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Cooling tower and water discharge of a nuclear power plant Water cooling is a method of
heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
removal from components and industrial equipment.
Evaporative cooling An evaporative cooler (also known as evaporative air conditioner, swamp cooler, swamp box, desert cooler and wet air cooler) is a device that cools air through the evaporation of water. Evaporative cooling differs from other air conditioning sy ...
using
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
is often more efficient than
air cooling Air cooling is a method of dissipating heat. It works by expanding the surface area or increasing the flow of air over the object to be cooled, or both. An example of the former is to add cooling fins to the surface of the object, either by maki ...
. Water is inexpensive and non-toxic; however, it can contain impurities and cause corrosion. Water cooling is commonly used for cooling automobile
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...
s and
power stations A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid. Many pow ...
. Water coolers utilising
convective heat transfer Convection (or convective heat transfer) is the heat transfer, transfer of heat from one place to another due to the movement of fluid. Although often discussed as a distinct method of heat transfer, convective heat transfer involves the combin ...
are used inside high-end
personal computers A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or techn ...
to lower the temperature of CPUs. Other uses include the cooling of
lubricant A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, t ...
oil in
pump A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they u ...
s; for cooling purposes in
heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
s; for cooling
building A building, or edifice, is an enclosed structure with a roof and walls standing more or less permanently in one place, such as a house or factory (although there's also portable buildings). Buildings come in a variety of sizes, shapes, and fun ...
s in
HVAC Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...
and in
chiller A chiller is a machine that removes heat from a liquid coolant via a vapor-compression refrigeration, vapor-compression, adsorption refrigeration, or absorption refrigerator, absorption refrigeration cycles. This liquid can then be circulated th ...
s.


Mechanism


Advantages

Water is inexpensive,
non-toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...
, and available over most of the earth's surface. Liquid cooling offers higher thermal conductivity than air cooling. Water has unusually high specific heat capacity among commonly available liquids at room temperature and atmospheric pressure allowing efficient heat transfer over distance with low rates of mass transfer. Cooling water may be recycled through a ''recirculating'' system or used in a single pass ''once-through cooling'' (OTC) system. Water's high
enthalpy of vaporization The enthalpy of vaporization (symbol ), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) that must be added to a liquid substance to transform a quantity of that substance into a gas. T ...
allows the option of efficient evaporative cooling to remove waste heat in
cooling tower A cooling tower is a device that rejects waste heat to the atmosphere through the cooling of a coolant stream, usually a water stream to a lower temperature. Cooling towers may either use the evaporation of water to remove process heat and ...
s or
cooling pond A cooling pond is a man-made body of water primarily formed for the purpose of cooling heated water and/or to store and supply cooling water to a nearby power plant or industrial facility such as a petroleum refinery, pulp and paper mill, chemica ...
s. Recirculating systems may be ''open'' if they rely upon evaporative cooling or ''closed'' if heat removal is accomplished in
heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
s with negligible evaporative loss. A heat exchanger or condenser may separate ''non-contact cooling water'' from a
fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
being cooled, or ''contact cooling water'' may directly impinge on items like
saw A saw is a tool consisting of a tough blade, wire, or chain with a hard toothed edge. It is used to cut through material, very often wood, though sometimes metal or stone. The cut is made by placing the toothed edge against the material and mo ...
blades where
phase Phase or phases may refer to: Science *State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter), a region of space throughout which all physical properties are essentially uniform * Phase space, a mathematic ...
difference allows easy separation. Environmental regulations emphasize the reduced concentrations of waste products in non-contact cooling water.


