Dual-mode hybrid two-phase loop for data center cooling and associated method of use

Abstract

A hybrid (mechanical-capillary-driven) two-phase loop (HTPL) and associated method of use for data centers. The dual-mode HTPL combines a loop thermosiphon (passive mode) and a pumped two-phase loop (active mode). The HTPL will consist of an evaporator (multiple evaporators used for a server rack), a condenser, a pump, and a liquid reservoir. The operation of the HTPL begins with the pumping of a subcooled liquid from the liquid reservoir to the liquid chamber of the evaporator, in which a fraction of the supplied liquid is drawn into the evaporator wick by capillary pumping. Then, the drawn liquid vaporizes in the evaporator wick by the heat input from a heat source (server electronics), and the saturated vapor exits the evaporator and flows through a vapor line to the condenser, where the vapor is condensed and subcooled. Subsequently, the condensate from the condenser flows back to the reservoir.

Description

TITLE: DUAL-MODE HYBRID TWO-PHASE LOOP FOR DATA CENTER COOLINGAND ASSOCIATED METHOD OF USECROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. § 119 to provisional patent application U.S. Serial No. 63 / 601,297, filed November 21, 2023. The provisional patent application is herein incorporated by reference in its entirety, including, without limitation, the specification, claims, and abstract, as well as any figures, tables, appendices, or drawings thereof.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTThis invention was made with government support under DE-AR0001752 awarded by the U.S. Department of Energy. The government has certain rights in the invention.TECHNICAL FIELD

[0002] The present disclosure generally relates to a Hybrid (mechanical-capillary-driven) Two- phase Loop (HTPL), which is an ideal cooling solution for data centers with numerous advantages: dual-mode operation (passive, active), low thermal resistance, high heat flux, low pumping power consumption (zero for passive mode), reliable operation, and fully scalable design.BACKGROUND

[0003] The background description provided herein gives context for the present disclosure. Work of the presently named inventors, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art.

[0004] The IT equipment in data centers generates heat, and as its capacity increases, it produces even more heat. Some organizations reduce their data center’s physical size to fit more into cabinets. However, smaller data centers now see heat densities that could not be contemplated a decade ago.

[0005] Thus, there exists a need in the art for an apparatus that cools a data center in both active and passive modes with low thermal resistance, high heat flux, low pumping power consumption (zero for passive mode), reliable operation, and a fully scalable design.SUMMARY

[0006] The following objects, features, advantages, aspects, and / or embodiments, are not exhaustive and do not limit the overall disclosure. No single embodiment needs to provide each and every object, feature, or advantage. Any of the objects, features, advantages, aspects, and / or embodiments disclosed herein can be integrated with one another, either in full or in part.

[0007] It is a primary object, feature, and / or advantage of the present disclosure to improve on or overcome the deficiencies in the art.

[0008] A dual-mode (passive-active) Hybrid (mechanical-capillary-driven) Two-phase Loop (HTPL) is proposed as an ideal cooling solution for data centers with numerous advantages: dualmode operation (passive, active), low thermal resistance, high heat flux, low pumping power consumption (zero for passive mode), reliable operation, and fully scalable design. The HTPL can operate in either passive or active mode using a control valve to toggle the HTPL operation between passive and active modes. The dual-mode HTPL combines a loop thermosiphon (passive mode without using power-consuming components such as a pump to circulate the fluid in the system) and a pumped two-phase loop (active mode). Multi-evaporator HTPL can be constructed in various configurations depending on cooling needs: series, parallel, and cascade.

[0009] The HTPL will consist of an evaporator (multiple evaporators used for a server rack), a condenser, a pump, and a liquid reservoir. The operation of the HTPL begins with the pumping of a subcooled liquid from the liquid reservoir to the liquid chamber of the evaporator, in which a fraction of the supplied liquid is drawn into the evaporator wick by capillary pumping. Then, the drawn liquid vaporizes in the evaporator wick by the heat input from a heat source (server electronics), and the saturated vapor exits the evaporator and flows through a vapor line to the condenser, where the vapor is condensed and subcooled. Subsequently, the condensate from the condenser flows back to the reservoir. The excess liquid from the liquid chamber returns to the reservoir through a liquid return line. Finally, the returned liquid is mixed with the subcooled condensate in the reservoir, which completes the fluid circulation. Passive (capillary-driven) phase separation and thin-film evaporation in a microporous layer achieve low thermal resistance and high heat flux cooling.

[0010] A dual-mode hybrid (mechanical-capillary-driven) two-phase loop (HTPL) is an ideal cooling solution for data centers with numerous advantages: dual-mode operation (passive, active), low thermal resistance < 0.01 K / W), high heat flux (> 300 W / cm2), low pumping power consumption (zero for passive mode; 0.45% of IT load for active mode), reliable operation, fully-scalable design (heat transfer area > 150 cm2), and a high TRL (> 5). This HTPL is a desirable combination of a loop thermosiphon, a loop heat pipe, and a pumped two-phase loop. Passive (capillary-driven) phase separation and thin-film evaporation in a microporous layer in the evaporator(s) in the dual-mode HTPL achieve low thermal resistance and high heat flux cooling. Thanks to vigorous improvements through hardware demonstration, computational modeling, design optimization, and advanced control, the HTPL can meet or exceed the performance targets for data center cooling.

[0011] It is still yet a further object, feature, and / or advantage of the present disclosure is a dualmode hybrid system for two-phase loop cooling of a data center that includes at least one evaporator having a liquid chamber and a wick, a condenser, a pump, a vapor line between the condenser and the at least one evaporator, a liquid reservoir, and a liquid return line between the evaporator and the liquid reservoir, wherein subcooled liquid from the condenser flows to the liquid chamber of the at least one evaporator by the pump in which a fraction of supplied liquid is drawn into the wick of the at least one evaporator by capillary pumping and where drawn liquid vaporizes in the wick of the evaporator by primary heat sources (CPU and GPU) in the data center servers and then this saturated vapor exits the at least one evaporator and flows through the vapor line to the condenser where this vapor is condensed and subcooled and then condensate from the condenser flows back to the liquid reservoir where excess liquid from a liquid chamber of the at least one evaporator returns to the liquid reservoir through the liquid return line where liquid in the liquid return line is mixed with subcooled condensate in the liquid reservoir to complete a fluid circulation cycle.

[0012] An aspect of the present disclosure is that at least one valve is in fluid connection with the pump.

