Mixing Homogeneity Research Articles

The Mixing Characteristics and Residence Time Distribution of Cut Tobacco Particles in Drum Mixer

Residence time distributions were determined for the continuous processing of cut tobacco in the rotary drum by introducing expanded cut tobacco tracers to the inlet of the processing system using the negative step change method. Effects of rotating speed of the rotary cylinder and solids flow rate on the mixing homogenization and residence time distribution (RTD) of experiment materials was investigated. PER-CSTR series model and multistage CSTR model were used to fit the experimental results. The result shows mixing homogenization increased significantly with the increasing feeding rate of cut tobacco and decreasing drum rotating speed. PER-CSTR series model is more suitable to describe the RTD characteristics of flow materials in drum. The axis movement of cut tobacco along the drum is approximate to the plug-flow.

The influence of operational parameters and feed preparation in a convective batch ribbon powder mixer

PurposeTo investigate the effect of feed preparation characteristics and operational parameters on mixing homogeneity in a convective batch ribbon mixer.MethodsLactose 100M, lactose 200M, ascorbic acid, and zinc oxide powders were used for the mixing study. Operational parameters studied were rotational speed and mixing time. The feed preparations studied were the use of preblending and the particle size of the feed materials. The blends of ascorbic acid, zinc oxide, and lactose were prepared with preblending and without preblending, prior to mixing at different blender rotation speeds and mixing times. Chemical tests were performed to measure the homogeneity of the ascorbic acid in the model mixture.ResultsWith preblending, a mixture with lactose 200M achieved the required homogeneity in a shorter period of time at a lower rotational speed.ConclusionThe results indicated that the homogeneity of the mixtures was influenced by the blender rotation speed and mixing time. Better mixing can be obtained with higher rotation speeds and longer mixing time. It was also observed that preblending and smaller feed particle size achieved the required homogeneity in a shorter period of time at a lower rotational speed. These results illustrate that using binders with a smaller particle size and a preblending technique improves the mixing process in a convective batch ribbon powder mixer. However, prolonged periods of high-speed mixing will lead to mixture segregation.

Synthesis of size controlled phase pure KNbO3 fine particles via a solid-state route from a core–shell structured precursor

From a core–shell structured precursor, comprising Nb2O5 core enveloped by KHCO3 in an equimolar proportion, phase pure KNbO3 (KN) fine particles were obtained by calcining in air at 600°C for 1h. Disintegrating the large agglomerated particles of KHCO3 prior to the precursor preparation enabled the micronization of the KN particle size down to 240nm, close to that of the starting Nb2O5, due to increased mixing homogeneity and consequent thorough enveloping of individual Nb2O5 particles. Based on these findings, together with the known coupling diffusion mechanism of potassium and oxygen into Nb2O5, it was concluded that the core–shell particles in the precursor serve as a separated reaction space to complete the formation of KN without appreciable coalescence or local sintering, as far as the firing temperature is low enough like those employed in the present study. Superiority of KHCO3 over K2CO3 or KNO3 as a potassium source was also discussed.

Analysis on Online Mixing Performance of Jet-Mixing Apparatus

Aimed at investigating the design method and test method of jet-mixing apparatus, numerical simulation and experiment research were both used to investigate the internal flow field of jet-mixing apparatus in this article. Numerical simulation scheme for interior flow field of jet-mixing apparatus was established, CFD software Fluent was used to investigate in concentration field of jet-mixing apparatus. The concept of IOS was brought forward to evaluate the homogeneity degree of pesticide and water. Investigation both carried on area ratio effect on the mix homogeneity of the jet-mixing apparatus and the distribution of pesticide concentration in the axial and radial of mixing tube.

