A coolant is a substance, typically liquid or gas, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosion of the cooling system. Some applications also require the coolant to be an electrical insulator.

• Antifreeze Coolant Color Chart
• Coolant Gauge
• Car Coolant
• Coolant Leak
• Coolant Temperature Sensor
• Coolant Temperature Sensor
• Coolant Flush Cost

While the term 'coolant' is commonly used in automotive and HVAC applications, in industrial processing heat transfer fluid 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 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 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.

Coolant burn-out is the term associated with the effect of temperatures rising above the boiling temperature for the process fluid. From: Tribology of Abrasive Machining Processes, 2004 Related terms. Coolant definition is - a usually fluid cooling agent. Recent Examples on the Web The refrigerator only used 127 grams — roughly one-quarter of a pound — of HFC-134a, and the coolant was tightly sealed in a network of pipes somewhere deep inside. — Phil Mckenna, The Courier-Journal, 'I tried to buy a climate-friendly refrigerator from GE.

Gases[edit]

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 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 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.

Two-phase[edit]

Some coolants are used in both liquid and gas form in the same circuit, taking advantage of 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 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. 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 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.

Liquids[edit]

Water is the most common coolant. Its high heat capacity and low cost makes it a suitable heat-transfer medium. It is usually used with additives, like corrosion inhibitors and antifreeze. Antifreeze, 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 therefore not toxic or difficult to dispose of ecologically.^[1]

• Very pure deionized water, due to its relatively low electrical conductivity, is used to cool some electrical equipment, often high-power transmitters and high-power vacuum tubes.
• Heavy water is a neutron moderator used in some nuclear reactors; it also has a secondary function as their coolant. Light water reactors, both boiling water and pressurised water reactors the most common type, use ordinary (light) water. Some designs, e.g. CANDU reactor, use both types; heavy water in the nonpressurized calandria tank as the moderator and a supplementary coolant, and light water as the primary heat transfer fluid.

Polyalkylene glycol (PAG) 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.^[2]

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 the container or loop system in question.^[3] Many oils have uses encompassing heat transfer, lubrication, pressure transfer (hydraulic fluids), sometimes even fuel, or several such functions at once.

• Mineral oils serve as both coolants and lubricants in many mechanical gears. Some vegetable oils, e.g. castor oil are also used. Due to their high boiling points, mineral oils are used in portable electric radiator-style space heaters in residential applications, and in closed-loop systems for industrial process heating and cooling. Mineral oil is often used in submerged PC systems as it is non-conductive and therefore won't short circuit or damage any parts.
  • Polyphenyl ether oils are suitable for applications needing high temperature stability, very low volatility, inherent lubricity, and/or radiation resistance. Perfluoropolyether oils are their more chemically inert variant.
  • An eutectic mixture of diphenyl ether (73.5%) and biphenyl (26.5%) is used for its wide temperature range and stability to 400°C.
  • Polychlorinated biphenyls and polychlorinated terphenyls were used in heat transfer applications, favored due to their low flammability, chemical resistance, hydrophobicity, and favorable electrical properties, but are now phased out due to their toxicity and bioaccumulation.
• Silicone oils and fluorocarbon oils (like fluorinert) are favored for their wide range of operating temperatures. However their high cost limits their applications.
• Transformer oil is used for cooling and additional electric insulation of high-power electric transformers. Mineral oils are usually used. Silicone oils are employed for special applications. Polychlorinated biphenyls were commonly used in old equipment, which now can possess risk of contamination.

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 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. ^[4]

Freons were frequently used for immersive cooling of e.g. electronics.

Molten metals and salts[edit]

Liquid fusible alloys can be used as coolants in applications where high temperature stability is required, e.g. some fast breedernuclear 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 the possible combinations is the mix of sodium fluoride and sodium tetrafluoroborate (NaF-NaBF₄). Other choices are FLiBe and FLiNaK.

Liquid gases[edit]

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-noiseamplifiers.

Carbon Dioxide (chemical formula is CO₂) - is used as a coolant replacement^[5] for cutting fluids. CO₂ can provide controlled cooling at the cutting interface such that the cutting tool and the workpiece are held at ambient temperatures. The use of CO₂ 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 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 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.

Nanofluids[edit]

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,^[6]titanium dioxide, carbon nanotubes, silica, or metals (e.g. copper, or silvernanorods) dispersed into the carrier liquid enhance the heat transfer capabilities of the resulting coolant compared to the carrier liquid alone.^[7] 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.^[8]

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 the thermal conductivity of water by 68%, and 0.5 vol.% of silver nanorods increased thermal conductivity of ethylene glycol based coolant by 98%.^[9] 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 the formation of the steam layer.^[10]Nanofluid with the concentration more than 5% acts like non-Newtonian fluids.

Solids[edit]

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 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.

