Improved drag force model and its application in simulating nanofluid flow

The circumferential distribution of the surrounding particles contribution to the drag force for the reference particle is firstly proposed and analyzed. A new formula for the drag exerted on a given particle under the interaction between particle clouds and fluid is derived. Analysis shows that even for spherical particles with symmetric shape, as the particle dispersion is nonsymmetric and the direction of the particle velocity differs from the reference particle, the direction of the drag and the particle velocity is not parallel; therefore, it increased the complexity of evolution process for the particle concentration. Due to special feature of nanoparticle surface adsorption, this study presents analysis of the radial viscosity distribution in the vicinity of liquid layer for the first time. The increasing in the viscosity of the nanolayer is considered a contributing factor to the viscosity of nanofluids as the experimental result is larger than the theoretical prediction. Considering the effect of multi-particles interaction and the characteristics of liquid layer, the new drag force model is constructed and applied to simulate the nanofluid flow. Comparison is made for computed drag force on particle between the traditional and present models. The trajectory and distribution of the nanoparticles, as well as the velocity contours of the fluid, are presented. The physical meanings of these results have been discussed.