Enhanced thermosyphon cooling systems and methods

Abstract

Enhanced thermosyphon cooling systems and methods. In some embodiments, an evaporator holds a volume of liquid coolant and includes at least one micro-pump positioned within the evaporator. The thermosyphon cooling system also includes a first conduit operably connected to the evaporator and to a condenser that is positioned above the evaporator and includes a separate second conduit operably connected between the condenser and the evaporator. A heat generating device including at least one heat generating surface is positioned such that the heat generating surface(s) is contacted by the liquid coolant. During cooling operation at least one micro-pump directs liquid coolant towards the heat generating surface(s) which causes, when a temperature threshold value is reached or exceeded, a phase change of the liquid coolant into a vapor which rises from the evaporator through the first conduit to the condenser where the vapor is cooled until experiencing a phase change back into a liquid form which then travels through the second conduit back to the evaporator.

Description

ENHANCED THERMOSYPHON COOLING SYSTEMS AND METHODSBACKGROUND

[0001] Embodiments of the invention generally relate to enhanced thermosyphon cooling systems, apparatus and methods, and more specifically to thermosyphon cooling systems and methods which, in some embodiments could utilize low power active cooling devices immersed in liquid coolant, such as micro-pumps or dual cool jets (DCJs), to improve and / or enhance cooling of heat generating electronic devices. In addition, some implementations may include passive and / or low power control components that function to equalize the flow rate distribution of thermosyphon liquid over the heat generating electronic devices resulting in improved cooling performance.

[0002] A data center may be defined as a building, or dedicated space within a building, or a group of buildings used to house computer systems and associated components, such as telecommunications and storage systems. Data centers have evolved recently from privately -owned, tightly controlled on-premises facilities housing traditional information technology (IT) infrastructure for the exclusive use of one company, to remote facilities or networks of facilities owned by cloud service providers housing virtualized IT infrastructure for the shared use of multiple companies and customers. Cloud data centers (or cloud computing data centers) house IT infrastructure resources for shared use by multiple users or customers (which users may number in the thousands or even hundreds of millions) typically via an Internet connection. Many of the largest cloud data centers, known as hyperscale data centers, are owned and operated by cloud service providers such as Amazon Web Services (AWS™), Google Cloud Platform™, IBM Cloud™, and Microsoft Azure™.

[0003] Data centers may include powerful server computers that deliver applications, services and data to end-user devices. Typical form factors for a data center include one or more of a plurality of rack-mount servers that may be stacked on top of each other in a rack to economize space, blade serv ers which fit into a chassis that holds multiple blades, and mainframe computers, which are high-performance computers with multiple processors that that can do the work of an entire room of rack-mounted servers or blade servers. The electronic equipment running in data centers generate heat and need to be always-On, at every level to provide services to customers and / or end-users. Thus, data centers must bedesigned and equipped to control environmental factors such as excessive heat that can damage or destroy hardware and lead to expensive or catastrophic downtime. Data centers therefore typically employ some combination of air cooling and liquid cooling to keep the server computers and other heat-generating electronic hardware operating in their proper temperature ranges.

[0004] Air cooling usually takes the form of computer room air conditioning (CRAC) which may cool an entire server computer room or may be targeted at specific rows or racks of servers. Some data centers utilize liquid cooling technologies, which may be used in addition to air cooling, that may pump liquid directly onto the heat generating processors and other heat generating components or devices, and some implementations of such liquid cooling systems various electronic devices, such a server computers, are entirely immersed in coolant.

[0005] Conventional data centers currently utilize about forty percent (40%) of their total energy consumption for cooling the heat generating server computers through a complex system involving heating, ventilation and air condition (HVAC) systems, chillers, and cooling towers. Such air-cooling systems are inefficient, utilizing a large amount of electricity and a large amount of potable water. In fact, current estimates are that data centers consume on the order of one-hundred Terawatt hours (100 TWh) per year solely for cooling purposes and consume over one-hundred and seventy-five billion (175 billion) gallons of fresh water globally. To put that in context, the water use of one large data center may equal the water usage of a small-to-medium town or city in the United States having a population of 10,000 to 50,000 people. Thus, companies or entities considering construction of anew aircooled data center may be geographically constrained due to lack of water availability. Thus, in addition to the fact that current data center cooling architectures are complex and expensive, it has become more and more difficult (and even more expensive) to find locations that can provide large amounts of water for cooling purposes. This is also true of other industrial applications (such as wind turbines, solar inverters, and the like) which may seek to utilize air-cooled systems for cooling heat-generating electronic devices.

[0006] In view of the drawbacks associated with air cooling systems highlighted above, two-phase thermosyphon cooling systems could reduce energy’ use to less than two percent (2%) of total energy consumption. Generally, in a two-phase thermosyphon passive cooling system heat dissipated from an electrical device or electric component is removedutilizing phase change of a coolant from a liquid to a vapor (e.g., boiling). FIG. 1 depicts a passive, two-phase thermosyphon cooling system 100 which is a pump-free, HV AC-less closed system that does not use water. The thermosyphon cooling system includes a heat source 104 which is connected to a heat sink 106 via a first conduit 108 and second conduit 110. Instead of water, the passive thermosyphon cooling system utilizes a low boiling point, low-pressure liquid refrigerant 102 (or di-electric coolant) which is shown inside the first conduit 108 and does not contain any water. When the liquid refrigerant 102 travels under gravity and contacts the heat source 104, which may be a heat generating electronic device (e.g., one or more processors of one or more server computers), the coolant then turns into a vapor 112 which rises upwardly in the second conduit 110 to the heat sink or condenser 106. In some embodiments, ambient air at an elevation flows about the heat sink 108, which cools the vapor such that it experiences a phase change back into a liquid coolant state. A blower or fan is not needed for moving air at elevation and thus no energy7is required to perform cooling. The liquid refrigerant 102 from the heat sink 106 flows back down in the direction of arrow 114 under the influence of gravity within the first conduit 108 to the heat source 104 where the cycle starts again, with vapor rising in the direction of arrow 116, to passively remove heat from the heat source 104. Thus, a thermosyphon cooling system like that shown in FIG. 1 utilizes passive flow of a liquid refrigerant that turns into a vapor which rises to a condenser and condenses back into a liquid without any need for a blower or pump, resulting in the use of zero energy for cooling. Due to the high heat dissipation rates involved in two- phase thermosyphon cooling, and since water is not needed, such passive thermosyphon cooling systems can enable data center operation any where in the world.

