Liquid Cooling Glossary Of Terms

Liquid Cooling Glossary of Terms

We’ve compiled this glossary to help you understand the different liquid cooling terms and acronyms. Click on the alphabetical links below to jump to the appropriate section.



Annual Failure Rate (AFR)
Annual Failure Rate (AFR) represents the estimated percentage of failures over a year. AFR is calculated by dividing the total number of failures in a year by the total number of operating hours. The AFR is a percentage and can be used to estimate the probability that a device or component will fail during a year of use.

AI (Artificial Intelligence)
Artificial Intelligence (AI) is the theory and development of computer systems that deal with models and systems for performing activities usually associated with and requiring human intelligence, functions such as reasoning, learning, visual perception, speech recognition, decision-making, and translation between languages.

Air Conditioner (AC | A/C | Air Con)
An air conditioner is a self-contained unit or system designed to perform the functions of cooling, circulating, filtering, dehumidifying or otherwise processing of air in a building or a vehicle.

Airflow Management
The process of directing and controlling air movement within an IT system or data center to cool IT equipment and components.

Ampere (A)
Ampere (A) is the unit of electric current in the International System of Units (SI). One ampere equals 1 coulomb (c) moving past a point in 1 second.

APDCA (Asia Pacific Data Center Association)
APDCA (Asia Pacific Data Center Association) is a new association launched in January 2024. The APDCA has been formed to represent the collective interest of the data center industry in the Asia Pacific region. Founding members of APDCA include data center operators, Digital realty, Equinix, Global Switch, NTT Global Data Centers and Vantage Data Centers.

ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers)
ASHRAE stands for the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. ASHRAE is a US non-profit, global organization whose stated mission is to serve humanity by advancing the arts and sciences of heating, ventilation, air conditioning, refrigeration and their allied fields. ASHRAE develops standards and guidelines for HVAC systems. ASHRAE has more than 50,000 members from over 130+ nations; their vision is to create a healthy and sustainable built environment for all.

ASIC (Application Specific Integrated Chip)
An ASIC (Application Specific Integrated Chip), is a type of special purpose device which can be used to accelerate AI (Artificial Intelligence) training.

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Bill of Materials (BOM)
A Bill of Materials, or BOM, is a full list of raw materials, components, assemblies, and other items needed to construct, manufacture, or repair a product, along with the quantities required to manufacture an end product.

Boiling Enhancement Coating (BEC)
A Boiling Enhancement Coating, or BEC, is a surface microstructure enhanced coating to improve heat transfer properties.

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Cable Routing Cable
Routing is the process of organizing and managing the placement of cables within an IT system or data center to ensure efficient operation, protection from stress and damage which may degrade operation, and provide ease of access.

Capillary Action
Capillary action is the ability of a liquid to flow through narrow spaces without external forces, such as gravity, due to surface tension and adhesive forces between the liquid and solid surfaces.

Carbon Usage Effectiveness (CUE)
A performance metric that helps data centre operators assess the amount of carbon emissions produced per unit of computing energy consumed. The measurement helps determine the amount of greenhouse gas (GHG) emissions produced per unit of IT energy consumed within a data centre. The CUE calculation divides the total CO2 emissions caused by total data centre energy by the energy consumption of the IT computing equipment.

Central Processing Unit (CPU)
The central processing unit (CPU) is an electrical processing unit of a computer that retrieves and executes instructions. The CPU is the system’s brain, guiding the computer through various problem-solving steps. The CPU is often known as the processor.

Chlorofluorocarbon (CFC)
Chlorofluorocarbons (CFCs) are non-toxic, non-flammable, organic chemicals that contain carbon (sometimes hydrogen), chlorine and fluorine. CFCs are used in the manufacture of aerosols, foams, packaging materials, solvents and refrigerants. CFCs are an EPA and UN-targeted greenhouse gas.

In an IT and computing sense, the chassis is a frame or housing that encloses the components of an IT system, such as a server or computer.

Chemical stability
Chemical stability is the resistance of a chemical to change in a chemical reaction. When viewed in a technical sense, it refers to the thermodynamic stability of a chemical system. In materials science, a chemical substance is said to be stable if it is not particularly reactive in the environment or during normal use and retains its useful properties on the timescale of its expected usefulness. In corrosion, it is the ability to resist corrosion under specific environmental conditions. It is the tendency of the material to resist change or decomposition due to internal reaction or due to the action of air, heat, light, pressure, etc. In the data centre, chemical stability is used as a parameter to evaluate a fluid for use.

Closed-loop System
A closed-loop system, with regards to cooling, is a system that is designed to circulate a coolant continuously in a sealed loop, with no direct interaction between the coolant and the external environment.

Cold Plate
A cold plate is a heat transfer device, often made from metal, aluminium, or copper – which transfers heat efficiently. The cold plate is in direct contact with the heat-generating component or assembly, which requires cooling. A cooling liquid is circulated through the cold plate to facilitate heat transfer from the device you are cooling into the fluid, which then circulates through a remote heat exchanger (HX). There, the heat dissipates into the ambient air or is removed more proactively by a secondary cooling system.

Computer Room Air Conditioning (CRAC)
A Computer Room Air Conditioner (CRAC) monitors and maintains temperature, air distribution and humidity in data centres, server and network rooms. CRAC units come in various capacities and cooling options, including DX, free-cooling, dual cool, chilled water and refrigerants. CRAC units come in upflow and downflow configurations for air movement.

