Impeller Rotational Speed Research Articles

Distribution and motion behavior of desulfurizer particles in hot metal with mechanical stirring

To improve the desulfurization efficiency of hot metal with mechanical stirring, the distribution and motion behavior of desulfurizer particles have been investigated by numerical simulation. The volume fraction of desulfurizer particles in different ladle regions and particle trajectory are further discussed. In addition, the effects of rotation speed and eccentricity of impeller have also been elucidated. The results show that the motion of desulfurizer particles in different ladle regions takes about 10s to reach a dynamic steady state. The particle volume fraction in upper circulation region (56.2%) is about 2.0 times that in middle agitation region (27.7%), and about 3.5 times that in lower circulation region (16.1%). The typical motion trajectories of desulfurizer particles can be summarized into four types. The largest particle volume fraction in upper circulation region is mainly attributed to the first and fourth types of motion trajectories, while the second and third types of trajectories contribute to the particle volume fraction in middle agitation region and lower circulation region respectively. The greater rotational speed is more conducive to desulfurization, however the rotation speed is not recommended to be >90 rpm to avoid the possibility of overflow during actual production process. Compared with the centric stirring, the impeller eccentricity of 100 mm is recommended and more beneficial to desulfurization.

Stage-wise characterization of the high shear granulation process by impeller torque changing rate

Fine cornstarch powders are wet granulated in a lab-scale high shear granulator. The torque required for maintaining the impeller passing through the bed with a constant rotating speed is monitored during the continuous binder addition granulation process. A new method is proposed to identify 6 stages during the granulation process based on the fraction of the positive impeller torque changing rate in a characteristic period of time. The morphologies and the behavior of the bed are found intrinsically different in the identified 6 stages. The influence of the impeller blade inclined angle on the impeller torque in each stage is initially reported. The impeller with planner 45° blades requires higher torques in Stages I and II due to the overall powder bed mass loading. The impeller with steeper 60° blades requires higher torques in Stages III and IV due to the higher collision frequencies between the blade and granules. The suitable granulation liquid binder to solid powder mass ratio can be readily identified in Stages II and III, and its range is found to increase with the increasing of the impeller rotational speed and is independent to the blade inclined angle.

Numerical and experimental analyses of a stirred vessel for a large volumetric flow rate of sparged air

Abstract Computational fluid dynamics (CFD) and experimental analyses of some of the basic characteristics of air sparging in a tall stirred vessel equipped with a three-stage impeller are presented. The impeller was assembled from a radial ABT impeller as the lower, a turbine 6PBT45 as the middle and an axial Scaba-type 3SHP1 impeller as the upper. All the impellers were of the same diameter, i.e., 225 mm, while the vessel diameter was 450 mm. The impeller's rotational speed was 178 r·min−1. The aeration regime was established with an air volumetric flow rate of 28.3 m3·h−1. To the best of our knowledge, this study is the first to consider the very high gassing rate by means of CFD in a tank stirred by three-stage axial/radial impellers. The numerical simulation was performed using the ANSYS Fluent (R17.2, 2016) code for solving the governing equations of fluid dynamics in single- and multi-phase systems. While discussing the bubble size distribution, a discrete population balance model (PBM) was used. Adopting CFD, the stirring power and the total void fraction (the total gas holdup) were calculated. The results were in good agreement with the measured values using a laboratory experimental device.

Experimental investigation of oil drops behavior in dispersed oil-water two-phase flow within a centrifugal pump impeller

