Showing papers on "Complete mixing published in 2017"

Response of suspended sediment particle size distributions to changes in water chemistry at an Andean mountain stream confluence receiving arsenic rich acid drainage

Abstract: Acid drainage is an important water quality issue in Andean watersheds, affecting the sustainability of urban, agricultural and industrial activities. Mixing zones receiving acid drainage are critical sites where changes in pH and chemical environment promotes the formation and dissolution of iron and aluminum oxy/hydroxides. These particles can significantly change the speciation of toxic metals and metalloids throughout drainage networks via sorption, desorption and settling processes. However, little is known about the behavior of particle size distributions (PSDs) in streams affected by acid drainage and their relationship to metal speciation. This work studied: (a) the PSDs for a wide range of mixing ratios found at a fluvial confluence affected by acid drainage, and (b) the response of PSDs and arsenic speciation to environmental changes found when the particles approach complete mixing conditions. The confluence between the Azufre River (pH ~ 2, high concentration of dissolved metals) and Caracarani River (pH = 8.6, low concentration of dissolved metals) was used as a representative model for study. Field measurements show a bimodal PSD with modal diameters of ~50 and 300 µm. At shorter distances from the junction the smaller modes with smaller particle volumes were dominant across the stream cross-sections. A systematic shift towards larger particle sizes and larger particle volumes occurred downstream. The analysis of laboratory PSDs for Azufre/Caracarani mixing ratios between 0.01 and 0.5 (pHs from 6.2 to 2.3) showed a bimodal trend with ~15 and 50 µm characteristic diameters; larger particles formed at higher pHs. When particle suspensions were transferred in laboratory experiments from very low pHs to full mixing conditions (pH ~ 2.8 and mixing ratio ~ 0.25) particle sizes varied, while the dissolved arsenic concentration decreased. The observed reaction kinetics were slow compared to the time scale of advective transport, creating opportunities for engineered controls for arsenic. This work contributes to a better understanding of the chemical-hydrodynamic interactions in watersheds affected by mining, and identifying opportunities to improve water quality at points of use. This article is protected by copyright. All rights reserved.

Mixing efficiency enhancing in micromixer by controlled magnetic stirring of Fe3O4 nanomaterial

Abstract: Rapid and complete mixing are fundamental criteria in the design of microfluidic chips and to date, magnetic stir bars are proving convenient and efficient tools for both macroscale and lab-on-chip applications. In this work, we implement magnetic stirring of Fe3O4 nanomateral to mediate active mixing in T-shape micromixers, where passive diffusion of two solutes (blue phenol dye and citric acid) has otherwise proven inefficient. The Fe3O4 magnetic nanoparticles are added to the citric acid which then transform into nano- or micro-rods that rotate synchronously with an external rotating magnetic field. As such, the local flow field that each rod generates can perturb the hydrodynamic flow in the mixing channel. The mixing performance with magnetic nanoparticles added at different concentrations and rotation speeds reveal that higher concentration of magnetic particles in the solution and fast rotation speeds improve the efficiency significantly. More efficient mixing with microrods is also achievable using wide channels and low flow rates. Efficient mixing has been realized for a 6.6 mT driving field if the magnetic materials are rotated at 10.47 rad sź1 and 0.05 wt% concentration. The same parameters applied to a 300 µm micro channel at 2 µL minź1 flow rate more than double the efficiency of a passive micromixer.

Variability of tracer breakthrough curves in mountain streams: Implications for streamflow measurement by slug injection

Abstract: Tracer dilution methods are commonly used to measure discharge in steep mountain streams. This research addressed knowledge gaps associated with dilution methods using original field data collected on nine streams in southwest British Columbia and discharge measurements conducted by Northwest Hydraulic Consultants Ltd. Minimum mixing lengths ranged between 2.4 and 24.5 stream wetted widths, but determining the mixing length can be confounded by surface-subsurface water fluxes. Probes need to be placed on opposite sides of the stream to verify adequate mixing, because probes located at different locations on the same of the stream sometimes suggested complete mixing had occurred when it in fact had not. For probes located downstream of complete mixing, breakthrough curves (BTCs) for probes located in the main current differed significantly from probes in zones with recirculating flow, even though they yielded discharge values within ± 10%. The peak of the BTC is a function of the mass of tracer injected, r...

