This article may be too technical for most readers to understand.(May 2022) |
Immersion cooling is an IT cooling practice by which complete servers are immersed in a dielectric, electrically non-conductive fluid that has significantly higher thermal conductivity than air. Heat is removed from a system by putting the coolant in direct contact with hot components, and circulating the heated liquid through heat exchangers. This practice is highly effective because liquid coolants can absorb more heat from the system, and are more easily circulated through the system, than air. Immersion cooling has many benefits, including but not limited to: sustainability, performance, reliability and cost.
Unlike many other devices, computers cannot use immersion water cooling, because ordinary water is electrically conductive and will break electronic components. Therefore, the fluids used in immersion cooling are dielectric liquids to ensure that they can safely come into contact with energized electronic components.
In general, the dielectric liquids used for immersion cooling fall into two categories: hydrocarbons (i.e. mineral, synthetic, or biological oils) and fluorocarbons (fully engineered liquids). Dielectric liquids are divided into single- and two-phase applications, which differ in whether or not the cooling fluid turns into a gas during the cooling cycle.
An enclosed chassis require dripless connectors to interface to the individual chassis. These chassis are usually based on traditional rack style implementations. The dripless connectors usually require a small closed-circuit cooling loop with a coolant to protect the flow integrity through relatively small pipes and connectors. The closed circuit is facilitated by a CDU or Coolant Distribution Unit, which usually can facilitate multiple racks at once.
An open bath refers to the "open" liquid–air interface and thus surface tension between the liquid and the air is a distinctive element. Open bath systems are usually tanks which contain a larger body of dielectric liquid where electronics are immersed into the bath. Multiple electronic assemblies share the same liquid. This liquid can be based on single- or two-phase technology. Regardless of the term, open-bath systems can be fully sealed, but are always opened from the top to service IT equipment. The coolant tank for open bath immersion systems is either connected to a CDU which circulates the dielectric liquid, or to an integrated heat exchanging device which is part of the tank. For a facility interface, CDUs are usually designed for 100 kW or more, whereas an integrated heat exchanging device is usually designed for 10-100 kW cooling capacity.
Hybrid cooling refers to combinations of enclosed and open bath apparatus. [3]
Immersion cooling reduces energy consumption through the elimination of the air cooling infrastructure including on-board server fans, CRACs, A/C compressors, air-circulation fans, necessary duct work, air handlers, and other active ancillary systems such as dehumidifiers. These systems are replaced with liquid circulation pumps and heat exchanger and/or dry cooler systems.
Power use at data centers is often measured in terms of power usage effectiveness (PUE). The definitions of PUE for air-cooled devices and liquid immersion cooled devices are different which makes such direct comparisons inaccurate. The PUE for air-cooled data centers includes the power used by the fans and other active cooling components found in the servers. The PUE for liquid immersion cooling excludes these values from the IT Equipment Energy component because these system elements (in particular on-board fans) are generally removed from the IT equipment as they are not necessary to circulate the dielectric coolants. This discrepancy in the definition of PUE for the different cooling methods results in the PUE of air-cooled data centers generally being overstated when compared against the PUE of a liquid immersion cooled facility of the same power usage. [4]
Servers and other IT hardware cooled by immersion cooling do not require fans to circulate the dielectric liquid, thus they are removed from the system prior to immersion. Thermal pastes which are typically used on heat spreaders for CPUs and other chips may require replacement with a different compound in order to avoid the thermal degradation within the dielectric liquid. [5] Depending on the type of application, solder, Indium foil, and thermally conductive epoxies may be used as a replacement materials.
