US20080066889A1

US20080066889A1 - Heat exchanging fluid return manifold for a liquid cooling system

Info

Publication number: US20080066889A1
Application number: US10/817,092
Authority: US
Inventors: Paul A. Knight; John D. Schwarzkopf; Charles L. Tilton
Original assignee: Isothermal Systems Research Inc
Current assignee: Isothermal Systems Research Inc
Priority date: 2003-02-19
Filing date: 2004-03-31
Publication date: 2008-03-20

Abstract

The present invention is a two-phase liquid cooling system that cools a plurality of electronic components connected in parallel. A pump delivers a cooling fluid, as a liquid, to a supply manifold wherein it splits into distinct branch lines. Preferably, the branch lines feed coolant to individual spray modules. The liquid coolant removes heat from the components to be cooled through evaporation. The resulting liquid and vapor mixture exits the spray modules via return branches. Each individual return branch feeds into a return manifold wherein the manifold is sized sufficiently for the separation of liquid and vapor under the influences of gravity. In addition, a heat exchanger is located within the return manifold and provides for the condensation of vapor. The heat exchanger may also provide liquid subcooling.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

We claim benefit under Title 35, United States Code, Section 120 of U.S. patent application Ser. No. 10/371,403 filed Feb. 19, 2003 entitle “Coolant Recovery System”. This application is a continuation-in-part of the 10/371,403 application which is currently pending and is hereby incorporated by reference into this application.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not related to this application.

BACKGROUND

1. Field of the Invention
The present invention relates generally to liquid cooling thermal management systems and more specifically it relates to a two-phase liquid cooling management system.
2. Description of the Related Art
Liquid cooling is well known in the art of cooling electronics. As air cooling heat sinks continue to be pushed to new performance levels, so has their cost, complexity, and weight. Liquid cooling systems provide advantages over air cooling systems in terms of heat removal rates, component reliability and package size.
Liquid cooling systems are comprised of many different species. Although each specie may have unique advantages and disadvantages, they are all designed to perform the same goal: remove heat from an electronic component. Generally, liquid coolant is placed in thermal contact with a component to be cooled wherein energy is transferred from the higher temperature component to the coolant. A pump circulates the liquid through the closed system, thus allowing the cooling fluid to continuously transfer thermal energy from the component to be cooled and to a desired location. Typically, the absorbed heat is removed from the cooling fluid through the use of a heat exchanger. Species of liquid cooling systems can be lumped into two categories: single-phase and two-phase. The phase signifies how the cooling fluid absorbs and exchanges energy.
Single-phase liquid cooling utilizes a pure liquid for absorbing heat from the component to be cooled. Energy is absorbed by the coolant through sensible heat gains. The temperature of the coolant increases as energy is absorbed according to well known engineering formulas. An example of a single-phase liquid cooling system is described by U.S. Pat. No. 6,234,240. Due to the simple nature of single-phase fluid flow and sensible heat gains, single-phase liquid cooling solutions are fairly straight-forward to design and implement.
The preferred method of liquid cooling is two-phase. A two-phase system absorbs energy from the component to be cooled by means of latent heat gains of its fluid. The temperature of the coolant does not necessarily change, but rather part of the coolant is vaporized as energy is absorbed. The vaporized coolant is then transferred to a heat exchanger, or condenser, where energy is removed from the vapor causing it to transform back to a liquid state. An exemplary two-phase cooling solution is described by U.S. Pat. No. 5,220,804, which describes how atomization of the cooling fluid, along with vapor management within the spray module, provides high heat flux thin film evaporative cooling.
The advantages of two-phase cooling over single-phase cooling are significant. Due to the amount of energy needed to vaporize a liquid in comparison to the energy required to raise its temperature, two-phase systems provide the ability to have more compact components, require less input energy and provide higher heat removal performance than single-phase systems.
Although both single-phase and two-phase liquid cooling solutions provide many advantages over air cooling solutions, they also have drawbacks. One such drawback is that liquid cooling can be more expensive than air cooling. In the case of a single processor application, an air cooling heat sink may be comprised of an aluminum extrusion and a fan. In the case of liquid cooling, for each processor, a pump, a heat exchanger, tubing, fittings, fluid and a thermal management unit are needed. Although the performance of liquid cooling may justify the increased cost over air cooling, liquid cooling a single processor may require a cost premium.
One of the ways to reduce costs of liquid cooling solutions is to cool multiple electronic components from a single closed loop liquid cooling system. In the case of a rack full of servers, many computer systems may be chained together. The result is a significant savings through economies of scale. Chaining electronic components together can be accomplished in two ways: parallel and series connections.
With series connections, the fluid is routed from one heat generating component to another, until all units have been cooled. Although this method is largely used with single phase systems, it can also be used with two-phase systems. A significant problem with series connections is that the cooling fluid is at a different thermal state at each electronic component along the chain. As one processor may go from a max power consumption state to an idle state, that processor may create a thermal cycle for the other processors in the system. Thermal cycling reduces component reliability.
With parallel connections, the fluid is routed from the pump directly to all components to be cooled. The fluid is also removed from the thermal management units via individual parallel branches. A prior art return system is shown in FIG. 1 of the attached drawings wherein each thermal management unit has a unique fluid path. Although this type of connection is used primarily with two-phase systems, it can be used with single-phase systems as well. Parallel connections remedy the disadvantages of series connections, but it too creates challenges.
A first challenge with parallel connections using two-phase flow is that the flow of fluid can be complicated. Vapor is significantly less dense than liquid and thus the mixture can create multiple flow patterns including: annular, slug and froth. The mode of flow can be difficult to predict and tests have shown the mode of flow to have a significant impact on the performance of a cooling system.
Another problem with parallel connections is that the numerous transitions can cause system back-pressures. Back-pressures, or restrictions downstream of a spray module, can cause an increased pressure level within a spray module and may result in reduced cooling performances.
Another problem with parallel connections is that in many computer cooling applications, the locations of particular processors may not be fixed. The parallel connections of the cooling system must be created in a fashion that provides configuration flexibility.
Thus, there is a need for a two-phase parallel liquid cooling solution capable of cooling many electronic components in non-specific configurations. It is highly desirable for such a system to provide consistent cooling performance under a wide range of conditions.