[0007] In other embodiments, the air flow over the heat sink could be driven by a blow er w ould need a small amount of energy (2% of total energy) to operate, relative to the current 40% of total energy required by state-of-the-art data centers. In other embodiments, the heat sink may be cooled by other fluids including water, refrigerants, and other gases, where available, permissible, and inexpensive.

[0008] In view of the drawbacks associated with conventional industrial cooling systems, the inventors recognized that it would be desirable to provide apparatus, systems and methods to improve and / or enhance thermosyphon cooling systems. Such an enhanced thermosyphon cooled data center may still utilize less than two percent (<2%) of the energy currently used by conventional air-cooled systems to cool industrial equipment and moreoverwould not consume any water, resulting in lower capital expenditure (CAPEX) and lower operating expenditure (OPEX).BRIEF SUMMARY OF THE INVENTION

[0009] Presented are enhanced thermosyphon cooling systems and processes. In an aspect, an enhanced thermosyphon cooling system includes an evaporator encompassing a liquid coolant, at least one micro-pump positioned within the evaporator, a first conduit operably connected to the evaporator, a condenser positioned above the evaporator and operably connected to the first conduit, and a second conduit operably connected between the condenser and the evaporator. A heat generating device having at least one heat generating surface is positioned such that at least the heat generating surface is contacted by the liquid coolant. In addition, during cooling operation the at least one micro-pump directs liquid coolant towards the at least one heat generating surface which causes, when a temperature threshold value is reached or exceeded, a phase change of the liquid coolant into a vapor which rises from the evaporator through the first conduit to the condenser where the vapor is cooled until experiencing a phase change back into a liquid form which travels through the second conduit back to the evaporator.

[0010] In some embodiments the heat generating surface(s) contacts the liquid coolant through a wall of the evaporator, or the heat generating device is positioned within the evaporator and is immersed in the liquid coolant. In addition, one or more of the micro- pump(s) may be immersed w ithin the liquid coolant. In some implementations, the at least one heat generating device is a vertical rack of server computers and a heat generating surface of each server computer is provided with liquid coolant via a first server conduit operably connected to the evaporator and returns vapor to the condenser via a second server conduit. In some implementations, at least one micro-pump may be positioned near the first server conduit of each server computer in the vertical rack and may be operable to improve flow7rate distribution of liquid coolant to each server computer in the vertical rack. In some embodiments, an external controller may be operably connected to the at least one micropump and may be operable, based on a temperature of at least one server computer of the vertical rack, to control the flow of the liquid coolant. In addition, at least one valve may be positioned near the first server conduit of each server computer in the vertical rack and may be operable to improve flow rate distribution of liquid coolant to each server computer in thevertical rack. In some implementations, one or more of the valves may be controllable via an external controller.

[0011] In some embodiments, an elevation structure may be included that elevates at least the condenser above the evaporator, wherein the elevation structure may be one of a tower, an office building, or a commercial building. Other types of elevation structures may also be used. In addition, some implementations of the thermosyphon cooling system may include an external controller operably connected to the at least one micro-pump and operable, based on a temperature of the heat generating device, to control the flow of the liquid coolant to enhance cooling. The thermosyphon cooling system may also include at least one of a fan or blower or pump for directing at least one of a gas or liquid to cool the condenser. In addition, a liquid bridge may be included that connects the first conduit to the second conduit for directing liquid coolant back to the evaporator. Some embodiments of the thermosyphon cooling system may also include a condenser / chiller positioned within the evaporator and immersed within the liquid coolant, wherein the condenser / chiller may be a component of a secondary heat dissipation loop. The condenser / chiller may utilize a working liquid and may be operably connected to a third conduit which channels the working liquid to cool a second heat generating device that may also be operably connected to a fourth conduit which channels vapor from the second heat generating device to the evaporator during cooling operation. In some embodiments the working liquid may be different from the liquid coolant.

[0012] In an aspect of the thermosyphon cooling system, a third conduit may be operably connected to the evaporator and to a second heat generating device, a fourth conduit may be operably connected to the second heat generating device and the evaporator, and a liquid pump may be positioned to direct liquid coolant from the evaporator to the second heat generating device during cooling operation, wherein the fourth conduit directs vapor back to the evaporator during the cooling operation. In another aspect of the thermosyphon cooling system, at least one heat generating surface may include at least one computer chip having a baseplate and mounted on a printed circuit board (PCB) wherein the baseplate may include at least one nucleate boiling and heat transfer enhancement feature. The at least one nucleate boiling and heat transfer enhancement feature may be at least one of an additive or fabricated mesh structure, finned surfaces having different shapes and spacing, pitted surface features, and drilled holes.

[0013] Technical advantages of some embodiments disclosed herein include providing an enhanced thermosyphon cooling system that utilizes less than two percent (<2%) of the energy currently used by conventional air-cooled systems to cool industrial equipment and moreover does not consume any water. This advantageously results in lower capital expenditure (CAPEX) and lower operating expenditure (OPEX). These goals are achieved by disclosed implementations that include passive and / or low power control components that function to equalize the flow rate distribution of cooling liquid over the heat generating electronic devices or heat generating surfaces. Specifically, example embodiments of enhanced thermosyphon cooling systems described herein are configured for cooling data center servers and utilize low power active cooling devices such as micro-pumps (such as dual cool jets (DCJs)). In addition, some disclosed implementations include flow control valves or orifices that are controllable to manage and / or control thermosyphon liquid coolant and / or vapor flow to further enhance performance.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 depicts a conventional passive thermosyphon cooling system.

[0015] FIGS. 2 A, 2B and 2C depict data center architectures that are each outfitted with a thermosyphon cooling system in accordance with embodiments of the disclosure.

[0016] FIG. 3 A depicts a single evaporator module implementation of a direct thermosyphon cooling system in accordance with some embodiments of the disclosure.

[0017] FIG. 3B is a partial side view of a server module to illustrate an embodiment wherein the entire server module including the heat-generating chip surfaces are within an evaporator and thus immersed in liquid refrigerant in accordance with some embodiments of the disclosure.

[0018] FIG. 3C is another partial side view of the server module of FIG. 3B depicting another implementation wherein the chip surfaces indirectly contact coolant in accordance with some embodiments of the disclosure.

[0019] FIGS. 4A to 4D depict different views of an exemplary embodiment of a synthetic jet assembly or dual cool jet (DC J) of a type which may be used with embodiments of the thermosyphon systems in accordance with some embodiments of the disclosure.

[0020] FIG. 5 illustrates a multiple loop thermosyphon system that uses the same working fluid in each loop according to some embodiments.

[0021] FIG. 6 illustrates a multiple loop thermosyphon system that uses different working fluids for cooling components in accordance with some embodiments.

