BACKGROUND OF INVENTION
1. Field of the Invention
Embodiments disclosed herein generally relate to a cooling system for cooling computer servers. More specifically, embodiments disclosed herein relate to an improved cooling system employing carbon nanotubes (CNTS) for use with computer servers.
2. Background Art
Removal of heat has become one of the most important challenges facing computer system designers today. The computer industry is challenged by thermal management of their high performance and high power electronic components. A number of attempts to improve thermal cooling have been taken in the past, such as by reducing thermal resistance of fan-driven cooling air and the junction temperature of high heat flux electronic components, such as central processing units (CPUs), application-specific integrated circuits (ASICs), and other high heat electronic components. However, the ever increasing demand for processing speed is pushing the envelope beyond what is attainable using traditional air cooling systems.
As the rate of power dissipation from electronics components, such as high performance server units, continues to increase, as shown in FIG. 1, standard conduction and forced-air convection fan air cooling techniques no longer provide adequate cooling for such sophisticated electronic components. A major obstacle in efficient thermal management of high power computer servers is the presence of hot spots on the electronic components and the inability of air cooling schemes to effectively remove heat directly from a point of generation. The reliability of electronic systems suffers when high temperatures at hot spot locations are permitted to persist. Conventional thermal control schemes, such as air cooling with fans, thermoelectric cooling, heat pipes, and passive vapor chambers have either reached their practical application limit, or will soon become impractical for high power electronic components such as computer server units.
When standard cooling methods are no longer adequate, computer manufacturers have to reduce the speed of their processors to match the capacity of existing cooling apparatus, take a reliability hit due to inadequate cooling using existing cooling apparatus, or delay release of their product until a reliable cooling apparatus for removal of heat from high heat dissipating electronic components are made available. Additionally, thermal management of high heat flux server units necessitates the use of bulky heat fan and heat sink assembly units.
SUMMARY OF INVENTION
In one aspect, embodiments of the present invention relate to a cooling system to cool the airflow through a electrical system, comprising: a CNT heat exchanger module disposed within a housing of the electrical system, the CNT heat exchanger module comprising: a member having a hole defined therethrough; and a plurality of carbon nanotubes (CNTs) disposed on the member; a cooling device disposed within the housing of the electrical system and configured to receive a coolant, wherein the coolant is propagated through the hole in the member so as to dissipate the heat generated by the electrical system; a unit board disposed within the housing of the electrical system; and an air flow device configured to pass air across at least a portion of the unit board and at least a portion of the CNT heat exchanger module.
In one aspect, embodiments of the present invention relate to a cooling apparatus for cooling an electrical system comprising: a member having a hole defined therethrough disposed near a heat-generating unit board; a plurality of carbon nanotubes (CNTs) attached to the member, wherein a coolant is propagated through the hole in the member so as to dissipate the heat generated by the heat-generating unit board; and an air moving device for moving air across at least a portion of the heat-generating unit board and across at least a portion of the member.
In one aspect, embodiments of the present invention relate to a method of cooling air flow through an electrical system, comprising: disposing a cooling apparatus near a heat-generating unit board, wherein the cooling apparatus comprises at least a member with CNTs disposed on the member; connecting the member to a cooling device; moving air across the heat-generated unit board; moving air across the member; and moving coolant from the cooling device through the member so as to transfer heat generated by the heat-generating unit board.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows a view of a prior art charting of power usage over time for packaging of electrical components.
FIG. 2 shows carbon nanotube (“CNT”) heat exchanger modules disposed near hot spots on an electrical component within a unit board and CNT heat exchanger modules disposed between unit boards and generally in the path of the airflow within the overall housing in accordance with embodiments disclosed herein.
FIG. 3 shows the flow of air along at least one unit board and at least one CNT heat exchanger module.
FIG. 4 shows a CNT heat exchanger modules disposed near a unit board comprised of at least one electrical component in accordance with embodiments disclosed herein.
FIG. 5 shows an arrangement of unit boards and CNT heat exchanger modules in accordance with embodiments disclosed herein.
FIG. 6 shows an arrangement of a unit board with CNT heat exchanger modules in accordance with embodiments disclosed herein.
FIG. 7A shows a CNT heat exchanger module connected to a condenser and compressor in accordance with embodiments disclosed herein.
FIG. 7B shows a CNT heat exchanger module connected to a liquid pump and cooling coil in accordance with embodiments disclosed herein.
FIG. 8A shows a plurality of CNT heat exchanger modules connected to a condenser and at least one compressor in accordance with embodiments disclosed herein.
