090301691 |
Kind Code |
A1 |
Mohapatra; Satish Chandra |
December 10, 2009 |
Active Multiphase Heat Transportation System
Abstract
Disclosed herein is a method and system for transporting heat
from a heat source to a heat sink. Containers containing a phase
change material in a first phase, a guide track leading from the
heat source to the heat sink, and a drive system are provided. The
phase change material in the first phase in the containers absorbs
the heat from the heat source on establishing thermal contact with
the heat source and changes to a second phase. The drive system
moves the containers containing the phase change material in the
second phase to the heat sink along the guide track. The phase
change material in the second phase in each of the containers
transfers the absorbed heat to the heat sink and changes to the
first phase. The heat source is cooled due to transportation of the
heat from the heat source to the heat sink.
Inventors: |
Mohapatra; Satish Chandra;
(Easton, PA) |
Correspondence
Address: |
Ashok Tankha
36 Greenleigh Drive
Sewell
NJ
08080
US
|
Assignee: |
Dynalene Inc.
|
Family ID: |
41399222 |
Appl. No.: |
12/481560 |
Filed: |
June 9, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61060140 |
Jun 10, 2008 |
|
|
|
Current U.S.
Class: |
165/104.17 |
Current CPC
Class: |
F28D 19/04 20130101;
H01L 2924/0002 20130101; F28D 15/0266 20130101; H01L 23/427
20130101; H01L 2924/0002 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
165/104.17 |
International
Class: |
F28D 15/00 20060101
F28D015/00 |
Claims
1. A method of transporting heat from a heat source to a heat sink,
comprising the steps of: providing a plurality of containers
containing a phase change material in a first phase, a guide track
leading from said heat source to said heat sink, and a drive
system; absorbing said heat from said heat source by said phase
change material in said first phase in said containers on
establishing thermal contact with said heat source, wherein said
phase change material in said first phase in said containers
changes to a second phase on said absorption of said heat; moving
said containers containing said phase change material in said
second phase to said heat sink along said guide track by said drive
system; and transferring said absorbed heat by said phase change
material in said second phase in each of said containers to said
heat sink, wherein said phase change material in said containers in
said second phase changes to said first phase on said transfer of
said absorbed heat; whereby said heat source is cooled due to said
transportation of said heat from said heat source to said heat
sink.
2. The method of claim 1, wherein said first phase is a solid phase
and said second phase is a liquid phase.
3. The method of claim 1, wherein said first phase is a liquid
phase and said second phase is a vapor phase.
4. The method of claim 1, wherein said phase change material is
selected from a group comprising metals, alloys, salts, salt
mixtures, salt hydrates, polymers, hydrocarbons, silicones,
fluorocarbons, hydrofluorocarbons, organic liquids, water, salt
water solutions, and a combination thereof.
5. The method of claim 1, wherein said guide track is a tube filled
with a non-flammable dielectric liquid.
6. The method of claim 5, wherein said phase change material in
each of said containers absorbs said heat from said heat source via
said non-flammable dielectric liquid.
7. The method of claim 5, further comprising the step of providing
a source plate for transferring said heat from said heat source to
said non-flammable dielectric liquid.
8. The method of claim 1, wherein said drive system comprises a
plurality of sets of electromagnetic coils, wherein said sets of
said electromagnetic coils are activated in succession for moving
said containers to said heat sink.
9. The method of claim 1, wherein said drive system comprises a
drive chain for carrying said containers to said heat sink.
10. The method of claim 1, wherein said drive system comprises a
wheel with sphere engaging teeth employed inside said guide track
to move said containers along said guide track, wherein said wheel
is moved by one of a motor and a spinning magnet.
11. The method of claim 1, wherein said containers are hollow balls
of one of a spherical shape, a cylindrical shape, and a cubical
shape.
12. The method of claim 1, wherein said containers have a diameter
ranging from about 10 nanometers to about 10 centimeters.
13. The method of claim 1, wherein said containers contain
headspace for allowing expansion of said phase change material.
14. A system for transporting heat from a heat source to a heat
sink, comprising: a plurality of containers containing a phase
change material in a first phase, wherein said phase change
material in said first phase in said containers absorb said heat
from said heat source on establishing thermal contact with said
heat source, wherein said phase change material in said first phase
in said containers changes to a second phase on said absorption of
said heat; a guide track leading from said heat source to said heat
sink; and a drive system for moving said containers containing said
phase change material in said second phase to said heat sink along
said guide track.
15. The system of claim 14, wherein said first phase is a solid
phase and said second phase is a liquid phase.
16. The system of claim 14, wherein said first phase is a liquid
phase and second phase is a vapor phase.
17. The system of claim 14, wherein said guide track is a tube
filled with a non-flammable dielectric liquid.
18. The system of claim 17, wherein said phase change material in
each of said containers absorbs said heat from said heat source via
said non-flammable dielectric liquid.
19. The system of claim 17, further comprising a source plate for
transferring said heat from said heat source to said non-flammable
dielectric liquid.
