The fluid that flows through a device in order to prevent its overheating it’s called a coolant. This is transferring the heat produced by that specific device to other devices that use or dissipate it. The best coolant has the following qualities: low viscosity, high thermal capacity, is low-cost, non-toxic and chemically inert, not producing any damage (corrosion) of the cooling system. Some applications also require the coolant to be an electrical insulator.
While in automotive, residential and commercial temperature-control applications, the term coolant is pretty ‚famous’, in industrial processing, heat transfer fluid is a more used technical term, in high temperature as well as low temperature manufacturing applications.
The 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 low temperatures, is more commonly known as refrigerant.