In oil production, one important artificial lift method involves the commonly used centrifugal pump. The use of this pump in the petroleum industry, however, is hindered by some unfavorable operational conditions. Operating centrifugal pumps with gas and viscous fluids, such as dispersions, may lead to a degradation of their performance. The objective of this paper is to analyze oil-water dispersions in a pump impeller, in order to investigate the behavior of oil drops, which may influence the pump working. Thus, experiments were carried out at different pump rotation speeds and water flow rates. Researchers used a facility with a pump prototype that enabled them to visualize the flow in all the impeller channels. Images, captured through a high-speed camera, revealed a unique flow pattern of oil drops dispersed in water. Processed with computer codes, the images indicated that the oil drops were, in general, spherical or elliptical, and only a few broke up in the impeller. The interaction with water caused the oil drops to rotate, deform, and deviate, thus moving in random paths. Size distributions suggested that the drops became smaller as the impeller rotation speed and water flow rate increased. This behavior was due to the turbulence-induced shear stress and kinetic energy. The oil drops’ equivalent diameters ranged from 0.1 to 6.0 mm; velocities took values measurable by units of m/s; accelerations reached hundreds of m/s2; and forces had magnitudes of thousandths of N. Researchers observed a clear dependence between flow conditions and drop dynamics. Carried by the water flow, the oil drops on the suction blade moved faster than those on the pressure blade of a channel. The drop dynamics were significantly influenced by the presence of adverse pressure gradients and water velocity fields.

Galvanic Corrosion of Steel in Agitated Vessels Used in Fertilizer Industry

Rates of mass transfer controlled Fe/Cu galvanic corrosion at the wall lining of a cylindrical agitated vessel in different fertilizer electrolytic media were studied. Variables investigated are impeller rotation speed, impeller geometry, electrolyte type, electrolyte concentration, area ratio (anode/cathode), electrolyte temperature, and effect of polyethylene oxide (drag reducing polymer) as a corrosion inhibitor. The corrosion rate was determined by following the change of the concentration of anode metal ions (Fe++) in the electrolyte with time. Scanning electron microscopy (SEM) was carried out for steel sheets subjected to different electrolytes. The results showed that the galvanic corrosion rate increased with increasing the impeller rotation speed, the electrolyte concentration, and temperature. The presence of polyethylene oxide decreased the rate of corrosion by 11–35.21% depending on polymer concentration and operating conditions. Axial flow impeller produces corrosion rates higher than that with the radial flow type under the same operating parameters. Application of the results in the design of agitated vessels handling fertilizer media was discussed.

Discrete element analysis of the particle mixing performance in a ribbon mixer with a double U-shaped vessel

In this study, a discrete element method is employed to simulate the mixing process of solid particles in a horizontal ribbon mixer with a double U-shaped vessel. A mixing index, i.e. the so-called Lacey index, is adopted to evaluate the mixing quality of particles. The effects of the operational and geometrical parameters including initial loading, particle size, impeller rotational speed, and inner blades on the mixing quality of particles have been investigated. Results suggest that the initial loading and the impeller rotational speed have significant effects on the mixing quality of particles, while the other two parameters have relatively small effects. Moreover, the effect of each parameter on the mixing quality has been explained by utilizing the relative velocity components between the centroids of particles after collision, and this ribbon mixer provides much more intense relative movements of particles along the vertical direction than the axial and side–side directions. Finally, the mixing performance between the ribbon mixers with respective single and double U-shaped vessels is compared. Results show that the ribbon mixer with a double U-shaped vessel shows better mixing performance under top–bottom and front–back initial loadings, however, worse mixing performance under side–side initial loading.

Experimental Analysis on the Velocity of Oil Drops in Oil–Water Two-Phase Flows in Electrical Submersible Pump Impellers

The objective of this research is to investigate the velocity of oil drops within the impeller of an electrical submersible pump (ESP) working with oil-in-water dispersion flows at different operational conditions. An experimental study was conducted using an ESP prototype with a transparent shell designed to enable flow visualization within the impeller channels. The tests were performed at three rotational speeds, 600, 900, and 1200 rpm, for three water flow rates, 80%, 100%, and 120% of the best efficiency point (BEP). A high-speed camera (HSC) with a lighting set captured images of the oil-in-water dispersion at 1000 frames per second. The images observation suggests the presence of a turbulent flow in the impeller. The turbulence, associated with high rotation Reynolds numbers, causes the oil drops to become smaller as the impeller rotational speed and the water flow rate increase. Despite this rotating environment, the oil drops generally have a spherical shape. Regarding the kinematics, the images processing reveals that the velocity of oil drops has a magnitude around a unit of m/s. The velocity depends on the oil drop position in the channel: oil drops that stay close to a suction blade (SB) have significantly higher velocities than oil drops that stay close to a pressure blade (PB). Considering a complex flow with water velocity profiles and pressure gradients, the analysis of oil velocity curves indicates the occurrence of accelerations that may be caused by drag and pressure forces acting on the oil drops.

