Showing papers on "Impeller published in 2011"

CFD simulation of stirred tanks: Comparison of turbulence models. Part I: Radial flow impellers

Abstract: A critical review of the published literature regarding the computational fluid dynamics (CFD) modelling of single-phase turbulent flow in stirred tank reactors is presented. In this part of review, CFD simulations of radial flow impellers (mainly disc turbine (DT)) in a fully baffled vessel operating in a turbulent regime have been presented. Simulated results obtained with different impeller modelling approaches (impeller boundary condition, multiple reference frame, computational snap shot and the sliding mesh approaches) and different turbulence models (standard k − e model, RNG k − e model, the Reynolds stress model (RSM) and large eddy simulation) have been compared with the in-house laser Doppler anemometry (LDA) experimental data. In addition, recently proposed modifications to the standard k − e models were also evaluated. The model predictions (of all the mean velocities, turbulent kinetic energy and its dissipation rate) have been compared with the experimental measurements at various locations in the tank. A discussion is presented to highlight strengths and weaknesses of currently used CFD models. A preliminary analysis of sensitivity of modelling assumptions in the k − e models and RSM has been carried out using LES database. The quantitative comparison of exact and modelled turbulence production, transport and dissipation terms has highlighted the reasons behind the partial success of various modifications of standard k − e model as well as RSM. The volume integral of predicted energy dissipation rate is compared with the energy input rate. Based on these results, suggestions have been made for the future work in this area.

Experimental Evidence of Rotating Stall in a Pump-Turbine at Off-Design Conditions in Generating Mode

Abstract: An experimental investigation of the rotating stall in reduced scale model of a low specific speed radial pump-turbine at runaway and turbine brake conditions in generating mode is achieved. Measurements of wall pressure in the stator are performed along with high-speed flow visualizations in the vaneless gap with the help of air bubbles injection. When starting from the best efficiency point (BEP) and increasing the impeller speed, a significant increase of the pressure fluctuations is observed mainly in the wicket gates channels. The spectral analysis shows a rise of a low frequency component (about 70% of the impeller rotational frequency) at runaway, which further increases as the zero discharge condition is approached. Analysis of the instantaneous pressure peripheral distribution in the vaneless gap reveals one stall cell rotating with the impeller at sub-synchronous speed. High-speed movies reveal a quite uniform flow pattern in the guide vanes channels at the normal operating range, whereas at runaway the flow is highly disturbed by the rotating stall passage. The situation is even more critical at very low positive discharge, where backflow and vortices in the guide vanes channels develop during the stall cell passage. A specific image processing technique is applied to reconstruct the rotating stall evolution in the entire guide vanes circumference for a low positive discharge operating point. The findings of this study suggest that one stall cell rotates with the impeller at sub-synchronous velocity in the vaneless gap between the impeller and the guide vanes. It is the result of rotating flow separations developed in several consecutive impeller channels which lead to their blockage.

Study of Flow-Induced Hemolysis Using Novel Couette-Type Blood-Shearing Devices

Abstract: To assist the development and application of blood-contacting medical devices, two novel flow-through Couette-type blood-shearing devices have been developed to study the quantitative relationship between blood damage indexes and flow-dependent parameters. One device is an axial flow-through Couette-type device supported by a pair of pin bearings adapted from the adult Jarvik 2000 blood pump. The other is a centrifugal flow-through Couette-type device supported with magnetic bearings adapted from the CentriMag blood pump. In both devices, a rotor spindle was used to replace the original impeller blades so that a small gap was created between the housing and the rotating spindle surface. Computational fluid dynamics simulations have shown that a uniform, high shear stress region can be generated inside the small gap while the shear stresses elsewhere are relatively low. The possibility of secondary blood damage caused by mechanical seals was eliminated due to the use of a magnetic rotor system. Blood flow through the gap was driven by an externally pressurized reservoir. By adjusting the rotational speed and blood flow rate, shear-induced hemolysis was quantified at a matrix of exposure time (0.039 to 1.48 s) and shear stress (50 to 320 Pa). All of the experiments were conducted at room temperature using heparinized ovine blood with a hematocrit value of 30%. The measured hemolysis levels were much lower than those published in the literature, and the overestimation of those earlier studies may be attributable to device-related secondary blood-damaging effects. A new set of coefficients for the power law model was derived from the regression of the experimental data.