[0013] Another aspect of the present disclosure is that the evaporator includes a plurality of evaporators connected in parallel, series, and / or cascade.

[0014] It is a further object, feature, and / or advantage of the present disclosure, which is a liquid cold plate for secondary heat sources (memories, storage devices, power inverter, etc.) in fluid connections for liquid supply and return with the evaporator.

[0015] Yet another aspect of the present disclosure is that the liquid cold plate receives heat from the secondary heat sources.

[0016] Another feature of the present disclosure is the secondary heat source, which includes computer memories, storage devices, and power inverter.

[0017] Yet another aspect of the present disclosure is the evaporator equipped with two electrodes that create an electroosmotic-driven liquid flow to the boiling surface, and there is a primary heat source that applies heat to the evaporator where capillary-driven thin film boiling on the boiling surface converts liquid into a vapor that exits the evaporator and flows back into the condenser.

[0018] Still, yet another feature of the present disclosure is a coolant distribution unit (CDU) that includes the condenser, the liquid and vapor reservoirs, the pump, solenoid valves, and the electronic controller.

[0019] Another feature of the present disclosure is the primary heat sources dissipating a large amount of waste heat is selected from the group consisting of computer processing units (CPUs) or graphical processing units (GPUs).

[0020] Still another aspect of the present disclosure is a dual-mode hybrid system for two-phase cooling of a data center that includes a condenser that receives coolant liquid, a liquid reservoir connected in a fluid relationship to the condenser, at least one liquid cold plate that receives liquid directly from the liquid reservoir in passive mode or through a pump that receives liquid from the liquid reservoir for supplying liquid to the at least one liquid cold plate in active mode, wherein the at least one liquid-cold plate receives heat from at least one primary or secondary heat source, at least one valve for diverting liquid through the pump or directly to the at least one liquid cold plate, depending on selection of active mode or passive mode, and at least one evaporator internally having a liquid chamber and a vapor chamber, wherein the liquid chamber is in fluid connection to the at least one liquid cold plate, wherein a fraction of supplied liquid is drawn into a wick of the at least one evaporator by capillary pumping and where drawn liquid vaporizes in the wick of the evaporator by a primary or secondary heat source and then this saturated vapor exits the at least one evaporator and flows through the vapor line to the condenser where this vapor is condensed and subcooled and then condensate from the condenser flows back to the liquid reservoir where excess liquid from a liquid chamber of the at least one evaporator returns to the liquid reservoir through a liquid return line where liquid in the liquid return line is mixed with subcooled condensate in the liquid reservoir to complete a fluid circulation cycle.

[0021] Still, another feature of the present disclosure is the at least one liquid cold plate is attached to the liquid lines (liquid supply and liquid return) of the dual-mode hybrid two-phaseloop, consisting of a Peltier (thermoelectric) cooler and an air heat sink that were attached to the liquid cold plate.

[0022] Still yet another feature of the present disclosure is a server enclosing the at least one evaporator and the at least one cold plate, and a coolant distribution unit that includes the condensers, the liquid reservoir, the vapor reservoir, the pumps, and the electric control system.

[0023] Another aspect of the present disclosure is at least one manifold with two connecting points for liquid and two connecting points for vapor flow located between the server and the coolant distribution unit.

[0024] An additional feature of the disclosure is utilizing a vapor reservoir connected to a vacuum pump to remove non-condensable gas trapped in the vapor reservoir.

[0025] Yet another feature of the method of the present disclosure is at least one porous plug connected between the liquid chamber of the at least one evaporator and the at least one liquid cold plate and at least one needle valve connected between the liquid chamber of the at least one evaporator and the liquid reservoir.

[0026] It is still yet another feature of the method of the present disclosure, which is at least one check valve between the vapor chamber of the at least one evaporator and the vapor reservoir.

[0027] In still yet another aspect of the present disclosure is a method for utilizing a dual-mode hybrid system for two-phase cooling of a data center that includes providing vapor from the at least on evaporator to a condenser, providing condensate liquid from the condenser into a liquid reservoir, pumping liquid from the reservoir with a pump to a cooling mechanism selected from the group consisting of at least one liquid cold plate combined with at least one liquid-cooled Peltier cooler or combined with at least one air heat sink that receives heat from a secondary heat source in either active or passive mode which are controlled by at least one valve, and providing liquid from the cooling mechanism to at least one evaporator, wherein a fraction of supplied liquid is drawn into a wick of the at least one evaporator by capillary pumping and where drawn liquid vaporizes in the wick of the evaporator by a primary heat source in the data center server and then this saturated vapor exits the at least one evaporator and flows through a vapor line to the condenser where this vapor is condensed and subcooled and then condensate from the condenser flows back to the liquid reservoir where excess liquid from a liquid chamber of the at least one evaporator returns to the liquid reservoir through the liquid return line where the liquid in the liquid return line is mixed in the liquid reservoir with subcooled condensate from the condenser to complete a fluid circulation cycle.

[0028] Another aspect of the method of the present disclosure is utilizing a vapor reservoir connected to a vacuum pump to remove non-condensable gas (NCG) (e.g., air) from the dualmode HTPL based on NCG detection using pressure, temperature, and / or NCG concentration measurements of a dual-mode hybrid system.

[0029] Yet another aspect of the present disclosure is liquid wicking through porous media from the liquid reservoir to the at least one evaporator to supply liquid via capillary pumping, eliminating the need for gravity-driven (hydrostatic) or mechanical (active) pumping.

[0030] In still yet another aspect of the present disclosure is periodically reversing the flow into and out of the evaporator, which can be used to equalize the temperature distribution within the liquid chamber of the evaporator.

[0031] Still another aspect of the method of the present disclosure is providing liquid from the cooling mechanism to a liquid chamber of the at least one evaporator through at least one porous plug, providing vapor from a vapor chamber of the at least one evaporator with at least one check valve, and providing liquid located between a liquid chamber of the at least one evaporator and the liquid reservoir in through a needle valve located between a liquid chamber of the at least one evaporator and the liquid reservoir in a fluid relationship.

[0032] These and / or other objects, features, advantages, aspects, and / or embodiments will become apparent to those skilled in the art after reviewing the following brief and detailed descriptions of the drawings. The present disclosure encompasses (a) combinations of disclosed aspects and / or embodiments and / or (b) reasonable modifications not shown or described.BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Several embodiments in which the present disclosure can be practiced are illustrated and described in detail, wherein like reference characters represent like components throughout the several views. The drawings are presented for exemplary purposes and may not be to scale unless otherwise indicated.

