Mixing Homogeneity Research Articles

Numerical simulation on stirring motion and mixing characteristics of ellipsoid particles

To investigate the motion characteristics and the law of identical property for particles obtained under segregation to uniform distribution conditions in forced agitation mixing, the mixing process of the same sized ellipsoidal particles at different rotating speeds in a U-tank is simulated using three-dimensional discrete element method. Macroscopic mixing law and partial mixing characteristics in particle mixing process are analysed in the view of single particle random motion trajectory and motion vector diagram of macroscopic particle flow. And the mathematical relation between mixability and revolutions of agitating blades is described quantitatively. Results show that convective mixing and four partial mixing characteristics control the mixing homogeneity process of identical property of segregation particles in forced agitation mixing. Mixability of segregation particles is independent of rotating speed of the agitating shaft, but has a direct correlation with revolutions. The relation between mixability and revolutions agrees with the exponential growth model. Research results can provide the basis and reference for equipment improvement and operating control of bulk material in the industry of the augmenting of mix.

Pilot-scale evaluation of an in situ amendment delivery and mixing device for contaminated sediment remediation applications

In situ sediment treatment technologies can be more economical alternatives than dredging and ex situ treatment; however, their development and application had been hindered due to uncertainties associated with the homogeneity of amendment delivery and mixing and the concern of contaminated sediment resuspension and amendment release into the water column. The purpose of this study was to evaluate the subaqueous amendment delivery and mixing efficiency of a novel pilot scale in situ sediment remediation system addressing these concerns. The in situ sediment treatment system consisted of a hydraulically operated steel casing that provided contained conditions for amendment delivery and mixing to occur and the mixing tool housed by this casing. The mixing tool consisted of a hollow vertical shaft with horizontal mixing blades. The device was capable of delivering amendments to subaqueous sediments during continuous mixing in the downward or upward vertical direction. Activated carbon was used as a tracer to evaluate the efficiency of reagent delivery and mixing. The delivery and mixing system operation was defined by the following parameters: mixing speed, vertical descent or ascent speed, mixing time, total processing time, sediment mixing depth, activated carbon slurry injection volume, pumping flow rate for activated carbon, and pumping pressure for activated carbon. Better amendment yield recoveries were observed at lower added activated carbon volumes, at higher mixing speeds, at lower pump flow rates, in case of thicker mixed sediment zones, and at horizontal locations closer to the center shaft. In general, poor amendment recoveries could be attributed to the limited capacity of the sediment pore space to accommodate the activated carbon slurry. Better recoveries close to the shaft might have occurred due to the fact that the amendment delivery pressure was not controlled and therefore was not constant through each reagent delivery port. The reagent stayed within the enclosure of the device, indicating that contained mixing conditions were achieved. The majority of the suspended sediment settled out fairly quickly from the overlying water column within the enclosure. The in situ remediation system showed potential in terms of successful amendment delivery and mixing into subaqueous sediments. Lower doses of activated carbon were mixed in more efficiently due to the limited availability of pore capacity and issues with powdered activated carbon retention in the sediment. The demonstration took place in sediments with large sand and gravel fractions; sediments containing larger silt and clay fractions are likely to behave differently in terms of sediment resuspension.

Nano-Halloysite Concentration Effects on Fracture Toughness of Diverse Epoxy Nanocomposites

Abstract We experimentally report material design of halloysite nanotube (HNT)/epoxy composites, focusing on the effects of HNT concentration on thermal and mechanical properties, especially fracture toughness, of diverse epoxy composites with as-received and phenylphosphonic-acid (PPA)-treated HNTs prepared by mechanical mixing or ball-milling homogenization. It is demonstrated that, with HNT added in the region of 0.0–10.0 wt. %, significantly reinforced fracture toughness of the epoxy composites can be achieved. The epoxy composites prepared by ball-milling homogenization have much more uniform HNT size and dispersion than those prepared by simple mechanical mixing, enhancing their fracture toughness. The morphology of treated HNTs changes from nanotubes to nanoplatelets; as a result, with a substantial increase in the total contact area between HNT and epoxy and enhancing the fracture toughness of epoxy composites. This higher HNT concentration and the higher fracture toughness are achieved for various epoxy composites. However, the optimal concentration of HNT is 5.0 wt. % in this study. The addition of further HNT achieves only marginal fracture toughness enhancement and more negative effects appear, such as HNT concentration gradient in cured epoxy composites, high potential decrease in glass transition temperature (Tg), and potential immature tensile failure.