Centrifugal pump apparatus

Abstract: In this centrifugal blood pump apparatus, one permanent magnet is provided in one surface of an impeller, a second permanent magnet is provided in an inner wall of a blood chamber, a third permanent magnet is provided in the other surface of the impeller, and a fourth permanent magnet and a rotor for driving the impeller to rotate are provided, with an diaphragm being interposed. An amount of change in attractive force between the first permanent magnet and the second permanent magnet and an amount of change in attractive force between the third and fourth permanent magnets when the impeller is eccentric are made substantially equal to each other. Therefore, a levitation position of the impeller can always be maintained at a substantially central position in a housing.

Experimental Investigation of Time-Frequency Characteristics of Pressure Fluctuations in a Double-Suction Centrifugal Pump

Abstract: Pressure fluctuation is the primary reason for unstable operations of double-suction centrifugal pumps. By using flush mounted pressure transducers in the semispiral suction chamber and the volute casing of a double-suction pump, the pressure fluctuation signals were obtained and recorded at various operating conditions. Spectral analyses were performed on the pressure fluctuation signals in both frequency domain and time-frequency domain based on fast Fourier transform (FFT) and an adaptive optimal-kernel time-frequency representation (AOK TFR). The results show that pressure fluctuations at the impeller rotating frequency and some lower frequencies dominated in the semispiral suction chamber. Pressure fluctuations at the blade passing frequency, the impeller rotating frequency, and their harmonic frequencies were identified in the volute casing. The amplitude of pressure fluctuation at the blade passing frequency significantly increased when the flow rate deviated from the design flow rate. At 107% of the design flow rate, the amplitude increased more than 254% than that at the design flow rate. The time-frequency characteristics of these pressure fluctuations were affected greatly by both operating conditions and measurement locations. At partial flow rates the pulsation had a great irregularity and the amplitudes at the investigated frequencies were much larger than ones at the design flow rate. An asymmetrical pressure fluctuation structure in the volute casing was observed at all flow rates. The pulsation behavior at the blade passing frequency was the most prominent near the volute tongue zone, and the pressure waves propagated in both the radial and circumferential directions.

Computational Approaches for Studying the Granular Dynamics of Continuous Blending Processes, 1 – DEM Based Methods

Abstract: Computational methods using mechanistic modeling with a specific application in the area of continuous blending are presented. These methods complement experimental designs and aim to reduce the amount of time, effort, and material required to characterize a device or a process. The discrete element methodis applied to the specific case of continuous mixing using two approaches. The first approach models an entire blender and studies the impact of changing impeller speed on residence time distribution (RTD), number of blade passes experienced by the powder, and mean centered variance of the particle residence time. The mean centered variance and the number of blade passes exhibit a maximum with increasing impeller speed, indicating optimal mixing behavior at an intermediate speed range. The second DEM approach utilizes a periodic slice of the full blender in order to explore in detail the effect of speed, fill level, and cohesion on mixing performance. The results show that the transverse mixing rates were generally higher than the corresponding axial mixing rates. Transverse diffusion was highest for large impeller speeds at larger fills, and axial diffusion was highest for large impeller speeds at smaller fills. Variations in particle‐ particle cohesion within the investigated range do not affect diffusion values significantly. The axial diffusion coefficient can be reasonably predicted from the residence time distribution using the 1D advection-diffusion model.

Estimation of radial load in centrifugal pumps using computational fluid dynamics

Abstract: The impeller of a centrifugal pump experiences a significant radial load when operating at off-design conditions. Its average magnitude can be reasonably estimated at the design stage by existing formulas. In contrast, the unsteady component is difficult to estimate since it is affected by the transient properties of the flow. This paper explores the use of a commercial CFD code to estimate the total radial load on the impeller of two test pumps. The full 3D-URANS equations were solved for several flow rates between 10%–130% of rated conditions. The predictions were validated with experimental data of global characteristics and unsteady pressure distribution round the impeller. The code was used to estimate the total radial load (steady and unsteady components) on the impellers as a function of flow rate. It was observed that the unsteady component can represent about a 40%–70% of the average magnitude when operating at off-design conditions.