[0022] FIG. 7 depicts an indirect thermosyphon cooling system in accordance with the some embodiments.

[0023] FIG. 8 depicts a vertical rack of heat generating devices or modules to help explain methods for improving thermosyphon coolant flow in accordance with some embodiments.DETAILED DESCRIPTION

[0024] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of embodiments. However, it will be understood by those of ordinary skill in the art that the embodiments may be practiced without these specific details. In other instances, w ell-known methods, procedures, components and circuits have not been described in detail so as not to obscure the embodiments.

[0025] One or more specific embodiments of the present invention will be described belovw In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. Thus, the various embodiments disclosed herein do not constitute a definition of all possible embodiments, and those skilled in the art will understand that the present invention is applicable to many other implementations and / or applications.

[0026] In general, and for the purpose of introducing concepts of novel embodiments disclosed herein, presented are systems, apparatus and methods for enhancing thermosyphoncooling systems especially with regard to the cooling of industrial electronic equipment. In example embodiments described herein, enhanced thermosyphon cooling systems may cool data center servers and may include low power active cooling devices such as micro-pumps or dual cool jets (DCJs). In some implementations, flow control valves or orifices may also be utilized to manage and / or control thermosyphon liquid coolant and / or vapor flow to further enhance performance.

[0027] FIGS. 2 A, 2B and 2C depict examples of data center architectures that are each outfitted with a thermosyphon cooling system. FIG. 2A depicts a stand-alone modular and conventional data center 200 including a plurality of racks 202A. 202B and 202C, wherein each rack may hold a number of server computers (not shown in detail) having processors and / or other components that radiate heat during operation. In some configurations, each rack includes a plurality of server computers stacked on top of each other which generate heat during operation within a closed room or building 204. Thus, the racks 202A, 202B and 202C may each be cooled using a thermosyphon cooling system (such as that shown in FIG. 1). In FIG. 2A the condenser 206 is located at an elevation above the server modules, and may be located for example, on the roof of the data center 200. In some implementations a fan 207 may be utilized to help cool the condenser 204 by pushing or venting heat away from the condenser 206 as depicted by arrow s 208. The embodiment shown in Fig 2A could represent a modular containerized data center including one or more equipment racks and located w ithin a building, such as in a building housing a conventional data center. Such data centers may provide a plurality of servers for use by clients to provide different functions, such as Bitcoin mining, running cloud computing applications, storing and / or cataloging data and / or other functions and / or operations.

[0028] FIG. 2B illustrates an elevated implementation of a stand-alone modular data center 210 which also includes a plurality of racks 212A, 212B and 212C. In this example, an elevation structure such as a tower 214 supports the data center 210 high above the ground, and may elevate it to a height of approximately zero to twenty -five (0- 25) meters above sea level (for example, if the data center is located near the shore of an ocean or other body of w ater), or to a height of up to 50 meters above sea level (or more, for example, if the data center is located inland). Of course, the elevation structure may be of different heights, but a particular height may be selected by an engineer or other knowledgeable person(s) so that a fan or blower (like the blower 207 of FIG. 2A) is not needed due to freely-available ambient air flow, at elevation, which will act to cool the condenser 216 located at the selectedelevation from the server racks such that the vapor inside will condense back into a liquid, as explained above. In addition, many different types of elevation structures could be used.

[0029] FIG. 2C depicts another implementation of an elevated stand-alone modular data center 220 located on one or more of the higher floors of a commercial building 222, which may be an office building, or warehouse, or the like. This implementation of the standalone data center 220 also includes a plurality of racks 224A, 224B and 224C elevated on an upper floor of an office building high above street level. A condenser 226 is located on the roof or elevated above the commercial building to utilize freely -available air flow (or it may be fitted with a blower like that shown in FIG. 2A).

[0030] FIG. 2C also depicts the rack 224C in greater detail in a partially exploded view of a modular server rack 230, which rack includes server modules 232, 234, 236. 238, 240, 242, 244 and 246 stacked on top of each other wherein at least a heat generating portion of the server modules 232-246 is positioned inside a thermosyphon system container 250. It should be understood that the racks 202A-202C shown in FIG. 2A and the racks 212-212C of FIG. 2B may also have the same or similar structure and / or configuration. In this embodiment, the heat generating elements (not shown) of the server modules 232-246 are liquid cooled within the container 250 by a liquid refrigerant or liquid coolant which, when it is heated past a threshold temperature value, turns into a vapor. Thus, when the data center is operational the heat generated by the server modules 232-246 is cooled by liquid coolant which experiences a phase change into a vapor that rises into a first conduit 252 which provides a pathway for the refrigerant vapor to rise into the condenser 226. Once in the condenser 226, the vapor cools and then condenses back into liquid form, and then a second conduit 254 provides a pathway or channel so that the liquid refrigerant flows back downward under the influence of gravity into the evaporator or thermosyphon system container 250. As the condenser 226 is physically located at an altitude where ambient wind and / or ocean breezes and the like frequently occur, in many embodiments there is no need to include a fan or blower. In other embodiments, a fan or blower may be used to drive air flow, or may be used in a hybrid mode wherein the fan and / or blower is turned On when the ambient air flow is unavailable to dissipate heat. Thus, the fan or blower may be utilized only when insufficient ambient air flow- rate is detected and / or w hen an increase in temperature past a threshold value in the condenser is detected and the like.

[0031] Accordingly, the thermosyphon systems 210 and 220 shown in F IGS. 2B and 2C. respectively, utilize freely-available ambient air flow at elevation such that these data center cooling systems do not require any energy to operate and do not utilize any water, which both are highly advantageous. In addition, although the thermosyphon system 200 shown in FIG. 2A utilizes a blow er or fan 206 to push air about the condenser 204, this design still uses less than two percent (2%) of the energy to cool the data center servers in racks 202A0-202C than conventional data center cooling systems, which utilize some combination of air cooling and liquid cooling to keep the server computers and other heatgenerating electronic hardware operating in their proper temperature ranges.

