Sergio A. Martínez-Delgadillo

Enhancing the electrochemical Cr(VI) reduction in aqueous solution.

In this study we present the cathodic Cr(VI) reduction using electrodissolution of iron anode. In batch experiments we tested four different cathodic materials; the best conditions were found when copper was used. It is observed that when more current is applied into the electrochemical cell faster reduction rates are achieved. Continuous experiments also reveal that Cr(VI) reduction could be done in a very efficient way. To confirm the experimental data, cyclic voltammetry was used and it was found that the cathodic Cr(VI) reduction is taking place.

Effect of low temperature thermal pre-treatment on the solubilization of organic matter, pathogen inactivation and mesophilic anaerobic digestion of poultry sludge.

Treatment of poultry industry effluents produces wastewater sludge with high levels of organic compounds and pathogenic microorganisms. In this research, the thermal pre-treatment of poultry slaughterhouse sludge (PSS) was evaluated for low temperatures in combination with different exposure times as a pre-hydrolysis strategy to improve the anaerobic digestion process. Organic compounds solubilization and inactivation of pathogenic microorganisms were evaluated after treatment at 70, 80 or 90°C for 30, 60 or 90 min. The results showed that 90°C and 90 min were the most efficient conditions for solubilization of the organic compounds (10%). In addition, the bacteria populations and the more resistant structures, such as helminth eggs (HE), were completely inactivated. Finally, the thermal pre-treatment applied to the sludge increased methane yield by 52% and reduced hydraulic retention time (HRT) by 52%.

RANS simulations of the U and V grooves effect in the subcritical flow over four rotated circular cylinders

This paper presents a CFD study about the effect of the V and U grooves in the flow over four cylinders in diamond shape configuration at subcritical flow conditions (Re = 41000). The k-ε Realizable turbulence model was implemented to fully structured hexahedral grids with near-wall refinements. Results showed that the numerical model was able to reproduce the impinging flow pattern and the repulsive forces present in the lateral cylinders of the smooth cylinder array. As a consequence of the flow alignment induced by the grooves, a jet-flow is formed between the lateral cylinders, which could cause an important vortex induced vibration effect especially in the rear cylinder. The magnitudes of the shear stresses at the valleys and peaks for the V grooved cylinders were lower than those of the U grooved cylinders, but the separation points were delayed due the U grooves presence. It is discussed the presence of a blowing effect caused by counter-rotating eddies located near the grooves peaks that cause a decrease of the shear stresses in the valleys, and promote them at the peaks.

A simple robust control approach for Cr(VI) regulation of wastewater at electrochemical mixed-flow reactors in series

In this article a simple feedback controller approach for the regulation of Cr(VI) from electrochemical mixed-flow reactors in series is presented. The control approach is based on simple step response models obtained experimentally during the operation of three electrochemical continuous reactors in series. Based on simple first-order model and first-order model plus input delay to account for dead times induced by the measurement of the Cr(VI) two controllers are derived. The proposed controllers are composed of two parts: an uncertainty observer to compensate uncertainties and neglected terms in the input-output models and an inverse dynamics feedback controller. Numerical simulations show good closed-loop performance and robustness properties.

Effect of Surface Contamination on the Drag of a Bubble Rising in a Line

The presence of surfactants critically increases the drag on bubbles rising in contaminated water compared with bubbles rising in pure water. This is explained by the Marangoni effect, occurring when the surface tension forces existing on the surface generate tangential shear stresses on the surface bubble. This mechanism has been studied by considering stagnant cap hypothesis to simulate the increase in the drag as a function of surface contamination. In this work, the steady drag for contaminated spherical bubbles was obtained numerically for \(0.1\le Re\le 200\) by using Comsol \({\text {Multiphysics}}^{\circledR }\) 3.5a assuming the stagnant cap hypothesis. The numerical values of the vorticity, flow velocity and pressure fields as function of the angle of superficial contamination and Re were examined. The agreement of the numerical results with reported drag values for clean and partially contaminated bubbles, as well as rigid spheres was proved. By using an appropriate normalization of the numerical data, a simple drag correlation for contaminated bubbles as a function of the spherical angle of the stiff surface zone was obtained.

Numerical Simulation of Flow Behavior within a Venturi Scrubber

The present work details the three-dimensional numerical simulation of single-phase and two-phase flow (air-water) in a venturi scrubber with an inlet and throat diameters of 250 and 122.5 mm, respectively. The dimensions and operating parameters correspond to industrial applications. The mass flow rate conditions were 0.483 kg/s, 0.736 kg/s, 0.861 kg/s, and 0.987 kg/s for the gas only simulation; the mass flow rate for the liquid was 0.013 kg/s and 0.038 kg/s. The gas flow was simulated in five geometries with different converging and diverging angles while the two-phase flow was only simulated for one geometry. The results obtained were validated with experimental data obtained by other researchers. The results show that the pressure drop depends significantly on the gas flow rate and that water flow rate does not have significant effects neither on the pressure drop nor on the fluid maximum velocity within the scrubber.

Numerical Simulation of the Subcritical Flow Over a Circular Cylinder With “U” and “V” Grooves

In this paper the comparative results of three numerical simulations of the subcritical turbulent flow over a circular cylinder (Re = 140,000) for the cases of a “U” grooved cylinder, a smooth cylinder, and a “V” grooved cylinder are presented. Due to the high resolution capabilities of the LES model, it was preferred over the RANS or URANS turbulence models. The simulation was carried out using the commercial CFD code ANSYS FLUENT V.12.0. The grid sizes were: 2.6 million cells for the smooth cylinder, and 14.5 and 13 million for the “U” grooved and “V” grooved cylinders respectively. In order to improve the quality of the solutions, the grids were structured and composed of hexahedral cells. Due to the requirements of the LES technique, the lower y+ values obtained were below 5. With the aim of capture the non-steady characteristics of this kind of flows, the simulations were performed over 8 vortex shedding cycles. Although the cross sections of the V and U grooves have almost the same shape, the resulting flow structures and calculated quantities such as the separation point, turbulent intensity in the normal and streamwise direction and recirculating bubble length were different for both cases. Apparently, the flow configuration resulted from the V grooves is similar to the smooth cylinder flow, being the U grooved cylinder flow different from both of them. This could be related to the drag reduction of about 27% obtained for the U grooved cylinder flow For the V grooved cylinder flow, the obtained drag presented an increase of about 7%.© 2013 ASME