2. Nanofluids: Definition & Classification

The need of advanced heat transfer fluid leads to develop nanofluids. Nanofluids are the conventional heat transfer fluids containing solid nanoparticles. The chapter deals with basic introduction of nanofluids, development history of nanofluids and different classifications of nanofluids. Different conventional fluids have been used as the working fluid to transfer the heat in various processes. As a working fluid, water is used extensively due to its immense availability, but not considered as an efficient heat carrier due to low thermal conductivity. The alternates of water, like engine oil, ethylene glycol, etc., are also applied to the various applications, but higher viscosity and toxic nature have restricted the employability of these substitutes in the heat transfer processes. Thus, water has remained the only accessible option as working fluids. However, during the last few decades, it is observed by the researchers that these conventional working fluids have low thermophysical properties which confine the convection heat transfer rate. Hence, by improving the thermophysical properties of the working fluids, the heat transfer can be increased. Nanofluids could be a new dawn to the highly efficient heat flow technologies