Influence of particle size on thermal conductivity and dynamic viscosity of water‐based Indian coal fly ash nanofluid

Abstract This study investigates the influence of particle size on thermal conductivity (TC) and dynamic viscosity of stable water‐based Indian coal fly ash nanofluid. Coal fly ash particles with an average particle size of 114, 89, 55.5, 30.36, and 11.5 nm were considered in the present study under the temperature range of 30–60°C with 0.5 vol% concentration at a pH range of 7.5–9. These nanoparticles were characterized by scanning electron microscope for morphology, dynamic light scattering was used to assess the average particle size, and zeta potential ( ζ ) for the stability of nanofluid samples. The difference in maximum TC enhancement between 11.5 and 114 nm sample was 9.4% at a temperature of 60°C and a volume concentration of 0.5%. Also, the maximum viscosity enhancement was 13.3% at a temperature of 30°C and the same volume concentration of 11.5 nm sample. The experimental results noticed that stability, TC, and dynamic viscosity increase with a reduction in particle size. Also, TC increases, whereas viscosity decreases with temperature increment.