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49-411: A radiator is always a source of heat to its environment, although this may be for either the purpose of heating an environment, or for cooling the fluid or coolant supplied to it, as for automotive engine cooling and HVAC dry cooling towers. Despite the name, most radiators transfer the bulk of their heat via convection instead of thermal radiation . The Roman hypocaust is an early example of

98-458: A dioyl dichloride or dioic acid is required to continue the process of polymerization through repeated esterification processes. A diol can be converted to cyclic ether by using an acid catalyst, this is diol cyclization . Firstly, it involves protonation of the hydroxyl group. Then, followed by intramolecular nucleophilic substitution, the second hydroxyl group attacks the electron deficient carbon. Provided that there are enough carbon atoms that

147-410: A phase transition , with the latent heat adding to the cooling efficiency. The latter, when used to achieve below- ambient temperature , is more commonly known as refrigerant . Air is a common form of a coolant. Air cooling uses either convective airflow (passive cooling), or a forced circulation using fans . Hydrogen is used as a high-performance gaseous coolant. Its thermal conductivity

196-546: A common ingredient of antifreeze products. Another example is propane-1,2-diol , or alpha propylene glycol, HO−CH 2 −CH(OH)−CH 3 , used in the food and medicine industry, as well as a relatively non-poisonous antifreeze product. On commercial scales, the main route to vicinal diols is the hydrolysis of epoxides . The epoxides are prepared by epoxidation of the alkene. An example in the synthesis of trans-cyclohexanediol or by microreactor : For academic research and pharmaceutical areas, vicinal diols are often produced from

245-406: A lower heat capacity and density than liquid coolants, a fairly large volume flow rate (relative to the coolant's) must be blown through the radiator core to capture the heat from the coolant. Radiators often have one or more fans that blow air through the radiator. To save fan power consumption in vehicles, radiators are often behind the grille at the front end of a vehicle. Ram air can give

294-438: A portion or all of the necessary cooling air flow when the coolant temperature remains below the system's designed maximum temperature, and the fan remains disengaged. As electronic devices become smaller, the problem of dispersing waste heat becomes more difficult. Tiny radiators known as heat sinks are used to convey heat from the electronic components into a cooling air stream. Heatsinks do not use water, rather they conduct

343-433: A solution of a suitable organic chemical (most often ethylene glycol , diethylene glycol , or propylene glycol ) in water, is used when the water-based coolant has to withstand temperatures below 0 °C, or when its boiling point has to be raised. Betaine is a similar coolant, with the exception that it is made from pure plant juice, and is not toxic or difficult to dispose of ecologically. Polyalkylene glycol (PAG)

392-557: A type of radiator for building space heating. Franz San Galli , a Prussian-born Russian businessman living in St. Petersburg , is credited with inventing the heating radiator around 1855, having received a radiator patent in 1857, but American Joseph Nason developed a primitive radiator in 1841 and received a number of U.S. patents for hot water and steam heating. Heat transfer from a radiator occurs by two mechanisms: thermal radiation and convection into flowing air or liquid. Conduction

441-496: Is (F 3 C) 2 C(OH) 2 , the hydrated form of hexafluoroacetone . Many gem-diols undergo further condensation to give dimeric and oligomeric derivatives. This reaction applies to glyoxal and related aldehydes . In a vicinal diol, the two hydroxyl groups occupy vicinal positions, that is, they are attached to adjacent atoms. These compounds are called glycols (though the term can be used more widely). Examples include ethane-1,2-diol or ethylene glycol HO−(CH 2 ) 2 −OH,

490-402: Is CO 2 ) - is used as a coolant replacement for cutting fluids. CO 2 can provide controlled cooling at the cutting interface such that the cutting tool and the workpiece are held at ambient temperatures. The use of CO 2 greatly extends tool life, and on most materials allows the operation to run faster. This is considered a very environmentally friendly method, especially when compared to

539-423: Is a chemical compound containing two hydroxyl groups ( −OH groups). An aliphatic diol may also be called a glycol . This pairing of functional groups is pervasive, and many subcategories have been identified. They are used as protecting groups of carbonyl groups , making them essential in synthesis of organic chemistry. The most common industrial diol is ethylene glycol . Examples of diols in which

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588-426: Is also used for fire protection of structures, where ablative coating is applied. Dry ice and water ice can be also used as coolants, when in direct contact with the structure being cooled. Sometimes an additional heat transfer fluid is used; water with ice and dry ice in acetone are two popular pairings. Sublimation of water ice was used for cooling the space suit for Project Apollo . Glycol A diol

637-522: Is frequently used in large commercial systems, and sulfur dioxide was used in early mechanical refrigerators. Carbon dioxide (R-744) is used as a working fluid in climate control systems for cars, residential air conditioning, commercial refrigeration, and vending machines. Many otherwise excellent refrigerants are phased out for environmental reasons (the CFCs due to ozone layer effects, now many of their successors face restrictions due to global warming, e.g.

