Showing papers on "Impeller published in 1995"

Three‐Dimensional Numerical Prediction of Stress Loading of Blood Particles in a Centrifugal Pump

Abstract: The successful use of centrifugal pumps as temporary cardiac assist devices strongly depends on their degree of blood trauma. The mechanical stress loading experienced by cellular components on their passage through the pump is a major cause of blood trauma. Prediction of the mechanical stresses will assist optimization of pump design to minimize hemolysis and platelet activation. As a theoretical approach to this task., the determination of the complete three-dimensional (3D) flow field including all regions of high shear stress is therefore required. A computational fluid dynamics (CFD) software package, TASCflow, was used to model flow within a commercially available pump, the Aries Medical Isoflow Pump. This pump was selected in order to demonstrate the ability of the CFD software to handle complex impeller geometries. A turbulence model was included, and the Newtonian as well as the Reynolds stress tensor calculated for each nodal point. A novel aspect was the assignment of scalar stress values to streaklines representing particle paths through the pump. Scalar stress values were obtained by formulating a theory that enables the comparison of a three-dimensional state of stress with a uniaxial stress as applied in all mechanical blood damage tests. Stress loading-time functions for fluid particles passing inlet, impeller, and outlet domains of the pump were obtained. These showed that particles undergo a complex, irregularly fluctuating stress loading. Future blood damage theories would have to consider an unsteady stress loading regime that realistically reflects the flow conditions occurring within the pump.(ABSTRACT TRUNCATED AT 250 WORDS)

Mean velocity field relative to a Rushton turbine blade

Abstract: The 3-D flow field relative to a rotating Rushton turbine blade is acquired for fully turbulent tank conditions by synchronizing LDA measurements with the output of a shaft-mounted encoder. This makes it possible to capture the impeller stream velocity field, including the details of the voritices behind the blades. Mean velocity data at three impeller speeds show the extent of periodicity and the axes and structure of the vortices. Pumping capacities are determined and it is shown that the radial jet is a consequence of fluid entrainment into the vortices. Deformation rates based on gradients of mean velocity are calculated. Close to the blade they can exceed impeller rotational frequency by as much as two orders of magnitude. To a first approximation, the normalized mean flow field is independent of impeller speed.

Mean Streamline Aerodynamic Performance Analysis of Centrifugal Compressors

Abstract: Aerodynamic performance prediction models for centrifugal compressor impellers are presented. In combination with similar procedures for stationary components, previously published in the open literature, a comprehensive mean streamline performance analysis for centrifugal compressor stages is provided. The accuracy and versatility of the overall analysis is demonstrated for several centrifugal compressor stages of various types, including comparison with intrastage component performance data. Detailed validation of the analysis against experimental data has been accomplished for over a hundred stages, including stage flow coefficients from 0.009 to 0.15 and pressure ratios up to about 3.5. Its application to turbocharger stages includes pressure ratios up to 4.2, but with test uncertainty much greater than for the data used in the detailed validation studies.

Method for reducing pumping damage to blood

Abstract: Methods are provided for minimizing damage to blood in a blood pump wherein the blood pump comprises a plurality of pump components that may affect blood damage such as clearance between pump blades and housing, number of impeller blades, rounded or flat blade edges, variations in entrance angles of blades, impeller length, and the like. The process comprises selecting a plurality of pump components believed to affect blood damage such as those listed hereinbefore. Construction variations for each of the plurality of pump components are then selected. The pump components and variations are preferably listed in a matrix for easy visual comparison of test results. Blood is circulated through a pump configuration to test each variation of each pump component. After each test, total blood damage is determined for the blood pump. Preferably each pump component variation is tested at least three times to provide statistical results and check consistency of results. The least hemolytic variation for each pump component is preferably selected as an optimized component. If no statistical difference as to blood damage is produced for a variation of a pump component, then the variation that provides preferred hydrodynamic performance is selected. To compare the variation of pump components such as impeller and stator blade geometries, the preferred embodiment of the invention uses a stereolithography technique for realizing complex shapes within a short time period.