Experimental Visualization of Two-Phase Flow Inside an Electrical Submersible Pump Stage

Abstract: Dynamic multiphase flow behavior inside a mixed flow Electrical Submersible Pump (ESP) has been studied experimentally and theoretically for the first time. The overall objectives of this study are to determine the flow patterns and bubble behavior inside the ESP and to predict the operational conditions that cause surging. An experimental facility has been designed and constructed to enable flow pattern visualization inside the second stage of a real ESP. Special high speed instrumentation was selected to acquire visual flow dynamics and bubble size measurements inside the impeller channel. Experimental data was acquired utilizing two types of tests (surging test and bubble diameter measurement test) to completely evaluate the pump behavior at different operational conditions. A similarity analysis performed for single-phase flow inside the pump concluded that viscosity effects are negligible compared to the centrifugal field effects for rotational speeds higher than 600 rpm. Therefore, the two-phase flow tests were performed for rotational speeds of 600, 900, 1200, and 1500 rpm. Results showed formation of a large gas pocket at the pump intake during surging conditions.© 2009 ASME

An Investigation of Stall Inception in Centrifugal Compressor Vaned Diffuser1

Abstract: In compression systems the stable operating range is limited by rotating stall and/or surge. Two distinct types of stall precursors can be observed prior to full scale instability: the development of long-wavelength modal waves or a short-wavelength, three-dimensional flow breakdown (so-called “spike” stall inception). The cause of the latter is not well understood; in axial machines it has been suggested that rotor blade-tip leakage flow plays an important role, but spikes have recently been observed in shrouded vaned diffusers of centrifugal compressors where these leakage flows are not present, suggesting an alternative mechanism may be at play. This paper investigates the onset of instability in a shrouded vaned diffuser from a highly loaded turbocharger centrifugal compressor and discusses the mechanisms thought to be responsible for the development of short-wavelength stall precursors. The approach combines unsteady 3D RANS simulations of an isolated vaned diffuser with previously obtained experimental results. The unsteady flow field simulation begins at the impeller exit radius, where flow is specified by a spanwise profile of flow angle and stagnation properties, derived from single-passage stage calculations but with flow pitchwise mixed. Through comparison with performance data from previous experiments and unsteady full-wheel simulations, it is shown that the diffuser is accurately matched to the impeller and the relevant flow features are well captured. Numerical forced response experiments are carried out to determine the diffuser dynamic behavior and point of instability onset. The unsteady simulations demonstrate the growth of short-wavelength precursors; the flow coefficient at which these occur, the rotation rate and circumferential extent agree with experimental measurements. Although the computational setup and domain limitations do not allow simulation of the fully developed spike nor full-scale instability, the model is sufficient to capture the onset of instability and allows the postulation of the following necessary conditions: (i) flow separation at the diffuser vane leading edge near the shroud endwall; (ii) radially reversed flow allowing vorticity shed from the leading edge to convect back into the vaneless space; and (iii) recirculation and accumulation of low stagnation pressure fluid in the vaneless space, increasing diffuser inlet blockage and leading to instability. Similarity exists with axial machines, where blade-tip leakage sets up endwall flow in the circumferential direction leading to flow breakdown and the inception of rotating stall. Rather than the tip leakage flows, the cause for circumferential endwall flow in the vaned diffuser is the combination of high swirl and the highly non-uniform spanwise flow profile at the impeller exit.Copyright © 2011 by ASME

Radially compressible and expandable rotor for a pump having an impeller blade

Abstract: The invention relates to a radially compressible and expandable rotor for a pump having at least one impeller blade, wherein the impeller blade has an impeller blade body whose material is elastically deformable as well as at least one stiffening strut which is at least partially embedded in the material of the impeller blade body. The struts are designed suitably in size, shape and arrangement and are integrated in suitable hollow spaces of the impeller blade body for stabilizing the impeller blade. Elements with tensile strength can additionally be provided.

Investigation of Periodically Unsteady Flow in a Radial Pump by CFD Simulations and LDV Measurements

Abstract: The periodically unsteady flow fields in a low specific speed radial diffuser pump have been investigated both numerically and experimentally for the design condition (Q des ) and also one part-load condition (0.5Q des ). Three-dimensional, unsteady Reynolds-averaged Navier―Stokes equations are solved on high-quality structured grids with the shear stress transport turbulence model by using the CFD (computational fluid dynamics) code CFX-10. Furthermore, two-dimensional laser Doppler velocimetry (LDV) measurements are successfully conducted in the interaction region between the impeller and the vaned diffuser, in order to capture the complex flow with abundant measurement data and to validate the CFD results. The analysis of the obtained results has been focused on the behavior of the periodic velocity field and the turbulence field, as well as the associated unsteady phenomena due to the unsteady interaction. In addition, the comparison between CFD and LDV results has also been addressed. The blade orientation effects caused by the impeller rotation are quantitatively examined and detailedly compared with the turbulence effect. This work offers a good data set to develop the comprehension of the impeller-diffuser interaction and how the flow varies with relative impeller position to the diffuser in radial diffuser pumps.