Computer Room Air Handler (CRAH)
A Computer Room Air Handler (CRAH), like CRAC units, is used to condition and cool data centres, servers and network rooms but is compressorless, using fans, cooling coils and chilled water to remove heat from the air. Unlike CRAH systems, CRAC units use mechanical refrigeration with compressors in-built.

Conduction is when heat transfers from one material to another through direct contact.

Conductive Fluids
Conductive Fluids are coolant fluids capable of conducting electric current where both negative and positive particles are present. Variances in fluid conductivity depend on ionic strength and temperature. Increased temperature increases conductivity measured in Siemens per meter (S/m) or milli-Siemens per centimetre (mS/cm).

A contaminant is a substance that contaminates another substance, material or environment in which it does not belong (i.e. in air or water). The contaminant can be present at levels that may cause harm or alter the material or environment’s intended performance or operational characteristics.

Convection is the rising motion of hotter areas of a liquid or gas and the sinking motion of cooler regions of a liquid or gas, sometimes forming a complete cycle. The convection process is often challenging to see, especially in the air.

A coolant is a substance, typically a liquid, used to reduce or regulate the temperature of a system. In liquid cooling, the fluid absorbs and transfers the heat away from the electronic components. An ideal coolant will have high thermal capacity and low viscosity, be low-cost, non-toxic, chemically stable, and neither cause nor promote corrosion of the cooling system.

Cooling Capacity
Cooling capacity is the ability of a cooling system to remove a certain amount of heat from a system in a given period, often expressed in kW or tons of cooling.

Cooling Distribution Units (CDUs)
A Cooling Distribution Unit (CDU) is a piece of equipment used in liquid cooling systems that pumps and conditions the coolant before distributing it to the components that require cooling. The CDU will drive a cold loop of coolant that absorbs heat from the IT racks or equivalent and rejects the heat into the facility water system (FWS). A CDU can be sized to mount within the IT rack or installed in the data centre floor or plant room to support the cooling of multiple racks. The fundamental components of a Coolant Distribution Unit are a heat exchanger and pumps to provide isolation of cooling loops in the transportation of heat from ITE out of the data center. CDUs can be used for linkage of specific applications such as cold plate to FWS solutions. There are a variety of situations where a CDU may be used in an FWS solution as well.

Cooling Tower
A Cooling Tower is a heat rejection device that uses the evaporation of water to transfer heat from a cooling system to the environment. Cooling towers are common in industrial cooling applications, including data centre applications.

Counterflow is the flowing of two fluids in opposite directions in adjacent parts of an apparatus, often used in heat exchangers and cooling systems to optimize heat transfer.
Crosstalk Crosstalk in electronics, is unwanted interference between adjacent electrical signals, which can result in reduced signal quality. Crosstalk is usually caused by undesired capacitive, inductive, or conductive coupling from one circuit or channel to another.

In a liquid cooling context, couplings are devices that are used to connect pipework of the same or different diameters. Grooved couplings connect two pipe sections with a groove rolled in the end (global standards associate specific groove dimensions based on pipe outer diameter). “Mission Critical Grade” grooved couplings are coupling solutions with design, quality control and installation verification processes to support 20+ year performance without issues).

Cubic Metre (Meter)
Cubic Metre (Meter) is a unit of volume in the International System of Units (SI). A cubic metre is defined as the volume of a cube with sides that are one metre in length, and its symbol is m³

Cubic Meter Per Hour (CMH)
Cubic Meter Per Hour (m³/h), is a measurement of airflow volume, determined by how many cubic meters of air pass by a stationary point in one hour.

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Data Centre / Data Center (DC)
A data centre (data center) is a facility that houses IT infrastructure, systems and related components, including servers, storage systems, and networking equipment, for building, running and delivering applications and services and storing and managing the data associated with those applications and services.

Deionized Water
Deionized water is a type of purified water that has had all or most of its mineral ions removed, which results in a liquid that is completely free of charge. You can use deionized water as a coolant in specific liquid cooling applications.

Dielectric Constant (Dk)
A dielectric constant of a substance or a material measures a material’s ability to store electrical energy in an electric field. The dielectric constant expresses the level at which a material holds or concentrates electric flux.

Dielectric Fluid
A dielectric fluid is a liquid with insulating properties used to cool electronic components and prevent electrical discharges. Common dielectric fluids include mineral oils or plant-based oils. Additional fluids such as silicones and fluorocarbons can be used where higher temperatures or a non-flammable fluid is required.

Dielectric Strength
Dielectric strength measures a material’s ability to withstand an electric field as an insulator without breaking down and allowing an electrical discharge to occur. Dielectric strength is defined as the maximum voltage required to produce a dielectric breakdown through the material in terms of Voltages per unit thickness.

Differential Impedance
Differential impedance is the difference in electrical impedance between two conductors, often used to characterize the performance of high-speed digital signals. For a printed circuit board (PCB), this is a pair of traces, also known as a differential pair. Maintaining the same differential impedance is vital to avoid reflections and maintain signal integrity.

Direct Liquid Cooling (DLC)
Direct Liquid Cooling (DLC) is a method of cooling that removes heat by circulating a coolant to IT electronics.

Direct-to-Chip (D2C or DTC) Cooling
Direct-to-chip cooling, or cold plate cooling, is a liquid cooling method that involves circulating a coolant in direct contact with the heat-generating components, such as processors and memory modules, to absorb and transfer heat away efficiently.

