Impeller Geometry Research Articles

Validating impeller geometry optimization for sound quality based on psychoacoustics metrics

The noise generated by vacuum cleaners is one of the dominant noise sources among household appliances with its suction unit as the key element of noise generation. The dominant noise source in the suction unit is its impeller, and that is why there were numerous efforts made to reduce its noise. The years of its optimization have consequently led to a stage, where the possibilities for further noise level reduction are limited. Because human perception of noise is not only influenced by sound pressure levels, it is possible to alter the sound of the impeller to be less annoying to the user. A new centrifugal impeller design was optimized for sound quality, resulting in triangular-shaped flow channels. The optimization process of impeller geometry was based on the sound quality calculated from measured psychoacoustic metrics using two noise annoyance models, Guoqing’s and Lipar’s. The validation of the result was performed by listening tests. Forty individuals participated in the listening tests of the suction units tested and rated the sounds using two sets of semantic differentials. The first set was used to evaluate the sound quality of the impeller, while the second set was used for the validation of these listening tests by evaluating psychoacoustic metrics. Validation results confirm that Lipar’s model of noise annoyance is suitable for evaluating centrifugal blower impeller noise. The subjective evaluation of psychoacoustic metrics, via listening tests of impeller noise, suggests that fluctuation strength and tonality are important features for the sound quality of impeller noise.

Design Method and Performance Prediction for Radial-Inflow Turbines of High-Temperature Mini-Organic Rankine Cycle Power Systems

The realization of commercial mini organic Rankine cycle (ORC) power systems (tens of kW of power output) is currently pursued by means of various research and development activities. The application driving most of the efforts is the waste heat recovery from long-haul truck engines. Obtaining an efficient mini radial inflow turbine, arguably the most suitable type of expander for this application, is particularly challenging, given the small mass flow rate, and the occurrence of nonideal compressible fluid dynamic effects in the stator. Available design methods are currently based on guidelines and loss models developed mainly for turbochargers. The preliminary geometry is subsequently adapted by means of computational fluid-dynamic calculations with codes that are not validated in case of nonideal compressible flows of organic fluids. An experimental 10 kW mini-ORC radial inflow turbine will be realized and tested in the Propulsion and Power Laboratory of the Delft University of Technology, with the aim of providing measurement datasets for the validation of computational fluid dynamics (CFD) tools and the calibration of empirical loss models. The fluid dynamic design and characterization of this machine is reported here. Notably, the turbine is designed using a meanline model in which fluid-dynamic losses are estimated using semi-empirical correlations for conventional radial turbines. The resulting impeller geometry is then optimized using steady-state three-dimensional computational fluid dynamic models and surrogate-based optimization. Finally, a loss breakdown is performed and the results are compared against those obtained by three-dimensional unsteady fluid-dynamic calculations. The outcomes of the study indicate that the optimal layout of mini-ORC turbines significantly differs from that of radial-inflow turbines (RIT) utilized in more traditional applications, confirming the need for experimental campaigns to support the conception of new design practices.

Mixing viscoplastic fluids in stirred vessels over multiple scales: A combined experimental and CFD approach

Dye visualisation techniques and CFD are used to characterise the flow of viscoplastic Carbopol™ solutions in stirred vessel systems over multiple scales. Centrally-mounted, geometrically-similar Rushton turbine (RT) impellers are used to agitate various Carbopol 980 (C980) fluids. The dimensionless cavern diameters, Dc/D, are scaled against a combination of dimensionless parameters: Rem−0.3Rey0.6n−0.1ks−1, where Rem, Rey, n and ks are the modified power-law Reynolds number, yield stress Reynolds number, flow behaviour index and impeller geometry constant, respectively. Excellent collapse of the data is demonstrated for the fluids and range of flows investigated. Additional data are collected using a pitched-blade turbine (PBT) with cavern size similarity being shown between the RT and PBT datasets. These results are important in the context of scale-up/scale-down mixing processes in stirred vessels containing complex fluids and can be used to show that flow similarity can be achieved in these systems if the processes are scaled appropriately.

Optimization of the Impeller Design for Mesenchymal Stem Cell Culture on Microcarriers in Bioreactors

AbstractWhen agitating mesenchymal stem cells adhered on microcarriers in bioreactors, a compromise has to be found between sufficient particle suspension and limitation of hydromechanical stresses. The present study proposes a strategy to improve the design of an ‘elephant ear' impeller at the just‐suspended state by varying its relative size, blade slope angle, and position in the reactor. To do that, computational fluid dynamics simulations were coupled with multi‐objective optimization to minimize the hydromechanical stress encountered by the microcarriers. Two minimization criteria were considered: (P/V)@p and the energy dissipation function EDC. On the basis of 31 conditions, an optimal impeller geometry is proposed.

