Mixing Performance Research Articles

Numerical investigation on mixing behaviour in the contact zone of an industrial‐scale dissolved air flotation tank

AbstractThe mixing behaviour of the wastewater and the recycle bubbly water in the contact zone could affect the separation performance of dissolved air flotation systems. In this study, the mixing characteristics in the contact zone of an industrial‐scale dissolved air flotation tank were investigated using the computational fluid dynamics method. At first, the influence of the turbulence model on the simulation results was clarified. It is demonstrated that the realizable k‐ε model could predict the gas holdup distribution with better accuracy, and the maximum relative deviation between the predicted gas holdup and the experimental results is only 10%. The influence of the geometry and operating parameters on the mixing process was then studied numerically. It is found that the mixing performance in the contact zone could be improved by decreasing the height position of the nozzle inlet in a certain range. The reason is that microbubbles disperse better in the bottom region and a double circulation flow state forms in the contact zone when the nozzle inlet is installed at a low height. Additionally, the mixing process could be further enhanced by decreasing the diameter of the nozzle inlet. As to the operating conditions, increasing the recycle ratio could not only increase the gas holdup but also improve the mixing performance in the contact zone. When the recycle flow rate remains constant, increasing the wastewater flow rate will lead to a decrease in gas holdup and deterioration of the mixing effect.

Numerical Research of Flame Propagation Process in a Supersonic Combustor with Multi-Strut

ABSTRACT The flame processes and the influence of different factors on the cross flame propagation width in a supersonic combustor equipped with multi-strut fueled with kerosene were analyzed to deepen the understanding of supersonic flame characteristics. Under the conditions of T t = 1680K, P t = 1.64Mpa, and Ma = 2.7, the numerical calculations using the multi-step combustion reaction mechanism were carried out. The mixing performance and flame propagation width could be improved by increasing the number of struts. In the multi-strut injection method, the cross flame was observed outside the central flame. The mechanism of cross flame formation was revealed. The establishment of the cross flame had a maximum spacing requirement between injection struts, but this limit could be expanded by the high temperature zone formed by the narrow-distance injection strut. The effects of igniter energy and ignition strut equivalence ratio on the flame diffusion process were studied. Then the boundary conditions required for the cross flame propagation were obtained. The results of this study are highly significant for enhancing the performance of large-scale supersonic combustors in the future.

The Design and Investigation of Hybrid a Microfluidic Micromixer

Today, microfluidics has become a revolutionary interdisciplinary topic with considerable attention in a wide range of biotechnology applications. In this research work, a numerical investigation of a microfluidic micromixer is carried out using a hybrid actuation approach with different micropillar shapes and gaps. For this purpose, COMSOL Multiphysics v.5.2. is used with three different physics, such as thermoviscous acoustic physics to solve acoustic governing equations, laminar physics to solve fluid flow governing equations, and diluted transport species to solve mixing governing equations. The simulations were carried out at different Reynolds numbers such as 2, 4, 6, 8, 10, and 12 with an oscillation frequency of 15 kHz. The results were in the form of acoustic characteristics such as acoustic pressure, acoustic velocity, acoustic stream, mixing index, and fluid flow behaviour at various Reynolds numbers. The results revealed that the inclusion of micropillars improved the mixing performance and strength of the acoustic field, resulting in an improvement of the mixing performance compared to the case without micropillars. In addition, the mixing performance is also investigated at different Reynolds numbers, and a higher mixing index is investigated at lower Reynolds numbers. Moreover, it was also investigated that blade-shaped micropillars with 0.150 mm gaps deliver the best results compared to the other cases, and the maximum and minimum values of the mixing index are 0.97 and 0.72, respectively, at Reynolds number 2. The main reason behind this larger mixing index at low Reynolds numbers is due to the inclusion of micropillars that enhance the diffusion rate and contact area, leading to the homogenisation of the heterogeneous fluids in the microchamber. The obtained results can be extremely helpful for the design and modifications of a hybrid microfluidics micromixer.

