Impeller Rotational Speed Research Articles

Granular Flow of Corn Stover Particles in a Helical Ribbon Stirred Tank

Abstract The flow characteristics and power consumption of corn stover particles in a helical ribbon stirred tank was investigated in the context of simultaneous saccharification and fermentation of corn stover at high solids loading. It was found that the particles in the tank can be divided into conveyed material and core material according to their flow characteristics. The flow of the former materials was frictional regime and the latter was intermediate flow; the conveyed material avalanched into the core at the top of granular bed. The granular bed dilated when the impeller was rotating, which was beneficial for the entrance of liquid enzyme into the solid phase and for the successful proceeding of the saccharification of the corn stover. The power of granular mixing was linearly proportional to the impeller rotational speed due to the discrete characteristic of the particles and flow dynamics of the conveyed material. The ratio of power consumption to the impeller rotational speed (P/N) was linear proportional to loading ratio and the dimensionless torque (M/mgR) was 0.48. The power consumption increased first and then decreased as the corn stover particles evolved from granular/wet granular to paste/slurry. The maximum power consumption was at 83 % (w/w) moisture content.

Local velocity scaling in T400 vessel agitated by Rushton turbine in a fully turbulent region

The hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV). The experiments were carried out in a fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a Rushton turbine 133 mm in diameter. The velocity fields were measured in the zone in upward flow to the impeller for impeller rotation speeds from 300 rpm to 850 rpm and three liquids of different viscosities (i.e. (i) distilled water, ii) a 28% vol. aqueous solution of glycol, and iii) a 43% vol. aqueous solution of glycol), corresponding to the impeller Reynolds number in the range 50 000 < Re < 189 000. This Re range secures the fully-developed turbulent flow of agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The axial turbulence intensity was found to be in the majority in the range from 0.388 to 0.540, which corresponds to the high level of turbulence intensity.

Integrated modeling to capture the interaction of physiology and fluid dynamics in biopharmaceutical bioreactors

Abstract The performance of a bioreactor is sensitive to local gradients of chemical and physical stimuli. Thus, this work presents a model, which captures spatial heterogeneity and interactions of biotic and abiotic phases in animal cell cultures. A computational fluid dynamics simulation that includes gas-liquid mass transfer and kinetics of carbon dioxide dissolution is developed to capture the variations of environmental parameters. Unstructured modeling is implemented to integrate growth, viability and productivity of cells. While predictive accuracy is valuable, it is important to balance it with computational feasibility. In this work, evolutions of hydrodynamics and cell population are obtained sequentially. The outcome is a deterministic model with extended integration between physical and biological phenomena which is computationally tractable. The model calculates the bioreactor performance as a function of time and process parameters such as impeller rotation speed and gas sparging flow rate, which makes it useful for bioprocess design and scheduling.

Control system of a performance test-bed for frost protection wind machines

Abstract: To test the performance and optimize operational parameters of various frost protection wind machines, a control system of performance test-bed was designed and developed based on Programmable Logic Controller (PLC) and touch screen. The system realized automatic control of operational parameters including hydraulic platform height, impeller rotation speed, depression angle, rotation range and cycle. Field case study results shows that the control accuracy of all the parameters was achieved with the average errors of 2.11 cm for height, 9.5 r/min for impeller rotation speed, 0.83° for pan-tilt rotation range and 0.061 min for rotation cycle. With the control of the test-bed, the performances of various wind machines, such as the distribution of airflow and temperature, and frost protection effect, could be tested under various working conditions, which provide experiment supports for developing wind machines adapted to different conditions with higher frost protection effect. Keywords: frost protection, wind machines, performance test-bed, design, control, PLC DOI: 10.3965/j.ijabe.20160906.1664 Citation: Hu Y G, Liu P, Asante E A, Wu W Y, Li P P. Control system of a performance test-bed for frost protection wind machines. Int J Agric & Biol Eng, 2016; 9(6): 36－43.

Prediction of centrifugal pump performance using energy loss analysis

In this work, a theoretical procedure has been developed to calculate the performance of a centrifugal pump using theoretical and empirical internal and external energy loss equations. These equations were implemented in the prediction program allowing the calculation of head, power and efficiency of the pump for varying input geometries, rotational speeds and fluid properties. The prediction program was tested for two centrifugal pumps of different impeller geometries handling either water or viscous fluids with different viscosities, at varying rotational speeds. Two different experimental rigs with different impeller geometries were used to generate experimental data. In the first rig, one impeller geometry was considered and data were obtained for three rotational speeds. In the second rig two different impellers of different geometries were also tested at different speeds. In both rigs, the centrifugal pump is composed of the two essential elements, namely the impeller and the casing. Good agreement was achieved when both predicted and experimental results were compared for all impeller geometries and rotational speeds considered.