20. The system of claim 14, wherein said drive system comprises a
plurality of sets of electromagnetic coils, wherein said sets of
said electromagnetic coils are activated in succession for moving
said containers to said heat sink.
21. The system of claim 14, wherein said drive system comprises a
drive chain for carrying said containers to said heat sink.
22. The system of claim 14, wherein said drive system comprises a
wheel with sphere engaging teeth employed inside said guide track
to move said containers along said guide track, wherein said wheel
is moved by one of a motor and a spinning magnet.
23. The system of claim 14, wherein said containers are hollow
balls of one of a spherical shape, a cylindrical shape, and a
cubical shape, wherein said containers contain headspace for
allowing expansion of said phase change material.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of provisional patent
application No. 61/060,140 titled "Freeze Tolerant Heat Transfer
System", filed on Jun. 10, 2008 in the United States Patent and
Trademark Office.
BACKGROUND
[0002] The method and system disclosed herein, in general, relates
to heat transfer systems. More particularly, the method and system
disclosed herein relates to an active multiphase heat
transportation system that transports heat from a heat source to a
heat sink.
[0003] Cooling of microprocessors and other electronic components
has become a major issue in recent times as faster and smaller
components are being designed. As a result, different cooling
technologies have been developed to effectively remove and
transport heat from the electronic components for faster and stable
operation. For example, for high power electronics, with a heat
flux of 500 W/cm.sup.2 to 2000 W/cm.sup.2, the need for advanced
cooling technologies has significantly increased due to the failure
of traditional heat transfer technologies.
[0004] There are two major problems associated with the removal of
heat from high power electronics. The first problem deals with
transferring heat from the electronic components into a heat
carrier that carries the heat away from the components. The second
problem relates to the transport of the large amount of heat, for
example, 100 W to 100 kW from the source to the sink without
significantly increasing the temperature of the heat carrier.
[0005] There are two types of systems commonly used for the removal
of heat from the electronics: a passive cooling system and an
active cooling system. In the passive cooling system, the thermal
energy is dissipated to the heat sink without the help of a dynamic
mechanical system. Examples of passive cooling systems are fin type
heat sinks, heat spreaders, and heat pipes. Fin type heat sinks and
heat spreaders being conduction based, cannot remove and transport
a large amount of heat per unit surface area. Conduction is a
slower mode of heat transport than convection and radiation. Heat
pipes being based on latent heat of evaporation of a liquid and
convection mode of heat transport, can remove and transport larger
amounts of thermal energy. However, heat pipes too have a limited
heat carrying ability because the convection process is natural and
not forced.
[0006] Active cooling systems typically utilize a pump and a
coolant to remove and transport thermal energy by forced
convection. These systems can be designed to handle a single phase
fluid or a two-phase fluid. In a single-phase fluid cooling system,
the heat transport depends only on the sensible heat carried by the
fluid, based on heat capacity of the fluid, whereas in a two-phase
pumped fluid cooled system, the heat transport depends on the
latent heat of evaporation or fusion carried by the fluid. Latent
heat based systems typically transport more amount of thermal
energy compared to the sensible heat based systems. However, the
state of the art two-phase active cooling systems are limited by
the natural convection of the vapor from the heat source to a heat
sink, which reduces efficiency of the heat transportation system.
Moreover, the design of two-phase active cooling systems for high
gravitational force environments and microgravity environments is
extremely complicated.
[0007] Several techniques to improve the energy transport
capabilities of single phase liquid cooling systems have been
experimented with. For example, microencapsulated phase change
materials have been added to the liquid coolant to form slurries
which have a greater heat capacity due to the latent heat of fusion
of the phase change material. However, the types of fluids
typically have a low percentage of phase change material loading,
often less than 5%, because higher concentrations of the phase
change material will increase the viscosity of the fluid to a level
that the fluid becomes difficult to pump. Microcapsules of the
phase change material could also break due to impact with pump
impellers and other components of the system. The microcapsules may
further agglomerate under certain conditions and block fluid flow
channels.
[0008] Dispersions of nanoparticles in the coolant, also referred
to as nanofluids, have been investigated for use in cooling systems
due to greater thermal conductivity. The greater improvement in the
thermal conductivity is important in case of laminar flow of the
coolant. In laminar flow, the heat transfer coefficient is directly
proportional to the thermal conductivity of the coolant.
Introduction of simple nanoparticles typically does not increase
the heat carrying capacity of a coolant.
[0009] Hence, there is a need for an active multiphase heat
transportation system that eliminates need for a pump and
significantly improves the heat transfer and transport ability of
the system.
SUMMARY OF THE INVENTION
[0010] This summary is provided to introduce a selection of
concepts in a simplified form that are further described in the
detailed description of the invention. This summary is not intended
to identify key or essential inventive concepts of the claimed
subject matter, nor is it intended for determining the scope of the
claimed subject matter.