Disadvantages

Water accelerates corrosion of metal parts and is a favorable medium for biological growth. Dissolved minerals in natural water supplies are concentrated by evaporation to leave deposits called scale. Cooling water often requires addition of chemicals to minimize corrosion and insulating deposits of scale and biofouling. Water contains varying amounts of impurities from contact with the atmosphere, soil, and containers. Manufactured metals tend to revert to ores via electrochemical reactions of corrosion. Water can accelerate corrosion of machinery being cooled as both an electrical conductor and solvent for metal ions and oxygen. Corrosion reactions proceed more rapidly as temperature increases. Preservation of machinery in the presence of hot water has been improved by addition of
corrosion inhibitor In chemistry, a corrosion inhibitor or anti-corrosive is a chemical compound that, when added to a liquid or gas, decreases the corrosion rate of a material, typically a metal or an alloy, that comes into contact with the fluid. The effectiveness ...
s including
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
,
chromates Chromate salts contain the chromate anion, . Dichromate salts contain the dichromate anion, . They are oxyanions of chromium in the +6 oxidation state and are moderately strong oxidizing agents. In an aqueous solution, chromate and dichromate i ...
and
phosphates In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...
. The first two have toxicity concerns; and the last has been associated with
eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
. Residual concentrations of biocides and corrosion inhibitors are of potential concern for OTC and blowdown from open recirculating cooling water systems. With the exception of machines with short design life, closed recirculating systems require periodic cooling water treatment or replacement raising similar concern about ultimate disposal of cooling water containing chemicals used with environmental safety assumptions of a closed system.
Biofouling Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, or small animals where it is not wanted on surfaces such as ship and submarine hulls, devices such as water inlets, pipework, grates, ponds, and rivers that ...
occurs because water is a favorable environment for many life forms. Flow characteristics of recirculating cooling water systems encourage colonization by
sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...
organisms to use the circulating supply of food,
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
and nutrients. Temperatures may become high enough to support
thermophilic A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between . Many thermophiles are archaea, though they can be bacteria or fungi. Thermophilic eubacteria are suggested to have been among the earl ...
populations. Biofouling of heat exchange surfaces can reduce heat transfer rates of the cooling system; and biofouling of cooling towers can alter flow distribution to reduce evaporative cooling rates. Biofouling may also create differential oxygen concentrations increasing corrosion rates. OTC and open recirculating systems are most susceptible to biofouling. Biofouling may be inhibited by temporary habitat modifications. Temperature differences may discourage establishment of thermophilic populations in intermittently operated facilities; and intentional short term temperature spikes may periodically kill less tolerant populations.
Biocide A biocide is defined in the European legislation as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism. The US Environmental Protection Agency (EPA) uses a slig ...
s have been commonly used to control biofouling where sustained facility operation is required.
Chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...
may be added in the form of
hypochlorite In chemistry, hypochlorite is an anion with the chemical formula ClO−. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite (household bleach) and calcium hypochlorite (a component of ble ...
to decrease biofouling in cooling water systems, but is later reduced to
chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
to minimize toxicity of blowdown or OTC water returned to natural aquatic environments. Hypochlorite is increasingly destructive to wooden cooling towers as pH increases. Chlorinated phenols have been used as biocides or leached from preserved wood in cooling towers. Both hypochlorite and
pentachlorophenol Pentachlorophenol (PCP) is an organochlorine compound used as a pesticide and a disinfectant. First produced in the 1930s, it is marketed under many trade names. It can be found as pure PCP, or as the sodium salt of PCP, the latter of which diss ...
have reduced effectiveness at pH values greater than 8. Non-oxidizing biocides may be more difficult to detoxify prior to release of blowdown or OTC water to natural aquatic environments. Concentrations of
polyphosphate Polyphosphates are salts or esters of polymeric oxyanions formed from tetrahedral PO4 (phosphate) structural units linked together by sharing oxygen atoms. Polyphosphates can adopt linear or a cyclic ring structures. In biology, the polyphosphate e ...
