Showing papers on "Impeller published in 2010"

Study of Solid−Liquid Mixing in Agitated Tanks through Computational Fluid Dynamics Modeling

Abstract: Solid−liquid mixing is one of the most important mixing operations due to its vast applications in many unit operations such as crystallization, adsorption, solid-catalyzed reaction, suspension polymerization, and activated sludge processes. In this study, a computational fluid dynamics (CFD) model was developed for solid−liquid mixing in a cylindrical tank equipped with a top-entering impeller to investigate the effect of impeller type (Lightnin A100, A200, and A310), impeller off-bottom clearance (T/6−T/2, where T is tank diameter), impeller speed (150−800 rpm), particle size (100−900 μm), and particle specific gravity (1.4−6) on the mixing quality. An Eulerian−Eulerian (EE) approach, standard k−e model, and multiple reference frames (MRF) techniques were employed to simulate the two-phase flow, turbulent flow, and impeller rotation, respectively. The impeller torque, cloud height, and just suspended impeller speed (Njs) computed by the CFD model agreed well with the experimental data. The validated CFD...

Parametric Design of a Waterjet Pump by Means of Inverse Design, CFD Calculations and Experimental Analyses

Abstract: The present paper describes the parametric design of a mixed-flow water-jet pump. The pump impeller and diffuser geometries were parameterized by means of an inverse design method, while CFD analyses were performed to assess the hydrodynamic and suction performance of the different design configurations that were investigated. An initial pump design was first generated and used as baseline for the parametric study. The effect of several design parameters was then analyzed in order to determine their effect on the pump performance. The use of a blade parameterization, based on inverse design, led to a major advantage in this study, because the three-dimensional blade shape is described by means of hydrodynamic parameters, such as blade loading, which has a direct impact on the hydrodynamic flow field. On the basis of this study, an optimal configuration was designed with the aim of maximizing the pump suction performance, while at the same time, guaranteeing a high level of hydrodynamic efficiency, together with the required mechanical and vibrational constraints. The final design was experimentally tested, and the good agreement between numerical predictions and experimental results validated the design process. This paper highlights the contrasting requirements in the pump design in order to achieve high hydrodynamic efficiency or good cavitation performance. The parametric study allowed us to determine design guidelines in order to find the optimal compromise in the pump design, in cases where both a high level of efficiency and suction performance must simultaneously be achieved. The design know-how developed in this study is based on flow field analyses and on hydrodynamic design parameters. It has therefore a general validity and can be used for similar design applications.

PIV Measurements and CFD Computations of Secondary Flow in a Centrifugal Pump Impeller

Abstract: Two-dimensional particle image velocimetry measurements and three-dimensional computational fluid dynamics (CFD) analyses have been performed on the steady velocity field inside the shrouded impeller of a low specific-speed centrifugal pump operating with a vaneless diffuser. Flow rates ranging from 80% to 120% of the design flow rate are considered in detail. It is observed from the velocity measurements that secondary flows occur. These flows result in the formation of regions of low velocity near the intersection of blade suction side and shroud. The extent of this jet-wake structure decreases with increasing flow rate. Velocity fields have also been computed from Reynolds-averaged Navier–Stokes equations with the Spalart–Allmaras turbulence model using a commercial CFD code. For the considered flow rates, the qualitative agreement between measured and computed velocity profiles is very good. Overall, the average relative difference between these velocity profiles is around 5%. Additional CFD computations have been performed to assess the influence of Reynolds number and the shape of the inlet velocity profile on the computed velocity fields. It is found that the influence of Reynolds number is mild. The shape of the inlet profile has only a weak effect at the shroud.

Blood pump with expandable cannula

Abstract: A blood pump includes an impeller having a plurality of foldable blades and a cannula having a proximal portion with a fixed diameter, and a distal portion with an expandable diameter. The impeller can reside in the expandable portion of the cannula. The cannula has a collapsed condition for percutaneous delivery to a desired location within the body, and an expanded condition in which the impeller can rotate to pump blood. A flexible drive shaft can extend through the cannula for rotationally driving the impeller within the patient's body.

Optimization of Stirring Parameters Through Numerical Simulation for the Preparation of Aluminum Matrix Composite by Stir Casting Process

Abstract: The flow behavior of the fluid has a significant effect on the particle distribution in the solid-liquid mixing vessel. The stir casting process is generally conducted in a closed crucible, in which the flow pattern is invisible. Therefore, numerical simulation is a forceful tool to guide the experimental research. In the present study, the fluid flow in the stirred crucible during stir casting has been simulated using finite element method. The effects of some important stirring process parameters, such as the blade angle, rotating speed, the diameter of the impeller, and the stirrer geometry, on the flowing characteristics of the molten matrix have been investigated in order to achieve the effective flow pattern to uniformly disperse the ceramic particles in the molten matrix. The simulation results show that the process parameters have significant effects on the flow behavior of the fluid in the stirred crucible. The various combinations of these parameters are beneficial to generate a suitable condition for the composite casting. Further experimental investigation reveals that the present work can provide a guide for the industrial preparation of aluminum matrix composite with a uniform particle reinforcement distribution by stir casting process.