Determining kinetics of fast exothermic reactions using a flow calorimeter

Continuous flow calorimeters are considered an emerging technique due to their ability to reduce safety issues associated with highly exothermic rapid reactions. In this study, a custom-made isoperibolic flow calorimeter was constructed, which uses a pyroelectric IR Sensor for temperature profile recording. The objective of this study is to validate the reactor concept for the determination kinetic parameters. Residence time distribution (RTD) analysis was conducted to assess the mixing performance of the packed-bed reactor employed in the calorimeter. This calorimeter was connected to a custom-made conductivity flow cell (CFC), to measure the in-line conductivity of the outlet stream. An axially dispersed plug flow reactor model (AD-PFR) is required to be able to incorporate the non-ideal behaviour of the flow. The experimental apparatus design and methodology was validated by conducting the hydrolysis of acetic anhydride. The activation energy, EA and the pre-exponential factor, ln(k0) for the hydrolysis of acetic anhydride were found to be 52.05 kJ mol−1 and 12.26 (s−1), respectively, which falls within the range of reported values. The new flow calorimeter proved to be effective, and accurate.

Developing an orbitally shaken bioreactor featuring a square vessel wall with a large circular chamfer

The impact of orbitally shaking bioreactors (OSRs) on the biopharmaceutical industry is becoming increasingly important. In the preliminary exploration of the orbitally shaking bioreactor performance, the vessel wall shape has a crucial influence on the mixing and mass transfer in the bioreactor. However, the shape of OSRs still maintains a cylindrical structure, significantly limiting the advantages of the orbital shaking mixing. Therefore, in order to further improve the mixing and mass transfer performance of OSRs, a novel wall shape is proposed in this paper. This novel wall shape consists of cylindrical and square parts and looks like a square tank with a large circular chamfer (STCC), which was found could effectively enhance the efficiency of material mixing and mass transfer theoretically. Based on the same specific volumetric power consumption, a comparative analysis was conducted on the mixing time and oxygen transfer efficiency of OSRs with different shape walls using simulation and experimental methods. The results showed that the OSR with STCC was expected to perform higher mixing and oxygen transfer efficiency than the OSR with cylindrical wall. These findings suggested a promising prospect for the future application of the OSRs with STCC.

Experimental and Numerical Investigations of Mixing Performance of Mixing Agitators of Deep Cement Mixing Ships

Recent decades have witnessed the increasing usage of deep cement mixing (DCM) mixers in the field of marine infrastructure construction. The mixing performance, including the torque history, can be helpful for structural safety evaluation, design, and the optimization of agitators, which is of engineering significance. However, to the best of the authors’ knowledge, there are no related publications that have reported the mixing behaviors of deep cement mixing agitators. In light of this, the present work conducts experimental and numerical investigations of the mixing behaviors of a DCM ship mixing agitator. To achieve this end, a model test device is established, and mixing experiments using two- and three-blade mixers are respectively conducted. Silt and clay soils are considered in the experiments with a three-blade mixer, while clay soils are used for those with a two-blade mixer. In addition, this work designs a torque transducer placed inside the rotating rod to accurately measure the torque history of the agitator during model test experiments. The experimental results show that, when mixing clay using agitators with different blades, the average torque value required for a two-blade agitator is slightly larger than that for a three-blade one. This study also presents a computational framework based on the arbitrary Lagrangian–Eulerian (ALE) method for an efficient and accurate modeling of the soil-mixing behaviors of the agitator. The numerical results are found to be in good agreement with the experimental data from model tests in terms of torque history, which demonstrates the effectiveness and capacity of our presented computational framework. The numerical results show that the average torque value is smaller at a higher rotational speed during the mixing of clay using a two-bladed agitator, but the effect of rotational speed on the torque history is small. The experimental and numerical methods introduced in the present work can act as a useful tool for investigations of mixing behaviors of DCM agitators.

Mixing Performance of a Passive Micromixer Based on Split-to-Circulate (STC) Flow Characteristics.

