Impeller Rotational Speed Research Articles

은 플레이크 분말의 입자크기에 미치는 기계적 밀링 공정변수의 영향

This study is focused on investigating the relation between the particle size of silver flake powder and mechanical milling parameters. Mechanical milling parameters such as ball size, impeller rotation speed and milling time of the attrition ball-mill were controlled to produce silver flake powder. The particle size of the silver flake powder increased with increasing ball size and impeller rotation speed. The change of the particle size of the silver flake powder with mechanical milling parameters was analyzed based on balls motion in the mill container of the attrition ball-mill. The silver flake particles were formed at the elastic deformation area of the ball due to the collision between balls. The change of the particle size of the silver flake powder with mechanical milling parameters well consists with the change of the collision energy of ball with parameters mentioned above.

Liquid‐Solid Mass Transfer Behavior of a Stirred‐Tank Reactor with a Fixed Bed at Its Bottom

AbstractThe mass transfer behavior of a new batch stirred tank with a fixed bed of Raschig rings at the bottom was studied using diffusion‐controlled dissolution of copper in acidified dichromate. Variables studied, amongst others, were the impeller rotation speed, Raschig ring diameter, fixed‐bed height, and impeller geometry. The rate of mass transfer from the fixed bed to the solution increased with increasing impeller rotation speed, decreasing particle size, and decreasing bed height. The axial‐flow turbine is more efficient in increasing the rate of mass transfer than the radial‐flow turbine. The presented reactor is especially useful for conducting diffusion‐controlled liquid‐solid catalytic reactions involving reactants that need to be dispersed first, such as sparingly soluble solid particles.

Effect of Cryomilling on Microstructure and Bonding Mechanism of Mg/B Composite Powders

Boron (B) has great potential to be the primary fuel in energetic systems for its high heating values per unit volume and mass. The existence of B2O3 layer on its surface holding the combustion of B back has limited its extensive utilization. Adding magnesium (Mg) into B can improve its poor combustion performance according to the previous research. A new technique, cryomilling, was employed to prepare Mg and B (Mg/B) composite powders. The powders were cryomilled with a ball-to-powder ratio (BPR) of 80: 1(w/w) and an impeller rotation speed of 400 rpm, 500 rpm and 600 rpm. The cryomilling time is 5 h, 6 h and 7 h. A small amount of ferrum (Fe) is introduced into the powders in spite that the main phases are Mg and B. The effects of cryomilling parameters, such as cryomilling time and rotation speed on Mg/B composite powders were investigated. The results show the amount of active Mg and B is over 80%. The bonding mechanism during the process is analogous to mechanical alloy.

Solid Particle Distribution in Centrifugal Impeller Contactors

The recently developed centrifugal impeller is examined to investigate the solid–liquid mixing in a mechanically agitated contactor. Using the sample withdrawal method, the effects of impeller geometrical parameters, impeller rotational speed (200–700 rpm), solid particle size (500–1100 µm), and solid loading (2–10 vol%) on the degree of homogeneity are studied. The axial and the radial solid concentration profiles and the minimum impeller speed for the complete homogenization are also determined. In comparison with a widely used propeller impeller, considerably higher homogeneity values in lower impeller speeds are obtained (90% homogeneity against 16% homogeneity at 200 rpm at the same conditions). Having also lower power consumption makes this a superior impeller in solid–liquid mixing processes especially in shear-sensitive systems.

Mass and heat transfer enhancement at the wall of cylindrical agitated vessel by turbulence promoters

Rates of liquid–solid mass transfer at a wall of stirred tank reactor lined with an array of vertical tubes turbulence promoter were studied using the dissolution of copper in acidified dichromate technique. Parameters studied are physical properties of the solution, impeller geometry, impeller rotation speed, cylinder diameter, circumferential distance between the vertical cylinders, and the effect of drag reducing polymers. The presence of vertical cylinders at the reactor wall increased the volumetric mass transfer coefficient compared to the presence of the wall without the cylinders by an amount ranging from 12.5% to 214.5%. The presence of Polyox WSR-301 drag reducing polymer decreased the rate of mass transfer by an amount ranging from 3.5% to 32.26% depending on polymer concentration and impeller rotation speed. All data were correlated by dimensionless mass transfer equations. The importance of the present results in building high space time yield catalytic reactors suitable for conducting diffusion controlled reactions was highlighted, also the possible role of the vertical tube array as a secondary built in heat transfer facility which assists external cooling jacket was noted.

