Showing papers on "Impeller published in 1996"

Impact of tank geometry on the maximum turbulence energy dissipation rate for impellers

Abstract: The maximum turbulence energy dissipation rate per unit mass, emax, is an important variable in dispersion systems, particularly for drop breakup and coalescence, and for gas dispersion. The effect of tank geometry (number of baffles, impeller diameter, and off-bottom clearance) on emax for four impellers (the Rushton turbine, RT; the pitched blade turbine, PBT; the fluidfoil turbine, A310; and the high-efficiency turbine, HE3) is examined. Mean and fluctuating velocity profiles close to the impellers were measured in a cylindrical baffled tank using laser doppler velocimetry. Local and maximum turbulence energy dissipation rates in the impeller region were estimated using e = Av3/L with A = 1 and L = D/10 for all four impellers. Factorial designs were used to test for the effects of single geometric variables under widely varying conditions and interactions between variables. Several factorial designs were used to ensure that real effects were separated from effects that appeared as an artifact of the experimental design. Results show that the tank geometry has a significant effect on emax, primarily with respect to variations in impeller diameter and interactions between the off-bottom clearance and impeller diameter. For the same power input and tank geometry, the RT consistently produces the largest emax and/or emax scaled with N3D2.

Method and apparatus for solid prototyping

Abstract: An improved extrusion-based manufacturing system includes one or more extruders, with each extruder containing at least two stages of increasing pressurization. In one of preferred embodiments, a first stage of pressurization is created by the motion of a solid wafer (314) of thermoplastic through an orifice (316) into a heater chamber (318), and a second stage of pressurization is provided by a conical viscosity pump (330), with extrusion material from the first stage pressurization maintaining a flow of thermoplastic fluid (320) through a communication channel (322) and fits into a rotary impeller (332) which a variable speed motor (336) rotates in a female collet (334) to drive the fluid extrusion material towards and out of a removable nozzle (338) and orifice (340) and all expected pump rates.

Substrate gradients in bioreactors: origin and consequences

Abstract: Gradients of glucose in time and space are shown in a 30 m3 cultivation of Saccharomyces cerevisiae grown in minimal medium to a cell density of 20 gl−1. The fed-batch concept was used with glucose as the limiting component which was fed continuously to the process. As the mean glucose concentration declined throughout the process, the level of glucose was at all times different in three sampling ports (bottom/middle/top) of the reactor. These gradients were furthermore shown to depend on the feed position. This means that if the feed was supplied in the relatively stagnant mixing zone above the top impeller, the gradients were more pronounced than by feed in the well mixed bottom impeller zone. A rapid sampling system was constructed, and continuous glucose samples of every 0.15 s were analysed from a point of the reactor. Fifty samples were collected with this system, but the amount and frequency is possible to change. The results of these series show a variance of the glucose concentration where at one stage, a peak appeared of a relative difference in concentration of 40 mgl−1. The pattern of these rapid glucose fluctuations was shown to depend on the turbulence level at the location of the feed. It was shown, that the fluctuations were more pronounced when the feed was localised in a relatively stagnant area than in the well-mixed impeller area, where the deviation from the mean was negligible. The fluid flow, in the impeller (gassed and ungassed) and bulk area (ungassed) of the reactor, was characterised by turbulence measurements using thermal anemometry. These types of areas resembles well the different areas of sampling as mentioned above. The turbulent frequencies in these areas were in the range of 10−1 to 104 Hz with the highest amplitudes at low frequencies. The spectra depicts a uniform time scale for all zones, especially at the low frequencies. The dominance of low frequency, high amplitude flow variations and the observed short-time oscillations in substrate concentration support the hypothesis of substrate transport over fairly long distances without substantial mixing both in the impeller, but especially, in the bulk zone of the reactor.