Boundedness of Marcinkiewicz integrals with mixed homogeneity along compound surfaces

In this note we establish the boundedness of Marcinkiewicz integrals with mixed homogeneity along compound surfaces, which improve and extend some previous results. The main ingredient is to present a systematic treatment with several singular integral operators. MSC:42B20, 42B15, 42B25.

MANUFACTURING AND PERFORMANCE EVALUATION OF A LOCAL ANIMAL FEED HORIZONTAL MIXER

The present research was carried out to manufacture and evaluate some operating parameters affecting the performance of an animal feed horizontal mixer to improve product quality. The mixer performance was studied as a function of change in material batch size and mixing time. Performance evaluation of the horizontal mixer was carried out in terms of mixing homogeneity, coefficient of variation, specific energy and mixing cost. The experimental results revealed that coefficient of variation; mixing homogeneity; specific energy and mixing costs were in the optimum region under the following conditions: - The mixer shaft is designed at a diameter of 80 mm. - Operate the mixer at a batch size of between 700 to 850 kg. - The mixing time should be of between 15 to 20 minutes.

Mixing Homogeneity and Rheological Characterization for Optimal Binder Formulation for Metal Injection Moulding

Mixing homogeneity and the feedstock rheological characteristic for optimal binder formulation in metal injection moulding is evaluated between Polypropylene (PP) and Sewage fat (SF) or Fat Oil Grease (FOG). Difference powder loading of SS316L also being used here to determine the possibility of the best binder formulation selected could be optimised for optimal powder loading base on rheological characteristic analysis. Two binder formulations of PP to SF being selected here are 60/40 and 70/30 accordingly with the powder loading of 60% and 55% for each binder formulation. The analysis will be base on viscosity, shear rate, temperature, activation energy, flow behaviour index and moldability index. It is found that rheological result shows all the two binder formulations with both powder loading exhibit pseudoplastic behaviour or shear thinning where the viscosity decrease with increasing shear rate. Feedstock viscosity also decrease with increasing temperature indication of suitability for moulding. Results from all the analysis conducted shows that the volumetric powder loading of 60% with binder volumetric of 60% for PP and 40% for SF contributes significant stability and suitability for optimum powder loading.

Mixing and Characterisation of Stainless Steel 316L Feedstock for Waste Polystyrene Binder System in Metal Injection Molding (MIM)

This paper describes the mixing process and homogeneity analysis of a newly developed binder system based on waste polystyrene (PS) and palm kernel oil (PKO) to produce feedstock for metal injection molding (MIM). Since mixing is a critical step in MIM process, hence the mixture of powder and binder should be homogeneous and injectable. In this study, water atomised Stainless Steel powder was mixed with a new binder system consisting of waste polystyrene and palm kernel oil in a Brabender Plastograph EC rotary mixer. Several tests were performed to assess the homogeneity of the feedstock that was produced at 60 vol.% powder loadings. The 60 vol.% was chosen because the Critical Powder Volume Concentration (CPVC) of the SS316L powder was found to be 64.8 vol.%. The tests conducted were density, binder burn-out and SEM morphology observation. It was found that the feedstock shows good homogeneity and suitable for further processing in MIM.

