Thermal performance enhancement in nanofluids containing diamond nanoparticles

Nanofluids, nanoparticle suspensions prepared by dispersing nanoscale particles in a base fluid, have been gaining interest lately due to their potential to greatly outperform traditional thermal transport liquids. Diamond has the highest thermal transport capacity in nature and diamond particles are often used as filler in mixtures for upgrading the performance of a matrix. It is reasonable to expect that the addition of diamond nanoparticles (DNPs) would lead to thermal performance enhancement in a base fluid. In this study, homogeneous and stable nanofluids composed of DNPs as the inclusions and a mixture of ethylene glycol (EG) and water as base fluid have been prepared. Acid mixtures of perchloric acid, nitric acid and hydrochloric acid were employed to purify and tailor the DNPs to eliminate impurities and to enhance their dispersibilty. Ultrasound and the alkalinity of solution are beneficial to the deaggregation of the soft DNP aggregations. The thermal conductivity enhancement of the DNP nanofluids increases with DNP loading and the thermal conductivity enhancement is more than 18.0% for a nanofluid at a DNP volume fraction of 0.02. Viscosity measurements show that the DNP nanofluids demonstrate Newtonian behaviour, and the viscosity significantly decreases with temperature. With increasing volume fraction of DNPs, the convective heat transfer coefficient increases first, and then decreases with a further increase in the volume fraction of DNPs. The nanofluid with a volume fraction of 0.005 has optimal overall thermal performance.