[0034] FIG. 1 shows a schematic of a dual-mode hybrid two-phase loop using an electroosmotic pump embedded in the evaporator of a loop thermosyphon for passive mode and an electroosmotic pumped two-phase loop for active mode.

[0035] FIG. 2 shows a schematic of a liquid cold plate for secondary heat sources, e.g., memories, storage devices, power inverter, etc..

[0036] FIG. 3 shows a schematic of an evaporator for primary heat sources, e.g., CPUs and GPUs.

[0037] FIG. 4 shows a schematic of a dual-mode two-phase loop using a mechanical pump for active mode and bypassing a deactivated pump for passive mode.

[0038] FIG. 5A shows a schematic of the dual-mode hybrid two-phase loop (HTPL) system.

[0039] FIG. 5B shows the dual-mode hybrid two-phase loop HTPL of FIG. 5A with multiple evaporators connected in parallel.

[0040] FIG. 6 shows a graph of evaporator thermal resistance of a loop thermosiphon in terms of heat input versus thermal resistance.

[0041] FIG. 7 shows a schematic diagram of thin film boiling in a capillary wick.

[0042] FIG. 8 shows a graphical representation of an extended meniscus (stationary) in a capillary wick showing three distinctive regions (adsorbed layer, thin film, and intrinsic meniscus), evaporation (rh) and the Marangoni flow due to a surface tension gradient.

[0043] FIG. 9 shows a graphical representation of a variation of the overall heat transfer coefficient and thermal resistances of thin-film evaporation with liquid film thickness.

[0044] FIG. 10 shows a top view of a server cooling architecture showing four evaporators in a parallel configuration for four CPUs in a 1U server.

[0045] FIG. 11 shows a top view of a server cooling architecture featuring liquid-cooled cold plates with extended fins (heat sink) for RAMs and small heat loads to ambient air in the server from various server internal components, e.g., power inverter, along with an evaporator arranged in a serial configuration.

[0046] FIG. 12 shows an isometric view of a server rack, showing multiple servers connected through vertical manifolds to a Coolant Distribution Unit (CDC) located above the server rack.

[0047] FIG. 13 shows a schematic of a dual-mode HTPL with two evaporators for two CPUs as primary heat sources, connected in parallel and liquid-cooled Peltier coolers for cooling of RAM and air in a 1U server and a Coolant Distribution Unit (CDU). A 1U server is a computer that fits into one unit of a standard server rack, where each unit is about 1.75 inches high. The “ 1U” stands for “one unit”.

[0048] An artisan of ordinary skill in the art need not view, within the isolated figure(s), the nearinfinite distinct combinations of features described in the following detailed description to facilitate an understanding of the present disclosure.DETAILED DESCRIPTION

[0049] The present disclosure is not to be limited to that described herein. Mechanical, electrical, chemical, procedural, and / or other changes can be made without departing from the spirit and scope of the present disclosure. No features shown or described are essential to permit the basic operation of the present disclosure unless otherwise indicated.

[0050] Referring now to FIG. 1, a dual -mode Hybrid (mechanical-capillary-driven) Two-phase Loop (“HTPL”) using an electroosmotic pump embedded in the evaporator with a loop thermosyphon for passive mode is generally indicated by numeral 10. There is a coolant distribution unit (CDU) 12. The coolant distribution unit CDU 12 is typically associated with a server.

[0051] The CDU 12 controls and distributes liquid coolant to manage the thermal load of high- performance processors and memory cards. It ensures efficient cooling, maintaining optimal temperatures and preventing overheating in data centers and high-density computing environments. The coolant distribution unit (CDU) 12 receives subcooled liquid that is pumped from a facility supply from a primary cooling loop 14 through a first liquid conduit 13 into a condenser 16.

[0052] There is a second liquid conduit 15 for liquid leaving the condenser 16. The primary cooling loop is the part of the system that contains the chillers and cooling towers and maintains a consistent flow of chilled water. The condenser 16 receives vapor 20 through a first vapor conduit 19 coming from an evaporator 28 having a vapor chamber 21 into the coolant distribution unit (CDU) 12 and converts this vapor 20 into a liquid that is received in a liquid reservoir 22 through a third liquid conduit 23. The condenser 16 removes heat from the vapor 20 and converts it into a liquid. From the liquid reservoir 22, the liquid flow 24 forms a secondary cooling loop 50. The liquid reservoir 22 has a vent 18 attached in a fluid relationship to a vacuum pump. This vent 18 is used to remove air, if present, as Non-condensable Gas (NCG) and to provide liquid charge to the liquid reservoir 22. This liquid flow 24 is through a fourth liquid conduit 27, then enters a liquid cold plate 25 that provides cooling for heat input from secondary heat sources 26, e.g., RAMs, in a server that is also shown in FIG. 2.

[0053] Liquid exiting the liquid cold plate 25 passes through a fifth liquid conduit 29 prior to entering evaporator 28. Therefore, the subcooled liquid is pumped by an electroosmotic pump embedded in liquid chamber 52 of the evaporator 28 from liquid reservoir 22 to liquid chamber52 of evaporator 28, where a fraction of the supplied liquid is drawn into an evaporator wick 48 by capillary-driven liquid flow 42.

[0054] Referring now to FIGS. 1 and 3, the evaporator 28 includes an electric insulating liner 36 surrounding the outer structure. There is a porous glass frit 38 that is, also known as fritted glass, is a solid, porous glass body made by fusing glass particles together. The glass is heated to a high temperature until the particles fuse, creating a porous material that allows liquids or gases to pass through. The bottom portion of the evaporator 28 receives heat input from primary heat sources 46, e.g., CPUs and / or GPUs, which creates capillary-driven thin-film boiling 44 in an evaporator wick 48. There is a loop thermosyphon (LTS) for passive mode and electroosmotic flow in active mode 40. There is internal liquid recirculation 32 in the liquid chamber 52 for active mode with an application of voltage to a pair of electrodes 34, supplying liquid 42 to an evaporator wick 48.