Local velocity scaling in upward flow to tooth impeller in a fully turbulent region

The hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV). The experiments were carried out in a fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a tooth impeller 133 mm in diameter. Distilled water was used as the agitated liquid. The velocity fields were investigated in the upward flow to the impeller for three impeller rotation speeds – 300 rpm, 500 rpm and 700 rpm, corresponding to a Reynolds number in the range 94 000 < Re < 221 000. This means that fully-developed turbulent flow was reached. This Re range secures the fully-developed turbulent flow in an agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The axial turbulence intensity was found to be in the majority in the range from 0.4 to 0.7, which corresponds to the middle level of turbulence intensity.

Multi-objective optimization of ORC parameters and selection of working fluid using preliminary radial inflow turbine design

Organic Rankine cycles (ORCs) are used to generate power from low temperature heat sources. In this study, 28 hydro carbon (HC), hydro fluorocarbon (HFC) and hydro fluoroolefin (HFO) working fluids are used for three different heat source temperatures (90, 120 and 150 °C). A 1-D radial-inflow turbine (RIT) design with loss calculations is incorporated into the model to add dynamic turbine stage efficiency. The turbine model is run together with the ORC, and real gas properties are used for the entire system. A genetic algorithm multi-objective optimization is used to design an ORC with minimum thermal conductance per net power output and maximum performance factor (PF). The decision variables are specific speed, condensation pressure, pressure ratio at the turbine stage, degree of superheating and pinch point temperature difference (PPTD) in the evaporator. Pareto frontiers are obtained at the end of the study, and a decision-making method (TOPSIS) is used to select an optimum solution for each working fluid. R1234yf, R1234ze(e) and isobutane are found to be the optimum working fluids at 90, 120 and 150 °C heat source temperatures respectively. For each solution, turbine geometry, fluid velocities and impeller rotational speed are calculated.

Improving uniform scattering device for straw-smashing, back-throwing, no-tillage planter under complete straw mulching condition

With the objective of obtaining a completely straw-mulched field, when no-tillage mechanical sowing is implemented with straw smashing, delivering, and back-throwing approaches, it may be difficult to scatter the smashed straw uniformly during a succeeding wheat sowing step. This is because the previous rice straw is substantial in quantity and has a high humidity and toughness, which may easily result in non-uniform straw mulching and thus sparse and weak seedlings of wheat. Therefore a force-dispersing and uniform-scattering device was designed. With the number of scattering impellers, impeller angle, and impeller rotation speed as the main factors and the percentage of pass for the scattering width and non-uniformity of the straw mulching as the assessment indices, single-factor experiments and orthogonal regressive tests were performed, and a dual-index (percentage of pass for the scattering width and non-uniformity of the straw mulching) fitted regression equation was established. The test results suggested that the main factors (from primary to secondary) that influence the indices were the impeller rotation speed, number of scattering impellers, and impeller angle. The optimal parameter combination for the uniform scattering device was four rows of impellers with an angle of 15°, rotation speed of 1015 r/min, percentage of pass of 72.65% for the scattering width, and a non-uniformity of 13.8% in the straw mulching. This combination can be used to realize a uniform scattering of the smashed straw along the seedling rows on the after-sowing ground. According to the field investigation of the wheat growth, the wheat emergence rate was 90.7%. The research results can provide a reference for improving the uniform scattering device for a straw-smashing, back-throwing, no-tillage planter for obtaining a completely straw-mulched field, enhancing the quality of the machinery operation, and ensuring good and strong seedlings after sowing. Keywords: complete straw mulching, no-tillage planter, uniform scattering of straw DOI: 10.25165/j.ijabe.20181106.4597 Citation: Gu F W, Gao X M, Wu F, Hu Z C, Chen Y Q, Zhang C. Improving uniform scattering device for straw-smashing, back-throwing, no-tillage planter under complete straw mulching condition. Int J Agric & Biol Eng, 2018; 11(6): 49–57.

