Brownian motion and thermophoretic effects of flow in channels using nanofluid: A two-phase model

Nanofluid is a new class of fluid that aims to enhance heat transfer. Nanoparticles sedimentation may play a role in the heat extractions from a hot surface. Brownian and thermophoretic effects may help in understanding the sedimentation effects. In the present paper, we attempted to investigate these phenomena (Brownian motion and thermophoretic effects) in three-rectangular channel configurations heated from below. The working fluids we considered are three different mixtures with 1%vol Al₂O₃ nanoparticles in various base fluids such as water, ethylene glycol, and a mix of 50% water and 50% ethylene glycol. Different flow rates were implemented in the model using the finite element technique. Results revealed that 1%vol Al₂O₃/water is the best mixture for heat removal based on thermal efficiency criteria. The presence of solid-blocks in the channel further enhanced the performance of the 1%vol Al₂O₃/water nanofluid; when the height/base of the blocks increases. As the nanoparticles diameter increases, the average Nusselt number and the thermal efficiency of nanofluid also increases. It appears that between 31 to100 nm particle diameter, the increase in heat extraction is minimal. For a Reynolds number below 600, as the nanoparticles diameter increase above 31 nm, the sedimentation increases accordingly. However, regardless of the nanoparticle's diameter, for a Reynolds number in the range of 840, uniform nanoparticles distribution is observed.