686-464: Is higher than all other gases, it has high specific heat capacity , low density and therefore low viscosity , which is an advantage for rotary machines susceptible to windage losses. Hydrogen-cooled turbogenerators are currently the most common electrical generators in large power plants. Inert gases are used as coolants in gas-cooled nuclear reactors . Helium has a low tendency to absorb neutrons and become radioactive . Carbon dioxide

735-456: Is not directly exposed. To increase the surface area available for heat exchange with the surroundings, a radiator will have multiple fins, in contact with the tube carrying liquid pumped through the radiator. Air (or other exterior fluid) in contact with the fins carries off heat. If air flow is obstructed by dirt or damage to the fins, that portion of the radiator is ineffective at heat transfer. Radiators are commonly used to heat buildings on

784-414: Is not normally a major source of heat transfer in radiators. A radiator may even transfer heat by phase change , for example, drying a pair of socks. In practice, the term "radiator" refers to any of a number of devices in which a liquid circulates through exposed pipes (often with fins or other means of increasing surface area). The term " convector " refers to a class of devices in which the source of heat

833-446: Is one technical term more often used in high temperature as well as low-temperature manufacturing applications. The term also covers cutting fluids . Industrial cutting fluid has broadly been classified as water-soluble coolant and neat cutting fluid. Water-soluble coolant is oil in water emulsion. It has varying oil content from nil oil (synthetic coolant). This coolant can either keep its phase and stay liquid or gaseous, or can undergo

882-486: Is reduced using the Cannizzaro reaction or by catalytic hydrogenation : 2,2-Disubstituted propane-1,3-diols are prepared in this way. Examples include 2-methyl-2-propyl-1,3-propanediol and neopentyl glycol . 1,3-Diols can be prepared by hydration of α,β-unsaturated ketones and aldehydes. The resulting keto-alcohol is hydrogenated. Another route involves the hydroformylation of epoxides followed by hydrogenation of

931-663: Is required, e.g. some fast breeder nuclear reactors . Sodium (in sodium cooled fast reactors ) or sodium- potassium alloy NaK are frequently used; in special cases lithium can be employed. Another liquid metal used as a coolant is lead , in e.g. lead cooled fast reactors , or a lead- bismuth alloy. Some early fast neutron reactors used mercury . For certain applications the stems of automotive poppet valves may be hollow and filled with sodium to improve heat transport and transfer. For very high temperature applications, e.g. molten salt reactors or very high temperature reactors , molten salts can be used as coolants. One of

980-417: Is the best known example encountered in laboratories. The phase change may not occur at the cooled interface, but on the surface of the liquid, to where the heat is transferred by convective or forced flow. Water is the most common coolant. Its high heat capacity and low cost make it a suitable heat-transfer medium. It is usually used with additives, like corrosion inhibitors and antifreeze . Antifreeze,

1029-495: Is used as high temperature, thermally stable heat transfer fluids exhibiting strong resistance to oxidation. Modern PAGs can also be non-toxic and non-hazardous. Cutting fluid is a coolant that also serves as a lubricant for metal-shaping machine tools . Oils are often used for applications where water is unsuitable. With higher boiling points than water, oils can be raised to considerably higher temperatures (above 100 degrees Celsius) without introducing high pressures within

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1078-487: Is used in Magnox and AGR reactors. Sulfur hexafluoride is used for cooling and insulating of some high-voltage power systems ( circuit breakers , switches , some transformers , etc.). Steam can be used where high specific heat capacity is required in gaseous form and the corrosive properties of hot water are accounted for. Some coolants are used in both liquid and gas form in the same circuit, taking advantage of

1127-459: Is used to cool nozzles of rocket engines . Waterless coolant is used as an alternative to conventional water and ethylene glycol coolants. With higher boiling points than water (around 370F), the cooling technology resists boil over. The liquid also prevents corrosion . Freons were frequently used for immersive cooling of e.g. electronics. Liquid fusible alloys can be used as coolants in applications where high temperature stability

1176-474: The oxidation of alkenes , usually with dilute acidic potassium permanganate or Osmium tetroxide. Osmium tetroxide can similarly be used to oxidize alkenes to vicinal diols. The chemical reaction called Sharpless asymmetric dihydroxylation can be used to produce chiral diols from alkenes using an osmate reagent and a chiral catalyst . Another method is the Woodward cis-hydroxylation (cis diol) and

1225-631: The European continent. In a radiative central heating system , hot water or sometimes steam is generated in a central boiler and circulated by pumps through radiators within the building, where this heat is transferred to the surroundings. In some countries, portable radiators are common to heat a single room, as a safer alternative to space heater and fan heater . Radiators are used in dry cooling towers and closed-loop cooling towers for cooling buildings using liquid-cooled chillers for heating, ventilation, and air conditioning (HVAC) while keeping

