WHAT IS A NANOFLUID? 30/06/2022 by A nanofluid is a fluid containing stably suspended nanoparticles with dimensions smaller than 100 nanometers (one billionth of a meter). The term “nanofluid” was first used by Choi (1995) to describe this new class of nanotechnology-based heat transfer fluids with enhanced thermal properties. In the past 10 years, the US Government has co-authored patents on two different nanofluids.