[0055] Referring now to FIG. 4, the dual-mode hybrid two-phase loop using a mechanical pump for active mode is shown as generally indicated by the numeral 1 for dual modes. As with the passive mode, there is a coolant distribution unit (CDU) 12. A CDU 12 is associated with a server. The CDU 12 controls and distributes liquid coolant to manage the thermal load of high- performance processors and memory cards. It ensures efficient cooling, maintaining optimal temperatures and preventing overheating in data centers and high-density computing environments. The coolant distribution unit (CDU) 12 receives subcooled liquid that is pumped from a facility supply from a primary cooling loop 14 through a first liquid conduit 13 into a condenser 16.

[0056] There is a second liquid conduit 15 for liquid leaving the condenser 16. The condenser 16 receives vapor 20 through a first vapor conduit 19 coming from an evaporator 28 into the condenser 16 in the coolant distribution unit (CDU) 12 and converts this vapor 20 into a liquid that is received in the liquid reservoir 22 through a third liquid conduit 23. The condenser 16 removes heat from the vapor 20 and converts it into a liquid. From the liquid reservoir 22, the liquid flow 24 can pass through a first two-way valve 64 for loop thermosyphon (LTS) in passive mode 30 into a liquid cold plate 25.

[0057] In the alternative, a pump 58 can actively pump liquid through a second two-way valve 66 for the active mode of the HTPL [hybrid (mechanical-capillary-driven) two-phase loop] 1 into the liquid cold plate 25 in active mode 52. This liquid flow 24 is through a fourth liquid conduit 27, then enters a liquid cold plate 25 that provides cooling for heat input from secondary heat sources 26, e.g., RAMs, in a server that is also shown in FIG. 2.

[0058] As shown in FIGS. 1 and 4, liquid supply 56 exiting the liquid cold plate 25 passes through a fifth liquid conduit 29 prior to entering an evaporator 28. Therefore, the subcooled liquid is pumped from liquid reservoir 22 to liquid chamber 52 of evaporator 28, where a fraction of the supplied liquid is drawn into an evaporator wick 48 by capillary-driven fluid flow 42. In active mode, a hybrid (mechanical-capillary-driven) two-phase loop 62 pumps excess liquid from the liquid chamber 52 through a liquid return 54 and then back into the liquid reservoir 22.

[0059] The HTPL [hybrid (mechanical-capillary-driven) two-phase loop 1], can operate in either passive or active mode. Mechanical-capillary-driven liquid flow of active mode HTPL operation is outlined in Mechanical-capillary-driven two-phase loop: Numerical modeling and experimental validation, October 2018 International Journal of Heat and Mass Transfer 125(14):972-982. The evaporator wick 48 is also described in additional detail in Receding liquid level in evaporator wick and capillary limit of loop thermosyphon, January 2020, International Journal of Heat and Mass Transfer 146(14): 118870

[0060] An evaporator 28 with only liquid supply 56 of the loop thermosiphon (passive design) is shown in FIG. 3, Minwoo Lee, Chanwoo Park, Receding liquid level in evaporator wick and capillary limit of loop thermosyphon, International Journal of Heat and Mass Transfer, 146 (2020) 118870).

[0061] This hybrid (mechanical-capillary-driven) two-phase loop (HTPL) 1 is an ideal cooling solution for data centers with numerous advantages: dual-mode operation (passive, active), low thermal resistance < 0.01 K / W), high heat flux (> 300 W / cm2), low pumping power consumption (zero for passive mode; 0.45% of IT load for active mode), reliable operation, fully scalable design (heat transfer area > 150 cm2), and a high TRL (> 5). The proposed hybrid (mechanical-capillary- driven) two-phase loop (HTPL) l is a desirable combination of a loop thermosiphon, a loop heat pipe, and a pumped two-phase loop. Passive (capillary-driven) phase separation and thin-film evaporation in a microporous layer are able to achieve low thermal resistance and high heat flux cooling.

[0062] This hybrid (mechanical-capillary-driven) two-phase loop (HTPL) 1 has been tested for excellent cooling performance (low thermal resistance, low pumping power consumption). A pumped HTPL (active design) using the same evaporator of the loop thermosiphon has been rigorously tested for superb performance (high heat flux, low pumping power consumption, robust operation, insensitive to orientation) and design optimization (multi evaporators, scalability).

[0063] Applying the dual-mode hybrid (mechanical-capillary-driven) two-phase loop (HTPL) 1 for data center cooling would be an innovative yet challenging application considering the mode transition, flow control and distribution, and pressure control required for multi-evaporator operation. Table 1 lists the measured performance data of prototype hybrid (mechanical -capillary- driven) two-phase loop (HTPL) 1 in both passive and active modes compared to the ARPA-E targets.

[0064] Table 1. Comparison of the performance data of HTPL and the COOLERCHIPS targets(Category A).

[0065] The dual-mode hybrid (mechanical-capillary-driven) two-phase loop (HTPL) 1 can include an evaporator 28, shown in FIG. 5A, or a plurality of evaporators 28 for blade servers 70 in a server rack cabinet 72, shown in FIG. 5B, a condenser 16, a pump 58, and a liquid reservoir 22, as shown in FIG. 5A.

[0066] The system is shown in FIG. 5A is comparable to the system shown in FIG. 4 described above. The operation of the dual-mode hybrid (mechanical-capillary-driven) two-phase loop HTPL 1 begins with the pumping of a subcooled liquid flow 24 from the liquid reservoir 22 to the liquid chamber 52 of the evaporator 28, in which a fraction of the supplied liquid is drawn into the evaporator wick 48 by capillary-driven liquid flow 42 creating capillary-driven thin-film boiling 44. Then, the drawn liquid vaporizes in the evaporator wick 48 by the heat input from primary heat sources 46, e.g., server electronics such as CPUs and GPUs, and the saturated vapor 20 exits the evaporator 28 and flows through a first vapor conduit 19 to the condenser 16, where the vapor 20 is condensed and subcooled. Subsequently, the condensate from the condenser 16 flows back to the liquid reservoir 22. The excess liquid from the liquid chamber 52 returns to the liquid reservoir 22 through a liquid return line 54. Finally, the returned liquid 54 ismixed with the subcooled condensate in the liquid reservoir 22, which completes the fluid circulation.