[0032] FIG. 3A depicts a single evaporator module implementation 300 of a direct thermosyphon cooling system in accordance with some embodiments. In this example, rack 302 includes serv er modules 304, 306. 308, 310, 312, 314, and 318 which are heat generating devices and have at least a portion of their heat generating components positioned in such manner to contact liquid refrigerant circulating within an evaporator 320 (which may also be called an evaporator module or evaporator container). As discussed earlier, the liquid refrigerant or di-electric coolant within the evaporator module 320 cools the heat generating components (e.g., processors) of each of the server modules 304-318. When the liquid refrigerant is heated past its boiling point then the liquid coolant turns into a vapor which rises through a first conduit 322 (which provides a pathway for the vapor) from the evaporator module 320 and then accumulates in the condenser 324. As the vapor cools w ithin the condenser 324, it condenses back into a liquid and flows under the force of gravity downwards through a second conduit 326 (which may be a pipe or other channeling means) back into the thermosyphon system container or evaporator module 320 where it again cycles through the process of cooling the heat generating components of the server modules 304-318 and turning into a vapor. Some examples of liquid coolants or advanced heat transfer fluids that may be utilized include, but are not limited to, a 3M Company product called NOVEC™ 649 which has a boiling point of 49°C at 1 atm (atmosphere), R1233ZD(E) provided by the A-GAS® Company w ich has a boiling point of 19° C at 1 atm, and Chemours SF33™ which has a boiling point of 33° C at 1 atm.

[0033] Referring again to FIG. 3A, also illustrated is an enlarged top view 330 of the server module 318 within the evaporator module 320 showing the ten chip surfaces 332, 333, 334, 335. 336, 337, 338, 339, 340 and 341 that generate heat during operation (for example, the heat generating elements may be microprocessors). The chip surfaces 332-341 may alsobe thought of as chip boiling surfaces because when the fluid refrigerant 342 contacts the heat-generating surfaces to draw away heat a portion of the liquid refrigerant comes to a boil and then experiences a phase change into vapor. Also shown immersed in liquid refrigerant 342 are micro-pump devices 344 and 346 which are controllable in some implementations, and these micro-pump devices may be dual cool jets (DCJs) as will be discussed in more detail below.

[0034] Referring yet again to FIG. 3A, in some embodiments the micro-pumps 344 and 346 are totally immersed or at least partially immersed or submerged within the liquid coolant 342 and may be operably connected to a control element (not shown, such as a remote controller which may be a remote computer or remote computer system). The micropumps are operable to push the liquid refrigerant 342 past the chip surfaces (or other heat generating elements) within the evaporator module 320 to enhance the flow of the liquid coolant over and past the heat generating chip surfaces. Thus, the micro-pumps 344 and 346 help delay surface dry-out or critical heat flux (CHF) about the various server modules in a rack, thus avoiding failure due to high temperatures. As mentioned above, in some implementations the micro-pumps are DCJs which may be positioned to push liquid coolant in a manner to contact specific server modules (or all of them) within specific racks (or in all of the racks). In some implementations, the DCJs are specifically actuated by a controller to enhance the thermosyphon flow of specific modules and also to improve liquid coolant flow uniformity across the heat generating elements of the server modules in the rack.

[0035] FIG. 3B is a partial side view 350 of the server module 318 illustrating an embodiment wherein the entire server module 318 of FIG. 3 A, including the heat-generating chip surfaces 332, 334, 336, 338, and 340. are positioned within the evaporator module 320 and immersed in the liquid refrigerant 342. In addition, micro-pumps 344 and 346 are shown within the evaporator module 320 and fully immersed in the liquid refrigerant, and in some implementations are positioned at different angles to pump liquid coolant 342 towards and about the chip surfaces 332, 334, 336, 338, and 340.

[0036] FIG. 3C is another partial side view 355 of the server module 318 illustrating another embodiment wherein the server module 318 of FIG. 3 A is located outside the evaporator module 320 with only the heat-generating chip surfaces 332, 334. 336, 338. and 340 contacting an outside wall portion of the evaporator module 320 which is cooled by the liquid refrigerant 342. In this embodiment, the micro-pumps 344 and 346 are located withinthe evaporator module 320 and thus are fully immersed in the liquid refrigerant 342 and are positioned to pump liquid coolant 342 towards the evaporator module wall that is in contact with the chip surfaces 332, 334, 336, 338, and 340.

[0037] FIGS. 3D, 3E and 3F illustrate different immersion cooling reservoir embodiments that function as evaporators in the thermosyphon loop in accordance with the disclosure. In FIGS. 3D-3F, a reservoir or evaporator 360 holds liquid coolant 362 and includes a chip or other heat generating component 364 having a baseplate 366 (or hot surface) that could have added surface enhancements. In some embodiments, the chip 364 is seated on a printed circuit board (PCB) 368 which may contain one more other electronic components (not shown). As shown, the PCB 368, chip 364 and surface 366 are all immersed in the liquid coolant 362 held within the evaporator 360. For the sake of simplicity, not shown in FIGS. 3D-3F are the condenser and the first and second conduits of the thermosyphon system.

[0038] In addition to the heat generating component 364, the baseplate 366 and the PCB 368, FIG. 3D shows that one or more DCJs 370. 372 and 374 (or other piezo actuated or pumped jets) are includes and are also submerged in the liquid coolant 362 within the evaporator 360. The DCJs 370, 372 and 374 may be controlled and / or utilized to pump and / or impinge liquid coolant 362 onto the heat generating surface or baseplate 366 of the chip 364 to enhance the passive thermosyphon flow and delay dry-out or critical heat flux (CHF). As also shown in FIG. 3D, the DCJs 370. 372 and 374 can be positioned at various and different angles relative to the baseplate to optimize heat transfer and fluid flow. In other embodiments, more or less DCJs could be used.

[0039] Referring now to FIG. 3E, the reservoir or evaporator 360 holds liquid coolant 362 and includes a chip 364 (or other heat generating component) having a baseplate 366. In some embodiments the baseplate 366 includes a microchannel surface (not shown) or other surface enhancement to improve heat transfer. Thus, the chip surface (or the evaporator hot (boiling) surface) may include one or more nucleating boiling enhancement features to increase critical heat flux and nucleate boiling heat transfer. For example, the chip surface(s) and / or some of the evaporator surfaces may include additive or conventionally fabricated mesh structures or other porous surfaces and structures (not shown) that may act as nucleation sites. In addition, finned surfaces (not shown) of different shapes and spacings including, but not limited to, rectangular, parabolic, airfoil, pins, studs and the like may beutilized on the chip surfaces, and such finned surfaces may have solid or porous surfaces that contact the liquid coolant 362. In some embodiments, fins could be aligned or staggered, and may be straight or wavy. Also, some or all of the chip surfaces could be pitted or include drilled holes.