We propose a novel passive micromixer leveraging STC (split-to-circulate) flow characteristics and analyze its mixing performance comprehensively. Three distinct designs incorporating submerged circular walls were explored to achieve STC flow characteristics, facilitating flow along a convex surface and flow impingement on a concave surface. Across a broad Reynolds number range (0.1 to 80), the present micromixer substantially enhances mixing, with a degree of mixing (DOM) consistently exceeding 0.84. Particularly, the mixing enhancement is prominent within the low and intermediate range of Reynolds numbers (0.1<Re<20). This enhancement stems from key flow characteristics of STC: the formation of saddle points around convex walls and flow impingement on concave walls. Compared to other passive micromixers, the DOM of the present micromixer stands out as notably high over a broad range of Reynolds numbers (0.1≤Re≤80).

The performance of hollow fiber direct contact membrane distillation modules

Computational fluid dynamics simulations were conducted in hollow fiber direct contact membrane distillation modules. The objective is to understand the impact of packing densities and incorporating flow mixers on the feed side of the system. The feed flow rate varies while the feed inlet and permeate inlet temperatures are fixed. Furthermore, finned hollow fibers are used as flow disruptors in the feed channel to mitigate temperature and concentration polarization and to enhance vapor flux. The laminar flow model is used to characterize velocity, temperature, and concentration fields. It is demonstrated that the packing ratio significantly influences when the flow rate is low. The tightly packed hollow fibers in the shell resulted in decreased permeating flux due to a lack of mixing in flow in the narrowed regions around hollow fibers. The data shows that the permeate flux was 14.5 % higher for a 25 % packing ratio compared to a 75 % packing ratio at a lower flow rate. In contrast, the flux decreases only 3 % at a higher flow rate with an increasing packing ratio. It is demonstrated that the presence of fins breaks the parallel flow and enhances the mixing performance by approximately 10 % While fin modifications can enhance flux performance and mitigate polarization issues, the decrease in the merit criterion suggests that the benefits must be weighed against the potential drawbacks, such as elevated energy consumptions due to the increase in pressure drops. This underscores the importance of a balanced approach in optimizing membrane module performance.

Intelligent design and seawater mixing performance of new synchronous grouting materials in a pure-solid-waste framework

Solid waste, as a reliable raw material substitute for synchronous grouting materials in shield tunneling, addresses the issue of recycling traditional waste. Additionally, geopolymer slurries utilizing waste exhibit excellent physical and chemical properties, meeting requirements for the stability and long-term performance of synchronous grouting materials. In this study, an environmentally friendly polymer grouting material based on pure solid waste was developed using sunflower stalk ash, blast furnace slag, and fly ash as raw materials. By varying the proportions of binder materials and quantity of seawater introduced, we systematically analyzed the applicability of grouting materials and reliability of seawater as a mixing medium in a comprehensive solid waste framework. We utilized an artificial intelligence integrated algorithm to predict the compressive strengths of cementitious materials with different ratios through forward performance prediction. The proportions were then inverted using a simulated annealing algorithm according to the strength required for actual engineering applications. The results demonstrated that under the dual effects of sunflower stalk ash alkalinity and seawater composite salts, more active Si and Al ions were released during the hydration process. The solid waste filling and accelerating effects of composite salt hydration can effectively improve the pore structure, resulting in a significant increase in early compressive strength. The artificial intelligence ensemble algorithm proved to be an effective model for predicting compressive strength and the simulated annealing algorithm successfully determined the optimal ratios for meeting practical production requirements. These findings provide a foundation for solid waste treatment and underground engineering using seawater resources, contribute to the preparation of high-performance slurries, and facilitate green development.

Predicting mixing degree of supersonic flow by a few target data using meta-learning

Predicting the mixing degree of supersonic flow is essential for designing compressible flow devices, such as scramjets, chemical lasers and ejectors. However, building appropriate predictive models of supersonic flow mixing degrees utilizing deep learning is challenging because the samples are expensive from computation or experiments. Herein, a meta-learning method is proposed to reduce the amount of target data required for training a mixing degree estimation by improving the pre-training performance. The datasets of multiple other inlet pressures are used as the pre-training datasets to allow the neural network to generalize to the target inlet pressure. A deep neural network pertained by a model-agnostic meta-learning algorithm estimates mixing degrees from the input information of a jet angle and an inlet temperature. The estimation accuracy is verified using the simulated dataset. Using 5 target data and 10 gradient steps, the meta-learning method achieves the averaged coefficient of determination of 0.95. Moreover, the meta-learning framework achieves mixing degree estimation more quickly and accurately than transfer learning and merged learning. This work provides a way to alleviate the required data usually insufficient for predicting the mixing performance for high-speed flow applications.