Surface roughness effects on the tribo-charging and mixing homogeneity of adhesive mixtures used in dry powder inhalers

For active pharmaceutical ingredients (APIs) delivered to the lung it is of main importance that they reach the deeper lung, in order to cause the intended therapeutic effect. To obtain inhalable powders that on the one hand are small enough to travel along the tiny airways finally reaching their target site and on the other hand show sufficient flowability, so-called adhesive mixtures are used. They consist of API particles in the size range of 0.5μm–5μm and carrier particles in the size range of 50μm–200μm, that, due to the size of the carrier, exhibit adequate flowability. However, when administered to the patient, the API has to separate from the carrier surface in order to be able to penetrate the deep lung. The performance of dry powder inhalers (DPIs) and adhesive mixtures is mainly governed by interparticle forces like Van der Waals and triboelectric forces. Carrier surface roughness modification is a new method to alter the contact area and thus the Van der Waals forces between API and carrier. Unfortunately the tribo-charging during handling, especially during the generation of the adhesive mixtures in a tumble blender, is strongly influenced by particle characteristics like particle surface roughness. Thus the mixing quality and stability and thereby the usability of the powder mixture might be additionally influenced by tribo-charging. Therefore the aim of the present work is to investigate whether tribo-charging during the mixing process is influenced by the carrier particle surface roughness. Further the influence of tribo-charging on mixing homogeneity is assessed. Net charge measurements are performed using a Faraday cup. As model API and carrier salbutamol sulfate and spray dried mannitol are used respectively. It is shown that the carrier particle characteristics impact tribo-charging of the pure carriers in a tumble blender. This influence is not observed for the adhesive mixtures of carrier and API. Nevertheless the homogeneity of the adhesive mixtures is still influenced by the charging of the carriers.

Evaluation of feedstock for powder injection molding

Methods to evaluate powder injection molding feedstock without performing the complete processing were developed to reduce the development-to-commercialization cycle time for feedstock. The mixing homogeneity of the powder and binder, rheological properties, mechanical property and shape retainability during debinding were characterized to evaluate the feedstock. The validity of using these parameters was investigated through comparison with various feedstocks. Based on these results, the evaluation methods developed in this work have potential to aid in the selection of proper feedstock without undergoing the subsequent processing.

Residence time distribution and heat transfer in circular pipe fitted with longitudinal rectangular wings

Numerical simulations are used to analyze the heat and mass transfer in a circular pipe fitted with longitudinal rectangular vortex generators for Reynolds number between 7500 and 15,000 based on the pipe diameter. The aim of the present study is to test and quantify the mixing efficiency of a new solution able to avoid the bypass region that exists in the center of the high efficiency vortex static mixer (HEV), and also to enhance the heat transfer without increasing the pressure losses. The rectangular wings used here generate each a streamwise counter-rotating vortex pair sweeping the volume of the mixer and act as internal agitator on the flow. The particle dispersion is investigated by analyzing Poincaré sections and by studying the residence time distribution (RTD). The two approaches show much better mass transfer performance and better mixing homogeneity for the new wings arrangement. The heat transfer is also investigated and it is shown that the thermal enhancement factor in the new arrangement is much greater than that of the conventional systems used in the industry. When compared to the HEV heat exchangers it is shown that the thermal enhancement in the present configuration reaches about 40% relative to the classic HEV and 15% relative to the reversed HEV.

Quantitative Mixing Analysis of Laminar Flow in Circle Grid Perforated Plate with 50% Porosity Static Mixer

The applications of the static mixers are widely applied in many industries to obtain the desired type of mixing. In this context, to perform the mixing process should have two different fluids that also have different properties which will combines it in a single equipment to make an another fluid. The main objective of this research study is to propose a new approach of fractal concept (circle grid perforated plate) for internal rapid mixing by determining the coefficient of variation (COV). This study was implemented by fully numerical simulations. The simulations of mixing fluid were carried out with the help of commercial computational fluid dynamic (CFD) package ANSYS CFX 14.0 software. The simulation was done primarily in cylindrical pipe with insertions of circle grid perforated plate with porosity of 50%. Three levels of laminar flow have been chosen to result in Reynolds numbers (Re) equal to 100, 200 and 400. The effectiveness of circle grid perforated plate static mixer has been evaluated by comparing the homogeneity level of mixing fluids to the Kenics static mixer that readily available in industries applications. Based on the research findings, the COV value for circle grid perforated plate with 50% porosity at Re 100 was 0.0744 which is out of the range while Reynolds number at 200 and 400 were 0.0483 and 0.0247 respectively which are in the range in term of reasonable target of mixing homogeneity. The values of COV between 0.01 and 0.05 are the reasonable target for many applications. In term of manufacturing cost and energy loss due to static mixer, definitely this new approach of 50% porosity circle grid perforated plate is better design compared to the Kenics static mixer because of lower number of inserts and simpler design of static mixer to produce.