Macroscopic impacts of cloud and precipitation processes in shallow convection

This paper presents application of the EULAG model combined with a sophisticated double-moment warm-rain microphysics scheme to the model intercomparison case based on RICO (Rain in Cumulus over Ocean) field observations. As the simulations progress, the cloud field gradually deepens and a relatively sharp temperature and moisture inversions develop in the lower troposphere. Two contrasting aerosol environments are considered, referred to as pristine and polluted, together with two contrasting subgridscale mixing scenarios, the homogeneous and the extremely inhomogeneous mixing. Pristine and polluted environments feature mean cloud droplet concentrations around 40 and 150 mg−1, respectively, and large differences in the rain characteristics. Various measures are used to contrast evolution of macroscopic cloud field characteristics, such as the mean cloud fraction, the mean cloud width, or the height of the center of mass of the cloud field, among others. Macroscopic characteristics appear similar regardless of the aerosol characteristics or the homogeneity of the subgrid-scale mixing.

Effects of titanate coupling agent on the dielectric properties of NiZn ferrite powders–epoxy resin coatings

During ferrite powder–polymer resin slurry preparation, the ferrite particles tend to hold together, forming agglomerates, which lead to the formation of micro-structural defects in the ferrite powder–polymer coatings. These defects affect the quality of magnetic devices. In this study, the titanate coupling agent effects on the NiZn ferrites powder dispersion in an epoxy resin and solvent system and the electromagnetic properties of NiZn ferrite powders–epoxy resin composite coatings are investigated. It was observed that the dispersion of NiZn ferrite powders and the affinity of NiZn ferrites and epoxy resin can be substantially enhanced by coating a titanate coupling agent onto the ferrite powder surfaces. This coating promotes mixing homogeneity and increases the dielectric constants at low frequencies (below 100 Hz) due to the increase in phase boundary between the NiZn ferrite powders and epoxy resin.

Fractal Analysis of Mixing in Zinc-Silica Composite Electrolyte by Particle Image Velocimetry

This paper investigates the mixing effect in zinc-silica composite electrolyte by particle image velocimetry (PIV) and fractal dimension method. Fifteen groups of orthogonal tests including different rotational speed, electric current and height of paddle are carried out to study the mixing homogeneity using fractal dimension method, it is found that the case with paddle height of 1cm, electric current of 0.25 A and rotational speed of 1000 rpm is better than the others, and at last the distribution of silica in composite coating provides a strong evidence for characterizing the mixing homogeneity.

Polyethyleneimine surfactant effect on the formation of nano-sized BaTiO 3 powder via a solid state reaction

Barium titanate powder is widely used in multilayer ceramic capacitors (MLCC) because of its’ superior ferroelectric and dielectric properties. Presently, barium titanate powder is mass-produced using a conventional solid state reaction. However, the conflicting literature reports clearly show that the solid state reaction mechanism is not well understood. Synthesizing nano-sized barium titanate powders with less agglomeration using a solid state reaction method at a low calcination temperature has become a hot research topic. This study examines the effect of polyethyleneimine (PEI) surfactant addition on BaTiO 3 formation in a solid sate reaction. XRD, DTA and TEM are used in this investigation. The results indicate that PEI addition can promote BaCO 3 and TiO 2 mixing homogeneity, which enhances the interfacial reaction between BaCO 3 and TiO 2. BaTiO 3 formation can be obtained through the interfacial reaction between BaCO 3 and TiO 2 at the intimate contact between the reactants and Ti +4 ion diffusion along the surfaces or grain boundaries of BaTiO 3 powders, thereby obtaining a single phase BaTiO 3 powder when calcining at low temperatures for a long period.

