Heat transfer measurements of Polyalpha-Olefin- boron nitride nanofluids for thermal management and lubrication applications

Abstract

In this paper, the first study is reported combining Polyalpha-Olefin (PAO) oil with hexagonal Boron Nitride (hBN) to produce new class of nanofluids for heat transfer and lubrication applications. The heat transfer performance of the nanofluids is studied experimentally along with their viscosity, specific heat, thermal diffusivity and thermal conductivity. Thermophysical properties relations are derived as a function of temperature and nano particle concentration. Heat transfer experiments are conducted for both the PAO base fluid and nanofluid as a function of Reynolds number. It is found that PAO/hBN nanofluids exhibit Newtonian behavior as a function of temperature (from −20 to 70 °C) and volume concentration (0.25–1%). The viscosity decreases with temperature for both base fluid and PAO/hNB nanofluids and increases with concentration. The specific heat increases with temperature by 44% from 45 °C to 95 °C for pure PAO and by 48% for nanofluid with 1% concentration. The thermal conductivity of nanofluids is significantly higher than that of pure PAO and it increases by increasing hBN concentration. The thermal conductivity decreases with temperature for pure PAO and nanofluids unlike other nanofluids. The heat transfer enhancement in terms of Nussel Number showed average and maximum values of 10%–13%, 17%–20% and 26%–29% for hBN concentration of 0.25%, 0.6% and 1%, respectively. Two competing phenomena affect the heat transfer performance: the increase/decrease in resistance to thermal diffusion sublayer when thermal conductivity increases and viscosity decreases, respectively. For the PAO/hBN nanofluids, the increase in thermal conductivity caused the heat transfer enhancement.