Inverse Design of a Centrifugal Pump on the Meridional Plane Using Ball-Spine Algorithm

In this work, an inverse design algorithm called Ball-Spine (BSA) is developed as a quasi-3D method and applied to the meridional plane of a centrifugal pump impeller in an effort to improve its performance. In this method, numerical analyses of viscous flow field in the passage between two blades are coupled with BSA to modify the corresponding hub and shroud geometries. Here, full 3D Navier-Stokes equations are solved within a thin plane of flow instead of solving inviscid, quasi-3D flow equations in the meridional plane. To demonstrate the validity of the present work, the performance of a centrifugal pump is first numerically investigated, and then compared against available experimental data. Defining a target pressure distribution on the hub and shroud surfaces of the flow passage, a new impeller geometry is then obtained in accordance with the modified pressure distribution. The results indicate a good rate of convergence and desirable stability of BSA in the design of rotating flow passages. Overall, the proposed design method resulted in the following major improvements: an increase in static pressure along the streamline, 5% of increase in the pump total head and delay in the onset of flow cavitation inside the impeller.

EFFECT OF DISC-BLADE INTERCEPTING ANGLE ON MIXING PERFORMANCE IN A MULTIPHASE STIRRED VESSEL

Abstract The impeller geometry is a determining factor for mixing efficiency in a stirred vessel. In this study, the effect of disc-blade intercepting angle on power number, just suspended speed and mass transfer coefficient was investigated in a multiphase system under turbulent conditions. The impellers used in this study were fabricated with 3D printing. The interactions between the experimental parameters were analysed using Response Surface Methodology (RSM). The impeller power number was found to have a linear positive relation with disc-blade intercepting angle from 30° to 90°. Beyond 90°, the impeller power number became lower with increment in the disc-blade intercepting angle. The results confirmed better suspension efficiency in the angle range of 50° to 120° in 5 wt% solid suspensions. The lowest specific power requirement (Ɛjs) at just suspension condition was observed in the angle range of 30° to 80°. The highest mass transfer coefficient was obtained for the impellers with disc-blade intercepting angle in the middle range. Two models were established on power number and mass transfer coefficient for various disc-blade intercepting angles. The study confirmed that the hydrodynamic and mass transfer performance of disc blade impellers could be maximized by changing the disc-blade intercepting angle for a selected system.

Effect of impeller geometry on performance characteristics of centrifugal compressor

Centrifugal Compressors play an essential role in oil, gas and petrochemical industries. Their extensive usage is due to their smooth operation and high reliability compared to other other compressor types. One of the main characteristics of these turbomachines is their performance curve, which is an important criterion for selecting the appropriate compressor for a desired working condition. In the presented article, the effect of impeller’s geometry on performance curve and other compressors characteristics is numerically investigated. The 3D CFD code is used to achieve the performance curves that are dedicated to each geometrical configuration. The results indicate that some of the selected geometrical parameters have a significant effect on performance curve margins. Increasing the shroud angle moves the surge point to the higher flow coefficients, while the pressure ratio remains constant and increasing the blade’s trailing edge angle, leads to increase in pressure ratio.

CFD Model of Agitated Vessel for the Removal of Cr(vi) by Nano-hematite Particles

The mixing operation and design of agitated vessels for various chemical engineering applications may still represent a challenge due to the complexity of hydrodynamic fields established inside the reaction system. Computational Fluid Dynamics (CFD) is considered a valuable tool for the investigation of the complex turbulent flow field proper of mechanically agitated vessel (MAV). The use of CFD may effectively support the process engineer for the selection of the most proper impeller/vessel geometry and operative conditions to achieve homogeneous and fully turbulent conditions. In this work, experimental tests and CFD simulations were performed to study the Cr(VI) removal efficiency through nano-hematite particles (nHP) in MAV. More in detail, some solutions of Cr(VI) were treated using lab-made nHP, produced by a spinning disk reactor, in lab-scale agitated vessel and the kinetic of the removal process was experimentally studied varying the reactor/impeller configuration (impeller geometry) and the impeller rotational velocity. The obtained results were interpreted according to a CFD model of the system hydrodynamic field based on the k-? turbulent model whereas the kinetic data were fitted to a suitable mass transfer kinetic model.