References[edit]

1. ^Betaine as coolantArchived 2011-04-09 at the Wayback Machine
2. ^Duratherm Extended Life Fluids
3. ^Paratherm Corporation
4. ^Sturgess, Steve (August 2009). 'Column: Keep Your Cool'. Heavy Duty Trucking. Retrieved April 2, 2018.
5. ^ctemag.com
6. ^'Noghrehabadi Bibliography'. Archived from the original on November 13, 2013. Retrieved November 13, 2013.
7. ^Wang, Xiang-Qi; Mujumdar, Arun S. (December 2008). 'A review on nanofluids - part II: experiments and applications'. Brazilian Journal of Chemical Engineering. 25 (4): 631–648. doi:10.1590/S0104-66322008000400002.
8. ^scienceblog.comArchived January 5, 2010, at the Wayback Machine
9. ^Oldenburg, Steven J.; Siekkinen, Andrew R.; Darlington, Thomas K.; Baldwin, Richard K. (9 July 2007). 'Optimized Nanofluid Coolants for Spacecraft Thermal Control Systems'. SAE Technical Paper Series. 1. pp. 2007–01–3128. doi:10.4271/2007-01-3128.
10. ^mit.edu

Antifreeze Coolant Color Chart

External links[edit]

Coolant Gauge

Gasoline engines, diesel engines, hybrid vehicles, and even electric cars naturally create heat. When you use your car’s heater, some of this heat is channeled into the cabin for your comfort. A majority of the heat, however, must be managed another way.

To ensure the engine stays at an optimal operating temperature, your car relies on a fluid called antifreeze, or engine coolant. Driving with low coolant could let your engine get too hot, which usually spells trouble for your engine, your vehicle, and your journey!

Car Coolant

Effects of Low Coolant in Car

Driving with low coolant can damage certain parts of your vehicle, which could require major repairs. Here are some things that can happen if you drive with low coolant.

Your engine could overheat.

Coolant helps pull heat away from the engine. So, without enough coolant, the engine could overheat or seize up. Continued use of an overheated engine could lead to permanent damage, such as pistons welding to the cylinders.

You could blow a head gasket.

If you’ve ever said, “I am about to blow a gasket,” to describe your mood — you know that this happening to your engine is bad news! Low coolant can sometimes cause a head gasket on your engine block to blow. If this happens, you may notice smoke emitting from the engine or tailpipe, a loss of power, engine knocking sounds, or decreased efficiency.

Your car could shut off.

Coolant Leak

Some cars have a safety system in place to automatically shut the engine off before it suffers significant damage — which can happen due to low coolant. While this may help save you from extensive repairs stemming from an overheated engine, it can be very dangerous depending on where you are driving when the engine shuts off.

Low Coolant Symptoms

Coolant Temperature Sensor

Low coolant symptoms can vary depending on how low your vehicle is on antifreeze. Typically, low coolant will trigger your antifreeze light. Some vehicles might display a “Check Coolant” message on the dashboard. If your coolant light is on, you may notice some of these oddities.

Coolant Temperature Sensor

The high-temperature gauge is near or in the red.

One tell-tale sign of low coolant is the high-temperature gauge on the dashboard. This gauge is designed to tell you when the engine is getting too hot. Most often, the gauge should stay near the center of the H and C symbols. If the gauge is reading close to the H, shut your engine down and have it towed to a Firestone Complete Auto Care near you for repairs.

The A/C system is malfunctioning.

When you use your vehicle’s heat, the coolant helps regulate the flow of hot air into the cabin. If the coolant is low and your air conditioning is running, you may notice hot air coming from your car A/C vents. (Psst! In winter, try these tips to stay warm when your heat isn’t working!)

There’s a sweet-smelling odor.

When there’s a coolant leak in your vehicle, you may notice a sweet smell in your air conditioning or under the hood. This is because antifreeze contains glycol, a sweet, viscous liquid used to help regulate the freezing and boiling point of water. While strange odors may be a sign of car issues, they are not always a clear indicator. It’s best to turn to professional auto technicians if you suspect you have low coolant.

Coolant Flush Cost

Your Coolant Level Sensor is faulty.

Sometimes, an illuminated coolant light may be due to a faulty coolant level sensor. If this sensor malfunctions, it could be causing the coolant light to turn on even if you don’t have low antifreeze levels.

Causes of Coolant Loss

Unlike engine oil, which can be changed as frequently as 3,000-5,000 miles, you normally don’t have to check and replace coolant as often. In fact, since coolant works within a closed system, it shouldn’t become low unless there’s a leak, in which case you should visit your local car care experts for radiator services and repairs. There are a few common ways in which coolant fluid can leak:

• External leaks from radiator hoses, connections between hoses, or from the radiator itself
• Radiator cap leaks due to a faulty seal on the cap where the pressurized coolant can leak out
• Internal leaks where coolant may leak out of places such as the engine’s head gasket

If you suspect that your vehicle has a coolant leak, visit a Firestone Complete Auto Care near you for a comprehensive system inspection. Whether you have a faulty Coolant Level Sensor or an internal leak, we’ll diagnose your low coolant issue, recommend the necessary repairs, and get you back on the road with a car that’s Fixed Right. Priced Right. Right on Time.