Experimental characterization of thermophysical properties and convective heat transfer behavior of hexagonal boron nitride nanofluids

Hexagonal boron nitride (hBN) is a highly stable dielectric ceramic material that exhibits versatile properties such as, exceptionally high thermal conductivity and good chemical inertness. In this study, preparation, stability and thermophysical properties and convective heat transfer characteristics of hBN containing DI water, ethylene glycol (EG) and EG-DI water mixture (by volume 50%) based nanofluids are experimentally investigated. Well dispersed, stable nanofluids, containing hBN nanoparticles are produced with a two-step method. The stability is evaluated by quantitative methods such as, time dependent Zeta Potential, and thermal conductivity measurements. Morphological characterization is completed by qualitative methods such as, ESEM (Environmental Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy). The thermal conductivity enhancement of nanofluids (vol. conc. range: 0.03-3%), is investigated in accordance with increase in viscosity. Thermally developing laminar forced convection of hBN-water nanofluids with a particle volume concentration range of 0.1-1% are considered for a Re range of 800-1700. It is observed that the hBN nanofluids have remarkably higher thermal conductivity values than their corresponding base fluids. Moreover, hBN-water nanofluids with relatively dilute particle suspensions, exhibit significant increase in thermal conductivity with respect to the viscosity increase. For the case of convective heat transfer behavior, the enhancement in the convective heat transfer coefficient of nanofluids is proportional to the observed thermal conductivity enhancement. Therefore, there is no abnormal enhancement in the measured Nusselt number, and measured values are in good agreement with predictions by standard laminar thermally developing flow correlations.