Impeller Velocity Research Articles

Analysis of Stress Characteristics of a Vertical Centrifugal Pump Based on Fluid-Structure Interaction

Vertical centrifugal pumps play a crucial role in numerous water conservancy projects. However, their continuous operation can lead to the development of cracks or even fractures in some centrifugal pump blades, resulting in a substantial adverse impact on the operation of the pumping station unit and jeopardizing safe production. This study employs the fluid-structure interaction method to comprehensively investigate the modal characteristics of the impeller, both in an air environment and immersed in water. Furthermore, the analysis of static and dynamic stress attributes is conducted. The natural frequency of the impeller when submerged in water is significantly lower than its frequency in an air medium, typically accounting for approximately 0.35 to 0.46 of the air-based natural frequency. There are conspicuous stress concentrations at specific locations within the system, specifically at the rounded corners of the blade back exit edge, the impeller front cover, the middle of the blade inlet edge, and the junction where the blade interfaces with the front and back cover. It is crucial to underscore that when the system operates under high-flow or low-flow conditions, there is a pronounced stress concentration at the interface between the impeller and the rear cover plate. Any deviation from the intended design conditions results in an escalation of equivalent stress levels. Through dynamic stress calculations during a single rotational cycle of the impeller, it is discerned that the cyclic nature of stress at the point of maximum stress is primarily influenced by the number of blades and the rotational velocity of impeller. This research carries significant implications for effectively mitigating blade fractures and cyclic fatigue damage, thereby enhancing the operational reliability of vertical centrifugal pumps in water conservancy applications.

Third Generation Lactic Acid Production by Lactobacillus pentosus from the Macroalgae Kappaphycus alvarezii Hydrolysates

The evaluation of macroalgae as a new raw material for diverse bioprocesses is of great interest due to their fast growth rate and low environmental impact. Lactic acid has a high value in the bio-based industry and is mainly produced via fermentation. The anaerobic lactic acid fermentation of Kappaphycus alvarezii hydrolysates using the high-producing strain Lactobacillus pentosus was evaluated for detoxified and non-treated hydrolysates prepared from concentrated algal biomass and dilute acid solution mixtures. A novel hydrolysate detoxification procedure, combining activated charcoal and over-liming, for 5-hydroxymethylfurfural (HMF) removal was used. L. pentosus was found to successfully ferment detoxified and untreated hydrolysates produced in up to 30% and 20% w/v solutions, respectively. Significant production rates (1.88 g/L.h) and short lag phases were achieved in bioreactor fermentation operating at 37 °C and pH 6 with 150 rpm impeller velocity. A 0.94 g/g yield from fermentable sugars (galactose and glucose) was achieved, indicating that K. alvarezii could be used as a raw material for lactic acid production, within the context of Third Generation (3G) biorefinery.

Production of metallic iron nanoparticles in a baffled stirred tank reactor: Optimization via computational fluid dynamics simulation

The aim of this work is to optimize iron nanoparticle production in stirred tank reactors equipped with two classical impellers: Rushton and four-pitched blade turbines, which are largely used in batch industrial synthesis and efficient scale-up. The main operative parameters of nanoparticle synthesis are the precursor initial concentration, reducing agent/precursor molar ratio, impeller–tank clearance, and impeller rotational velocity. These parameters were varied during the synthesis to find the optimal operating values based on the Fe(0) (%) production, zeta potential, particle size distribution, and powder X-ray diffraction pattern obtained. We found that the optimal operating conditions for nanoparticle production were an impeller velocity of 1500rpm, initial iron precursor concentration of 20mM, molar ratio of reducing agent to iron precursor of 3mol/mol, and impeller clearance of 0.25 and 0.4 times the vessel diameter for Rushton and four-pitched blade impellers, respectively. Setting these conditions achieved a total conversion of 0.94–0.98 and yielded a product with a unimodal size distribution and average diameters in the range 30–50nm. The computational fluid dynamics results agreed with the expectations, and the obtained mixing Damkohler numbers show that the process is mixed controlled.