FIG. 8B shows a plurality of CNT heat exchanger modules connected to a cooling coil and at least one liquid pump in accordance with embodiments disclosed herein.
FIG. 9 shows a member with a certain size and shape wherein the CNTs are attached and arranged in accordance with embodiments disclosed herein.
FIGS. 10A and 10B show a CNT heat exchanger module comprised of at least one member, carbon nanotubes (“CNTs”), and a porous material that covers the member and CNTs in accordance with embodiments disclosed herein.
FIGS. 11A-11E show members with CNTs attached of variable size and shape in accordance with embodiments disclosed herein.
FIG. 12 shows a view of a member with CNTs attached thereto in accordance with embodiments disclosed herein.
FIGS. 13A and 13B show members comprised of a combination of materials in accordance with embodiments disclosed herein.
FIG. 14 shows a member with CNTs attached to the exterior and to the interior in accordance with embodiments disclosed herein.
FIGS. 15A and 15B show a second member within a member both having a hole therethrough in accordance with embodiments disclosed herein.
FIGS. 16A, 16B, and 16C show members wherein different types and sizes of CNTs are attached at different angles in accordance with embodiments disclosed herein.
DETAILED DESCRIPTION
Specific embodiments of the present invention will now be described in detail with reference to the accompanying figures. Like elements in the various figures may be denoted by like reference numerals for consistency.
Advances in nano-materials and the development of economical and robust manufacturing methods for carbon nanotubes is making it possible to incorporate carbon nanotube (“CNT”) technology design and fabrication of heat exchangers using highly efficient CNT technology. When used as a heat absorbing and heat rejecting heat exchanger for an active cooling unit (pumped liquid or refrigeration system), substantial amount of heat may be removed without need for use of bulky and inefficient conventional refrigeration components.
Referring now the FIG. 2, a unit board 11 comprised of at least one circuit board 13 with integrated circuits 14 attached thereto, with CNT heat exchanger modules 8 disposed with different positional arrangements in relation to each other, is shown in accordance with an embodiment of the invention. Further, additional CNT heat exchanger modules 8a may be placed at particular IC hot spots 14 for additional cooling. These additional CNT heat exchanger modules 8a may be sized and shaped for cooling IC hot spots 14 specifically. Additional CNT heat exchanger modules may also be placed between levels within the housing of a computer server for additional cooling.
In other embodiments of the invention, thermal management of a high heat flux server box is achieved using a cooling system 15, which may include a removable modular liquid or refrigeration unit utilizing CNT heat exchangers 8, for cooling of the heat generating processor and electronics components by placing the self-contained and easily removable CNT heat exchanger modules 8 in the direction of cooling air flow 3 at desired locations in a server chassis, also known as a housing 12. CNT heat exchangers 2 absorb the heat, acting as the absorbing unit of the active cooling system, from the propagation of air over the CNT heat exchangers causing the absorption of heat by the cooling coil (heating of the cooling fluid in the case of liquid cooling and boiling of refrigerant in the case of the refrigeration cooling, wherein both may be called coolants) and therefore reducing the temperature of the air flowing through the heat absorbing CNT heat exchanger. Absorbed heat is then moved through a member, with a hole defined therethrough, using the coolant and the absorbed heat is released to the ambient away from the electronics components over the board and out of the server chassis. In accordance with other embodiments of the invention described herein, a miniature liquid pump or a miniature refrigeration compressor unit may be used with the CNT heat exchanger module. The advantage of such a design is the increase in thermal performance and a reduction in cost for the packaging material, allowing traditional air-cooling schemes to be used for thermal management of high heat processors. Another advantage is minimizing the size and space utilization due to the high thermal performance of CNT heat exchangers. Further, the ability to form and build heat exchangers of different geometrical configurations may also be an advantage of the design.
Referring now to FIG. 3, air entering the cooling system 15 passing through the housing 12 and propagating over a first unit board 11 is shown in accordance with an embodiment disclosed herein. After passing over the unit board 11, the air is at a temperature Tc1, which is comparably hotter than the initial air coming in. The air then passes through a CNT heat exchanger module 8 and is cooled down to a cooler temperature. The air then continues to travel over another unit board 11 causing it to heat and then over at least one CNT heat exchanger module 8 for cooling. For example, the air may be cooled to room temperature, and the cooled air will be re-used to cool down the next unit board. Known CNT fabrication technology may enable the design, creation and placement of CNT heat exchangers of various shapes at various locations, thus the air flowing over the heat generating electrical components, such as processors and ASICS, may be lowered to the design temperature. Therefore, multiple CNT heat exchangers may help in maintaining the air temperature flowing over an array of electrical components.