Numerical Simulation of the Transient Flow in a Centrifugal Pump During Starting Period

Abstract: Computational fluid dynamics were used to study the three-dimensional unsteady incompressible viscous flows in a centrifugal pump during rapid starting period (≈0.12 s). The rotational speed variation of the field around the impeller was realized by a dynamic slip region method, which combines the dynamic mesh method with nonconformal grid boundaries. In order to avoid introducing errors brought by the externally specified unsteady inlet and outlet boundary conditions, a physical model composed of a pipe system and pump was developed for numerical self-coupling computation. The proposed method makes the computation processes more close to the real conditions. Relations between the instantaneous flow evolutions and the corresponding transient flow-rate, head, efficiency and power were analyzed. Relative velocity comparisons between the transient and the corresponding quasisteady results were discussed. Observations of the formations and evolutions of the primary vortices filled between the startup blades illustrate the features of the transient internal flow. The computational transient performances qualitatively agree with published data, indicating that the present method is capable of solving unsteady flow in a centrifugal pump under transient operations.

Rotor for an axial flow pump for conveying a fluid

Abstract: The invention relates to a rotor for an axial flow pump for conveying a fluid having an axis of rotation and having an impeller blade which has at least one part surface which extends transversely to the axis of rotation and beyond it, wherein the impeller blade has throughgoing webs or a network of webs which connect a different marginal regions of the impeller blades to one another. A good compressibility is hereby achieved in the radial direction with high stability during operation.

Fluid pump having at least one impeller blade and a support device

Abstract: A fluid pump has at least one impeller blade which is rotatable about an axis of rotation and conveys a fluid in operation. The fluid pump has a support device which supports the at least one impeller blade in at least one support region. The support device is changeable between a first state in which the at least one impeller blade is radially compressed and a second state in which the at least one impeller is radially expanded. The at least one impeller blade extends at least partly radially inwardly with respect to the axis of rotation from the at least one support region in the radially expanded state of the blade.

Multi-objective optimization of a centrifugal compressor impeller through evolutionary algorithms:

Abstract: This paper presents the design optimization of a centrifugal compressor impeller with a hybrid multi-objective evolutionary algorithm. Reynolds-averaged Navier—Stokes (RANS) equations are solved with the shear stress transport turbulence model as a turbulence closure model. Flow analysis is performed on a hexahedral grid through a finite-volume solver. Two objectives, viz., the isentropic efficiency and the total pressure ratio (PR), are selected with four design variables that define the impeller hub and shroud contours in meridian terms for optimizing the system. The validation of numerical results was performed through experimental data for the total PR and the isentropic efficiency. Objective-function values are numerically evaluated through the RANS analysis at design points that are selected through the Latin hypercube sampling method. A fast and elitist non-dominated sorting genetic algorithm (NSGA-II) with an e-constraint strategy for local search coupled with a surrogate model is used for...

Turbulent flow of shear-thinning liquids in stirred tanks—The effects of Reynolds number and flow index

Abstract: LDA measurements are reported on the turbulent velocity fields in vessels agitated by a Rushton turbine and containing Newtonian as well as non-Newtonian, shear-thinning fluids. Ten different liquids were investigated, with flow indices varying from 1.00 down to 0.56. Experiments were performed in three vessel sizes, viz. 28.6, 44.1, and 62.7 cm in diameter, at various impeller speeds. The main issue of the paper is the question whether or not, and if so to what extent, turbulent flow of shear-thinning fluids differs from that of Newtonian liquids, or – in other words – whether and when turbulent flow of shear-thinning liquids exhibits Reynolds number similarity. The experimental data presented comprise profiles of the mean velocity components and the rms fluctuating velocity components as a function of the radial position in the tank at the height of the impeller disc as well as similar profiles in the impeller outflow near to the impeller tip. The effects – if any – of both Reynolds number and flow index on these profiles are assessed. Fit equations are presented for the various profiles in the various liquids. These fit equations are claimed to be valid throughout the ranges of Reynolds numbers and flow indices covered by the experiments presented. The idea is that these fit equations may be used to validate Computational Fluid Dynamics (CFD) simulations of the Reynolds Averaged Navier–Stokes (RANS) type for agitated shear-thinning liquids, even for liquids and conditions not investigated in this study as long as falling within the Reynolds number and flow index ranges investigated. © 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Axial Magnetic Bearing Development for the BiVACOR Rotary BiVAD/TAH