Door Heat Exchanger (DHx) or Rear Door Heat Exchanger (RDHx)
A Door Heat Exchanger (DHx) or Rear Door Heat Exchanger (RDHx) is a specialized component mounted to the rear of an IT rack that operators can use for liquid-to-air or air-to-liquid heat rejection.

Dry Coolers
Dry Coolers use air to remove excess heat externally. A dry cooler typically features a microchannel coil or a finned tube heat exchanger (HX) and fans, where the fans direct airflow through the HX.

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Energy Reuse Effectiveness (ERE)
Energy Reuse Effectiveness (ERE) is a metric for measuring the benefit of reusing energy from a data center. It provides a straightforward but powerful way to quantify the efficiency of energy reuse practices. ERE is calculated by dividing the total facility energy by the IT equipment energy, then subtracting any reused energy, such as waste heat, that is redirected and repurposed for additional purposes, such as district heating. A higher ERE indicates a more significant proportion of waste heat being repurposed.

Energy Reuse Factor (ERF)
The Energy Reuse Factor (ERF) is a ratio of the data center energy that is reused elsewhere in the facility and the total energy brought into the data center control volume (which includes IT, cooling, power, lighting, etc). The ratio is calculated by taking the energy measurement of the reused component and dividing it by the total energy used by the data center facility. The ERF will range from 0 to 1.0. When the value is at 0.0, it means that no energy is reused, while a value of 1,0 means that all of the energy brought into the data center control volume is reused.

Evaporative Cooling
Evaporative Cooling is a cooling method that uses the evaporation of a liquid to remove latent heat from a surface, from which evaporation takes place. The process is used in industrial and domestic cooling systems in conjunction with liquid cooling systems. The process of evaporative cooling can also be witnessed in the physical basis of sweating.

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Fan Control
Fan control is the management of the rotational speed of an electric fan. In computers, various computer fans provide adequate cooling, and different fan control mechanisms balance their cooling capacities and the noise they generate. Fan control mechanisms balance cooling capacities and the noise that systems generate.

Fan Emulator
A fan emulator is a device that simulates the operation of a fan by generating electrical signals typically produced by a functioning fan.

Firmware is a type of software that is embedded in a piece of hardware, such as a server or computer, which controls its core functions and operations. Firmware is usually stored on a read-only memory (ROM) chip. Hardware such as cameras, mobile phones, network cards, optical drives etc to function smoothly.

Flash Point
The Flash Point is the minimum temperature (corrected to a standard pressure of 101.3 kPa) at which the application of an ignition source causes the vapours of a liquid to ignite under specific test conditions. The lower the flash point, the easier it is to ignite a liquid solvent.

Flow rate
Flow rate is a term used in fluid dynamics to describe the volume of fluid that passes through a cross-section of a surface area per unit of time. It is the volume of fluid per time the fluid has flowed.

Fluid Dynamics
Fluid dynamics is a subdiscipline of fluid mechanics that describes the flow and behaviour of fluids, such as liquids and gases, and the forces that affect their motion.

Fluorocarbons are chemical compounds that only contain carbon and fluorine atoms – often used as Refrigerants, Insulation, fire protection, Lubricants and Dielectric fluids.

Forced Convection
Forced Convection is a specific type of heat transfer in which fluids are forced to move by an external means, either a fan or a pump, in order to increase the level of heat transfer.

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Gigawatt-hour (GWh)
Gigawatt-hour (GWh) is a unit of energy equivalent to one billion (1,000,000,000) watt-hours or one million kilowatt-hours. Gigawatt-hours are mostly used as a measurement of the output of large electric power stations. One gigawatt could power 10 million watt bulbs.

Global Warming
Potential (GWP) Global Warming Potential (GWP) measures how much infrared thermal radiation a greenhouse gas would absorb over a given time frame after it has been emitted into the atmosphere.

Globally Harmonized Systems of Classification and Labelling of Chemicals (GHS)
The Globally Harmonized System of Classification and Labeling of Chemicals (GHS) is an internationally agreed-upon system created by the United Nations. It is designed to standardize and harmonize the classification and labelling of chemicals globally to enhance the protection of human health and the environment during the handling, transport, and use of chemicals.

Graphic Processing Unit (GPU)
A Graphics Processing Unit (GPU) is a specialist processing unit designed for handling massive parallel computations efficiently. GPU is an increasingly common term due to the ongoing growth of Artificial Inteligence (AI). GPUs are important in the context of AI, as AI models rely on servers equipped with GPUs to perform training at a faster rate.

Greenhouse gases (GHGs)
Greenhouse Gases (GHGs) are gases in the Earth’s atmosphere that trap heat, causing the greenhouse effect, which contributes to global warming. Greenhouse Gases let sunlight pass through the atmosphere, but they prevent the heat that the sunlight brings from leaving the atmosphere.

GTE (Geothermal Energy)
GTE stands for Geothermal Energy which is heat within the earth’s core. Geothermal energy is defined as a renewable energy source because heat is continually produced inside the earth. More data center operators are exploring GTE as a means of sourcing clean and renewable energy for their data center facilities.

Heat Exchanger
A Heat Exchanger (HX) is a device that transfers heat from one medium (often fluid) to another between two isolated liquid circuits and prevents mixing. The HX is frequently used in liquid cooling systems to dissipate heat from the coolant, facilitating the process of heat exchange. The flow arrangement of fluids can be counter-flow, where liquid passes from opposite ends, or parallel-flow, where liquids travel in parallel in the same direction.