Pressure Pulsations of the Blade Region in S-Shaped Shaft-Extension Tubular Pumping System

The three-dimensional unsteady numerical method is applied to investigate the pressure fluctuation of the S-shaft extension pumping system. Some monitor pointers are set at the key positions of blade region to capture the changing rules of the pressure pulsations, from which the data are collected through time-domain and spectrum analysis. The predicted head and efficiency were validated by the comparison with the tested results, and the comparison result shows that the unsteady flow characteristic of pumping system can be simulated by this method. The pulsating amplitude decreases gradually from blade tip to hub, under the condition of large flow rate for both the inlet and outlet of the impeller, in the way different from the smaller flow rate condition. Through adjusting the impeller rotation speed and the number of blades, the dominant frequency can be controlled. For the same monitor point at the impeller, as the flow coefficient is becoming larger, the pulsating amplitude decreases, in which case, it decreases firstly and then increases between the impeller and the guide vane, and the pulsating amplitude is smallest on the high efficiency condition. The rotation speed of impeller has little effect on the dominant frequency at the outlet of guide vane.

S0220102 拍動流下における小柄患者用補助人工心臓の耐久性試験装置の開発([S022-01]循環器系医療機器セッション(1),バイオエンジニアリング部門)

To confirm the long-term durability for developing pediatric ventricular assist device (VAD) under pulsatile flow condition, a mock circulation was consisted of a diaphragm pump with a mechanical heart valve, a reservoir, a compliance tank, a resistance and simple-layout flow paths made of polymer or titanium. The VAD was installed behind the diaphragm pump. Saline added with glycerin was used as a blood analog fluid whose viscosity coincided with that of blood at the temperature of 37 C. The pulsatile flow condition was set within the flow rate range to realize positive flow rate and positive head at the impeller rotational speed which realized the flow rate of 2 L/min and the pressure of 100 mmHg with considering daily variation. In order to obtain the required flow rate, the size of pump valve, the size of pulsatile pump, the mechanism of piston reciprocating motion, and the flow resistance were newly adjusted. As a result, the same size check valve and the 80% large size pulsatile pump were adopted. The quick-return motion mechanism was constructed. The flow resistance were automatically adjusted as the order. Finally, the objected pulsatile flow rates were obtained for the durability test of a pediatric VAD with being confirmed with automatic mode-switching.

Free Rotating Vaneless Diffuser of Diffuser Diameter Ratio 1.30 with Different Speed Ratios and its Effect on Centrifugal Compressor Performance Improvement

Free rotating vaneless diffuser is one of the novel methods in the design of radial diffuser for reducing the energy losses associated with diffusion. In the present study, the impeller with a stationary vaneless diffuser of diffuser diameter ratio 1.40 and impeller with a free rotating vaneless diffuser of diffuser diameter ratio 1.30 along with stationary vaneless diffuser at downstream for the remaining radius ratio, running at speed ratios 0.25 and 0.75 times the impeller rotational speed are analyzed. A higher static pressure rise with reduced losses is achieved by free rotating vaneless diffuser configuration, Free RVD30 SR0.75. The static pressure recovery coefficient increased by 23 to 80%, by rotating the diffuser independently over the entire flow range. Also, losses are lesser due to reduced shear between the through flow and independently rotating walls of the diffuser. The efficiency of both Free RVD30 SR0.25 and Free RVD30 SR0.75 are marginally lesser by 3.5 to 5.3% with SVD. This clearly reveals that the diffusion rate is higher in the free rotating vaneless diffuser configuration.

Removal of copper powder from aqueous solution by cementation using an agitated vessel

The present study is concerned with the removal of copper powder from aqueous solution by cementation on a stationary disc placed inside an agitated vessel. The influence of several parameters on the rate of cementation, such as initial copper sulphate concentration, impeller rotational speed, presence of surfactant (Triton X-100), distance between the disc and the impeller, type of blade turbine and presence of baffles, has been investigated. The rate of cementation was found to increase with increasing impeller rotational speed and initial copper sulphate concentration. On the other hand, the rate decreases with increasing distance between the disc and the impeller. The rate of cementation was inhibited in solutions containing Triton X-100. Performance of a four-blade 90° turbine with regard to the rate of copper cementation was superior to the performance of a four-blade 45° pitched turbine. The present data can be correlated in terms of mass transfer coefficient of cementation asSh=0.905 Sc0.33 Re0.89 (d/l)0.41 (four-blade 90° turbine);Sh=0.815 Sc0.33Re0.79 (d/l)0.47 (four-blade 45° pitched turbine),for the conditions 2035<Sc<2810 and 35, 000<Re<179, 000.