s or
phosphonate In organic chemistry, phosphonates or phosphonic acids are organophosphorus compounds containing groups (where R = alkyl, aryl, or just hydrogen). Phosphonic acids, typically handled as salts, are generally nonvolatile solids that are poorly ...
s with zinc and chromates or similar compounds have been maintained in cooling systems to keep heat exchange surfaces clean so a film of gamma iron oxide and
zinc phosphate Zinc phosphate is an inorganic compound with the formula Zn3( PO4)2. This white powder is widely used as a corrosion resistant coating on metal surfaces either as part of an electroplating process or applied as a primer pigment (see also red lead ...
may inhibit corrosion by passivating anodic and cathodic reaction points. These increase salinity and total dissolved solids, and
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
compounds may provide the limiting essential nutrient for algal growth contributing to biofouling of the cooling system or to eutrophication of natural aquatic environments receiving blowdown or OTC water. Chromates reduce biofouling in addition to effective corrosion inhibition in the cooling water system, but residual toxicity in blowdown or OTC water has encouraged reduced chromate concentrations and use of less flexible corrosion inhibitors. Blowdown may also contain
chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...
leached from cooling towers constructed of wood preserved with
chromated copper arsenate Chromated copper arsenate (CCA) is a wood preservative containing compounds of chromium, copper, and arsenic, in various proportions. It is used to impregnate timber and other wood products, especially those intended for outdoor use, in order to pr ...
.
Total dissolved solids Total dissolved solids (TDS) is a measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionized, or micro-granular ( colloidal sol) suspended form. TDS concentrations are often repor ...
or TDS (sometimes called filtrable residue) is measured as the mass of residue remaining when a measured volume of
filtered Filtration is a physical separation process that separates solid matter and fluid from a mixture using a ''filter medium'' that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filter m ...
water is
evaporate Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...
d.
Salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...
measures water
density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
or
conductivity Conductivity may refer to: *Electrical conductivity, a measure of a material's ability to conduct an electric current **Conductivity (electrolytic), the electrical conductivity of an electrolyte in solution **Ionic conductivity (solid state), elec ...
changes caused by dissolved materials. Probability of scale formation increases with increasing total dissolved solids. Solids commonly associated with scale formation are
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
and
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
and
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ar ...
. Corrosion rates initially increase with salinity in response to increasing electrical conductivity, but then decrease after reaching a peak as higher levels of salinity decrease dissolved oxygen levels. Some groundwater contains very little oxygen when pumped from wells, but most natural water supplies include dissolved oxygen. Corrosion increases with increasing oxygen concentrations. Dissolved oxygen approaches saturation levels in cooling towers. Dissolved oxygen is desirable in blowdown or OTC water being returned to natural aquatic environments. Water ionizes into
hydronium In chemistry, hydronium (hydroxonium in traditional British English) is the common name for the aqueous cation , the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid is d ...
(H3O+)
cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
s and
hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...
(OH)
anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
s. The concentration of ionized
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
(as protonated water) in a cooling water system is expressed as pH. Low pH values increase rate of corrosion while high pH values encourage scale formation.
Amphoterism In chemistry, an amphoteric compound () is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used. One type of amphoteric species are amphiproti ...
is uncommon among metals used in water cooling systems, but
aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...
corrosion rates increase with pH values above 9.
Galvanic corrosion Galvanic corrosion (also called bimetallic corrosion or dissimilar metal corrosion) is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. A sim ...
may be severe in water systems with
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
and aluminum components.
Acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
may be added to cooling water systems to prevent scale formation if the pH decrease will offset increased salinity and dissolved solids.


