SYNTHESIS AND EXPERIMENTAL INVESTIGATION OF RHEOLOGICAL BEHAVIOR OF EG AND WATER BASED hBN NANOFLUIDS

Hexagonal boron nitride (hBN) is a ceramic material with high thermal conductivity and superior chemical stability that makes it a suitable candidate for nanofluid synthesis. The studies that focus on hBN nanofluids are mostly limited to hBN-oil dielectric nanofluids. However, using hBN with other base fluids has also significant potential applications. This study focuses on stability and rheological behavior of hBN-water and hBN-ethylene glycol nanofluids that have not been investigated in detail. Nanofluids with hBN nanoparticles of an effective diameter of 70 nm are synthesized using the two-step method. The main problem in this method is sedimentation as a result of disproportionate amount of clustering of nanoparticles within the nanofluids. In the preparation procedure of nanofluids, sonication and pH level control are used. The stability of the hBN-water nanofluids is determined either by quantitative methods such as zeta potential measurements and/or effective particle size measurements via dynamic light scattering, or qualitative methods such as SEM (Scanning Electron Microscopy) and STEM (Scanning Transient Electron Microscopy). Following the investigation of the effect of several parameters, such as sonication time, pH level of the suspension on the stability of the nanofluids, rheological behavior is investigated experimentally. Rheology experiments are conducted with a cone plate rheometer. In these experiments different volume concentrated (0.5-1%) nanofluids are considered. Validation studies for preparation and characterization methods are carried out with alumina (Al2O3), nanofluids which are synthesized by dispersing gamma-Al2O3 nanoparticles of 15 nm into deionized water.