1274-478: The R134a). Heat pipes are a special application of refrigerants. Water is sometimes employed this way, e.g. in boiling water reactors . The phase change effect can be intentionally used, or can be detrimental. Phase-change materials use the other phase transition between solid and liquid. Liquid gases may fall here, or into refrigerants, as their temperature is often maintained by evaporation. Liquid nitrogen

1323-549: The aldehyde. This method has been used for 1,3-propanediol from ethylene oxide . More specialized routes to 1,3-diols involves the reaction between an alkene and formaldehyde , the Prins reaction . 1,3-diols can be produced diastereoselectively from the corresponding β-hydroxy ketones using the Evans–Saksena , Narasaka–Prasad or Evans–Tishchenko reduction protocols. 1,3-Diols are described as syn or anti depending on

1372-532: The angle strain is not too much, a cyclic ether can be formed. 1,2-diols and 1,3-diols can be protected using a protecting group. Protecting groups are used so that the functional group does not react to future reactions. Benzylidene groups are used to protect 1,3-diols. There are extremely useful in biochemistry as shown below of a carbohydrate derivative being protected. Diols can also be used to protect carbonyl groups. They are commonly used and are quite efficient at synthesizing cyclic acetals. These protect

1421-595: The carbonyl groups from reacting from any further synthesis until it is necessary to remove them. The reaction below depicts a diol being used to protect a carbonyl using zirconium tetrachloride. Diols can also be converted to lactones employing the Fétizon oxidation reaction. In glycol cleavage , the C−C bond in a vicinal diol is cleaved with formation of ketone or aldehyde functional groups. See Diol oxidation . In general, organic geminal diols readily dehydrate to form

1470-488: The carrier liquid enhance the heat transfer capabilities of the resulting coolant compared to the carrier liquid alone. The enhancement can be theoretically as high as 350%. The experiments however did not prove so high thermal conductivity improvements, but found significant increase of the critical heat flux of the coolants. Some significant improvements are achievable; e.g. silver nanorods of 55±12 nm diameter and 12.8 μm average length at 0.5 vol.% increased

1519-446: The chiller coolant isolated from the surroundings. Radiators are used for cooling internal combustion engines , mainly in automobiles but also in piston-engined aircraft, railway locomotives , motorcycles , stationary generating plants and other places where heat engines are used ( watercrafts , having an unlimited supply of a relatively cool water outside, usually use the liquid-liquid heat exchangers instead). To cool down

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1568-468: The container or loop system in question. Many oils have uses encompassing heat transfer, lubrication, pressure transfer (hydraulic fluids), sometimes even fuel, or several such functions at once. Fuels are frequently used as coolants for engines. A cold fuel flows over some parts of the engine, absorbing its waste heat and being preheated before combustion. Kerosene and other jet fuels frequently serve in this role in aviation engines. Liquid hydrogen

1617-484: The coolant; today, however, all but the smallest engines use pumps . Up to the 1980s, radiator cores were often made of copper (for fins) and brass (for tubes, headers, and side-plates, while tanks could also be made of brass or of plastic , often a polyamide ). Starting in the 1970s, use of aluminium increased, eventually taking over the vast majority of vehicular radiator applications. The main inducements for aluminium are reduced weight and cost. Since air has

1666-427: The formation of the steam layer. Nanofluid with the concentration more than 5% acts like non-Newtonian fluids . In some applications, solid materials are used as coolants. The materials require high energy to vaporize; this energy is then carried away by the vaporized gases. This approach is common in spaceflight , for ablative atmospheric reentry shields and for cooling of rocket engine nozzles . The same approach

1715-417: The heat engine, a coolant is passed through the engine block , where it absorbs heat from the engine. The hot coolant is then fed into the inlet tank of the radiator (located either on the top of the radiator, or along one side), from which it is distributed across the radiator core through tubes to another tank on the opposite end of the radiator. As the coolant passes through the radiator tubes on its way to

1764-512: The heat from the source. High-performance heat sinks have copper to conduct better. Heat is transferred to the air by conduction and convection; a relatively small proportion of heat is transferred by radiation owing to the low temperature of semiconductor devices compared to their surroundings. Radiators are also used in liquid cooling loops for rejecting heat. Radiators are found as components of some spacecraft. These radiators work by radiating heat energy away as light (generally infrared given

1813-431: The high specific latent heat of boiling/condensing phase change , the enthalpy of vaporization , in addition to the fluid's non-phase-change heat capacity . Refrigerants are coolants used for reaching low temperatures by undergoing phase change between liquid and gas. Halomethanes were frequently used, most often R-12 and R-22 , often with liquified propane or other haloalkanes like R-134a . Anhydrous ammonia