Evaluation of the hemolysis and fluid dynamics of a ventricular assist device under the pulsatile flow condition

When the rotary blood pumps are used as ventricular assist devices, the pump flow rate will have a pulsatile component even at a constant impeller rotational speed due to the remaining beating of the natural heart. However, previous studies on the in vitro hemolysis evaluation of a rotary blood pump have always been conducted under steady states and this pulsation was not taken into account. In this study, the hemolysis in a centrifugal blood pump is evaluated under the pulsatile flow condition in vitro. The required time-varying flow rate is obtained by conducting a system simulation of the pump-assisted cardiovascular system, and realized by controlling a pulsation unit in the experiments. The results of our tests indicate a significant increase in hemolysis under the pulsatile flow condition compared with the non-pulsatile condition. To reveal the flow characteristics responsible for the higher hemolysis, transient computational fluid dynamic simulations are then performed. This study suggests that traditional hemolysis evaluation under the steady states may not fully represent the hemolytic performance in the clinical use. For the ventricular assist pumps at the design stage, eliminating the concern about the extra hemolysis under the pulsatile condition will be helpful for the subsequent in vivo experiments.

Cardiac Magnetic Resonance Imaging of Mechanical Cavopulmonary Assistance

Mechanical circulatory support (MCS) options are limited for patients with dysfunctional single ventricle physiology. To address this unmet clinical need, we are developing an axial-flow blood pump to provide mechanical assistance to the cavopulmonary circulation. In this study, we investigate the use of high-resolution cardiac magnetic resonance imaging (MRI) to visualize the complex fluid flow conditions of mechanical circulatory assist in two patient-specific Fontan anatomies. A three-bladed axial-flow impeller coupled to a supportive cage with a four-bladed diffuser was positioned in the inferior vena cava (IVC) of each Fontan anatomy. Cardiac magnetic resonance (CMR) imaging and power efficiency studies were conducted at physiologic relevant parameters with cardiac outputs of 2, 3, and 4 L/min with impeller rotational speeds of 2000 and 4000 rpm. The axial-flow impeller was able to generate improved flow in the total cavopulmonary connection (TCPC). The higher rotational speed was able to redistribute flow in the TCPC anastomosis aiding in removing stagnant blood. No retrograde flow was observed or measured in the superior vena cava (SVC). As an extension of the CMR data, a scalar stress analysis was performed on both models and found a maximum scalar stress of approximately 42 Pa for both patient anatomies. The power efficiency experiments demonstrated a maximum energy gain of 8.6 mW for TCPC Anatomy 1 and 12.58 mW for TCPC Anatomy 2 for a flow rate of 4 L/min and at 4000 rpm. These findings support the continued development of axial blood pumps for mechanical cavopulmonary assist.

CFD study on double- to single-loop flow pattern transition and its influence on macro mixing efficiency in fully baffled tank stirred by a Rushton turbine

Abstract For a fully baffled tank stirred by a Rushton turbine (RT), the flow pattern will change from double- to single-loop as the off bottom clearance (C) of the RT decreases from one third of the tank diameter. Such a flow pattern transition as well as its influence on the macro mixing efficiency was investigated via CFD simulation. The transient sliding mesh approach coupled with the standard k-e turbulence model could correctly and efficiently reproduce the reported critical C range where the flow pattern changes. Simulation results indicated that such a critical C range varied hardly with the impeller rotation speed but decreased significantly with increasing impeller diameter. Small RTs are preferable to generating the single-loop flow pattern. A mechanism of the flow pattern transition was further proposed to explain these phenomena. The discharge stream from the RT deviates downwards from the horizontal direction for small C values; if it meets the tank wall first, the double-loop will form; if it hits the tank bottom first, the single-loop will form. With the flow pattern transition, the mixing time decreased by about 35% at the same power input (P), indicating that the single-loop flow pattern was more efficient than the double-loop to enhance the macro mixing in the tank. A comparison was further made between the single-loop RT and pitched blade turbine (PBT, 45°) from macro mixing perspective. The single-loop RT was found to be less efficient than the PBT and usually required 60% more time to achieve the same level of macro mixing at the same P.