Relationship Between Unsteady Flow, Pressure Fluctuations, and Noise in a Centrifugal Pump—Part B: Effects of Blade-Tongue Interactions

Abstract: Maps of pressure distributions computed using PDV data, combined with noise and local pressure measurements, are used for identifying primary sources of noise in a centrifugal pump In the vicinity of the impeller pressure minima occur around the blade and near a vortex train generated as a result of non-uniform outflux from the impeller The pressure everywhere also varies depending on the orientation of the impeller relative to the tongue Noise peaks are generated when the pressure difference across the tongue is maximum, probably due to tongue oscillations, and when the wake impinges on the tip of the tongue

A Simulation of the Unsteady Interaction of a Centrifugal Impeller With Its Vaned Diffuser: Flow Analysis

Abstract: The aim of this paper is to help advance one`s understanding of the complex, three-dimensional, unsteady flow associated with the interaction of a splittered centrifugal impeller and its vaned diffuser. A time-resolved simulation is presented of the Krain stage performed using a time-accurate, three-dimensional, unstructured mesh, solution-adaptive Navier-Stokes solver. The predicted flowfield, compared with experiment where available, displays a complex, unsteady interaction, especially in the neighborhood of the diffuser entry zone, which experiences large periodic flow unsteadiness. Downstream of the throat, although the magnitude of this unsteadiness diminishes rapidly, the flow has a highly distorted three-dimensional character. The loss levels in the diffuser are then investigated to try and determine how time-mean loss levels compare with the levels expected from equivalent steady flow analysis performed by using the circumferentially averaged exit flow from the impeller as inlet to the diffuser. It is concluded that little loss could be attributed directly to unsteady effects but rather that the principal cause of the rather high loss levels observed in the diffuser is the strong spanwise distortion in swirl angle at inlet, which initiates a strong hub/corner stall.

Turbomachinery with variable angle fluid guiding devices

Abstract: A turbomachinery is presented to provide stable operation at fluid flow rates much lower than the design flow rate without introducing surge in the device. This is achieved by providing a diffuser with variable angle vanes. The vane angle at low flow rates is adjusted so as to minimize the diffuser loss of the exiting fluid stream from the impeller. Since the flow angle of the exit flow of the impeller is a function only of the non-dimensional flow rates, and does not depend on the flow angle at the inlet the impeller, therefore, the vane angles can be regulated to achieve a stable operation of the impeller without producing surge of the turbomachinery at flow rates lower than the design flow rate. To optimize the performance of the turbomachinery, in addition to the variable angle vanes, an inlet guide vane having variable vane angle is provided so that the turbomachinery can be operated at the required flow rate and head pressure. The concept is demonstrated in a turbomachinery provided with variable diffuser vanes and an inlet guide vane.

Bearing arrangement for molten aluminum pumps

Abstract: A molten aluminum pump comprised of an impeller attached to a vertical rotary shaft, the shaft forming a connecting portion between a motor and the impeller and being comprised of a refractory material without a radial bearing surface The impeller is housed within a pumping chamber of a base member wherein rotation of the shaft and impeller draws molten aluminum into the chamber and forces the molten aluminum through an outlet in the chamber The motor is secured to the shaft with a rigid coupling and at least one bearing journaling the coupling

Recent Studies of the Centrifugal Blood Pump with a Magnetically Suspended Impeller

Abstract: We have been developing a centrifugal blood pump with a magnetically suspended impeller. To improve pump efficiency, we investigated the pump performances of many kinds of impeller vanes and diffusers, as well as the flow in the gap between the impeller discs and the pump housing. We found the vanes and the diffusers with high pump efficiency; however, high efficiency does not mean low hemolysis. It seems important to prevent generation of small-sized eddies with high shear stress. Hemolysis tests are carried out to find the optimal vane profile and gap clearance. The index of hemolysis and temperature change of our pump is better than those of the Biopump. Short-term in vivo studies show that the layer of white thrombi adheres to the machined rough surface of polycarbonate, which composes the narrow gap (0.2 mm) between the impeller and the pump wall, but a smooth surface coated with silicon prevents adhesion of that layer.