Enhancing mix proportion design of low carbon concrete for shield segment using a combination of Bayesian optimization-NGBoost and NSGA-III algorithm

The demand for segment concrete increases rapidly with the expansion of urban rail transit and underground space, which may lead to carbon emissions (CE). In the production of segment concrete, using supplement cementitious materials (SCM) can be used to reduce CE instead of cement. However, SCM contents are usually determined by many orthogonal experiments, which are often time-consuming and only consider the limited experimental variables. Therefore, a novel hybrid intelligent algorithm combining Bayesian optimization (BO), natural gradient boosting (NGBoost) and non-dominated sorting genetic algorithm (NSGA)-III is proposed, which overcomes these disadvantages. Firstly, NGBoost model after hyperparameter optimization using BO is used to establish a nonlinear mapping relationship between segment concrete mix proportion and performance, which was used as the fitness function of the non-dominated sorting genetic algorithm (NSGA-III). Secondly, the optimal Pareto solutions were obtained through NSGA-III, and the reasonable range of segment concrete mixing proportion was obtained. Finally, a segment concrete production case was used to verify the effectiveness of the proposed algorithm. The results showed that the proposed hybrid algorithm combining proposed scheme decision strategy can obtain an optimal design scheme for concrete mix proportion. In addition, the comprehensive optimization rate of the obtained optimal scheme compared to the experimental optimal group was 11.5%. Moreover, the amount of phosphorous slag (PS) and granulated blast furnace slag (GBFS) in the optimal scheme was 26%, with a mass ratio of 1:2. Compared to the experimental optimal group, the optimal scheme can reduce the cost and CE per cubic meter by 31.64 yuan and 31.04 kg, respectively. Furthermore, the hybrid algorithm proposed can accurately obtains an optimal amount of SCM, which could be used as a supporting tool to reduce the production cost and CE of segment concrete. Overall, this research contributes to combining machine learning algorithms with actual production processes, which overcomes the data limitations of traditional experiments. It also provides a new intelligent approach and reference cases for the low-carbon design and sustainable development of building materials such as concrete.

Enhancing mixing performance in a square electroosmotic micromixer through an off-set inlet and outlet design

This study addresses the critical need to enhance mixing quality and cost efficiency in electroosmotic micromixers, crucial for various applications, such as chemical synthesis, medical diagnostics, and biotechnology, utilizing the precision of microfluidic devices. The intricate dynamics of time-dependent electroosmotic vortices induced by microelectrodes are investigated, exploring the nonlinear physics principles driving mixing enhancement. Specifically, an examination is made of how nonlinear phenomena, such as convective flow instabilities, chaotic advection, and nonlinear interactions between fluid flow and channel geometry, contribute to observed improvements in mixing performance. Through comprehensive numerical simulations employing finite element-based solvers, the impact of relevant parameters, such as voltage amplitude (V0), frequency (f), Reynolds number (Re), and Debye parameter (k), on mixing performance is systematically analyzed. Findings reveal that optimizing these parameters, coupled with the strategic design of micromixers featuring offset inlets and outlets, leads to a remarkable mixing quality of 98.44%. Furthermore, a methodology is proposed for selecting the optimal micromixer configuration (MM1), balancing mixing quality, and cost efficiency. This study advances the understanding of electroosmotic micromixers and provides practical guidelines for optimizing microfluidic device performance in diverse applications.