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Heat Exchanger
A Heat Exchanger (HX) is a device that transfers heat from one medium (often fluid) to another. It is often used in liquid cooling systems to dissipate heat from the coolant, facilitating the process of heat exchange.

Heat Load
The heat load is the heat a device generates that a cooling system must remove to maintain a given operating temperature. In buildings, a heat load refers to the amount of heating or cooling necessary to maintain the required temperature in a building or space.

Heat Pipe
A heat pipe is a heat transfer device that uses a working fluid’s evaporation and condensation (phase transition) within a sealed enclosure to transfer heat between a heat source and a heat sink.

Heat Sink
A heat sink (or heatsink) is a passive heat exchanger, often made of metal, that increases the surface area in contact with the cooling medium. The heat sink transfers the heat generated by an electronic device to a fluid medium, often air or a liquid coolant, where it is moved away from the device, allowing regulation of the temperature of the device.

Heat Spreader
A heat spreader is a heat device that is usually made of a highly conductive material such as copper. It helps to distribute heat more evenly across a larger surface area, thereby improving heat dissipation and thermal performance. By enabling the dissipation of heat from a higher-temperature source to a cooler medium, such as ambient air, it facilitates the process of heat transfer.

Heat Transfer Coefficient
Heat transfer coefficient is a measure of the effectiveness of a material or cooling medium in transferring heat, it is often used to evaluate the performance of heat exchangers and other cooling components, including cold plates.

Heat Transfer Effectiveness
Heat Transfer Effectiveness is a measure of a system’s ability to transfer thermal energy from one medium to another.

Hydrofluorocarbons (HFCs) are synthetic organic compounds containing fluorine and hydrogen atoms. They are the most common type of organofluorine compounds. Most HFCs are gases at room temperature and pressure, and they are commonly used as refrigerants in air conditioning and refrigeration applications.

High-Performance Compute (HPC)
High-Performance Computing (HPC), refers to the practice of aggregating computing power in a way that delivers much greater performance than you could realise out of a typical desktop computer or workstation to solve advanced computing problems via GPU compute clusters, in science, engineering and business related fields.

Hot-Swap (Hot Swappable)
A device that allows components (fans, controllers, pumps) to be replaced or added to an IT/Cooling system without interrupting its operation.

Hydrophilic is a property of a material or surface that is attracted to water and allows water to spread across or penetrate it, making it “water-loving.”

Hydrophobic is a property of a material or surface that repels water and does not easily allow water to spread across or penetrate it; it repels water.

H100 is a particular type of GPU via the manufacturer, Nvidia. H100 GPUs have become popular as solutions for Artificial Intelligence (AI) training because they can deliver optimized performance.

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Integrated Circuit.

Immersion is a cooling technique that involves submerging electronic and IT componentry components in a dielectric fluid to absorb and dissipate heat.

Indium Foil
Indium Foil is a malleable, thermally conductive material often used as a thermal interface material (TIM) in immersion cooling applications due to its compatibility with dielectric fluids and excellent heat transfer properties.

Information Technology Equipment (ITE)
Information Technology Equipment (ITE) refers to the physical hardware and devices used to process, store, manage, or transmit information, such as computers, servers, networking devices, and ancillaries.

Ingress Protection (IP)
Ingress Protection (IP) is a standard used to define the sealing effectiveness of electrical enclosures against intrusion from foreign bodies (tools, dirt, etc.) and moisture. It is defined in the international standard EN 60529 (British BS EN 60529:1992, European IEC 60509:1989).

Ingress Protection (IP)
Rating Ingress Protection (IP) ratings measure a device’s resistance to solids and water. IP is an international standard (IEC 60529) used to rate the degree of protection or sealing effectiveness in electrical enclosures against intrusion of objects, water, dust or accidental contact.

Insulation are materials or techniques used to reduce the transfer of energy between two objects or environments. i.e. materials used to insulate something – fit insulation to all exposed pipework.

ISO is an International Organization for Standardization, a global organization that creates international standards for various industries and sectors. With regards to data centers and sustainability, ISO-14000 is a commonly applied standard. It looks at standardization for minimizing the adverse environmental impact of organizations. Although not designed specifically for data ccenters, it can be a key set of guidelines that data center operators can use to adopt better sustainability outcomes.

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Kelvin (K)
Kelvin (K) is the SI base unit of thermodynamic temperature (equivalent in size to the degree Celsius).

Kilogram (kg)
Kilogram (kg) is the SI base unit of mass, where 1 kg is equivalent to approximately 2.205 lb); the unit measure was introduced as a unit of mass for the metric system.

Kilopascal (kPa)
Kilopascal (kPa) is the SI unit of pressure, equal to one thousand pascals. 1kPa is approximately the pressure exerted by a 10-g mass resting on a 1-cm x 1cm area.

Kilowatt (kW)
A kilowatt (kW), is a unit of power, equal to 1,000 watts (w) of electrical power.

Kilowatt-hour (kWh)
A kilowatt-hour (kWh) is measure of electrical energy equivalent to a power consumption of 1,000 watts (w) per 1 hour.

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Laminar Flow
Laminar Flow is the property of fluid particles in fluid dynamics characterized by smooth and orderly fluid motion, with minimal mixing and disruption of boundary layers. Each layer moves smoothly past the adjacent layers with little or no mixing. The fluid tends to flow smoothly at low velocities without lateral mixing, and adjacent layers slide past one another. This process can result in lower heat transfer rates compared to turbulent flow.