Power curves and flow patterns for a range of impellers in newtonian fluids: 40<Re<5x105

Abstract: The mixing pattern and power number in a stirred vessel depend not only on the impeller design but also on the impeller/tank geometry and flow regime. The relationship between these parameters is reported for a Rushton turbine (6DT), six-bladed 45°-pitched turbine pumping down (6MFD) and (6MFU) up and three proprietary impellers. The impellers were used over a wide range of impeller diameter (D)/vessel diameter (T) and impeller clearance (C)/T values. Flow patterns were recorded and power numbers were measured as a function of Reynolds number from about 40 to about 50,000 in Newtonian fluids. The results obtained were used to aid in the study of the impellers in solid-liquid and three-phase systems.

Dynamically balanced pump impeller

Abstract: In a non-metallic pump for pumping molten metal including a shaft, a motor at one end of the shaft, an impeller at the other end of the shaft, and a base having a chamber in which the impeller is rotatable, the improvement being a dynamically balanced impeller comprising a cylindrical center hub and five vanes extending outwardly from the hub, wherein the vanes are equally spaced around the periphery of the hub.

Relationship Between Unsteady Flow, Pressure Fluctuations, and Noise in a Centrifugal Pump—Part A: Use of PDV Data to Compute the Pressure Field

Abstract: Velocity distributions determined by using Particle Displacement Velocimetry are used for computing the pressure field within the volute of a centrifugal pump. It is shown that blade-tongue interactions and nonuniform outflux from the impeller are primary contributors to local pressure fluctuations and far field noise. Consequently, a slight increase in the space between the impeller and the tongue causes significant changes in flow structure and reductions in the resulting noise. The impact is significant as long as the tongue-impeller gap is less than 20 percent of the impeller radius. It is also shown that the vorticity distributions, particularly the large vortex trains associated with the jet/wake phenomenon, dominate variations in the total pressure. Thus, it is unlikely that a potential flow model can provide any realistic description of the flow structure

Centrifugal Pump Performance During Transient Operation

Abstract: The effect of transient operation on the hydrodynamic performance of a centrifugal pump impeller was investigated experimentally. All experiments were conducted in the Naval Undersea Warfare Centers Impeller Test Facility (ITF), which was designed and built for transient and steady-state operation impeller research. TheITF provides transient operation through simultaneous control of both impeller rotational speed and flow rate over time. The impeller was accelerated from rest with peak angular accelerations up to 720 radians/s 2 and inlet flow mean accelerations up to 1.7 g, reaching a peak rotational speed of 2400 rpm and a flow rate of 416 l/s. The impeller was then decelerated to rest. Results showed substantial transient effects in overall impeller performance and demonstrated that the quasi-steady assumptions commonly used for the design of impellers that operate under high transient (accelerating or decelerating) conditions are not valid

Pump and flow sensor combination

Abstract: A pump for use in additive systems such as foam chemical additive systems for fire fighting water, the pump including impeller elements and flow meter elements in a common casing. The pump casing provides a gear pump arrangement using two enmeshed gears on an inlet side, and a closely adjacent gear flow meter arrangement downstream of the gear pump arrangement within the same pump casing. The gear flow meter elements are driven only by the force of liquid pumped by the enmeshed gears of the gear pump and cause very low pressure drop across the flow meter elements. Therefore, inaccurate measurements of flow rates due to slippage and viscosity variation are reduced compared to measuring the rotary speed of gear pump gears directly. The system is optimally used to meter and add foam chemical into a pressurized water line for fighting fires.

Method and apparatus for inhibiting oxidation in pumps for pumping molten metal

Abstract: In a pump for pumping molten metal including a motor and a shaft connected at an upper end to the motor and at a lower end to an impeller which is rotatable in a molten metal bath, the improvement being an apparatus for impeding oxidation of the shaft, including a gas source for releasing gas and a gas feed tube in fluid communication with the gas source, the gas feed tube being positioned to direct gas along the outer surface of the shaft.

