Search Results (34)

Polyurethane adhesives often suffer from high viscosity, poor flowability, and limited mass transfer efficiency, making it challenging for conventional single-shaft or twin-shaft mixing systems to achieve uniform mixing in large-capacity equipment. This study investigates the differential speed coupling mechanism of a 600 L eccentric four-shaft mixer for high-viscosity polyurethane adhesive systems using computational fluid dynamics (CFD). The effects of different differential speed ratios on flow field evolution and mixing performance were systematically analyzed through multiple indicators, including power consumption per unit volume, velocity variation coefficient, effective mixing region ratio, vortex core coverage, and maximum Lyapunov exponent (LLE). Among the investigated conditions, the 50:100 differential speed ratio exhibited a more favorable circulation pattern, forming a closed-loop circulating flow field in the entire reactor, with an effective mixing region accounting for 60%, a velocity variation coefficient of only 0.38, and a power consumption per unit volume as low as 21.2 W/m³. A constant speed of 100:100 easily generates dead zones in the interaxial flow field, while a high differential speed of 100:50 leads to excessive disturbances and energy waste. Moderate differential speed can generate large-scale coupled vortices, thereby enhancing mixing through coupled axial transport, radial dispersion, and tangential shear. An eccentric four-shaft mixer combined with reasonable differential speed control can effectively improve flow field uniformity and reduce potential mixing limitations in large-scale polyurethane adhesive systems. Among the three investigated differential speed ratios, the 50:100 condition exhibited the most favorable overall mixing performance. These findings provide numerical insights into the selection of differential speed operating conditions for high-viscosity polyurethane adhesive mixing systems. Full article

Particle-laden pipe flows are ubiquitous in food, chemical and pharmaceutical processes, where solid particles significantly alter fluid deformation and mixing. Understanding these transport mechanisms is critical for process optimisation. A Lagrangian analysis framework based on a SPH-DEM simulation is proposed to compute finite-time Lyapunov exponent (FTLE) fields and extract Lagrangian coherent structures (LCSs) for non-Newtonian particle-laden pipe flows. The method directly exploits the inherently Lagrangian particle trajectories and computes the FTLE fields using the SPH interpolation scheme, avoiding the costly numerical integration required by conventional Eulerian approaches. Subsequently, LCSs are extracted via a ridge detection algorithm and the combined FTLE is introduced to quantify mixing intensity. The framework is validated against the Kármán vortex street benchmark, showing good agreement with experiment and numerical results. Then the validated framework is applied to non-Newtonian particle-laden pipe flows for a wide range (0 vol.%~30 vol.%) of particle loading. Results reveal a critical concentration range of 20 vol.%~30 vol.%, where the cross-sectionally average combined FTLE increases with concentration up to 20 vol.%, indicating enhanced mixing, but decreases beyond 30 vol.% as particle–particle interactions suppress near-wall fluid deformation. These findings provide a robust Lagrangian tool and new quantitative insights for optimising mixing and transport in industrial particulate flows, such as in food processing pipelines and chemical reactors. Full article

Constrained by the low grade and poor floatability of the run-of-mine ore, the beneficiation of porphyry-type copper–molybdenum sulfide ores generates large quantities of molybdenum tailings, leading to significant environmental risks and resource losses and necessitating urgent recovery and reutilization. In this study, a representative sample of molybdenum tailings with a Mo grade of 0.354% was investigated to analyze its process mineralogy. The results show that molybdenite predominantly exists as fine, flaky particles intimately intergrown with quartz, pyrite, and aluminosilicate minerals, exhibiting an extremely low degree of liberation and an overall ultrafine particle size. Laboratory flotation tests show that the flotation kinetics conform to a first-order model; however, a considerable amount of molybdenum remains in the tailings, indicating that the mineralization process needs to be intensified. Through structural optimization and confined-space design, a vortex-based mineralization reactor was developed. Computational fluid dynamics simulations demonstrate that the mineralizer can generate flow fields with high turbulence intensity and dissipation rates and can induce high-energy, small-scale micro-vortices. On this basis, a semi-industrial rougher flotation system was established by coupling the developed mineralizer with a flotation column. Under optimized operating conditions, namely a feed pressure of 0.06 MPa and an impeller frequency of 20 Hz, single-stage treatment of the tailings produced molybdenum concentrates with a grade of 1.90% and a recovery of 81.29%, while the Mo grade of the tailings was reduced to 0.08%. The results are markedly superior to those obtained using a conventional laboratory flotation cell, demonstrating a substantial enhancement in mineralization efficiency and molybdenum recovery. The proposed approach, therefore, provides a practical reference for the flotation recovery of molybdenum tailings as well as other micro-fine, low-grade metal tailings. Full article