Abstract: A suspension system for the BiVACOR biventricular assist device (BiVAD) has been developed and tested. The device features two semi-open centrifugal impellers mounted on a common rotating hub. Flow balancing is achieved through the movement of the rotor in the axial direction. The rotor is suspended in the pump casings by an active magnetic suspension system in the axial direction and a passive hydrodynamic bearing in the radial direction. This paper investigates the axial movement capacity of the magnetic bearing system and the power consumption at various operating points. The force capacity of the passive hydrodynamic bearing is investigated using a viscous glycerol solution. Axial rotor movement in the range of ±0.15 mm is confirmed and power consumption is under 15.5 W. The journal bearing is shown to stabilize the rotor in the radial direction at the required operating speed. Magnetic levitation is a viable suspension technique for the impeller of an artificial heart to improve device lifetime and reduce blood damage.

Blood pump apparatus

Abstract: A blood pump apparatus comprises a housing, a centrifugal pump section including an impeller and rotating inside the housing to feed a fluid by a centrifugal force, an impeller rotational torque generation section for attracting thereto said impeller and rotating said impeller; and a plurality of grooves for hydrodynamic bearing provided on an inner surface of said housing at a side of said impeller rotational torque generation section, each of the grooves for hydrodynamic bearing having a first side and a second side both extending from a periphery of said portion in which a groove for hydrodynamic bearing is formed toward a central side thereof and opposed to each other, a third side connecting one end of said first side and one end of said second side to each other, and a fourth side connecting said other end of said first side and said other end of said second side to each other; said first side and said second side are formed as a circular arc respectively in such a way that centers of said circular arcs are different from each other.

Stability Improvement of High-Pressure-Ratio Turbocharger Centrifugal Compressor by Asymmetrical Flow Control-Part II: Nonaxisymmetrical Self-Recirculation Casing Treatment.

Abstract: This is part II of a two-part paper involving the development of an asymmetrical flow control method to widen the operating range of a turbocharger centrifugal compressor with high-pressure ratio. A nonaxisymmetrical self-recirculation casing treatment (SRCT) as an instance of asymmetrical flow control method is presented. Experimental and numerical methods were used to investigate the impact of nonaxisymmetrical SRCT on the surge point of the centrifugal compressor. First, the influence of the geometry of a symmetric SRCT on the compressor performance was studied by means of numerical simulation. The key parameter of the SRCT was found to be the distance from the main blade leading edge to the rear groove (Sr). Next, several arrangements of a nonaxisymmetrical SRCT were designed, based on flow analysis presented in part I. Then, a series of experiments were carried out to analyze the influence of nonaxisymmetrical SRCT on the compressor performance. Results show that the nonaxisymmetrical SRCT has a certain influence on the performance and has a larger potential for stability improvement than the traditional symmetric SRCT. For the investigated SRCT, the surge flow rate of the compressor with the nonaxisymmetrical SRCTs is about 10% lower than that of the compressor with symmetric SRCT. The largest surge margin (smallest surge flow rate) can be obtained when the phase of the largest Sr is coincident with the phase of the minimum static pressure in the vicinity of the leading edge of the splitter blades.

Single stage, axial symmetric blower and portable ventilator

Abstract: A blower (10) includes a housing (20) including a proximal opening (23) and a distal opening (25) that are co-axially aligned, a stator component (30) provided to the housing, an impeller (60) positioned between the proximal opening of the housing and the stator component, and a motor (40) adapted to drive the impeller. The impeller includes a plurality of impeller blades. The stator component includes a plurality of air directing grooves (35) along its exterior surface. The leading edge of the air directing grooves extend tangentially outwards from the outer tips of the impeller blades and are configured to collect the air exiting the impeller blades and direct it from a generally tangential direction to a generally radial direction by dividing the air from the impeller and directing the air along a curved path towards the distal opening so that airflow becomes substantially laminar.