Investigation on inlet recirculation characteristics of double suction centrifugal compressor with unsymmetrical inlet

The inlet recirculation characteristics of double suction centrifugal compressor with unsymmetrical inlet structures were studied in numerical method, mainly focused on three issues including the amounts and differences of the inlet recirculation in different working conditions, the circumferential non-uniform distributions of the inlet recirculation, the recirculation velocity distributions of the upstream slot of the rear impeller. The results show that there are some differences between the recirculation of the front impeller and that of the rear impeller in whole working conditions. In design speed, the recirculation flow rate of the rear impeller is larger than that of the front impeller in the large flow range, but in the small flow range, the recirculation flow rate of the rear impeller is smaller than that of the front impeller. In different working conditions, the recirculation velocity distributions of the front and rear impeller are non-uniform along the circumferential direction and their non-uniform extents are quite different. The circumferential non-uniform extent of the recirculation velocity varies with the working conditions change. The circumferential non-uniform extent of the recirculation velocity of front impeller and its distribution are determined by the static pressure distribution of the front impeller, but that of the rear impeller is decided by the coupling effects of the inlet flow distortion of the rear impeller, the circumferential unsymmetrical distribution of the upstream slot and the asymmetric structure of the volute. In the design flow and small flow conditions, the recirculation velocities at different circumferential positions of the mean line of the upstream slot cross-section of the rear impeller are quite different, and the recirculation velocities distribution forms at both sides of the mean line are different. The recirculation velocity distributions in the cross-section of the upstream slot depend on the static pressure distributions in the intake duct.

Influence of the addition sequence of PVA-fibers and water on mixing and rheological behavior of mortars

ABSTRACT The mixing process of fiber-containing cementitious suspensions is a crucial factor to obtaining a good dispersion of fibers and guarantee adequate mechanical performance of the hardened products. The addition of fibers into the suspension causes reduction of the fluidity of the system due to factors inherent to the fibers, the matrix and their interaction. During mixing, these interactions make dispersion and homogenization processes more difficult due to the formation of fibers - particles agglomerates. Conventional techniques to assess workability of mortars are inadequate to evaluate the rheological behavior of fiber-reinforced systems, in which parameters like viscosity and yield stress are not completely taken into account. Therefore, this work employs rotational rheometry to evaluate the influence of fiber and water addition sequences on mixing and rheological behavior of mortars containing Polyvinyl Alcohol (PVA) fibers. Constant test parameters were: mixing time of 317s; impeller velocity 126.5 rpm; water flow 128g/s. A constant mix design was used with a water content of 16%wt, and a 0.2%vol of fibers were added to the reference composition. Four mixing sequences were studied: S1 and S2 are based on the addition of fibers at different stages of the mixing process; while in S3 and S4 not only the fibers are added at different stages, but also the water addition is performed in two steps (25% first and 75% latter).Results showed that it is possible to optimize the mixing step of fiber-containing systems by changing the moment of fiber addition into the mixture. The introduction of fibers after mixing the dry mortar with water, when it already had achieved its fluidity point, demanded a lower mixing effort and produced a more flowable material.

Substantiation of parameters and estimation of strength for basic structural units of axial tunnel fan

The authors determine basic parameters for elements of axial tunnel fan VO-21(t) with direct annular diffuser. The algorithm is proposed for calculating aerodynamic parameters of the axial fan using ANSYS CFX software, which allows modeling, computation and analysis of effect exerted by various parameters of the fan air section on the fan aerodynamics. It is found that it is possible to reduce the fan impeller metal consumption and inertia moment by redistributing normal inertia force of blades from the boss to the disks. The admissible impeller velocity is related with the thickness of the impeller disks.

Design, Numerical Analysis and Manufacture of Radial Pump Impellers with Various Blade Geometries

Impeller blade geometry plays a dominant role on the velocity profile of the fluid flowing through the pump. Although blades’ design is based on fluid dynamics considerations, it is sometimes limited by the available manufacturing methods, due to the required complexity in the geometry. In the present paper, the evolution of the velocity field in the blade passages of two anew designed radial pump impellers with different curvature and outlet blade angle is examined in order to verify their optimum design and characteristics. The numerical solution of the discrete three-dimensional, incompressible Navier-Stokes equations over a structured grid is accomplished with a commercial CFD finite-volume code. For each impeller, pressure and relative velocity distributions are presented and analyzed. The flow patterns in the blade passages are monitored and the mechanisms that dominate the flow field in the different regions of the impeller geometry are discussed. Furthermore, the new impellers that were tested numerically are manufactured in a CNC Milling Centre under the operation of sculptured surfaces; thus the feasibility of manufacturing the improved geometries is exhibited.

