Stirring Mechanism Research Articles

Stirring Enhances Removal of Oil by Kapok Fiber

The natural hollow fiber, namely kapok, has been studied for the removal of oil, particularly in the area of oil spill clean-up. The hydrophobic nature of the natural absorbent has been demonstrated to exhibit (or show potential to exhibit) excellent oil absorption properties. Kapok fiber is inexpensive, readily available, very lightweight which makes it easy for transportation and its excellent buoyancy eases retrieval. Reusability of the material up to 15 cycles has been reported and this supports its being environmental-friendly. This paper looks into the oil absorption capacity of raw kapok fiber that can be dramatically enhanced by the simple mechanism of stirring. The oil absorption capacity is greatly increased to more than 200 times the mass of kapok used, i.e., with stirring, 1 g of the kapok fiber is able to absorb at least 200 g of the oil (200 g/g) which in this case is the refined palm oil used for cooking. The paper also discusses the reasons for the improvement due to stirring. And as a natural agricultural product which is abundant, besides being environmental-friendly, its application would be a sustainable approach to control water pollution due to oil spills and industrial organic contaminants.

Experimental Evaluation of the Statistical Isotropy of a Reverberation Chamber’s Plane-Wave Spectrum

Synthetic-aperture measurements in a loaded reverberation chamber are used to calculate power-angle profiles describing the instantaneous distribution of received power versus azimuth angle-of-arrival. Averaging multiple power-angle profiles leads to estimates of the reverberation chamber's power-angle spectrum. A comparison to simulated power-angle spectra for an ideal reverberation chamber indicates that the loaded reverberation chamber tends to provide a statistically anisotropic plane-wave spectrum. Analysis of the measurements' power-delay-angle profiles suggest that this anisotropy due to both the presence of unstirred multipath components and strong early-time stirred multipath components arising from reflections off of the mode-stirring paddles' planar surfaces. Guidelines are provided for minimizing the effect of a statistically anisotropic plane-wave spectrum, such as the use of additional stirring mechanisms and minimizing the contributions of unstirred multipath components.

Recovery of temperature, salinity, and potential density from ocean reflectivity

This work explores a method to recover temperature, salinity, and potential density of the ocean using acoustic reflectivity data and time and space coincident expendable bathythermographs (XBT). The acoustically derived (vertical frequency >10 Hz) and the XBT-derived (vertical frequency <10 Hz) impedances are summed in the time domain to form impedance profiles. Temperature (T) and salinity (S) are then calculated from impedance using the international thermodynamics equations of seawater (GSW TEOS-10) and an empirical T-S relation derived with neural networks; and finally potential density (ρ) is calculated from T and S. The main difference between this method and previous inversion works done from real multichannel seismic reflection (MCS) data recorded in the ocean, is that it inverts density and it does not consider this magnitude constant along the profile, either in vertical or lateral dimension. We successfully test this method on MCS data collected in the Gulf of Cadiz (NE Atlantic Ocean). T, S, and ρ are inverted with accuracies of δTsd=0.1°C, δSsd=0.09, and δρsd=0.02kg/m 3. Inverted temperature anomalies reveal baroclinic thermohaline fronts with intrusions. The observations support a mix of thermohaline features created by both double-diffusive and isopycnal stirring mechanisms. Our results show that reflectivity is primarily caused by thermal gradients but acoustic reflectors are not isopycnal in all domains.

Treatment of Textile Dyes by Bio-chemical Process in Stirred Tank Sequencing Batch Bioreactor (STSBBR)