Steady-state modeling and experimental measurement of a baffled impeller stirred tank

Abstract: An approximate steady-state method is devised for computing the flow field in a baffled, impeller-stirred tank reactor. The flow field in a cylindrical tank with a 45° pitched-blade impeller rotating at 100 rpm and four stationary rectangular side-wall baffles is simulated using a new approximate steady-state approach. The method provides an alternative to a full unsteady Navier-Stokes simulation. The new steady-state analysis involves accurately defining the geometry of the mixing tank using a multiblock grid technique. The flow is solved from a rotating frame of reference for a single position of the impeller relative to the side-wall baffles. The steady-state numerical results are then spatially averaged and compared with time-averaged data obtained experimentally using laser Dopler velocimetry (LDV). Spatially averaged numerical predictions obtained using this approximate steady-state method for the radial and axial velocity components agree well with the LDV data. The predicted magnitude of the tangential velocity component, however, is higher than the experimentally measured values. Closer agreement of the tangential velocities with experimental values is obtained using a finer grid and it is found that a relatively fine grid is needed for accurately predicting the tangential velocity magnitude. Use of this approximate steady-state method allows designers of mixing vessels to obtain flow-field results for baffled vessels much more efficiently than using full unsteady Navier-Stokes simulations.

Surge detection device and turbomachinery therewith

Abstract: A turbomachine having variable-angle diffuser vanes operates by regulating the angle of the diffuser vanes on the basis of the sensors disposed on the pump body or pipes of a surge detection device. The onset of surge can be forecast by measuring the fluctuations in the operating parameter(s) over a measuring interval of time computed on the basis of the operating characteristics of the impeller of the turbomachine. The onset of surge is prevented by adjusting the angle of the diffuser vanes in accordance with the sampling duration for parameter fluctuations over the measuring interval of time, and by adjusting the diffuser vanes to maintain the operating parameter fluctuations of the fluid machinery below a threshold value of the turbomachine derived from the design flow rate of the turbomachine. Application of the surge detection device in combination with fluid flow guide vanes and blades of the turbomachine enables full utilization of the potential capability of the turbomachine.

Environmentally safe pump including seal

Abstract: A motor driven environmentally safe pump includes a sealed motor housing (22) sealingly affixed to a sealed pump housing. The pump housing defines a fluid pumping chamber (43) in which is a fluid pumping impeller (46). A triplex rotating seal (31) is disposed rearward of impeller (46) within an annular fluid chamber (87) so as to prevent the fluid being pumped via the impeller (46) from leaking along the shaft (23) toward the motor (21). A piston seal (32) is provided adjacent a second fluid chamber (204), the piston seal also for preventing fluid from leaking into the motor housing and damaging the motor.

Effect of Modification to Tongue and Impeller Geometry on Unsteady Flow, Pressure Fluctuations and Noise in a Centrifugal Pump

Abstract: Particle Image Velocimetry (PIV), pressure and noise measurements are used to study the effect of modifications to tongue and impeller geometries on the flow structure and resulting noise in a centrifugal pump. It is demonstrated that the primary sources of noise are associated with interactions of the non-uniform outflux from the impeller (jet/wake phenomenon) with the tongue. Consequently, significant reduction of noise is achieved by increasing the gap between the tongue and the impeller up to about 20% of the impeller radius. Further increase in the gap affects the performance adversely with minimal impact on the noise level. When the gap is narrow, the primary sources of noise are impingement of the wake on the tip of the tongue, and tongue oscillations when the pressure difference across it is high. At about 20% gap, the entire wake and its associated vorticity trains miss the tongue, and the only (quite weak) effect of nonuniform outflux is the impingement of the jet on the tongue. An attempt is also made to reduce the non-uniformity in outflux from the impeller by inserting short vanes between the blades. They cause reduction in the size of the original wakes, but generate an additional jet/wake phenomenon of their own. Both wakes are weak to a level that their impacts on local pressure fluctuations and noise are insignificant. The only remaining major contributor to noise is tongue oscillations. This effect is shown to be dependent on the stiffness of the tongue.Copyright © 1995 by ASME

Critical impeller speed for solid suspension in multi‐impeller three phase agitated contactors