BRIEF SUMMARY OF THE INVENTION

In order to solve the problems of the prior art, and to provide a liquid cooling solution that allows multiple components to be cooled in parallel, a heat exchanging fluid return manifold has been developed.
The present invention is a two-phase liquid cooling system that cools a plurality of electronic components connected in parallel. A pump delivers a cooling fluid, as a liquid, to a supply manifold wherein it splits into distinct branch lines. Preferably, the branch lines feed coolant to individual spray modules. The liquid coolant removes heat from the components to be cooled through evaporation. The resulting liquid and vapor mixture exits the spray modules via return branches. Each individual return branch feeds into a return manifold wherein the manifold is sized sufficiently for the separation of liquid and vapor under the influences of gravity. In addition, a heat exchanger is located within the return manifold and provides for the condensation of vapor. The heat exchanger may also provide liquid subcooling.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, and accompanying drawings

BRIEF DESCRIPTION OF THE DRAWINGS

In the course of the detailed description to follow, reference will be made to the attached drawings. These drawings show different aspects of the present invention and, where appropriate, reference numerals illustrating like structures, components, and/or elements in different figures are labeled similarly. It is understood that various combinations of the structures, components, and/or elements other than those specifically shown are contemplated and within the scope of the present invention:

FIG. 1 is a block diagram of a prior art thermal management system having a plurality of thermal management units fluidly connected in parallel;

FIG. 2 is a block diagram of a liquid cooling system according to the present invention;

FIG. 3 is a front view of an electronic system supporting multiple electronics enclosures, each containing heat generating electronic components that are cooled by the liquid cooling system of FIG. 2;

FIG. 4 is a partial perspective view showing the heat exchange return manifold of FIG. 3;

FIG. 5 is a top partial view of the right side of the electronic system of FIG. 3, wherein the heat exchange return manifold is shown mounted in front of the right rack rail and without a cap, for clarity;

FIG. 6 is a top partial view of the right side of the electronic system of FIG. 4, wherein the heat exchange return manifold is shown mounted integral to the rack rail and without a cap, for clarify; in addition, an alternative square exchange fluid channel is shown;

