Impeller Rotational Speed Research Articles

Investigation of mechanisms on leading edge vortex generation and suppression in vaned diffuser of a centrifugal compressor

This study numerically investigates the mechanisms for generating and suppressing the leading edge vortex (LEV) in a vaned diffuser of a centrifugal compressor, aiming to enhance the compressor's stable operating range. Detailed analyses focus on the mechanisms of the rotating stall and the initiation process of the LEV. Notably, the end wall contouring method is applied to vaned diffuser to suppress the LEV and improve diffuser stability. The suppression mechanisms of the LEV are examined to deepen the understanding of stability enhancement mechanisms. Results demonstrate that, under stall conditions, the vaned diffuser experiences two-cell rotating stalls moving opposite to the impeller rotation direction, each rotating at approximately 12% of impeller rotation speed. The formation of diffuser stall is attributed to a longitudinal vortex developing from the LEV and causing the passage blockage. The increasing spanwise distortion of leading edge (LE) incidence angles and circumferential distortion of static pressures at the diffuser inlet promote the evolution of the longitudinal vortex from LEV. The end wall contouring of vaned diffuser effectively enhances the compressor's stable operating range by 15.10% and 8.90% toward lower flow rate conditions for machine Mach numbers 1.3 and 1.2, respectively. At near-stall points, the end wall contoured diffuser reduces spanwise distortion of LE incidence angles and circumferential distortion of static pressures at the diffuser inlet, mitigates the LE flow separation and corner separation, suppresses the generation and development of the LEV, delays the onset of rotating stall in vaned diffuser, and thereby improves the stable operating range of centrifugal compressor stage.

The effect of impeller height and rotation speed on the Kambala reactor desulfurization process

To improve the utilization efficiency of desulfurizer in the Kambala reactor liquid iron desulfurization process and prolong the life of the impeller, the height of the impeller and its optimal matching rotation speed are optimized. Through numerical simulation, the mixing effect of different height impellers under different rotation speeds is studied, the movement and distribution modes of desulfurizer particles are analyzed, the pumping capacity and power are calculated, and the influence of impeller height and optimal matching rotation speed on the desulfurization effect has been clarified. The numerical simulation results show that the optimization of impeller height and optimal matching rotation speed can improve the mixing effect. The height of the impeller increases, and its optimal matching rotation speed decreases. Based on the results, in existing models, it is recommended to run at 60 r/min with an impeller height of 800 mm for optimal mixing performance.

Energy dissipation and time–frequency analysis of characteristics induced by vortex breakdown in an axial flow pump

Vortex breakdown in a pump sump is a complex and negative factor for the pump. Different from my previous study that focused mainly on the development process of vortex and its damage to the pump, this paper is from a new perspective that studies the energy dissipation and time–frequency characteristics induced by vortex breakdown. The tested data of pressure and velocity in the process of vortex breakdown were obtained by the model. Considering the gas–liquid two-phase flow of the vortices, a new numerical simulation approach is conducted and verified. The results show that the development rules of vortex breakdown reveal that the breakdown is initiated near the blade. The residual disturbance in the flow field continues to propagate after vortex breakdown, inducing unstable flow inside the runner and causing additional energy dissipation. The time–frequency characteristics induced by vortex breakdown indicated that the runner rotation speed has a significant effect on the vortex breakdown. The frequency of vortex breakdown is relatively small under high-speed rotation. Through discussion, it can be concluded that in order to reduce the harm of vortex breakdown, it can take measures such as controlling the impeller rotation speed, stalling anti-vortex measures, and adjusting operating conditions.

Effect of inside Surface Baffle Conditions on Just Drawdown Impeller Rotational Speed

The effect of inside surface baffle installation conditions on the minimum impeller rotational speed for just the drawdown of floating solid NJD was investigated. The inside surface baffle condition is the condition in which a partial baffle is placed with a clearance between the baffle and the vessel wall. In this study, a baffle with an insertion length of 0.2 times the liquid height was used. Moreover, the effect of baffle angle on NJD was investigated. The NJD was measured visually at least three times. The results showed that the effect of the radial installation position of the inside surface baffle on NJD depended on the impeller position. In addition, even baffles placed parallel to the tangential flow were found to decrease NJD.