A water model study on mixing behaviour in a Kaldo furnace using acid–base neutralization decolourization method combined with RGB-based image analysis

Mixing time is usually used as an important parameter for quantifying the mixing performance of multiphase flow in a metallurgical bath. However, the topic of the mixing time of a Kaldo furnace for copper anode slime treatment has received little attention from scholars to date; this concept is important for guiding the optimization of high-efficiency smelting in the Kaldo furnace. In the present work, the mixing behaviour of gas-liquid two-phase flow in a Kaldo furnace was simulated using a scaled-down 1:4.5 water model fabricated from transparent acrylic plastic. A visualization technique and a quantitative characterization method for mixing performance in the Kaldo furnace—acid-base neutralization decolourization combined with RGB-based image analysis—were innovatively proposed. This approach can not only determine the global mixing level η¯(t) and track the frequency distribution of the local mixing performance ξk(t) of the fluid region during the mixing process but also quantify the mixing time. In addition, based on the proposed method and by using dimensional analysis, the effects of operating parameters (such as the gas flow rate Q, injection lance height h, rotation speed ω, liquid volume fraction φ, inclination angle θ, and liquid viscosity μl) on the mixing time of gas-liquid two-phase flow in the molten bath were discussed. On this basis, the empirical equation of the mixing time as a function of h, ω, φ, the modified Froude number (Fr'), μl and θ was established as the first quantitative relationship of the mixing time for the Kaldo furnace.

Performance of bituminous concrete mixes using waste eggshell as a bitumen modifier

Performance of bituminous concrete mixes using waste eggshell as a bitumen modifier

Hydrodynamic intensification and interfacial regulation strategy for the mixing process of non-Newtonian fluids

Efficiently realizing laminar flow mixing of non-Newtonian fluids is a key challenge faced by conventional stirred reactors. In this study, an innovative strategy is proposed to regulate the flow pattern from radial to axial flow by changing the interface evolution of the flow field, so as to solve the problem of uneven mixing materials in laminar flow. An innovative combination of the RGB (Red, Green, Blue) brightness analysis and quantitative analysis area method was used to quantitatively describe the mixing performance of the three stirred reactor in the laminar flow. We found that the coloring area ratio of the dual shaft off-centred mixer (DSO) mixer was approximately 165.7 % and 93.8 % higher than that of the single shaft central (SSC) and single shaft off-centred mixer (SSO), respectively. Results showed that the DSO mixer can directionally adjust the stable interface of the flow field, and then obtain the ideal velocity distribution and flow pattern. Importantly, it is found that the mixer has an inherent axial mixing limit in the laminar flow. Increasing the Reynolds number can only shorten the time for the mixing system to reach the steady state, and cannot further improve the axial transport capacity of the system. Compared to the SSC and SSO systems, the DSO mixer demonstrated a reduction of nearly 20 % in overall mixing time and power consumption. Through comparative analysis of pressure distribution and Poincaré cross section, the DSO mixing system can switch chaos oscillation and realize the “globally chaotic mixing” from “locally chaotic mixing”. Remarkably, this work highlights the potential of DSO mixer as a simple and efficient system for laminar flow mixing applications, such as polymerization processes, biological fermentation.

Study on the bubble breakup and internal flow characteristics in the pulsed jet ejector

To intensify the bubble breakup in the ejector, a novel pulsed jet ejector is designed in this work. The pulsed jet is introduced into the ejector by one fluidic oscillator. A high-speed camera experiment is conducted to capture the progress of bubble breakup. The intensification mechanism of pulsed jet on bubble breakup in ejector is investigated by numerical simulation. The experimental results indicate that the introduction of the pulsed jet effectively induces the occurrences of pressure fluctuations and vortex collision, prompting the deformation of bubbles to produce microbubbles. It is also found that the bubble diameter and number of microbubbles mainly depend on the process of bubble breakup in the divergent section, and the bubble diameter distribution is significantly influenced by the variation of Reynolds number. The variations of the vortex structure are induced by the pulsed jet, which is a key factor influencing mixing efficiency and bubble breakup effects. In addition, pulsed jet ejectors have superior mixing performance compared to conventional ejectors.

Orientation effects on mixed convective performance of twisted pin fin heat sink: Experimental investigation

In the current work, an experimental study is carried out to examine the heat transfer performance and friction effects on a pin fin matrix of a heat sink for different design variables and operating conditions. This examination aims to assess the thermo-hydraulic performance of the heat sink with three orientations (90°, 180°, and 270°). In the presence of three heat loads (66 W, 91 W, and 121 W), each of these orientations is tested with three twisting angles (30°, 60°, and 90°) for different pin fins cross-sections of square and hexagonal at various ranges of air Reynolds number (Re) (3182 to 9971). The downward position of a heat sink achieves a higher Nusselt number (Nu) than the sideward and upward positions. The fin pin with a twisting angle 30° has superior efficiency for three orientation angles and hexagonal and square cross sections. Square pin fin records the lower thermal performance at Re = 3182, orientation angle (β) = 270˚, and pin twist angle (θ) = 30°, and the best at Re = 9971, β = 180°, and θ = 90°. Compared to 60˚ and 90˚, the pin fins had a reduced pressure loss at a twisting angle of 30°.

