Molecular dynamics modeling of nano-fluid separation in nanomembranes

Nanofluids separation processes in nanomembranes have been simulated by the molecular dynamics method. The porous membrane was modeled by regular packing of hard spheres of the same radius. In this paper, the modeling results are presented for a system in which the grains and nanoparticles have diameters of 4d and 5d, respectively, where d is the diameter of the carrier fluid molecule. The impact of the membrane porosity, their granule packing type, pore sizes, nanoparticle diameters, and density of the carrier gas on the separation rate was studied. The nanofluid separation efficiency was determined by the speed of molecule transport through the porous membrane. The total mass flux is the sum of the diffusion and convective fluxes. It was established that the convective flux exceeds the diffusion one by two orders of magnitude. Thus molecule transport through the membrane is basically determined by the convective transport. The dependence of the separation rate on the porosity is nonlinear and it is described well by the quadratic function of the volume concentration of the nanoparticles. The greatest separation rate is provided by the membrane with the body-centered cubic packing of the grains. The filtration is stopped only in the case where the size of the porous media throats is on the order of the size of filtered molecules. It is shown that the separation rate can be controlled by varying parameters of the filtered nanofluid and membrane.