Long-term durability test of axial-flow ventricular assist device under pulsatile flow.

A long-term durability test was conducted on a newly developed axial-flow ventricular assist device (VAD) with hydrodynamic bearings. The mock circulatory loop consisted of a diaphragm pump with a mechanical heart valve, a reservoir, a compliance tank, a resistance valve, and flow paths made of polymer or titanium. The VAD was installed behind the diaphragm pump. The blood analog fluid was a saline solution with added glycerin at a temperature of 37°C. A pulsatile flow was introduced into the VAD over a range of flow rates to realize a positive flow rate and a positive pressure head at a given impeller rotational speed, yielding a flow rate of 5L/min and a pressure of 100mmHg. Pulsatile flow conditions were achieved with the diastolic and systolic flow rates of ~0 and 9.5L/min, respectively, and an average flow rate of ~5L/min at a pulse rate of 72bpm. The VAD operation was judged by not only the rotational speed of the impeller, but also the diastolic, systolic, and average flow rates and the average pressure head of the VAD. The conditions of the mock circulatory loop, including the pulse rate of the diaphragm pump, the fluid temperature, and the fluid viscosity were maintained. Eight VADs were tested with testing periods of 2years, during which they were continuously in operation. The VAD performance factors, including the power consumption and the vibration characteristics, were kept almost constant. The long-term durability of the developed VAD was successfully demonstrated.

Numerical evaluation of mass transfer coefficient in stirred tank reactors with non-Newtonian fluid

In fermentation processes, a constant supply of oxygen is fundamental for cell growth. The supply rate is controlled by the volumetric mass transfer coefficient. The literature reports few numerical studies evaluating the volumetric mass transfer coefficient for aerated systems with non-Newtonian fluids in stirred tanks. The aim of this work was to undertake a numerical study of the main hydrodynamic and mass transfer parameters, including average gas hold-up, and power number. Xanthan gum solutions were used to simulated. The simulations were performed with different impeller rotational speeds (600 to 1000 revolution per minute) and specific gas flow rates (0.4 to 1.2 volume of gas per volume of liquid per minute), adopting an Euler-Euler approach and assuming uniform spherical bubbles. The turbulence was simulated with k−e turbulence model and sst shear stress transport turbulent model. The numerical results were compared with experimental values available in the literature. The results showed good agreement between the numerical and experimental values of gas hold-up, power number, and volumetric mass transfer coefficient. The sst shear stress transport turbulence model provided better results, compared to the standard k−e model, for simulation of volumetric mass transfer coefficient in a non-Newtonian fluid under the conditions used. Simulations for uniform bubbles with 3 millimeters diameter gave mass transfer coefficient values that were close to the experimental data.

Predicting breakage of high aspect ratio particles in an agitated bed using the Discrete Element Method

Predicting particle breakage is critical for the control of particle size in some bulk solids handling processes, such as those found in the pharmaceutical, food, consumer product, and mineral processing industries. This article presents a computational study of the breakage of high aspect ratio particles subject to mechanical agitation using the Discrete Element Method (DEM), in which a particle, represented by a string of bonded spheres, breaks at the center of a bond where the tensile or shear stress exceeds the material strength. The numerical model is validated using experimental results from the breakage of blackboard chalk sticks subject to uniaxial compression in a cylindrical container. The validated model is used to investigate particle breakage when agitated by rotating blades, which is encountered in a range of pharmaceutical processes, such as agitated filter drying, rotary tablet press feeding, and powder blending. The simulation results show that the breakage rate, that is the rate of particle size reduction (or the rate of fragment mass increase), increases as the applied pressure, impeller rotational speed, particle-particle friction, or particle-equipment friction increases. However, the extent of breakage per impeller revolution is independent of impeller rotational speed. Most importantly, it is found that the extent of particle breakage is a function of the work performed on the material, and the parameters in this function depend on the particle-particle and particle-wall friction coefficients. Large friction coefficients enable the input energy to break the particles more efficiently.