[0011] The method and system disclosed herein addresses the above
stated need for an active multiphase heat transportation system
that eliminates need for a pump and significantly improves the heat
transfer and transport ability of the system. The active multiphase
heat transportation system disclosed herein comprises multiple
containers, a guide track, and a drive system. The containers are,
for example, hollow spherical, cylindrical, or cubical steel balls.
The containers used in the active multiphase heat transportation
system disclosed herein have a diameter ranging, for example, from
about 10 nanometers to about 10 centimeters. The containers contain
a phase change material in a first phase. The first phase is, for
example, a solid phase or a liquid phase. The containers contain
headspace for allowing expansion of the phase change material. The
phase change material is selected from a group comprising, for
example, metals, alloys, salts, salt mixtures, salt hydrates,
polymers, hydrocarbons, silicones, fluorocarbons,
hydrofluorocarbons, organic liquids, water, salt water solutions,
and a combination thereof. The guide track leads from the heat
source to the heat sink. The guide track is, for example, a tube
filled with a non-flammable dielectric liquid.
[0012] The phase change material in the first phase in the
containers absorbs heat from the heat source on establishing
thermal contact with the heat source and changes to a second phase.
For example, the phase change material in a solid phase in the
containers absorbs the heat from the heat source and changes to a
liquid phase. In another example, the phase change material in a
liquid phase in the containers absorbs the heat from the heat
source and changes to a vapor phase. The phase change material
absorbs the heat from the heat source via the non-flammable
dielectric liquid. In an embodiment, a source plate is provided for
transferring the heat from the heat source to the non-flammable
dielectric liquid. The drive system moves the containers containing
the phase change material in the second phase, for example, the
liquid phase or the vapor phase to the heat sink along the guide
track. The drive system comprises, for example, multiple
electromagnetic coils, a cog with sphere engaging teeth driven by a
motor, or a drive chain driven by a motor. In an embodiment, the
drive system comprises multiple sets of the electromagnetic coils.
The sets of the electromagnetic coils are activated in succession
for moving the containers to the heat sink. In another embodiment,
the drive chain operated by an external motor carries the
containers to the heat sink. In another embodiment, a wheel with
sphere engaging teeth is employed inside the guide track to move
the containers along the guide track. The wheel is moved by, for
example, a motor or a spinning magnet.
[0013] The phase change material in the second phase in each of the
containers transfers the absorbed heat to the heat sink and changes
to the first phase. For example, the phase change material in the
liquid phase in each of the containers transfers the absorbed heat
to the heat sink and changes to the solid phase. In another
example, the phase change material in the vapor phase in each of
the containers transfers the absorbed heat to the heat sink and
changes to the liquid phase. The heat source is cooled due to the
transportation of the heat from the heat source to the heat
sink.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The foregoing summary, as well as the following detailed
description of the invention, is better understood when read in
conjunction with the appended drawings. For the purpose of
illustrating the invention, exemplary constructions of the
invention are shown in the drawings. However, the invention is not
limited to the specific methods and instrumentalities disclosed
herein.
[0015] FIG. 1 illustrates a method of transporting heat from a heat
source to a heat sink.
[0016] FIG. 2 exemplarily illustrates a system for transporting
heat from a heat source to a heat sink.
[0017] FIG. 3 exemplarily illustrates a drive system comprising
three sets of electromagnetic coils for moving multiple containers
along a guide track.
[0018] FIG. 4 exemplarily illustrates a list of potentially usable
phase change materials with melting temperature and latent heat of
fusion of each of the phase change materials.
[0019] FIG. 5 exemplarily illustrates a control system for the
drive system.
[0020] FIG. 6A exemplarily illustrates thermal conduction between a
source plate and a non-flammable dielectric liquid in a guide
track.
[0021] FIG. 6B exemplarily illustrates thermal conduction between
the non-flammable dielectric liquid in the guide track and the heat
sink.
[0022] FIG. 7 exemplarily illustrates an embodiment of a drive
system for moving multiple containers along a guide track.
DETAILED DESCRIPTION OF THE INVENTION
[0023] FIG. 1 illustrates a method of transporting heat from a heat
source 204 to a heat sink 205. The heat source 204 is, for example,
a microprocessor, any electronic component, solar radiation, a
mechanical system that generates heat, etc. The heat sink 205 is,
for example, a fan cooled radiator or a liquid cooled heat
exchanger. A system 200 for transporting heat from a heat source
204 to a heat sink 205, herein referred to as an "active multiphase
heat transportation system" 200 is exemplarily illustrated in FIG.
2. The active multiphase heat transportation system 200 comprising
multiple containers 201, a guide track 202 leading from the heat
source 204 to the heat sink 205, and a drive system 203 is provided
101. The containers 201 are disposed within the guide track
202.