Steam power stations

Few other cooling applications approach the large volumes of water required to condense low pressure steam at
power station A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid. Many p ...
s. Many facilities, particularly electric power plants, use millions of gallons of water per day for cooling. Water cooling on this scale may alter natural water environments and create new environments.
Thermal pollution Thermal pollution, sometimes called "thermal enrichment", is the degradation of water quality by any process that changes ambient water temperature. Thermal pollution is the rise or fall in the temperature of a natural body of water caused by hum ...
of rivers, estuaries and coastal waters is a consideration when siting such plants. Water returned to aquatic environments at temperatures higher than the ambient receiving water modify aquatic habitat by increasing biochemical reaction rates and decreasing oxygen saturation capacity of the habitat. Temperature increases initially favor a population shift from species requiring the high-oxygen concentration of cold water to those enjoying advantages of increased metabolic rates in warm water. Once-through cooling (OTC) systems may be used on very large rivers or at
coastal The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
and
estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...
sites. These power stations put the
waste heat Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility ...
into the river or coastal water. These OTC systems thus rely upon a good supply of river water or seawater for their cooling needs. Such facilities are built with intake structures designed to pump in large volumes of water at a high rate of flow. These structures tend to also pull in large numbers of fish and other aquatic organisms, which are killed or injured on the intake screens.EPA (2014)
"Cooling Water Intakes."
/ref> Large flow rates may immobilize slow-swimming organisms including
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
and
shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...
on
screens Screen or Screens may refer to: Arts * Screen printing (also called ''silkscreening''), a method of printing * Big screen, a nickname associated with the motion picture industry * Split screen (filmmaking), a film composition paradigm in which m ...
protecting the small bore tubes of the heat exchangers from blockage. High temperatures or pump turbulence and shear may kill or disable smaller organisms passing the screens entrained with the cooling water. Over 1,200 power plants and manufacturers use OTC systems in the U.S. and the intake structures kill billions of fish and other organisms each year. More agile aquatic
predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
s consume organisms impinged on the screens; and warm water predators and
scavenger Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding b ...
s colonize the cooling water discharge to feed on entrained organisms. The U.S.
Clean Water Act The Clean Water Act (CWA) is the primary federal law in the United States governing water pollution. Its objective is to restore and maintain the chemical, physical, and biological integrity of the nation's waters; recognizing the responsibiliti ...
requires the
Environmental Protection Agency A biophysical environment is a biotic and abiotic surrounding of an organism or population, and consequently includes the factors that have an influence in their survival, development, and evolution. A biophysical environment can vary in scale f ...
(EPA) to issue
regulation Regulation is the management of complex systems according to a set of rules and trends. In systems theory, these types of rules exist in various fields of biology and society, but the term has slightly different meanings according to context. For ...
s on industrial cooling water intake structures. EPA issued final regulations for new facilities in 2001 (amended 2003), and for existing facilities in 2014.


Cooling towers

As an alternative to OTC, industrial cooling towers may use recirculated river water, coastal water (
seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appro ...
), or well water. Large mechanical induced-draft or forced-draft cooling towers in industrial plants continuously circulate cooling water through heat exchangers and other equipment where the water absorbs heat. That heat is then rejected to the atmosphere by the partial evaporation of the water in cooling towers where upflowing air is contacted with the circulating downflow of water. The loss of evaporated water into the air exhausted to the atmosphere is replaced by "make-up" fresh river water or fresh cooling water; but volumes of water lost during evaporative cooling may decrease natural habitat for aquatic organisms. Since the evaporation of pure water is replaced by make-up water containing carbonates and other dissolved salts, a portion of the circulating water is also continuously discarded as "blowdown" water to prevent the excessive build-up of salts in the circulating water; and these blowdown wastes may change the receiving water quality.


Internal combustion engines

The
water jacket A water jacket is a water-filled casing surrounding a device, typically a metal sheath having intake and outlet vents to allow water to be pumped through and circulated. The flow of water to an external heating or cooling device allows precise t ...
around an engine is very effective at deadening mechanical noises, which makes the engine quieter.


Open method

An open water cooling system makes use of
evaporative cooling An evaporative cooler (also known as evaporative air conditioner, swamp cooler, swamp box, desert cooler and wet air cooler) is a device that cools air through the evaporation of water. Evaporative cooling differs from other air conditioning sy ...
, lowering the temperature of the remaining (unevaporated) water. This method was common in early internal combustion engines, until scale buildup was observed from dissolved salts and minerals in the water. Modern open cooling systems continuously waste a fraction of recirculating water as blowdown to remove dissolved solids at concentrations low enough to prevent scale formation. Some open systems use inexpensive
tap water Tap water (also known as faucet water, running water, or municipal water) is water supplied through a tap, a water dispenser valve. In many countries, tap water usually has the quality of drinking water. Tap water is commonly used for drinking, ...
, but this requires higher blowdown rates than deionized or
distilled water Distilled water is water that has been boiled into vapor and condensed back into liquid in a separate container. Impurities in the original water that do not boil below or near the boiling point of water remain in the original container. Thus, di ...
. Purified water systems still require blowdown to remove accumulation of byproducts of chemical treatment to prevent corrosion and biofouling.