Latent Heat
Latent heat is the heat required to convert a solid into a liquid or vapour, or a liquid into a vapour, during a phase change, without change of temperature.

Latent Heat of Vaporization
The latent heat of vaporization of a substance is the quantity of heat in joules required to convert 1 kilogram of the liquid (at its boiling point) to vapour or gas, without any change in temperature, i.e. at a constant temperature.

Liquid is a state of matter that has a definite volume but no fixed shape. It is characterized by its ability to flow and take the shape of the container it is placed in. i.e. water or oil.

Liquid Cooling
Liquid cooling is a method of cooling that uses the convection or circulation of a liquid to extract heat from components without using air as the cooling medium.

Liquid-to-Air Heat Exchanger
A Liquid-to-Air Heat Exchanger is a device designed to transfer heat from a liquid to the surrounding air. It is often used in liquid cooling systems and in industrial processes.

Liquid-to-Liquid Heat Exchanger
A Liquid-to-Liquid Heat Exchanger is a device that transfers heat from one liquid to another without mixing the fluids. It passes the two fluids close to each other while ensuring they are separated by a barrier. Liquid-to-liquid heat Exchangers are often used in cooling systems to separate primary and secondary coolant loops.

Litres / Liters (L)
Litres or Liters, is the SI unit of volume. It is equal to 1 cubic decimetre (dm³), 1,000 cubic centimetres (cm³) or 0.001 cubic metres (m³). In the US, a litre is equivalent to 0.264 gallons. A litre occupies a volume of 10 cm x 10 cm x 10 cm.

Litres / Liters per minute (L/m)
Litres (Liters) per minute is a unit of measurement for flow rate, precisely the volume of liquid (in litres) that passes a given point in a minute. Litres per minute is commonly used as a term within Cooling Distribution Units and relates to how much fluid will be passed over the GPU/CPU to cool the processor.

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Maintenance Window
A maintenance window is a scheduled period designated in advance by technical, support, and service staff during which preventative maintenance tasks that could disrupt operations are carried out. Preventative tasks may include software updates, repairs, or replacements. By conducting these in a maintenance window, you can ensure minimal disruption and that our system runs optimally.

The manifold distributes cooling liquid from a central pipe to multiple pipes, alternatively from multiple to one, and can be located with the Cooling Distribution Unit (CDU), at the row-level or inside the rack. The cooling liquid requires two-way transport called supply and return.

Material Compatibility
Material compatibility is the ability of different materials to exist or function together without mutually detrimental effects. It refers to a material’s resistance to corrosion, rust, or staining when it comes into contact with a different material or chemical.

Megawatt (MW)
A Megawatt (MW) is a power unit equal to one million watts of electrical power.

Megawatt-hour (MWh)
Megawatt-hour (MWh) is a measure of electrical energy equivalent to one million watts of power consumption for one hour.

Microchannel Heat Sink
A microchannel heat sink contains microchannels that increase the surface area in contact with a coolant and enhance heat transfer.

Microchannels are small channels or passages within a heat exchanger, cold plate, or other cooling device with a hydraulic diameter below 1mm, usually 1-99μm that increase the surface area in contact with a coolant and enhance heat transfer. They are used in fluid control, heat transfer, and cell migration observation.

Mineral Oil
Mineral oil is a liquid obtained from refining crude oil to make gasoline and other petroleum products. It is also referred to as a dielectric fluid used for lubrication, specifically as base oil. More generally, mineral oil is a transparent, colourless oil composed mainly of alkanes and cycloalkanes. Mineral oil is commonly used in immersion cooling applications due to its insulating properties and relatively low-cost base.

In liquid cooling. mist is the liquid droplets of a substance or mixture suspended in a gas (usually air).

A motherboard is the primary printed circuit board inside general purpose computers. The motherboard holds and allows communication between many of the crucial electronic components of a system, such as the central processing unit (CPU) and memory.

MTCO2e (Million Tonnes of carbon dioxide equivalent)
MTCO2e – Metric Tons of carbon dioxide equivalent, is a unit of measurement that allows the effect of different greenhouse gases and other factors to be compared using carbon dioxide as a standard. 1 tonne is equal to 1,000 kilograms. The unit allows us to compare the potential global warming potential (GWP) impact of an emission of one greenhouse gas (such as nitric oxide).

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A nanofluid is an engineered fluid that contains nanometer-sized particles, called nanoparticles. These fluids are engineered colloidal suspensions of nanoparticles in a base fluid. The nanoparticles used in nanofluids are typically made of metals, oxides, carbides, or carbon nanotubes. Common base fluids include water, ethylene glycol and oil. Nanofluids can exhibit enhanced thermal conductivity and heat transfer properties compared to conventional fluids.

Network Interface Card (NIC)
A Network Interface Card (NIC) is a computer hardware component or circuit board installed in a computer to provide a physical connection to a network. NICs can be used for wired and wireless connections.

Network Switch
A network switch connects devices in a network to each other, enabling them to talk by exchanging data packets to receive, process and forward data to the destination device. Network switches can be hardware devices that manage physical networks or software-based virtual devices.

Non-Condensable Gas (NCG)
Non-Condensable Gas (NCG) is a gas that does not condense (change from vapour to liquid) under a cooling system and normal compression refrigeration conditions. NCGs are air, nitrogen, carbon dioxide, argon, and oxygen.

Non-Conductive Fluids
Non-conductive fluids are coolant fluids that are incapable of conducting an electric current, commonly referred to as dielectrics. They can also be referred to as insulators and contain or stop the flow of electrons.

