Modulation of Internal Tides by Turbulent Mixing in the South China Sea

Modulations of internal tides (ITs) including the baroclinic tidal energy budget, the incoherency, and the nonlinear interactions among different tidal components by turbulent mixing in the South China Sea (SCS) are investigated through numerical simulations. The baroclinic tidal energy budget can hardly be affected by the structure of mixing. Meanwhile, change in the mixing intensity in a reasonable range also cannot obviously modulate the baroclinic tidal energy budget in the SCS. Compared to the baroclinic energy budget, the distributions of conversion and dissipation are more sensitive to the change of mixing. Turbulent mixing also modulates the incoherency of ITs by changing the horizontal density in the ocean. The horizontal variation of density adds incoherence to ITs largely by affecting the internal tidal amplitudes. Furthermore, nonlinear interactions among different components of ITs are generally modulated by the mixing intensity, whereas the variation of the mixing structure can hardly influence the nonlinear interactions. Therefore, the diapycnal diffusivity can set to be horizontally and vertically homogeneous in most of the internal tidal simulations, except for those in which the incoherency of ITs needs to be simulated. However, excessive strong mixing will destroy the stratification. Thus, the optimum range for IT simulations in the SCS is from O (10–5) to O (10–3) m2s–1.

Optimization of the Structural Design of the Process of Fertilizer Mixing and Biomodification of Solid Mineral Fertilizers

A rational structural construction of the general process of fertilizer mixing and biomodification of solid mineral fertilizers is proposed. It covers all the process steps starting from the receipt of individual mixing components at the enterprise fertilizer mixing section through to the shipment of the finished biomodified fertilizer mixture to the finished product warehouse. The condition of synchronous operation of units and assemblies of a fertilizer mixing line is substantiated, where its maximum productivity, high mixing intensity and good quality of the mixture are achieved.

Enhancing Efficiency of Anaerobic Digestion by Optimization of Mixing Regimes Using Helical Ribbon Impeller

The appropriate mixing system and approach to effective management can provide favorable conditions for the highly sensitive microbial community, which can ensure process stability and efficiency in an anaerobic digester. In this study, the effect of mixing intensity on biogas production in a lab-scale anaerobic digester has been investigated experimentally and via modeling. Considering high mixing efficiency and unique feature of producing axial flow, helical ribbon (HR) impeller is used for mixing the slurry in this experiment under various conditions. Three parallel digesters were analyzed under identical operating conditions for comparative study and high accuracy. Effects of different mixing speeds (10, 30, and 67 rpm for 5 min h−1) on biogas production rate were determined in 5-L lab-scale digesters. The results demonstrated 15–18% higher biogas production at higher mixing speed (67 rpm) as compared to 10 rpm and 30 rpm and the results proved statistically significant (p < 0.05). Biogas production at 10, 30, and 67 rpm were 45.6, 48.6, and 52.5 L, respectively. Higher VFA concentrations (7.67 g L−1) were recorded at lower mixing intensity but there was no significant difference in pH and ammonia at different speeds whereas the better mixing efficiency at higher speeds was also the main reason for increase in biogas production. Furthermore, model simulation calculations revealed the reduction of dead zones and better homogeneous mixing at higher mixing speeds. Reduction of dead zones from 18% at 10 rpm to 2% at 67 rpm was observed, which can be the major factor in significant difference in biogas production rates at various mixing intensities. Optimization of digester and impeller geometry should be a prime focus to scale-up digesters and to optimize mixing in full-scale digesters.

Degradation of tetracycline using nanoparticles of zero-valent iron and copper

Tetracycline (TC) is one of the most persistent pharmaceuticals in the ecosystem. Advanced oxidation processes (AOPs) are suitable and effective technology for treating wastewater contaminated with antibiotics such as TC. In this manner, Fenton-like reaction is effective for wastewater treatment from toxicity and non-biodegradable organic pollutants using bimetallic nanoparticles. This study aims to verify the effect of AOPs using ZVI/Cu bimetallic nanoparticles on removing the TC antibiotic via a Fenton-like reaction, and what is necessary to evaluate the factors that influence the reaction i.e. pH, ZVI/Cu dose, stirring intensity, H2O2 concentration, and initial TC dosage. The obtained results indicated that the TC removal reached up to 82.3% with an initial TC dose of 8 μg/L. in addition, the TC degradation process is more effective in an acidic medium than in an alkaline medium. Furthermore, the TC removal reached up to 85.1% with a ZVI/Cu dose of 1.2 g/L. On the other hand, the optimum mixing intensity value was 200 rpm, and the optimum H2O2 dose was 2 g/L according to the conditions of the present study.

The Dynamics of Globally Unstable Air-Helium Jets and Its Impact on Jet Mixing Intensity

The paper presents experimental investigations of the low-density air-helium jets. The paper is aimed at the analysis of the flow conditions promoting the local absolute instability leading to global flow oscillations. A number of the test cases are analysed with a wide range of the shear layer thickness showing conditions favorable for the global modes and also mixing intensity triggered by such a regime. It is shown that high mixing intensity is determined not only by the global regime but also by the vortex pairing process. The results are compared with a recently proposed universal scaling law for an onset into the global mode. The results turn out to be far from this scaling law and the reasons for such discrepancies are discussed. The measurements show also that if the shear layer at the nozzle exit is thin enough the global modes are suppressed. The mechanism leading to the global mode suppression under such conditions is carefully analysed.