Abstract: The critical impeller speed for solid suspension in gas-liquid-solid systems has been measured in multi-impeller agitated contractors of 0.15 and 0.30 m and ID and 1.0 m height. Three types of impellers, i.e. disk turbine (DT), pitched turbine downflow (PTD) and pitched turbine upflow (PTU) were used. Air, deionised water and sand particles were used as the gas, liquid and solid phases, respectively. The superficial gas velocity and solid loading were varied in the ranges 0–15 mm/s and 0.5 to 10% w/w, respectively. The effects of impeller type and its diameter, particle size and loading and gas flow rate were studied. Some measurements of gas hold-up and mixing time were also made in order to get some insight of the hydrodynamic behaviour of the reactor. The critical impeller speed for solid suspension in the presence of gas (nisg) was found to be more than that in the absence of the gas and the increase of critical speed correlated well with the gas flow rate. The influence of particle—liquid parameters on solid suspension speed in the gassed system was similar to but relatively weaker than that in the ungassed condition.

Seal-less Centrifugal Blood Pump with Magnetically Suspended Rotor: Rot-a-Flot

Abstract: Limitations of current centrifugal blood pumps are related to heat generation of bearings and leakage of seals, to dead water zones, and to poor efficiency. A new concept is proposed in this paper to ameliorate these problems based on a miniaturized magnetic drive, and a prototype is introduced. The pump rotor is suspended and driven by a radial permanent magnetic field that stabilizes the impeller in 4 of the 6 spatial degrees of freedom and allows it to be top-spun on a single blood-flushed pivot bearing with minimal load and friction. A shrouded impeller with an open center and 4 logarithmically curved channels is run inside a cone-and-plate-type housing with a spiral volute chamber. In vitro testing was performed comparing this design with the BioMedicus, St. Jude, and Sarns pumps. The prototype is demonstrated to have the smallest internal volume (35 ml), surface (190 qcm), and passage time (0.5 s at 4 L/min), as well as the highest hydraulic efficiency (up to 0.4) of all devices studied.

Blood pump having magnetic attraction

Abstract: A blood pump used for heart-lung machines comprising an impeller, a casing having a suction inlet and a delivery outlet and rotatably encasing the impeller, a magnetic driver disposed outside the casing, and a magnetic attraction force adjuster. The impeller has a rotationally symmetric shape, such as a conical shape, is equipped with vanes having a pumping function on the side surface thereof and is also equipped with magnets, such as permanent magnets. The magnetic driver for rotating the impeller in cooperation with the magnets comprises a magnet assembly magnetically connected to the magnets and a rotation driver for rotating the magnet assembly. The magnetic attraction force adjuster adjusts the magnetic attraction force generated between the magnets and the magnet assembly by adjusting the gap between the magnets and the magnet assembly or by adjusting the exciting current of electromagnets when electromagnets are used for the magnet assembly. One of the pivot and pivot bearing for supporting the rotation shaft of the impeller is made of ceramics and the other is made of synthetic resin.

Aerodynamics of a Centrifugal Compressor Impeller With Transonic Inlet Conditions

Abstract: Performance and laser measurement results are presented for a transonic centrifugal compressor stage, equipped with a backswept rotor designed for 586m/s tip speed and a mean relative inlet tip Mach number of 1.30. The flow field features of the rotor are analysed in detail with the help of laser measurements and the results obtained from a 3D viscous calculation. Both laser measurements and calculations are carried out for the impeller's design point and a comparison between measured and calculated data is presented for four measurement planes representing the inlet, exit and channel flow conditions. The maximum relative Mach number is found to be 1.45 and jet/wake type flow exists in the rear part of the flow channel with the wake concentrating in the shroud region. For the operating point investigated, the wake development is due more to the strong shround curvature in the meridional plane than to a shock induced boundary layer separation. Laser measurments and calculations point to a significant flow displacement in the impeller exit region caused by the wake flow. The theoretical results indicate that a flow separation occurs also at the front side of the vaneless diffuser.