Potential of an asymmetrical agitation in industrial mixing

Mixing is one of the most fundamental operations in chemical engineering. Stirred tanks are widely used in the manufacture of such materials as chemicals, paints, inks, electronics materials, ceramics, foods, pharmaceuticals and cosmetics. Suitable mixing is indispensable to the purpose achievement of a process. Eccentric mixing, in which an impeller installed at eccentric position in a vessel, is one of the traditional methods of promoting mixing. An asymmetrical flow which occurs in vessel is complicated, and it promotes mixing, distribution, and mass transfer. In this study, a new mixing method which eccentric mixing using a large type impeller which attracts attention in recent years is shown. The high performance of a large impeller can be combined with the advantages of an eccentric impeller by using the impeller at an eccentric position. The power consumption and mixing time for MAXBLEND, which is a type of large impeller, were investigated. The power consumption, P , and mixing time, θ M , were measured under various eccentric conditions. The relation between the power number ( N p ) and Reynolds number ( Re ) and that between the dimensionless mixing time ( nθ M ) and Re were investigated. When eccentric mixing is used industrially, we should be concerned about the horizontal load to a agitating shaft. The large oscillating horizontal load causes serious problems, such as the falling off of the impeller or the breakage of the motor, mechanical seal or gearbox. It is, therefore, important to understand the relation between these values and the impeller rotational speed when designing the mixing equipment and determining the operating conditions. In this study, the torque and horizontal load were measured in eccentric mixing under various eccentric conditions. The averages of both, the torque and the horizontal load, and their standard deviations, corresponding to the amplitude of fluctuation, were shown. Doi : 10.12777/ijse.5.2.73-80 [ How to cite this article : Nishi, K., Enya, N., Sonoda, K., Misumi, R., Kaminoyama, M. (2013). Potential of an asymmetrical agitation in industrial mixing. International Journal of Science and Engineering , 5(2),73-80. Doi: 10.12777/ijse.5.2.73-80 ]

Ion-Exchange-Assisted Electrochemical Removal of Heavy Metals from Dilute Solutions in a Stirred-Tank Electrochemical Reactor: A Mass-Transfer Study

The rate of diffusion-controlled removal of Cu2+ from a dilute solution containing a fluidized bed of ion-exchange resin in a batch stirred parallel-plate electrochemical reactor was investigated. The variables studied were the concentration of ion-exchange resin, impeller rotation speed, and impeller geometry. The rate of mass transfer of Cu2+ removal was measured in three cases, namely, (i) ion exchange without electrolysis, (ii) electrolysis without ion exchange, and (iii) combined electrolysis and ion exchange. The presence of ion-exchange resin during electrolysis was found to increase the rate of Cu2+ removal by a factor ranging from 1.18 to 1.78 compared to that obtained by electrolysis alone. A simple mathematical model was developed to account for the enhancing effect of ion-exchange particles. The electrical energy consumption decreased in the presence of ion-exchange resin by an amount ranging from 3.6% to 53%. The radial-flow impeller was found to give higher rates of removal than the axial-fl...

Enrichment implication of froth flotation kinetics in the separation and recovery of metal values from printed circuit boards

The e-waste printed circuit boards (PCBs) are rich in metal content and processing these wastes for extracting the metal values and removing the non-metallic constituents is a prospective proposition. Froth flotation methodology was observed to be a promising technique for rejecting plastics from the comminution product. It has been shown that nearly reagent-free flotation of relatively coarse size (−1.0mm) pulverized e-waste is feasible with a reasonably good product at a high yield and excellent recovery. In the present research work, enrichment of ground 1.0mm PCB powder was investigated through flotation route by varying the operating variables such as frother dosage, pulp density, air flow rate and rotational speed of impeller. The liberation studies accomplish that liberation of metal value from non-metallic constituents at −1.0mm size is excellent and the particulate system is significantly rich in metal value, containing around 23% metal. In-depth study of froth flotation kinetics is primarily focused on high rejection of plastics and also identification of optimum operating conditions for the same. Single-stage flotation enhances metal content from 23% to over 37%, contributing a mass yield of around 75% with recovery of nearly 95% metal values, suffering nominal loss of around 4% metal value only, while effectively rejecting 32% of the materials in feed through float fraction. The interdependence of kinetics and process variables has been discussed and it has been concluded that a high rotor speed aids efficient rejection of the plastics. However, addition of frother is essential to help stabilize the froth and enhance the kinetics, while efficient pre-concentration is facilitated through a combination of moderate air flow with low pulp density. Generation of pre-concentration through flotation route from the entire −1.0mm comminution product stands accomplished.