Coupling Between Velocities in a Radial Supercharger

We have analyzed the velocities of the medium and impeller in a radial supercharger with consideration of the Coriolis acceleration. We have derived an expression for determining the angular velocity of the medium that differs from the angular velocity of the impeller. Dependences have been obtained to determine the velocity of the medium at the exit from the impeller on the inclination angle of the supercharger blades and their coupling with the circumferential velocity of the impeller in the absence of energy losses. Graphical dependences of velocities on the inclination angle of the blades at different ratios of inside radius to outside radius have been constructed.

Influence of light flux and hydrodynamic flow regime on the photoreduction of Cr(VI) on the CuAl2O4/TiO2 hetero-junction

The reduction of HCrO4− to trivalent state by photo-assisted mediated CuAl2O4/TiO2 catalysis was investigated in a baffled stirred reactor. The spinel CuAl2O4 shows a chemical stability in acidic media. Its conduction band lies below the potential of HCrO4−/Cr3+ leading to a spontaneous reduction under visible light via TiO2. Both hexavalent chromium conversion and salicylic acid oxidation concomitantly occur in less than ∼1h, and obey to an apparent first order kinetic according to the Langmuir–Hinshelwood model. Salicylic acid removal rate is slower compared to chromium conversion. The adsorption process is strongly multi-layered following a Freundlich isotherm. The influence of Rushton impellers on the photocatalytic reaction was studied. The best performance is achieved by a six-blade Rushton at turbulent-flow regime, involving interaction between flow around rotating impeller blades and the fixed baffles. The impeller dimensions reveal significant changes on the photocatalytic activity. Both of increased impeller velocity and incident light flux promoted Cr(VI) photoreduction.

Baker's Yeast Behavior during Vacuum Agitated Contact Drying

AbstractDrying is considered as an intensive operation that consumes large quantities of energy. Usually, baker's yeast is obtained using freeze drying or fluidized‐bed drying, both of which are considered as expensive technologies. So, exploring other techniques such as contact drying could limit this disadvantage. In addition, no work dealing with contact drying of baker's yeast has been accomplished yet. Therefore, here, the behavior of baker's yeast during vacuum agitated contact drying is presented. The results show that the drying process can be divided into three phases: the pasty phase, the lumpy phase, and the granular phase. The influence of the drying parameters, such as the temperature, the impeller velocity, and the initial mass, was also studied. It was found that the wall temperature and the impeller velocity have a positive effect on the drying kinetics, as their increase allows a reduction in the drying time. Nevertheless, an increase in the pressure level or the initial mass of the product caused the drying time to increase.

Design and Study on Mortar Pump's Impeller Based on Bezier and Mechanical Mechanics

This article determined the blade profile by using the Bezier Curve.Start with ensuring the blade Angle and the blade profile , this paper designed a new impeller, avoided the appearance of the "S" shape of the blade profile, it ensured the smoothness of the blade profile. Compared with the traditional design of the impeller,Combined with mechanical mechanics software CFX, this article took a numerical calculation and simulation about the impeller and the hydrographic basin , compared the two impeller's residuals, velocity vector,pressure distribution and pressure water room's static pressure distribution,analysed and evaluated the performance of the pump.

