Conventional Impeller Research Articles

Numerical investigation of flow mechanisms of tandem impeller inside a centrifugal compressor

This study numerically investigated a single stage centrifugal compressor ‘‘Radiver’’ with a wedge diffuser and several tandem-designed impellers to explore the flow phenomena within the tandem impeller and the potential to enhance compressor performance. The results demonstrate that tandem design and clocking fraction (λs) significantly affects the compressor performance. The compressor stage with tandem impellers of Series A of boundary layer growth interruption alone are observed to have a widely operating range but efficiency and total pressure ratio penalty compared with that of conventional impeller. The tandem impeller with at least the same impeller efficiency as the conventional design is considered as a critical design criteria so that further modification process based on the flow characteristic of tandem impeller is necessary. In order to restrain the inducer wake and exducer shock losses, parameters modification of blade angle and thickness distributions are necessary and the modified tandem impeller of Series B is obtained. The modified tandem impeller with 25% clocking arrangement shows an 8.45% stall margin increase and maintains the total pressure ratio and efficiency as the conventional design, which proves the potential of tandem impeller to improve compressor stage performance. It is noteworthy that the tandem impellers of Radiver have not shown obviously balanced exit flow field and the fundamental mechanism of stall margin extending of tandem impeller lies on the improved impeller/diffuser matching performance resulting from the incidence angle variation at diffuser inlet.

Optimal Design of a Novel ‘S-shape’ Impeller Blade for a Microbubble Pump

The newly designed impeller blade, a so-called novel ‘S-shape’ blade, used for microbubble pumps has been introduced to enhance pump performance. Unlike a conventional blade having separated blades, like cantilever-shape blades, the newly designed impeller has a continuous blade, thus having a relatively robust structure as compared to a conventional impeller. The optimal blade design of the ‘S-shape’ blade has been demonstrated to obtain a higher pump efficiency. To analyze the three-dimensional flow field inside the pump by numerical simulation, a general analysis code, ANSYS CFX, is employed in the present work. The computed pump efficiency has a maximum error of 4 percent compared to the experimental data. The optimal design of the pump impeller blade is based on geometric constraints considering blade manufacturing, and uses three design variables: the number of blades, the blade thickness and the radius of the blade rib. The response surface method, a global optimization method, is employed to optimize the pump impeller blade. Throughout the blade optimization of the ‘S-shape’ blade, it is found that the chief influence on the pump efficiency is the number of the impeller blades. Pump efficiency, an object function, is increased by up to 35.3 percent, which corresponds to a 3.7 percent increase compared to the reference one. It is no use to say that the ‘S-shape’ blade having a continuously connected blade has more rigid characteristics. The larger pressure increases of the optimized pump along with the volute casing wall is observed from the middle position of the rotational direction, which comes from the increase of momentum energy due to larger circulating flow inside each blade passage as compared to the reference one. The detailed flow field inside the pump blades is also analyzed and compared.

Bach impeller for suspension microcarrier cultures of mesenchymal stromal cells

Background & Aim Mesenchymal stromal cells (MSC) form the majority of very promising late stage clinical trials for indications like stroke, heart failure and osteoarthritis. As the industry seeks to meet the requirements for commercial scale offerings to large patient populace, production of these cell therapies will have to be met in scalable suspension culture vessels. We evaluated the Bach impeller that has an exponential spiral design which operates by creating fluid-fluid motion to culture MSC at 1 and 5 litre scale compared to the conventional axial flow impeller and paddle blade impeller. Simulations indicated that suspension of microcarriers would be rapid (approx. 5 mins) at 100rpm and the Bach would be able to provide 3-4 times the oxygen transfer capability of the axial flow impeller at the equivalent power per unit volume input. Methods, Results & Conclusion Culture of Wharton Jelly MSC at 1 litre with Solohill microcarriers showed 25% improved cell densities of the Bach impeller over the axial flow and paddle impellers: 4 × 10e5 cells/ml vs. 3 × 10e5 cells/ml. This was primarily due to extensive clumping of cell-microcarrier aggregates seen in the conventional impellers from day 3 onwards; whereas the laminar flow prevented aggregation up to the final day of harvesting. Significantly, when MSC were cultured on Cytodex microcarriers at 1 litre, cell yields increased dramatically to 15 × 10e5 cells/ml; viability and identity were equivalent to axial flow or spinner flask cultures. Furthermore, when MSC cultures were scaled further to 5 litre, the Bach yielded 13 × 10e5 cells/ml, and high viability. Thus, the Bach impeller is suitable for microcarrier suspension cultures of both polystyrene as well as hydrogel based microcarriers, and is a promising new impeller to add to the field of regenerative medicine for cell therapy manufacturing.