Mixing behaviour of miscible liquid-liquid multiphase flow in stirred tank with different marine propeller installment by computational fluid dynamics method

Abstract: This paper presents a three-dimensional and transient computational fluid dynamics (CFD) simulation of the miscible liquid-liquid system (water-molasses) in a stirred tank operated in turbulence regime. The mixing process is crucial role when the viscosity and density of the solution are different, even though the solution mutually dissolved. There are two configurations used in the modelling. The first configuration is a conical- bottomed cylindrical tank equipped with a side-entry marine propeller and the second one is equipped with the top-entry marine propeller. The geometry of tank (D = 0.26 m and H = 0.363 m) and propeller (d = 0.033 m) are the same in both configurations. The transient calculations were conducted using the mixture modelmultiphase flow approach coupled with RANS (Standard k - E) turbulence model with time step is 0.01 s. Amultiple refference frame approach was applied to modelling propeller motion. The mixing behaviour and theprediction of the moment of impeller and shaft are compared between top-entry and side-entry configuration. Some simulation results included the flow pattern recognition and distribution of molasses was discussed. The flow pattern in the top-entry configuration was indicating a stable double loop circulation. Whereas the flow patterns in side-entry configuration showing loop circulation around the marine propeller, some unstable and disordered flow pattern also formed around the tank wall. The variation of the flow pattern which happened showed the instability of the mixing process in side-entry configuration. There is a significant different mixing process produced from the side entering and top entering based on the distribution of molasses inside the tank. The result of CFD-simulation shows that the moment of impeller and shaft decrease for the side-entry configuration, and increase for top-entry configuration toward complete mixing.

Computational Fluid Dynamic Simulation of Mixing in Circular Cross Sectional Microchannel

Abstract: The application of process intensification has been catching up with the trend already observed in the chemical engineering area, where the use of microfluidic devices has already been elevated to production scale. Microreactor technology, an element of process intensification, offers potential benefits to the future of chemical engineering for its well-defined high specific interfacial area available for heat and mass transfer resulting in higher transfer rates and enhances safety due to its low hold-ups. In relation to the time-scale of chemical kinetics, diffusive transport in micro-devices is faster than in conventional mixers. Since mixing has a crucial impact on the overall performance of micro reaction processes, the need for measuring and comparing mixing performance have also increased. To exploit the resulting potential, the mixing behaviour of flow mixers on micro-scales need to be further investigated. In this work, three-dimensional Computational Fluid Dynamics (CFD) model with circular cross section micro channel has been developed instead of rectangular cross section done by other researchers as circular micro channel can withstand large pressure difference without undergoing any significant distortion where non-circular cannot. The CFD simulation was carried out using COMSOL Multiphysics 4.2a software to investigate the effects of “T” and “Y” micro channel configurations, inlet velocity and diffusion coefficient towards the mixing quality in the micro reactor. The results demonstrated that inlet velocity and diffusion coefficient has significant effects on mixing performance where low inlet velocity and high diffusion coefficient value resulted in better mixing performance. It was found that “Y”-shaped micro channel showed complete mixing at a shorter distance as compared to “T”-shaped micro channel and the minimum mixing length of micro channel needed for complete mixing is 20 mm.

A CFD investigation of mixing profiles within a micro-coiled flow inverter

Abstract: Background/Objectives: Due to the low Reynolds number (Re) in microfluidic domain, the predominant laminar flow might inhibit effective mixing in micro-Coiled Flow Inverter (mCFI). Fluid dynamics within the mCFI was simulated with Computational Fluid Dynamics (CFD) software to investigate the mixing profile. Methods/Statistical Analysis: Fluid flow was simulated with the software FLUENT with Species Transport (ST) setting, to replicate the mixing of two water bodies. Geometry of the mCFI was designed with a tubing diameter of 0.5 mm and curvature ratio of λ = 10. Fluid flow rate was adjusted to attain 25≤ Re ≤ 250. Findings: A mixing time of 0.59s was achieved with Re = 250. However complete mixing was still achievable even in Re = 25 albeit with a longer mixing time. Application/Improvements: Flow inversion is improved the mixing condition in micro-structured tubing, in enhancement of the diffusive mixing in microfluidics.

Shock-excitation material mixing and filling device and material mixing and filling method for spectral samples

Abstract: The invention provides a shock-excitation material mixing and filling device and a material mixing and filling method for spectral samples The device includes a frame, a two-phase vibrating device, a material mixing and filling apparatus, and a control unit The method includes the steps of: 1) placing ore powders into crucibles, which are buckled vertically, in the material mixing and filling apparatus, and performing rotational turning, eccentric vibration and vertical periodical shaking to achieve complete stirring and mixing of the multi-component ore powders; 2) through action of a tilt motor, overturning the crucibles buckled vertically, and with combination of rotation, eccentric vibration and vertical periodical shaking, filling cavities in carbon rods with the mixed ore powder in the crucibles; and 3) repeating the steps to complete mixing of the ore powders in multiple batches and filling of the materials in the carbon rods The device has creative design and structure and high automation degree, greatly improves work efficiency of material mixing and filling and has advantages on improvement of spectral analysis precision and work efficiency

Commercial tea brewing station

Abstract: A commercial tea brewing station entrains a hot tea flow through a brew basket with an intermittent liquid sweetener flow to dissolve the liquid sweetener in the hot tea brew. A high velocity diluting flow is delivered to the concentrated sweetened tea at an angle to create turbulent back flow, further promoting complete mixing and dissolving of the sweetener and the diluting water, so that no manual mixing step is required.

