Development of CuO-ethylene glycol nanofluids for efficient energy management: Assessment of potential for energy recovery

Ethylene glycol (EG) plays an important role as coolant in sub-artic and artic regions owing to its low freezing point. However one of the limitations of ethylene glycol for energy management is its low thermal conductivity, which can be improved by addition of nanoparticles. In the present work, cupric oxide nanoparticles have been synthesized followed by dispersion in ethylene glycol through extended probe ultrasonication without addition of chemical dispersing agent. Temperature dependency of thermal conductivity of 1 vol% CuO-ethylene glycol nanofluid exhibited a minimum at a critical temperature corresponding to lower thickness of interfacial layers and negligible Brownian motion. The influence of liquid layering on thermal conductivity was predominant at temperatures below critical temperature leading to higher thermal conductivity at lower temperature. Brownian motion-induced microconvection resulted in thermal conductivity increase with temperature above the critical temperature. About 14.1% enhancement in thermal conductivity was obtained at 50 °C for 1 vol% CuO-ethylene glycol nanofluid. The viscosity of CuO-ethylene glycol nanofluid was lower than the viscosity of ethylene glycol at temperatures below 50 °C and 120 °C for 1 vol% and 0.5 vol% CuO-ethylene glycol nanofluids. Our data reveal that the CuO-ethylene glycol nanofluids are better coolants than ethylene glycol for transient cooling under constant heat flux conditions with 11.8% enhancement in heat transfer rate for 1 vol% CuO-ethylene glycol nanofluid. Hence the use of ethylene glycol-based nanofluids is a promising approach for energy management.