Referring now the FIG. 4, a unit board 11 comprised of at least one circuit board 13 with integrated circuits 14 attached thereto, with CNT heat exchanger modules 8 disposed with different positional arrangements in relation to each other, is shown in accordance with an embodiment of the invention. This embodiment illustrates that a CNT heat exchanger modules 8 may not need to cover the entire airflow stream and may be selectively placed to help cool select portions of the unit board 11. Further, the hole openings to the members of the CNT heat exchanger modules 8 need not be found on the same side, thereby allowing for a balancing of cooling devices as opposed to having to have an off balance arrangement of cooling devices off one side of the computer server or additional member extensions to reach remote cooling devices placed elsewhere due to other design considerations.
Referring now to FIG. 5, a cooling system 15 is shown in accordance with an embodiment of the invention. By using the high thermal conductivity of carbon nanotube heat exchanger fins 2, the size may be dramatically reduced and the heat exchanging efficiency is greatly improved. Therefore, CNT heat exchanger modules 8 may be placed between unit boards 11, both of which are within the housing 12 of the electrical system or computer server. Further, the unit boards 11 and the CNT heat exchanger modules 8 are arranged such that the airflow 3 goes from a unit board 11 to pick up heat, then to a CNT heat exchanger module 8 to dissipate the heat and then onto the next heated unit board 11. As seen in FIG. 6, other embodiments exist for a unit board 11 that generate more heat than one CNT heat exchanger module 8, also known as a CNT heat exchanger module 8, may dissipate alone or for a unit board 11 that require a lower initial air temperature passing over. In these embodiments, a second, and even a third, or potentially more, CNT heat exchanger modules 8 may be placed in a row to lower the temperature of the air. As a result, a CNT heat exchanger module 8 utilizing CNT heat exchangers 2, also known as a modular removable active cooling unit 8 for a given embodiment, may assist fan air cooling schemes to provide cooling for much higher levels of heat removal without requiring the use of many oversized heat sinks or a greater number of cooling fans.
Referring now to FIGS. 7A and 7B, the CNT heat exchanger modules 8 may be used with either a refrigeration type cooling mechanism 9 (shown in FIG. 7A) or a liquid-pump type cooling mechanism 10 (shown in FIG. 7B). For the refrigeration type cooling mechanism, a compressor 9b and a condenser 9 is utilized to achieve the desired coolant cooling as it propagated through the CNT heat exchanger module 8. For the liquid-pump cooling mechanism, a liquid pump 10b and a cooling coil 10 are utilized to achieve the desired cooling as the coolant propagates through the CNT heat exchanger module 8 collecting the thermal energy. A person of ordinary skill in the art can appreciate that there may be more components in a refrigeration or a liquid cooling system.
In other embodiments of the invention, more than one CNT heat exchanger module 8 are attached to a refrigeration system 9 comprised of a condenser and at least one compressor as shown in FIG. 8A. Additionally, a single compressor may be used rather than individual compressors 9b for each of the CNT heat exchanger modules 8. Similarly, for embodiments using a liquid-pump system 10 as shown in FIG. 8B, more than one of the CNT heat exchanger modules 8 may be attached to the same liquid-pump system 10, wherein the liquid-pump system comprises at least one cooling coil 10 and at least one liquid pump 10b.
FIG. 9 shows an embodiment of the invention in which a member 1 is formed into a shape having three of four sides of a rectangle and has the plurality of CNTs attached vertically thereto. Other embodiments of the invention, for example as shown in FIG. 10A, have a member 1 and CNTs 2, which are formed as CNT heat exchanger fins, enclosed within a porous material 7, also called a porous module 7. The porous material 7 may provide a more rigid or durable property to the CNT heat exchanger module 8 while still allowing for air to flow through and over the CNTs 2 and the member 1. The CNT heat exchanger module 8 has the benefit of creating a modular component that may be placed and removed with ease from within and around desired installation points. Specifically, placing the modular components near unit boards while also being in the path of air flowing through the electrical system, specifically a computer server.
In other embodiments of the invention, a CNT heat exchanger module, also known as a modular removable active cooling unit 8, utilizing CNT heat exchangers 2 are used for cooling and thermal management of high heat server boxes. In addition to providing substantial heat removal ability, these embodiment allow for the reduction in size and the number of heat sink and all other second level thermal management mechanism currently in practice.
Further, other embodiments of the invention, for example as shown in FIG. 10B, illustrate that a CNT heat exchanger module 8 may also be made up of more than one member 1 each with attached CNT heat exchanger fins 2. More specifically, both members may be enclosed within the same porous module 7. This allows for larger CNT heat exchanger modules that have the same density and coolant flow as the CNT heat exchanger module embodiment of FIG. 10A while also retaining the modular nature.