Bearingless blood pump and electronic drive system

Abstract: A magnetically operated blood pump includes a rotor with an impeller that rotates within a housing, and the housing fastens to a driver that preferably electromagnetically controls the speed and disposition of the impeller in response to sensed conditions. The impeller and housing constitute a disposable assembly in which permanent magnets embedded in the impeller stabilize its position to maintain pumping tolerances in at least one dimension, and also couple to external fields to rotate the impeller. In one embodiment concentric arrangements of cylinder magnets passively maintain radial centering, while coils in the driver are actuated to simultaneously produce a rotational torque and to correct axial or tilt displacements. In a preferred embodiment of this type, sensors around the periphery detect axial displacement and/or tilt as the impeller turns, while the drive circuit responds to the sensor signal to produce compensating phase changes in the coil drive signals. The drive coils are disposed in a common plane and are symmetrically spaced about the central axis, and the phase changes in their drive signals result in a compensating axial force, which may be different in each of the coils to correct tilt. In another or further embodiment, the rotor is freely suspended such that blood washes over one or more surfaces of the rotor, and fluid pressure produces a net restoring force on the rotor to counteract changes in tilt or axial position within the housing. In this case, the driver need only drive rotation of the pump. The drive unit works with a variety of multipole impeller pumps, including ones with magnetic segmented rotors and conventional mechanical support bearings such as ones with a jewel or shaft bearing element. In other embodiments, plural sets of magnets provide passive constraint of radial disturbances and two tilt movements, while axial disturbances are corrected either passively by hydrodynamic surfaces or actively with the driver. The driver unit may include a hand crank assembly, enabling continued operation during power outages.

The Influence of Rushton Impeller Blade and Disk Thickness on the Mixing Characteristics of Stirred Vessels

Abstract: The influence of impeller blade and disk thickness on the mixing characteristics of stirred vessels operating with a single Rushton impeller have been investigated. Laser Doppler anemometry (LDA) measurements of the mean and fluctuating velocities, ensemble-averaged over both 360° of impeller revolution and between a specific impeller blade pair (over 60°), were performed in vessels of diameter (T) 100 mm and 294 mm in order to characterize the flow in the impeller vicinity and to assess the effect of vessel scale. The velocity profiles are presented and flow numbers (Fl) are calculated, which show Fl to decrease by up to 15% as the ratio of impeller blade and disk thickness (t) to diameter (D), was increased from 0.008 to 0.033. Torque measurements performed using a telemetric strain gauge arrangement showed a reduction in impeller power number (Po) by up to 33%, with a similar increase in impeller thickness ratio, while the mixing time (t M ) increased by around 15% with increasing t/D. The effects of t/D on the mean and fluctuating velocity components in the two vessels are also reported and the influence of vessel scale on the flow characteristics is assessed.

System and method of controlling rotation of a downhole instrument package

Abstract: A system for controlling the rotation of a roll stabilizable control unit in a steerable rotary drilling assembly comprises an instrument carrier rotatably mounted on a support connected to the drill string. A first rotatable impeller is mounted for rotation by a flow of drilling fluid over the impeller and is coupled to the instrument carrier so as to transmit a torque to it. Sensors carried by the instrument carrier sense the rotational orientation of the instrument carrier and produce a control signal indicative of its rotational orientation, and the torque applied to the instrument carrier by the impeller is controlled, at least partly in response to said signal, so that the instrument carrier can, for example, be roll stabilized if required. A second rotatable impeller is coupled to the instrument carrier for transmitting to it a second torque, which may also be controlled, in the opposite direction to the torque transmitted by the first impeller. The provision of two opposed impellers allows the rotation of the control unit to be controlled over a greater range than is possible with a single impeller.

