(168r) Flow around Nanoscale Arrays Extending From the Wall of Microfluidic Ducts

The hydrodynamic behavior of flow around carbon nanotubes or nanoposts is of interest for applications such as microfluidic devices, reducing drag on surfaces, and for improving carbon nanotube synthesis processes. The method of choice for the simulation of the behavior of fluids in the vicinity of carbon nanotubes (CNT) is molecular dynamics (MD). Such studies have been conducted using nonequilibrium MD for the case of flow around infinite CNTs [1,2]. A significant finding from these simulations was that the drag on the nanotubes was in very good agreement with predicted behavior from macroscopic Stokes-Oseen equations [1]. This conclusion suggested that simulations based on macroscopic equations and the continuum approximation can provide reliable results for drag and for flow around CNTs and nanoscale structures. Based on this premise, one could use conventional computational fluid dynamics and continuum Navier-Stokes equations to simulate the microscopic flow fields around CNTs. The use of conventional CFD allows the simulation of flow around not only one but multiple nanotubes. The nanotubes can be attached on a surface, and they can exhibit different patterns instead of being infinitely long [3].

The present work explores the case of flow of water in microchannels when arrays of multiwalled carbon nanotubes (MWCN) extend from the duct wall to the outer flow. The nanotubes are arranged in a linear array of identical nanotubes placed one next to the other on a line perpendicular to the direction of flow. The flow is simulated using the lattice Botlzmann method (LBM), which is an effective and inherently parallelizable numerical method for the simulation of microfluidic flows in complicated geometries. A house hybrid MPI/Open MP parallelized scheme is employed in order to take advantage of the inherent LBM parallelizability. The tubes are modeled as lines of LBM grid points that are assumed to be rigid. The simulations are three-dimensional, and are conducted for various water velocities, and tube spacing. The presentation will include the description of the numerical methodology and the validation of the method for known cases of flow in microfluidics. Microducts with semi-circular crossections are simulated, in addition to simulations of microducts with rectangular cross-sections. The goal is to explore not only the development of the flow filed, but also the effects of the flow field and of the presence of the nanotubes on heat transfer from the microduct wall to the fluid.

References cited: 1. Walther, J. H.; Werder, T.; Jaffe, R. L.; Koumoutsakos, P. Phys. Rev. E, 2004, 69, 062201. 2. Kotsalis, E. M.; Walther, J. H.; Koumoutsakos, P. Int. J. Multiphase Flow, 2004, 30, 995. 3. Ford, A.; Papavassiliou, D.V., Ind. Eng. Chem. Res., 45(5), 1797-1804, 2006.