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Open Bath Immersion (OBI)
Open Bath Immersion is a type of immersion cooling setup where Information Technology Equipment (ITE) is submerged fully in an open-to-air cooling liquid bath or tank with an open-to-air interface of the fluid.

Open-loop System
In an open-loop cooling system, the cooling medium, typically water, is circulated through a loop that is open to the environment.

Operating Humidity Range
Operating Humidity Range is an acceptable range of humidity levels in which a piece of hardware, device, system, or process can operate without experiencing degradation in performance, reliability, or operational life cycle.

Operating pressure
Operating pressure is the pressure at which a system or a part of a system operates under normal or specified conditions.

Operating Temperature Range
This is the safe temperature range in which a piece of hardware, device, system, or process can operate without experiencing degradation in performance, reliability, or longevity. The device will operate effectively within a specified operating temperature range, outside this range of safe operating temperatures, the device may fail.

Overclocking is the practice of increasing the operating frequency of a processor or other electronic component (including GPUs) beyond its specifications intended by the manufacturer to achieve higher performance, which can result in increased heat output and cooling requirements.

Oxidation Stability
Oxidation stability is a fluid’s resistance to oxidative degradation over time and is an important quality parameter.

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Parallel Flow
Parallel flow refers to the relationship between the flow directions of the hot and cold fluids. With parallel flow, the fluids travel through the heat exchanger in the same direction to optimize heat transfer.

Partial Immersion
Partial immersion is a cooling method in which only a portion of the electronic components is submerged in a dielectric (non-conductive) fluid to absorb and dissipate heat.

Passively Cooled
Passively cooled is a type of cooling that uses natural convection or radiation to dissipate heat without fans, pumps, or additional active components.

Perfluorocarbons (PFCs)
Perfluorocarbons (PFCs) are compounds, that are manmade and consist of carbon and fluorine. Perfluorocarbons are generally colourless, odourless non-flammable gases at environmental temperatures and mostly chemically unreactive. Perfluorocarbons are used as coolants in immersion cooling due to their high thermal stability and electrical insulating properties.

Phase Change Material (PCM)
A phase change material is a substance that releases and absorbs energy (heat) during its phase transition. It is used in heating or cooling and to store or release heat.

In the context of Liquid Cooling, pipework contains liquid and allows the flow to transport liquids. Pipework is typically cylindrical and connected together to form a system that supports flow rate and pressures based on system requirements.

Pipework Design
Pipework Design and the integrity of pipework start with design requirements, which include multiple components such as spatial requirements, minimizing frictional points, pipe diameter, pipe joints, isolation, condensation, cost, heat load, and cooling duty, building codes including seismic and regulatory compliance.

Power Distribution Unit (PDU)
A device used to manage and distribute electric power, especially to racks of computers and networking equipment located within a data centre.

Power Factor
Power Factor is the ratio of real power (kilowatt) to apparent power kilovolt-ampere for any given load and time.

Power Usage effectiveness (PUE)
PUE is a data center efficiency metric used to describe facility overhead power defined as the energy entering the facility divided by the energy used by the IT equipment.

Pressure Drop (often abbreviated to dP or ΔP)
Pressure Drop is defined as the decrease in pressure that occurs as a fluid flows through a system, such as a cooling loop or heat exchanger, due to frictional forces and other factors as the fluid flows through a conduit (such as a channel pipe or tube). The friction converts some of the fluid’s hydraulic energy to thermal energy (internal energy). As the thermal energy cannot be converted back to hydraulic power, the fluid experiences a pressure drop. The main determinants of resistance to fluid flow are fluid velocity through the pipe and fluid viscosity.

Pounds Per Square Inch (PSI)
PSI is a unit of pressure (non-SI) expressed in pounds of force per square inch of area.

Primary Coolant
The primary coolant fluid is in direct contact with the heat-generating components in a cooling system and is responsible for absorbing and transferring heat away from those components.

Printed Circuit Board (PCB)
A printed circuit board (PCB) is a non-conductive, flat panel with conductive lines printed or etched onto it. Electronic components are fixed on the board, and the traces connect the components to make a working circuit or assembly.

Pump Control
Pump control is the process of monitoring and regulating the speed and, therefore, the capacity of the pump systems to optimize cooling performance. ”

Pumped Liquid Cooling
Pumped liquid cooling is an efficient method of liquid cooling that uses pumps to circulate the coolant through a loop, passing through a heat source and a heat sink. In some applications, pumps can circulate coolant to areas with the most heat and the greatest requirement for heat removal, ensuring optimal cooling performance. ”

Pumped Refrigerant Cooling
Pumped refrigerant cooling is a type of liquid cooling that uses a refrigerant rather than water or another dielectric fluid as the coolant.

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A radiator is a heat exchanger used to dissipate heat by radiation from a coolant into the surrounding environment.

Redundancy in an HVAC or similar system ensures uninterrupted and reliable operation, mitigating the risks associated with equipment failure or maintenance by including additional components, systems, or processes.

Refrigeration Cycle
A refrigeration cycle is a thermodynamic cycle that transfers heat from a lower-temperature region to a higher-temperature region, routing heat away from the area you want to cool. Refrigeration Cycles are often used in cooling systems to maintain a stable operating temperature.

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Safety Data Sheet (SDS)
Safety data sheets provide detailed information about chemical products and specific substances that help users of those chemicals and substances to make a risk assessment.