This study investigates a shielded reactor coolant pump (RCP) using a thermo-fluid–structure interaction approach to numerically simulate the internal flow characteristics, impeller forces, and rotor vibration modes during rapid start-up following a loss of power accident under high-temperature and high-pressure conditions. A three-dimensional fluid–structure coupling model was established, employing the SST k-ω turbulence model and a one-way fluid–structure interaction method. The effects of three different start-up acceleration rates on pump head, pressure pulsation, vortex structures, turbulent kinetic energy distribution, and dynamic stress on the impeller were systematically analyzed. The results indicate that the medium-acceleration scenario (4.5 s start-up time) exhibits the most favorable performance in terms of pressure pulsation control, vorticity suppression, and stress distribution, effectively avoiding cavitation and structural resonance while ensuring a smooth and reliable start-up process. Modal analysis reveals that the rotor system is predominantly characterized by bending vibrations with satisfactory torsional stiffness and appropriately set critical speeds, presenting no resonance risks. This research provides theoretical foundations and engineering references for the safe restart of RCPs under extreme operational conditions. Full article

This article presents an experimental study on the hydrodynamics of coolant flow within the pressure vessel of a small modular reactor (SMR) cooled with water, including areas such as the annular downcomer, bottom chamber, and core-simulating channels that are being developed for use in land-based nuclear power plants. This paper describes the experimental setup and test model, measurement techniques used, experimental conditions under which this research was conducted, and results obtained. This study was conducted at the Nizhny Novgorod State Technical University (NNSTU) using a high-pressure aerodynamic testing facility and a scale model that included structural components similar to those found in loop-type reactors. Experiments were performed with Reynolds numbers (Re) ranging from 20,000 to 50,000 in the annular downcomer space of the test model. Two independent techniques were used to simulate the non-uniform flow field in the pressure vessel: passive impurity injection (adding propane to the airflow) and hot tracer (heating one of the reactor circulation loops). The axial velocity field at the inlet to the reactor core was also investigated. This study provided information about the spatial distribution of a tracer within the coolant flow in the annular downcomer and bottom chamber of the pressure vessel. Data on the distribution of the contrasting admixture are presented in plots. The swirling nature of the coolant flow within the pressurized vessel was analyzed. It was shown that the intensity of mixing within the bottom chamber of the pressure vessel is influenced by the presence of a central vortex. Parameters associated with the mixing of admixtures within the model for the pressure vessel were estimated. Additionally, the possibility for simulating flow with different temperature mixing processes using isothermal models was observed. Full article

Understanding and modeling the effect of magnetic fields on flows that present separation properties, such as those over a backward-facing step (BFS), is critical due to its role in metallurgical processes, nuclear reactor cooling, plasma confinement, and biomedical applications. This study examines the hydrodynamic and magnetohydrodynamic numerical solution of an electrically conducting fluid flow in a backward-facing step (BFS) geometry under the influence of an external, uniform magnetic field applied at an angle. The novelty of this work lies in employing an in-house finite-volume solver with a collocated grid configuration that directly applies a Newton–like method, in contrast to conventional iterative approaches. The computed hydrodynamic results are validated with experimental and numerical studies for an expansion ratio of two, while the MHD case is validated for Reynolds number $Re=380$ and Stuart number $N=0.1$. One of the most important findings is the reduction in the reattachment point and simultaneous increase in pressure as the magnetic field strength is amplified. The magnetic field angle with the greatest influence is observed at $\phi =\pi /2$, where the main recirculation vortex is substantially suppressed. These results not only clarify the role of magnetic field orientation in BFS flows but also lay the foundation for future investigations of three-dimensional configurations and coupled MHD–thermal applications. Full article