[0067] The cross-sectional view of the evaporator 28 is shown in FIG. 5A, illustrating the capillary-driven liquid flow 42 over a very short distance, e.g., a few millimeters, from the liquid chamber 52 to the surface of the wick 48 in the vapor chamber 21 as compared to the height of a typical server rack 72, e.g., two meters, shown in FIG. 5B. Note that capillary-driven liquid flow 42 is in the opposite direction of the heat input 46 in the evaporator 28 makes the evaporator 28 fully scalable to any size in lateral directions, and the short capillary flow path, i.e., small flow resistance or pressure drop, increases the capillary limit, i.e., maximum heat flux for a given capillary pressure head, of the dual-mode hybrid (mechanical-capillary-driven) two-phase loop HTPL 1. A porous plate 60 in the evaporator 28 separates the liquid chamber 52 from the vapor chamber 21. The tubular posts 43 connecting the liquid chamber 52 and vapor chamber 21 are used for capillary-driven liquid flow 42. The tubular posts 43 can be uniformly and / or non- uniformly spaced to supply the liquid to the entire wick 48 within the capillary limit. Each evaporator 28 is in direct contact with a blade server 70. A blade server typically consists of a chassis, or box-like structure, housing multiple thin, modular electronic circuit boards, known as server blades. The term “blades” is due to their ultra-thin shape. Each blade contains a single server, often dedicated to a single application. Moreover, 3D printing can be utilized to manufacture the 3D complex wick structure of the evaporator 28.

[0068] The dual-mode HTPL 1 combining a loop thermosiphon (passive mode) and a pumped two-phase loop (active mode), will be tested using the first two-way valve 64 and second two- way valve 64 to toggle the operation between the passive and active modes. Technical challenges in the development of the dual-mode multi-evaporators 28, shown in FIG. 5B includes control of complex fluidic interaction (two-phase flow instabilities and flow distribution and regulation) between the evaporators under various (dynamic and asymmetric) heat loadings. Various configurations (series, parallel, and cascade) of the multi -evaporator system, are shown in FIG. 5B, and can be utilized.

[0069] The measured evaporator thermal resistance (“R” is equal to heat flux-based thermal resistance from the evaporator surface and two-phase fluid) of the thermosiphon was 0.097 K- cm2 / W (illustrated by the arrow designated by numeral 80 in FIG. 6 for an input heat flux (q” m of 130.2 W / cm2over a heat transfer area (Ah) of 5.76 cm2which is equivalent to a convective heat transfer coefficient (hc=l / R”) of 103,000 W / m2-K and a thermal resistance[R=R’7Ah=(hcAh)'1] of 0.0168 K / W. By increasing the heat transfer area at the same heat flux, the thermal resistance can be significantly reduced since it is inversely proportional to the heat transfer area. That is, an ultra-low thermal resistance (R) of 0.0024 K / W can be achieved with a large heat transfer area of 40 cm2for a heat flux of 130.2 W / cm2.

[0070] It can be noted that the evaporator 28 is fully scalable to larger sizes because of the phase separation and the counterflow arrangement of the capillary-driven liquid flow 42 and heat input 46. The pump 58 power consumption of the dual-mode hybrid (mechanical-capillary-driven) two- phase loop (HTPL) 1 running in the active mode was measured to be 6 W for a heat flux of about 227 W / cm2over a heat transfer area of 5.76 cm2, removing a total heat transfer of 1339 W, which translates to 0.45% of the heat load which equates to the IT load.

[0071] Based on the actual dimensions of the dual-mode hybrid (mechanical-capillary-driven) two-phase loop (HTPL) 1, the volume of the coolant distribution unit (CDU) 12 of the proposed HTPL 1 for 123 kW cooling power is estimated to be less than 0.5 m3. Therefore, the power density (IT power divided by the total volume of the server rack (1 m3) and external cooling component (CDU 0.5 m3) outside the server rack) is estimated to be larger than 80 kW / m3. Water was the working fluid of choice for the HTPL 1 for its excellent thermophysical properties (high heat pipe figure of merit) for electronic cooling temperature (-90° C) (stated in the FOA). However, the relatively poor dielectric property of water could be a potential concern for high- power electronics. There are potentially alternative dielectric fluids such as R1234ze (GWP=7, ODP=0) and R-1234yf (GWP=4, ODP=0), although their thermophysical properties (surface tension, latent heat, and so forth.) are not as good as water.

[0072] A Multi-Scale Meniscus Thin-Film Evaporation Enhancement using Hierarchical Tri- Porous Media was used to systematically investigate the meniscus thin-film evaporation, which is the fundamental phenomenon commonly found in phase change processes. This type of analysis is described in V. P. Carey, Liquid-vapor phase-change phenomena, 2nd ed., Taylor and Francis, New York, 2008. The meniscus thin-film evaporation is found in bubble growth and departure in pool boiling, slug and annular flows in flow boiling falling-film evaporation, and wick boiling in capillary porous structures (evaporator wick 48). As shown in FIG. 7, the meniscus topology, dynamics (receding and advancing), and thin-film evaporation play significant roles in the phase change processes for various surface configurations showing thin-film boiling in a capillary wick 48 in terms of the meniscus 82, vapor 84, liquid 86 and solid 88 being shown.

[0073] The extended meniscus (from Greek for crescent) is a curved liquid region near a three- phase (gas-liquid-solid) contact line, which undergoes a drastic change in the liquid film thickness from nano to micro to macro-scales. The extended meniscus is divided into three distinctive regions, as shown in FIG. 8, where: (i) is the adsorbed layer [intermolecular-bonding forces between the liquid and solid molecules of thickness < 0(10 nm); (ii) is the thin-film evaporating region which is the disjoining-pressure- dominant region of thickness > 0(100 nm) where evaporation dominantly occurs due to the small thermal resistance of thin liquid film; and (iii) is the intrinsic meniscus where capillary-pressure-dominant region of thickness > 0(100 pm). The apparent static contact angle (CA), 6*c, is defined near the intrinsic meniscus, which determines the wettability of fluid on a specific solid surface.

[0074] Many studies, e.g., V. P. Carey, Liquid-vapor phase-change phenomena, 2nd ed., Taylor and Francis, New York, 2008, have shown that the suppression effects of the disjoining and capillary pressures on the meniscus evaporation are due to reduced equilibrium vapor pressure resulting in a peak in the evaporation heat transfer (q" = m’hfg) in the thin film region as shown in FIG. 8. The heat transfer from the thin-film region with a thickness below 1 pm accounts for more than 50% of the total evaporation heat transfer.

