US20090301691A1

US20090301691A1 - Active Multiphase Heat Transportation System

Info

Publication number: US20090301691A1
Application number: US12/481,560
Authority: US
Inventors: Satish Chandra Mohapatra
Original assignee: Dynalene Inc
Current assignee: Dynalene Inc
Priority date: 2008-06-10
Filing date: 2009-06-09
Publication date: 2009-12-10

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.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

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

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.
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/cm²to 2000 W/cm², the need for advanced cooling technologies has significantly increased due to the failure of traditional heat transfer technologies.
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.
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.
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.
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.
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.
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

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.
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.
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.
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

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.

FIG. 1 illustrates a method of transporting heat from a heat source to a heat sink.

FIG. 2 exemplarily illustrates a system for transporting heat from a heat source to a heat sink.

FIG. 3 exemplarily illustrates a drive system comprising three sets of electromagnetic coils for moving multiple containers along a guide track.

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.

FIG. 5 exemplarily illustrates a control system for the drive system.

FIG. 6A exemplarily illustrates thermal conduction between a source plate and a non-flammable dielectric liquid in a guide track.

FIG. 6B exemplarily illustrates thermal conduction between the non-flammable dielectric liquid in the guide track and the heat sink.

FIG. 7 exemplarily illustrates an embodiment of a drive system for moving multiple containers along a guide track.

DETAILED DESCRIPTION OF THE INVENTION

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.
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®. 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 208 a, 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.
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.
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.
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° C. to 50° 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 208 a 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.
The phase change material in the first phase 208 a, 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 208 a in the containers 201 changes to a second phase 208 b 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.
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 208 a 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.
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 208 a 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/cm²may 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/cm²to 2000 W/cm².
The drive system 203 moves 103 the containers 201 containing the phase change material in the second phase 208 b, 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 203 a.
Where the drive system 203 comprises multiple sets of the electromagnetic coils 203 a, the sets of the electromagnetic coils 203 a 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 203 b, 203 c, and 203 d of electromagnetic coils 203 a as exemplarily illustrated in FIG. 3.
The first set 203 b of electromagnetic coils 203 a from the electromagnetic coils 203 a is first activated. The electromagnetic coils 203 a are activated by passing a current through each of the electromagnetic coils 203 a. Each of the electromagnetic coils 203 a produces a controlled magnetic field within the guide track 202, when a current passes through electromagnetic coils 203 a. The strength of the magnetic field, represented herein by “B”, is calculated using the formula B=μ_oi_on, where μ_ois the permeability constant=4π×10⁻⁷Tesla Meter/Ampere, i_ois 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.
In FIG. 3, the individual electromagnetic coils 203 a from the first set 203 b are labeled with the numeral “1”. The containers 201 containing the phase change material in the second phase 208 b, for example, the liquid phase or the vapor phase are magnetically attracted to the closest electromagnetic coil from the first set 203 b of electromagnetic coils 203 a. Each of the containers 201 containing the phase change material in the second phase 208 b tries to move towards the closest electromagnetic coil from the first set 203 b. 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 203 b.
The first set 203 b of electromagnetic coils 203 a is then deactivated and a second set 203 c of electromagnetic coils 203 a from the electromagnetic coils 203 a is activated. In FIG. 3, the individual electromagnetic coils 203 a from the second set 203 c are labeled with the numeral “2”. The containers 201 containing the phase change material in the second phase 208 b are now magnetically attracted to the closest electromagnetic coil from the second set 203 c of electromagnetic coils 203 a. Each of the containers 201 containing the phase change material in the second phase 208 b tries to move towards the closest electromagnetic coil from the second set 203 c. 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 203 c.
The second set 203 c of electromagnetic coils 203 a is then deactivated and a third set 203 d of electromagnetic coils 203 a from the electromagnetic coils 203 a is activated. In FIG. 3, the individual electromagnetic coils 203 a from the third set 203 d are labeled with the numeral “3”. The containers 201 containing the phase change material in the second phase 208 b are now magnetically attracted to the closest electromagnetic coil from the third set 203 d. Each of the containers 201 containing the phase change material in the second phase 208 b tries to move towards the closest electromagnetic coil from the third set 203 d. 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 203 d. The successive orientation of the containers 201 underneath the electromagnetic coils 203 a from the first set 203 b, the second set 203 c and the third set 203 d, results in a substantially linear motion of the containers 201 within the guide track 202.
Therefore in this example, by successively activating the three sets 203 b, 203 c, and 203 d of electromagnetic coils 203 a, each of the containers 201 is moved from a position directly underneath an electromagnetic coil from the first set 203 b to a position directly underneath an electromagnetic coil from the third set 203 d. By reactivating the three sets 203 b, 203 c, and 203 d 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.
In an embodiment, a control system 501 with a power supply 502 as illustrated in FIG. 5 is optionally used to operate the sets 203 b, 203 c, and 203 d of electromagnetic coils 203 a. The strength of the current passing through the electromagnetic coils 203 a, 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 203 b, 203 c, and 203 d of electromagnetic coils 203 a 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.
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.
The phase change material in the second phase 208 b in each of the containers 201 transfers 104 the absorbed heat to the heat sink 205 and changes to the first phase 208 a. 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 208 b 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 208 b 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.
The containers 201 at the heat sink 205 now contain the phase change material in the first phase 208 a, 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 208 a 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.
In the case of the electromagnetic coils 203 a, 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.
Since there are no electromagnetic coils 203 a 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×Cosine 45×Cosine 45×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.
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.
The speed of motion of the containers 201 along the guide track 202 depends on the magnetic field generated by the electromagnetic coils 203 a. The magnetic field in turn depends on current passed through the electromagnetic coils 203 a. When current passes through the electromagnetic coils 203 a, resistive heat is generated. The resistive heat is computed as i²R, where “i” is the current flowing through the electromagnetic coils 203 a and “R” is the resistance of the electromagnetic coils 203 a. 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 203 a 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.
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.
FIG. 4 exemplarily illustrates a list of potentially usable phase change materials with melting temperature T_meltingand 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.
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 (¼″ 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 203 a 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° C.
The microprocessor produces heat during its operation and boils the HFC fluid when the temperature of the heated surface reaches 40° 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 203 a 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° 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° 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° 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.
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.

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.