Active mixing of two-component viscoelastic silicone ink at molecular level for spatiotemporally controlled 3D/4D printing of cellular silicones

3D printed silicones have demonstrated great potential in diverse areas such as soft robots, tissue engineering, flexible sensors and energy dissipation. However, most silicone inks face inevitable curing issue once it is prepared. During the materials extrusion based printing process, the curing-related viscosity change in silicone inks hamper the ink stability and printing controllability, leading to complex relationship among ink properties and printing parameters, as well as printing structures and material properties of final products. Herein, this work presents active mixing of two component silicone ink to realize stable printing, achieving exact and continuous match of ink properties and printing parameters. Using a specially formulated ink containing separate starting components with reactive groups, catalyst and thixotropic agents, this work studies the active mixing process thoroughly for the first time from molecular level to materials performances under various conditions regarding inlet flow rates, impeller rotation speed and component ratios. Besides, cellular silicones with controlled distribution of component ratios and tailored gradient structures are printed, leading to integrated manufacturing of compression performance and shape morphing property. This work will pave way for active mixing and printing of two-component silicones, and provide guidance for other reactive multi-material 3D printing systems.

Mass Transfer Behavior and Energy Utilization Efficiency of a Fixed Bed Suspended in a Stirred Tank Reactor

AbstractThe present study contributes to overcoming the serious drawback of the traditional stirred slurry catalytic reactor, namely, the costly and time‐consuming separation of the catalyst particles from the final product using a stationary fixed bed of Raschig rings placed above a rotating impeller. The rate of diffusion‐controlled reactions was measured in terms of the mass transfer coefficient under different conditions of impeller rotation speed, Raschig ring diameter, and bed height. The rate of mass transfer was determined by a technique which involves measuring the rate of diffusion‐controlled dissolution of copper in acidified dichromate. The data were correlated by a dimensionless correlation which can be used to scale up and design the reactor. The reactor performance was measured in terms of the mass transfer coefficient and the energy utilization efficiency. Possible applications of the reactor in conducting diffusion‐controlled reactions were highlighted.

Analysis of Mixing Efficiency in a Stirred Reactor Using Computational Fluid Dynamics

Lead recycling is very important for reducing environmental pollution risks and damages. Liquid lead is recovered from exhaust batteries inside stirred batch reactors; the process requires melting to be cleaned. Nevertheless, it is necessary to establish parameters for evaluating mixing to improve the efficiency of the industrial practices. Computational fluid dynamics (CFD) has become a powerful tool to analyze industrial processes for reducing operating costs, avoiding potential damages, and improving the equipment’s performance. Thus, the present work is focused on simulating the fluid hydrodynamics inside a lead-stirred reactor monitoring the distribution of an injected tracer in order to find the best injection point. Then, different injected points are placed on a control plane for evaluation; these are evaluated one by one by monitoring the tracer concentration at a group of points inside the batch. The analyzed reactor is a symmetrical, vertical batch reactor with two geometrical sections: one cylindrical body and a semi-spherical bottom. Here, one impeller with four flat blades in a shaft is used for lead stirring. The tracer concentration on the monitoring points is measured and averaged for evaluating the efficiency inside the tank reactor. Hydrodynamics theory and a comparison between the concentration profiles and distribution of tracer curves are used to demonstrate both methods’ similarities. Then, the invariability of the tracer concentration on the monitoring points is adopted as the main parameter to evaluate the mixing, and the best injection point is found as a function of the shortest mixing time. Additionally, the influence of the impeller rotation speed is analyzed as an additional control parameter to improve industrial practices.