PIV Experimental Study of the Axial Flow Blood Pump’s Internal Flow Field Under Pulsatile Condition

Taking the axial flow blood pump as the research object, we used the particle image velocimetry (PIV) to measure the flow distribution of inlet, outlet and impeller at the changing rotation speed. Effects of the acceleration and deceleration process on the change of internal flow field were compared and analyzed. The experimental results show that the flow field of inlet and outlet area of the blood pump is stable at the constant working speed, but the vortex and reflux exist in the impeller area. However, acceleration of the impeller increases the flow field’s volocity and disturbance. Deceleration of the impeller rotation speed reduces the flow velocity, and the flow state of overall flow field is relatively stable. Design of the pulsatile blood pump should be optimized in order to reduce the occurrence of hemolysis in the process of acceleration and deceleration.

Wet-granulation process: phenomenological analysis and process parameters optimization

Wet granulation is a size-enlargement process applied in many industrial fields, such as pharmaceutical, nutraceutical, zootecnichal, to improve flowability and compressibility properties of powders. In this work analysis of the particle size distribution (PSD) of granules was performed to understand the phenomena involved during the granulation process and to optimize the operating conditions. Hydroxypropyl methylcellulose (HPMC) granules were produced spraying distilled water as liquid binder on powders in a low-shear granulator. The experimental campaign was planned using the full factorial design statistical technique varying two factors (impeller rotation speed and binder flow rate), each at three intensities. PSDs of HPMC granules at different granulation times were obtained by an ad hoc dynamic image analysis device based on the free falling particle scheme. PSD measurements showed that wet granules size depends on the simultaneous presence of nucleation, agglomeration and breakage phenomena. The process parameters optimization was carried out using response surface methodology (RSM) and using the granulation yield (% w/w of wet granules within the size range 2000–10,000 μm) as the main variable of interest.

Mixing assessment of non-cohesive particles in a paddle mixer through experiments and discrete element method (DEM)

In this study the mixing kinetics and flow patterns of non-cohesive, monodisperse, spherical particles in a horizontal paddle blender were investigated using experiments, statistical analysis and discrete element method (DEM). EDEM 2.7 commercial software was used as the DEM solver. The experiment and simulation results were found to be in a good agreement. The calibrated DEM model was then utilized to examine the effects of the impeller rotational speed, vessel fill level and particle loading arrangement on the overall mixing quality quantified by the relative standard deviation (RSD) mixing index. The simulation results revealed as the impeller rotational speed was increased from 10 RPM to 40 RPM, generally a better degree of mixing was reached for all particle loading arrangements and vessel fill levels. As the impeller rotational speed was increased further from 40 RPM to 70 RPM the mixing quality was affected, for a vessel fill level of 60% and irrespective of the particle loading arrangement. Increasing the vessel fill level from 40% to 60% enhanced the mixing performance when impeller rotational speed of 40 RPM and 70 RPM were used. However, the mixing quality was independent of vessel fill level for almost all simulation cases when 10 RPM was applied, regardless of the particle loading arrangement. Furthermore, it was concluded that the particle loading arrangement did not have a considerable effect on the mixing index. ANOVA showed that impeller rotational speed had the strongest influence on the mixing quality, followed by the quadratic effect of impeller rotational speed, and lastly the vessel fill level. The granular temperature data indicated that increasing the impeller rotational speed from 10 RPM to 70 RPM resulted in higher granular temperature values. By evaluating the diffusivity coefficient and Peclet number, it was concluded that the dominant mixing mechanism in the current mixing system was diffusion.