[0024] The containers 201 are, for example, hollow spherical,
cylindrical or cubical metal balls such as the commercially
available steel balls manufactured by Industrial Tectonics
Inc.RTM.. The containers 201 have different sizes. For example, the
containers 201 used in the active multiphase heat transportation
system 200 disclosed herein have a diameter ranging from about 10
nanometers to about 10 centimeters. The containers 201 contain a
phase change material in a first phase 208a, for example, a solid
phase or a liquid phase. As used herein, the term "phase change
material" refers to a substance with a high heat of fusion or
evaporation which is capable of storing and releasing large amounts
of energy. These substances change phase from the solid phase to
the liquid phase at the melting point or from the liquid phase to
the vapor phase at the boiling point and vice versa. Heat is
absorbed or released when the phase change material changes from a
solid phase to a liquid phase or from a liquid phase to a vapor
phase, and heat is emitted when the phase change material changes
from the liquid phase to the solid phase or from a vapor phase to a
liquid phase. The heat involved in the conversion of the phase is
herein referred to as "latent heat". The phase change material is
selected from a group comprising, for example, metals, alloys,
salts, salt mixtures, salt hydrates, polymers, hydrocarbons,
silicones, fluorocarbons, hydrofluorocarbons (HFCs), organic
liquids, water, salt water solutions, and a combination
thereof.
[0025] Each of the containers 201 comprises a small hole through
which the phase change material is introduced into each of the
containers 201. A small headspace 601 is provided in each of the
containers 201 to allow for expansion and contraction of the phase
change material due to absorbed and emitted heat, as exemplarily
illustrated in FIGS. 6A-6B. The hole is then re plugged with solder
material and polished to create a smooth surface. The resultant
density of each of the containers 201 after the introduction of the
phase change material is close to the density of a non-flammable
dielectric liquid 209 in the guide track 202 so that the weight of
the containers 201 is balanced by the buoyancy in the non-flammable
dielectric liquid 209. The resultant density of each of the
containers 201 after the introduction of the phase change material
is, for example, 1.5 to 2.0 g/cc.
[0026] As illustrated schematically in FIG. 2, the guide track 202
is a closed loop from the heat source 204 to the heat sink 205. The
guide track 202 forms a loop from the heat source 204 to the heat
sink 205 and back from the heat sink 205 to the heat source 204.
The guide track 202 is, for example, a tube filled with a liquid.
In certain electronic cooling applications, a non-flammable
dielectric liquid 209 may be desired to prevent fire and
short-circuiting in case of a leak. The guide track 202 is, for
example, made of aluminum. The guide track 202 is sealed during
operation, and is fluid-tight to prevent escape of the
non-flammable dielectric fluid 209. The pressure inside the guide
track 202 during operation is maintained at an optimum and does not
affect the boiling properties of the non-flammable dielectric fluid
209.
[0027] The non-flammable dielectric liquid 209 in the guide track
202 is, for example, a perfluorocarbon or a hydrofluorocarbon (HFC)
with a boiling point of about 40.degree. C. to 50.degree. C. The
non-flammable dielectric liquid 209 absorbs heat from the heat
source 204 and starts boiling. The boiling liquid converts to vapor
and condenses on the outsides of the containers 201 disposed within
the guide track 202, imparting the latent heat of vaporization to
the phase change material in the first phase 208a in the containers
201. In an embodiment, the guide track 202 comprises temperature
sensors 206 and 207 for measuring temperature of the non-flammable
dielectric liquid 209 at different points along the guide track
202. For example, the guide track 202 comprises a heat source
temperature sensor 206 and a heat sink temperature sensor 207. The
temperature sensors 206 and 207 are positioned so as not to
obstruct movement of the containers 201 within the guide track 202.
The guide track 202 is disassembled for changing or replenishing
the non-flammable dielectric liquid 209 or the containers 201. The
guide track 202 further comprises a filling and draining port (not
shown) for changing or replenishing the non-flammable dielectric
liquid 209. The guide track 202 further comprises a transparent
section (not shown) for enabling visual observation of the
containers 201 in motion within the guide track 202.
[0028] The phase change material in the first phase 208a, for
example, a solid phase or a liquid phase in the containers 201
absorbs 102 the heat from the heat source 204 on establishing
thermal contact with the heat source 204. The phase change material
in the first phase 208a in the containers 201 changes to a second
phase 208b on the absorption of the heat. For example, the phase
change material in the solid phase in the containers 201 changes to
a liquid phase on the absorption of the heat. In another example,
the phase change material in the liquid phase in the containers 201
changes to a vapor phase on the absorption of the heat. The phase
change material used in this case is, for example, methanol,
because of high latent heat of evaporation of approximately 1100
kJ/kg. Other potentially usable liquid to vapor phase change
materials are fluorocarbon materials, acetone, and methylene
chloride. If liquid to vapor phase change material is used in the
containers 201, the pressure inside the containers 201 should not
affect the boiling point of phase change material significantly,
which in turn depends on the amount of phase change material filled
in each of the containers 201. Liquid to vapor phase change
materials within the containers 201 have higher latent heat as well
as heat transfer coefficients. However, a greater amount of phase
change material can be accommodated into the containers 201 if a
solid to liquid phase change material is used. To enhance the heat
transfer in solid to liquid phase change material, nanoparticles or
carbon nanotubes may be incorporated in the phase change material
to increase the thermal conductivity of the solid to liquid phase
change material.
