Rotation Speed Of Stirrer Research Articles

Fouling of a Heated Rod in a Stirred Tank System

A batch stirred tank device has been developed for measuring fouling from oil samples. The unit consists of a baffled tank equipped with a centrally mounted long blade stirrer, and an electrically heated rod located at 40% of the radius of the tank. Heat transfer from the rod was first characterized. The velocity field was measured, from which the approach velocity to the probe was determined, which allowed the wall shear on the heating probe to be calculated from a literature equation. Fouling of a heavy oil fraction was studied in 1- to 2-day experiments with bulk oil temperatures typically at 320°C, initial probe surface temperatures to 536°C, and stirrer speeds of 100–900 rpm. Micrometer-sized iron oxide particles were added to the oil, such that fouling was due to a combination of particle deposition and coke formation. Deposition rates were measured thermally from the change in heat transfer coefficient when fouling was relatively heavy, and by thickness and mass accumulation when fouling was light. Effects of oil type, film temperature, stirrer rotation speed (or probe wall shear stress), and concentration of suspended particles on deposition rate and deposit composition are presented.

Effective parameters for the adsorption of chromium(III) onto iron oxide magnetic nanoparticle

Most of the industrial wastewaters comprise toxic, biologically non-biodegradable, and heavy metals which tend to accumulate in the biological organisms causing different diseases. There are some novel technologies and strategies to remove these pollutants. Using the magnetic nanoparticles which are cheap, recyclable, and reusable can be considered as an effective method for removing the pollutants as they do not require conservation or complicated equipments. Using this method, dangerous and rare heavy metals can be restored to the industry. In this study, magnetic nanoparticles with the size of 30 nm were prepared and used for the removal of chromium from synthetic wastewater polluted by chromium sulfate. For this purpose, removal of various concentrations of chromium(III) from wastewater was investigated. The best concentration was achieved in the removal efficiency of 99.1 %. The optimal values of pH, rotation speed of magnetic stirrer, time, temperature, and the amount of nanoparticles were determined according to the primary concentration (500 mg/L). The mechanism of chromium adsorption onto iron oxide (Fe3O4) magnetic nanoadsorbent was also investigated. The results showed both Freundlich and Longmuir isotherms to be the best fit for the chromium adsorption, with Freundlich isotherm being more suitable.

Removal of nickel ions by cementation on zinc from NiSO4 solution in presence of accelerator non-toxic organic compounds

This work deals with the removal of nickel ions by cementation on zinc from dilute nickel sulphate solution. The effect of different parameters such as, initial nickel ion concentration, temperature, rotation speed of a magnetic stirrer and concentrations of 1-aryl-3-(1-phenylpyrazolo [3,4-b]quinoxalin-3-yl)-2-propenone derivatives on the rate of nickel ion removal were investigated. The cementation reaction followed first‐order kinetics and diffusion controlling steps. The rate of cementation was found to increase in the presence of pyrazolo-quinoxaline derivatives. The value of activation energy and the increase in the rate of cementation with stirring support the fact that cementation of Ni2+ on Zn is diffusion controlled. The deposit morphology of nickel in the presence of chalcones was found to be dendritic. The dendrites create a local surface roughness which induces the formation of eddies. These eddies enhance the rate of nickel cementation. The experimental results were analysed by quantum chemical calculations.

Shear stresses and mass transfer at the base of a stirred filtration cell and corresponding conditions in narrow channels with spacers

This study aims to adequately characterize shear stresses and mass transfer coefficients at the membrane surface of a high pressure stirred filtration cell, and to determine equivalent conditions for flow in narrow channels with spacers. Employing electro-chemical techniques, measurements were made of local wall stresses and transfer coefficients, and of space-average mass transfer rates, at various Schmidt numbers and Reynolds numbers 6500–39,000. The local measurements revealed salient features of momentum and mass transfer at the cell base, and the average quantities were successfully correlated with the respective Reynolds numbers. Furthermore, from detailed numerical and experimental studies of cross-flow in narrow spacer-filled channels (simulating conditions in spiral-wound membrane modules), relevant data on wall shear stress and mass transfer were selected for comparison with the new results from the stirred-cell. This comparative data analysis allows estimation of the stirrer rotational speed ω which corresponds to equal area-average shear stress (or mass transfer coefficient) at the membrane surface of stirred cell and of spacer-filled channel (for specific cross flow velocity U). The range of ω values, corresponding to a certain U range, is different for the cases of matching mean shear stress or mass transfer rates in the two flow systems.

Influence of rotational speed on materials flow during semi-solid stirring joining of SiCp/A356 composites

A new process of vacuum-free semi-solid stirring joining on SiCp/A356 composites was investigated. The physical model and mathematical model of fixed-point stirring experiment were developed to study the influence of rotational speed to the mechanical effect of materials flow during semi-solid stirring joining. Numerical simulation and experimental results showed that the rotation of stirrer can induce an alternating pressure effect on the interface between the semi-solid filler metal and the aluminium-matrix composites. A larger rotation speed of stirrer will increase the convection of semi-solid filler metal, and exert larger pressure and wall shear stress towards the joining interface, further increase the extrusion and crushing effects to surface oxide film on the brazing side, and make it conducive to removal of oxide film, increase the forming rate of the interface.

