Study of fluid displacement in 3D porous media with an improved multi-component pseudopotential lattice Boltzmann method

We generalize to three dimensions (3D) a recently developed improved multi-component pseudopotential lattice Boltzmann method and analyze its applicability to simulate flows through realistic porous media. The model is validated and characterized via benchmarks, and we investigate its performance by simulating the displacement of immiscible fluids in 3D geometries. Two samples are considered, namely, a pack of spheres obtained numerically, and a Bentheimer sandstone rock sample obtained experimentally. We show that, with this model it is possible to simulate realistic viscosity ratios, to tune surface tension independently and, most importantly, to preserve the volume of trapped fluid. We also evaluate the computational performance of the model on the Graphical Processing Unit (GPU) and mention the implemented optimizations to increase the computational speed and reduce the memory requirements.Comment: arXiv admin note: text overlap with arXiv:2111.0866

Intensification of the Rate of Diffusion-controlled Electrochemical and Catalytic Reactions at a Helical Coil by a Fixed Bed Turbulence Promoter

Intensifications of the rate of diffusion-controlled electrochemical and catalytic reactions taking place at the outer surface of a helical coil imbedded in an inert fixed bed of cylinders acting as turbulence promoters was studied using the electrochemical technique. The technique involved measuring the limiting current of the cathodic reduction of K3Fe(CN)6 in a large excess of NaOH as a supporting electrolyte. The variables studied were solution velocity, packing cylinder diameter, helical coil tube diameter, and physical properties of the solution. The rate of mass transfer at the outer surface of the coil was found to increase with increasing solution velocity and decreasing packing cylinder diameter, helical coil tube diameter was found to have a little effect on the rate of mass transfer. The data were correlated with the dimensionless equation Sh = 7.14*10(-4) *Sc(0.33)*Re(0.52) *(dp/d)(-2.32) Implication of the above equation for the design and operation of the present reactor was pointed out. The potential importance of using the inner surface of the coil as a builtin heat transfer facility for conducting exothermic electrochemical and catalytic reactions requiring rapid cooling was highlighted. The possibility of using multiple imbedded coaxial helical coils of different coil diameter in practical catalytic reactors to increase their rate of production was noted

The limiting current for reduction of ferricyanide ion at nickel: the importance of experimental conditions

Steady state, hydrodynamic voltammetry is a well established technique to measure the rate of mass transport of an electroactive species to, or from, a solid surface electrode in an aqueous electrolyte. Limiting current measurements during the reduction of ferricyanide (hexacyanoferrateIII) ion at a nickel rotating disc electrode (RDE) are critically considered, and the accuracy of the technique is quantitatively assessed. The importance of surface pretreatment, type of indifferent electrolyte, and the effect of sunlight are considered. Limiting current values can show large deviations from the values predicted by the Levich equation for laminar flow to a polished RDE when unsuitable conditions are employed, despite the appearance of well-defined limiting current plateaux. Using appropriate pretreatment and experimental procedures, the averaged mass transport coefficients or limiting currents values can be obtained, which are close to the values predicted by the Levich equation for laminar flow to a hydrodynamic smooth RDE