Role of impeller design for the cultivation of stem cells in stirred-tank bioreactors

Background & Aim The routine use of stem cells and stem cell-derived cells in drug research and regenerative medicine requires the constant supply of high cell numbers in consistent quality. Stirred-tank bioreactors have emerged as promising cultivation systems, which facilitate close control of critical process parameters and have proven their value for efficient process scaling. Cell cultivation on microcarriers or as cell aggregates are two widely used methods for expanding anchorage-dependent cells in stirred-tank bioreactors. Suitable agitation conditions have to be established to keep cell aggregates or microcarriers in suspension while avoiding damaging shear forces. Methods, Results & Conclusion We have developed a novel 8-blade impeller to improve the cultivation of stem cells as aggregates and on microcarriers in the DASbox Mini Bioreactor System. Use of this impeller supported the formation and growth of cell aggregates in the bioreactor. Cell aggregate formation was more efficient than when using a conventional pitched-blade or Rushton-type impeller. Furthermore, microcarriers could be efficiently brought to and kept in suspension. Our results suggest that the impeller shape is an important parameter to consider when optimizing the agitation conditions in stirred-tank bioreactors.

Numerical investigation of a highly loaded centrifugal compressor stage with a tandem bladed impeller

This study numerically investigated a highly loaded centrifugal compressor stage with various tandem-designed impellers and a wedge diffuser using a state-of-the-art multi-block flow solver to better understand the fundamental mechanism of tandem impellers. The flow topologies in the impeller are analyzed in detail to identify the underlying physical mechanism of the effect of the tandem-impeller design on the performance of the compressor stage. Particular emphasis is placed on the evolution of the flow structure in the tandem bladed impeller by varying the inducer–exducer clocking arrangements. The results demonstrate that a tandem compressor design is more efficient than a conventional compressor design for the majority of the tested clocking configurations, and the tandem clocking friction significantly affects the impeller performance. For the tested centrifugal compressor stage, an approximately 1.4% increase in isentropic efficiency and 1.3% increase in stall margin are achieved with an inducer–exducer clocking fraction of 25%. The improvement in the primary centrifugal compressor stage performance by the tandem-impeller design is a result of the manipulation of the flow structure and the reduction in the highly distorted jet/wake exit flow pattern. Compared to the conventional impeller designs, the tandem-impeller clocking arrangement variation significantly affects the high-momentum flow along the exducer suction surface and inducer wake diffusion, inlet axial velocity, and flow angle of the exducer blade. Therefore, this variation is advantageous for shortening the length of the boundary layers on both parts of the blade and enables an intense mixing at the exducer passage to improve the flow uniformity of the impeller exit. As a result, the impeller efficiency, diffuser recovery, and stalling margin can be improved compared with the conventional design.

Ionic Liquids: A Plausible Future of Bio-lubricants

This paper reviews the development of bio-lubricants from conventional impeller pressed natural oils to a new class of green bio-lubricants referred to as ionic liquids (ILs) at room temperature. The attraction to bio-lubricants began with natural oils due to their low friction and wear characteristics owing to high lubricity. To better control the tribological behavior, natural oils were introduced to additives, such as lamellar solid powders. Looking to the future, room-temperature IL lubricants derived from biological feedstock are seen as prospective alternatives and solutions to the issues associated with currently available bio-lubricants. Hence, a comprehensive investigation on the tribological properties of novel bio-based IL lubricant is carried out. A simplistic IL feasibility study has also been performed wherein pin-on-disk tests were conducted to analyze the friction and wear behavior under ambient conditions. The ILs demonstrate improved tribological performance when compared to conventional petroleum-based and bio-based lubricants in their purified forms at various levels. The mechanisms concerning the chemical composition of the ILs and their tribological properties imbibed by the bio-lubricants are discussed while highlighting its plausible industrial application.

Hydraulic Design and Power Characterization of Closed Turbine-Type Agitator

Abstract Designs of impeller as an agitator with alteration and modification of a conventional turbine type impeller were proposed to improve the power characteristics and to provide a favorable efficiency. For development of the turbine type impeller, a concept of the alterative design was for the impeller blades to transmit fully energy. This impeller has shrouds structurally and was named “closed impeller”. For baffled vessels agitated by the closed impellers, the internal liquid flow as well as the bulk liquid flow were examined to be analyzed for energy consideration. The closed impeller being modified, its internal flow was observed to be appreciably smooth along the blade surfaces. In evaluation in terms of hydraulic and energetic efficiencies indicating the phenomenon in the impeller swept region and that in the rest, respectively, the closed impellers were demonstrated to have improved power characteristics as an increased transmission and consequent uniformized dissipation.