Skeletal muscle myosin light chain composition of highly‐trained endurance runners

Individual slow (MHC I) and fast (MHC IIa) twitch muscle fibers from highly-trained competitive runners display a greater contractile velocity (Vo) compared to moderately-active individuals. Myosin light chains (MLC) have been implicated in altering myofiber Vo, but this relationship is ambiguous in human skeletal muscle. Therefore, the purpose of this study was to examine MLC composition and its association with single muscle fiber contractile function in competitive (RUN; 71±1 ml·kg−1·min−1, 95±2 km/wk running) and recreational runners (REC; 47±2 ml·kg−1·min−1, <25 km/wk). SDS-PAGE, silver staining, and densitometry were used to assess MLC composition in mixed muscle homogenates and individual myofibers (MHC I and IIa) obtained from skeletal muscle biopsy samples. At the mixed muscle level, MLC 2f was lower (p<0.05) in RUN compared to REC with trends (p<0.08) for greater 1s, 2s and lower 3f ratios. The MLC profile of MHC I fibers was similar between RUN and REC. However, the MLC profile of the MHC IIa fibers from RUN contained less MLC 1s and greater amounts of 1f and 2s (p<0.05) compared to REC. These data suggest that only subtle differences exist in the MLC profile between RUN and REC. Therefore, it is likely that MLC composition contributes only a minor, if any, role in the robust differences in contractile function between competitive and recreational runners. Supported by NIH Grant AG032127

Synthesis of ZrO2–SiO2 mixed oxide by alcohol-aqueous heating method

The preparation of ZrO2–SiO2 mixed oxide has been carried out simply by heating an alcohol-aqueous mixture. Preparation conditions such as volume ratio of alcohol to water and prehydrolysis time of tetraethoxysilane had more important effect on the homogeneity of mixed oxide. A self-catalytic effect on the resultant Zr–O–Si formation is observed. By employing FT-IR, XRD, NH3-TPD and pyridine adsorption FT-IR techniques, the mixing homogeneity of the mixed oxides in terms of the amount of Zr–O–Si hetero-linkages has been investigated in detail. The results indicate that the amount of Zr–O–Si hetero-linkages increases with the increase of ZrO2 content in mixed oxides. Moreover, the phase segregation and acidity generation of mixed oxides are studied and factors responsible for good mixing are also discussed. Using this approach, a series of highly homogeneous mixed oxides with ZrO2 content of 20–70 mol% are obtained at the optimized preparation condition.

Environmentally benign dry mechanical mixing of nano-particles using magnetically assisted impaction mixing process

The effectiveness of magnetically assisted impaction mixing (MAIM), an environmentally benign mechanical process, in mixing SiO 2 + TiO 2 and SiO 2 + Al 2O 3 nanoparticle mixtures has been examined. Experiments were carried out at different magnet-to-sample weight ratios, processing times, and magnet sizes. The homogeneity of mixing (HoM) was evaluated at the micron scale using field-emission scanning electron microscopy and energy dispersive X-ray spectroscopy, and at sub-micron scale through electron energy loss spectroscopy and transmission electron microscopy. The HoM improved with an increase in the magnet-to-sample weight ratio and processing time, and a decrease in the magnet size; over the range of conditions tested, the HoM was found to depend on the product of processing time and the number of magnets per unit powder mass. Optimized MAIM process achieved HoM values that were comparable to those attained with Rapid Expansion of Supercritical or High-Pressure Suspensions and sonication of a suspension of the nanoparticles in supercritical CO 2.

Singular integrals with mixed homogeneity in product spaces

Let Ω ∈ L(logL+)2(Sn−1 × Sm−1) (n, m 2) satisfy some cancellation conditions. We prove the Lp boundedness (1 < p < ∞ ) of the singular integral T f (x1,x2) = p. v. ∫ ∫ Rn×Rm Ω(y1,y ′ 2)h(ρ1(y1),ρ2(y2)) ρα 1 (y1)ρ β 2 (y2) f (x1 − y1,x2 − y2)dy1 dy2, where ρ1 , ρ2 are some metrics which are homogeneous with respect to certain non-isotropic dilations. We also study the above singular integral along some surfaces. Mathematics subject classification (2010): 42B20, 42B25.