Design of stirred digester with optimization of energy and power consumption

The goal of the present study was to design a new stirred digester according to laboratory experiments. For this purpose, amount of methane produced from co‐digestion of municipal waste, kitchen waste, and cow manure in different treatments was measured in laboratory conditions for 37°C. The substrate characteristics such as both total and volatile solids, pH, EC, amount of total carbon, nitrogen, phosphorus, potassium, and sulfate which can manage the methane production were measured. The results showed that the amounts of these characteristics were in suitable ranges for biogas production. The laboratory experiment results were then used to design an anaerobic digester for single‐family homes based on energy efficiency and mixing cost. As a result, the digester diameter, digester height, slurry height, baffle width, impeller diameter, blade width, blade length, and volume of designed stirred digester were determined as 57, 90, 60, 4.75, 25, 4, 10 cm, and 229 L, respectively. Furthermore, pitched blade turbine with six blades at 45° for speed of 300 rpm not only required a low power but also produced a high torque. Therefore, while the designed biogas plant consumes low energy, it has high mixing cost.Nowadays, the researchers in bio‐system engineering focus on the designing biogas plant according to the direct relation among the power, torque, and energy. The novelty of the article is not only an evaluation of main substrate characteristics on methane production, but also design a new digester with high methane content at suitable pressure based on the best relation among the equipment dimensions of digester determined using shape factors. Furthermore study of impeller types and rotation speeds for providing high torque in low power and reducing energy consumption indirectly, and uses rule of thumb for power consumption to determine the best impeller type and rotation speed. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 104–110, 2017

Effects of processing parameters and blade patterns on continuous pharmaceutical powder mixing

The present study summarizes the experimental characterization of a new continuous powder mixer (GCG-70 by Glatt®) using common pharmaceutical ingredients. The powder hold-up and residence time distribution were used to characterize the bulk behavior of the mixer as a function of impeller rotational speed, total throughput (mass flow rate) and blade configuration. The relative standard deviation (RSD), calculated from samples taken at the outlet of the blender, was used to characterize its mixing performance. The hold-up and the mean residence time decreased with increasing impeller rotational speed. The mean centered variance and the number of blade passes increased with increasing impeller rotational speed. The effect of the blade configuration on the mixing dynamics diminished as the rotation rate increased. The hold-up and mean residence time were sensitive enough to demonstrate the effects of blade configurations. The mixing performance, depending on the processing parameters, was found to be between 5% and 10% RSD for 5% w/w active pharmaceutical ingredient (API), and <3% for 30% w/w API. These results showed improvements in the mixing performance when compared to studies of other continuous mixers using similar materials and analytical techniques for quantification.

Coupled Hydraulic and Electronic Regulation of Cross-Flow Turbines in Hydraulic Plants

AbstractThe potential benefit of coupling hydraulic and electronic regulation to maximize the energy production of a cross-flow turbine in hydraulic plants is analyzed and computed with reference to a specific case. Design criteria of the cross-flow turbine inside hydraulic plants are first summarized, along with the use of hydraulic regulation in the case of constant water head and variable discharge. Optimal turbine impeller rotational speed is derived, and traditional as well as innovative systems for electrical regulation are presented. A case study is analyzed to evaluate the potential energy production according to the expected monthly mean flow distribution and two possible choices: CFT1 with the hydraulic regulation, and CFT2 with coupled hydraulic and electric regulations. The return time of capital investment (RCI), computed for both the solutions, showed that the CFT2 solution provides an increment of the total produced energy, along with an increment of approximately 30% of the corresponding R...

Investigation of gas dispersion characteristics in stirred tank and flotation cell using a corrected CFD-PBM quadrature-based moment method approach

In this study, the population balance model (PBM) is coupled with computational fluid dynamics (CFD) to investigate the steady-state bubble size distribution in two types of process equipment namely, a standard Rushton turbine stirred tank reactor and a generic lab-scale flotation cell. The coupling is realized using Fluent 15.07 software, and the numerical model is validated for the stirred tank reactor. The population balance equation (PBE) is solved using the quadrature method of moments (QMOM) technique along with a correction procedure implemented to check and correct invalid moment sets. The breakage and coalescence of bubbles due to turbulence are considered. The breakage rate and daughter size distribution models proposed by Laakkonen et al. (2007) are considered. For modeling coalescence rate, models proposed by Coulaloglou and Tavlarides (1977) are considered. The interaction between the phases is handled by considering the drag model proposed by Lane et al. (2005) while ignoring the other interphase forces. The correction algorithm has been successfully implemented, and improved predictions of gas volume fraction and Sauter mean diameter (SMD, d32) have been observed with a good match between the predictions and experimental measurements. The local SMD predictions are compared against predictions from the past studies and the superiority of the current approach for moderate gassing rates is established. The CFD-PBM approach is then used to study and characterize different flow regimes occurring in a generic mechanical flotation cell at different aeration rates and impeller rotation speeds. Also, power numbers are calculated from torque data and are found to drop considerably with an increase in aeration rate and impeller rotation speed as the flow regime approaches recirculating flow. The predicted SMD for flotation cell indicates that smaller bubbles are concentrated near the high turbulence impeller stream, the lower recirculation region, and close to the tank walls. On the other hand, large bubbles are formed in the upper tank region and are concentrated around the shaft during the flooding, loading, and transition flow regimes. In the future, the corrected QMOM approach will be further extended by implementing kinetic models capable of predicting the flotation rate constant using local bubble size information obtained from CFD-PBM simulations.

