Heat transfer, thermophysical and rheological behavior of highly stable few-layers of h-BN nanosheets/EG-based nanofluid

Abstract

The thermal conductivity of boron nitride at room temperature is approximately 400 W/m.K. This amount is much larger than metals and ceramic materials. Theoretical studies show that boron nitride monolayers have much higher thermal conductivity than their bulk counterpart. On the other hand, the low stability of few-layer boron nitride nanomaterials in base fluids, limits their use in cooling systems. In this work, highly stable boron nitride nanosheets with a production yield of 65% were prepared using liquid phase exfoliation, and the thermophysical and rheological behavior of these nanosheets versus nanosheets concentration and temperature were investigated. The results showed that by increasing the nanosheets’ concentration and temperature, thermal conductivity increases, and a 24% increase in 1 vol% concentration of nanosheets was observed. Viscosity changes in terms of shear rate indicate a thinning behavior at low shear rates with increasing concentrations of nanosheets. Investigating the thixotropy behavior of this nanofluid has been studied for the first time. The presence of the hysteresis loop at low shear rates confirmed the shear-thinning behavior of this nanofluid with increasing concentration. In addition, a 30% increase in heat transfer in the smooth tubes was observed without increasing the friction coefficient in the turbulent flow so can be introduced as an efficient nanofluid in increasing the thermal efficiency of efficient solar collectors.