Distribution of Energy Between Convective and Turbulent-Flow for 3 Frequently Used Impellers

Abstract: Turbulence energy dissipation is important in the study of turbulent mixing phenomena in stirred tanks. This paper investigates the characteristics of the turbulence energy dissipation and the overall energy distribution in the impeller region of a stirred tank. One radial flow impeller (Rushton turbine (RT)) and two axial flow impellers (the pitched blade turbine (PBT) and a fluidfoil turbine (A310)) were used. The mean and root-mean-square velocity (RMS) profiles close to the three impellers were measured in a cylindrical baffled tank using laser Doppler anemometry (LDA). The average turbulence energy dissipation, e i was calculated using a macroscopic energy balance equation over several control volumes. The local turbulence energy dissipation e was estimated using e=Av 3 /L with A=1 and L=D/10. Integration of the local dissipation over a control volume consistently gave results within 6% of the macroscopic energy balance. The bulk of the energy is dissipated in the small volume occupied by the impeller and the impeller discharge stream for all three impellers: in order of increasing percentages 38.1% (A310), 43.5% (RT) and 70.5% (PBT). The dominant characteristics of energy distribution are different for each impeller. The A310 was most efficient at generating convective flow. The RT generated the most turbulence, and the PBT derived a much larger portion of its energy from the return flow.

An LDA study of the turbulent flow field in a baffled vessel agitated by an axial, down-pumping hydrofoil impeller

Abstract: The turbulent flow of water in a cylindrical, baffled vessel with an axial flow hydrofoil impeller, either a Chemineer HE3 (CHE3) or a Prochem Maxflo T (PMT), has been studied using a laser Doppler anemometer. Using ensemble averaging, the mean axial and radial flow and the associated fluctuating components were obtained for the whole of the vessel; plus similar data for the tangential component close to the impeller. Assuming axial symmetry, flow rates were calculated as were flow numbers and circulation flow numbers. Power numbers were also determined. All the data obtained were used to compare the circulation efficiency of the two hydrofoils plus a pitched blade and a Rushton turbine. This comparison showed that the CHE3 required a power input of about 2/3 of that for the PMT and about 1/3 of that for the pitched blade and Rushton turbine to obtain the same axial-radial circulation in the tankz.

Particle suspension in the turbulent regime: The effect of impeller type and impeller/vessel configuration

Abstract: Particle suspension in water has been studied using Rushton turbines, pitched blade turbines (pumping upwards and downwards), Chemineer HE3 and Lightnin A310 hydrofoils pumping downwards, and Ekato Intermig agitators Flat and profiled bottoms have been used The dimensionless parameter S, which is related to the minimum impeller speed for complete solids suspension based on the work of Zwietering, has been used to generalize the results for two different particles The configuration requiring the lowest specific energy dissipation rate in the flat-bottomed tank was a downward- pumping impeller of 035 to 04 times the vessel diameter with a clearance off the base of 1/4 the vessel height Under these conditions, the main flow pattern was such that the piles of solids associated with the regions of flow reversal at the periphery and of the centre of the base were both removed at about the same speed By modifying the base to fill in these zones where solids collect, the minimum specific energy dissipation rate associated with this configuration using the HE3 hydrofoils could be further reduced by a factor of about 4 to 5 Compared to the HE3 hydrofoils, the Rushton turbines and the Intermigs required minimum specific energy dissipation rates for suspension 5 to 10 times higher at equivalent clearances and vessel base configurations

Suppression of Secondary Flows in a Mixed-Flow Pump Impeller by Application of Three-Dimensional Inverse Design Method: Part 1—Design and Numerical Validation

Abstract: This paper describes the design of the blade geometry of a medium specific speed mixed flow pump impeller by using a three-dimensional inverse design method in which the blade circulation (or rV θ ) is specified. The design objective is the reduction of impeller exit flow nonuniformity by reducing the secondary flows on the blade suction surface. The paper describes in detail the aerodynamic criteria used for the suppression of secondary flows with reference to the loading distribution and blade stacking condition used in the design. The flow through the designed impeller is computed by Dawes' viscous code, which indicates that the secondary flows are well suppressed on the suction surface. Comparison between the predicted exit flow field of the inverse designed impeller and a corresponding conventional impeller indicates that the suppression of secondary flows has resulted in substantial improvement in the exit flow field. Experimental comparison of the flow fields inside and at exit from the conventional and the inverse designed impeller is made in Part 2 of the paper.