FIG. 7, is a top partial view of the right side of an alternative cooling panel version of the liquid cooling system of FIG. 2;

FIG. 8, is a round alternative embodiment of the heat exchange return manifold according the present invention; and

FIG. 9, is a finned alternative embodiment of the round embodiment of the present invention shown in FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Many of the fastening, connection, manufacturing and other means and components utilized in this invention are widely known and used in the field of the invention are described, and their exact nature or type is not necessary for a person of ordinary skill in the art or science to understand the invention; therefore they will not be discussed in detail.
Applicant hereby incorporates by reference U.S. Pat. No. 5,220,804 for a high heat flux evaporative cooling system. Although spray cooling is herein described as the preferred method of two-phase cooling, the present invention is not limited to such a system. Spray cooling is only discussed in detail to provide a known preferred embodiment. In addition to two-phase spray cooling, the present invention is applicable to, but not limited to, single-phase cooling and refrigeration systems.
FIG. 2 shows a liquid cooling system 20, according to the present invention. A plurality of thermal management units 22, such as described by U.S. Pat. No. 5,220,804, are thermally connected to a plurality of heat generating electronic components (not shown). A supply liquid 70 is pressurized by a pump 51 within a pump system 50. Supply liquid 70 may be any commonly known or used cooling fluid, including but not limited to Fluorinert (a trademark of 3M). The supply liquid 70 may also be a multi-component fluid, such as but not limited to water-air mixtures. Pump system 50 may include a reservoir 52 for providing a continuous supply of liquid coolant to pump 51 and other liquid cooling components such as, but not limited to, fluid filters and control system components. After exiting pump system 50, supply liquid 70 is delivered to a supply manifold 71 wherein it is dispersed to a plurality of supply branches 72. Each of supply branches 72 delivers a portion of supply liquid 70 to a thermal management unit 22. Supply liquid 70 within thermal management unit 22, absorbs heat from the one or more electronic components. The absorbed heat continuously transforms supply fluid 70 into a return fluid 73. Preferably, return fluid 73 is a two-phase fluid. Wherein return fluid 73 is a multi-component mixture, at least one of the components is transformed to a two-phase fluid within unit 22. A plurality of control valves 24 provides the means of controlling the heat absorption rate of each management unit 22 and the quality of return fluid 73. Control valve 24 also provide the means of equalizing pressures across the plurality of management unit 22 caused by varying head pressures. A plurality of return branches 74 removes return fluid 73 from the plurality of management units 22.
Unlike the prior art, portions of return fluid 73 within the plurality of return branches 74 do not rejoin in a manifold prior to being delivered to a heat exchanger. Also, unlike the prior art, portions of return fluid 73 within the plurality of return branches 74 do not rejoin in a manifold prior to being delivered to a separator. Liquid cooling system 20, and according to the present invention, utilizes a novel heat exchange return manifold 30.
Heat exchange return manifold 30 is comprised of a return channel 34, a cap 31 and a vent valve 32. Heat exchange return manifold 30 provides the means of removing energy from return fluid 73 while minimizing system backpressures. Return channel 34 is sized sufficiently to allow for gravity driven liquid—vapor separation within, wherein the liquid is encouraged to fall. Unlike the liquid, non-condensable gasses are encouraged to rise to vent valve 32 where they can be purged from the system. Non-condensable gases may be in solution within the liquid cooling fluid and then separated through the evaporation process. For optimal system performance it is desirable to remove non-condensable gases from the system.
In addition to liquid—vapor-gas separation, return channel 34 is preferably sized sufficiently to house an exchange channel 78. Exchange channel 78 contains a flow of an exchange fluid 75, such as but not limited to facility water, chilled air, or fluid from a secondary cooling system. The thermal connection between the colder exchange fluid 75 and warmer return channel 34, results in an energy exchange according to well known heat transfer principles and heat exchanger design. The flow and temperature of exchange fluid 75 is sufficient to absorb energy at the same rate that the plurality of electronic components produce it. The result is the condensing of vapor within heat exchange manifold return 30 and the ability to transport the released energy from the electronic components to a desired location, such as but not limited to outside a building. If it is desirable to exchange heat with the local environment return manifold 30 may be constructed from a thermally conductive material such as aluminum. Oppositely, if it is desirable to not exchange heat with the local environment, return manifold 30 may be constructed from an insulating material such as plastic. The construction and assembly methods for return manifold 30 are common to well known engineering and design practices. It is desirable to construct exchange chamber 78 in a fashion that promotes thin film condensing and resists fluid pileups.