The temperatures used in immersion cooling are determined by the highest temperature at which the devices being immersed can reliably operate. For servers this temperature range is typically between 15 and 65 °C (59 and 149 °F); [6] however, in ASIC-based crypto mining devices, this range is often extended up to 75 °C. [7] This increase in the high end of the temperature range allows data center operators to use entirely passive dry coolers, or much more efficient evaporative or adiabatic cooling towers [8] instead of chiller-based air cooling or water chillers. This increase in the temperature range also allows operators using single-phase immersion coolants to more effectively use the change in outdoor temperatures to get more efficient cooling from their systems because the single-phase systems are not limited in their effectiveness by the boiling point of the coolant as is the case with two-phase coolants. [9]
Multiple relevant brands like Intel and Facebook have already validated the advantages of submerging servers. [10] [11]
Current commercial applications for immersion cooling range from datacenter-oriented solutions for commodity server cooling, [12] [13] server clusters, HPCC applications [14] and cryptocurrency mining. [15] and mainstream cloud-based and web hosting architectures. Electric vehicle and battery manufacturers also employ liquid immersion cooling in batteries, drive-train, kinetic energy recovery systems, electric motors, electric motor controllers, and other on-board electronic subsystems.[ citation needed ] Liquid immersion cooling is also used in the thermal management of LEDs, lasers, X-Ray machines, and magnetic resonance imaging devices.[ citation needed ]
Immersion cooling is applied to electronic components in deep-sea research where remotely operated underwater vehicles with electronic equipment are filled with single-phase liquid dielectrics to both protect them from corrosion in seawater and as a pressure-compensating fluid to prevent the housing from being crushed by the extreme pressure exerted on the ROV while working in the deep sea.[ citation needed ] This application also includes the cooling of the electric motors used for under sea propulsion.
Until about 2014, the technology was typically only utilized in special very intensive supercomputing projects, like the Cray Computer Applications. [16] Even though the expected increase in global energy consumption by data centers has remained steady, [17] there is an increased focus on energy efficiency which has driven the utilizing of liquid immersion cooling in both data centers and crypto mining operations to reevaluate its application. The advent of new very high density CPUs and GPUs for use in real-time processing, artificial intelligence, machine learning, and data mining operations is leading users and data center operators to evaluate liquid immersion cooling for ability to cool high density racks as well as reduce the total mechanical footprint of data centers.
The growing adoption of higher TDP CPU and GPU chipsets in the data center in recent years has seen immersion cooling scale as a data center solution for addressing the technical limitations of air-cooled platforms. With platforms like NVIDIA's Grace-Blackwell GB200 NVL72 requiring up to 140kW of cooling per rack [18] , large-scale liquid cooling is emerging as an important technology to deliver hosting capability for these new platforms. This large-scale need is driving new form factors, industry adoption and methods of deployment - in 2023 Firmus Technologies launched a single-phase immersion platform that is capable of retrofitting entire air-cooled data halls via 1MW modules [19] , committing to install the technology across regions in Singapore, India and Australia.
This section needs additional citations for verification .(February 2022) |
19th and 20th century immersion milestones:
21st century immersion milestones:
Open-bath immersion cooling is a data center cooling technique that implies fully submerging IT equipment in dielectric liquid. The "open" aspect does not refer to an open or sealed system, but refers to the "open" liquid-air interface and thus surface tension between the liquid and the air is a distinctive element. [30]
These baths allow the coolant fluid to be moved through the hardware components or servers submerged in it. [31]
Dual-loop single-phase immersion requires circulation of the dielectric liquids by pumps or by natural convection flow. [32] These liquids always remain in liquid state while operating. They never boil or freeze. The dielectric coolant is either pumped through an external heat exchanger where it is cooled with any facility coolant, or the facility coolant is pumped through an immersed heat exchanger, which facilitates heat transfer within the dielectric liquid.
In two-phase systems, fluorocarbons [33] are used as heat transfer fluids. Heat is removed in a two-phase system, where the liquid boils when it comes in contact with hot components due to its low boiling point. [34] The system takes advantage of a concept known as "latent heat" which is the heat (thermal energy) required to change the phase of a fluid, this occurs when the two-phase coolant comes in contact with the heated electronics in the bath that are above the coolants boiling point. After the two-phase coolant enters its gas phase it must be cooled or condensed, typically through the use of water-cooled coils placed in the top of the tank. After it is condensed, the two-phase coolant drips back into the primary cooling tank. The two-phase coolant in the tank generally remains at its "saturation temperature". Energy transferred from the servers into the two-phase coolant will cause a portion of it to boil off into a gas. The gas rises above the liquid level where it contacts a condenser which is cooler than the saturation temperature. This causes the gaseous coolant to condense back into a liquid and fall back into the bath. [35]
Sealed server immersion cooling encloses servers in liquid-tight casings. The dielectric coolant is circulated inside or pumped through each server to collect heat from the components. The heated fluid is circulated to a heat exchanger in the rack where it is either circulated directly outside the building to a cooling tower or to a heat exchanger or cooled directly at the rack with a facility coolant infrastructure. [36] The main advantage of this approach is that servers are mounted in self-contained vessels that can be replaced in the rack without accessing the fluid. A disadvantage is that not all hardware can be used as the vendor defines the hardware specs of the sealed servers.