In this paper, we present the results of heat transfer studies on short-channel structured packing in chemical reactors. Heat transfer coefficients, streamlines, and fluid temperatures were determined using CFD (Computational Fluid Dynamics). CFD simulations were performed for three modified short-channel structures, in which the front of the walls was rounded to eliminate inlet vortices and the outlet was modified (in three versions) to minimize outlet vortices that disturb the fluid flow. CFD simulations for a classic short-channel structure with straight walls were also performed. The results proved that modified structures experienced significantly more intensive heat transport compared to classic structures. Among the tested modifications, the most promising was Modification 1, for which the Nusselt number increased from 65% to 15% depending on the structure length and the Reynolds number. Additionally, for all modifications considered, there was no inlet vortex, which significantly reduced the transport intensity in the classic structure. Further down the channel, the transport intensity was similar for all structures, including the classic structure. The smoothest flow at the outlet of the structure was observed for Modification 1. Full article

As the core equipment for efficient wastewater treatment, the internal structure of microporous aeration bioreactors directly determines the mass transfer efficiency and treatment performance. Based on Computational Fluid Dynamics (CFD) technology, this study explores the optimization mechanism of a Spherical Grid-Structured on the internal flow field of the reactor through a 3D numerical simulation system, aiming to improve the aeration efficiency and resource utilization. This study used a combination of experimental and numerical simulations to compare and analyze different configurations of the Spherical Grid-Structure. The simulation results show that the optimal equilibrium of the flow field inside the reactor is achieved when the diameter of the grid sphere is 2980 mm: the average flow velocity is increased by 22%, the uniformity of the pressure distribution is improved by 25%, and the peak turbulent kinetic energy is increased by 30%. Based on the Kalman vortex street theory, the periodic vortex induced by the grid structure refines the bubble size to 50–80 microns, improves the oxygen transfer efficiency by 20%, increases the spatial distribution uniformity of bubbles by 35%, and significantly reduces the dead zone volume from 28% to 16.8%, which is a decrease of 40%. This study reveals the quantitative relationship between the structural parameters of the grid and the flow field characteristics through a pure numerical simulation, which provides a theoretical basis and quantifiable optimization scheme for the structural design of the microporous aeration bioreactor, which is of great significance in promoting the development of low-energy and high-efficiency wastewater treatment technology. Full article

This paper presents an experimental study comparing the aeration efficiencies of hyperbolic funnels and a cylindrical reactor, focusing on key parameters such as dissolved oxygen (DO) concentration, standard oxygen transfer rate (SOTR₂₀), and standard aeration efficiency (SAE). The unique geometry of the hyperbolic funnel induces a helical water flow, which expands the gas–liquid interfacial area within the water vortex, thereby enhancing aeration efficiency via vortex dynamics. The cylindrical reactor forms larger water “umbrellas” at its outlet due to increased internal water pressure, specifically optimizing the umbrella-driven aeration. The study also evaluated a three-funnel cascade system, demonstrating that a single funnel operating in the umbrella regime is more aeration-efficient than multiple funnels in cascade, as additional funnels reduce the SAE, due to the increased pumping height required. Further experiments using 3D-printed funnels investigated the influence of outlet diameter on flow rates and aeration efficiency. Our results indicated that larger outlet diameters allowed higher flow rates and umbrella sizes, yielding a superior aeration efficiency and outperforming all other reactors tested. The study also highlights the importance of funnel positioning relative to the water reservoir, which significantly influences both the SOTR₂₀ and SAE. For the reactor investigated, a height of 75 cm was optimal for balancing both parameters. Whereas the SOTR₂₀ values of the lab reactors were lower than those of commercial systems, due to the lower flow rates, the SAE values were notably high, surpassing those of mechanical aeration systems. Our findings suggest that hyperbolic funnels are a promising and highly efficient alternative for wastewater and groundwater aeration, with a strong potential for scalability. Full article