Rough singular integrals and maximal operators with mixed homogeneity along compound curves

The parabolic singular integrals along certain compound curves as well as the related maximal operators are considered. Under rather weakened size conditions on the integral kernels both on the unit sphere and in the radial direction, the -mapping properties for such operators are established. Some previous results are greatly extended and improved.

Zirconia–alumina–nanodiamond composites with gemological properties

Nanodiamonds have excellent mechanical and optical properties with a wide range of potential applications as a filler material for nanocomposites. Here, we present a new family of zirconia–alumina–nanodiamond composites using two main processing routes: (1) a colloidal method, and (2) power mixing homogenization. Composites with detonation nanodiamonds quantities ranging within 0.3–5 vol.% followed by a pulsed electrical current sintering at a temperature range from 1,200 to 1,500 °C have been analyzed, and a significant enhancement in mechanical properties, i.e., indentation hardness (16.17 GPa), fracture toughness (15.5 MPa m1/2), and bending strength (1,600 MPa), could be observed. To support these excellent properties, TEM, color, reflectivity, and Raman spectroscopy measurements were also carried out. The microstructure of the composites is very homogeneous with average grain sizes between 200 and 500 nm depending on the processing temperature. Two morphologies are present: (a) intergranular dispersion of alumina grains and nanodiamonds distributed along the grain boundaries of the ZrO2 matrix, and (b) intragranular nano-dispersion of ZrO2 particles with sizes 20–80 nm located inside the alumina grains. In the present article, we show, for the first time in the scientific literature, a continuous palette of gray color gradation of new ceramic materials of metalized colors (white index L* 98–40) for gemological applications.

Influence of Italian ryegrass (Lolium multiflorum Lam.) as intercrop with spring barley (Hordeum vulgare L.) on the diversity of weed communities

<p class="abstracttekst">The paper presents results of 3 years of studies (2009–2011) on the influence of Italian ryegrass on the development of weed communities in spring barley (without chemical weeds control) cultivated after potato, spring wheat and spring barley. The reaction of spring barley to the choice of the forecrop was compared with identical plots with pure stand of that cereal where herbicides were applied for weeds control. Evaluation of infestation with weeds was conducted during barley tillering and before harvest. That evaluation considered the number and composition of weed species. During harvest, the dry mass of weeds was also considered. The results were used for determination of Shannon-Wiener diversity index and species homogeneity coefficient, Simpson’s index of dominance as well as Sørensen similarity index.</p>Spring barley weeding was significantly higher in case of cultivating it in mixed stand with Italian ryegrass (without chemical control), than in pure stand (with control). In the plots with mixed crop, lower diversity and homogeneity of weeds’ communities were recorded than in pure stand. Barley in mixed crop sown after spring barley, during both times of evaluation (spring and before harvest), increased the value of the index of dominance according to the number of species the most. As concerns the composition of species, number and biomass, the communities of pure stand and mixed crop with Italian ryegrass on the plot after potato were the most similar.

Hardy spaces associated with different homogeneities and boundedness of composition operators

It is well known that standard Calderón–Zygmund singular integral operators with isotropic and nonisotropic homogeneities are bounded on the classical H^p(\mathbb{R}^m) and nonisotropic H^p_{h}(\mathbb{R}^m), respectively. In this paper, we develop a new Hardy space theory and prove that the composition of two Calderón–Zygmund singular integral operators with different homogeneities is bounded on this new Hardy space. Such a Hardy space has a multiparameter structure associated with the underlying mixed homogeneities arising from the two singular integral operators under consideration. The Calderón–Zygmund decomposition and an interpolation theorem hold on these new Hardy spaces.