Slurry Flow and Erosion Prediction in a Centrifugal Pump after Long-Term Operation

After long-term operation, the material loss due to slurry erosion often leads to significant changes in the impeller geometry. This change can, in turn, affect the flow characteristics and the erosion mechanism in a centrifugal pump. To investigate this matter, we consider two geometric models based on a prototype stainless steel impeller, which failed due to huge erosion problems from the pulp slurry. These two models are different in the degree of wear, with one model at the pre-erosion stage and the other with worn blades. For both models, the flow characteristics have been obtained in the Eulerian reference frame by means of the SST k-ω model. Then, in order to determine the erosion patterns, the particles have been tracked in the Lagrangian reference frame. In this way, the influence of the flow characteristics on the erosion patterns has been analyzed. Results show that the geometric variations greatly affect the flow characteristics, and consequently the erosion patterns. Particularly, it has been found that the clearance flow plays a significant role in defining erosion characteristics, such as erosion distribution, areas, and rates. Interestingly, the simulation results for current study show that the erosion rates after long-term operation greatly decrease near both the outlet edge and the blade bottom. It follows also that for accurate erosion predictions, these geometric variations have to be considered in the numerical model. This paper provides a better understanding of the complex erosion mechanism in centrifugal pumps, which can help to reduce the wear in future designs.

A Review of Design Considerations of Centrifugal Pump Capability for Handling Inlet Gas-Liquid Two-Phase Flows

Most of the pumps working under two phase flows conditions are used in petroleum industry applications, like electrical submersible pumps (ESP) for hydrocarbon fluids, in chemistry, nuclear industries and in agriculture for irrigation purposes as well. Two-phase flows always deteriorate overall pump performances compared with single flow conditions. Several papers have been published aiming to understand flow physics and to model all the main mechanisms that govern gas pocket formation and surging phenomena. These mechanisms depend on the pump type, the impeller geometry, the rotational speed, design and off-design liquid flow rate conditions, the volumetric gas fraction, the fluid properties and the inlet pressure. In the present paper, a review on two phase performances from various centrifugal pumps designs is presented, mainly based on experimental results. The main focus is devoted to detect the significant geometrical parameters that: (1) Modify the pump head degradation level under bubbly flow regime assumption; (2) Allow single stage centrifugal pumps keep working under two-phase flow conditions with high inlet void fraction values before pump shut down, whatever the pump performance degradations and liquid production rates should be. Because most of the published experimental studies are performed on dedicated laboratory centrifugal pump models, most of the present review is based on air-water mixtures as the working fluid with inlet pressures close to atmospheric conditions. The following review supposes that gas phase is considered as a non-condensable perfect gas, while the liquid phase is incompressible. Both phases are isolated from external conditions: neither mass nor heat transfer take place between the phases.

Designing of lab-scale anaerobic digester equipped with maxblend impeller to evaluate effect of mixing on anaerobic digestion

Operational parameters can be easily controlled at lab scale experiments for an anaerobic digestion process. Our aim is to design a lab-scale digester equipped with an impeller to investigate how the geometry of impeller and different mixing modes effect the biogas yield of digester. Further, the methods of measuring the gas volume, gas composition, mixing intensity, torque, temperature are discussed in this article. The assembling of 4 liters digester is described which can be operated at various operating parameters which control the anaerobic digestion process. Mixing is very important to enhance efficiency of an anaerobic digester. To attain mixing Maxblend impeller is used in this lab-scale digester due to its better performance for mixing and power consumption. Various design consideration has been described.

Galvanic Corrosion of Steel in Agitated Vessels Used in Fertilizer Industry

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

Microfluidic Extractive Crystallization for Spherical Drug/Drug-Excipient Microparticle Production

Granulation is a common manufacturing step for pharmaceutical drug products, which improves powder flowability, compactibility, and ensures tablet content uniformity. Granules of uniform content can conventionally be challenging to obtain due to powder segregation and mixing issues prior to granulation. Spherical crystallization—a method where drug crystals are directly formed into spherical granules—is a promising way to overcome issues with mixing and form granules with uniform content. However, a common challenge of existing quasi emulsion solvent diffusion or solvent extraction methods for spherical crystallization involving miscible solvents in stirred batch vessels is the coarse control over particles sizes, as they are sensitive to multiple scale-up factors (mixing efficiency, impeller and vessel geometry, inlet configuration). This limits the method in terms of content uniformity, which in turn limits the extent to which granules with tunable dissolution profiles can be created. Here, we propose a...

