Peng Wang

Aeration conditions are critical for controlling hydrodynamics and membrane fouling in membrane bioreactors (MBRs), yet the role of aeration position in integrated sewage treatment systems remains poorly quantified. This study investigates an integrated anaerobic–anoxic–oxic–MBR membrane tank using a computational fluid dynamics-population balance model with non-Newtonian rheology of the mixed liquor. Aeration positions 5–45 mm below the membrane module were evaluated for their effects on flow structure, bubble distribution, and membrane-surface shear. The model was validated against measured bubble rise velocities, with a maximum relative error of 4.67%. The results demonstrate that aeration position strongly governs the formation of high-velocity cores, low-velocity zones, and gas holdup distribution, and thus the spatial patterns of turbulent kinetic energy and gas–liquid shear on the membrane surface. Increasing the aeration position to an intermediate level enhances bottom turbulence and mixing, reduces the fraction of low-velocity regions, and alleviates sludge deposition, whereas excessively high aeration positions lead to non-uniform velocity and gas distribution and aggravated local membrane fouling. Under practical operating conditions, an intermediate aeration position also helps control local sludge concentration and floc size, thereby mitigating pore blocking development. Overall, the findings highlight aeration position as a key yet often overlooked design and operational parameter for optimizing integrated MBR performance.

This study investigates the factors influencing the performance characteristics of annular jet pumps (AJPs) conveying non-Newtonian fluids, to enhance their suction capability for marine organisms such as jellyfish, which exhibit properties close to non-Newtonian fluids. Based on the power-law fluid model, realizable k-ε model, and volume of fluid (VOF) model, shear-thinning carboxymethyl cellulose (CMC) was selected to simulate marine organisms like jellyfish. Fluent software was employed to numerically simulate the performance characteristics and internal flow field of the annular jet pumps. The results demonstrate that the shear-thinning effect of non-Newtonian fluids reduces the maximum efficiency point of annular jet pumps and decreases the flow rate ratio corresponding to this efficiency point. As the concentration of CMC solution increased to 0.5%, the maximum efficiency point decreased by 5.5%, and the flow rate ratio corresponding to this efficiency point dropped from 1 to 0.8. These findings provide reference and insights for analyzing the full flow field of annular jet pumps pumping shear-thinning non-Newtonian fluids and for structural design of such pumps.

As key emergency equipment, high-flow pump devices play a vital role in urban flood control and drainage, and their hydraulic performance directly influences the safety and stability of the entire system. To meet diverse drainage demands during emergency operations, a new type of high-flow drainage pump, capable of operating in series, parallel, and variable-speed modes, has been developed. Using the SST k-ω turbulence model combined with entropy production theory and pressure pulsation analysis, unsteady numerical simulations were conducted to investigate the transient internal flow under series and parallel operating conditions. The numerical model was verified through comparison with experimental hydraulic-performance data, demonstrating good agreement. The results show that under series operation, the pump speed decreases from 1500 r/min to 193 r/min before reversing to −1748 r/min, while under parallel operation the runaway speed reaches −1657 r/min. The flow rate and torque exhibit strong nonlinear variations, with reverse flow and oscillatory behavior appearing in the impeller passages. During the runaway stage, entropy production peaks at 28.17 W/K under series conditions and 29.09 W/K under parallel conditions, with turbulent dissipation accounting for more than 69% of the total. High-entropy regions extend toward the impeller outlet, while energy losses are predominantly concentrated in the secondary suction chamber, contributing 47.56% and 57.12% under the respective conditions. Pressure pulsation analysis indicates that the dominant frequency components are concentrated at the blade-passing frequency (100 Hz) and its harmonics, with the strongest fluctuations near the primary impeller outlet. These results provide theoretical and engineering guidance for improving the efficiency and stability of emergency drainage systems.

Low specific speed centrifugal pumps exhibit narrow and long impeller flow channels that induce internal flow instability, leading to pump oscillation, noise, and inefficiency. Splitter blades serve as an effective optimization method for such pumps. This study combines experimental and numerical approaches to investigate the spatiotemporal flow evolution in splitter blade sub-channels, identifying instability mechanisms at the leading edge, midsection, and trailing edge of the blade. Results demonstrate higher flow rates in the pressure side sub-channels compared to the suction side ones. Pressure pulsation is primarily governed by the jet-wake structure and rotor–stator interaction at flow channel outlets. Analysis of liquid flow angle, turbulence kinetic energy, and eddy viscosity distribution establishes correlations between high turbulence areas and the frequent occurrence of phenomena such as vortices and flow separation.

Integrated wastewater treatment equipment is widely utilized in remote areas of China due to its compact footprint and low operational costs. However, a lack of detailed understanding of internal flow field characteristics often results in compromised treatment efficiency and excessive energy consumption. This study addresses this gap by employing a hybrid approach integrating particle image velocimetry (PIV) experiments and computational fluid dynamics (CFD) simulations to investigate internal flow characteristics—including velocity fields and vorticity patterns—within the aerobic tank. Through precise regulation of inlet and nitrification reflux velocities, the CFD model was validated against PIV data. The validation scope was expanded from localized subsets to the full computational domain, confirming the predictive accuracy of the CFD model, with a maximum relative error of less than 18.6%. Simulation results demonstrate that at an inlet velocity of 0.697 m/s and a reflux velocity of 0.979 m/s, achieves homogeneous mixing with a stable velocity distribution, uniform vorticity dispersion, and consolidated vortex core structures. This optimized configuration enhances wastewater treatment efficiency while achieving approximately 15% energy savings in pump power.

The high-power consumption and excessive heat generation in data centers present challenges to thermal management. As a critical component of liquid cooling systems, the circulation pump's stability and reliability are directly impacted by cavitation and air entrainment, which degrade performance. This study investigates the effects of cavitation with entrained air under various rotational speeds and air volume fractions on centrifugal pump performance, pressure pulsation, and cavitation behavior. Experiments were conducted using a closed-loop test rig at three rotational speeds (2900, 2300, and 1800 r/min). The impact of different air volume fractions on the time-domain and frequency-domain characteristics of pressure pulsations was systematically analyzed. The results reveal that: (1) The maximum efficiency under air entrainment conditions exceeds that under natural cavitation. This condition optimizes the pressure distribution within the impeller channels, particularly near the impeller outlet. (2) Air entrainment effectively suppresses high-amplitude pressure fluctuations caused by cavitation collapse, especially at high air volume fraction (1.6%), with varying effects observed during the cavitation stage depending on the air volume fractions. (3) The ratio of rotational speed to bubble volume fraction determines the frequency-domain characteristics, manifesting as a combination of blade frequency, broadband, and low-frequency signals, influencing flow field stability and energy distribution. (4) Cavitation and air–cavitation interference frequencies cluster around St = 6, indicating bubble aggregation, collapse, and fragmentation under impeller rotation, with distinct interaction patterns at different speeds. This study provides a novel theoretical explanation of the mechanisms by which bubble aggregation and fragmentation induce flow instability under low-speed conditions.