CFD modeling of hydrodynamic characteristics of a gas–liquid two-phase stirred tank

A three-dimensional CFD model was developed in this work to simulate hydrodynamic characteristics of a gas–liquid two-phase stirred tank with two six-bladed turbines and four baffles, coupling of the Multiple Size Group model to determine bubble size distribution. Important hydrodynamic parameters of the multi-phase system such as volume-averaged overall and time-averaged local gas holdups and axial liquid velocities along time and transversal courses were simulated and analyzed in detail, under varied operating conditions (inlet air flow rate and impeller rotation speed). Model predictions of local transient gas holdup and liquid velocity distributions on vertical and horizontal sections of the tank were also carried out. The overall flow patterns were discussed in detail to assess the mixing. Bubble size distributions were further predicted to reveal the unique properties of gas phase. Experimental measurements of overall gas holdups and local axial liquid velocities were used to validate the developed model.

&lt;b&gt;Numerical investigation of flow induced by a disc turbine in unbaffled stirred tank&lt;/b&gt; - doi: 10.4025/actascitechnol.v35i3.15554

The flow generated by a disc turbine in a cylindrical unbaffled tank was numerically modeled. This study was carried out for shear-thinning fluids. Analyses concern the effect of impeller rotational speed, fluid rheology and impeller blade curvature on the mean velocities and power consumption. It was found that the cavern size and the power consumption are higher for extreme shear thinning fluids. It was found also that the best performance is achieved at high Reynolds number and flat-blade turbine. Predictions have been compared with literature data and a satisfactory agreement has been found.

007 ANALYSIS OF THE LEFT VENTRICULAR ASSIST DEVICE (LVAD) ACOUSTIC SIGNAL: A NOVEL CLINICAL DIAGNOSTIC METHOD FOR SUSPECTED PUMP THROMBOSIS

Introduction Left Ventricular Assist Devices (LVADs) are an established treatment for advanced heart failure in appropriately selected patients. Pumps have gradually become smaller and more durable, are associated with survival benefits, improvement in functional status and quality of life in patients with advanced heart failure. Despite impressive advances in device technology, pump thrombosis remains a serious complication and a definitive diagnostic method is currently unavailable. Rotary pumps produce a characteristic acoustic signal which is primarily determined by rotation speed and impeller symmetry. Our group have evaluated a novel method of pump thrombus diagnosis based on the analysis of the acoustic signal produced by implanted LVADs. The aim of this study was to compare the acoustic characteristics of normal devices with those with suspected pump thrombosis. Methods The control group consisted of 20 ambulatory heart failure patients receiving support with an axial impeller Thoratec HeartMate II (n=10) or centrifugal HeartWare HVAD (n=10). The pump thrombosis group consisted of four patients, that is, Heartmate II (n=2), HVAD (n=2). Recordings were made with the patient in a semi-recumbent position at the clinical pump speed (typically circa 9000 rpm for HeartMate II and 3000 rpm for HVAD) with purpose made recording stethoscope placed on the chest wall in the 9mitral9 position and were analysed using analysis software developed in house (Matlab, Mathworks Inc). Fast Fourier Transformation (FFT) of the acoustic signal was used in order to reveal the constituent frequency components. Results Acoustic profiles were readily obtainable from all patients and the FFT spectra were dependent on the LVAD impeller symmetry and rotation speed. In HeartMate II (HMII) patients, FFT spectral peaks were present at the impeller rotation frequency 152.1±2.5 Hz and blade passing frequency of 3 times this value (456.1±7.4 Hz), reflecting the presence of 3 flow channels in the impeller. For HVAD recipients, FFT spectral peaks were present at the impeller rotation frequency 48.6±2.2 Hz and blade passing frequency 194.5±8.6 Hz, reflecting the presence of four impeller flow channels. In LVAD patients with suspected pump thrombosis, additional FFT spectral peaks to those described above were detected. Successful resolution of the pump thrombus episodes (normalisation of pump power and blood trauma biomarkers) in the two HVAD patients after 6 and 14 days was associated with normalisation of the FFT traces. Conclusions The appearance of atypical FFT spectral peaks during pump thrombus episodes is likely to be related to a combination of unbalanced impeller motion, changes in blood flow and increased turbulence. Acoustic monitoring is a simple non-invasive method which is likely to have clinical utility in the diagnosis of pump thrombus episodes in LVAD patients.