[0075] It is known that the average heat transfer coefficient, e.g., < ( 104~ 105W / m2-K), of the thin film evaporation is an order of magnitude larger than that of pool boiling, e.g., < ( 103~l 04W / m2- K). From a thermal analysis shown in FIG. 9, using the thermal circuit for the thin-film evaporation of a flat- water film based on 1-D conduction and Schrage’s evaporation model, the results of the overall heat transfer coefficient (hevp) and thermal resistances (ReVp=Rk+ Riv) are shown in Fig. 4(c). ReVp, Rk, and Riv are the thermal resistances of overall heat transfer, conduction, and interfacial evaporation of the liquid film, respectively. FIG. 9 suggests that there is an optimum film thickness 89 for a maximum heat transfer coefficient (hevp as a result of the competing effect between Riv and Rk.

[0076] The preferred embodiment is a server cooling architecture that was conducted based on the 1U server form factor (1.75-inch height x 19-inch width x 24-inch depth). Multiple evaporators for multiple heat sources (CPUs or GPUs) for a 1U server were considered. The evaporators were connected in a parallel configuration as a more conservative design for even cooling performance, although this configuration requires more connection lines than a series configuration.

[0077] Referring now to FIG. 10, illustrates the cooling design of a 1U server with four evaporators 28 for four CPUs as primary heat sources of a server. The evaporators 28 are connected in parallel to maintain the same liquid supply temperature for each evaporator 28. A low-profile evaporator 28 with side fluid connecting ports was designed to fit into a 1U server form factor. The evaporator 28 size can optionally be determined based on the latest chipset design. The chipset using an LGA 4677 socket has an effective heat transfer area of 3750 mm2(= 75 mm x 50 mm). The evaporator 28 for the hybrid two-phase loop (HTPL) 1 can have three connections: one for liquid supply 56, a second for liquid return 54, and a third for vapor 20 exit. Note that the loop thermosyphon (LTS) 60 requires only one liquid supply 56 exit and one vapor 20 exit, and the second liquid return line 54 will be deactivated to block the liquid return by closing the second two-way valve 66. Each connection is linked to a manifold block 101 in a server for either distributing to multiple liquid supply lines or collecting from multiple liquid return and vapor exit lines in a server. The vapor lines require a larger diameter than the liquid lines due to the high flow rate of low-density vapor flow. Each connection pipe 20, 54, 56 ends with a quick coupling to prevent fluid and vacuum leaks during the hot swapping of servers. Each connection pipe for vapor flow 20, and liquid flows 54, 56 ends are connected to the vertical manifolds 100 in a server rack.

[0078] The complete server cooling architecture necessitates auxiliary cooling capability for secondary heat sources such as memory and small heat loads from various server components, e.g., power inverter. Liquid-cooled cold plates 25 were utilized for memory cooling, while extended fins on the liquid cold plates 25 were employed for air cooling of auxiliary heat loads. An evaporator 28 and the liquid cold plate 25 are arranged in a serial configuration, as illustrated in FIG. 11. The evaporator and liquid cold plates can be connected in series and cascade configurations.

[0079] This preferred embodiment for multi-scale data center cooling architecture from serverlevel to data center-level, principle of dual-mode hybrid two-phase loop (HTPL) 1 and operational procedures and conditions for optimized performance of the HTPL 1 is shown in FIGS. 12 and 13 and 14. A Coolant Distribution Unit (CDU) 12 houses condensers 16, pumps 58, liquid reservoirs 22, and a flow control system for passive and active modes. For redundancy, each component in the CDU 12 could be paired with an identical twin for backup or dual operation. The liquid reservoir 22 and condenser 16 will be located above a server rack in proximity to the facility coolant line 14, while pump 58 can be located on the floor for priming of the condensate liquidfrom the liquid reservoir 22 above the 42U server rack 94. Reservoir 22 will be cooled by facility coolant 14 if more liquid subcooling is required. The vapor reservoir 112, situated above the 42U server rack 94 at the likely highest point of the two-phase system, allows for the accumulation of Non-Condensable Gas (NCG, e.g., air) existing in the two-phase system. The vapor reservoir 112 will be used as a device to purge the NCG using vacuum pump 114 and two-way valve 68 based on pressure, temperature, and concentration monitoring in real-time as needed. A server 94, including essential components like evaporators 28, heat sources 26, 46, and memory cold plates 25, can be assembled using a blend of 3D printing and conventional machining to create a prototype prior to production for in-depth exploration of system packaging, aiding in necessary design adjustments and optimization. Additionally, the wick surfaces 48 of the evaporator 28 have been fabricated to assess manufacturability and property measurements such as wicking height, porosity, and permeability.

[0080] As previously described, the coolant from facility 14 from the primary cooling loop enters the first fluid conduit 13 and then enters condenser 16. The liquid then exits the condenser through a second liquid conduit 15. This cooling fluid in the condenser 16 operates to convert vapor 20 that is also entering the condenser 16 and converts it to liquid that enters a liquid reservoir 22 that holds this liquid that is derived from converted vapor. When the dual-mode hybrid two-phase loop (HTPL) 1 is in passive mode, the liquid from the liquid reservoir can flow directly into at least one Peltier cooler 96 through a liquid supply 56. A Peltier cooler is filled up with semiconductor material sandwiched between two parallel plates. Passing an electrical current through the device activates the Peltier effect. This creates a temperature gradient between the two plates. These temperature gradients allow objects to be cooled. In this case, the liquid supply 56 from the liquid reservoir 22 passes into a first Peltier cooler 96 that cools a secondary heat source 26, e.g., RAMs. The liquid supply 56 then passes through a second Peltier cooler 97 that preferably, but not necessarily, cools the hot air heated by secondary heat sources in a server 90.

[0081] The liquid 56 can then go into a plurality of evaporators 28, 122. There may be at least one porous plug 120, 121, respectively, with specified flow resistances installed in fluid lines to balance flow among evaporators and servers. These porous plugs 120, 121 are made from sintered metal particles and mesh screens and are placed in the liquid lines. The permeability and length of the porous plugs 120, 121 determine the flow resistance. In the illustrative, but nonlimiting embodiment, there is a first evaporator 28 and a second evaporator 122, each having a liquidchamber 52 where liquid enters, providing cooling from the heat generated by a primary source, e.g., CPUs and GPUs 46. The fluid then exits through a liquid return line 54 that is controlled by a needle valve 110 that is located downstream of the evaporators 28, 122, is used to restrict the exit of liquid 54, increasing liquid pressure within the evaporators 28, 122 and thereby increasing liquid flow to the vapor chamber 21, 124, respectively, and enhancing its heat flux limit. In passive mode, two second two-way valves 66 are closed, which would block liquid from the liquid reservoir 22 from going back from the evaporators into the liquid reservoir 22 and from leaving the liquid reservoir and going into the pump 58.