Numerical Modeling of Hemodynamics with Pulsatile Impeller Pump Support

Abstract: There is significant interest in the development and application of variable speed impeller-pump type ventricular assist devices designed to generate pulsatile blood flow. However, no study has so far been carried out to investigate the systemic cardiovascular response to various aspects of pump motion. In this article, a numerical model is constructed for the simulation of the cardiovascular response in the heart failure condition under representative cases of pulsatile impeller pump support. The native cardiovascular model is based on a previously validated model, and the impeller pump is modeled by directly fitting the pressure-flow curves that describe the pump characteristics. The model developed is applied to study circulatory dynamics under different degrees of phase shift and pulsation ratio in the pump motion profile. The characteristic variables are discussed as criteria for the evaluation of system response for comparison of the pulsatile flows. Simulation results show that a constant pump speed is the most efficient work mode for the rotary pump, and with the application of either a phase shift of 75% and a pulsation ratio of 0.5, or a phase shift of 42% and a pulsation ratio of 0.55, it is possible to generate arterial pulse pressure with the maximal magnitude of about 28 mmHg. However, this is achieved at the cost of reduced cardiac output and pump efficiency.

Stability Improvement of High-Pressure-Ratio Turbocharger Centrifugal Compressor by Asymmetric Flow Control-Part I: Non-Axisymmetrical Flow in Centrifugal Compressor.

Abstract: The history of turbocharging is almost as old as that of the internal combustion engine. A turbocharger consists of a compressor and a turbine. The compressor is driven by the turbine extracting energy from exhaust gases. Compared to a naturally aspirated engine, the benefits of a turbocharged engine are increased power, lower fuel consumption, and reduced emissions [1,2]. High-pressure-ratio turbocharging technology is the developing trend of turbocharged internal combustion engines due to the following reasons: 1) significant downsizing to mitigate CO2 emission and reduce fuel consumption [3], 2) satisfying rigid future emission regulations, i.e., NOx treatment by engine control means high rates of exhaust gas recirculation (EGR) [3,4], and 3) the facilitation of high altitude operation [5]. However, a high pressure ratio causes the flow in the compressor to be transonic. Hence, the stable flow range is narrowed, since the stall incidence decreases with an increased relative Mach number at the inlet of the impeller [6]. Therefore, map width enhancement is a major issue for state-of-the-art high-pressure-ratio compressor design and development. A turbocharger centrifugal compressor comprises an impeller, a diffuser, and a volute. While the former two are periodically symmetric in the circumferential direction, the volute is asymmetric due to its gas-collection function. It is usually designed as a spiral-collection overhung housing that collects the air from the diffuser and passes it to the pipe system. It has been recognized that the improvement of centrifugal compressor performance requires a good understanding of the flow mechanisms inside the volute [7–9]; especially the interaction among the volute-diffuser-impeller [10,11]. The volute is mostly designed in a way to shape a uniform circumferential static pressure distribution both in the volute and the diffuser. However, the volute acts as a diffuser at lower than the design flow rate and acts as a nozzle at higher than the design flow rate, respectively. A number of authors have researched this subject. It has already been confirmed that the asymmetrical configuration has a significant impact on the flow field in the diffuser and in the impeller [12,13]. This circumferential asymmetry has been recognized and intensive experimental investigations of the flow within the volute and the propagation of the distortion into upstream components were carried out for subsonic compressor units [14,15]. The work of Sorokes et al. confirmed that the pressure nonuniformity extended upstream of the impeller, implying that the impeller was subjected to varying inlet and exit conditions. The computational fluid dynamics (CFD) results further implied that the inlet flow distortion caused a large leading edge pressure differential along with a large negative incidence, which may induce a flow separation and thus a very disturbed flow field in the impeller [14]. A three-dimensional unsteady analysis of the flow in the impeller with circumferential distortion of the outlet static pressure was investigated using a numerical method by Fatsis et al. [16]. The perturbation was thus propagated upstream from the impeller outlet and influenced the incidence at the blade leading edges and other flow parameters. Gu et al. [10,11] found that the performance parameters of the single impeller passage differed because of the asymmetric flow at the outlet of the impeller. There was almost no phase shift between the distortion in the diffuser and impeller according to their results, and it was considered that the unsteady effects of the volute-impeller interaction can be neglected when the Strouhal number is small enough. Little detailed measurement was carried out in the impeller to investigate the asymmetric flow. Furthermore, to the authors’ knowledge, very little research work has been focused on the impact of the volute on the flow field in a high-pressure-ratio turbocharger centrifugal compressor. The purpose of this two-part paper is first to understand the asymmetry of flow field due to the asymmetric geometry of the volute and, subsequently, to develop a novel asymmetric flow control method to widen the stable flow range of a turbocharger centrifugal compressor with a high-pressure-ratio, the narrowing flow range of which is of utmost importance for its application. In Part I, the nonaxisymmetrical flow characteristics in the high-pressure-ratio turbocharger centrifugal compressor are investigated by using experimental and numerical means, the results of which are the basis for the work presented in Part II.