Mixing of medium viscosity liquids in a stirred tank with fractal impeller

Mixing of viscous liquids in a stirred tank is a daunting task. The present paper explores the possibility of using a fractal impeller for mixing of viscous liquids in a stirred tank. The analysis includes power consumptions characteristics, mixing characteristics and the flow patterns in the stirred tank. Ultrasonic velocity profiler (UVP) was used to measure the local velocities in the stirred tank. Fractal impeller found to exhibit different power consumption characteristics than known for conventional impellers. For the range of viscosities 0.58–0.192 Pa s, mixing time found to be directly proportional to the power consumption per unit mass. The normalised mean radial velocity profiles were found to be independent of fluid viscosities studied in the present work.

Design and Analysis of Airfoil-Shaped Impeller Blades of Centrifugal Pump

This paper deals with a comparative study of the outlet pressure-energy between a conventional and normal blade impeller and an airfoil-shaped blade impeller of a centrifugal pump. Although the volute casing is an important component along with an impeller [1], the present comparative analysis makes the volute casing redundant to the study, hence neglected. All centrifugal pumps are usually designed and manufactured using backward swept blades with equal camber on the top and bottom sides. An increased camber on the top side is an ideal trait for a lift generating airfoil. The purpose is to implement the principle of lift generation of airfoil for centrifugal pumps. As a result, a local suction side and pressure side can be visualized using CFX-post processor. The 3D analysis of such a centrifugal pump impeller is designed in SOLIDWORKS® and analyzed using ANSYS® CFX. The SST (Menter’s Shear Stress Transport) model is used as it combines both the k-ω and k-ε turbulence models.

Design of Stirrer Impeller with Variable Operational Speed for a Food Waste Homogenizer

A conceptualized impeller called KIA is designed for impact agitation of food waste in a homogenizer. A comparative analysis of the performance of KIA is made with three conventional impeller types, Rushton, Anchor, and Pitched Blade. Solid–liquid mixing of a moisture-rich food waste is simulated under various operational speeds, in order to compare the dispersions and thermal distributions at homogenous slurry conditions. Using SolidWorks, the design of the impellers employs an Application Programming Interface (API) which acts as the canvas for creating a graphical user interface (GUI )for automation of its assembly. A parametric analysis of the homogenizer, at varying operational speeds, enables the estimation of the critical speed of the mixing shaft diameter and the deflection under numerous mixing conditions and impeller configurations. The numerical simulation of the moisture-rich food waste (approximated as a Newtonian carrot–orange soup) is performed with ANSYS CFX v.15.0. The velocity and temperature field distribution of the homogenizer for various impeller rotational speeds are analyzed. It is anticipated that the developed model will help in the selection of a suitable impeller for efficient mixing of food waste in the homogenizer.

Pumping Unit Power-Density Improvement by Application of Counter-Rotating Impellers Design

In many industrial areas, downsizing the pumping system is a decisive aim of the designers. The reasons could be multiple means; in a single-stage pump, increasing the power density of the pump means actually reducing the production costs. The main goal of this study was the comparison in terms of power density of a conventionally designed single-stage pump with a novel design concept based on the counter-rotating (CR) principle. In order to simplify the experimental investigations for the present study, the volute geometry was fixed instead of reducing the pump outflow diameters for a fixed design point. The energy concentration was then increased by raising the developed hydraulic power within the same envelope. The design of the impellers was carried out with an in-house design tool, based on inverse design method. Numerical results highlight the advantageousness of the new layout, in terms of power concentration, compared to the conventional impeller. Numerical predictions are also in significant agreement with the experimental investigation results, obtained in a specifically developed CR motors test rig. The experimental optimization of the rotational speed ratio of the CR impellers has shown the possibility to further increase the head in off-design condition and thereby the pump power density.