[0040] FIG. 3F depicts another immersion cooling reservoir embodiment wherein the evaporator 360 holds a liquid coolant 362 but wherein only the baseplate 366 (or hot surface) of the chip 364 is immersed in the liquid coolant. Such an embodiment reduces compatibility issues and / or compatibility risks by limiting the number of components (here, to the baseplate and the chip) that have direct contact with the liquid coolant 362. In other words, the number of different materials and / or components which may be found on the PCB 368 that may not generate heat and that could be exposed to the coolant is significantly reduced or eliminated. This is advantageous because in immersion cooling applications, the coolant 362 that is utilized must be chemically compatible with the plurality of materials with which it comes into direct contact to ensure multiple years of operation without corrosion or degradation issues. For example, with regard to the implementations shown in FIGS. 3D to 3E, the liquid coolant 362 is required to be compatible with the PCB 368, the chip 364, the baseplate 366, any adhesive material(a) such as solder (not shown) that are present, any types of metals and / or plastics found in the PCB or chip or baseplate, and any other materials that may be found in such components. In addition, with regard to FIG. 3D, the liquid coolant is required to be compatible with the DCJs 370, 372 and 374 or other t pes of micro-pumps for implementations that utilize such components. In contrast, in FIG. 3F the liquid coolant 362 need only be compatible with the chip 364 and the baseplate 366 because the PCB 368 is located outside of the evaporator 360 and does thus does not come into direct contact with the liquid coolant. It should be understood, however, that in some implementations one or more micro-pumps (such as the DCJs 370-374 shown in FIG. 3D) may also be positioned within the evaporator 360 of FIG. 3F and immersed in the liquid coolant.

[0041] FIGS. 4A to 4D depict different view s of an exemplar}' embodiment of a synthetic jet assembly or dual cool jet (DCJ) 400 of a type which may be utilized in some embodiments of the thermosyphon systems disclosed herein. Referring to FIG. 4A, the DCJ 400 includes two piezoelectric actuators (or other suitable actuators) that cause deflection of opposing flexible diaphragm w alls of a housing in order to change the volume within the internal chamber of the housing so as to generate and project a flow out from an orifice of the housing. As shown in FIG. 4, the DCJ 400 includes a synthetic jet 402. a cross-section ofwhich is illustrated in FIG. 4B which is taken along L-shaped line 42, and a mounting device 404 which may be a U-shaped bracket that is affixed to a housing or body 406 at one or more locations. A driver circuit 408 can be externally located or affixed to the mounting device 404 as shown. In some embodiments, the circuit driver 408 may be remotely located away from the DCJ 400.

[0042] FIG. 4B is a side view 415 of the DCJ assembly 400 of FIG. 4A. Referring now to both FIGS. 4A and 4B, the housing 406 defines and partially encloses an internal chamber or cavity 420 which, in accordance with embodiments disclosed herein, has a liquid coolant 422 found therein. While the housing 406 and the internal chamber 420 can take virtually any geometric configuration or shape, for purposes of discussion the housing 406 is shown in cross-section in FIG. 4B as including a first plate 424 and an opposing second plate 426 maintained in a spaced apart relationship by a spacer element 428. In some embodiments, the spacer element 428 may maintain a separation of approximately one millimeter (1mm) between the first plate 434 and the second plate 426. How ever, it should be understood that in some embodiments the physical dimensions of a DCJ may differ and thus, for example, the spacer element 428 may maintain a separation that is more than or less than 1mm, which may depend on the application. Referring again to FIG. 4B, one or more orifices 430 are formed between the first and second plates 424. 426 and the side walls of spacer element 428 in order to place the internal chamber 420 in fluid communication with a surrounding, exterior environment 432. In some implementations, the spacer element 428 may include a front surface (not shown) in which one or more orifices 430 are formed.

[0043] According to various embodiments, the first and second plates 424, 426 may be formed from a metal, plastic, glass, and / or ceramic material. Likewise, the spacer element 428 may be formed from a metal, plastic, glass, and / or ceramic material. Suitable metals may include, but not be limited to, materials such as nickel, aluminum, copper, and molybdenum, or alloys such as stainless steel, brass, bronze, and the like. Suitable polymers and plastics may include, but are not limited to, thermoplastics such as polyolefins, polycarbonate, thermosets, epoxies, urethanes, acrylics, silicones, polyimides, and photoresist-capable materials, and other resilient plastics. Suitable ceramics include, for example, titanates (such as lanthanum titanate, bismuth titanate, and lead zirconate titanate) and molybdates. Furthermore, various other components of the DCJ 400 may be formed from metal as w ell. In some implementations, the plates, spacer element and other components of the DCJ may be manufactured of materials that do not adversely interact with liquid coolant and / or that iscompatible with the liquid coolant. Accordingly, the specific materials used to fabricate the first and second plates 424, 426 and the spacer element 428 (and any of the other elements or aspects of the DCJs) may be a function of the type of liquid coolant being utilized in a thermosyphon system.

[0044] Referring again to FIGS. 4A and 4B, a first actuator 434 and a second actuator 436 are each coupled to respective first and second plates 424, 426 to form first and second composite structures or flexible diaphragms 438, 440. The flexible diaphragms 438, 440 are controlled by the driver 408 which receives control signals or instructions from a controller or control unit 442. As shown in FIG. 4A, the controller 442 is electronically coupled to the driver 408. In some embodiments, the controller 442 may be integrated into the driver 408 and may be remotely located from the DCJ 400. For example, each flexible diaphragm 438, 440 may be equipped with a metal layer and a metal electrode may be disposed adjacent to the metal layer so that diaphragms 438, 440 may be moved via an electrical bias imposed between the electrode and the metal layer. Moreover, controller 442 may be configured to provide instructions to generate the electrical bias by any suitable device, such as, for example, a computer, logic processor, or signal generator.

[0045] In some DCJ implementations, the actuators 434, 436 are piezoelectric motive (piezomotive) devices that may be actuated by application of a harmonic alternating voltage that causes the piezomotive devices to rapidly expand and contract. During operation, controller 442 (in conjunction with driver 408) generates a drive signal that causes an electric charge to be transmitted to piezoelectric actuators 434, 436, which undergo mechanical stress and / or strain responsive to the charge(s). The stress / strain of piezomotive actuators 434, 436 causes deflection of respective first and second plates 424, 426 such that a time-harmonic or periodic motion may be achieved. The resulting volume change in the internal chamber 420 causes an interchange of fluid between the internal chamber 420 and the exterior volume 432.

[0046] In some embodiments the actuators 434, 436 may include devices other than piezoelectric motive devices, such as hydraulic, pneumatic, magnetic, electrostatic, and ultrasonic materials. Accordingly, the control system 442 would then be configured to activate respective actuators 434, 436 in corresponding fashion to provide a rapidly alternating electrostatic voltage to actuators 434, 436 in order to activate and flex respective first and second plates 424, 426.