A Three-Zone Modeling Approach for Centrifugal Compressor Slip Factor Prediction

Accurate estimation of slip factor is of paramount importance to ensure centrifugal compressor work input is adequately predicted during the preliminary design process. However, variations in the flow field at impeller exit in both the pitchwise and spanwise directions complicate the evaluation procedure considerably. With the increasing implementation of engine downsizing technologies in the automotive sector, achieving a wide operating range has become a factor of prime importance for centrifugal compressors used in automotive turbocharging applications. As a result of the design features required to achieve this aim, modern impeller geometries have been shown to exhibit an approximately parabolic variation in slip factor across their respective operating maps. By comparison, traditional slip correlations typically exhibit a constant, or at best monotonic, relationship between slip factor and impeller exit flow coefficient. It is this lack of modeling fidelity which the current work seeks to address. In order to tackle these shortcomings, it is proposed that the impeller exit flow should be considered as being made up of three distinct regions: a region of recirculation next to the shroud providing aerodynamic blockage to the stage active flow, and a pitchwise subdivision of the active flow region into jet and wake components. It is illustrated that this hybrid approach in considering both spanwise and pitchwise stratification of the flow permits a better representation of slip factor to be achieved across the operating map. The factors influencing the relative extent of each of these three distinct regions of flow are numerous, requiring detailed investigations to successfully understand their sources and to characterize their extent. A combination of 3D computational fluid dynamics (CFD) data and gas stand test data for six automotive turbocharger compressor stages was employed to achieve this aim. Through application of the extensive interstage static pressure data gathered during gas stand testing at Queen's University Belfast, the results from the 3D CFD models were validated, thus permitting a more in-depth evaluation of the flow field in terms of locations and parameters that could not easily be measured under gas stand test conditions. Building on previous knowledge gained about the variation in shroud side recirculation with geometry and operating condition, the characteristic jet/wake flow structure emanating from the active flow region of the impeller was represented in terms of area and mass flow components. This knowledge allowed individual slip factor values for the jet and wake to be calculated and combined to give an accurate passage average value which exhibited the distinctive nonlinear variation in slip across the operating map which is frequently absent from existing modeling methods. Fundamental considerations of the flow phenomena in each region provided explanation of the results and permitted a modeling approach to be derived to replicate the trends observed in both the experimental data and the CFD simulations.

Numerical Simulation of Centrifugal Pump and Effect of Impeller Geometry on Its Performance

In the presented paper, the effect of impeller geometric parameters on the performance of centrifugal pump has been investigated. This study was performed for different flow rates and rotational speeds, allowing to obtain the performance curve for the centrifugal pump. Three dimensional computational fluid dynamic simulation of the impeller and volute for a centrifugal pump has been performed using ANSYS CFX software (a high-performance computational fluid dynamics software tool that delivers reliable and accurate solutions). The pump has an outside impeller diameter of 205 mm, impeller outlet width of 16 mm, rotational speed 1450 rpm, seven impeller blade and a specific speed of 28. By increasing the impeller outer diameter and outlet width, both net head and power consumed are increased. In addition, it was noticed that the best efficiency point (BEP) was achieved at volume flow rate higher than design flow rate. The performed simulations indicated that; by changing the impeller outer diameter from 200 mm to 210 mm, the flow rate of BEP increases about by 14.7%. By changing the impeller outlet width from 14 mm to 18 mm, the flow rate of BEP increased by about 9%, and the efficiency of BEP reduced by approximately 0.5%. It was also noticed that, increasing the rotational speed will cause an increase in the net head and consumed power. An increase of 13.8% for the flow rate of BEP was observed when changing the rotational speed from 1400 rpm to 1500 rpm, with the same BEP.

Reconstruction and Prediction of Flow Field Fluctuation Intensity and Flow-Induced Noise in Impeller Domain of Jet Centrifugal Pump Using Gappy POD Method

To analyze the interrelations among impeller blade geometry, flow field fluctuation intensity and impeller-induced hydrodynamic noise of jet centrifugal pump (JCP), a Gappy proper orthogonal decomposition (POD) method combined with computational fluid dynamics/computational fluid acoustics (CFD/CFA) technique was proposed to reconstruct and predict the unsteady flow field fluctuation intensity and flow-induced noise in impeller region. The snapshot sets were composed of blade profile parameters, flow field fluctuation intensity data and the data of sound pressure level of hydrodynamic noise in the frequency domain. Similar mesh reconstruction and flow field interpolation were carried out to have the same number of flow field data. The snapshot sets were decomposed into a linear combination of orthogonal bases using the singular value decomposition (SVD) method. The orthogonal basis coefficients corresponding to the objective variables were fitted by the least square method. The results show that the proposed method has a good accuracy in predicting the flow field fluctuation intensity and flow-induced noise of the JCP impeller domain. The relative error of pressure fluctuation intensity field is less than 4.0%, relative velocity fluctuation intensity field is less than 3.0%, turbulent kinetic energy fluctuation intensity field is less than 4.5%, and impeller-induced hydrodynamic noise is less than 10%. Taking the method as a surrogate model to predict the flow field fluctuation intensity and the radiation level of hydrodynamic noise in the optimization process of centrifugal pump impeller, it could not only reduce the calculation amount and time significantly and improve optimization speed and efficiency greatly but could also provide a reference for vibration characteristics of the models.