[0029] In an embodiment, the thermal contact is established via a
source plate 605 and the non-flammable dielectric liquid 209 in the
guide track 202, as exemplarily illustrated in FIG. 6A. FIG. 6A
exemplarily illustrates thermal conduction between the source plate
605 and the non-flammable dielectric liquid 209 in the guide track
202. The source plate 605 is attached to the aluminum skin of the
guide track 202. In another example, the guide track 202 is a part
of the source plate 605. The non-flammable dielectric liquid 209 is
located on the other side of the aluminum skin of the guide track
202 from the source plate 605. The source plate 605 is thermally
connected to the heat source 204 and absorbs heat from the heat
source 204. The heat source 204 conducts heat to the source plate
605 and the source plate 605 conducts the heat to the guide track
202. The source plate 605 thereby transfers heat 604 from the heat
source 204 to the non-flammable dielectric liquid 209. The phase
change material in the first phase 208a absorbs the heat 604 from
the heat source 204 via the source plate 605 and the non-flammable
dielectric liquid 209 in the guide track 202. The boiling
temperature of the non-flammable dielectric liquid 209 is slightly
higher than the melting temperature of the phase change
material.
[0030] The non-flammable dielectric liquid 209 is thermally
connected to the source plate 605 and absorbs the heat 604 from the
source plate 605. The non-flammable dielectric liquid 209 absorbs
the heat 604 in the form of both sensible heat, which raises the
temperature of the non-flammable dielectric liquid 209, and as
latent heat which changes the non-flammable dielectric liquid 209
from the liquid phase 602 to a vapor phase 603. The vapor thus
obtained contains both the sensible heat and the latent heat of
vaporization. The vapor condenses on the outer surfaces of the
containers 201 containing the phase change material, thereby
imparting the latent heat to the phase change material in the first
phase 208a in the containers 201. By utilizing the non-flammable
dielectric liquid 209 and the latent heat to impart heat 604 to the
phase change material, large amounts of heat can be transferred to
the phase change material without significantly raising the
operating temperature of the phase change material. For example, up
to 10 kilowatts of heat with a heat flux of about 1200
watts/cm.sup.2 may be transferred. In addition to the heat from the
heat source 204, the non-flammable dielectric liquid 209 also
absorbs and transfers to the phase change material waste heat from
other minor heat sources, for example, heat leaked from different
components. Critical heat flux of the non-flammable dielectric
liquid 209 is optimized to obtain a heat dissipation value of
approximately 500 W/cm.sup.2 to 2000 W/cm.sup.2.
[0031] The drive system 203 moves 103 the containers 201 containing
the phase change material in the second phase 208b, for example,
the liquid phase or the vapor phase, to the heat sink 205 along the
guide track 202. In an embodiment, the drive system 203 comprises
multiple electromagnetic coils 203a.
[0032] Where the drive system 203 comprises multiple sets of the
electromagnetic coils 203a, the sets of the electromagnetic coils
203a are activated in succession for moving the containers 201 to
the heat sink 205. Consider an example where the drive system 203
comprises three sets 203b, 203c, and 203d of electromagnetic coils
203a as exemplarily illustrated in FIG. 3.
[0033] The first set 203b of electromagnetic coils 203a from the
electromagnetic coils 203a is first activated. The electromagnetic
coils 203a are activated by passing a current through each of the
electromagnetic coils 203a. Each of the electromagnetic coils 203a
produces a controlled magnetic field within the guide track 202,
when a current passes through electromagnetic coils 203a. The
strength of the magnetic field, represented herein by "B", is
calculated using the formula B=.mu..sub.oi.sub.on, where .mu..sub.o
is the permeability constant=4.pi..times.10.sup.-7 Tesla
Meter/Ampere, i.sub.o is the current in the electromagnetic coil,
and n is the number of loops or turns in the electromagnetic coil.
Direction of the magnetic field depends on direction of the current
in the electromagnetic coil. Hence, the magnetic field can be
reversed by reversing the direction of the current. The magnetic
field produces a force that acts on the containers 201. The force
is proportional to the magnetic field strength.
[0034] In FIG. 3, the individual electromagnetic coils 203a from
the first set 203b are labeled with the numeral "1". The containers
201 containing the phase change material in the second phase 208b,
for example, the liquid phase or the vapor phase are magnetically
attracted to the closest electromagnetic coil from the first set
203b of electromagnetic coils 203a. Each of the containers 201
containing the phase change material in the second phase 208b tries
to move towards the closest electromagnetic coil from the first set
203b. Since movement of the containers 201 is limited within the
guide track 202, each of the containers 201 containing the phase
change material orients itself so that the center of the container
201 is directly underneath the closest electromagnetic coil from
the first set 203b.