Referring now to FIGS. 11A through 11E, a member 1 configured in any shape desired is shown in accordance with embodiments disclosed herein. This feature allows for design flexibility and maximization of surface area with which to provide contact with the airflow 3 in any given electrical system that is being cooled. Specifically, FIG. 11A shows an embodiment wherein the member 1 bent is a plurality of shapes any one of which may be chosen or a combination may be used. FIG. 11B discloses an embodiment wherein the member 1 is sized to be small while still having the CNTs attached thereto, which provides a system that is microfluidic. A person of ordinary skill in the art knows that microfluidics deals with the behavior, precise control, and manipulation of fluids that are geometrically constrained to a small, typically sub-millimeter, scale and would also be familiar with the components used for such an application. Other embodiments provide a member 1 that is almost the same size as the CNTs that are attached, which would provide a system that is nanofluidic. Similarly, a person of ordinary skill in the art is familiar with the components used in a nanofluidic application. Using the existing CNT growth technology, a desirable microchannel configuration with a fine control on the microchannel's flow passage width, length, and geometrical configurations may be build to maximize the ability of the cooling systems for the highest and most effective heat removal ability for the most restrictive server location.
Other embodiments provide a member 1 that is far larger than the CNTs attached thereto as shown in FIG. 11C. Other embodiments of the invention provide for a member 1 that is bent is such a manner as to required three axis's creating a three dimensional shape, shown in FIG. 11D. Other embodiments allow the entering direction 4 and the exiting direction 5 to vary in angle, as opposed to having the entering direction 4 and the exiting direction 5 at 180 degrees from each other, as shown in FIG. 11E.
Referring now to FIG. 12, a member 1 is shown with at least one CNT 2 attached in accordance with an embodiment disclosed herein. The member has a hole that extends therethrough, and through which a coolant is propagated. The coolant may be either a gas or liquid coolant. The member 1 is placed along the airflow path 3 of an electrical component cooling system that is cooling an electrical system using the airflow 3. The airflow 3 is designed to travel over heat producing electrical systems such as computer components like CPUs and memory units. The thermal energy picked up by the air as the air passes over the electrical components, moves along, and passes over the member 1 and the CNTs 2 attached to the member 1. The thermal energy is transferred to the member 1 and the CNTs 2, thereby cooling the air in the airflow 3. The thermal energy is then transferred laterally down the CNTs 2 to the member 1. Next, both the thermal energy from the CNTs 2 and the member 1 are transferred to the coolant that is flowing through the member 1 entering 4 and exiting 5 from one end of the member to the other.
Referring now the FIGS. 13A and 13B, a member 1 is shown that is formed from a combination of materials in a composite-like layered form in accordance with an embodiment disclosed herein. Specifically, in FIG. 13A, the member 1 is formed from a CNT that is then wrapped with metal such as copper or metal alloy. In FIG. 13B, a member 1 is shown in which the inner layer of the member 1 is a metal followed by a CNT which is covered in another layer. Other embodiments may exist where the member 1 comprises at least one of a metal, a polymer, a plastic, an epoxy, a CNT, or any combination of such materials. A desired combination, or use of a specific material, will depend on the thermal conductivity desired, fabrication ability and limitations, as well as the size, shape, and strength needed for the member 1 given a desired cooling application. The ability to use any of a plurality of materials for the member structure provides a designer the flexibility to create a large variety of designs to fit many types of cooling applications.
Referring now to FIG. 14, a member 1 is shown with CNTs 2 attached to both the interior and the exterior surface of the member 1 in accordance with an embodiment disclosed herein. By allowing for placement of CNTs on the exterior, similar to FIG. 12, the surface area that comes into contact with the incident airflow 3 may be increased and heat transfer, and therefore cooling, may be increased and thereby improved dramatically. Similarly, CNTs 2 may be placed along the inside of a member 1 so that the surface area that comes into contact with the coolant traveling through that space is increased as well.
FIGS. 15A and 15B refer to an embodiment of the invention known as a secondary loop indirect-contact cooling system. Specifically, this embodiment includes a member 1 with a hole therethrough. Additionally, this embodiment has a second member 6 that also has a hole therethrough. The second member 6 is disposed within the hole of the first member 1. As shown in FIG. 15B, the coolant, coming from the refrigeration or liquid cooling system, will propagate in a direction 4 in through the hole in the first member 1 and then propagate in a direction 5 out through the hole in the second member 6 back to the refrigeration or liquid cooling system. CNTs (not shown) may be located on any one of the surfaces, such as, the interior or exterior of the first member 1, or the interior or exterior of the second member 6. Further, the CNTs located between the interior of member 1 and the exterior of the second member 6 may be disposed such that one end of the CNT attaches to the interior surface of member 1 and the other end of the CNT attaches to the exterior of the second member 6. This would provide a dual benefit of first increasing the surface area through which the thermal energy may be passed to the propagating coolant in the hole, or chamber, of member 1. Secondly, this may provide structural support for the second member 6 and for the overall cooling system.