Induction motor driven seal-less pump

Abstract: A seal-less pump and electric motor assembly includes a motor rotor fixed to a driving shaft connected to an impeller in the pump assembly. The rotor and impeller are enclosed in a common housing such that the rotor rotates within any fluid being pumped by the impeller. The portion of the housing circumscribing the rotor includes a plurality of axially extending, circumferentially spaced strips of magnetic material penetrating through plastic material of the housing. Each of the strips coincide with corresponding ones of the pole teeth of a motor stator circumscribing the outer portion of the housing such that the strips in the housing act as extensions of the pole teeth. In one embodiment, the strips of magnetic material in the housing are formed by molding powdered iron in a plastic binder material. The strips are then placed in a mold in which the housing is formed by injecting plastic. The plastic binder in the strips melds with the injected plastic to form a continuous housing for enclosing the rotor. The ferromagnetic material strips extend through the housing and are spaced from the rotor surface by a normal air gap distance so as to improve the efficiency of the motor by having the magnetic strip act as extensions of the motor stator pole teeth. In one embodiment, the rotor includes a shaft, a core including a molded magnetic powder and plastic composite material surrounding the shaft, and an annular corrosion resistant electrically conductive tube surrounding the core.

Steady and unsteady computation of impeller-stirred reactors

Abstract: A general computational approach is presented for numerical modeling of viscous flow in baffled, impeller-stirred-tank reactors. A multiblock, body-fitted grid structure facilitates modeling of various impeller and baffle designs, and a new procedure offers averaged velocity data from a complex 3-D CFD dataset. Impellers are modeled precisely, eliminating the need for inputting experimental velocity data for boundary conditions. The method can be used quickly to obtain extremely detailed flow computations at a fraction of the cost of computing unsteady moving grid solutions. A steady-state computational approach that neglects the relative motion between impeller and baffles yields numerical results comparably accurate to full unsteady computations for laminar flow at a fraction of the time and expense. The approximate steady-state method is used to predict power requirements of a Rushton turbine in laminar flow. An unsteady, moving grid technique provides time-accurate solutions for the flow inside an impeller-stirred reactor with side-wall baffles. These computed results are compared with those using the approximate steady-state method and with experimental measurements. The unsteady, moving grid method uses two different initial conditions: one starting from rest and the other starting from an approximate steady-state solution obtained at the starting position of the impeller relative to the baffles. For unsteady simulations of laminar flow in stirred vessels, the final operating condition can be achieved much more efficiently if the solution obtained from the steady-state procedure is used as an approximate initial condition.

Computational snapshot of flow generated by axial impellers in baffled stirred vessels

Abstract: The ability to numerically simulate the flow in baffled, stirred vessels is fast becoming vital to their optimal design. Most of the past attempts have adopted a black box treatment to the impeller swept region, requiring experimentally-based input. More recent efforts are based on the computation of the full time varying flow field within and outside the impeller swept region. An intermediate approach has been developed in this paper, in which a quasi-steady flow is computed for any momentary impeller position. The method captures almost all the significant details of the flow both within and outside the impeller without requiring any empirical input/adjustable parameter. The method was applied to the flow generated by an axial impeller which is the most widely used impeller in the process industries. The case of a fully baffled vessel with standard pitched blade turbine was simulated using a FLUENT code. The time-averaged momentum transport equations were solved along with a turbulence model. The time derivative terms in the full transport equations were formulated in terms of spatial derivatives for the impeller swept region. The impeller rotation was simulated in terms of appropriate source terms at the blade surfaces. The model predictions were compared with the published experimental data obtained using the laser Doppler anemometer. It must be emphasized again that all the predictions were obtained by specifying just an impeller geometry, location and tip speed without requiring any boundary conditions near the impeller. The influence of impeller clearance on the generated flow was also correctly simulated. The approach can be used as a general purpose design tool for screening various mixer configurations and to evolve an optimum stirred vessel design.