Liquid‐Solid Mass Transfer Behavior of a New Stirred‐Tank Reactor with a Packed Bed Fixed to its Wall

AbstractRates of liquid‐solid mass transfer at a packed bed of Raschig rings fixed to the wall of a stirred tank were measured by a technique which involves the diffusion‐controlled dissolution of copper in acidified dichromate. Variables studied were impeller rotation speed, impeller geometry, Raschig ring diameter, bed thickness, presence of baffles, physical properties of the solution, and effect of superimposed flow. Mass transfer data for the batch reactor were correlated by a dimensionless equation. For a given set of conditions, the radial‐flow impeller was found to produce higher rates of mass transfer than the axial‐flow impeller. The presence of baffles increased the rate of mass transfer inside the bed. Applications of the suggested reactor in conducting different diffusion‐controlled liquid‐solid reactions were evaluated.

Stirred tank membrane emulsification using flat metallic membranes: A dimensional analysis

The performance of a membrane emulsification unit, using flat membranes in a stirred tank, has been examined by dimensional analysis. The dimensionless numbers were defined in terms of shear and membrane pore size. Dimensionless droplet size prediction models based on simple force balances were used to select the most representative dimensionless numbers including operating parameters. Oil-in-water emulsions were produced with tailor-made metallic membranes with pore sizes of 30 and 50μm. Results showed that monodisperse emulsions were produced with span values around 0.5, significantly lower than when a rotor-stator homogenizer is used. The influence of the selected operating parameters (impeller rotational speed, continuous phase viscosity and dispersed phase flux) on droplet size distribution was studied and experimental results were compared with droplet size prediction models. Impeller rotational speed and membrane pore size were the key parameters influencing emulsion droplet size and monodispersity. A correlation based on the Euler dimensionless number, including all the operating parameters is proposed.

Dynamic Characteristics of Rotating Stall in Mixed Flow Pump

Rotating stall, a phenomenon that causes flow instabilities and pressure hysteresis by propagating at some fraction of the impeller rotational speed, can occur in centrifugal impellers, mixed impellers, radial diffusers, or axial diffusers. Despite considerable efforts devoted to the study of rotating stall in pumps, the mechanics of this phenomenon are not sufficiently understood. The propagation mechanism and onset of rotating stall are not only affected by inlet flow but also by outlet flow as well as the pressure gradient in the flow passage. As such, the complexity of these concepts is not covered by the classical explanation. To bridge this research gap, the current study investigated prerotation generated at the upstream of the impeller, leakage flow at the tip clearance between the casing and the impeller, and strong reserve flow at the inlet of the diffuser. Understanding these areas will clarify the origin of the positive slope of the head-flow performance curve for a mixed flow pump. Nonuniform pressure distribution and adverse pressure gradient were also introduced to evaluate the onset and development of rotating stall within the diffuser.

Hydrodynamics in a vessel stirred by simple and double helical ribbon impellers

Abstract The present paper treats the agitation of shear thinning fluids in a cylindrical unbaffled vessel with a flat-bottom. Two kinds of impellers have been used: simple and double helical ribbons. This work is achieved with the help of CFD package (CFX-12.0), which is based on the finite volume method to solve the continuity and momentum equations. The effect of impeller rotational speed, fluid rheology, impeller size, impeller clearance from the tank bottom on the flow fields and power consumption have been investigated. Finally, a comparison between the two impellers is made. It was found that the best performance is obtained with double helical ribbon impeller placed at the middle of the tank, with moderate blade size and operating at Re g &gt; 20. Our results have been compared with those of other literatures and a satisfactory agreement is observed.

Study air–water system in horizontal loop geometry

To enhance the understanding of hydrodynamic of air–water multi-phase flow inside a toroidal geometry, experiments were carried out in horizontal torus reactor. Compared with vertical flow, the flow in horizontal milli torus reactor was characterized by one additional flow pattern. In vertical position two flow regimes are considered: not-dispersed and dispersed flow while in horizontal position three flow regimes have been distinguished: stratified flow, dispersed flow and mixed flow regimes. The mixing time is measured by a conductimetric method as described by (Benkhelifa et al., 2000). The effect of both superficial gas velocities and impeller rotation speeds has been studied. The mixing time has been decreased by increasing both the superficial gas velocity and the impeller rotation speed and has been shorter than the one given for the horizontal configuration. The axial dispersion inside the reactor was modelled by the Zhang's model. The obtained results are in a good agreement with Zhang's model.