FIG. 4 shows heat exchange return manifold 30 in further detail. The plurality of return branches 72, each carrying a portion of return fluid 73, preferably join heat exchange return manifold 30 at acute angle, as described by U.S. patent application Ser. No. 10/769,259 entitled “Low Momentum Loss Fluid Manifold System” filed on Jan. 30, 2004, herein incorporated by this reference. Although the described method of reducing momentum loss is preferable, return branch 72 may perpendicularly join heat exchange return manifold 30. The acute angle further reduces system backpressures and further encourages liquid to fall in the direction of gravity. Also shown in FIG. 4 is exchange chamber 78. Exchange fluid 75 enters exchange chamber 78 through inlet 76. After exchange fluid 75 absorbs energy from return fluid 73 it travels through exit 77. Although the shape of exchange chamber 78, as shown in FIG. 4, is ideal for having the fluid enter and exit through the same side, the present invention is not limited to such a configuration. It is possible to have exchange fluid 75 enter or exit from opposite sides.
FIG. 3 shows a preferred application of the present invention. An electronics system 40 is shown, typical of a system found in data-networks and teleco-networks. A rack 41 is mounted to a floor by a base 42. A left rail 45 and a right rail 44 extend upwards from base 42 and are connected to and support a top 43. Rails 44 and 45 provide the means for mounting a one or more electronics enclosure 47. The one or more electronics enclosure 47 houses heat generating electronic components and the plurality of thermal management units 22. Electronics enclosure 47 may be, but is not limited to being a router, hub, switch, server, or computer system. It should be known to one skilled in the art that rack 41 is not limited to an open channel rack as shown, instead it may be part of a cabinet type system. It should also be known that multiples of electronic system 40 may be placed side by side to form a lineup.
One of the many benefits of heat exchange return manifold 30 is that significant amounts of heat can be exchanged by a single cooling system; thus providing significant economies of scale and reductions in cost. Heat exchange return manifold 30 may be placed in numerous locations within electronic system 40 and locations in a lineup. Each optimal location may be application specific and partly a function of the type of electronics used, type and quantity of cables connecting the electronics, and the total amount of heat generated. FIG. 5 shows a square embodiment of heat exchange return manifold 30 mounted directly in front of left rail 45. By utilizing quick disconnect fittings 39, such as are commercially available from Colder Products Company, the embodiment of FIG. 5 provides the opportunity to place electronics system 40 against a wall and still retain configuration flexibility. Heat exchange return manifold 30 may also be mounted along left rail 45, or behind either rail 44 or 45.
FIG. 6 shows an alternative rack-integrated embodiment of the present invention wherein heat exchange return manifold 30 is captured by part or all of rails 44 or 45. This embodiment provides protection of the liquid within heat exchange return manifold 30 and takes advantage of a typically unutilized portion of rack 41. Also shown in FIG. 6 is a square version of exchange channel 78.
FIG. 7 shows a stand-alone version of liquid cooling system 20 according to the present invention. A cooling panel system 60 is placed adjacent and in fluid connection with rack 41. Panel 60 houses all the system components contained within pump system 50, thus freeing further space within rack 41 for housing electronic components. Unlike the previous embodiments, panel system 60 is not constrained in size to rack 41. Panel system 60 may be sized to remove very large amounts of heat, sufficient to potentially cool multiples of electronic system 40 in a lineup, resulting in further improvements in economies of scale. Cooling panel systems 60 may be structurally supported by rack 41, or may be independently secured to ground.
FIG. 8 and FIG. 9 shows a coaxial version of heat exchange return manifold 30 which further supports that manifold 30 can be made from a wide range of shapes. FIG. 9 shows both exchange fins 38 and return fins 39 which increase contact area and resulting heat transfer rates between exchange fluid 75 and return fluid 73. Both, or either, of fins 38 and 39 may be used with the aforementioned embodiments. A wide range of shapes of fins 38 and 39 are possible by making heat exchange return manifold from extruded aluminum.
While the heat exchanging fluid return manifold system herein described constitutes preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of assemblies, and that changes may be made therein with out departing from the scope and spirit of the invention.