The study on the preparation process of PEG pellets by vibration nozzle method

Background: Uniform size beads can be easily produced by vibration nozzle method. Objective: In this article, the pellets of polyethylene glycol are prepared by a vibration nozzle machine. Thickness of nozzle wall, rotation speed of stirrer, and voltage of excitation are discussed in this article.Results and Discussion: A nozzle wall of thickness ≤0.1 mm is applied to decrease the adherence of jet. The stirring device with 20 rotations/min on the upper side of condensed column is used to disperse unsolidified polyethylene glycol pellets. The effect of parameters including vibration frequency f, jet velocity v, and voltage of excitation V on the average diameter d and standard deviation SD% are investigated by response surface methodology and Weber equation. A very good linear regression between d and v/f is presented under optimum V (in this article V = 3.0 V). Both high v and low SD% can also be obtained by optimum V

Analysis of ball movement for research of grinding mechanism of a stirred ball mill with 3D discrete element method

A simulation of the three-dimensional motion of grinding media in the stirred media mill for the research of grinding mechanism has been carried out by 3-dimensional discrete element method (DEM). The movement of ball assemblies was graphically displayed with some snapshots from start of the milling to 0.20 s. From these simulation results, the grinding zone in the mill was confirmed to be distributed into two regions, which is near the stirrer and the side wall of mill around the stirrer. The power changing the rotation speed of stirrer was examined based on the micro interactive forces at all the contact points between ball-to-ball and between ball-to-stirrer. DEM is a very powerful tool for the microanalysis of movement of balls, which could not have been solved by a conventional experimental method.

Aqueous microdrop manipulation and mixing using ferrofluid dynamics

In this letter, the authors present a simple method to manipulate free microdroplets using ferrofluid dynamics. For droplet transport, a set of periodic lines of ferrofluid on top of a silicon wafer is created by a single strip magnet and dynamically changed by the rotation of a magnetic stirrer underneath it. It is demonstrated that the speed of droplet movement depends on the rotation speed of the magnetic stirrer as well as the size of the droplet. For better droplet mixing efficiency, a discontinuous pattern at the mixing spots is created by adding a smaller strip magnet to the above setup.

Influence of slurry rheology on stirred media milling of quartzite

The role of slurry rheology in stirred media milling of quartzite has been investigated by varying important grinding parameters such as media bead density and size, addition of chemicals, solids concentration, stirrer rotational speed as well as the combined effect of these factors. Media bead density has an evident but complex effect on stirred milling performance, depending on stirrer rotational speed and solids concentration. The effect of media bead size on the ultra-fine grinding of quartzite is relevant to the feed size. Optimal ratio of media bead size to the median size of a feed is between 150 and 200. The combined effect of grinding bead size and stirrer speed or solids concentration is insignificant. The addition of Dispersant S40 or a lower solids concentration results in better grinding performance (i.e., a higher energy efficiency and a smaller median size) due to the maintenance of lower viscosities at shear rates investigated during grinding. Stirrer rotational speed interacts with solids concentration. For a given solids concentration, an optimal stirrer speed exists. The observed phenomena can be explained by the interaction of slurry rheology and the stress intensity of individual grinding bead. In addition, an empirical particle size-energy model provides a good fit ( R 2 > 0.904) to the grinding results under the experimental conditions investigated. Furthermore, the wear of grinding media beads is involved. ZrO 2 beads have a lowest wear rate whereas the wear of SiO 2 beads is most serious. The wear rate of Al 2O 3 beads is related to bead size.

LiCl-KCl/Cd系での希土類元素の物質移動係数の撹拌速度依存性

LiCl-KCl/Cd系での希土類元素の物質移動係数の撹拌速度依存性

Modeling of mixing for stirred bioreactors: 3. Mixing time for aerated simulated broths

This paper presents the experiments on mixing efficiency for aerated media for a laboratory stirred bioreactor with a double turbine impeller. The effects of stirrer rotation speed, air volumetric flow rate and stirrer position on the shaft on mixing time for aerated water and simulated broths (CMCNa solutions) were analyzed. Compared to non-aerated broths, the results indicated that the variation of mixing time with the considered parameters is very different, due to the complex flow mechanism of the gas-liquid dispersion, a mechanism which is changed by changing the broth properties or fermentation conditions. Using the Statistics Toolbox of MATLAB some correlations between the mixing time and rotation speed, air volumetric flow rate and stirrer position on the shaft were established. The proposed equations agree well with the experiments, the average deviation being ?9.02%.