Properties of a monopivot centrifugal blood pump manufactured by 3D printing.

An impeller the same geometry as the impeller of a commercial monopivot cardiopulmonary bypass pump was manufactured using 3D printing. The 3D-printed impeller was integrated into the pump casing of the commercially available pump to form a 3D-printed pump model. The surface roughness of the impeller, the hydraulic performance, the axial displacement of the rotating impeller, and the hemolytic properties of the 3D-printed model were measured and compared with those of the commercially available model. Although the surface roughness of the 3D-printed model was significantly larger than that of the commercially available model, the hydraulic performance of the two models almost coincided. The hemolysis level of the 3D-printed model roughly coincided with that of the commercially available model under low-pressure head conditions, but increased greatly under high-pressure head conditions, as a result of the narrow gap between the rotating impeller and the pump casing. The gap became narrow under high-pressure head conditions, because the axial thrust applied to the impeller increased with increasing impeller rotational speed. Moreover, the axial displacement of the rotating impeller was twice that of the commercially available model, confirming that the elastic deformation of the 3D-printed impeller was larger than that of the commercially available impeller. These results suggest that trial models manufactured by 3D printing can reproduce the hydraulic performance of the commercial product. However, both the surface roughness and the deformation of the trial models must be considered to precisely evaluate the hemolytic properties of the model.

CFD Simulation of Gas-Liquid in an Agitated Vessel

Background/Objectives: In chemical industries, understanding of fluid mixing is significant. The objective is to determine optimum conditions of gas-liquid mixing by changing impeller blade's gradient, number of impeller and rotation rate. Methods/Statistical Analysis: In this work, by using a computational fluid dynamic (CFD); Ansys© Fluent software, we simulated numerically a gas-liquid mixing in an agitated vessel equipped with a pitched-blade impeller. In this study, the range of the impeller blade's gradient is between 0° to 90° with three number of impellers; impeller (a), (b) and (c) and the impeller rotation speed rate which is between 90 to 120 rpm are used. Findings: The reconstruction images of the nitrogen gas in the distilled water mixing in the agitated vessel are obtained from the Ansys© simulation. Based on the simulation results, the gradient of blades impeller at 60°, three numbers of impeller (c) and 90 rpm rotation rate are chosen as the optimum condition for well mixing condition for gas nitrogen in the agitated vessel. These three parameters indicated the most appropriate condition for distribution of the nitrogen gas in the agitated vessel. Application/Improvements: This modelling have various applications in optimization and design of a wide range of gas-liquid processes industry where the mixing process will affects about 25% of all process industry operations.

Mass and heat transfer behaviour of catalytic and electrochemical stirred tank reactors employing metallic screens lining as a reaction surface

AbstractLiquid‐solid mass transfer behaviour of a rectangular stirred tank reactor lined with single screens and stacks of closely packed screens was studied in relation to catalytic and electrochemical reactor design by the electrochemical technique. Variables studied were impeller rotation speed, mesh number, and wire diameter of the screen, as well as physical properties of the solution, number of screens per stack, and impeller geometry. The rate of mass transfer increased with increasing impeller rotation speed and decreased with increasing screen mesh number and number of screens per stack. Radial flow turbine impellers produced higher rates of mass transfer than axial flow impellers. The data were correlated by dimensionless mass transfer equations. A comparison between the volumetric mass transfer coefficient at a stirred single‐screen electrode and at a stirred flat plate electrode shows that the volumetric mass transfer coefficient at the single screen is higher than that at the flat plate by a factor ranging from 7.3–22.5, depending on the operating conditions. For screen stacks, the ratio between the stack volumetric mass transfer coefficient and the flat plate value ranges from 2–46 depending on the operating conditions.The importance of the present results in the design and operation of catalytic and electrochemical reactors used to conduct diffusion‐controlled reactions was highlighted. The possibility of using screens as turbulence promoters to enhance the rate of heat transfer between the reactor wall and the surrounding cooling jacket was noted.