Pressurization

Water cooling also has a
boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding envir ...
temperature of around 100 degrees C at atmospheric pressure. Engines operating at higher temperatures may require a pressurized recycle loop to prevent overheating. Modern automotive cooling systems often operate at to raise the boiling-point of the recycling water coolant and reduce evaporative losses.


Antifreeze

The use of water cooling carries the risk of damage from freezing. Automotive and many other engine cooling applications require the use of a water and
antifreeze An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, all ...
mixture to lower the freezing point to a temperature unlikely to be experienced. Antifreeze also inhibits corrosion from dissimilar metals and can increase the boiling point, allowing a wider range of water cooling temperatures. Its distinctive odor also alerts operators to cooling system leaks and problems that would go unnoticed in a water-only cooling system. The heated coolant mixture can also be used to warm the air inside the car by means of the
heater core A heater core is a radiator-like device used in heating the cabin of a vehicle. Hot coolant from the vehicle's engine is passed through a winding tube of the core, a heat exchanger between coolant and cabin air. Fins attached to the core tubes ser ...
.


Other additives

Other less common chemical additives are products to reduce surface tension. These additives are meant to increase the efficiency of automotive cooling systems. Such products are used to enhance the cooling of underperforming or undersized cooling systems or in racing where the weight of a larger cooling system could be a disadvantage.


Power electronics and transmitters

Since approximately 1930 it is common to use water cooling for tubes of powerful transmitters. As these devices uses high operation voltages (around 10 kV), the use of deionized water is required and it has to be carefully controlled. Modern solid-state transmitters can be built so that even high power transmitters do not require water cooling. Water cooling is however also sometimes used for thyristors of HVDC valves, for which also the use of deionized water is required.


Liquid cooling maintenance

Liquid cooling techniques are increasingly being used for the thermal management of electronic components. This type of cooling is a solution to ensure the optimisation of energy efficiency while simultaneously minimising noise and space requirements. Especially useful in supercomputers or Data Centers as maintenance of the racks is quick and easy. After disassembly of the rack, advanced technology quick release couplings eliminate spillage for the safety of operators and protects the integrity of fluids (no impurities in the circuits). These couplings are also capable of being locked (Panel mounted?) to allow blind connection in difficult to access areas. It is important in electronics technology to analyse the connection systems to ensure: * Non-spill sealing (clean break, flush face couplings) * Compact and lightweight (materials in special aluminum alloys) * Operator safety (disconnection without spillage) * Quick-release couplings sized for optimized flow * Connection guiding system and compensation of misalignment during connection on rack systems * Excellent resistance to vibration and corrosion * Designed to withstand a large number of connections even on refrigerant circuits under residual pressure