A Framework for the Development of Integrated and Computationally Feasible Models of Large-Scale Mammalian Cell Bioreactors

Industrialization of bioreactors has been achieved by applying several core concepts of science and engineering. Modeling has deepened the understanding of biological and physical phenomena. In this paper, the state of existing cell culture models is summarized. A framework for development of dynamic and computationally feasible models that capture the interactions of hydrodynamics and cellular activities is proposed. Operating conditions are described by impeller rotation speed, gas sparging flowrate, and liquid fill level. A set of admissible operating states is defined over discretized process parameters. The burden on a dynamic solver is reduced by assuming hydrodynamics at its fully developed state and implementation of compartmental modeling. A change in the conditions of operation is followed by hydrodynamics switching instantaneously to the steady state that would be reached under new conditions. Finally, coupling the model with optimization solvers leads to improvements in operation.

Experimental evaluation of temperature rise in centrifugal pumps at partial flow rates

When the centrifugal pumps operate near shut-off condition, different kinds of energy losses happen from inlet to discharge nozzle leading to lower hydraulic performance and overall efficiency. A part of dissipated energy turns into heat and increases the operating liquid temperature. This may seem to be very dangerous when talking about pumping oil or any other flammable chemical liquids. In the present investigation, several centrifugal pumps were selected to perform experimental analysis of measuring temperature rise at inlet and discharge nozzles during part load operation. Pumps were entirely insulated using glass wool to prevent heat leakage from pump casing to the environment and pure water was selected to play as the working fluid. Temperature rise of pumps was reported from start time up to assuaging steady-state condition. Obtained results demonstrated that higher rotational speed of impeller led to higher value of outlet water temperature in a shorter time rather than lower rotational speeds. Steady-state temperature values were used to establish a novel relation for temperature rise that can be implemented for wide range of centrifugal pumps.

Turbulent flow in a vessel agitated by side entering inclined blade turbine with different diameter using CFD simulation

Single phase turbulent flow in a vessel agitated by side entering inclined blade turbine has simulated using CFD. The aim of this work is to identify the hydrodynamic characteristics of a model vessel, which geometrical configuration is adopted at industrial scale. The laboratory scale model vessel is a flat bottomed cylindrical tank agitated by side entering 4-blade inclined blade turbine with impeller rotational speed N=100-400 rpm. The effect of the impeller diameter on fluid flow pattern has been investigated. The fluid flow patterns in a vessel is essentially characterized by the phenomena of macro-instabilities, i.e. the flow patterns change with large scale in space and low frequency. The intensity of fluid flow in the tank increase with the increase of impeller rotational speed from 100, 200, 300, and 400 rpm. It was accompanied by shifting the position of the core of circulation flow away from impeller discharge stream and approached the front of the tank wall. The intensity of fluid flow in the vessel increase with the increase of the impeller diameter from d=3 cm to d=4 cm.

Influence of attrition variables on iron ore flotation

Abstract The presence of slimes is harmful to the flotation process: the performance and consumption of reagents are negatively affected. Traditionally, the desliming stage has been responsible for removing slimes. However, depending on the porosity of the mineral particles, desliming may not be sufficient to maximize the concentration results. An attrition process before the desliming operation can improve the removal of slime, especially when slimes cover the surface and/or are confined to the cavities/pores of the mineral particles. Attrition is present in the flowcharts of the beneficiation process of phosphate and industrial sand (silica sand). Research has been undertaken for its application to produce pre-concentrates of zircon and iron ore. However, there is still little knowledge of the influence of the attrition variables on the beneficiation process of iron ore. This study presents a factorial design and analysis of the effects of these variables on the reverse flotation of iron ore. The standard of the experimental procedures for all tests included the attrition of pulp, under the conditions of dispersion, desliming and flotation. The parameter analysed (variable response) was the metallurgical recovery in reverse flotation tests. The planning and analysis of the full factorial experiment indicated that with 95% reliability, the rotation speed of the attrition cell impeller was the main variable in the attrition process of the iron ore. The percentage of solid variables in the pulp and the time of the attrition, as well as their interactions, were not indicated to be significant.