René Sanjuan-Galindo

Despite the established effectiveness of ultrasonic cavitation in sonochemical disinfection, energy demand and scalability constraints motivate alternative cavitation-based reactor concepts. Here, we report a hydrodynamic cavitation device inspired by the snapping mechanism of pistol shrimp for bacterial inactivation. An electric motor, speed reducer, and gear assembly actuate a claw-like element whose abrupt closure impulsively accelerates the surrounding liquid, generating periodic cavitating jets. Unlike conventional hydrodynamic cavitation reactors that rely on high-power pumping and large hydraulic circuits, the proposed configuration employs a compact mechanical architecture with moderate electrical input and no chemical additives. Cavitation develops within a confined chamber that promotes repeated pressure transients and localized energy concentration during collective bubble collapse. Experiments demonstrate effective inactivation of Escherichia coli at low initial concentrations. Although the dominant pathway cannot be conclusively identified, the observed inactivation is consistent with pressure-transient-mediated effects, potentially amplified by localized shear stresses and microjet formation near solid interfaces. These results support mechanically driven hydrodynamic cavitation as a promising bioinspired approach for further development and controlled optimization in water disinfection 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.

Se presenta el análisis numérico de la dispersión de un contaminante gaseoso en un medio poroso infinito formado de un arreglo ordenado de partículas con diferentes razones de diámetros (DR). El intervalo cubierto fue 0.2<DR<0.8, el cual corresponde a variaciones sistemáticas en el grado de expansión-contracción de las trayectorias de poro, no incluidos en modelos convencionales. Las porosidades (f) correspondientes a los DR, cubrieron el intervalo 0.27<f<0.72. El número de Reynolds de poro (Re) fue igual a 50×103, correspondiendo a un flujo turbulento completamente desarrollado. Los resultados mostraron que para el caso de DR=0.2 y f=0.27, se forman estructuras de flujo recirculantes y elongadas, las cuales cubren los espacios intersticiales en los poros, provocando una intensificación de la dispersión del trazador y un menor tiempo de homogeneización. En los modelos de mayor DR y menor f, aunque las velocidades locales fueron mayores, las estructuras rotacionales fueron inhibidas y el tiempo de homogeneización aumentó. Considerando que los modelos de mayor f contienen menor cantidad de fase sólida, dicho efecto, puede ser considerado para optimizar el funcionamiento de dispositivos ingenieriles tales como aletas de enfriamiento, arreglos de tubos en intercambiadores de calor y mezcladores estáticos entre otros.

The rheological properties and surface tension (σ) of culture broths with suspended particles are factors that affect the performance of fermentation processes. This article presents the first report concerning the evolution of suspended particles, rheological properties and σ of culture broths during the liquid culture of Steinernema colombiense and its symbiont bacterium, in a medium containing 1.25% (w/v) egg yolk. Cultures started with 1087 infective-juveniles/mL and finished with 53,583 individuals/mL after 10 days. Culture broths were moderately concentrated suspensions with total particles volume fraction in the range 0.08–0.14. The suspended particles were nematodes of different sizes depending on their developmental stage, and egg yolk particles. Rheological properties corresponded to pseudoplastic fluids with flow behaviour index values ≲0.3 (dimensionless), greatly determined by the symbiotic bacterium activity. After nematode inoculation, the apparent viscosity values (η_a; Pa s) for the whole culture broth and its supernatants were in the ranges 0.010–0.018 and 0.008–0.015, respectively. Concerning σ, their values were in the range 31.22–37.74 mN/m, probably determined by the contents of egg yolk.

The present work describes the dispersion process of a viscous fluid in water in a cylindrical vessel agitated at Re = 24,000. The formation of viscous filaments and other amorphous structures in turbulent conditions produced in the early stage, before oil drops saturate the continuous phase, is shown. The oil-phase evolution is followed with high-speed video recordings and compared with the flow pattern produce in the liquid bulk. The effects of four kinds of perturbations are identified: intermittences in the radial velocity, turbulent fluctuations, rotation, and the stretching. As a consequence, the viscous-phase experiences instabilities that include random deformation, elongation, hairpin filaments formation, folding, and fragmentation. In the final part of this study, a mechanism describing the drop size reduction has been proposed.