Surfactant-free synthesis and experimental analysis of Mn-doped ZnO–glycerol nanofluids: an ultrasonic and thermal study

Abstract

A simplistic and environment-friendly approach has been used to prepare surfactant-free Mn-doped ZnO–glycerol nanofluids using high power sonicator. Thermal conductivity of the prepared nanofluids has been measured as a function of temperature and concentration. Maximum thermal conductivity enhancement ~ 32% at 40 °C has been observed with very low nanoparticles loading (2.0 vol% of Mn-doped ZnO-nanoparticles) which is significantly larger than the presently synthesized ZnO–glycerol nanofluids, and that of reported earlier on ZnO-ethylene glycol, and other glycerol-based nanofluids. Our present investigation shows that the thermal conductivity of nanofluids can be increased up to a significant level by changing other physical properties of incorporated nanoparticles than increasing concentration of nanoparticles to a large extent. Various physical phenomena including Brownian motion induced convection effect in conjunction with ballistic diffusion have been proposed for anomalous thermal conductivity enhancement. This may be valuable for various cooling applications and may open avenues for further exploration of efficient heat management with the help of nanosized doped metal oxide suspensions.