Response Surface Modeling of Processing Parameters for the Preparation of Phytosterol Nanodispersions Using an Emulsification–Evaporation Technique

AbstractThe purpose of this study was to optimize the production parameters for water‐soluble phytosterol nanodispersions. Response surface methodology (RSM) was employed to model and optimize three of the processing parameters: mixing time (t) by conventional homogenizer (1–20 min), mixing speed (v) by conventional homogenizer (1,000–9,000 rpm) and homogenization pressure (P) by high‐pressure homogenizer (0.1–80 MPa). All responses [i.e., mean particle size (PS), polydispersity index (PDI) and phytosterols concentration (Phyto, mg/l)] fitted well to a reduced quadratic model by multiple regressions after manual elimination. For PS, PDI and Phyto, the coefficients of determination (R2) were 0.9902, 0.9065 and 0.8878, respectively. The optimized processing parameters were 15.25 min mixing time, 7,000 rpm mixing speed and homogenization pressure 42.4 MPa. In the produced nanodispersions, the corresponding responses for the optimized preparation conditions were a PS of 52 nm, PDI of 0.3390 and a Phyto of 336 mg/l.

Understanding granular mixing to enhance coating performance in a pan coater: Experiments and simulations

The knowledge of the particle flow and mixing in a pan coater is critical to optimize the design and operation of coating equipment. Mixing is an important but poorly understood aspect of coating of pharmaceutical dosage forms (tablets). Our study focuses on the fundamental mechanisms of granular flow and mixing and their relationship to the coating performance. A quantitative method is developed and validated to characterize the mixing process throughout the mixing vessel. This method is used to establish a baseline determination of mixing homogeneity as a function of various mixing conditions. White and red non-pareils of 5–6 mesh size are loaded in the ellipsoid pan coater to check the effect of initial loading (side–side and front–back), fill level, orientation of the vessel and the vessel speed on granular mixing. Video-imaging and discrete-pocket samplers are used to quantify mixing and to finally estimate the optimal operating conditions. DEM (Discrete Element Method) based numerical model was also developed to study the effect of granular mixing in a pan coater. When the axis of rotation of the mixer is horizontal (no tilt), slower axial dispersion is observed in both the experiments and simulations, than the radial convection. However, tilt enhances axial mixing, and faster axial mixing is seen for higher tilt angles from the horizontal. The speed of the rotating vessel has a nominal effect on the rate of mixing in a coating pan, as observed from the experimental and simulation studies. Moreover, fill level has no significant effect on the rate of mixing. Coating experiments are performed in the pan coater where white non-pareils being coated by spraying Opadry II solution. DEM simulation of coating is performed with post processing particle dynamics data. The effects of various operational and spray parameters are determined on the coating performance. Optimal coating performance is attained at an optimal mixing condition.

Synthesis of Sr 2SiO 4 nanometer particles from the core–shell precursor of SrCO 3/SiO 2

This study presents the formation mechanism for Sr 2SiO 4 synthesized from coated SrCO 3 with gel-derived SiO 2. The experimental results indicate that Sr 2SiO 4 formation from the mechanical mixed precursor with poor mixing homogeneity was dominated by the thermal decomposition of SrCO 3 at higher temperatures. Conversely, the SrCO 3/SiO 2 core–shell precursor can facilitate the formation of Sr 2SiO 4 from the direct reaction between SrCO 3 and SiO 2 at lower calcination temperatures. In addition, raising the coating pH and temperature can promote the shell layer growth that further facilitated Sr 2SiO 4 formation. A nearly pure α-Sr 2SiO 4 product with particle size around 20–50 nm can be obtained at 800 °C for 3 h.

Thermal chaotic mixing of power-law fluids in a mixer with alternately rotating walls

We investigate the enhancement of both mixing and heat transfer in a two-rod mixer for highly viscous non-Newtonian fluids. The mixer is composed of two vertical circular rods in a cylindrical tank. Chaotic flows are obtained by imposing the temporal modulations of the rotational velocities of the walls. We study the effects of different stirring protocols, which lead to non-chaotic and chaotic flows, on the efficiency of both mixing and heat transfer for three different rheological fluid behaviors: shear-thinning, Newtonian and shear-thickening. For this purpose, we use statistical indicators that characterize the mean value of the fluid temperature and its homogenization. We find that chaotic mixing is suitable for shear-thickening fluids for which we observe a clear enhancement of the thermal mixing (heat extraction and homogenization). This is due to the increase in the apparent fluid viscosity in the vicinity of the rotating walls. This aspect confirms the relevance of chaotic mixing for highly viscous fluids.