Computer usage

Water cooling often adds complexity and cost in comparison to air cooling design by requiring a pump, tubing or piping to transport the water, and a radiator, often with fans, to reject the heat to the atmosphere. Depending on the application, water cooling may create an additional element of risk where leakage from the water coolant recycle loop may corrode or short-circuit sensitive electronic components. The primary advantage of water cooling for cooling CPU cores in computing equipment is transporting heat away from the source to a secondary cooling surface to allow for large, more optimally designed
radiator Radiators are heat exchangers 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. A radiator is always a ...
s rather than small, relatively inefficient fins mounted directly on the heat source. Cooling hot computer components with various fluids has been in use since at least the
Cray-2 The Cray-2 is a supercomputer with four vector processors made by Cray Research starting in 1985. At 1.9 GFLOPS peak performance, it was the fastest machine in the world when it was released, replacing the Cray X-MP in that spot. It was, i ...
in 1982, using
Fluorinert 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 wit ...
. Through the 1990s, water cooling for home PCs slowly gained recognition among enthusiasts, but it started to become noticeably more prevalent after the introduction of the first Gigahertz-clocked processors in the early 2000s. As of 2018, there are dozens of manufacturers of water cooling components and kits, and many computer manufacturers include preinstalled water cooling solutions for their high-performance systems. Water cooling can be used to cool many computer components, but usually it is used for the CPU and
GPUs A graphics processing unit (GPU) is a specialized electronic circuit designed to manipulate and alter memory to accelerate the creation of images in a frame buffer intended for output to a display device. GPUs are used in embedded systems, mobil ...
. Water cooling usually uses a
water block A water block is the watercooling equivalent of a heatsink. It is a type of plate heat exchanger and can be used on many different computer components, including the central processing unit (CPU), GPU, PPU, and northbridge chipset on the mothe ...
, a
water pump A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they u ...
, and a water-to-air heat exchanger. By transferring device heat to a separate heat exchanger which can variously be made large and use larger, lower-speed fans, water cooling can allow quieter operation, improved processor speeds (
overclocking In computing, overclocking is the practice of increasing the clock rate of a computer to exceed that certified by the manufacturer. Commonly, operating voltage is also increased to maintain a component's operational stability at accelerated spe ...
), or a balance of both. Less commonly, Northbridges, Southbridges,
hard disk drives A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk platter, platters ...
,
memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...
,
voltage regulator module A voltage regulator module (VRM), sometimes called processor power module (PPM), is a buck converter that provides microprocessor and chipset the appropriate supply voltage, converting , or to lower voltages required by the devices, allowing dev ...
s (VRMs), and even
power supplies A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a res ...
can be water-cooled. Internal radiator size may vary: from 40mm dual fan (80mm) to 140 quad fan (560mm) and thickness from 30mm to 80mm. Radiator fans may be mounted on one or both sides. External radiators can be much larger than their internal counterparts as they do not need to fit in the confines of a computer case. High end cases may have two rubber grommeted ports in the back for the inlet and outlet hoses which allows external radiators to be placed far away from the PC. A ''T-Line'' is used to remove trapped air bubbles from the circulating water. It is made with a t-connector and a capped-off length of tubing. The tube n acts as a mini-reservoir and allows air-bubbles to travel into it as they are caught into the "tee" connector, and ultimately travel out of the system (bleeding). The capped line may be capped with a fill-port fitting to allow release of trapped gas and addition of liquid. Water coolers for desktop computers were, until the end of the 1990s, homemade. They were made from car
radiators Radiators are heat exchangers 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. A radiator is always a s ...
(or more commonly, a car's