Influence of Impeller Geometry on Hydromechanical Stress in Stirred Liquid/Liquid Dispersions

Hydromechanical stress is a crucial parameter for a broad range of multiphase processes in the field of (bio)chemical engineering. The effect of impeller type and geometry on hydromechanical stress in stirred tanks is important. The present study aims at characterizing conventional and new impeller types in terms of particle stress. A two-phase liquid/liquid noncoalescing dispersion system is employed, and the drop breakage is monitored in-line in a stirred tank. The published effects of agitation on drop deformation are confirmed and expanded significantly for five modified new impeller types. Radial impellers are advantageous for applications where low shear conditions are desired. A modified propeller with a peripheral ring and the developed wave-ribbon impellers present remarkable results by producing significantly low and high hydromechanical stress, respectively. The results obtained are correlated in terms of mean and maximum energy dissipation rate, as well as circulation frequency in the impeller...

Multi-Objective Genetic Algorithm Assisted by an Artificial Neural Network Metamodel for Shape Optimization of a Centrifugal Blood Pump.

A centrifugal blood pump is a common type of the pump used as a left ventricular assist device (LVAD) in the medical industries. The reduction of the LVADs hemolysis level to reduce the blood damage is one of the major concerns in designing of such devices. Also, the enhancement of the LVADs efficiency to decrease the battery size is another design requirement. The blood damage critically depends on the state of the blood being pumped. Besides the blood state, the blood damage also depends on the pump impeller and volute geometries. In this research, a multi-objective optimization of a centrifugal blood pump is performed. A complete 3D-optimization platform is established for both impeller and volute of a centrifugal blood pump consisting of parametric modeling, automatic mesh generation, computational fluid dynamics (CFD) simulation, and optimization strategy. A vast number of cases with various impeller and volute shapes are numerically simulated. Three different metamodels are created using artificial neural networks (ANNs) in order to approximate the pump hydraulic efficiency, hemolysis index (HI), and pressure head. The inverse of the relative pressure head is defined as the first objective and the summation of relative hemolysis index and the inverse of the relative efficiency is assumed as the second objective. Non-dominated Sorting Genetic Algorithm-II (NSGA-II) is used to find the Pareto Front. A set of optimal points is selected. Finally, for the physiological flow conditions, the optimum design that provides 11.9% HI reduction and 7.2% efficiency enhancement is selected.

Shape optimization of a centrifugal blood pump by coupling CFD with metamodel-assisted genetic algorithm.

A centrifugal blood pump is a common type of pump used as a left ventricular assist device in the medical industries. Therefore, the improvement of the device bio-compatibility to reduce the blood damage and to increase the efficiency has become a major challenge. In the current work, a metamodel-assisted genetic algorithm is employed to simultaneously optimize the impeller and volute geometries of a typical centrifugal blood pump. The overall shape of the base design is inspired from HeartMate3 LVAD, and the main dimensions of the base design including inlet and outlet radius, blade angle distribution, volute cross-section area distribution, etc., are designed in our laboratory. Three different scenarios are investigated using three different objective functions, i.e., (1) hydraulic efficiency, (2) pressure head, and (3) hemolysis index (HI). The results showed that the shape optimized by pump efficiency has also nearly the same level of HI as the shape optimized by HI. Hence, to reduce computation time, one can use efficiency instead of HI as an objective function. However, one must check the HI level after such optimization to see whether it is within the acceptable range of HI for such bio application.

Three-dimensional CFD simulations to study the effect of impeller geometry on internal flow field in ADS upward spiral flow target

ABSTRACT The relationship between flow field characteristics and geometrical structures is an important issue in designing liquid metal spallation target for accelerator-driven sub-critical system (ADS). Upward spiral flow target (USFT) is a new type ADS windowless target in which an impeller is employed to generate upward spiral flow and regulate internal flow field. The impeller comprises a central shaft and several identical blades, and its geometry is very crucial for designing the target. In this paper, series models with different geometric parameters of the shaft and the blades are simulated by ANSYS CFX to analyse the distributions of internal flow field and the dimensions of stagnation zone in USFT. The results show that the shaft plays a primary role in guiding the upward flow while the blades are significant for generating the spiral flow. Finally, an optimized model with preferred geometric parameters is obtained by comparing the overall simulation results. The whole research has foundational signification for further studying USFT.