Lattice Boltzmann simulation of convective heat transfer of non-Newtonian fluids in impeller stirred tank

Abstract

Lattice Boltzmann simulation of convective heat transfer of non-Newtonian fluids in an impeller stirred tank is performed. The curved and moving boundary methods combined with the unknown-index algorithm are used to solve the flow and thermal fields induced in a cold tank by an oscillating hot impeller. For a given maximum radius of the blades, the simulation results show that a rectangular impeller of large aspect ratio induces stronger heat transfer effect on the tank walls than the small aspect ratio. This is because the latter would cause worse field synergy than the former, i.e. the induced local velocities of fluid are mostly perpendicular to the temperature gradients. The convection effects on the tank walls are also improved as the oscillation amplitude of impeller increases until the swept areas of impeller are close to whole azimuth of the tank, i.e., oscillation amplitude of 90°. The maximum Nusselt number on the tank walls for power-law fluid flows of n=0.7, 1 and 1.5 occurs at oscillation amplitude of 75°. Finally, it is found that the heat transfer effect on the tank walls is reduced as the power-law index of fluid increases.