Sergio Alejandro Martínez Delgadillo

This article analyzes the applications of computational fluid dynamics (CFD) in addressing the issue of flow patterns in a realistic urban landscape, specifically in the Metropolitan Area of Monterrey. CFD enables the simulation of physical phenomena such as turbulence, which is useful for studying the transport behavior of pollutants in urban environments. The computational model was obtained from satellite imaging and covered a surface of about 1.134 km × 1.227 km. It was composed of 173 urban blocks, representing around 3570 houses, including hospitals, schools, recreation centers and other gathering places. The population of the urban landscape was estimated at around 11,400 inhabitants. Three velocity scenarios, low, average, and high (air gusts), were simulated, using data from a local weather station. The Reynolds numbers (Re) ranged from 1.9 × 10⁶ to 21.2 × 10⁶, falling within the fully developed turbulence regime, which was modeled using the renormalization group (RNG) k–ε turbulence model. Results showed that the mean velocity patterns were preserved independent of the Reynolds number (Re) and were characterized by regions of high velocity in the main avenues, as well as other regions of low velocity between urban blocks. This methodology may also be applicable for understanding the flow patterns of similar urban regions composed of irregularly arranged low-rise blocks.

Efficient mixing in stirred tanks is essential for chemical and biochemical processes. Tubular baffles offer potential energy savings and multifunctionality (e.g., as heat exchangers); however, their interaction with common impeller types is not well understood. This study uses computational fluid dynamics (CFD) simulations to evaluate the hydrodynamic performance of a novel tubular baffle design compared to conventional flat baffles with three impellers: a Rushton turbine (RT), a pitched blade turbine (PBT), and a hydrofoil (HE3). Dimensionless analysis (power number, N_P; and pumping number, N_Q), flow visualization, and vorticity dynamics were employed. The results show that, by attenuating large-scale recirculation, tubular baffles reduce power consumption by 64%, 13%, and 23% for the HE3, PBT, and RT, respectively. However, the HE3 impeller experienced a 30% decrease in pumping capacity, which confined the flow to the lower tank. The PBT showed a 10% increase in N_Q and intensified bottom circulation. The RT uniquely generated distributed, high-intensity turbulence along the baffle height while maintaining its characteristic dual-loop structure. The analysis critiques the local pumping efficiency metric and advocates for a global flow assessment. The HE3 is optimal for efficient bulk blending at low power; the PBT is optimal for strong bottom circulation processes; and the RT is optimal for applications requiring enhanced interfacial processes, where baffles serve a dual function. This work provides a framework for selecting energy-efficient agitation systems by coupling impeller performance with global tank hydrodynamics.

The photocatalysts of TiO₂ doped with carbon, boron, nitrogen, and sulfur were synthesized and evaluated, with the aim of improving their efficiency in dye degradation under UV and visible light irradiation. The samples were structurally and optically characterized using X-ray diffraction (XRD), Raman spectroscopy, and UV-Vis spectroscopy. All materials retained the anatase phase, although doping affected their crystallinity and optical properties. C–TiO₂ and N–TiO₂ stood out due to their enhanced absorption in the visible region. The photocatalytic activity was evaluated using the dyes Acid Orange 7 and Reactive Black 5 under both UV and visible light irradiation. C–TiO₂ exhibited the highest efficiency under both conditions, especially under visible light, outperforming undoped TiO₂. N–TiO₂ also showed improved performance in the degradation of Reactive Black 5. These results confirm that doping with non-metallic elements, particularly carbon enhances the performance of TiO₂ under visible light irradiation, highlighting its potential for the treatment of dye-contaminated wastewater.

Emerging pollutants, especially pharmaceuticals like paracetamol, pose serious environmental risks due to their persistence and toxic effects on aquatic organisms. The objective of this study was to evaluate the effectiveness of photocatalytic processes in degrading this pollutant using various types of TiO₂ catalysts: untreated (TiO₂), thermally treated (TiO₂+T), treated with temperature and ultrasound (TiO₂+T+US), and nanoparticulate (TiO₂ -NP). The results showed that TiO₂-NP at 0.3 g/L achieved the highest efficiency (98% removal), while the TiO₂+T+US catalyst reached 94% at 1.6 g/L. It also evaluated the reusability of the catalysts, observing a slight decrease in efficiency after the first cycle. Degradation kinetics were determined and followed a first-order model

This study investigated the sono-chemical degradation of Reactive Black 5 (RB5) dye in aqueous solutions using low-frequency ultrasound (42 kHz, 100 W), optimizing power per unit volume (P/V) and pH. Initial RB5 concentrations ranged from 1 to 24 mg·L⁻¹, with P/V of 500 to 1000 mW·mL⁻¹ and pH of 2.0 and 8.0. Results showed that at 1000 mW·mL⁻¹ and pH 2.0, degradation was up to 45% higher than at 500 mW·mL⁻¹, with pseudo-first-order kinetic constants increased by up to 40%. Phytotoxicity assays with Hordeum vulgare and Brachypodium sp. revealed that RB5 concentrations ≥ 5 mg·L⁻¹ reduced germination by over 40%, with Brachypodium sp. being more sensitive. Low-frequency sonolysis offers an efficient strategy to mitigate textile effluent toxicity, with potential for sustainable applications.

The wall-modeled-large eddy simulation (WMLES) technique was used to analyze turbulent flow in a porous medium composed of a staggered arrangement of square cylinders. The study focused on a porosity range of 0.3–0.8 at a pore Reynolds number of 104. The research provides novel information on pressure and shear force distributions around the cylinders and time-averaged values of particle drag and fluctuating lift coefficients. Results indicate that flow physics are mainly driven by an expansion region in front of the central particle and another one in the rear, where the flow is contracted and strongly accelerated. In the first region, velocities, turbulence kinetic energy (k), and its dissipation rate (ε) are attenuated by a sudden pressure increase, while in the contraction region, the effect is the opposite. As porosity decreases, flow gradients and the overall levels of k, ε, and normalized Reynolds stresses become more significant. Turbulent anisotropy increases as porosity decreases below 0.6. Hydrodynamic stresses in the last interval present relatively uniform levels, which is a unique feature that may be considered in designing dedicated engineering devices with controlled stresses.