The Effective Thermal Conductivity of Water Based Alumina Nanofluids in the Fully Developed Laminar Flow in a Circular Tube Under a Constant Wall Heat Flux Condition

The effective thermal conductivities of dispersed Alumina nanoparticles in DI water are measured under convective flow conditions to compare with those measured at static conditions. The considered particle volume fractions of the nanafluids are 2% and 4%. The measurements are conducted in the fully developed laminar flow in a circular tube subjected to constant surface heat flux. Results show that the augmentation of the effective thermal conductivity of Alumina nanofluids under the convective flow condition is smaller than that at the static condition. It can be explained by the migration of dispersed nanoparticles in the base fluid under the convective flow condition. Due to the particle movement to the center of the tube by thermophoretic diffusion, the particle concentration near the heating wall is getting lower than the uniform concentration at the static condition. Hence, the heat conduction from the heating wall to convective nanofluid becomes lower than that at the static condition.