Some hydrocarbon-based immersion cooling fluids provide a fire hazard as they have a fire point. [37]
In the last few years[ when? ], immersion cooling in particular for bitcoin mining has become a popular method to generate usable heat. In cold climates a single ASIC miner can provide ultra-high-efficiency[ citation needed ] electric heat conversion sufficient to heat an entire home. Immersion cooling offered a means to silently convert the waste heat from the mining operation to heat water, melt snow, power in-floor heating, and heat hot tubs, pools, shops, outbuildings, sheds, and greenhouses. There is a compelling case to combine bitcoin mining operations with indoor vertical farms and traditional greenhouses to offset or eliminate the heating cost of the facilities. Indoor and outdoor recreation facilities both public and private can also benefit from the "free" waste heat. Some companies provide computing-based heating for residential and commercial operations.[ citation needed ]
Overheating of Li-ion cells and battery packs is an ongoing technological challenge for electrochemical energy conversion and storage, including in electric vehicles. Immersion cooling is a promising thermal management technique to address these challenges. [38] Immersion cooling of batteries is specifically beneficial in abuse conditions, where the thermal propagation is needed to be avoided across the battery module or pack. Immersion cooling is gaining prominence as an emerging application within the automotive industry. With a heat transfer capability 50 to 100 times greater than indirect cooling methods, immersion cooling stands out as an efficient and powerful solution. [39] Presently, immersion cooling is predominantly utilized in motorsport and high-end vehicle models, showcasing its effectiveness in cutting-edge automotive technologies. [40]
A radiator is a heat exchanger used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in cars, buildings, and electronics.
Liquid nitrogen (LN2) is nitrogen in a liquid state at low temperature. Liquid nitrogen has a boiling point of about −196 °C (−321 °F; 77 K). It is produced industrially by fractional distillation of liquid air. It is a colorless, mobile liquid whose viscosity is about one-tenth that of acetone (i.e. roughly one-thirtieth that of water at room temperature). Liquid nitrogen is widely used as a coolant.
A heat pipe is a heat-transfer device that employs phase transition to transfer heat between two solid interfaces.
Water cooling is a method of heat removal from components and industrial equipment. Evaporative cooling using water is often more efficient than air cooling. Water is inexpensive and non-toxic; however, it can contain impurities and cause corrosion.
A data center or data centre is a building, a dedicated space within a building, or a group of buildings used to house computer systems and associated components, such as telecommunications and storage systems.
Liquid cooling refers to cooling by means of the convection or circulation of a liquid.
For fluid power, a working fluid is a gas or liquid that primarily transfers force, motion, or mechanical energy. In hydraulics, water or hydraulic fluid transfers force between hydraulic components such as hydraulic pumps, hydraulic cylinders, and hydraulic motors that are assembled into hydraulic machinery, hydraulic drive systems, etc. In pneumatics, the working fluid is air or another gas which transfers force between pneumatic components such as compressors, vacuum pumps, pneumatic cylinders, and pneumatic motors. In pneumatic systems, the working gas also stores energy because it is compressible.
A chiller is a machine that removes heat from a liquid coolant via a vapor-compression, adsorption refrigeration, or absorption refrigeration cycles. This liquid can then be circulated through a heat exchanger to cool equipment, or another process stream. As a necessary by-product, refrigeration creates waste heat that must be exhausted to ambience, or for greater efficiency, recovered for heating purposes. Vapor compression chillers may use any of a number of different types of compressors. Most common today are the hermetic scroll, semi-hermetic screw, or centrifugal compressors. The condensing side of the chiller can be either air or water cooled. Even when liquid cooled, the chiller is often cooled by an induced or forced draft cooling tower. Absorption and adsorption chillers require a heat source to function.
Computer cooling is required to remove the waste heat produced by computer components, to keep components within permissible operating temperature limits. Components that are susceptible to temporary malfunction or permanent failure if overheated include integrated circuits such as central processing units (CPUs), chipsets, graphics cards, hard disk drives, and solid state drives.