heater core A heater core is a radiator-like device used in heating the cabin of a vehicle. Hot coolant from the vehicle's engine is passed through a winding tube of the core, a heat exchanger between coolant and cabin air. Fins attached to the core tubes ser ...
),
aquarium An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...
pumps and home-made water blocks, laboratory-grade PVC and silicone tubing and various reservoirs (homemade using plastic bottles, or constructed using cylindrical acrylic or sheets of acrylic, usually clear) and or a
T-Line Cooling tower and water discharge of a nuclear power plant 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 no ...
. More recently a growing number of companies are manufacturing water-cooling components compact enough to fit inside a computer case. This, and the trend to CPUs of higher power dissipation, has greatly increased the popularity of water cooling. Dedicated overclockers have occasionally used
vapor-compression refrigeration Vapour-compression refrigeration or vapor-compression refrigeration system (VCRS), in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for air conditioning of buildings ...
or thermoelectric coolers in place of more common standard heat exchangers. Water cooling systems in which water is cooled directly by the evaporator coil of a phase change system are able to chill the circulating coolant below the ambient air temperature (impossible with a standard heat exchanger) and, as a result, generally provide superior cooling of the computer's heat-generating components. The downside of phase-change or thermoelectric cooling is that it uses much more electricity, and
antifreeze An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, all ...
must be added due to the low temperature. Additionally, insulation, usually in the form of lagging around water pipes and neoprene pads around the components to be cooled, must be used in order to prevent damage caused by
condensation Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor to ...
of water vapour from the air on chilled surfaces. Common places from which to borrow the required
phase transition In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of ...
systems are a household
dehumidifier A dehumidifier is an air conditioning device which reduces and maintains the level of humidity in the air. This is done usually for health or thermal comfort reasons, or to eliminate musty odor and to prevent the growth of mildew by extracting w ...
or
air conditioner Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
. An alternative cooling system, which enables components to be cooled below the ambient temperature, but which obviates the requirement for antifreeze and lagged pipes, is to place a thermoelectric device (commonly referred to as a 'Peltier junction' or 'pelt' after Jean Peltier, who documented the effect) between the heat-generating component and the water block. Because the only sub-ambient temperature zone now is at the interface with the heat-generating component itself, insulation is required only in that localized area. The disadvantage of such a system is a higher power dissipation. To avoid damage from condensation around the Peltier junction, a proper installation requires it to be "potted" with silicone epoxy. The epoxy is applied around the edges of the device, preventing air from entering or leaving the interior. Apple's
Power Mac G5 The Power Mac G5 is a series of personal computers designed, manufactured, and sold by Apple Computer, Inc. from 2003 to 2006 as part of the Power Mac series. When introduced, it was the most powerful computer in Apple's Macintosh lineup, and ...
was the first mainstream desktop computer to have water cooling as standard (although only on its fastest models).
Dell Dell is an American based technology company. It develops, sells, repairs, and supports computers and related products and services. Dell is owned by its parent company, Dell Technologies. Dell sells personal computers (PCs), servers, data ...
followed suit by shipping their XPS computers with liquid cooling, using
thermoelectric cooling Thermoelectric cooling uses the Peltier effect to create a heat flux at the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side o ...
to help cool the liquid. Currently, Dell's only computers to offer liquid cooling are their
Alienware Alienware is an American computer hardware subsidiary of Dell. Their product range is dedicated to gaming computers which can be identified by their alien-themed designs. Alienware was founded in 1996 by Nelson Gonzalez and Alex Aguila, and is ...
desktops. Asus are the first and only mainstream brand to have put water cooled laptops into mass production. Those laptops have a built in air/water hybrid cooling system and can be docked to an external liquid cooling radiator for additional cooling and electrical power.