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.

Numerical simulation on macro-instability of coupling flow field structure in jet-stirred tank

The velocity field macro-instability (MI) can help to improve the mixing efficiency. In this work, the MI features of flow field induced by jet-stirred coupling action is studied by using computational fluid dynamics (CFD) simulations. The numerical simulation method of jet-stirred model was established based on standard turbulent equations, and the impeller rotation was modeled by means of the Sliding Mesh (SM) technology. The numerical results of test fluid (water) power consumption were compared with the data obtained by power test experiments. The effects of jet flow velocity and impeller speed on MI frequency were analyzed thoroughly. The results show that the calculated values of power consumption agree well with the experiment measured data, which validates the turbulent model, and the flow structure and MI frequency distribution are affected by both impeller speed and jet flow rate. The amplitude of MI frequency increases obviously with the increasing rotation speed of impeller and the eccentric jet rate, and it can be enhanced observably by eccentric jet rate, in condition of comparatively high impeller speed. At this time, the MI phenomenon disappears with the overall chaotic mixing.

Impact of impeller design on high-shear wet granulation

In recent decades, three-blade impellers have been well-established in pharmaceutical high-shear granulation. However, three-blade impellers often require high rotation speeds to initiate product circulation and to provide proper granulation performance. With high rotation speeds much energy is introduced, which is indeed favourable for granule consolidation, however it comes with undesirable thermal stressing and increased granule breakage rates. In order to improve the mixing and granulation behaviour for a more robust process, a new impeller design has been developed that works at lower rotation speeds. The impeller consists of two blades with elongated side wings. In this work, the performance of both impeller designs is intensively studied. Firstly, the mixing behaviour is experimentally investigated in a laboratory mixer (10L in volume) and at production scale (600L). The mixing homogeneity of coloured sugar pellets is examined by the digital image analysis (DIA) for several impeller rotation speeds. In a second study, discrete element method (DEM) simulations are employed to obtain shear forces and force distributions at a single-particle scale. The third study is the comparison of granulation performance using a placebo formulation in the frame of a full factorial design of experiments (DoEs). The mixing investigations show that the two-blade impeller has great potential for scale-up. The DEM simulation confirms that both impeller types investigated apply almost the same shear forces on particles. The granulation performance in the DoE is proven to be better for the two-blade impeller. Larger drive torque is measured, product temperature increases significantly less with reduced thermal stressing, and larger granules are produced. Additionally, particle growth behaviour is more robust as it depends only on the amount of liquid added and is unaffected by the impeller's rotation speed.

Production of emulsion in tank mixer with sieve bottom

This paper presents a unique equipment design which can be used in creating liquid-liquid dispersions, named the sieve emulsification mixer (SEM). SEM consists of a tank equipped with sieve at the bottom, impeller and circulating pump. In built experimental set-up the set of experiments has been performed, which assessed influence of four process parameters: feed flow rate, recirculation flow rate, rotational speed of impeller and processing time. The obtained results prove that with use of SEM it is possible to produce emulsions with droplets of the Sauter mean diameter close to the mesh size (i.e. 20μm), therefore this technology could be a good alternative to membrane-based emulsification processes.

CFD of mixing of multi‐phase flow in a bioreactor using population balance model

Mixing in bioreactors is known to be crucial for achieving efficient mass and heat transfer, both of which thereby impact not only growth of cells but also product quality. In a typical bioreactor, the rate of transport of oxygen from air is the limiting factor. While higher impeller speeds can enhance mixing, they can also cause severe cell damage. Hence, it is crucial to understand the hydrodynamics in a bioreactor to achieve optimal performance. This article presents a novel approach involving use of computational fluid dynamics (CFD) to model the hydrodynamics of an aerated stirred bioreactor for production of a monoclonal antibody therapeutic via mammalian cell culture. This is achieved by estimating the volume averaged mass transfer coefficient (kL a) under varying conditions of the process parameters. The process parameters that have been examined include the impeller rotational speed and the flow rate of the incoming gas through the sparger inlet. To undermine the two-phase flow and turbulence, an Eulerian-Eulerian multiphase model and k-ε turbulence model have been used, respectively. These have further been coupled with population balance model to incorporate the various interphase interactions that lead to coalescence and breakage of bubbles. We have successfully demonstrated the utility of CFD as a tool to predict size distribution of bubbles as a function of process parameters and an efficient approach for obtaining optimized mixing conditions in the reactor. The proposed approach is significantly time and resource efficient when compared to the hit and trial, all experimental approach that is presently used. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:613-628, 2016.