Experimental investigation on the thermal transport properties of ethylene glycol based nanofluids containing low volume concentration diamond nanoparticles

Homogeneous and stable ethylene glycol based nanofluids containing low volume concentration diamond nanoparticles have been prepared. Diamond nanoparticles, purified and surface modified by the mixture acid, consist of the highly defective structure and the active functional groups on the surface. Ultrasound and the alkalinity of solution are beneficial to the deaggregate of soft diamond particle aggregation, and the diameters of purified nanodiamond are changed from 30–50 nm to 5–10 nm. The thermal conductivity enhancement decreases with elapsed time for 1.0 vol.% DNP–EG nanofluid at pH = 7.0. While for the stable nanofluids at pH = 8.5, there is no obvious thermal conductivity decrease within 6 months. The thermal conductivity enhancement values are up to 17.23% for the 1.0 vol.% nanofluid at 30 °C. Viscosity measurements show that the nanofluids demonstrate Newtonian behavior, and the viscosity significantly decreases with the temperature.