Velocity profiles in a baffled vessel with single or double pitched-blade turbines

Abstract: A laser-Doppler velocimetry (LDV) apparatus and a computational fluid dynamic (CFD) software package (FLUENT) were used to experimentally determine and numerically predict the velocities in a baffled vessel agitated by one or two 45{degree} pitched-blade turbines. The flow characteristics in the impeller regions were measured by LDV and used as boundary conditions in the numerical computations. Turbulence effects were simulated using either the {kappa}-{epsilon} model or algebraic stress model (ASM). The CFD predictions were compared to the LDV measurements in terms of average velocities in all three directions as well as turbulent kinetic energies. Predictions based on ASM were typically in closer agreement with the experimental data than those based on the {kappa}-{epsilon} model. Flow patterns in both configurations were dominated by the axial and tangential components. The presence of the upper impeller altered the flow considerably, producing a strong vertical recirculation pattern between the impellers and significantly reducing the circulation flow below the lower impeller.

The laminar and turbulent flow pattern of a pitched blade turbine

Abstract: The flow field generated by the pitched-blade turbine in both laminar and turbulent operation has been investigated using laser Doppler velocimetry (LDV) and digital particle image velocimetry (DPIV) experimental techniques. This data has been used to critically evaluate the performance of computational fluid mixing (CFM) tools. It has been found that current CFM software can accurately predict the laminar flow behaviour of the pitched-blade impeller if the proper velocity boundary conditions are provided around the entire periphery of the impeller. In turbulent operation, CFM simulations predict some of the features of the flow field, but dramatically underpredict the total energy dissipation rate in the vessel. They are not currently capable of describing the large-scale instabilities in the flow detected by DPIV.

Pump for pumping molten metal having cleaning and repair features

Abstract: A pump for pumping molten metal includes a motor supported by motor mounting structure above a bath of the molten metal. A shaft has one end connected to the motor. An impeller is connected to the other end of the shaft. The motor mounting structure supports the motor above a bath of molten metal. A device connects the motor to the base member, facilitating replacement of the shaft. The pump may be cleaned by rotating the shaft in a shaft sleeve, the impeller being disposed in an impeller chamber of a base. The rotational velocity of the shaft is adjusted to approximate the velocity at which cavitation occurs in the pump. Metal oxides inside the shaft sleeve are then removed from the pump.

Method for fluxing molten-metal

Abstract: An improved method for treating a body of molten aluminum using an impeller suitable for dispersing fluxing gas or solid particles in the body of molten aluminum. The method produces increased shear forces in the body of molten aluminum and reduces vortex formation. The method comprises providing a body of molten aluminum and projecting an impeller on a shaft into the body, the impeller comprising a rectangular-shaped body having a first rectangular-shaped face and a second rectangular-shaped face disposed substantially opposite the first face, the faces substantially parallel to the shaft and defined by a length L and a height H wherein the length L is greater than the height H. Fluxing gas and particles are dispersed in the body by rotating the impeller in one direction and thereafter reversing the direction of rotation of the impeller to a counter direction, the direction of rotation of the impeller being reversed periodically to provide increased shear forces in the body for improved dispersion of the gas or the particles in the body.

Wind turbine booster

Abstract: A booster (34) for a wind turbine (12) of the type containing an impeller (14) having a plurality of radial curved vanes (16) mounted on a shaft (18) connected to an electric generator (20). The booster (34) comprises a structure (36) mounted in a stationary manner about the impeller (14) for increasing rotation speed of the radial curved vanes (16) on the shaft (18) and operate more efficiently the electric generator (20), to put out more electrical energy therefrom.

An experimental investigation of stator induced unsteadiness on centrifugal impeller outflow

Abstract: Detailed flow measurements were taken in a centrifugal turbomachine model to investigate the aerodynamic influence of the vaned diffuser on the impeller flow. The model consists of an unshrouded centrifugal impeller with backswept blades and a rotatable vaned diffuser, which enables a continuous variation of the vaned diffuser location with respect to the measuring points. Phase-locked ensemble-averaged velocity components have been measured with hot-wire probes at the impeller outlet for 30 different relative positions of the probe with respect to the diffuser vanes. The data also include the distribution of the ensemble-averaged static pressure at the impeller front end, taken by means of miniature fast response pressure transducers flush-mounted at the impeller stationary casing. By circumferentially averaging the results obtained for the different circumferential probe locations, the periodically perturbed impeller flow has been split into a relative steady flow and a stator-generated unsteadiness. The results for the different probe positions have also been correlated in time to obtain instantaneous flow field images in the relative frame, which provide information on the various aspects of the diffuser vane upstream influence on the relative flow leaving the impeller.