[0047] FIGS. 4C and 4D depict side views 425, 435 of the DCJ of FIGS. 4A and 4B to illustrate the operation of the DCJ 400 according to some embodiments. Referring to FIG. 4C, the control system 442 controls the actuators 434 and 436 to cause the first plate 424 and the second plate 426 to move outwardly in the direction of arrows 444 with respect to the internal chamber 420. As the first and second plates 424, 426 flex outwardly, the internal volume of internal chamber 420 increases, which causes the fluid 446 to rush into the internal chamber 420 as depicted by arrows 448. When the first and second plates 424, 426 move outward from internal chamber 420, vortices are already removed from edges of orifice 430 and thus are not affected by the ambient fluid 446 being drawn into internal chamber 420. Meanwhile, a jet of ambient fluid 446 is synthesized by vortices creating strong entrainment of ambient fluid 446 drawn from large distances away from orifice 430.

[0048] FIG. 4D depicts the DCJ as the control system 442 controls the actuators 434, 436 to cause the first and second plates 424. 426 to flex inward into internal chamber 420, as depicted by arrows 450. The internal volume of internal chamber 420 thus decreases, and liquid coolant 422 is ejected outwardly as a cooling jet through orifice 430 in the direction indicated by the set of arrows 452 toward a heat generating device 454 to be cooled. For example, the device 454 may be a temperature-dependent power producing device or a temperature-dependent power consuming device (such as a server computer). As the liquid coolant 422 exits the internal chamber 420 through the orifice 430, the flow separates at the sharp edges of orifice 430 and creates vortex sheets which roll into vortices and begin to move away from edges of orifice 430.

[0049] Although the DCJ 400 depicted in FIGS. 4A-4D is described as having a single orifice 420 therein, in some embodiments of such a micro-pump multiple orifices with multiple actuators may be utilized. In addition, while the DCJ actuators in FIGS. 4A-4D are shown and described as having an actuator element included on each of first and second plates, but some embodiments may include only a single actuator element positioned on one of the plates. Furthermore, a DCJ or micro-pump may be shaped and / or include plates provided in a circular, rectangular, or alternatively shaped configuration, rather than in a square configuration as shown in FIGS. 4A-4D.

[0050] FIG. 5 illustrates a multiple loop thermosyphon system 500 that uses the same working fluid in each loop according to some embodiments. Specifically, the multiple loop thermosyphon system 500 includes an evaporator 501 having a central liquid reservoir 505containing liquid coolant 506. The central liquid reservoir 505 is part of both the first cooling loop 502 and the second cooling loop 504. In particular, the first cooling loop 502 includes the central liquid reservoir 505, a first conduit 508 including a pump 510 which pumps liquid coolant 506 from the central liquid reservoir 505 to contact a heat generating component 512 and cool it. A second conduit 514 is provided that directs liquid coolant back to the central liquid reservoir 505. Thus, the first cooling loop conducts single phase heat transfer as the liquid coolant 506 does not meet or exceed a threshold temperature value needed to cause a phase change and thus the liquid coolant does not pass through a phase change into vapor.

[0051] Referring again to FIG. 5, the second coolant loop 504 includes the central liquid reservoir 505 as an evaporator 501 with at least one auxiliary device 516, and PCBs 507, 509 and 511 which include chips (not shown) immersed in the liquid coolant 506. Also immersed in the liquid coolant are micro-pumps 518A, 518B, 518C which may be dual cool jets (DCJs). The auxiliary device(s) 516 may be one or more central processing unit (CPU) cards and / or other electrical systems that have heat generating components or heat generating elements which are directly contacting the liquid coolant or are immersed therein, and those heat generating components may become hot enough to heat the liquid coolant to reach and / or exceed a threshold temperature value which causes a phase change of the liquid coolant into vapor 520. The vapor 520 then rises through a third conduit 522 to a condenser 524 which is positioned at an elevation where ambient air flow, that is freely available or driven by a blower or fan (not shown), can cool the condenser sufficiently over time to cause the vapor to condense back into the liquid state. Thus, when the vapor condenses back into the liquid coolant it then travels down a fourth conduit 528 and back into the central liquid reservoir 505 to continue with the multiple loop cooling cycle. In some embodiments, the second coolant loop 504 includes a liquid bridge 526 which may be provided to capture liquid coolant from the third conduit 522 when vapor happens to cool and experience a phase change back to liquid coolant before reaching the condenser 524. Thus, in such a case liquid bridge 526 returns the liquid coolant back to the central liquid reservoir 505.

[0052] Referring again to FIG. 5, it should be understood that different combinations of “M” evaporators andC'N” condensers may be utilized in some embodiments, wherein both “M” and ”N" may be more than one, and wherein “M” and "CN” may or may not equal each other. In addition, in some embodiments of the multiple loop thermosyphon a thermally - conductive mounting plate or base plate (not shown) attached to one or more of the heat generating devices (such as computer chips) could be utilized within the evaporator 501.Such a mounting plate or base plate may have nucleating boiling enhancement features to increase critical heat flux and nucleate boiling heat transfer. The surface enhancement features of such a mounting plate may include additive or conventionally fabricated mesh structures that act as nucleation sites and / or finned surfaces of different shapes and spacing including, but not limited to, rectangular, parabolic, airfoil, pins, studs and other ty pes. Such fins could be aligned or staggered and could be straight or waw. In addition, some or all surfaces could be pitted or contain drilled holes.

[0053] FIG. 6 illustrates a multiple loop thermosyphon 600 that uses different working fluids for cooling components according to some embodiments. Similar to the multiple loop thermosyphon 500 of FIG. 5, the multiple loop thermosyphon 600 includes an evaporator 601 having a central liquid reservoir 605 containing liquid coolant 606. In this implementation, the central liquid reservoir also includes a condenser / chiller 607 having a working fluid (liquid or gas(es)) contained therein that may be different than the liquid coolant 606. In this embodiment of a multiple loop thermosyphon, the central liquid reservoir605, functioning as a condenser / chiller, is part of each of a first cooling loop 602 (or first heat dissipation loop) and a third cooling loop 608 (or third heat dissipation loop), and functions as an evaporator in a second cooling loop 604 (which can be thought of as a central thermosyphon passive cooling loop or central thermosyphon passive heat dissipation loop). In this example, the first cooling loop 602 includes a first conduit 609 having a blower or pump 610 which pumps liquid coolant 606 from the central liquid reservoir 605 to contact and cool a heat generating component 612. A second conduit 614 is provided that directs heated liquid coolant back to the central liquid reservoir 605. Thus, the first cooling loop 602 conducts single phase heat transfer as the liquid coolant 606 does not meet or exceed a threshold temperature value as it cools the component 612 that is needed to cause a phase change, and thus the liquid coolant does not pass through a phase change and returns to the evaporator 601 as a liquid.