[0082] In active mode, liquid from the liquid reservoir 22 goes through the pump 58 before going to the first liquid-cooled Peltier cooler 96, and the direct liquid supply 56 is blocked by the first two-way valve 64. The active mode components and flow path are identified by the numeral 116. Periodically reversing the flow into and out of the evaporator can be used to equalize the temperature distribution within the evaporator’s liquid chamber 52. As previously described in the other embodiments above. Liquid wicking through porous media from a liquid reservoir 22 to the evaporator 28 supplies liquid via capillary pumping, eliminating the need for gravity-driven (hydrostatic) or mechanical (active) pumping. This process integrates liquid wicking with capillary action within the evaporator 28, 122.

[0083] In the Hybrid Two-phase Loop (HTPL) 1, evaporators 28, 122 are used to cool primary heat sources like CPUs and GPUs. Liquid cold plates 25, combined with air heat sinks 106 or thermoelectric (Peltier) coolers 96, 97 are used to cool memory and auxiliary components such as the power inverter and storage. These Peltier coolers 96, 97 cooled by the liquid flow 56, 54 into / from the evaporators 28, 122, act as heat pumps to lower the temperature of hot air and RAM below that of the liquid 56, 54. The ideal placement for the Peltier coolers 96, 97 is along the liquid return line 54, where the liquid’s temperature is higher than that of the liquid supply 56 due to heat transfer from the evaporator 28. 122. As solid-state thermoelectric devices with no moving parts, Peltier coolers 96, 97 operate with minimal electrical power consumption.

[0084] The evaporators 28, 122 in servers 90 will be connected via manifolds 100 to a coolant distribution unit (CDU) 12, which typically houses pumps 58 and condensers 16, a vapor reservoir 112 and a liquid reservoir 22 and an electric control system 130. The vapor reservoir 112 is used to collect non-condensable gas (NCG) such as air and purge it using a vacuum pump 114 and two- way valve 68 if the system pressure exceeds the saturation pressure by a certain extent. The liquid reservoir 22, which stores the condensate from the condenser 16, is used to cool down the liquidfor subcooling and create enough hydrostatic pressure for the priming of pump 58. The liquid reservoir 22 will be located above the pump 58 to avoid possible cavitation in the suction line and be located below condenser 16 to feed condensate to liquid reservoir 22 by gravity. The liquid reservoir 22 can be cooled by facility coolant 14. The pump 58 can be located on the floor level outside the CDU 12 because it is heavy and a source of vibration. Condenser 16 will be located close to the facility coolant 14 to avoid lengthy connections.

[0085] The vapor 20 exiting the first evaporator 28 exits through a first check valve 126, and vapor 20 exiting the second evaporator 122 exits through a second check valve 128 that then passes to a vapor reservoir 112 that is connected in vapor relationship to a two-way valve 68 and vacuum pump 114 prior to providing vapor 20 back into the condenser 16 through a second vapor conduit 118. Checkvalves 126, 128 in the vapor lines from evaporators 28, 122 are used to prevent unintended heating caused by the hot vapor flow from neighboring evaporators under high heat inputs from heat sources.

[0086] From the foregoing, it can be seen that the present disclosure accomplishes at least all of the stated objectives.LIST OF REFERENCE CHARACTERS

[0087] The following table of reference characters and descriptors are not exhaustive, nor limiting, and include reasonable equivalents. If possible, elements identified by a reference character below and / or those elements which are near ubiquitous within the art can replace or supplement any element identified by another reference character.

[0088] Table 1: List of Reference CharactersGLOSSARY

[0089] Unless defined otherwise, all technical and scientific terms used above have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of the present disclosure pertain.

[0090] The terms “a,” “an,” and “the” include both singular and plural referents.

[0091] The term “or” is synonymous with “and / or” and means any one member or combination of members of a particular list.

[0092] As used herein, the term “exemplary” refers to an example, an instance, or an illustration, and does not indicate a most preferred embodiment unless otherwise stated.

[0093] The term “about” as used herein, refers to slight variations in numerical quantities with respect to any quantifiable variable. An inadvertent error can occur, for example, through the use of typical measuring techniques or equipment or from differences in the manufacture, source, or purity of components.

[0094] The term “substantially” refers to a great or significant extent. “Substantially” can thus refer to a plurality, majority, and / or a supermajority of said quantifiable variables, given proper context.

[0095] The term “generally” encompasses both “about” and “substantially.”

[0096] The term “configured” describes a structure capable of performing a task or adopting a particular configuration. The term “configured” can be used interchangeably with other similar phrases, such as constructed, arranged, adapted, manufactured, and the like.

[0097] Terms characterizing sequential order, a position, and / or an orientation are not limiting and are only referenced according to the views presented.

[0098] The “invention” is not intended to refer to any single embodiment of the particular invention but encompass all possible embodiments as described in the specification and the claims. The “scope” of the present disclosure is defined by the appended claims, along with thefull scope of equivalents to which such claims are entitled. The scope of the disclosure is further qualified as including any possible modification to any of the aspects and / or embodiments disclosed herein which would result in other embodiments, combinations, sub combinations, or the like that would be obvious to those skilled in the art.

Claims

CLAIMSWhat is claimed is:

1. A dual-mode hybrid system for two-phase loop cooling of a data center comprising of: at least one evaporator having a liquid chamber and a wick; a condenser; a pump; a vapor line between the condenser and the at least one evaporator; a liquid reservoir; and a liquid return line between the condenser and the liquid reservoir, wherein subcooled liquid from the liquid reservoir flows to the liquid chamber of the at least one evaporator by the pump in which a fraction of supplied liquid is drawn into the wick of the at least one evaporator by capillary pumping and where drawn liquid vaporizes in the wick of the evaporator by a primary heat source in the data center and then this saturated vapor exits the at least one evaporator and flows through the vapor line to the condenser where this vapor is condensed and subcooled and then condensate from the condenser flows back to the liquid reservoir where excess liquid from a liquid chamber of the at least one evaporator returns to the liquid reservoir through the liquid return line where liquid in the liquid return line is mixed with subcooled condensate in the liquid reservoir to complete a fluid circulation cycle.

2. The dual-mode hybrid system for two-phase loop cooling of a data center, according to claim 1, further comprising at least one valve in fluid connection with the pump.