Transient internal characteristic study of a centrifugal pump during startup process

The transient process of a centrifugal pump existed in a variety of occasions. There were a lot of researches in the external characteristic in startup process and stopping process, but internal characteristics were less observed and studied. Study of the internal flow field had significant meanings. The performance of a pump could be evaluated and improved by revealing the flow field. In the other hand, the prediction of external characteristic was based on the correct analysis of the internal flow. In this paper, theoretical method and numerical simulation were used to study the internal characteristic of a centrifugal pump. The theoretical study showed that the relative flow in an impeller was composed of homogeneous flow and axial vortex flow. The vortex intensity was mainly determined by angular velocity of impeller, flow channel width and blade curvature. In order to get the internal flow field and observe the evolution of transient internal flow in the impeller, Computational Fluid Dynamics(CFD) were used to study the three-dimensional unsteady incompressible viscous flows in a centrifugal pump during starting period. The Dynamic Mesh (DM) method with non-conformal grid boundaries was applied to get the external characteristic and internal flow field. The simulate model included three pumps with different blade numbers and the same blade curvature. The relative velocity vector showed that there was a big axial vortex in impeller channel. At the beginning, the vortex was raised in the pressure side of the impeller outlet and with time went on, it shifted to the middle flow channel of the impeller and the vortex intensity increased. When the speed and flow rate reached a definite value, the influence of the axial vortex began to get smaller. The vortex developed faster when the flow channel got narrower. Due to the evolution of axial vortex, the slip factor during starting period was smaller than that in quasi-steady condition. As a result, transient head was lower than quasi-steady head in startup process.

3-D Numerical Simulation on Unsteady Turbulent Flow of Rotational Flow Self-Priming Pump

The three-dimensional unsteady turbulent flow of rotational flow self-priming pump was simulated by using Reynolds time-averaged N-S equations and the standard k-ε turbulent model, sliding mesh model of static-dynamic coupled models and SIMPLE arithmetic. The static pressure distribution of the pump central rotative surface and relative velocity of the impeller central rotative surface in a complete application cycle were analyzed. The rule of instantaneous head in a impeller channel cycle was studied, and the positions of maximal head and minimal head were analyzed. It revealed that the unsteady method can truly simulate the changes of the rotational flow self-priming pump interior flow, and the unsteady characteristic of interior flow in rotational flow self-priming pump is obvious and it changes as the relative position of impeller and volute change. The change is periodical, and its frequency is relate to the impeller number and the rotate speed of the pump.

Numerical and experimental comparison of the vaned diffuser interaction inside the impeller velocity field of a centrifugal pump

The paper refers to the analysis of interactions between the impeller and the vaned diffuser based on the air model of a radial flow pump. The study deals with a numerical simulation of the flow for a full 360° entire impeller and diffuser. The task is carried out closely under the design operating conditions and for one particular position of the impeller blade with respect to the diffuser frame. Among all the results, the focus is mainly on the flow pattern at the exit part inside the impeller facing the diffuser vanes. The results are compared to the available PIV measurements.

Impact of Fan Gap Flow on the Centrifugal Impeller Aerodynamics

The effect of a gap between an inlet duct and a rotating impeller in a centrifugal fan is often neglected in the impeller design calculations or design-related computational fluid dynamics (CFD) analyses. This leads to an arbitrary determination of the gap size for the final fan configuration. Since the gap guides the volute flow back to the impeller flow field near the shroud high-curvature turning area, the low-momentum jet formed by the gap flow could prevent local flow from separation, reducing the local flow turning losses. However, this jet flow has enlarged flow separation in the blade passage, producing shedding vorticity in the downstream passage-flow. The passage-flow separation and the downstream volute flow, which is also affected by the passage-flow separation, have a higher impact on flow losses than the blade leading edge separation. If the gap size is not selected carefully, the combined effect of the passage-flow separation and downstream volute flow losses reduces the fan’s overall performance between 2% points and 5% points as demonstrated in the current study. In this paper, local impeller velocity distributions obtained from both design-CFD and analysis-CFD calculations are compared along the shroud from the gap to the blade trailing edge. The overall impeller flow fields with and without the gap and volute effects are also compared and discussed based on the CFD solutions. Finally, an example of controlling the gap effect is shown.