Optimization of conditions for submerged cultivation of the basidiomyceteCoriolus hirsutus, a producer of extracellular laccase

The effects of various factors on the biosynthesis of extracellular laccase (EC 1.14.18.1) by the basidiomyceteCoriolus hirsutus (Wulf.:Fr.) Quel. no. 072 during submerged cultivation were examined. Optimal parameters for cultivation in a fermenter of 101 were determined: temperature, 28°C; stirrer rotation speed, 160 rpm; and the inoculum volume, 15% of the working volume of the fermenter. The filtrate contained peroxidase, laccase, and phenol oxidase activities and displayed a high thermal stability.

Feedstream jet intermittency phenomenon in a continuous stirred tank reactor

A feedstream jet intermittency phenomenon and its onset conditions in a continuous stirred tank reactor are detected for the first time using a laser sheet induced fluorescence visualisation technique. The aim of the present investigation is to determine the operating conditions for which the intermittency phenomenon occurs in stirred tank reactors. The jet intermittency parameters studied are: stirrer type (Rushton and 45° pitched blade turbines, profiled Mixel TTP propeller), stirrer rotational speed, fluid viscosity, feeding rate and the feed point location in the tank. In the case of the Rushton turbine stirred tank reactor, diagrams of intermittency occurrence are reported. These diagrams represent the feeding jet velocity as a function of specific power input or local fluid velocity in the tank. It was not possible to derive from these diagrams any valuable correlation. In order to predict and scale-up the occurrence of intermittency in industrial stirred reactors, dimensionless correlations characterising intermittency occurrence in these devices have been modelled for the three types of stirrers. The dominant variables determining the occurrence of intermittency is the ratio of the jet velocity v J to the tip velocity v tip.

Perfectly stirred catalytic reactor

A heterogeneous, perfectly stirred catalytic reactor with internal recirculation, with the catalyst placed in a fixed bed, was developed in order to characterize several catalysts employed in ammonia industry. For carbon-dioxide methanation on an Ni/Al 2O 3 catalyst, the perfect mixing was obtained at a stirrer rotation speed of 1000–2600 rpm, which ensured the same reaction rate, regardless of composition and feeding gas flow rate.

Effect of Initial Oxygen Concentration on the Rate of SiO2 Inclusion Removal from Molten Cu.

The effect of initial total oxygen concentration, [mass%O]T0, on the rate of inclusion removal from molten copper has been investigated.Under the mechanical stirring condition, it is found that the rate constant of inclusion removal, kO, is dependent on [mass%O]T0 and almost independent of the rotation speed of stirrer. From the results of microscopic observation of inclusion particles with SEM, size distribution of inclusion particles is obtained. The rate constant, kO, increases with increasing initial value of number density and mean radius of inclusion particles. Agglomeration of inclusion particles affects the rate of inclusion removal.Under Ar gas injection stirring condition, kO increases with increasing gas flow rate, while it does not apparently depend on [mass%O]T0, and the effect of the agglomeration on the rate of inclusion removal is much smaller than that under the mechanical stirring condition. It is considered that the inclusion particles are removed from the melt mainly through adhesion to the gas bubble-metal interface.

Kinetics of Phosphorus Transfer between Iron Oxide Containing Slag and Molten Iron of High Carbon Concentration under Ar-O2 Atmosphere.

In the present report, the results are described of kinetic experiments of phosphorus reaction in a molten CaO-Li2O-SiO2-FeO-Fe2O3 slag/Fe-4.4%C molten metal/Ar-O2 gas (PO2=0-0.2 atm) system. The experimental temperature is 1300°C and the slag-metal bath is stirred by an eccentric alumina stirrer (rotation speed, R=30-300 rpm). From the experimental results, it is found that dephosphorization rate increases with increasing the oxygen partial pressure of the Ar-O2 gas atmosphere. The change in the stirrer's rotating speed does not affect the dephosphorization rate obviously, while rephosphorization rate increases with increasing the stirring speed. It is also shown that maximum phosphorus concentration ratio, ((%P)/[%P])max, obtained at the time point when the phosphorus reaction changes from dephosphorization to rephosphorization, increases with the increase in the ratio of ferric iron to total iron of the slag. The ((%P)/[%P])max ratio decreases with increasing the stirring speed in the range of R>50 rpm. The relation between the experimental conditions and the rate of the phosphorus reaction accompanied by simultaneous slag-metal-gas reactions are interpreted qualitatively in terms of the change in a hypothetical slag-metal interfacial oxygen potential. The experimental results are explained quantitatively by means of a mathematical kinetic model calculations. The model calculation fits the experimental results resonably well.

Contact drying modelling of agitated porous alumina beads

Contact drying of porous alumina beads (hygroscopic material) was studied at atmospheric pressure in an agitated laboratory disc dryer in order to have a better understanding of the heat and mass transfer phenomena occuring during the process. Drying kinetics and temperature profiles were determined as a function of operating parameters, namely, the initial moisture content, the plate temperature and the agitation frequency. These data (drying kinetics, temperature profile) were modelled using a contact drying model adapted to this hygroscopic material. The experimental data which are a function of two main parameters, namely, the plate temperature and the stirrer rotation speed, were in good agreement with the model prediction.