Parenteral formulation of larotaxel lipid microsphere tackling poor solubility and chemical instability

The purpose of this study was to develop a parenteral larotaxel lipid microsphere (LTX-LM) and evaluate its stability. The preformulation study showed that LTX possessed poor solubility (0.057 μg/mL in aqueous phase) and chemical instability. LM was selected as the drug carrier due to its higher drug-loading capacities, higher physicochemical stability and reduced irritation and toxicity. High speed shear mixing and high-pressure homogenization were employed to prepare the LTX-LM. Particle size distribution (PSD), zeta-potential, drug content and entrapment efficiency (EE) were taken as indexes to optimize formulations. The dissolution studies were performed using a ZRS-8G dissolution apparatus according to the paddle method. Degradation kinetics test, freezing and thawing test and long term stability test were combined to evaluate the physicochemical stability of LTX-LM. From the degradation kinetics results, the shelf lives (T90%) of LTX in LM at 25 and 4°C (165, 555 days) were about 20 times as long as those in aqueous phase (200, 676 h), which were dramatically prolonged. The activation energies in aqueous solution and in LM calculated from the slopes were 41.93 and 42.25 kJ/mol. And its frequency factors (A) were 4.9 × 10(3)/s and 2.3 × 10(2)/s, respectively. Freezing and thawing test showed the PSD of LTX-LM became larger and wider increasing from 166.9 ± 53.2 nm to 257.4 ± 85.5 nm with more freeze-thaw cycles. From the long term stability test results, all the parameters changes were in qualified range.

Mixing enhancement by pulsating chaotic advection

The purpose of this study is to investigate transverse mixing enhancement by superposition of periodic time dependence, in the form of pulsation, on a twisted pipe flow in which the fluid particles trajectories are spatially chaotic. The pulsation makes the secondary flow structure more complex, resulting in stronger velocity gradients that enhance stretching and folding, the main mechanisms of chaotic mixing. Here, the chaotic configuration is six alternating 90° curved pipes. The imposed pulsating conditions range as follows: steady Reynolds numbers 420≤Rest≤1000, velocity component ratios 1≤(β=Umax,osc/Um,st)≤4 and frequency parameters 8.37<(α=r0(ω/ν)0.5)<24.5. The secondary velocity fields are measured by particle image velocimetry. The axial vorticity and transverse strain rate at the outlet of each curved pipe in pulsatile flow are compared with those of the steady flows. Analysis of these criteria for mixing assessment shows that β≥2 and α≤15 are favourable pulsating conditions for transverse mixing enhancement. Moreover, in some pulsation conditions, the cell centres visit a zone in the flow cross-section that is much larger than in the steady case, implying that pulsation also contributes to mixing homogenization.

Influence of Polymorphisms in the Prion Protein Gene on the Pathogenesis and Neuropathological Phenotype of Sheep Scrapie after Oral Infection

The prion protein gene (Prnp) plays a crucial role in the susceptibility of sheep to scrapie in terms of attack rate and/or incubation period. However, the influence of Prnp on the pathogenesis of the disease, specifically the involvement of tissues of the lymphoreticular system (LRS), pathways of neuroinvasion and neuropathological phenotypes, remains controversial. This study reports the onset and progression of disease-associated prion protein (PrP(d)) accumulation in the LRS and nervous tissues of sheep of six different Prnp genotypes infected by oral administration of the same mixed scrapie brain homogenate. Sheep homozygous for glutamine (Q) at codon 171 of PrP, with either valine (V) or alanine (A) at codon 136 (i.e. VRQ/VRQ, VRQ/ARQ and ARQ/ARQ), showed early and consistent PrP(d) accumulation in LRS tissues of the pharynx and gut. In contrast, LRS involvement was minimal, inconsistent and occurred late in the incubation period in sheep heterozygous for arginine (R) at codon 171 (i.e. VRQ/ARR and ARQ/ARR). Despite this difference, all five groups were susceptible to infection and developed clinical disease, albeit with significantly different incubation periods (shortest in VRQ/VRQ and longest in ARQ/ARR sheep). The remaining group of ARR/ARR homozygous sheep did not show evidence of infection at the end of the experiment or at previous predetermined time points. As for LRS tissues, the sites of initial PrP(d) accumulation in the brain were determined immunohistochemically. These were the same in all susceptible sheep (except for ARR/ARR sheep), regardless of their Prnp genotype which, together with an early and consistent accumulation of PrP(d) in circumventricular organs and a late or inconsistent involvement of the enteric and autonomic nervous system and of the spinal cord, suggests neuroinvasion occurring via the blood. The neuropathological phenotype (PrP(d) profile in the central nervous system) of clinically affected sheep was similar in the three V136 carrier groups, but showed some differences in the two A136 homozygous groups, suggesting a codon 136-driven selection of different strains from the mixture contained in the inoculum. ARQ/ARR sheep showed an irregular distribution of brain PrP(d), contrasting with the more widespread distribution of the other four groups. The results indicate that (1) ARQ/ARR sheep are more susceptible to oral scrapie infection than would be predicted from incidence figures in natural disease, (2) amplification and accumulation of PrP(d) in LRS tissues is host genotype dependent, but does not necessarily have a marked effect on the outcome of the infection and (3) the neuropathological phenotype of scrapie is related to the host genotype, but possibly in combination with the infecting source.