Cavitation is a phase-change phenomenon from the liquid to the gas phase due to an increased flow velocity. As it causes severe erosion and noise, it is harmful to hydraulic machinery such as pumps, valves, and screw propellers. However, it can be utilized for water treatment, in chemical reactors, and as a mechanical surface treatment, as radicals and impacts at the point of cavitation bubble collapse can be utilized. Mechanical surface treatment using cavitation impacts is called “cavitation peening”. Cavitation peening causes less pollution because it uses water to treat the mechanical surface. In addition, cavitation peening improves on traditional methods in terms of fatigue strength and the working life of parts in the automobile, aerospace, and medical fields. As cavitation bubbles are utilized in cavitation peening, the study of cavitation bubbles has significant value in improving this new technique. To achieve this, many numerical analyses combined with field experiments have been carried out to measure the stress caused by bubble collapse and rebound, especially when collapse occurs near a solid boundary. Understanding the mechanics of bubble collapse can help to avoid unnecessary surface damage, enabling more accurate surface preparation, and improving the stability of cavitation peening. The present study introduces three cavitation bubble types: single, cloud, and vortex cavitation bubbles. In addition, the critical parameters, governing equations, and high-speed camera images of these three cavitation bubble types are introduced to support a broader understanding of the collapse mechanism and characteristics of cavitation bubbles. Then, the results of the numerical and experimental analyses of non-spherical cavitation bubbles are summarized. Full article

In developing materials for the nuclear industry, it is crucial to enhance both alloy composition and processing methods. This study focuses on investigations of applying radial-shear rolling (RSR) to a Zr-1%Nb alloy ingot, aiming to refine its microstructure and improve its properties for nuclear applications. This method, with complex vortex metal flow inside of a casted workpiece, has not been previously tested for processing zirconium ingots, so experimental verification of its applicability is of scientific interest. The 30 mm diameter ingot, produced by vacuum induction melting, was initially rolled to 20 mm at 800 °C to eliminate defects and refine the cast structure. A second rolling stage reduced the diameter to 13 mm at 530 °C, resulting in an ultrafine-grained structure. The RSR method effectively combines structural refinement and defect healing within fewer cycles, making it suitable for producing components for nuclear reactors. This approach demonstrates a potential reduction in traditional processing steps, providing a more efficient route for preparing high-quality materials for nuclear applications. Full article

Gravity settling is a widely employed technology that removes oil from produced water in oilfields. However, with the transition of reservoir development to low-permeability reservoirs, conventional produced water settling tanks face limitations in the treatment efficiency and coagulant dosage. This study presents an innovative approach that optimizes sedimentation tank structures and integrates micro-vortex flow technology to enhance coagulation and flocculation. Through chemical dosage experiments, comparative experiments, and long-term observation, the micro-vortex flow reactor demonstrates a 9.4% increase in oil removal efficiency while reducing the coagulant dosage by 30.0%. The MOR equipment achieved a 20.5% higher oil removal efficiency than conventional methods while maintaining effluent oil and suspended solids below 20 mg/L. The long-term observation experiment of MOR equipment further highlights oil removal efficiency of 94.2% and the micro-vortex reactor’s excellent anti-pollution performance. The MOR equipment significantly reduces the land occupancy area by over 50% compared to conventional methods, thanks to the implementation of micro-vortex flow technology that effectively addresses the limitations associated with traditional settling tanks. This study contributes to advancing efficient and sustainable practices in waterflooding reservoirs, particularly for meeting stringent standards of water injection in low-permeability oilfields. Full article

Highly indium-rich group-III nitrides are attracting attention for advancing our capacity to create highly effective optical emitters at extended visible/IR wavelengths or for enhancing bandgap engineering possibilities within the group-III nitride material framework. Current methods of synthesis are constrained in their efficacy, partially owing to the low decomposition temperature of indium nitride. Implementation of a new design of a vertical high-pressure spatial chemical vapor deposition (HPS-CVD) reactor with six separated precursor source zones and a rotating wafer carrier disk carrying four 2-inch wafers is proposed and analyzed using COMSOL Multiphysics as a commercial computational fluid dynamics (CFD) program to study the fluid phenomena inside the numerical domain. This study focuses on understanding the different flow patterns within the chambers at super-atmospheric conditions (5 atm to 30 atm) and identifying suitable operating conditions under which smooth and dominant vortex-free flow is achieved. Four 2-inch wafers are heated to maintain a temperature of 1200–1300 K at each pressure and gas type. Three different gas types (nitrogen, hydrogen, and ammonia) are used, and the impacts of different inlet flow velocities and rotational speeds are investigated and discussed. An operating matrix is presented for each analyzed system pressure providing suitable combinations of these operational variables for smooth flow in the chambers. Each gas type was identified to have a range of suitable rotational and inlet velocity regimes at each operating pressure. Overlap of these three gas-specific operating condition windows resulted in the identification of a generally suitable operating condition for smooth flow patterns in the system regardless of the gas type used, as required for the growth of group-III nitride materials. Full article