Sales Bill Of Materials (SBOM)
A Sales Bill Of Materials (SBOM) lists the parts, components, items, materials and additional related services (e.g. warranties) required to develop the product as the customer has ordered. The SBOM details how the finished product and components are grouped or packaged for sale as they appear in the sales record.

Secondary Coolant
The Secondary Coolant is a fluid used in an indirect cooling system to transfer heat between the primary coolant and the heat sink or heat exchanger.

A server is a computer, device or computer program that manages access to a network’s centralized resource or service.

Server Cooling
Server cooling relates to managing the operating temperature of servers and their components, maintaining performance and preventing failures and outages.

Server Rack
A server rack is a standardized structure, predominantly in a vertical orientation frame, designed to house and organize multiple servers, networking equipment, switches, storage devices, and other IT hardware in a data center or server room.

Server Room
A server room is a dedicated space in a building or facility devoted to operating computer servers.

Single-Phase (Cooling)
Single-phase cooling, specifically related to liquid cooling, is a cooling process in which the coolant does not boil or undergo a phase change at any point during the cooling cycle but remains a liquid throughout.

Single-phase Immersion Cooling (1PIC | 1PHIC)
Single-phase immersion cooling (1PIC | 1PHIC) uses a dielectric fluid that remains in a liquid state throughout the cooling process and extracts the heat directly from the componentry.

Smart Newtork Controller Interface (SmartNIC)
A SmartNIC, or a ‘Smart Network Controller Interface’, is a network card that can process network traffic directly, rather than relying on a server’s CPU for processing.

Spray Cooling
Spray cooling is a method of cooling electronic componentry by spraying a liquid coolant directly onto the components to absorb and dissipate the heat. The droplets spread on the surface and evaporate or form a thin liquid film, removing large amounts of energy. Users can produce various types of sprays by using specific nozzle types.

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Temperature Gradient
Temperature gradient is the change in temperature with displacement in any given direction, which affects the rate of heat transfer.

Terawatt (TW)
A Terawatt is a unit of power equal to one trillion watts.

Terawatt-hour (TWh)
Terawatt-hour (TWh) is a unit of energy representing one trillion watt hours

The Green Grid (TGG)
The Green Grid (TGG) is an affiliate member organization of the Information Technology Industry Council (ITI). TGG works globally to create tools, provide technical expertise, and advocate for optimising the energy and resource efficiency of Data Center ecosystems, enabling a low carbon economy. TGG is an open industry consortium of data center operators, cloud providers, technology and equipment suppliers, facility architects, and end-users. TGG offers the technical expertise that the data center industry and governments use for insight and counsel regarding data center efficiency and sustainability. The TGG’s mission is to work globally to create tools, provide technical expertise, and advocate for optimising the energy and resource efficiency of Data Center ecosystems, enabling a low carbon economy.

Thermal Conductivity
Thermal conductivity is the ability of a material to conduct heat from one side to the other. It is represented by the thermal conductivity coefficient λ. Smaller λ indicates that the material has more substantial heat insulation and preservation.

Thermal design power (TDP)
Thermal Design Power (TDP) is a metric used by manufacturers of computing components, primarily CPUs and GPUs, to specify the theoretical amount of heat a component is expected to generate under maximum or high load conditions.

Thermal Expansion
Thermal expansion is the change in the shape, area, volume and density of a material in response to changes in temperature.

Thermal Interface Material (TIM)
A Thermal Interface Material (TIM) is any substance placed between two surfaces to improve their thermal contact and enhance heat transfer from one material to the other.

Thermal Resistance
Thermal resistance is a measure of a material’s resistance to heat flow. Thermal resistance determines the heat insulation property of a textile material. The higher the thermal resistance, the lower the heat loss.

A thermocouple is a temperature sensor that measures temperature. A thermocouple consists of two different types of metals joined together at one end. When the junction of the two metals is heated or cooled, a voltage is created that can be correlated back to the temperature.

Thermosyphon is a passive cooling system where a coolant is circulated by natural convection caused by a difference in density between the hot and cold portions of the liquid, without the need for pumps or other active components.

Three phase power
Three-phase power is a common method of alternating current (AC) power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power.

Top of Rack (ToR)
Top-of-rack (ToR) switching is a data centre design principle where computing equipment like servers, appliances, and other switches within the same or adjacent rack connect to an in-rack network switch, providing localized, dedicated networking resources.

Total cost of ownership (TCO)
Total Cost of ownership (TCO) is a financial estimate that looks at the purchase price of an asset plus the costs of operation of that asset. TCO helps consumers assess direct and indirect costs related to purchasing any capital investment to allow for easy comparison. Assessing TCO means taking a more significant perspective on the asset and its value over time. TCO includes:

  • The purchase price of a piece of capital equipment, plus operating costs, over the equipment’s life span.
  • Looking at TCO is a way of assessing the long-term value of a purchase to a company/individual.

Total Cost to the Environment (TCE)
Total Cost to the Environment (TCE) is a concept and metric used to assess the comprehensive environmental impact of a product, service, or operation, considering all relevant environmental costs from cradle to grave.

Turbulent Flow
Turbulent flow is a fluid (gas or liquid) flow regime where the fluid undergoes irregular and chaotic fluctuations or mixing, which can enhance heat transfer by disrupting boundary layers. In turbulent flow, the fluid’s speed at a point continuously changes in magnitude and direction. The movement contrasts laminar flow, where the fluid moves in smooth paths or layers.