[0035] The first set 203b of electromagnetic coils 203a is then
deactivated and a second set 203c of electromagnetic coils 203a
from the electromagnetic coils 203a is activated. In FIG. 3, the
individual electromagnetic coils 203a from the second set 203c are
labeled with the numeral "2". The containers 201 containing the
phase change material in the second phase 208b are now magnetically
attracted to the closest electromagnetic coil from the second set
203c of electromagnetic coils 203a. Each of the containers 201
containing the phase change material in the second phase 208b tries
to move towards the closest electromagnetic coil from the second
set 203c. Each of the containers 201 containing the phase change
material now orients itself so that the center of the container 201
is directly underneath the closest electromagnetic coil from the
second set 203c.
[0036] The second set 203c of electromagnetic coils 203a is then
deactivated and a third set 203d of electromagnetic coils 203a from
the electromagnetic coils 203a is activated. In FIG. 3, the
individual electromagnetic coils 203a from the third set 203d are
labeled with the numeral "3". The containers 201 containing the
phase change material in the second phase 208b are now magnetically
attracted to the closest electromagnetic coil from the third set
203d. Each of the containers 201 containing the phase change
material in the second phase 208b tries to move towards the closest
electromagnetic coil from the third set 203d. Each of the
containers 201 containing the phase change material now orients
itself so that the center of the container 201 is directly
underneath the closest electromagnetic coil from the third set
203d. The successive orientation of the containers 201 underneath
the electromagnetic coils 203a from the first set 203b, the second
set 203c and the third set 203d, results in a substantially linear
motion of the containers 201 within the guide track 202.
[0037] Therefore in this example, by successively activating the
three sets 203b, 203c, and 203d of electromagnetic coils 203a, each
of the containers 201 is moved from a position directly underneath
an electromagnetic coil from the first set 203b to a position
directly underneath an electromagnetic coil from the third set
203d. By reactivating the three sets 203b, 203c, and 203d
successively in the same order at a predetermined frequency, each
of the containers 201 can be continually moved along the guide
track 202 from the heat source 204 to the heat sink 205. In an
example, to sustain a high heat flux, the containers 201 are moved
at a predetermined speed in the order of 0.1 meters per second. The
motion of the containers 201 along the guide track 202 helps to
mechanically scour the vapor bubbles, formed due to the boiling
non-flammable dielectric liquid 209, from the outer surfaces of the
containers 201. In an embodiment, the system 200 comprises a guide
track 202 of square cross-section and cylindrical containers 201 to
enable higher heat transfer per unit volume of the guide track
202.
[0038] In an embodiment, a control system 501 with a power supply
502 as illustrated in FIG. 5 is optionally used to operate the sets
203b, 203c, and 203d of electromagnetic coils 203a. The strength of
the current passing through the electromagnetic coils 203a, and
hence the strength of the magnetic field is variably controlled by
the control system 501. Temperature sensors, for example, the heat
source temperature sensor 206 and the heat sink temperature sensor
207 are placed along specific points on the guide track 202 to
detect temperatures at those points. The placement of the
temperature sensors 206 and 207 is, for example, near the heat
source 204 and the heat sink 205 as exemplarily illustrated in FIG.
2. The heat source temperature sensor 206 and the heat sink
temperature sensor 207 are connected to the control system 501 and
monitor the temperatures at the heat source 204 and the heat sink
205. The strength of the magnetic field or the frequency of
activation of the three sets 203b, 203c, and 203d of
electromagnetic coils 203a is varied by a feedback control of the
control system 501 based on the monitored temperatures. Hence, the
feedback control of the control system 501 determines the speed of
movement of the containers 201 within the guide track 202, and
hence the amount of heat transferred between the heat source 204
and the heat sink 205. The control system 501 also regulates the
speed of the fan 503 in the heat sink 205.
[0039] In another embodiment, the drive system 203 comprises a
drive chain (not shown) or a drive belt (not shown) present along
the entire length of the guide track 202 from the heat source 204
to the heat sink 205 and back from the heat sink 205 to the heat
source 204, including the portion of the guide track 202 in thermal
contact with the heat source 204 and the heat sink 205. The drive
chain or a drive belt carries the containers 201 to the heat sink
205. The containers 201 are placed on the drive chain or the drive
belt. The drive chain or the drive belt is, for example, driven
using a prime mover (not shown) such as a motor and a gear system.
In an embodiment, the containers 201, for example, the hollow balls
are shaped to form links in a chain as illustrated in FIG. 7. The
container chain is, for example, driven using a prime mover such as
a motor and a gear system. The container chain comprises the hollow
balls connected together using short lengths of strings 701. In
this embodiment, the drive system 203 comprises a wheel with sphere
engaging teeth 703 employed inside the guide track 202 to move the
containers 201 along the guide track 202. A single cog with the
sphere-engaging teeth 703 and driven by a motor drives the
container chain. FIG. 7 illustrates a section 702 of a cog wheel,
wherein the sphere-engaging teeth 703 engage the hollow balls. To
avoid penetration of the sealed guide track 202 by the cog or a
drive shaft of the motor, the drive power is transmitted using, for
example, a spinning magnet (not shown) to drive the cog.