Enhanced Mixing Towards the Production of Fatty Acid Methyl Esters by In Situ Transesterification of Eucheuma Cottonii: Experimental and Computational Fluid Dynamics (CFD) Analysis

Biodiesel is one of the alternative replacements for the conventional fossil fuel-based diesel as the demand for energy is increasing with the increasing world population. The production of biodiesel (also known as fatty acid methyl esters (FAME)) from macroalgae (E. cottonii) is the focus in this study. Conventionally, production of FAME from macroalgae will be carried out through the two-step transesterification processes, which consists of extraction of algal oil (lipids and free fatty acids) and subsequent transesterification step. However, the two-step transesterification method is time and energy consuming processes and thus ways to enhance the production yield of the biodiesel produced are being studied. This paper concentrates on utilization of enhanced mixing technique via in situ transesterification (ISTE) process in FAME production which elucidate the effects of reaction time and mixing intensity. The ISTE reaction was carried out at the ratio of biomass: Methanol (MeOH): Hydrochloric Acid (HCl) (w/v/v) of 1:20:5 and a reaction temperature of 60 °C. The total reaction time for the reaction was 90 minutes, where samples were collected at 30 minutes interval. The increase in reaction time and mixing intensity gave a significant positive impact on the production of FAME. At 90 minutes of reaction time and impeller rotational speed of 900rpm, the maximum amount of methyl palmitate and methyl stearate produced were 0.5729 wt% and 0.0559 wt% respectively. The results of contour of volume fraction (VF) of palmitic acid obtained from Computational Fluid Dynamics (CFD) analysis from the Aspen Fluent Software is in good agreement to the experimental results of the study.

CFD Simulation on The Effect of Impeller Immersion Depth and Impeller Rotational Speed on The Flow Pattern and Temperature Drop of Molten Ferronickel During Desulphurization Process

Desulphurization is the purifying process of molten ferronickel from sulphur impurity. During the desulphurization process using a ladle furnace equipped with an impeller, the fluid flow characteristics and the temperature drop of molten ferronickel are important things that must be observed. One approach that can be done to find out the fluid flow characteristics and temperature drops is through Computational Fluid Dynamics (CFD) simulation. The limitation of the simulation in the previous study did not simulate the effect of operating parameters such as impeller immersion depth and impeller rotational speed on the temperature drop of molten metal. Therefore, the simulation carried out in this study was a CFD simulation on the effect of impeller immersion depth and impeller rotational speed on the temperature drop of molten ferronickel during the desulphurization process. This study began by comparing the initial simulation results with a prototype experiment and simulation that another researcher conducted to validate the simulation model. After the selected model had been validated, the main simulations were carried out with variations in the immersion depth and impeller rotation speed. Variations in impeller immersion depth were 700 mm and 900 mm, while variations in impeller rotational speed were 30 rpm, 40 rpm, 50 rpm, and 60 rpm. The simulation began with creating a 3D design of an impeller and 2236 mm high ladle furnace using Ansys SpaceClaim. Then, the meshing and setup process was carried out using Ansys Fluent. The simulation was set by activating the Volume of the Fluid model, the Multiple Reference Frame model, the energy model, and the Renormalization Group (RNG) k-ɛ turbulent model. Based on the simulation results, the impeller immersion depth affects the size of the recirculation flow pattern and the characteristics of the molten ferronickel temperature profile. The impeller rotational speed affects molten ferronickel's vortex depth, velocity, and temperature drop. If the impeller is immersed deeper, the upper recirculation zone will be larger than the lower recirculation zone and the molten ferronickel temperature in the upper area will be hotter, while the bottom area will be colder. The faster the rotation of the impeller is the deeper the vortex, the higher the velocity of molten ferronickel, and the greater the temperature drop of molten ferronickel. The desulfurization process is influenced by a combination of mechanical operating parameters, such as the depth of immersion and impeller rotational speed, which result in ideal mixing characteristics. Impeller immersion depth of 900 mm and impeller rotational speed of 50 rpm are the ideal operational parameters for the desulfurization process in this study. A more uniform distribution of temperature profiles in the ladle's top and lower zones is produced by this parameter. There is slight difference in the size of the upper and lower recirculation flow zones when the impeller immersion depth is 900 mm. With an impeller rotating at 50 rpm, there is a temperature decrease of roughly 24 °C and a vortex depth that is almost at the top of the impeller.

