Thermo-hydraulic characteristics of Al2O3-water nanofluid by preconditioned LBM

The nanofluids under magnetic fields show great potential in microchannel cooling and thermal absorption of the miniaturized devices. Studies about the lattice Boltzmann method (LBM) have been focusing on the effects of nanoparticle types, volume fractions, and magnetic field intensity at low Reynolds numbers. However, less effort has been made to elucidate the interactions between external forces at large Reynolds numbers. In this work, we firstly developed a preconditioned LBM (PLBM) to overcome the divergence problem of the original LBM caused by variable physical properties and Reynolds numbers, followed by investigating the thermo-hydraulic characteristics of Al2O3-water nanofluid in a microchannel with temperature-dependent physical properties and slip boundary conditions. The effects of the external magnetic field, buoyancy force, and volume fraction of nanoparticles are discussed, and the entropy generation is analyzed. When the magnetic field is applied, the average shear stress is twice that without a magnetic field and the average Nusselt number increases by about 10% and further by about 20% at higher buoyancy forces. Besides, the magnitudes of the entropy generation caused by magnetic field irreversibility are higher than that caused by the heat transfer irreversibility. The numerical study developed in this work elucidates the effects of external force and extends the simulation performance of the existing LB models.