Rotordynamic Force Prediction of a Shrouded Centrifugal Pump Impeller—Part I: Numerical Analysis

Computational fluid dynamics (CFD) is employed to calculate the fluid-induced forces in the leakage path of an incompressible shrouded centrifugal impeller. Numerical solutions of the whirling shrouded impeller at the centered position provide the radial and tangential impedances that can be modeled as a quadratic function of whirl frequency. Calculated impedance results on a face-seal impeller can be modeled with a second-order function of whirl frequency and the predicted rotordynamic coefficients show reasonable agreement with the test results by Bolleter et al. (1989, “Hydraulic Interaction and Excitation Forces of High Head Pump Impellers,””Pumping Machinery: Third Joint ASCE/ASME Mechanics Conference, La Jolla, CA, pp. 187–194). However, the present analysis shows that the calculated impedance curves for a conventional wear-ring seal impeller using three-dimensional (3D) numerical approach have “bumps” and “dips” which can be observed in the bulk flow analysis of impeller models by Childs (1989, “Fluid-Structure Interaction Forces at Pump Impeller-Shroud Surfaces for Rotordynamic Calculations,” J. Vib., Acoust., Stress, Reliab. Des., 111(3), pp. 216–225). After reviewing previous predictions and experiments that showed the bump and dip in the computed and measured forces, the current study focuses on the estimation of the possible sources causing the peaks. The selected possible sources are inlet tangential velocity at the shroud entrance, flow rate of primary passage, shape of the shroud leakage path, and seal clearance. The fluid-induced forces of the conventional wear-ring seal impeller are calculated and analyses on the effects of these variables are provided.

Suspended Droplet Polymerization in an Unstable, Vibrating Shallow-Bed Reactor

A piston-driven shallow bed reactor (5.9 cm high) was used to conduct suspension polymerization under unstable flow conditions, which produced excellent mixing and droplet breakage. The instability started at the air/solution interface and carried through to the complete solution volume. The liquid interfacial instability described in the classic paper on this subject [T. B. Benjamin and F. Ursell, Proc. R. Soc. London A, Math. Phys. Sci. 1954, 225, 505–515] leads to a set of Mathieu equations, which map out regions of instability to guide the selection of amplitude and frequency. The current work operated exclusively in the half-frequency region of the instability curves. The performance was compared with a conventional impeller reactor. Both reactors operated in the power range of 0.3–20 W/kg. Only the piston reactor was capable of producing microparticles smaller than the Komolgorov scale, for the amine-initiated Michael addition of a trithiol to a triacrylate. The Hinze breakage model was used to correlate the mean particle sizes for impeller work. The pulsed-piston reactor particle size data required testing sub-Kolmogorov models to fit the mean particle size, and a viscous model [R. Shinnar, J. Fluid Mech. 1961, 10, 259–275] gave a good fit. Reactions conducted in the stable region of the Mathieu equation were highly ineffective.

Effect of number of branches on the performance of fractal impeller in a stirred tank: Mixing and hydrodynamics

Number of blades of an impeller, impeller design and its positioning in a stirred tank is known to affect the mixing in a stirred tank reactor. The extent of non-uniformity in mixing from conventional impellers can be reduced significantly using a space-filling impeller like a fractal impeller. In this work, we report the effect of number of branches (and hence the number of blades) of fractal impeller on power consumption, mixing and hydrodynamics. Velocity measurements were carried out using ultrasonic velocity profiler (UVP). Measurements showed that the performance of fractal impeller with different configuration is equivalent, however, better than standard impellers in terms of mixing achieved per unit power consumption. No significant difference was observed in radial and axial mean velocity profiles for three different configurations. However, the tangential velocity was found higher for four branches than two and three branches FI. Two distinct circulation loops were observed in upper as well as lower half of the vessel in r–z plane. Strong tangential flow throughout the baffled vessel helps to achieve good mixing even at low rotational speeds.

Influence of low-specific speed pump modifications on stability of Y-Q curve

Contribution is focused on modification of low-specific speed pump impellers with respect to stability of their Y-Q curves (i.e. head curves). The design modifications are driven by analysis of the dissipated power. First, dissipated power is evaluated by CFD software in individual working parts of the pump and then its dependence on flow rate is investigated. Pressure fields within the pump are also carefully examined. Special attention is paid to impellers and configuration of the blade channels and recirculating channels. Results point to significant influence of the proper inflow to recirculating channels and also to role of the volute, which is more pronounced than in conventional impellers. All integral characteristics from CFD simulations are verified experimentally.