Intensification of the rate of heat and mass transfer at the wall of a stirred tank reactor by integrating a helical coil turbulence promoter with the tank wall

ABSTRACT The influence of a helical coil turbulence promoter on liquid-solid mass transfer rates in a stirred tank was investigated using a technique that involved measuring the rate of diffusion-controlled copper dissolution in acidified dichromate. The study examined the effects of helical coil tube diameter (d), helical coil pitch (p), impeller rotation speed, impeller geometry (axial and radial), the presence of baffles, and solution physical properties. The presence of the helical coil near the reactor wall significantly enhanced mass transfer rates, with a factor ranging from 1.01 to 2.48. This improvement was accompanied by a corresponding increase in the volumetric mass transfer coefficient (kA), ranging from 2.68 to 4.55, depending on operating conditions. Further analysis revealed that the average mass transfer coefficient increased with decreasing coil tube diameter, while coil pitch had a minimal impact. Additionally, radial flow turbines demonstrated superior mass transfer performance compared to axial flow turbines. The presence of baffles also promoted higher mass transfer rates compared to unbaffled reactors. The experimental data were successfully correlated using dimensionless correlations, emphasizing the significance of these correlations in scaleup and design optimization of catalytic stirred tank reactors with efficient cooling systems.

Analysis of cohesive particles mixing behavior in a twin-paddle blender: DEM and machine learning applications

This research paper presents a comprehensive discrete element method (DEM) examination of the mixing behaviors exhibited by cohesive particles within a twin-paddle blender. A comparative analysis between the simulation and experimental results revealed a relative error of 3.47%, demonstrating a strong agreement between the results from the experimental tests and the DEM simulation. The main focus centers on systematically exploring how operational parameters, such as impeller rotational speed, blender's fill level, and particle mass ratio, influence the process. The investigation also illustrates the significant influence of the mixing time on the mixing quality. To gain a deeper understanding of the DEM simulation findings, an analytical tool called multivariate polynomial regression in machine learning is employed. This method uncovers significant connections between the DEM results and the operational parameters, providing a more comprehensive insight into their interrelationships. The multivariate polynomial regression model exhibited robust predictive performance, with a mean absolute percentage error of less than 3% for both the training and validation sets, indicating a slight deviation from actual values. The model's precision was confirmed by low mean absolute error values of 0.0144 (80% of the dataset in the training set) and 0.0183 (20% of the dataset in the validation set). The study offers valuable insights into granular mixing behaviors, with implications for enhancing the efficiency and predictability of the mixing processes in various industrial applications.

Comparison of the Shutdown Transitions of the Full-Flow Pump and Axial-Flow Pump

In this study, a comparative analysis of the shutdown transitions of a full-flow pump and an axial-flow pump was carried out through numerical simulation and model tests. The UDF method was used to achieve control of the impeller rotational speed during shutdown. The results show that during the shutdown transition, the rate of decline of rotational speed, flow rate, and torque of the axial-flow pump are greater than those of the full-flow pump, so the axial-flow pump stops faster than the full-flow pump. The axial force of the axial-flow pump is significantly lower than that of the full-flow pump, and the maximum value of the radial force of the axial-flow pump is approximately 1.14 times that of the full-flow pump. Due to the influence of the clearance backflow vortex, the impeller inlet and outlet of the full-flow pump generate clearance backflow vortices in the near-wall area, resulting in the overall flow pattern of the impeller chamber being worse than that of the axial-flow pump and the hydraulic loss being greater than that of the axial-flow pump. The runaway speed and flow rate of the axial-flow pump are higher than those of the full-flow pump. Due to the influence of the clearance backflow, the range of the high entropy production rate at the suction side of the impeller of the full-flow pump is always larger than that of the axial-flow pump. The research results in this paper can provide theoretical support for the selection and operation of pumps in large low-head pumping stations.

An experiment-informed discrete element modelling study of knife milling for flexural biomass feedstocks