An investigation of mixing in micro coiled flow inverter in varying tube diameter with fixed reynolds number

Abstract: Micro-scaled Coiled Flow Inverter (MCFI) is a scaled down version of a Coiled Flow Inverter (CFI) which utilizes the principle of flow inversion for process intensification. MCFI is constructed with tubing less than 1.0mm. The microfluidic nature of MCFI caused by low Reynolds number (Re) laminar flow posed as a challenge to achieve effective mixing. Simulation was implemented with Computational Fluid Dynamics (CFD) software FLUENT to visualize the mixing of MCFI with different diameters. Fluid flow of the mixing of two water bodies was simulated. Geometry of the MCFI was designed with tubing diameters of 1.0mm, 0.8mm, 0.6mm and 0.5mm to investigate the effect of cross-sectional diameter towards mixing efficiency. The curvature ratio (λ) was fixed at 10 to reduce the complexity of the system. Fluid flow rate was calculated and adjusted to obtain Re 250 for each tubing size. Velocity profile of tubing within the range of diameter investigated showed negligible difference. Simulation results showed a parabolic velocity profile for straight tube, while skewed velocity profiles were observed within the straight coil and MCFI. MCFI with the tubing diameter of 0.5 mm achieved complete mixing at normalized tube length of 0.69, equivalent to 175mm. MCFI with ID 1.0 mm showed 54.5% mixing, while MCFI with ID 0.8 mm and 0.6 mm showed 69.6% and 78.9% mixing respectively at the outlet. Similarly, fluid in straight tube and straight coil had also failed to achieve complete mixing. Results obtained suggested smaller tubing diameter indeed led to better mixing process in MCFI, in expense of an increase in pressure

Mass transfer in bodies of classical shapes in a semicontinuous complete mixing apparatus

Abstract: Analytical solutions of problems of the diffusion revovery of a substance from solid bodies of classical shapes in a semicontinuous complete mixing apparatus (batch for the solid phase and continuous for the liquid phase) were found using the method of integral Laplace transforms. The mathematical models developed were applied to studying leaching of zinc chloride from vulcanized fiber.

Design of Hardware Mixing Model for ICA Algorithms Using Wireless MIMO System

Abstract: Independent component analysis (ICA) is a signal processing technique used for un-mixing of the recorded mixed signals. Un-mixing is based on the fact that the ICA algorithms must know the mixing model in advance i.e., how the signals are mixed. In the literature, different mixing models are presented for the ICA algorithms in digital domain, while the mixing phenomena normally occur in analog domain. The existing mixing models include linear mixing, non-linear mixing, instantaneous mixing, convolutive mixing and over complete mixing. Various algorithms are presented for these mixing models because the algorithm basically explores the mixing model and blindly un-mix the mixed data based on this information. We consider the instantaneous mixing model in this paper and propose a hardware design of the mixing model for ICA algorithms. The proposed model represents unity mixing, scaled mixing and ill-conditioned mixing. These mixing models are basically different conditions of the instantaneous mixing model. It is hoped that this model will serve as a test bench for evaluating the performance of the ICA algorithms. We simulate the proposed model using 16-QAM signals for all the three mixing conditions. The FastICA and the OBAICA algorithms are used to evaluate the proposed mixing models for un-mixing. Results obtained are such that the unity mixing provides excellent performance of the algorithms, while the scaled mixing provides good performance and the ill-conditioned mixing gives worse performance of the algorithms. Moreover, to the best of our knowledge, we are the first to present the hardware mixing model for ICA algorithms.

Obtaining complete mixing using hydrodynamic analysis on batch reactor

Abstract: This research aims to find the best possible mixing conditions in a multi-phase reactor consist of wastewater, activated sludge and aeration. This has been done by analyzing flow profiles in the system using experimental and computational work. Hydrodynamic characteristics, such as influent flow rate, aerator configuration, baffle installment, play important role for wastewater treatment process. Determination of influent flow rate and the reactor configuration have done by analyzing flow profile in laboratory scale single-phase reactor with the dimension of 16 L. Velocity profile was developed from tracer study. There were 2 influent flow rate variations of 0,0095 L/s and 0,02 L/s, in 3 variations of reactor configuration. The first variation was without modification (control), the second was baffled reactor and the third was porous reactor. From the experimental work, it was obtained that the influent flow rate of 0,0095 L/s gave longer Residence Time Detention (RTD) and longer time to reach the outlet than flow rate of 0,02 L/s. The baffled configuration gave longer RTD and longer time to reach the outlet as well than other configuration. This two results was reasonable since the first influent flow rate and the baffled reactor have higher effective volume than other variations. In multi-phase system, experimental work was done in batch system to observe the contact between air-bubble and sludge in reactor, which then calibrated using CFD (Computational Fluid Dynamic) model. The result showed that the model of mixture in k- equation was considerable to use in future simulation work. The using of diffuser could increase mixing condition inside the reactor due to its higher effective volume.