1862-492: The hydroxyl functional groups are more widely separated include 1,4-butanediol HO−(CH 2 ) 4 −OH and propylene-1,3-diol , or beta propylene glycol, HO−CH 2 −CH 2 −CH 2 −OH . A geminal diol has two hydroxyl groups bonded to the same atom. These species arise by hydration of the carbonyl compounds. The hydration is usually unfavorable, but a notable exception is formaldehyde which, in water, exists in equilibrium with methanediol H 2 C(OH) 2 . Another example

1911-423: The industrial perspective, the dominant reactions of the diols is in the production of polyurethanes and alkyd resins . Diols react as alcohols , by esterification and ether formation. Diols such as ethylene glycol are used as co- monomers in polymerization reactions forming polymers including some polyesters and polyurethanes . A different monomer with two identical functional groups, such as

1960-615: The most powerful superconducting magnets , are reached using liquid helium . Liquid hydrogen at -250 to -265 °C can also be used as a coolant. Liquid hydrogen is also used both as a fuel and as a coolant to cool nozzles and combustion chambers of rocket engines . A new class of coolants are nanofluids which consist of a carrier liquid, such as water, dispersed with tiny nano-scale particles known as nanoparticles . Purpose-designed nanoparticles of e.g. CuO , alumina , titanium dioxide , carbon nanotubes , silica , or metals (e.g. copper , or silver nanorods ) dispersed into

2009-402: The opposite tank, it transfers much of its heat to the tubes which, in turn, transfer the heat to the fins that are lodged between each row of tubes. The fins then release the heat to the ambient air. Fins are used to greatly increase the contact surface of the tubes to the air, thus increasing the exchange efficiency. The cooled liquid is fed back to the engine, and the cycle repeats. Normally,

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2058-436: The possible combinations is the mix of sodium fluoride and sodium tetrafluoroborate (NaF-NaBF 4 ). Other choices are FLiBe and FLiNaK . Liquified gases are used as coolants for cryogenic applications, including cryo-electron microscopy , overclocking of computer processors, applications using superconductors , or extremely sensitive sensors and very low- noise amplifiers . Carbon Dioxide (chemical formula

2107-418: The radiator does not reduce the temperature of the coolant back to ambient air temperature, but it is still sufficiently cooled to keep the engine from overheating. This coolant is usually water-based, with the addition of glycols to prevent freezing and other additives to limit corrosion , erosion and cavitation . However, the coolant may also be an oil. The first engines used thermosiphons to circulate

2156-414: The related Prévost reaction (anti diol), which both use iodine and the silver salt of a carboxylic acid. Other routes to vic-diols are the hydrogenation of acyloins and the pinacol coupling reaction. 1,3-Diols are often prepared industrially by aldol condensation of ketones with formaldehyde . You can use many different starting materials to produce syn- or anti-1,3-diols. The resulting carbonyl

2205-499: The relative stereochemistries of the carbon atoms bearing the hydroxyl functional groups. Zincophorin is a natural product that contains both syn and anti 1,3-diols. Diols where the hydroxyl groups are separated by several carbon centers are generally prepared by hydrogenation of diesters of the corresponding dicarboxylic acids : 1,4-butanediol , 1,5-pentanediol , 1,6-hexanediol , and 1,10-decanediol  [ es ] are important precursors to polyurethanes . From

2254-408: The temperature of a system. An ideal coolant has high thermal capacity , low viscosity , is low-cost, non-toxic , chemically inert and neither causes nor promotes corrosion of the cooling system. Some applications also require the coolant to be an electrical insulator . While the term "coolant" is commonly used in automotive and HVAC applications, in industrial processing heat-transfer fluid

2303-499: The temperatures at which spacecraft try to operate) because in the vacuum of space neither convection nor conduction can work to transfer heat away. On the International Space Station , these can be seen clearly as large white panels attached to the main truss . They can be found on both crewed and uncrewed craft. Coolant A coolant is a substance, typically liquid, that is used to reduce or regulate

2352-422: The thermal conductivity of water by 68%, and 0.5 vol.% of silver nanorods increased thermal conductivity of ethylene glycol based coolant by 98%. Alumina nanoparticles at 0.1% can increase the critical heat flux of water by as much as 70%; the particles form rough porous surface on the cooled object, which encourages formation of new bubbles, and their hydrophilic nature then helps pushing them away, hindering

2401-557: The use of petroleum oils as lubricants; parts remain clean and dry which often can eliminate secondary cleaning operations. Liquid nitrogen , which boils at about -196 °C (77K), is the most common and least expensive coolant in use. Liquid air is used to a lesser extent, due to its liquid oxygen content which makes it prone to cause fire or explosions when in contact with combustible materials (see oxyliquits ). Lower temperatures can be reached using liquified neon which boils at about -246 °C. The lowest temperatures, used for

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