Coolant is a substance that comes in liquid or gas form and used in regulating or reducing temperature of the system. The ideal coolant is something that has low viscosity, low-cost, chemically inert, non toxic, has high thermal capacity and neither promotes nor cause corrosion of cooling system. Some applications need the coolant to be electrical insulator too.
When the term coolant is used, we often associate it to automotive as well as HVAC applications but industrial coolant is a lot different since it’s more of a technical aspect and used generally in low and high temperature manufacturing applications. The term is covering cutting fluids at the same time. Coolants may stay on its phase, gaseous or liquid or, it may undergo a transition with latent heat adding to efficiency of cooling. Now say for example that the latter is put into use to achieve below ambient temperature, then it is known as refrigerant.
A common type of coolant in the market 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. Thermal conductivity is higher in comparison to other gases because it has low density and high specific heat density and for that, it’s low viscosity that is a big benefit for systems using rotary machines that are susceptible to windage losses. Currently, many big power plants are using hydrogen cooled turbo generators in their electrical generator.
Inert gases are used as coolants for the gas cooled nuclear reactors. Helium has this low tendency to absorb neutrons and become radioactive. Actually, carbon dioxide is also used for mixing it 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. The steam however could be used where there’s high specific heat capacity that’s required in gaseous form.
A very common type of coolant 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. Antifreeze solution is made out of suitable organic chemicals oftentimes diethylene glycol, propylene glycol or ethylene glycol in water. A similar coolant is betain but with an exception that it’s manufactured using pure plant juice. The pure de-ionized water is utilized to cool electrical equipment because of its low electrical conductivity.