Coolant is that type of substance that is used for reducing or regulating the system’s temperature that comes in gas or liquid form. The best coolants you can get is something that have low viscosity, low-cost, chemically inert, non toxic, has high thermal capacity and not promoting or causing corrosion of the cooling system. As a matter of fact, few applications for such need it to be good electrical insulator too.
While the phrase coolant is referred often to HVAC and automotive applications, industrial coolant is more of a technical as it’s found in heat transfer fluid that are frequently used in low and high temperature manufacturing applications. This term covers cutting fluids too. As for the coolants, it can actually stay on its phase, gaseous or liquid and at times, it undergoes a transition with latent heat which then adds the cooling efficiency. When the latter is used to attain below ambient temperature, it is called automatically as refrigerant.
One typical type of coolant that is used today is air. Air cooling is using either forced circulation using fans or, convective airflow otherwise known as passive cooling. For the high performance gaseous coolant, hydrogen is what being used most of the time. The thermal conductivity is a lot higher compared to all other gases, it has low density and high specific heat density and as a result, low viscosity which is actually a benefit for rotary machines that are vulnerable to windage losses. Currently, many big power plants are using hydrogen cooled turbo generators in their electrical generator.
As for nuclear reactors that are gas cooled, what is used in this purpose is inert gases. Helium basically has low tendency to absorb neutrons and for that, the odds of it becoming radioactive is less. Carbon dioxide is actually used to be mixed with AGR reactors and Magnox. In regards to sulfur hexafluoride however, this is utilized to insulate and even cool high voltage power systems; to give you examples, it can be switches, transformers, circuit breakers and so on. Whenever there is a need for high specific heat capacity in gaseous form, then expect that steam is what used.
A popular type of coolant used is water. Its low cost as well as high heat capacity has made it ideal for heat transfer medium. Most of the time, technicians are combining it with additives like antifreeze as well as corrosion inhibitors. In most cases, diethylene glycol, propylene glycol or ethylene glycol mixed in water is the components of antifreeze. Betain however is made using pure plant juice but is likely similar with water coolants. Pure de-ionized water is used for cooling electrical equipment due to its low electrical conductivity.