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Water cooling is a method of heat removal from components and industrial equipment. Evaporative cooling using water is often more efficient than air cooling. Water is inexpensive and non-toxic; however, it can contain impurities and cause corrosion.
Water cooling is commonly used for cooling automobile internal combustion engines and power stations. Water coolers utilising convective heat transfer are used inside high-end personal computers to lower the temperature of and other components.
Other uses include the cooling of lubricant oil in ; for cooling purposes in ; for cooling in HVAC and in .
Water contains varying amounts of impurities from contact with the atmosphere, soil, and containers. Being both an electrical conductor and a solvent for metal ions and oxygen, water can accelerate corrosion of machinery being cooled. Corrosion reactions proceed more rapidly as temperature increases. Preservation of machinery in the presence of hot water has been improved by addition of corrosion inhibitors including zinc, chromates and phosphates. The first two have toxicity concerns; and the last has been associated with eutrophication. 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 occurs because water is a favorable environment for many life forms. Flow characteristics of recirculating cooling water systems encourage colonization by sessile organisms using the circulating supply of food, oxygen and nutrients. Temperatures may become high enough to support thermophilic populations of organisms such as types of fungi. 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 more susceptible to biofouling. Biofouling may be inhibited by temporary habitat modifications. Temperature differences may discourage the establishment of thermophilic populations in intermittently operated facilities, and intentional short-term temperature spikes may periodically kill less tolerant populations. have been commonly used to control biofouling where sustained facility operation is required.
Chlorine may be added in the form of hypochlorite to decrease biofouling in cooling water systems, but is later reduced to chloride to minimize the 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 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 or with zinc and chromates or similar compounds have been maintained in cooling systems to keep heat exchange surfaces clean enough that a film of gamma iron oxide and zinc phosphate can inhibit corrosion by passivating anodic and cathodic reaction points. These increase salinity and total dissolved solids, and phosphorus 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 lower chromate concentrations and the use of less-flexible corrosion inhibitors. Blowdown may also contain chromium leached from cooling towers constructed of wood preserved with chromated copper arsenate.
Total dissolved solids or TDS (sometimes called filterable residue) is reported as the mass of residue remaining when a measured volume of filtered water is . Salinity indicates water density or conductivity changes caused by dissolved materials. Probability of scale formation increases with increasing total dissolved solids. Solids commonly associated with scale formation are calcium and magnesium both as carbonate and sulfate. 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. Increasing oxygen concentrations accelerate corrosion. Dissolved oxygen approaches saturation levels in cooling towers. It is beneficial in blowdown or OTC water being returned to natural aquatic environments.
Water ionizes into hydronium (H3O+) and hydroxide (OH−) . The concentration of ionized hydrogen (as protonated water) in a cooling water system is reported as the pH level. Low pH values increase the rate of corrosion; high pH values encourage scale formation. Amphoterism is uncommon among metals used in water cooling systems, but aluminum corrosion rates increase with pH values above 9. Galvanic corrosion may be severe in water systems with copper and aluminum components. Acid can be added to cooling water systems to prevent scale formation if the pH decrease will offset increased salinity and dissolved solids.
Once-through cooling (OTC) systems may be used on very large rivers or at coastal and estuarine sites. These power stations put the waste heat into the river or coastal water. These OTC systems thus rely upon an ample supply of river water or seawater for their cooling needs. Such facilities are built with intake structures designed for bringing 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 fish screen.EPA (2014). "Cooling Water Intakes." Large flow rates may trap slow-swimming organisms including fish and shrimp on fish screen protecting the small bore tubes of the heat exchangers from blockage. High temperatures or pump turbulence and shear may kill or disable smaller organisms that pass through the screens entrained with the cooling water. More than 1,200 power plants and manufacturing facilities in the U.S. use OTC systems; the intake structures kill billions of fish and other organisms each year. More-agile aquatic consume organisms impinged on the screens; and warm water predators and colonize the cooling water discharge to feed on entrained organisms.
The U.S. Clean Water Act required the Environmental Protection Agency (EPA) to issue on industrial cooling water intake structures.United States. Clean Water Act, Section 316(b), . EPA issued final regulations for new facilities in 2001 (amended 2003),EPA. Cooling Water Intake Structures. Final rule: 2001-12-18, . Amended: 2003-06-19, . and for existing facilities in 2014.EPA. "National Pollutant Discharge Elimination System—Final Regulations To Establish Requirements for Cooling Water Intake Structures at Existing Facilities and Amend Requirements at Phase I Facilities" Final rule. Federal Register, . 2014-08-15.
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 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 in 1982, which used Fluorinert. Through the 1990s, water cooling for home PCs slowly gained recognition among enthusiasts, but it became 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 for many computer components, but usually it is used for the CPU cooling and GPUs. Water cooling typically uses a water block, a pump, and a water-to-air heat exchanger. By transferring device heat to a separate larger heat exchanger using larger, lower-speed fans, water cooling can allow quieter operation, improved processor speeds (overclocking), or a balance of both. Less commonly, Northbridges, Southbridges, Hard disk, memory, voltage regulator modules (VRMs), and even Power supply can be water-cooled.
Internal radiator size may vary: from 40 mm dual fan (80 mm) to 140 quad fan (560 mm) and thickness from 30 mm to 80 mm. 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 allow 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 removed from the system by bleeding. The capped line may be capped with a fill-port fitting to allow the release of trapped gas and the addition of liquid.
Water coolers for desktop computers were, until the end of the 1990s, homemade. They were made from car radiators (or more commonly, a car's heater core), aquarium 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. 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 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 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 of water vapour from the air on chilled surfaces. Common places from which to obtain the required phase transition systems are a household dehumidifier or air conditioner.
An alternative cooling scheme, which also enables components to be cooled below the ambient temperature while obviating 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 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 was the first mainstream desktop computer to have water cooling as standard (although only on its fastest models). Dell followed suit by shipping their XPS computers with liquid cooling, using thermoelectric cooling to help cool the liquid. Currently, Dell's only computers to offer liquid cooling are their Alienware 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.
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; however, by the end of the war lighter weapons that rivaled 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 in Sweden relies on snow-cooling from Meltwater to cool its data centers, medical equipment, and maintain a comfortable ambient temperature.
Some nuclear reactors use heavy water as coolant. Heavy water is employed in because it is a weaker neutron absorber. 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) RBMK.
High-grade industrial water (produced by reverse osmosis or distillation) and potable water are sometimes used in industrial plants requiring high-purity cooling water. Production of these high-purity waters creates waste byproduct containing the concentrated impurities from the source water.
In 2018, researchers from the University of Colorado Boulder and University of Wyoming invented a radiative cooling metamaterial known as "RadiCold", which has been 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 away the sun's rays while at the same time allowing the surface to discharge its heat as infrared thermal radiation.
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