3D Numerical Simulation of Turbulent Flow in Postpositional Bulb Tubular Pump

The computational fluid dynamics(CFD) method is used to investigate the three-dimensional(3D) flow fields in a postpositional bulb tubular pump.In the numerical modeling,RNG k-e turbulence model and SIMPLE algorism are employed.The velocity distribution and pressure of vertical plane at BEP are analyzed,as well as the velocity of impeller outlet,guide-vane outlet and the tail of the bulb.The focus is on the static pressure distribution of blade pressure surface and suction surface as well as the relative velocity distribution near the airfoil cross-sections under different conditions(the designed condition,large and small flow rates conditions).The hydraulic losses of various components of tubular pump are also calculated,and it is found that the guide vane and bulb unit occupy major share in hydraulic losses.The comparison between the mathematical model calculation result and the model-tested pump performance data shows that the calculation result agrees well with the test data in nearby the high efficiency area;however,deviation exists between them under large flow and small flow working conditions.Using CFD method to simulate the internal flow field of tubular pump can provide the basis for further design optimization of the tubular pump.

Super Fine Powderization of Korean Ginseng Using Low Temperature Turbo Mill

It is investigated whether ginseng can be milled into super fine powder below 50μm, changing the circumferential velocity of impeller of a turbo mill(100, 110 and 120m/s). The mean particle size is 113.3μm in control but is decreased abruptly into 11.9μm at 120m/s. The largest particle diameter at 97% of volume distribution is reduced into below 32μm at 120m/s from below 725μm at control. The particle size distribution between d(0.1) and d(0.9) is 334μm at control, but is decreased into less than 26μm in all conditions after milling. It shows that ginseng can be milled into super fine powder by the turbo mill, which has the narrow particle size distribution.

Estimation of crystallization kinetics for an organic fine chemical using a modified continuous cooling mixed suspension mixed product removal (MSMPR) crystallizer

The crystallization kinetics of an important organic fine chemical was determined using a modified laboratory scale continuous cooling mixed suspension mixed product removal (MSMPR) crystallizer with a product recycle loop designed for use with limited quantities of available material. A convenient method of monitoring steady state in the MSMPR using lasentec focussed beam reflectance measurement (FBRM) is also described. The effect of supersaturation, suspension density of the crystallizer content, impeller velocity (turnover time) and configuration on the growth and nucleation rates was studied. An observed deviation from the McCabe Δ L law for small crystal sizes was attributed to either size-dependent growth (SDG) or growth rate dispersion (GRD) mechanisms and hence complicated the estimation of growth and nucleation rates. SDG was successfully modelled using a three-parameter exponential SDG model. Growth rates estimated from the SDG model were compared to a GRD model using discrete growth probability distributions.

Influence of the aeration rate on the yields of the biocontrol nematode Heterorhabditis megidis in monoxenic liquid cultures.

The entomopathogenic nematode-bacterium complex Heterorhabditis megidis Photorhabdus luminescens was cultured in 10-1 internal loop bioreactors with marine impellers at aeration rates of 0.3 vvm and 0.7 vvm. Process parameters like impeller velocity and oxygen saturation were controlled at equal set points. The bacterial density was assessed at 24 h. Nematode dauer juveniles (DJ) were then inoculated and the development to adults after 8 days and final DJ yields after 16 days were recorded. The bacterial population density and the nematode inoculum development was variable and was not influenced by the aeration rate. A significant effect on the yield was recorded at the highest aeration rate. This result was confirmed by a direct comparison in two 5-1 internal loop glass bioreactors at 0.3 vvm and 1.0 vvm, which were inoculated with nematode and bacterium pre-cultures from the same flask culture. Possible reasons for the positive correlation between aeration rate and DJ yield are discussed.

Flow Visualization Measurement for Shear Velocity Distribution in the Impeller-Casing Gap of a Centrifugal Blood Pump.

A flow visualization study of a centrifugal blood pump was conducted to find the shear and velocity profiles in the back gap between the impeller and the casing. For a wide range of Reynolds numbers and specific speeds, it was found that high shear exists only in the boundary layers of the moving and stationary walls. The velocity profile was essentially laminar. It was also found that the total thickness of the high shear regions is 0.3-0.6mm for conditions of artificial heart and the thickness is determined only by Reynolds number. Hence, it can be concluded that reducing the impeller velocity is the only way to reduce wall shear stress and that increasing the gap width is not effective.