[0054] Referring again to FIG. 6, a second coolant loop 608 includes the chiller coil 607 having a working fluid (liquid or gases) therein that is different than the liquid coolant606, and a third conduit 630 having a liquid pump or liquid blower 632 which pumps or directs the working fluid to contact the heat generating component 634. In some embodiments, after contacting the heat generating component 634 the working fluid experiences a phase change to a vapor and is then channeled via a fourth conduit 636 back to the chiller coil 607 which is immersed in the liquid coolant 606 and then cooled down back toa working fluid phase, and then cycled back via the liquid pump 632. However, in other embodiments the working fluid (or air) in the second coolant loop 608 does not experience a phase change and thus a heated liquid (or heated air) is returned to the container 607 which is then cooled by the liquid coolant 606 before it is pumped back via liquid pump 632 to cool the component 634. Thus, in some implementations the combination of single-phase heated liquids being returned from both the first coolant loop 602 and the second coolant loop 608 may cause a portion of the liquid coolant 606 in the evaporator 601 to experience a phase change to vapor 620 which then must be handled by the condenser 624 as explained below. In some other implementations, the combination of a single-phase heated liquid and a vapor being returned from the first coolant loop 602 and a vapor being returned from the second coolant loop 608 may cause a portion of the liquid coolant 606 in the evaporator to experience a phase change to vapor 620 which then must be handled by the condenser 624 as explained below.

[0055] The system shown in FIG. 6 also includes a central thermosyphon loop 604 which includes the evaporator 601 containing heat generating components 618A, 618B and 618C (which may be PCBs, for example) and the chiller coil 607 immersed in the liquid coolant 606. In some embodiments the central thermosyphon loop 604 also includes micropumps such as DCJs (not shown) immersed within the liquid coolant 606 that may be controllable via a controller (not show n) to direct liquid coolant about the heat generating components 618C, 618B and 618C and the condenser and / or chiller coil 607 to enhance cooling. And as discussed earlier, when the liquid coolant 606 meets or exceeds a threshold temperature value then a phase change occurs and vapor 620 rises through a fifth conduit 622 to the condenser 624. As discussed above, this may occur due to a combination of the heated liquids (or heated vapor) returning from cooling the heat generating components 612 and 634. Thus, vapor rises to the condenser 624 which may be positioned at an elevation where ambient air (natural winds or air driven by a blower or fan) cools the condenser 624 sufficiently over time to cause the vapor to experience a phase change and condense back into the liquid coolant state. When that occurs, the condensed liquid coolant in the condenser then travels down a sixth conduit 628 and back into the central liquid reservoir 605. In some embodiments, a liquid bridge 626 may be provided from the fifth conduit 622 to the sixth conduit 628 to capture and return any liquid coolant for vapor that experienced a phase change before reaching the condenser 624, thus returning that liquid coolant to the central liquid reservoir 605.

[0056] FIG. 7 depicts an indirect thermosyphon cooling system 700 in accordance with some embodiments. In this example, a vertical rack 702 of heat generating elements (such as data center server module rack) is operably connected to a thermosyphon evaporator 704 which is operably connected to a condenser 706. The thermosyphon evaporator 704 includes a central liquid reservoir 708 that holds liquid coolant (or air) 709, and the cooling system utilizes a liquid pump 710 in a first conduit 712 to supply liquid coolant (or air) to the vertical rack 702 of heat generating components, such as the servers as depicted. In this example implementation, each server in vertical rack 702 has a return path or pipe to a second conduit 714 which returns heated liquid (or air) to the thermosyphon evaporator 704. Thus, all of the servers in rack 702 are cooled by a separately pumped two-phase liquid or a single-phase liquid (or air). Accordingly, some embodiments may utilize an air-to- thermosyphon or liquid-to-thermosyphon heat exchanger as the thermosyphon evaporator 704. When a two-phase liquid coolant is utilized, either heated liquid coolant or vapor is returned via the second conduit 714 to the thermosyphon evaporator 704. When vapor is returned, or when the returned heated liquid causes liquid coolant 709 in the central liquid reservoir 708 to experience a phase change, the vapor rises via a third conduit 716 to the condenser 706 where it is cooled and again experiences a phase change back to liquid and flows via the fourth conduit 718 back down to the central liquid reservoir 708 within the evaporator 704. Such a system is advantageously easy to retrofit to existing server racks, for example, being connectable to either a server cabinet rear door or to a front door (not shown).

[0057] FIG. 8 depicts a vertical rack 800 of heat generating devices or modules 806A- 806L to help explain methods for improving thermosyphon coolant flow, in both direct and indirect configurations, in accordance with some embodiments. Such vertically stacked heat sources 806A, 806B, 806D, 806E, 806F, 806G, 806H, 8061, 806J, 806K and 806L as shown in FIG. 8 can be found, for example, in data centers and / or server farms and / or in other facilities utilizing a plurality of electronic devices and / or components that are inserted into racks or vertical holders. When attempting to cool each of the stacked heat sources 806A- 806L, the flow of a two-phase coolant of a passive thennosyphon cooling system (such as those discussed above with regard to FIGS. 5-7) is influenced by hydrostatic pressure due to the liquid head difference between where the liquid coolant first enters the stack from the inlet conduit 802 and which coolant continues to flow into the areas about each of the heat sources under the force of gravity (as shown), and then is returned as a vapor via the conduit 804 w hich channels the vapor from each of the heat sources to a condenser (not shown, butsee FIGS. 5-7 for examples). Thus, the difference in elevation of each module 806A-806L could lead to changes in flow rate distribution, with the uppermost module 806A experiencing the lowest flow rate of coolant and the lowermost module 806L experiencing the highest flow rate of coolant. In order to mitigate such coolant flow distribution problems by more evenly distributing liquid coolant, in some embodiments controllable pulsed piezoelectric jets (DCJs) 808A, 808B, 808D, 808E, 808F. 808G, 808H. 8081. 808J, 808K and 808L, or other controllable micro-pumps, may be provided and positioned at a point where liquid coolant enters a pathway to each of the heat sources 806A-806K, as shown to provide an auxiliary pumping mechanism in one or more modules. In some embodiments, one or more of the DCJs 808A-808L may be positioned internally to the heat source cold plate (or baseplate, not shown) or externally and then actuated as a function of flow rate. For example, if a measured value of a computer chip junction temperature for server 806A is too high then the DC J 808A may be controlled by a controller (not shown) to pump coolant at a high rate past that server 806 A. In addition, if the computer chip junction temperature for server 806K is low then the DCJ 808K may be controlled to either not pump at all or to pump liquid coolant at a low rate. Such operation of the DCJs may include utilizing one or more temperature sensors (not shown, which may be functionally integrated into one or more of the servers) to measure the computer chip junction temperature(s) and / or the temperature(s) of other heat generating components.