Active feedback loop to control body pitch in STOL/VTOL free wing aircraft

Abstract: An aircraft control system for controlling an aircraft, particularly a free wing aircraft in low speed or hover regimes. An air speed sensor measures air speed of the aircraft and outputs an air speed signal to a control processor which processes the air speed signal with a speed control input signal. A control actuator actuates an aircraft control surface in response to the control surface control signal. The air speed sensor may include a shaft mounted impeller located in an airstream of the aircraft. A rotational speed sensor, coupled to the impeller, measures a rotational speed of the impeller and outputs a rotational speed signal as the air speed signal. In an alternative embodiment, the air speed sensor may include a vane located in an airstream of the aircraft and deflected in response to air flow in the airstream. In another embodiment, the speed sensor may include an angular position sensor which measures an angle between a free wing and the aircraft fuselage and outputs an angle measurement signal as the air speed signal. The aircraft control surface may comprises a control boom pivotally attached to a fuselage of the aircraft of a trim tab pivotally attached to a fuselage of the aircraft.

Studies of High Solidity Ratio Hydrofoil Impellers for Aerated Bioreactors. 1. Review

Abstract: This first part of a four-part series of papers presents a review of the literature on high solidity ratio axial flow hydrofoil impellers. Interest in the application of high-flow, low power number, hydrofoil impellers, such as the Prochem Maxflo T and the Lightnin A315, has developed over recent years and has largely been stimulated by reports of improved fermentation performance relative to the Rushton disc turbine. Initially, the review briefly examines the characteristics of the radial flow Rushton turbine, as traditionally used in fermenters, with particular reference to its weaknesses. It also discusses the use of pitched blade turbines (mixed flow impellers) for air dispersion since these show some characteristics similar to those of the axial flow hydrofoils. The consideration of these two impeller types provides the background to explain the advantages and potential problems associated with high solidity ratio, axial flow, downward pumping hydrofoils. These aspects are discussed in relation to existing literature which is still relatively scarce. Finally, the advantages of retrofitting are introduced. Parts 2–4 report on a recent, detailed, fluid dynamic study of the Prochem Maxflo T and Lightnin A315 hydrofoil impellers which extends our knowledge of these important impeller types.

Development of an Axial Flow Ventricular Assist Device: In Vitro and In Vivo Evaluation

Abstract: A collaborative effort between Baylor College of Medicine and NASA/Johnson Space Center is underway to develop an axial flow ventricular assist device (VAD). We evaluated inducer/impeller component designs in a series of in vitro hemolysis tests. As a result of computational fluid dynamic analysis, a flow inducer was added to the front of the pump impeller. According to the surface pressure distribution, the flow inducer blades were connected to the impeller long blades. This modification eliminated high negative pressure areas at the leading edge of the impeller. Comparative studies were performed between inducer blade sections that flowed smoothly into the impeller blades (continuous blades) and those that formed discrete separate pumping sections (discontinuous blades). The inducer/impeller with continuous blades showed significantly (p < 0.003) lower hemolysis with a normalized index of hemolysis (NIH) of 0.018 +/- 0.007 g/100 L (n = 3), compared with the discontinuous model, which demonstrated an NIH of 0.050 +/- 0.007 g/100 L (n = 3). The continuous blade model was evaluated in vivo for 2 days with no problems. One of the pumps evaluated ran for 5 days in vivo although thrombus formation was recognized on the flow straightener and the inducer/impeller. As a result of this study, the pump material was changed from polyether polyurethane to polycarbonate. The fabrication method was also changed to a computer numerically controlled (CNC) milling process with a final vapor polish. These changes resulted in an NIH of 0.0029 +/- 0.0009 g/100 L (n = 4), which is a significant (p < .0001) value 6 times less than that of the previous model.(ABSTRACT TRUNCATED AT 250 WORDS)

Ceramic pivot bearing arrangement for a sealless blood pump

Abstract: A centrifugal blood pump, used for heart-lung machines or the like, having at least one impeller, a casing having an inlet and an outlet, the casing formed to have a space for rotatably housing the at least one impeller and a magnetic drive disposed outside the casing. The impeller may have vanes attached thereto for forcing fluid through the casing. Further the vanes may have magnets imbedded therein. The magnetic drive and the imbedded magnets cooperate to rotate the impeller. The impeller may have pivots integrated at opposing ends for allowing the impeller to rotate about a horizontal axis. The pivots may be supported by pivot bearings disposed within the casing. The pivots and the pivot bearings may be made of a ceramic material.