A bacterial isolate Pseudomonas sp. was isolated from the solid waste slump collected from a local duping site of Sylhet district and was efficiently utilized for the removal of dye (Orange 3R) from simulated synthetic waste water in a lab scale Stirred Tank Sequencing Batch Bioreactor (STSBBR) in batch mode. A reactor with 2 L capacity (working volume 0.5 L) equipped with suitable control means and stirring mechanism was operated at room temperature and pH 6.6 ± 1 in fill-react-settling-draw mode with different initial dye concentrations (50, 100, 150, 200 &amp; 300 ppm) where the hydraulic retention time was maintained for 12-72 hours depending on the adaptation of waste water by the bacterial strain. The efficiency of the reactor was analyzed with respect to three strands and found to be negative correlation with the concentration of the dye. Overall color, COD, and BOD in the Stirred tank bioreactor system (STSBBR) were removed by 49.67, 37.45 and 33.89%, respectively with 50 ppm dye concentration and HRT of 24 h. The efficiency of the reactor was found to be in negative correlation with the concentration of the dye. This STSBBR system was found very effective for efficient biological treatment of such dyeing industry waste water by the bacterial strain Pseudomonas sp. DOI: http://dx.doi.org/10.3329/jce.v27i2.17808 Journal of Chemical Engineering, IEB Vol. ChE. 27, No. 2, December 2012: 77-82

Swallowing a cellular automaton pill: Predicting drug release from a matrix tablet

Matrix tablets are drug delivery devices designed to release a drug in a controlled manner over an extended period of time. We develop a cellular automaton (CA) model for the dissolution and release of a water-soluble drug and excipient from a matrix tablet of water-insoluble polymer. Cells of the CA are occupied by drug, excipient, water or polymer and the CA updating rules simulate the dissolution of drug and excipient and the subsequent diffusion of the dissolved substances. In addition we simulate the possible fracture of brittle drug and excipient powders during the tablet compression and the melting of the polymer during a possible thermal curing process. Different stirring mechanisms that facilitate the transport of dissolved drug in the fluid in which the tablet is immersed are modeled in the water cells adjacent to the boundary of the tablet. We find that our simulations can reproduce experimental drug release profiles. Our simulation tool can be used to streamline the formulation and production of sustained release tablets.

Development of Feeding & Stirring Mechanisms for Stir Casting of Aluminium Matrix Composites

Composite materials, (composites) are engineered or naturally occurring materials made from two or more constituent materials with significantly different properties, which remain, separate and distinct at the macroscopic or microscopic scale even after they are made into a single material. The constituent materials used in it will compensate each other's limitations, so that theresulting material would constitute the advantages of all the included materials. Therefore combining specific materials we would achieve material, which could serve the specific application extensively and so now a days composite materials plays a wide and extensive role in manufacturing engineering components. There are several types of composite materials and methods for manufacturing them. In this paper manufacturing of metal matrix composites by stir casting is taken into focus, manufacturing of Aluminium Alloy (LM6)-SiC particle reinforced MMC by stir casting is the objective. They are widely used in automotive, aeronautical application and so it is given the prime importance. The methodology opted for manufacturing is stir casting because it is the cheapest and easiest and the applications like automotive and aeronautics involves manufacturing and utilization of large number of components, so the price should be low and the process should be easy and simple. Lot of researches is going on this area by varying different parameters. This paper focuses on designing, fabricating and testing different stirrers and feeders and utilizing them in stir casting for the manufacturing of Aluminium silicon carbide composite materials. Then the significance of individual stirrers and feeders are compared and the best one is identified. The significance of each stirrer and feeder is found by testing the specimen.

Welding Performance of a Homemade Friction Stir Welding Tool

Homemade Friction Stir Welding (FSW) Tool utilizing conventional milling machine has been developed. The FSW tool made from mild steel was designed and fabricated. Experimental investigation of FSW process of the Aluminum alloy specimens to observe its mechanical performances was performed. To evaluate its performance, hardness test, tensile test as well as visual inspections of the welding result were performed. Hardness number in the welding region was measured about 40-60% lower than the base metal, and heat affected zone region. The tensile test result varies with maximum 100 MPa. The imperfection of final form of metal due to the stirring mechanism was inspected. The presence of void/crack at cross-section of the welded specimen was observed. It was found that by applying suitable configuration, the use of mild steel as the FSW tool was reasonable for performing FSW process. It was concluded that, using a relatively low cost FSW tool, a quite satisfactory result of welding performance was achieved.