Claims

1. A liquid cooling system for cooling a plurality of electronic components comprising:

a plurality of thermal management blocks in thermal connection with said electronic components and capable of receiving a supply of liquid coolant, wherein said plurality of thermal management blocks absorb heat from said plurality of electronic components and transform said supply of liquid coolant into a supply of two-phase fluid having a vapor portion and a liquid portion, said plurality of thermal management blocks also fluidly connected to a plurality of return channels for transferring said supply of two-phase fluid to a heat exchanging return manifold;

wherein said heat exchanging return manifold is sized sufficiently for gravity to separate said liquid portion from said vapor portion;

wherein said heat exchanging return manifold contains a cold fluid channel for transforming said vapor portion into a condensed liquid; and

a pump fluidly connected to said heat exchanging return manifold and for transforming said liquid portion and said condensed liquid into said supply of liquid coolant.

2. The liquid cooling system of claim 1, further including a reservoir fluidly connected to said pump and for holding an amount of said liquid portion and an amount of said condensed liquid.

3. The liquid cooling system of claim 1, wherein said cold fluid channel is connected to a facility water system.

4. The liquid cooling system of claim 1, wherein said cold fluid channel is connected to a secondary cooling system.

5. The liquid cooling system of claim 4, wherein said secondary cooling system is a refrigeration system.

6. The liquid cooling system of claim 1, wherein said cold fluid channel sub-cools said liquid portion.

7. The liquid cooling system of claim 1, wherein said cold fluid channel sub-cools said condensed liquid.

8. The liquid cooling system of claim 1, wherein said supply of liquid coolant is a multi-component mixture.

9. The liquid cooling system of claim 1, wherein said plurality of thermal management blocks provide spray cooling.

10. A liquid cooling system comprising:

a plurality of thermal management blocks fluidly connected in parallel, said blocks creating a flow of two-phase cooling fluid for absorbing heat from a plurality of electronic components;

a heat exchanging return manifold fluidly connected to said plurality of thermal management blocks and containing a liquid cooling line;

wherein said heat exchanging return manifold is sized sufficiently to separate said two-phase cooling fluid into a generally distinct liquid fluid portion and a generally distinct vapor fluid portion; and

wherein said liquid cooling line causes said vapor fluid portion to condense.

11. The liquid cooling system of claim 10, wherein said liquid cooling line is connected to a facility water system.

12. The liquid cooling system of claim 10, wherein said liquid cooling line is connected to a secondary cooling system.

13. The liquid cooling system of claim 10, wherein said secondary cooling system is a refrigeration system.

14. The liquid cooling system of claim 10, wherein said liquid cooling line provides thermal management of said liquid fluid portion.

15. The liquid cooling system of claim 14, wherein said thermal management includes sub-cooling said liquid fluid portion.

16. The liquid cooling system of claim 10, wherein said two-phase cooling fluid is a multi-component mixture.

17. The liquid cooling system of claim 10, wherein said plurality of thermal management blocks are spray cooling thermal management blocks.

18. The liquid cooling system of claim 17, wherein said spray cooling thermal management blocks include at least one atomizer.

19. A method of removing heat from a two-phase electronic cooling system containing a plurality of thermal management units fluidly connected in parallel, said method comprising:

delivering a two-phase fluid from said plurality of thermal management units to a heat exchange return manifold;

sizing said heat exchange return manifold sufficiently to allow gravity to separate said two-phase fluid into a liquid portion and a vapor portion;

providing a liquid cooling line within said heat exchange return manifold for condensing said vapor portion; and

fluidly connecting a pump to said liquid portion.

20. The method of removing heat from a two-phase electronic cooling system of claim 19, further including connecting said liquid cooling line to a secondary cooling system.