Two Phase (Electrical Power Context)
In an electrical power context, two-phase refers to a type of power system that uses two alternating currents (AC) that reach their peak instantaneous values sequentially.

Two Phase (Liquid Context)
Two Phase, in a liquid context, refers to a cooling method that leverages the heat absorbing phase change, where the fluid undergoes a phase change and becomes a gas as electronic devices and componentry heat it.

Two-phase Immersion Cooling (2PIC| 2PHIC)
Two-phase Immersion Cooling (2PIC, 2PHIC) is a type of cooling technology where you submerge electronic components in a bath of dielectric fluid that undergoes a phase change from liquid to vapor and back to liquid as it absorbs and releases heat. With a lower boiling point, the fluid boils on the surface of the heat-generating IT components, and the rising vapor passively takes care of the heat transfer.

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Underclocking reduces the operating frequency of a processor or other electronic components below their designed operating parameters to decrease power consumption and heat output. It is important to note that extreme underclocking may impact performance.

Underwriters Laboratories (UL)
Underwriters Laboratories (UL) is a global safety science company, and it is the largest and oldest independent testing laboratory in the United States. UL plays a crucial role in ensuring the safety of various products before they are introduced to the global market.

Uninterruptible Power Supply (UPS)
An Uninterruptible Power Supply (UPS) is a device that maintains power in the event of a failure, providing emergency power to a load when the primary power source, typically mains power, has failed. A UPS commonly will include a battery that is kept charged and ready, and when power fails, the battery will supply power.

United Nations (UN)
The United Nations (UN) is an international organization founded in 1945. Currently made up of 193 Member States, the UN and its work are guided by the purposes and principles contained in its founding Charter. All UN Member States are members of the General Assembly. States are admitted to membership by a decision of the General Assembly upon the recommendation of the Security Council.

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A substance in the gaseous state at a temperature lower than its critical point.

Vapor Pressure
Vapor pressure is the pressure a vapor exerts in equilibrium with its corresponding liquid or solid form, or both at a given temperature. Vapor pressure is a measure of the tendency of a material to change into the gaseous or vapor state, and it increases with temperature. The temperature at which the vapour pressure at the surface of a liquid becomes equal to the pressure exerted by the surroundings is called the boiling point of the liquid.

Vapor Quality
Vapour quality is the mass fraction of vapour in the liquid-vapour mixture, such that dry vapour is equivalent to a quality equal to 1, i.e. 100% vapour. On the other hand, values between 0 and 1 indicate water content in the mixture, with value 0 being for saturated liquid. Vapor quality is essential when viewing the two-phase mixture in an immersion system and the dielectric coolant in use.

Variable Frequency Drive (VFD)
A variable frequency drive (VFD), is a device that controls the speed and torque of an electric motor by varying the frequency of the electrical power supplied to it.

Viscosity is a measure of a fluid’s resistance to flow, which involves its resistance to deformation at a given rate. The higher the viscosity of a liquid, the thicker it is and the greater the resistance to flow. Viscosity is defined scientifically as a force multiplied by a time divided by an area. Thus, its SI units are Newton seconds per square meter or Pascal seconds.

Volt (V)
A volt is the SI unit of electromotive force, the difference of potential that would carry one ampere of current against one ohm resistance.

Voltage Regulator (VR)
A voltage regulator (VR) is a system designed to automatically maintain a constant voltage of a power source within acceptable limits.

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The entity (individual or company) that provides a warranty.

Warranty Period
The period during which the warrantor is responsible for certain aspects of a product’s performance and condition as outlined in the warranty, under appropriate use and with proper maintenance, as outlined in the warranty document.

Warranty & Warranty Statement
A warranty is a written guarantee issued to the purchaser of an article by its manufacturer, promising to repair or replace it if necessary within a specified period.

Water Cooling
Water Cooling is a method of cooling electronic components by circulating water or a water-based coolant through pipes. The liquid takes the heat from the components and dissipates it into a radiator. The concept operates like the engine cooling system in a car, where coolant is pumped through the engine and to the radiator.

Water Usage Effectiveness (WUE)
WUE is a sustainability metric used in the data center industry to assess the efficiency of water usage. WUE is calculated by dividing the total amount of water a data center uses by the energy the IT equipment consumes. WUE as a metric has grown in prominence, given the growing efforts by data center operators to show that they are using water and energy efficiently.

Watt (W)
A Watt (W) is an SI unitof the rate of energy transfer over a unit of time, with one watt equal to one joule (J) per second: W = J/s. A joule is the standard unit of energy or work in the SI standard, which defines the joule in terms of kilograms, meters and seconds.

Wet-Bulb Globe Temperature (WBGT)
The WetBulb Globe Temperature (WBGT) is a measure of the heat stress in direct sunlight, which takes into account temperature, humidity, wind speed, sun angle, and cloud cover (solar radiation).

Wetted Surface Area
The surface area of a component that is in direct contact with the working fluid, coolant or gas.

Workload relates to the computing resources, amount of processing or computational tasks performed by a system or component and the time it takes to complete a task or generate an outcome, which can affect its thermal output and cooling requirements.

World Semiconductor Council (WSC)
The World Semiconductor Council (WSC) is an international forum that brings together industry leaders to address issues of global concern to the semiconductor industry. Comprised of the semiconductor industry associations (SIAs) of the United States, Korea, Japan, Europe, China and Chinese Taipei, the goal of the WSC is to promote international cooperation in the semiconductor sector to facilitate the healthy growth of the industry from a long-term, global perspective.

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