[0040] The phase change material in the second phase 208b in each
of the containers 201 transfers 104 the absorbed heat to the heat
sink 205 and changes to the first phase 208a. For example, the
phase change material in the liquid phase in each of the containers
201 transfers the absorbed heat to the heat sink 205 and changes to
the solid phase. In another example, the phase change material in
the vapor phase in each of the containers 201 transfers the
absorbed heat to the heat sink 205 and changes to the liquid phase.
In an embodiment, the heat sink 205 is a radiator cooled by a fan
503. In another embodiment, the heat sink 205 is a liquid cooled
heat exchanger. The heat sink 205 comprises a metal structure with
fins. The metal used in the heat sink 205 has high thermal
conductivity and the fins provide a large surface area. The heat
sink 205 is in direct thermal contact with, for example, the
aluminum skin of the guide track 202. The guide track 202 may also
be a part of the heat sink 205. The non-flammable dielectric liquid
209 in the guide track 202 at the heat sink 205 is in thermal
contact with the heat sink 205 via the aluminum skin of the guide
track 202, and therefore is at a lower temperature than the phase
change material in the second phase 208b in the containers 201.
When the containers 201 reach the heat sink 205, the phase change
material transfers the absorbed heat to the non-flammable
dielectric liquid 209 at the lower temperature. FIG. 6B exemplarily
illustrates thermal conduction between the non-flammable dielectric
liquid 209 in the guide track 202 and the heat sink 205. The
transfer of heat 604 between the phase change material in the
second phase 208b and the heat sink 205 is exemplarily illustrated
in FIG. 6B. The heat transfer 604 near the heat sink 205 occurs as
the heat transfer 604 occurring at the heat source 204, but in the
reverse direction. The heat sink 205 absorbs the heat 604 from the
non-flammable dielectric liquid 209 and dissipates the heat, for
example, into the atmosphere using the fan 503.
[0041] The containers 201 at the heat sink 205 now contain the
phase change material in the first phase 208a, for example, the
solid phase or the liquid phase. The drive system 203 moves the
containers 201 back towards the heat source 204. When the
containers 201 reach the heat source 204, the phase change material
in the first phase 208a is ready to absorb the heat from the heat
source 204 again. The heat source 204 is therefore cooled due to
the transportation of the heat from the heat source 204 to the heat
sink 205.
[0042] In the case of the electromagnetic coils 203a, the drive
system 203 is not present along the portion of the guide track 202
in thermal contact with the heat source 204 and the heat sink
205.
[0043] Since there are no electromagnetic coils 203a along the
portion of the guide track 202 in thermal contact with the heat
source 204, the containers 201 in that portion of the guide track
202 will not be moved by magnetic attraction. However, the
containers 201 in the portion of the guide track 202 immediately
upstream of the portion in thermal contact with the heat source 204
are moved due to magnetic attraction and hence will exert a force
on the containers 201 in the portion in thermal contact with the
heat source 204, causing the containers 201 to move. As illustrated
in FIG. 2, the containers 201 travel through a U-shaped turn in the
guide track 202 near the heat source 204, the force exerted on each
successive container drops. After undergoing a 180 degree turn, for
example, after 4 turns of 45 degrees each, the resultant force on
the containers 201 leaving the portion in thermal contact with the
heat source 204 is approximately 25% (Cosine 45.times.Cosine
45.times.Cosine 45.times.Cosine 45) of the original force exerted
by the containers 201 entering the portion in thermal contact with
the heat source 204. The force is enough to transport the
containers 201 out of the portion in thermal contact with the heat
source 204 without the help of a magnetic field along the portion
in thermal contact with the heat source 204.
[0044] Frictional force between the containers 201 and inner walls
of the guide track 202 is insignificant because the containers 201
are almost floating in the non-flammable dielectric liquid 209 in
the guide track 202 liquid owing to the small difference in
density. Under the earth's gravitational field as well as in a
microgravity environment, there will be very little frictional
force, whereas, under high gravitational acceleration (high g)
conditions the frictional force may be amplified. However, in case
of applications like aeronautics, the high g conditions typically
exist only for a few minutes during take-offs. In the high g
conditions, drag force exerted on the balls by the non-flammable
dielectric liquid 209 may be significant enough to consider.
However, using low viscosity liquids, for example, fluorocarbons,
will cause generation of lower drag forces.
[0045] The speed of motion of the containers 201 along the guide
track 202 depends on the magnetic field generated by the
electromagnetic coils 203a. The magnetic field in turn depends on
current passed through the electromagnetic coils 203a. When current
passes through the electromagnetic coils 203a, resistive heat is
generated. The resistive heat is computed as i.sup.2R, where "i" is
the current flowing through the electromagnetic coils 203a and "R"
is the resistance of the electromagnetic coils 203a. The generated
resistive heat could be detrimental to the system 200 and possibly
degrade surrounding insulating materials. Increasing the number of
turns in the electromagnetic coils 203a would increase the magnetic
strength generated by a lower current, but at the same time would
increase the size and the weight of the system 200. Therefore, an
optimum level of the magnetic strength is reached in order to move
the containers 201 at a required minimum velocity.