[0058] In some other embodiments having vertically stacked heat sources such as that shown in FIGS. 7 and 8, valves (for example, electronically controlled solenoid valves or manual valves), or orifices, or other low-power controllable obstruction features, could also be utilized to control the flow resistance of the stacked heat sources 806A-806L, and thereby control and / or even out the flow distribution. Such controllable obstruction features provide the ability to redistribute the flow of liquid coolant and could be used in addition to, or exclusively from, the use of micro-pumps or DCJs 808A-808L. For example, a valve or an orifice could be adjusted to have higher flow resistance at one or more of the bottom server modules than that of the serv er modules nearest the top of the vertical rack of servers, which valves could be completely opened.

[0059] Thus, embodiments disclosed herein provide technical improvements to thermosyphon cooling system designs and operation. Based on the systems and processes disclosed herein a thermosyphon cooling system may be designed to efficiently cool heat generating electronic devices and / or components of an industrial facility, such as a serverfarm or data center or other heat generating electrical and electronic systems in a manner that advantageously utilizes very little power and that consumes no water. Moreover, the disclosed thermosyphon cooling systems and processes result in lowering capital expenditure (CAPEX) and lowering operating expenditure (OPEX).

[0060] Although specific hardware and data configurations have been described herein, note that any number of other configurations may be provided in accordance with embodiments of the present invention (e.g., some of the information associated with the databases described herein may be combined or stored in external systems). Moreover, although some embodiments are focused on data centers and / or server farms (which are utilized to mine Bitcoin, for example) having a plurality of heat generating server computers, any of the embodiments described herein could be applied to other types of physical systems that generate heat including power generating windmills, locomotives, airplane engines, and autonomous vehicles (including vehicles with heat generating engines such as automobiles, trucks, drones, submarines, etc.).

[0061] The present invention has been described in terms of several embodiments solely for the purpose of illustration. Persons skilled in the art will recognize from this description that the invention is not limited to the embodiments described but may be practiced with modifications and alterations limited only by the spirit and scope of the appended claims.

Claims

WHAT IS CLAIMED IS:1 . A thermosyphon cooling system comprising: an evaporator encompassing a volume of liquid coolant; at least one micro-pump positioned within the evaporator; a first conduit operably connected to the evaporator; a condenser positioned above the evaporator and operably connected to the first conduit; and a second conduit operably connected between the condenser and the evaporator; wherein a heat generating device comprising at least one heat generating surface is positioned such that the at least one heat generating surface is contacted by the liquid coolant; and wherein during cooling operation the at least one micro-pump directs liquid coolant towards the at least one heat generating surface which causes, when a temperature threshold value is reached or exceeded, a phase change of the liquid coolant into a vapor which rises from the evaporator through the first conduit to the condenser where the vapor is cooled until experiencing a phase change back into a liquid form which travels through the second conduit back to the evaporator.

2. The thermosyphon cooling system of claim 1 wherein one of: the at least one heat generating surface contacts the liquid coolant through a wall of the evaporator, or the heat generating device is positioned within the evaporator and is immersed in the liquid coolant.

3. The thermosyphon cooling system of claim 1 wherein the at least one micro-pump is immersed within the liquid coolant.

4. The thermosyphon cooling system of claim 1, wherein the at least one heat generating device comprises a vertical rack of server computers wherein a heat generating surface of each server computer is provided with liquid coolant via a first server conduit operably connected to the evaporator and returns vapor to the condenser via a second server conduit.

5. The thermosyphon cooling system of claim 4, further comprising at least one micropump positioned near the first server conduit of each server computer in the vertical rack and is operable to improve flow rate distribution of liquid coolant to each server computer in the vertical rack.

6. The thermosyphon cooling system of claim 5, further comprising an external controller operably connected to the at least one micro-pump and operable, based on a temperature of at least one server computer of the vertical rack, to control the flow of the liquid coolant.

7. The thermosyphon cooling system of claim 4, further comprising at least one valve positioned near the first server conduit of each server computer in the vertical rack and operable to improve flow rate distribution of liquid coolant to each server computer in the vertical rack.

8. The thermosyphon cooling system of claim 1 further comprising an elevation structure that elevates at least the condenser above the evaporator.

9. The thermosyphon cooling system of claim 8 wherein the elevation structure comprises one of a tower, an office building, or a commercial building.

10. The thermosyphon cooling system of claim 1. further comprising an external controller operably connected to the at least one micro-pump and operable, based on a temperature of the heat generating device, to control the flow of the liquid coolant to enhance cooling.

11. The thermosyphon cooling system of claim 1, further comprising at least one of a fan or blower or pump for directing at least one of a gas or liquid to cool the condenser.

12. The thermosyphon cooling system of claim 1, further comprising a liquid bridge connecting the first conduit to the second conduit for directing liquid coolant back to the evaporator.

13. The thermosyphon cooling system of claim 1 , further comprising a condenser / chiller positioned within the evaporator and immersed within the liquid coolant, wherein the condenser / chiller is a component of a secondary heat dissipation loop.

14. The thermosyphon cooling system of claim 13, wherein the condenser / chiller utilizes a working liquid and is operably connected to a third conduit which channels the w orking liquid to cool a second heat generating device that is also operably connected to a fourth conduit which channels vapor from the second heat generating device to the evaporator during cooling operation.

15. The thermosyphon cooling system of claim 14 wherein the working liquid is different from the liquid coolant.

16. The thermosyphon cooling system of claim 1, further comprising: a third conduit operably connected to the evaporator and to a second heat generating device; a fourth conduit operably connected to the second heat generating device and the evaporator; and a liquid pump positioned to direct liquid coolant from the evaporator to the second heat generating device during cooling operation, and wherein the fourth conduit directs vapor back to the evaporator during cooling operation.

17. The thermosyphon cooling system of claim 1, wherein the at least one heat generating surface comprises at least one computer chip having a baseplate and mounted on a printed circuit board (PCB).

18. The thermosyphon cooling system of claim 17, wherein the baseplate comprises at least one nucleate boiling and heat transfer enhancement feature.

19. The thermosyphon cooling system of claim 18, wherein the at least one nucleate boiling and heat transfer enhancement feature comprises at least one of an additive or fabricated mesh structure, finned surfaces having different shapes and spacing, pitted surface features, and drilled holes.

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