3. The dual -mode hybrid system for two-phase loop cooling of a data center, according to claim 1, wherein the evaporator includes a plurality of evaporators connected in a parallel, series or cascade configuration:

4. The dual-mode hybrid system for two-phase loop cooling of a data center, according to claim 1, further comprising a liquid cold plate in fluid connection with the liquid reservoir and the evaporator.

5. The dual -mode hybrid system for two-phase loop cooling of a data center, according to claim 4, wherein the liquid cold plate receives heat from a secondary heat source.

6. The dual-mode hybrid system for two-phase loop cooling of a data center, according to claim 1, further comprising periodically reversing the flow into and out of the evaporator can be used to equalize temperature distribution within the liquid chamber of the evaporator.

7. The dual-mode hybrid system for two-phase loop cooling of a data center, according to claim 1, wherein the evaporator includes two electrodes and a porous membrane in the liquid chamber of the evaporator that creates an electroosmotic flow, and there is a primary heat source that applies heat to the evaporator where capillary thin film boiling converts liquid with capillary flow into vapor that is provided back into the condenser.

8. The dual -mode hybrid system for two-phase loop cooling of a data center, according to claim 1, further comprising liquid wi eking through porous media from the liquid reservoir to the at least one evaporator to supply liquid via capillary pumping, eliminating the need for gravity- driven (hydrostatic) or mechanical (active) pumping.

9. The dual-mode hybrid system for two-phase loop cooling of a data center, according to claim 1, wherein the primary heat source is selected from the group consisting of computer processing units (CPUs) or graphical processing units (GPUs) or high-power components and the secondary heat source includes computer memories.

10. A dual-mode hybrid system for two-phase loop cooling of a data center comprising of: a condenser that receives coolant liquid; a liquid reservoir connected in fluid relationship to the condenser; at least one liquid cold plate that receives liquid directly from the liquid reservoir in passive mode or through a pump that receives liquid from the liquid reservoir for supplying liquid to the at least one liquid cold plate in active mode, wherein the at least one liquid-cold plate receives heat from at least one secondary heat source. at least one valve for diverting liquid through the pump or directly to the at least one liquid cold plate, depending on selection of active mode or passive mode; andat least one evaporator having a liquid chamber and a vapor chamber separated by a porous plate with tubular posts, wherein the liquid chamber is in fluid connection to the at least one liquid cold plate, wherein a fraction of supplied liquid is drawn through the tubular posts into a wick of the at least one evaporator by capillary pumping and where drawn liquid vaporizes in the wick of the evaporator by a primary heat source and then this saturated vapor exits the at least one evaporator and flows through the vapor line to the condenser where this vapor is condensed and subcooled and then condensate from the condenser flows back to the liquid reservoir where excess liquid from a liquid chamber of the at least one evaporator returns to the liquid reservoir through a liquid return line where liquid in the liquid return line is mixed with subcooled condensate in the liquid reservoir to complete a fluid circulation cycle.

11. The dual -mode hybrid system for two-phase loop cooling of a data center, according to claim 10, wherein the at least one liquid cold plate is attached to a cooling mechanism selected from the group consisting of a Peltier cooler and / or an air heat sink12. The dual-mode hybrid system for two-phase loop cooling of a data center, according to claim 11, a server enclosing the at least one evaporator and the at least one cold plate and a coolant distribution unit that includes the condensers, the liquid reservoir, a vapor reservoir, at least one pump, and an electric control system.

13. The dual -mode hybrid system for two-phase loop cooling of a data center, according to claim 10, wherein the secondary heat source is selected from the group consisting of computer memories or air in the server and the primary heat source is selected from the group consisting of computer processing units (CPUs) or graphical processing units (GPUs) or high-power components.

14. The dual-mode hybrid system for two-phase loop cooling of a data center, according to claim 12, further comprising at least one manifold with two connecting points for liquid and two connecting points for vapor flow located between the server and the coolant distribution unit.

15. The dual -mode hybrid system for two-phase loop cooling of a data center, according to claim 10, further comprising a vapor reservoir connected to a two-way valve and a vacuum pump that removes non-condensable gas trapped in the vapor reservoir.

16. The dual -mode hybrid system for two-phase loop cooling of a data center, according to claim 10, further comprising at least one porous plug connected between the liquid chamber of the at least one evaporator and the at least one liquid cold plate and at least one needle valve connected between the liquid chamber of the at least one evaporator and the liquid reservoir.

17. The dual -mode hybrid system for two-phase loop cooling of a data center, according to claim 15, further comprising at least one check valve between the vapor chamber of the at least one evaporator and the vapor reservoir.

18. A method for utilizing a dual-mode hybrid system for two-phase loop cooling of a data center comprising of: providing cooled liquid to a condenser; providing liquid from the condenser into a liquid reservoir; pumping liquid from the reservoir with a pump to a cooling mechanism selected from the group consisting of at least one liquid cold plate combined with at least one liquid-cooled Peltier cooler or combined with at least one air heat sink that receives heat from a secondary heat source in active mode or directly in passive mode with modes controlled by at least one valve; and providing liquid from the cooling mechanism to at least one evaporator, wherein a fraction of supplied liquid is drawn into a wick of the at least one evaporator by capillary pumping and where drawn liquid vaporizes in the wick of the evaporator by a primary heat source in the data center and then this saturated vapor exits the at least one evaporator and flows through a vapor line to the condenser where this vapor is condensed and subcooled and then condensate from the condenser flows back to the liquid reservoir where excess liquid from a liquid chamber of the at least one evaporator returns to the liquid reservoir through the liquid return line where the liquid in the liquid return line is mixed with subcooled condensate in the liquid reservoir to complete a fluid circulation cycle.

19. The method for utilizing a dual -mode hybrid system for two-phase loop cooling of a data center, according to claim 18, comprising utilizing a vapor reservoir connected to a vacuum pump to remove non-condensable gas trapped in the vapor reservoir.

20. The method for utilizing a dual-mode hybrid system for two-phase loop cooling of a data center according to claim 18, providing liquid from the cooling mechanism to a liquid chamber of the at least one evaporator through at least one porous plug, providing vapor from a vapor chamber of the at least one evaporator with at least one check valve, and providing liquid located between a liquid chamber of the at least one evaporator and the liquid reservoir in through a needle valve located between a liquid chamber of the at least one evaporator and the liquid reservoir in a fluid relationship.

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