Nanofluids are gaining importance nowadays in cooling applications due to their enhanced thermophysical and heat transfer characteristics. As researchers treat nanofluids as bulk macroscale continuum fluids, it is challenging to understand the nanoscale aspects of a nanofluid. From the heat transfer point of view, nanofluids can be treated as a bulk fluid with a separate set of properties. Nanofluids may be defined as a dilute colloidal suspension of nanometer-sized particles dispersed in a base fluid, as shown in Fig. 8.1. A colloidal dispersion is formed by mixing the insoluble solid particles with base fluids, such as water or ethylene glycol. The examples of nanofluids include Al \(_2\) O \(_3\) –water, CuO–water, and Cu–water.