Dynamics of fluid and light intensity in mechanically stirred photobioreactor

Turbulent flows in a single-stage and a two-stage impeller-stirred photobioreactor with a simple geometric configuration were analyzed using computational fluid dynamics. The trajectories of the microorganisms entrained in the flow field were traced by the particle tracking method. By projecting these trajectories onto a radial–axial (r−z) plane with a given azimuth angle, we were able to observe four different dynamics zones: circulation, pure rotation, trap, and slow-motion. Within the pure rotation zone, turbulence can be observed near the edges of the impeller. The light intensity and the light/dark cycles subjected by the microorganisms differ significantly in these zones. These differences can be further changed by providing different incident light illuminations on the reactor surface. The dynamics zones can be altered by modifying the geometric configuration of the reactor and the impeller stirring mechanism. In combination with the utilization of different incident light illuminations, the light intensity dynamics and the light/dark cycles subjected by the microorganisms can be controlled such that an optimal photobioreactor design with a high efficiency of light utilization and a high formation rate of the biochemical products can be realized.

Large deviations of the empirical currents for a boundary-driven reaction diffusion model

We derive a large deviation principle for the empirical currents of lattice gas dynamics which combine a fast stirring mechanism (Symmetric Simple Exclusion Process) and creation/annihilation mechanisms (Glauber dynamics). Previous results on the density large deviations can be recovered from this general large deviation principle. The contribution of external driving forces due to reservoirs at the boundary of the system is also taken into account.

Coplanar circumbinary debris discs

We present resolved Herschel images of circumbinary debris disks in the alpha CrB (HD139006) and beta Tri (HD13161) systems. We find that both disks are consistent with being aligned with the binary orbital planes. Though secular perturbations from the binary can align the disk, in both cases the alignment time at the distances at which the disk is resolved is greater than the stellar age, so we conclude that the coplanarity was primordial. Neither disk can be modelled as a narrow ring, requiring extended radial distributions. To satisfy both the Herschel and mid-IR images of the alpha CrB disk, we construct a model that extends from 1-300AU, whose radial profile is broadly consistent with a picture where planetesimal collisions are excited by secular perturbations from the binary. However, this model is also consistent with stirring by other mechanisms, such as the formation of Pluto-sized objects. The beta Tri disk model extends from 50-400AU. A model with depleted (rather than empty) inner regions also reproduces the observations and is consistent with binary and other stirring mechanisms. As part of the modelling process, we find that the Herschel PACS beam varies by as much as 10% at 70um and a few % at 100um. The 70um variation can therefore hinder image interpretation, particularly for poorly resolved objects. The number of systems in which circumbinary debris disk orientations have been compared with the binary plane is now four. More systems are needed, but a picture in which disks around very close binaries (alpha CrB, beta Tri, and HD 98800, with periods of a few weeks to a year) are aligned, and disks around wider binaries (99 Her, with a 50 yr period) are misaligned, may be emerging. This picture is qualitatively consistent with the expectation that the protoplanetary disks from which the debris emerged are more likely to be aligned if their binaries have shorter periods.

Improvement of Photoluminescence Uniformity of Porous Silicon by using Stirring Anodization Process

The electrolyte stirring method of anodization etch ing process for manufacturing porous silicon (PS) is re ported in this work. Two experimental setups of nature air stirring (PS- ASM) and electrolyte stirring (PS-ESM) are employed to clari fy the influence of stirring mechanisms on electrochemical etching proc ess. Compared to traditional fabrication without any stirring appara tus (PS-TM), a large plateau region of PS surface structure is obtained from samples with both stirring methods by the 3D-profiler measurement. Moreover, the light emission response is also improved by both pr oposed electrolyte stirring methods due to the cycling force in electr olyte could effectively enhance etch-carrier distribution while the electrochemical etching process is made. According to the analysis of statistical calculation of photoluminescence (PL) intensity, lo wer standard deviations are obtained from PS-samples with studied stirring methods, i.e. the uniformity of PL-intensity is effectively improved. The calculated deviations of PL-intensity are 93.2, 74. 5 and 64, respectively, for PS-TM, PS-ASM and PS-ESM.