Evaluating Commercial Loop-Mediated Isothermal Amplification Master Mixes for Enhanced Detection of Foodborne Pathogens.

Loop-mediated isothermal amplification, LAMP, is nowadays the most popular isothermal nucleic acid amplification technique, and as such, several commercial, ready-to-use master mixes have flourished. Unfortunately, independent studies to determine their performance are limited. The current study performed an independent evaluation of the existing ready-to-use commercial LAMP master mixes WarmStart® LAMP Kit, LavaLAMP™ DNA Master Mix, Saphir Bst Turbo GreenMaster, OptiGene Fast Master Mix ISO-004, and SynLAMP Mix. To reduce bias, three different genes, namely ttr (Salmonella spp.), rfbE (E. coli O157), and hly (Listeria monocytogenes), were targeted. The comparison was based on amplification speed, performance with decreasing DNA concentrations, and the effect of five typical LAMP reaction additives (betaine, DMSO, pullulan, TMAC, and GuHCl). Significant differences were observed among the different master mixes. OptiGene provided the fastest amplification and showed less detrimental effects associated with the supplements evaluated. Out of the chemicals tested, pullulan provided the best results in terms of amplification speed. It is noteworthy that the different additives impacted the master mixes differently. Overall, the current study provides insights into the performance of commercial LAMP master mixes, which can be of value for the scientific community to better select appropriate reagents when developing new methods.

CFD Analysis of Laminar Mixing Mechanism and Performance in an Oscillatory Baffled Reactor

AbstractThe mixing mechanism in an oscillatory baffled reactor (OBR) at the low oscillatory Reynolds number was analyzed using numerical simulation. OBR is a tubular reactor in which baffles are placed at equal intervals, and the interaction between the baffles and oscillatory flow mixes the fluid. At the low oscillatory Reynolds number, mixing induced by the folding and stretching of the fluid was observed at each baffle section. This was caused by the radial flow in the vicinity of the baffles when the direction of the oscillatory flow was reversed. The mixing performance was quantified by applying virtual particle tracing, setting up a virtual boundary surface, and following the changes in its area over time. The area increased exponentially, confirming the chaotic mixing characteristics.

Service mix and financial performance in rural hospitals: A contingency theory perspective.

Rural hospitals are increasingly at risk of closure. Closure reduces the availability of hospital care in rural areas, resulting in a disparity in health between rural and urban citizens, and it has broader economic impacts on rural communities as rural hospitals are often large employers and are vital to recruiting new businesses to a community. To combat the risk of closure, rural hospitals have sought partnerships to bolster financial performance, which often results in a closure of services valuable to the community, such as obstetrics and certain diagnostic services, which are viewed as unprofitable. This can lead to poor health outcomes as community members are unable to access care in these areas. In this article, we explore rural hospital service offerings and financial performance, with an aim to illuminate if specific service offerings are associated with positive financial performance in a rural setting. Our study used hospital organization data, as well as county-level demographics with periods of analysis from 2015 and 2019. We employed a pooled cross-sectional regression analysis with robust standard errors examining the association between total margin and service lines among rural hospitals in the United States. The findings suggest that some services deemed unprofitable in urban and suburban hospital settings-such as obstetrics and drug/alcohol rehabilitation-are associated with higher margins in rural hospitals. Other unprofitable service lines-such as psychiatry and long-term care-are associated with lower margins in rural hospitals. Our results suggest the need of rural hospitals to choose services that align with environmental circumstances to maximize financial performance. Hospital administrators in rural settings need to take a nuanced look at their environmental and organizational specifics when deciding upon the service mix. Generalizations regarding profitability should be avoided to maximize financial performance.