Numerical Calculation of 2D, Unsteady Flow in Centrifugal Pumps: Impeller and Volute Interaction

Abstract: A numerical model is developed for calculating the two-dimensional, unsteady, incompressible and turbulent flow within the rotating impeller and stationary volute of an industrial centrifugal pump. The objective is the investigation and comprehension of the instantaneous behaviour of centrifugal pumps, aiming at the reduction of vibrations, radial forces and hydraulic noise. The computation is performed within a blade-to-blade streamtube for the impeller and a tube normal to the axis of rotation for the volute. The equations to be solved are the unsteady Reynolds-averaged Navier-Stokes equations along with the continuity equation and the unsteady κ-e equations for turbulence modelling. The finite volume method is applied for space discretization and an implicit scheme for time discretization. A multidomain overlapping grid technique is used for matching together the relative flow field calculated within the rotating impeller and the absolute one calculated within the stationary volute. In this way the impeller and volute interaction is directly taken into account. The numerical model is validated for a centrifugal pump of N q = 32 under design flow conditions.

Determination of 3-D flow fields in agitated vessels by laser-Doppler velocimetry : Effect of impeller type and liquid viscosity on liquid flow patterns

Abstract: Radial, axial and tangential velocities were measured in a dished-bottom stirred vessel with a Rushton turbine, and two axial agitators: the Mixel TT and the Lightnin A310, for turbulent (in plain water) and near-laminar (in 1% CMC solution) flow regime. The long-term flow patterns, comprising a single circulation loop for the two axial agitators and a dual one for the Rushton turbine, mask a low-frequency periodic disruption. For all three agitators, a region at the upper part of the vessel was found, where liquid rotates counter-clockwise to the impeller rotation. The Rushton turbine was the most effective in terms of overall liquid circulation, the Lightnin A310 exhibited a poor circulation, with velocities in some parts lower than 1% of the impeller tip speed, while the Mixel TT yielded the best pumped flow rate to power ratio. When the liquid viscosity was increased, the pumped flow rate decreased for all agitators, but the reduction in the amount of liquid circulated was more considerable. In the viscous liquid, the axial agitators developed a radiality, with 10-15% of the flow being ejected radially rather than axially.

Apparatus and method for heating a fluid by induction heating

Abstract: In a heating apparatus for the heating of a solid or fluid medium, several permanent magnets are arranged on the periphery of a rotor which produce a magnetic field in whose region an electrically-conducting medium is arranged. The magnetic field from the permanent magnets is radiated approximately radially. By rotation of the rotor, a relative motion arises between the permanent magnets and the electrically-conducting medium, and eddy currents are effected within the medium, thereby causing heating of the same. Electrically-conductive water can be provided as the medium to be heated. In this embodiment electrically-conductive water is fed through a helical conducting coil, with an inlet and outlet side arranged around the rotor in proximity thereto, and is connected to a line which feeds to a user from the outlet side and back to the inlet side in a closed cycle. With this heating apparatus, heat is transferred to the medium with an improved efficiency. In a second embodiment, permanent magnets are arranged on opposing rotating discs so that they produce a magnetic field between the discs. An electrically-conductive material to be heated is placed between the disks, within the magnetic field. In a third embodiment, permanent magnets are arranged on opposing sides of a centrifugal pump having an electrically-conductive impeller. The discs are stationary. Heat is generated in the impeller when it is rotated. The impeller provides both the heating and the flow of the heated fluid.

Molten metal shaft and impeller bearing assembly

Abstract: A molten metal impeller having a base portion including a circumferential notch. The notch having a generally radial wall and a generally axial wall, at least one of the radial or axial walls including a plurality of grooves. A ceramic bearing ring is cemented into the notch.