Effect of Al2O3 phases on the enhancement of thermal conductivity and viscosity of nanofluids in engine oil

Thermal conductivity of alpha-Al2O3 was measured using hot wire method. alpha-Al2O3 (20 nm in size) was synthesized by microwave method for which, the results were compared with commercially available gamma-Al2O3. Thermal conductivity of nanofluids was investigated considering, it is dependency on Al2O3 phase. It was observed that by adding 3 wt% of nano gamma-Al2O3 and alpha-Al2O3 to the engine oil, thermal conductivity increases by 37 and 31%, respectively. The corresponding viscosity increase for the same amount of nano gamma-Al2O3 and alpha-Al2O3 were 36 and 38%, respectively. It was concluded that the differences in thermal conductivity originate from higher specific surface area of gamma-Al2O3 compared to the alpha-Al2O3 which is the result of porosity difference, obtained during the synthesis process.