Low-profile blowers and methods

Abstract: A blower configured to be positioned in confined spaces and to provide ventilation of a fluid, such as temperature controlled air, is disclosed. In various embodiments, the blower is configured to have a reduced axial thickness, which can be desired in such confined spaces. In some embodiments, the blower has an integral filter, a wire channel for the routing of one or more wires, and/or an exposed backplate. In some embodiments, the blower has a snap-fit circuit board, containment system for mounting the motor, one or more vanes for directing fluid flow, shrouded impeller, and/or integrated connector.

Numerical, Hydraulic, and Hemolytic Evaluation of an Intravascular Axial Flow Blood Pump to Mechanically Support Fontan Patients

Abstract: Currently available mechanical circulatory support systems are limited for adolescent and adult patients with a Fontan physiology. To address this growing need, we are developing a collapsible, percutaneously-inserted, axial flow blood pump to support the cavopulmonary circulation in Fontan patients. During the first phase of development, the design and experimental evaluation of an axial flow blood pump was performed. We completed numerical modeling of the pump using computational fluid dynamics analysis, hydraulic testing of a plastic pump prototype, and blood bag experiments (n = 7) to measure the levels of hemolysis produced by the pump. Statistical analyses using regression were performed. The prototype with a 4-bladed impeller generated a pressure rise of 2–30 mmHg with a flow rate of 0.5–4 L/min for 3000–6000 RPM. A comparison of the experimental performance data to the numerical predictions demonstrated an excellent agreement with a maximum deviation being less than 6%. A linear increase in the plasma-free hemoglobin (pfHb) levels during the 6-h experiments was found, as desired. The maximum pfHb level was measured to be 21 mg/dL, and the average normalized index of hemolysis was determined to be 0.0097 g/100 L for all experiments. The hydraulic performance of the prototype and level of hemolysis are indicative of significant progress in the design of this blood pump. These results support the continued development of this intravascular pump as a bridge‐to‐transplant, bridge‐to‐recovery, bridge-to-hemodynamic stability, or bridge-to-surgical reconstruction for Fontan patients.

Centrifugal pump device

Abstract: This centrifugal blood pump device comprises an impeller which is provided within a blood chamber, a permanent magnet which is provided to one surface of the impeller, a permanent magnet which is provided to the inner wall of the blood chamber, permanent magnets which are provided to the other surface of the impeller, and multiple sets of magnetic bodies and coils, which are disposed within a motor chamber and which rotationally drive the impeller with a partition wall located between the impeller and the sets of magnetic bodies and coils. The magnetic bodies are formed in a solid cylindrical shape. The configuration enables the impeller to be smoothly activated for rotation by controlling a coil current.

Study of Pressure Fluctuations and Induced Vibration at Blade-Passing Frequencies of a Double Volute Pump

Abstract: Strong impeller–volute interaction is a major source of high-pressure pulsations and vibration in high-powered pumps. The present study aims at establishing the foundation for correlating the pressure field with the vibration of the pump and identifying effective solutions to reduce flow-induced vibration in double volute pumps. Experiments were carried out on a model boiler feed pump stage to investigate the distribution of the pressure fluctuations inside the pump and pump vibration under different operating conditions. Critical zones of high-pressure fluctuations have been identified near the volute tongues, indicating strong impeller–volute interaction due to improper radial gap design. Vibrations closely follow the behavior of the pressure fluctuations under different operating conditions. High speeds combined with off-design flow rates result in higher pressure fluctuations inside the pump, which in turn excite vibrations of pump components. Measurements at discharge and suction pipes cannot represent the true behavior or the magnitudes of pressure fluctuations inside the pump, and hence cannot be correlated to pump vibration with fidelity. The clearance between impeller and volute tongues needs to be optimized by experimentation to minimize flow-induced pump vibration.