Purification process of phosphoric acid by vertical zone‐melting technique

AbstractThe efficiency of vertical zone‐melting technique as a function of molten‐zone length, number of zone passes, molten‐zone velocity and phosphoric acid concentration on the purification process of phosphoric acid is studied. The results showed that adopting a relatively long molten‐zone length in the initial passes to effect a rapid movement of impurities and a short molten‐zone length in the later passes to obtain greater purification; additional zone‐passes cannot be made as impurities redistribution approaches limiting distribution; for stirring mechanism is not adopted in the present study and as diffusion is the only mixing process, slow molten‐zone velocity 3–6 mm h−1 is better; the purification efficiency increases with phosphoric acid concentration, and 94–99.8% concentration of phosphoric acid is better. © 2012 Canadian Society for Chemical Engineering

Advances in mode-stirred reverberation chambers for wireless communication performance evaluation

Reverberation chambers (RC) are a popular tool for laboratory wireless communication performance evaluation, and their standardization for Over-The-Air (OTA) measurements is underway. Yet, the inherent limitations of single-cavity RCs to emulate isotropic Rayleigh-fading scenarios with uniform phase distribution and high elevation angular spread put their representation of realistic scenarios into jeopardy. Recent advances in the last few years, however, have solved all these limitations by using more general mode-stirred reverberation chambers (MSC), wherein the number of cavities, their stirring and coupling mechanisms, and their software postprocessing algorithms is far from simple, representing a new era for wireless communications research, development, and over-the-air testing. This article highlights recent advances in the development of second-generation mode-stirred chambers for wireless communications performance evaluation.

Fabrication of highly homogeneous As2Se3 glass under argon flow

The present study relates to a new method for the synthesis of As2Se3 glass in a controlled atmosphere. The advantage of this technique is that it does not require sealing of the silica reaction container and therefore makes it likely to substitute the current industrial batch by batch synthesis which actually needs very expensive single-use sealed silica vessels.An experimental device has been developed for these purposes. It is equipped with a stirring mechanism to homogenize the molten bath. In order to avoid contamination by oxygen and moisture, the synthesis is carried out under argon flow (pressure of 1bar). Material losses during synthesis can be reduced to less than 2% when temperature is progressively increased up to 430°C. Bulk glass ingots are finally obtained according to a two-step annealing process. Their chemical composition is analyzed by EDS and shows a variation range of less than 0.2%. The excellent reproducibility of the given method is also confirmed by the refractive indexes, that do not differ for more than 1·10−3 from one another.Adverse absorption bands due to oxygen do not occur in the 8–12μm spectral region when 1000ppm of Mg is added. As no distilling operation has been carried out until now, the magnesium oxide partially keeps staying in the glass and leads to scattering losses at short wavelengths.

Simulation of continuous stirred ultrafiltration process: an approach based on surface renewal theory

ABSTRACTUltrafiltration (UF) is an important operation in many processes, including foods and pharmaceuticals, and shear enhanced dead‐end systems are particularly suitable for small‐scale operations. Most industrial applications require a high permeate flux and maximum solute rejection, combined with long membrane life. A rigorous surface renewal model has been developed which describes the mass transfer processes occurring in a single stirred UF cell. The model takes into consideration two distribution functions of random surface elements, one with respect to their point of origin and the other related to the corresponding residence time on the membrane surface. The back transport flux and the permeate flux are evaluated at the membrane surface in order to develop a component balance equation. The component balance equation and a rejection–flux relationship arising from irreversible thermodynamics are solved simultaneously to allow a dynamic simulation. The dynamic simulation enables a more complete understanding of the permeate flux, membrane surface concentration and permeate concentration under various operating conditions. For validation of the proposed model, experiments were conducted on UF of polyethylene glycol 6000 (PEG 6000) solution in a continuous stirred UF cell comprising a cellulose acetate membrane of 5000 Da molecular weight cut‐off. Model predicted values are in excellent agreement with the experimental results. The effects of different stirring mechanisms on mass transfer with flat disk, propeller and turbine impellers were also characterized using the developed model. Copyright © 2010 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

ON THE EFFICIENCY OF THE TIDAL STIRRING MECHANISM FOR THE ORIGIN OF DWARF SPHEROIDALS: DEPENDENCE ON THE ORBITAL AND STRUCTURAL PARAMETERS OF THE PROGENITOR DISKY DWARFS