Homogeneity of the Subgrid-Scale Turbulent Mixing in Large-Eddy Simulation of Shallow Convection

Abstract This paper presents an approach to locally predict homogeneity of the subgrid-scale turbulent mixing in large-eddy simulation of shallow clouds applying double-moment warm-rain microphysics. The homogeneity of subgrid-scale mixing refers to the partitioning of the cloud water evaporation due to parameterized entrainment between changes of the mean droplet radius and changes of the mean droplet concentration. Homogeneous and extremely inhomogeneous mixing represent two limits of possible scenarios, where the droplet concentration and the mean droplet radius remains unchanged during the microphysical adjustment, respectively. To predict the subgrid-scale mixing scenario, the double-moment microphysics scheme is merged with the approach to delay droplet evaporation resulting from entrainment. Details of the new scheme and its application in the Barbados Oceanographic and Meteorological Experiment (BOMEX) shallow convection case are discussed. The simulated homogeneity of mixing varies significantly inside small convective clouds, from close to homogeneous to close to extremely inhomogeneous. The mean mixing characteristics become more homogeneous with height, reflecting increases of the mean droplet size and the mean turbulence intensity, both favoring homogeneous mixing. Model results are consistent with microphysical effects of entrainment and mixing deduced from field observations. Mixing close to homogeneous is predicted in volumes with the highest liquid water content (LWC) and strongest updraft at a given height, whereas mixing in strongly diluted volumes is typically close to extremely inhomogeneous. The simulated homogeneity of mixing has a small impact on mean microphysical characteristics. This result agrees with the previous study applying prescribed mixing scenarios and can be explained by the high humidity of the clear air involved in the subgrid-scale mixing.

Modeling microphysical effects of entrainment in clouds observed during EUCAARI-IMPACT field campaign

Abstract. This paper discusses aircraft observations and large-eddy simulation (LES) modeling of 15 May 2008, North Sea boundary-layer clouds from the EUCAARI-IMPACT field campaign. These clouds are advected from the northeast by the prevailing lower-tropospheric winds and featured stratocumulus-over-cumulus cloud formations. An almost-solid stratocumulus deck in the upper part of the relatively deep, weakly decoupled marine boundary layer overlays a field of small cumuli. The two cloud formations have distinct microphysical characteristics that are in general agreement with numerous past observations of strongly diluted shallow cumuli on one hand and solid marine stratocumulus on the other. Based on the available observations, a LES model setup is developed and applied in simulations using a novel LES model. The model features a double-moment warm-rain bulk microphysics scheme combined with a sophisticated subgrid-scale scheme allowing local prediction of the homogeneity of the subgrid-scale turbulent mixing. The homogeneity depends on the characteristic time scales for the droplet evaporation and for the turbulent homogenization. In the model, these scales are derived locally based on the subgrid-scale turbulent kinetic energy, spatial scale of cloudy filaments, mean cloud droplet radius, and humidity of the cloud-free air entrained into a cloud, all predicted by the LES model. The model reproduces contrasting macrophysical and microphysical characteristics of the cumulus and stratocumulus cloud layers. Simulated subgrid-scale turbulent mixing within the cumulus layer and near the stratocumulus top is on average quite inhomogeneous, but varies significantly depending on the local conditions.