Heat transfer fluid

Any gas or liquid specifically manufactured for the purpose of transmitting heat from one system to another.

A coolant for instance is a fluid that flows through a device in order to prevent its overheating, such as water cooling down a car engine.

In a solar collector, a heat transfer fluid heats up in the collector under the effect of the sun and then flows through a heat exchange to warm a separate tank of water providing hot water for domestic use or for heating a building.

Source: GreenFacts

PCBs