Polymer powders mixing part II: Multi-component mixing dynamics using RGB color analysis

In this work, the mixing quality of a multi-component blend of particles is determined using Multivariate Image Analysis of RGB images combined with the Grey Level Co-occurrence Matrix (GLCM) texture analysis. The mixing dynamics and flow behavior are studied in terms of mixing homogeneity and time to achieve equilibrium for binary, ternary and quaternary mixtures of equal size particles. The parameters studied are rotational speed, filling ratio, initial powder composition and particle sizes. Using the experimental data in the rolling regime, a second order model is proposed to predict the mixing curve as a function of time.

Non-invasive imaging of shallow bubble columns using electrical capacitance tomography

This paper deals with application of non-invasive electrical capacitance tomography to study the hydrodynamics of shallow bed bubble columns. Two bubble columns with different height to diameter ratio were used. Air–kerosene system that represents dielectric two-phase mixture was investigated. The ECT provided good measurement of the gas holdup at different gas velocities compared to the classical pressure measurements. The ECT was able to provide the gas hold up and the bubble velocities distribution across the column diameter at different gas velocities. The study revealed that spatial gas holdup and bubble velocity distributions are sharp with parabolic shape in the small bubble column (HD/DC=5). However, in the large bubble column (HD/DC=4) the gas holdup and bubble velocity profiles were flatter indicating improvement in the mixing homogeneity and leading to well-mixed reactor. 3D graphical visualization of the flow regimes and transition points were also examined using the ECT. In the small bubble column flow regimes were heterogeneous to slugs flow especially at high flow rate, resulted in downward flow near the walls and imperfect mixing.

Comparison of the carbothermal reduction and nitridation reactivity among .GAMMA.-, .DELTA.-, and .ALPHA.-Al2O3

The carbothermal reduction and nitridation (CRN) reactivity of alumina (Al2O3) to aluminum nitride (AlN) under a flow of nitrogen was investigated for transition aluminas (γ- and δ-Al2O3) and α-Al2O3 with the same particle size and mixing homogeneity with carbon. The aluminas were obtained by calcining a (hydroxo)(succinato)Al(III) complex under a flow of nitrogen, argon, or mixed gas of nitrogen and carbon monoxide. The transition aluminas were converted to AlN without any transformation into α-Al2O3. The CRN reactivity of Al2O3 decreased in the following order: γ-Al2O3 > δ-Al2O3 >> α-Al2O3. The difference in their CRN reactivities was attributed to the difference in the ratio of AlO4 sites to AlO6 sites among the three phases. The CRN reactivity decreased with increasing crystallinity.

THE INFLUENCES OF POWDER MIXING PROCESS ON THE QUALITY OF W-CU COMPOSITES

The mixing homogeneity of powders has a significant influence on the quality of composites fabricated from a powder metallurgy process. The factors that influence the homogeneity include the powder mixer, the medium, and the ball-milling procedure. In this paper, the influences of powder mixers and mixing media on the quality of tungsten-particle reinforced copper matrix composites are studied. Apart from dry mixing, other media used in the wet mixing process include n-butyl alcohol, camphor oil, and paraffin oil. Comparisons on mixing feature are made to a TURBULA® mixer and a Random mixer. The TURBULA® mixer is commercially available, and the Random mixer is an in-house designed machine. Our results show that using paraffin oil as the mixing medium, one may obtain optimal homogeneity in the composites. The Random mixer is superior to the TUBULA® mixer due to the fact that the Random mixer offers an avalanching motion creating pure shear forces onto the powders.