Coolant is a kind of substance that is either in gas or liquid form that’s being used to regulate or reduce 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. 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. Now say for example that the latter is put into use to achieve below ambient temperature, then it is known as refrigerant.
Air is a very common form of coolant in the market. There are a couple of ways to which air cooling is used and it’s through passive cooling or also known as convective airflow as well as forced circulation by making use of fans. Hydrogen is being used as well for high performance gaseous coolant. 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.
The inert gases are being used as coolants for gas cooled nuclear reactors. The helium has low tendency of absorbing neutrons and becoming radioactive. In reality, AGR reactors and Magnox are mixed with carbon dioxide. On the other hand, sulfur hexafluoride is used to cool and insulate some high voltage power systems like 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 very common type of coolant is water. The low cost and high heat capacity it has makes it ideal for heat transfer medium. It is usually used with additives such as 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. Because of the low electrical conductivity of pure de-ionized water, it’s widely used for regulating the temperature on electrical equipment.