High indium-content group-III nitrides are of interest to further expand upon our ability to produce highly efficient optical emitters at longer visible/IR wavelengths or to broaden bandgap engineering opportunities in the group-III nitride material system. Current synthesis approaches are limited in their capabilities, in part due to the low decomposition temperature of indium nitride. A new high-pressure spatial chemical vapor deposition (HPS-CVD) has been proposed which can operate at pressures up to 100 atmospheres, thereby significantly raising the growth temperature of indium nitride more than 100 kelvins and permitting the investigation of the impact of pressure on precursor stability and reactivity. This study systematically analyzes an HPS-CVD reactor design using computational fluid dynamic modeling in order to understand favorable operating conditions for growth of group III nitrides. Specifically, the relationship between inlet gas type (nitrogen, hydrogen, or ammonia), inlet gas velocity, gas flow rate, and rotational speed of the wafer carrier is evaluated for conditions under which a smooth and dominant vortex-free flow are obtained over the wafer. Heater power was varied to maintain a wafer temperature of 1250–1300 K. Favorable operating conditions were identified that were simultaneously met for all three gas types, providing a stable operating window for a wide range of gas chemistries for growth; at one atmosphere, a disk rotational speed of 50 rpm and a flow rate of 12 slm for all gas types is desired. Full article

Polyglycolic acid (PGA) nanoparticles show promise in biomedical applications due to their exceptional biocompatibility and biodegradability. These nanoparticles can be readily modified, facilitating targeted drug delivery and promoting specific interactions with diseased tissues or cells, including imaging agents and theranostic approaches. Their potential to advance precision medicine and personalized treatments is evident. However, conventional methods such as emulsification solvent evaporation via batch synthesis or tubular reactors via flow chemistry have limitations in terms of nanoparticle properties, productivity, and scalability. To overcome these limitations, this study focuses on the design and development of a 3D-printed vortex tube reactor for the continuous synthesis of PGA nanoparticles using flow chemistry. Computer-aided design (CAD) and the design of experiments (DoE) optimize the reactor design, and computational fluid dynamics simulations (CFD) evaluate the mixing index (MI) and Reynolds (Re) expression. The optimized reactor design was fabricated using fused deposition modeling (FDM) with polypropylene (PP) as the polymer. Dispersion experiments validate the optimization process and investigate the impact of input flow parameters. PGA nanoparticles were synthesized and characterized for size and polydispersity index (PDI). The results demonstrate the feasibility of using a 3D-printed vortex tube reactor for the continuous synthesis of PGA nanoparticles through flow chemistry and highlight the importance of reactor design in nanoparticle production. The CFD results of the optimized reactor design showed homogeneous mixing across a wide range of flow rates with increasing Reynolds expression. The residence time distribution (RTD) results confirmed that increasing the flow rate in the 3D-printed vortex tube reactor system reduced the dispersion variance in the tracer. Both experiments demonstrated improved mixing efficiency and productivity compared to traditional tubular reactors. The study also revealed that the total flow rate had a significant impact on the size and polydispersity index of the formulated PGA nanoparticle, with the optimal total flow rate at 104.46 mL/min, leading to smaller nanoparticles and a lower polydispersity index. Additionally, increasing the aqueous-to-organic volumetric ratio had a significant effect on the reduced particle size of the PGA nanoparticles. Overall, this study provides insights into the use of 3D-printed vortex tube reactors for the continuous synthesis of PGA nanoparticles and underscores the importance of reactor design and flow parameters in PGA nanoparticle formulation. Full article