Copper nanofluids: Synthesis and thermal conductivity

A novel one-step chemical reduction method is developed to fabricate nanofluids with very tiny spherical copper nanoparticles. Their chemical and colloidal stability is studied by adjusting their pH value with citric acid. Their thermal conductivity is also measured by the transient hot-wire method. The particle size can be varied from 6.4 nm to 2.9 nm by changing the surfactant concentration. The thermal conductivity data show the existence of a critical particle size below which the nanoparticles cannot significantly enhance fluid conductivity due to the particle conductivity reduction and the solid-liquid interfacial thermal resistance increase as the particle size decreases. By considering these two factors, we have also made some theoretical analysis to find the possible critical particle size.