Ships and boats

Water is an ideal cooling medium for vessels as they are constantly surrounded by water that generally remains at a low temperature throughout the year. Systems operating with sea water need to be manufactured from
cupronickel Cupronickel or copper-nickel (CuNi) is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese. The copper content typically varies from 60 to 90 percent. (Monel is a nickel-copper alloy that contains a minimu ...
,
bronze Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals, such as phosphorus, or metalloids such ...
,
titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
or similarly corrosion-resistant materials. Water containing sediment may require velocity restrictions through piping to avoid erosion at high velocity or blockage by settling at low velocity.


Other applications

Plant
transpiration Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. Water is necessary for plants but only a small amount of water taken up by the roots is used for growth a ...
and animal
perspiration Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distrib ...
use evaporative cooling to prevent high temperatures from causing unsustainable metabolic rates.
Machine gun A machine gun is a fully automatic, rifled autoloading firearm designed for sustained direct fire with rifle cartridges. Other automatic firearms such as automatic shotguns and automatic rifles (including assault rifles and battle rifles) a ...
s used in fixed defensive positions sometimes use water cooling to extend barrel life through periods of rapid fire, but the weight of the water and pumping system significantly reduces the portability of water-cooled firearms. Water-cooled machine guns were extensively used by both sides during
World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
, however by the end of the war lighter weapons which rivalled the firepower, effectiveness and reliability of water-cooled models began to appear on the battlefield, thus water-cooled weapons have played a far lesser role in subsequent conflicts. A
hospital A hospital is a health care institution providing patient treatment with specialized health science and auxiliary healthcare staff and medical equipment. The best-known type of hospital is the general hospital, which typically has an emerge ...
in
Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
relies on snow-cooling from melt-water from to cool its data centers, medical equipment, and maintain a comfortable ambient temperature. Some nuclear reactors use heavy water as cooling. Heavy water is employed in
nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...
s because it is a weaker
neutron absorber In applications such as nuclear reactors, a neutron poison (also called a neutron absorber or a nuclear poison) is a substance with a large neutron absorption cross-section. In such applications, absorbing neutrons is normally an undesirable eff ...
. This allows for the use of less enriched fuel. For the main cooling system, normal water is preferably employed through the use of a heat exchanger, as heavy water is much more expensive. Reactors that use other materials for moderation (graphite) may also use normal water for cooling. High-grade industrial water (produced by
reverse osmosis Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane to separate ions, unwanted molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pre ...
or
distillation Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...
) and potable water are sometimes used in industrial plants requiring high-purity cooling water. Production of these high purity waters creates waste byproduct
brine Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for br ...
s containing the concentrated impurities from the source water. In 2018, researchers from the
University of Colorado Boulder The University of Colorado Boulder (CU Boulder, CU, or Colorado) is a public research university in Boulder, Colorado. Founded in 1876, five months before Colorado became a state, it is the flagship university of the University of Colorado syst ...
and
University of Wyoming The University of Wyoming (UW) is a public land-grant research university in Laramie, Wyoming. It was founded in March 1886, four years before the territory was admitted as the 44th state, and opened in September 1887. The University of Wyoming ...
invented a radiative cooling
metamaterial A metamaterial (from the Greek word μετά ''meta'', meaning "beyond" or "after", and the Latin word ''materia'', meaning "matter" or "material") is any material engineered to have a property that is not found in naturally occurring materials. ...
known as "RadiCold", being developed since 2017. This metamaterial aids in cooling of water and increasing the efficiency of power generation, in which it would cool the underneath objects, by reflecting the sun's rays while at the same time allowing the surface to discharge its heat as an infrared thermal radiation.


See also

*
Cooling pond A cooling pond is a man-made body of water primarily formed for the purpose of cooling heated water and/or to store and supply cooling water to a nearby power plant or industrial facility such as a petroleum refinery, pulp and paper mill, chemica ...
*
Deep lake water cooling Deep water source cooling (DWSC) or deep water air cooling is a form of air cooling for process and comfort space cooling which uses a large body of naturally cold water as a heat sink. It uses water at 4 to 10 degrees Celsius drawn from deep area ...
*
Free cooling Free cooling is an economical method of using low external air temperatures to assist in chilling water, which can then be used for industrial processes, or air conditioning systems. The chilled water can either be used immediately or be stored fo ...
*
Full immersion cooling 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 overhea ...
*
Heat pipe A heat pipe is a heat-transfer device that employs phase transition to transfer heat between two solid interfaces. At the hot interface of a heat pipe, a volatile liquid in contact with a thermally conductive solid surface turns into a vapor ...
cooling *
Hopper cooling Hopper cooling is a simple form of water cooling used for small stationary engines. The defining feature of hopper cooling, amongst other water-cooled engines, is that there is no radiator (engine cooling), radiator. Cooling water is heated by the ...
*
Oil cooling Oil cooling is the use of engine oil as a coolant, typically to remove surplus heat from an internal combustion engine. The hot engine transfers heat to the oil which then usually passes through a heat-exchanger, typically a type of radiator kno ...
*
Peltier Peltier is a French surname. Notable people with the surname include: * Autumn Peltier (born 2004), climate activist * Harvey Peltier, Jr. (1923-1980), American politician *Harvey Peltier, Sr. (1899-1977), American politician *Jean Charles Athanase ...
cooling *
Thermosiphon Thermosiphon (or thermosyphon) 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 heat ...
(passive heat exchange)


References


Bibliography

* * * * * King, James J. ''The Environmental Dictionary'' (3rd Edition). John Wiley & Sons (1995). * Reid, George K. ''Ecology in Inland Waters and Estuaries.'' Van Nostrand Reinhold (1961).


External links


Basic Theory and Practice of Cooling Towers


{{DEFAULTSORT:Water Cooling Engine cooling systems Cooling technology Computer hardware cooling Water pollution