(Abridged) The tidal stirring model posits the formation of dSph galaxies via the tidal interactions between rotationally-supported dwarfs and MW-sized host galaxies. Using a set of collisionless N-body simulations, we investigate the efficiency of the tidal stirring mechanism. We explore a wide variety of dwarf orbital configurations and initial structures and demonstrate that in most cases the disky dwarfs experience significant mass loss and their stellar components undergo a dramatic morphological and dynamical transformation: from disks to bars and finally to pressure-supported spheroidal systems with kinematic and structural properties akin to those of the classic dSphs in the Local Group (LG). Our results suggest that such tidal transformations should be common occurrences within the currently favored cosmological paradigm and highlight the key factor responsible for an effective metamorphosis to be the strength of the tidal shocks at the pericenters of the orbit. We demonstrate that the combination of short orbital times and small pericenters, characteristic of dwarfs being accreted at high redshift, induces the strongest transformations. Our models also indicate that the transformation efficiency is affected significantly by the structure of the progenitor disky dwarfs. Lastly, we find that the dwarf remnants satisfy the relation Vmax = \sqrt{3} * sigma, where sigma is the 1D, central stellar velocity dispersion and Vmax is the maximum halo circular velocity, with intriguing implications for the missing satellites problem. Overall, we conclude that the action of tidal forces from the hosts constitutes a crucial evolutionary mechanism for shaping the nature of dwarf galaxies in environments such as that of the LG. Environmental processes of this type should thus be included as ingredients in models of dwarf galaxy formation and evolution.

Self-consistent unstirred layers in osmotically driven flows

It has long been recognized that the osmotic transport characteristics of membranes may be strongly influenced by the presence of unstirred concentration boundary layers adjacent to the membrane. Previous experimental as well as theoretical works have mainly focused on the case where the solutions on both sides of the membrane remain well mixed due to an external stirring mechanism. We investigate the effects of concentration boundary layers on the efficiency of osmotic pumping processes in the absence of external stirring, i.e. when all advection is provided by the osmosis itself. This case is relevant in the study of intracellular flows, e.g. in plants. For such systems, we show that no well-defined boundary-layer thickness exists and that the reduction in concentration can be estimated by a surprisingly simple mathematical relation across a wide range of geometries and Péclet numbers.

The mechanism of stirring of liquid metal in the nugget in resistance welding

The mechanism of stirring of liquid metal in the nugget in resistance welding

Are debris discs self-stirred?

This paper considers the evidence that debris disks are self-stirred by the formation of Plutos. A model for the dust produced during self-stirring is applied to statistics for A stars. As there is no significant difference between excesses of A-stars <50Myr old, we focus on reproducing the broad trends, the "rise and fall" of the fraction of stars with excesses. Using a population model, we find that the statistics and trends can be reproduced with a self-stirring model of planetesimal belts with radii distributed between 15-120AU. Disks must have this 15AU minimum radius to show a peak in disk fraction, rather than a monotonic decline. Populations of extended disks with fixed inner and/or outer radii fail to fit the statistics, due mainly to the slow 70um evolution as stirring moves further out in the disk. This conclusion, that debris disks are narrow belts, is independent of the significance of 24um trends for young A-stars. We show that the statistics can also be reproduced with a model in which disks are stirred by secular perturbations from a nearby eccentric planet. Detailed imaging is therefore the best way to characterise the stirring mechanism. From a more detailed look at beta Pictoris Moving Group and TW Hydrae Association A-stars we find that the disk around beta Pictoris is likely the result of secular stirring by the proposed planet at ~10AU; the structure of the HR 4796A disk also points to sculpting by a planet. The two other stars with disks, HR 7012 and eta Tel, possess transient hot dust, though the outer eta Tel disk is consistent with a self-stirred origin. Planet formation provides a natural explanation for the belt-like nature of debris disks, with inner regions cleared by planets that may also stir the disk, and the outer edges set by where planetesimals can form. [abridged]

电磁搅拌对激光熔覆WC-Co基合金涂层的组织结构和硬度的影响及机理研究

电磁搅拌对激光熔覆WC-Co基合金涂层的组织结构和硬度的影响及机理研究