A Multiphase Numerical Heat Transfer Evaluation of Al2O3—Air Nano-fluid Flow in a Pipe Under Turbulent Flow Conditions

A numerical analysis was conducted in a circular pipe for the nano-fluid flow using Al2O3 as the nano-particle with air as the base fluid. A uniform heat flux condition was maintained over the circular tube while varying the nanoparticle concentration, pipe diameter and inlet flow velocity (turbulent flow). A multiphase approach using Eulerian model employing partial differential equation modulation for granular properties with RNG k-ε turbulent model was adopted to accurately predict the nano-fluid thermo-hydrodynamic behavior. The numerical multiphase approach revealed that nano-fluid using air highly enhanced the heat transfer performance. By varying the pipe diameter from 5 to 20 mm, and nanoparticle concentration from 0 to 5%, it was observed that the heat transfer effectiveness and profit index lie in the range of 25–130, and 35–200 respectively. The dispersion of nanoparticles enhanced the thermal conductivity caused by Brownian motion leading to a better heat transfer performance. With a lower specific heat, the thermal diffusivity of the fluid increased with the addition of nano-particles leading to a reduced inner wall temperature. The analysis within the boundary layer supports the enhanced thermal performance caused by particle motion. Within the same pipe diameter, the heat transfer effectiveness ratio went on decreasing along the pipe length. This could be credited to the reduction in temperature difference between the wall and the flowing fluid highlighting the enhanced performance of nano-fluids.