In the FIGS. 15A and 15B, the shapes of both members 1 and 6 are shown to be the same, however, other embodiments exist where the members are any of a plurality of shapes. Further, FIGS. 15A and 15B show the second member 6 disposed in the middle of the hole of member 1, although other embodiments exist where the second member 6 is located closer to, or connected to the edge of member 1.
One benefit of the embodiments shown in FIGS. 15A and 15B and discussed above is the use of a single stretch of material, in the shape of a member with an additional internal second member, to provide the functionality of both transmitting and returning of the propagating coolant from a single end of the member 1. This lowers the number of connection locations needed to a cooling device, thereby lowering the possibility of leaks. In a case where a leak does occur, repair is simplified for at least the reason that because there is only one connection location, it may be the only connection location at which a leak may occur. One benefit of an embodiment where the second member 2 is design as a thermal insulator rather than a conductive member is that the coolant that is thermally saturated will not propagate along the conductive interior surface of the first member 1, but rather through and within the second member 2 which would be insulated so as to eliminate heat transfer back out through the member 1 to the CNTs 2 or the airflow 3.
Referring now to FIG. 16A, a plurality of different CNTs of all shapes sizes, lattice structures, and wall thicknesses may be used in combination or alone providing a large variety of embodiments. Once a CNT type is chosen, the CNTs 2 may be attached to the member 1 at any angle and still perform the desired functionality, as shown in FIG. 16B. This is useful because having the flexibility to attached the CNTs at different angles allows for the use of cheaper and faster methods of manufacture. Further, a combination of both type and angle could be used in other embodiments of the invention thereby not only still providing for increased surface area, but also, providing a cost effective method of manufacture and potentially upkeep as well. In other embodiments of the invention, the CNT type and attaching angle that provides the maximum surface area is chosen depending on the given cooling to be done. The CNT type and angle of attachment may be chosen independently or dependently of the shape of the member 1 chosen as shown in FIG. 16C. In other embodiments of the invention, one CNT type is chosen and is attached at a perpendicular angle to the surface of the member 1. See, for example, FIG. 9. Another embodiment of the invention is an application where CNT heat exchangers are used for direct heat removal by attaching a liquid or refrigeration-cooled CNT heat sink to the back (or lid) of a high heat dissipating processor.
In addition to the above discussed benefits and advantages, embodiments of the present disclosure may provide for one or more of the following advantages. First, embodiments disclosed herein may provide for active fluid cooling that may provide desired thermal management solution to a wide range of thermal dissipation applications. Additionally, utilization of CNT material and technology may provide the highest known thermal conductivity (higher than diamond) for a heat exchange medium while possibly providing geometrical flexibility for desirable and space-fitting heat exchanger design and fabrication. Further, the application of a cooling system in according with one of the above embodiments may dramatically improve thermal management of high power computer servers by reducing temperature of the cooling air to inlet conditions at any given location inside of the server box. The proposed embodiments may provide the ability to utilize effective cooling mediums ranging from water, water-glycol, dielectrics to direct expansion refrigeration coolants that are associated with the high thermal conductivity of the CNT material. This may provide the highest level of thermal transport ever experienced in the electronics industry.
Combining highly conductive CNT material in the form of configurable microchannel heat exchangers with an active refrigeration or liquid cooling solution may provide the widest range of thermal management schemes ever developed in the electronics industry for flexible cooling of electronics components in data centers. As opposed to other applications of active cooling systems, utilizing CNT technology may provide the most efficient and flexible manufacturing method for building heat exchangers used in a closed loop of an active cooling system. By virtually removing the hot regions inside of a server box, through a cooling system 15 as described in the above embodiments which utilize highly flexible CNT microchannel heat exchangers 2, the reliability of the parts may be increased. Using a removable modular cooling system as described at least one of the above embodiments, which utilize CNT technology in heat exchangers, may provide an opportunity for drastically reducing the cost of thermal management of servers in data centers by minimizing irreversibility and inefficiencies associated with the traditional computer room air conditioner (“CRAC”), fans and heat sink schemes.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
Patent Application
20100032141