Numerical investigation & comparison of a tandem-bladed turbocharger centrifugal compressor stage with conventional design

Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-bladed centrifugal compressor are presented in comparison to a conventional compressor. Stage characteristics are explored for various tip clearance levels, axial spacings and circumferential clockings. Conventional impeller was modified to tandem-bladed design with no modifications in backsweep angle, meridional gas passage and camber distributions in order to have a true comparison with conventional design. Performance degradation is observed for both the conventional and tandem designs with increase in tip clearance. Linear-equation models for correlating stage characteristics with tip clearance are proposed. Comparing two designs, it is clearly evident that the conventional design shows better performance at moderate flow rates. However; near choke flow, tandem design gives better results primarily because of the increase in throat area. Surge point flow rate also seems to drop for tandem compressor resulting in increased range of operation.

Performance Evaluation of Tandem Bladed Centrifugal Compressor

A tandem-bladed centrifugal compressor which may have better performance than the conventional designs has not yet been studied for its potential turbocharger application. In addition, no numerical study of the entire stage (including tandem impeller and volute) has been performed to fully exploit the benefits of such design with variation in axial clearance levels, circumferential clocking fractions, blade geometries/angles, number of inducer blades and the thickness of inducer blades. This paper presents a thorough experimental and numerical study on the performance of a moderate pressure ratio, unshrouded, tandem-bladed centrifugal compressor in comparison to a conventional compressor of commercial use in china for turbocharger application. The characteristics of a tandem compressor are investigated and compared for various parameters. Conventional impeller was first modified into tandem-bladed design but with no modifications in backsweep angle, meridional gas passage and camber distributions in order to have a true comparison. The tandem design was further modified and investigated by (1) narrowing down the meridional gas passage, (2) using straight or concave leading edge of exducer, (3) reducing the thickness and (4) the number of inducer blades. CFD and experimental results were found to be in good agreement. The study reveals a shift of surge point towards lower mass flow rate in all cases of tandem designs. A maximum of 25% increase in the range of operation is observed. All in all there is little influence of the different circumferential clocking fractions and axial spacings of the inducer. Computational investigations of a modified tandem compressor with 20% reduction in inducer thickness have shown better performance than the conventional design. Use of fourteen inducer blades with reduced blade thickness can further enhance the performance.

Numerical Simulation and Orthogonal Design Method Research Effect of Splitter Blade's Main Geometry Factors on the Performance of Pump as Turbine

In order to research the effect of splitter blades main geometry factors on the performance of pump as turbine, the L9(34)orthogonal design scheme has been developed based on four factors which contain the blades circumferential biasing degrees, the outlet deflection angle, the outlet diameter and the number of blade. According to this design scheme, numerical simulation of centrifugal pump (ns48) as turbine has been done. By range analysis of computational results, the best design scheme of splitter blades and the level of each factor for the primary and secondary order of turbine efficiency (the outlet deflection angle, the outlet diameter, the number of blade, and blades circumferentially biasing degrees) are obtained. The internal characteristics analysis was done on centrifugal pump (ns48) as turbine at its optimal operating conditions. The results shows, compared with conventional impeller, that the internal velocity and pressure field distribution using the design scheme of composite impeller is more reasonable.

A novel impeller configuration to improve fungal physiology performance and energy conservation for cephalosporin C production

Effects of impeller configuration on fungal physiology and cephalosporin C production were investigated by an industrial strain Acremonium chrysogenum in a 12m3 bioreactor equipped with conventional and novel impeller configuration, respectively. The cell growth and oxygen uptake rate (OUR) profiles were little affected by the impeller configurations. However, differing impeller combinations significantly affected the morphology, which in turn influenced cephalosporin C production. Under the novel impeller configuration, the production of cephalosporin C was 10% higher and an excessive amount of dispersed arthrospores was also observed. Computational fluid dynamics (CFD) simulation further revealed that poor mass and energy exchange as well as inhomogeneous environment existed in the bioreactor equipped with conventional impeller configuration. For equivalent power dissipation, the volume oxygen transfer coefficient (KLa) could be enhanced by 15% compared with that of conventional impeller configuration. Power consumption was dramatically decreased by 25% by using novel impeller configuration.

Structural Optimization Design and Analysis of Impeller Based on Comprehensive Performance

Based on the product integrated design theory, the key part of large-scale centrifugal compressor — the impeller is researched. Structural optimization design and analysis on the conventional impeller is completed by the finite element method, and then the strength characteristic and the distortion tendency of the impeller under the action of the inertial force are obtained, the stress distribution of the impeller assembly structure after reaching stability in the assembly process is also obtained. The correctness and effectiveness of structural optimization design of the impeller are verified by the analysis results, and the comprehensive performance of the impeller has been greatly improved. The results above are also laid the foundation for optimization design and innovative design for other mechanical key components.