[0046] The design of the system 200 disclosed herein incorporates
the advantages of a heat pipe and an active liquid cooled system
with a very high loading of the phase change material. The system
200 works like a heat pipe with a forcibly increased heat transfer
capacity. To maximize efficiency, the system 200 is well insulated
except for the sections where heat is transferred from one
component to another.
[0047] FIG. 4 exemplarily illustrates a list of potentially usable
phase change materials with melting temperature T.sub.melting and
latent heat of fusion of each of the phase change materials. The
potentially usable phase change materials are, for example,
eicosane, pentacosane, tritriacontane, camphene, (+)-camphene, and
(-)-camphene. The phase change material is selected based on
predetermined criteria, for example, latent heat of fusion or
evaporation, phase transition temperature in a predefined
temperature range, narrow phase transition temperature range,
compatibility with steel, and ready availability. Among the phase
change materials listed in FIG. 4, (-)-camphene, (+)-camphene,
camphene, and eicosane are the most suitable phase change materials
based on temperature range, high latent heat of fusion,
availability, and cost criteria. All the phase change materials
illustrated in FIG. 4 are compatible with carbon steel.
[0048] Consider an example where a microprocessor inside a computer
is cooled using the active multiphase heat transportation system
200 disclosed herein. In this example, the active multiphase heat
transportation system 200 comprises a copper heat exchanger with
channels as the heat source 204, an aluminum tube (1/4'' inside
diameter) as the guide track 202, hollow carbon steel spheres (
3/16'' outside diameter) as the containers 201 containing eicosane
as the phase change material, and an aluminum radiator with a fan
503 as the heat sink 205. In this example, the copper heat
exchanger being the heat source 204 is referred to by the numeral
204, the aluminum tube being the guide track 202 is referred to by
the numeral 202, the hollow carbons steel spheres being the
containers 201 are referred to by the numeral 201, and the aluminum
radiator 205 being the heat sink 205 is referred to by the numeral
205. The microprocessor in the computer is attached to the copper
heat exchanger 204. The aluminum tube 202 forms a closed loop from
the copper heat exchanger 204 to the aluminum radiator 205 and back
from the aluminum radiator 205 to the copper heat exchanger 204.
The aluminum tube 202 in this example has three electromagnetic
coils 203a arranged as illustrated in FIG. 3. The aluminum tube 202
and the channels inside the copper heat exchanger 204 and the
aluminum radiator 205 are filled with an HFC fluid having a boiling
point of 40.degree. C.
[0049] The microprocessor produces heat during its operation and
boils the HFC fluid when the temperature of the heated surface
reaches 40.degree. C. The hollow carbon steel spheres 201 are moved
at a speed of 0.1 m/s inside the aluminum tube 202 and the channels
by the electromagnetic force from the three electromagnetic coils
203a being turned ON and OFF in a particular order as described in
the detailed description of FIG. 3. The vapor bubbles generated
from the boiling HFC fluid rise up and come in contact with the
colder hollow carbon steel spheres 201 and then condense on the
surface at 40.degree. C. The latent heat of evaporation is
transferred to the hollow carbon steel spheres 201 and the eicosane
present inside the hollow carbon steel spheres 201 starts to melt
at about 36.degree. C. The hollow carbon steel spheres 201
containing the molten eicosane move through the channels in the
copper heat exchanger 204 and then through the aluminum tube 202 to
the aluminum radiator 205. When the hollow carbon steel spheres 201
reach the aluminum radiator 205, they come in contact with the
colder HFC fluid (colder than 30.degree. C.) in the surrounding.
The molten eicosane starts to transfer heat to the HFC fluid and in
the process the molten eicosane undergoes a phase change from the
liquid phase to the solid phase. The heat from the HFC fluid is
transferred to the fins of the aluminum radiator 205 and then to
the ambient air by means of the fan 503. The heat from the
microprocessor is therefore transferred to the ambient air with a
series of phase change processes.
[0050] The foregoing examples have been provided merely for the
purpose of explanation and are in no way to be construed as
limiting of the present invention disclosed herein. While the
invention has been described with reference to various embodiments,
it is understood that the words, which have been used herein, are
words of description and illustration, rather than words of
limitation. Further, although the invention has been described
herein with reference to particular means, materials and
embodiments, the invention is not intended to be limited to the
particulars disclosed herein; rather, the invention extends to all
functionally equivalent structures, methods and uses, such as are
within the scope of the appended claims. Those skilled in the art,
having the benefit of the teachings of this specification, may
effect numerous modifications thereto and changes may be made
without departing from the scope and spirit of the invention in its
aspects.
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