Fluorinert is the trademarked brand name for the line of electronics coolant liquids sold commercially by 3M. As perfluorinated compounds (PFCs), all Fluorinert variants have an extremely high global warming potential (GWP), so should be used with caution (see below). It is an electrically insulating, stable fluorocarbon-based fluid, which is used in various cooling applications. It is mainly used for cooling electronics. Different molecular formulations are available with a variety of boiling points, allowing it to be used in "single-phase" applications, where it remains a liquid, or for "two-phase" applications, where the liquid boils to remove additional heat by evaporative cooling. An example of one of the compounds 3M uses is FC-72 (perfluorohexane, C6F14). Perfluorohexane is used for low-temperature heat-transfer applications due to its 56 °C (133 °F) boiling point. Another example is FC-75, perfluoro(2-butyl-tetrahydrofurane). There are 3M fluids that can handle up to 215 °C (419 °F), such as FC-70 (perfluorotripentylamine).
Perfluoro(2-methyl-3-pentanone) is a fluorinated ketone with the structural formula CF3CF2C(=O)CF(CF3)2, a fully-fluorinated analog of ethyl isopropyl ketone. It is used as an electronics coolant liquid and fire protection fluid sold commercially by 3M under brand names such as Novec 1230, Novec 649, and FK-5-1-12. It is also known as “waterless water” or “dry water”.
A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosion of the cooling system. Some applications also require the coolant to be an electrical insulator.
A shell-and-tube heat exchanger is a class of heat exchanger designs. It is the most common type of heat exchanger in oil refineries and other large chemical processes, and is suited for higher-pressure applications. As its name implies, this type of heat exchanger consists of a shell with a bundle of tubes inside it. One fluid runs through the tubes, and another fluid flows over the tubes to transfer heat between the two fluids. The set of tubes is called a tube bundle, and may be composed of several types of tubes: plain, longitudinally finned, etc.
Thermosiphon is a method of passive heat exchange, based on natural convection, which circulates a fluid without the necessity of a mechanical pump. Thermosiphoning is used for circulation of liquids and volatile gases in heating and cooling applications such as heat pumps, water heaters, boilers and furnaces. Thermosiphoning also occurs across air temperature gradients such as those utilized in a wood fire chimney or solar chimney.
Radiators are heat exchangers used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plants or any similar use of such an engine.
Aquasar is a supercomputer prototype created by IBM Labs in collaboration with ETH Zurich in Zürich, Switzerland and ETH Lausanne in Lausanne, Switzerland. While most supercomputers use air as their coolant of choice, the Aquasar uses hot water to achieve its great computing efficiency. Along with using hot water as the main coolant, an air-cooled section is also included to be used to compare the cooling efficiency of both coolants. The comparison could later be used to help improve the hot water coolant's performance. The research program was first termed to be: "Direct use of waste heat from liquid-cooled supercomputers: the path to energy saving, emission-high performance computers and data centers." The waste heat produced by the cooling system is able to be recycled back in the building's heating system, potentially saving money. Beginning in 2009, the three-year collaborative project was introduced and developed in the interest of saving energy and being environmentally-safe while delivering top-tier performance.
iDataCool is a high-performance computer cluster based on a modified IBM System x iDataPlex. The cluster serves as a research platform for cooling of IT equipment with hot water and efficient reuse of the waste heat. The project is carried out by the physics department of the University of Regensburg in collaboration with the IBM Research and Development Laboratory Böblingen and InvenSor. It is funded by the German Research Foundation (DFG), the German state of Bavaria, and IBM.
In fluid thermodynamics, a heat transfer fluid is a gas or liquid that takes part in heat transfer by serving as an intermediary in cooling on one side of a process, transporting and storing thermal energy, and heating on another side of a process. Heat transfer fluids are used in countless applications and industrial processes requiring heating or cooling, typically in a closed circuit and in continuous cycles. Cooling water, for instance, cools an engine, while heating water in a hydronic heating system heats the radiator in a room.
The integral molten salt reactor (IMSR) is a nuclear power plant design targeted at developing a commercial product for the small modular reactor (SMR) market. It employs molten salt reactor technology which is being developed by the Canadian company Terrestrial Energy.
Temperature chaining can mean temperature, thermal or energy chaining or cascading.