Goodarz Ahmadi

Effect of flow velocity on fiber efficiency and particle residence time during filtration of aqueous dispersions - An experimental and simulation study

ABSTRACT We extend our recent (Rastegar, Ahmadi, and Babu 2017) experimental and computational study of the performance of fibrous filters for the removal of large particles from aqueous dispersions by including the effect of flow velocity on the fiber efficiency and residence time. Dispersions of particles in the size range of 35–600 nm and zeta potential range of −50 to 50 mV were considered. The effect of velocity on minimum efficiency and most penetrating particle size was investigated. The Navier–Stokes equations were solved numerically for a single fiber at different inlet velocities using the ANSYS-FLUENT package and the motion of particles was tracked using the Lagrangian analysis including the hydrodynamic drag, lift, gravity, hydrodynamic retardation, Brownian, van der Waals (vdW), and electric double layer (EDL) forces. The hydrodynamic retardation, EDL, and vdW forces were incorporated in the calculations by developing a user-defined function (UDF) that was compiled with the code. Particular attention was given to the effect of velocity on fiber efficiency due to Brownian, EDL, and vdW forces. It was shown that the CFD results are in a good agreement with the efficiencies calculated from the experimental data obtained by filtering aqueous colloidal ceria dispersions of different zeta potentials at different flow rates.

Volume of Fluid Simulations of Multiphase Flow through Fractures: Analysis of Individual Fractures for Application in Reservoir Scale Models

Geological Carbon Dioxide Sequestration requires a fundamental understanding of modeling multiphase flows in fractured media. Subsurface flow is highly dependent upon the rock structure within the flow domain, with high permeability and fractured regions dominating the transport of the fluids. Discrete-fracture simulators often assume the cubic law relationship for single phase flow through a smooth set of parallel plates, and with good reason. The number of fractures that need to be modeled at the reservoir scale may greatly exceed 10,000; and the relationship between the pressure field and the fluid flow needs to be easily describable in order for the model to be computationally efficient. The work described in this paper examines two-phase, immiscible flows through rough fractures. Computations are performed utilizing the full multiphase Navier-Stokes equations for flow through CT scanned fractures in Berea sandstone. A number of computer simulations are performed, and an empirical model is generated that is similar to the cubic law, yet accounts for the roughness of the fracture and the interaction of the invading and defending fluids and the effect of capillary forces. The fracture roughness and capillary forces are shown to restrict the flow; hence the standard cubic law tends to over-estimate the flow rate of the invading fluid.