A discrete element method (DEM) based approach is used to study the relationships between material attributes (MAs), processing parameters (PPs), and quality attributes (QAs) for the knife milling of maize stalks. An approximate DEM shape model was conceptualized based on real maize stalks and calibrated based on experimental bending test data for flexural properties (elastic bending stiffness, elastic bending angle limit, elastoplastic ratio, etc.). DEM simulations of maize stalk comminution in a Jordan Reduction Solutions (“JRS”) knife mill were performed to investigate the relationships between the MAs (maize stalk size and breakage stress limit), PPs (impeller rotational speed), and QAs (mass throughput and output particle size distribution (PSD)). The DEM results suggest that stalk length has little influence on mass throughput and PSD, whilst stalks with larger cross sections tend to generate larger sizes of milled particles given the same breakage stress limit. Both the DEM and experimental results show that faster impeller rotation (or higher power) does not necessarily generate higher throughput or smaller output PSD, especially for maize stalks of higher breakage stress limit. The correlations between these MAs, PPs and QAs are found highly stochastic, though breakage stress limit dictates mass throughput, regardless of stalk size. The DEM-predicted output particle size tended to match the experimental data with coarse PSDs based on sieve size but showed weakened fidelity with finer material, indicating the potential for further model improvement.

Comparison between CFD simulation and affinity laws and analysis of the degree of reaction.

Computational Fluid Dynamics (CFD) is a modern technology used to study fluid flow. Experimental methods for predicting the turbomachinery performance involve greater time consumption and financial resources compared to the CFD approach. For the centrifugal pump the impeller is the main component, as it transfers energy to the fluid. The pump flow rate and the total head are directly associated with the impeller rotation speed. The purpose of this paper is to present the analysis and comparison of numerical simulation results using Computational Fluid Dynamics of a centrifugal pump impeller under three different rotation speeds: 3500 rpm (nominal), 3100 rpm and 2700 rpm. The software used was ANSYS-CFX®, the turbulence model adopted was the Shear Stress Transport (SST). Eight operating points were simulated for each rotation. The simulation provided the characteristic curves, pressure distribution, and total and static pressure at the inlet and the outlet of the impeller. The degree of reaction was calculated. The results were compared by application of affinity laws, and showed agreement with them. The results also showed that the degree of reaction increased with increasing flow rate, and it was coherent with the backward curved blade impeller. The simulations show that the energy portions that make up the total energy transferred by the impeller agree with the affinity laws.

Computational fluid dynamics analysis of a novel continuous cementing slurry mixer

To improve the uniformity of continuous slurry mixing in well cementing, a novel continuous mixing system is proposed in this paper. The CFD model of the mixing system is established by employing the Eulerian multiphase flow model, k-ε model, and Multiple Reference Frames (MRF) method to simulate the flow of the two-phase fluids and the rotation of the agitator, respectively. A segmented control simulation method, which includes a dynamic “monitoring-assignment” approach capable of handling secondary mixing processes in engineering, is proposed to calculate the slurry mixing process in the continuous system. A comparative analysis of the control effectiveness is conducted to demonstrate the feasibility of this method. Using the validated model and method, the mixing process of the slurry in the system is investigated. The obtained data is analyzed based on four indicators: uniformity calculation, power, velocity component, and solid volume fraction, to evaluate the effects of impeller diameter and rotational speed on slurry uniformity. The data shows that both impeller diameter and rotational speed significantly affect the slurry uniformity in the continuous mixing system, while only impeller diameter has a greater impact on the flow field and flow pattern inside the stirred tank. It is observed that increasing the impeller diameter and rotational speed beyond a certain point does not further improve slurry uniformity, and excessive impeller diameter and rotational speed may lead to a decrease in uniformity due to stratification in the tank, along with a significant increase in power consumption. The proposed novel structure and method can provide valuable references for the industry, and the research findings can offer scientific guidance for achieving efficient well cementing operations in engineering.

Predictive modeling of mixing time for super-ellipsoid particles in a four-bladed mixer: A DEM-based approach

Numerical simulations of super-ellipsoid particles in a four-bladed mixer using the discrete element method is presented. The effect of number of particles, blade rake angle and impeller rotation speed, on the performance of the mixer was examined. Mixing mechanism and flow pattern of particles were studied through velocity profiles, particle trajectories and granular temperature. It was found that the spherical particles mix faster than the prolate and the oblate particles. In case of using acute blade rake angles, the mixing is slower than obtuse angle. It was found that the granular temperature is higher in the vicinity of the wall for all particle shapes. The spherical particles have the highest granular temperature than the prolate and the oblate particles, which have same granular temperatures. To predict the mixing time, regression models were employed. The voting regressor model was shown to be successful at predicting the mixing time.

Pengaruh Bentuk Impeller pada Proses Koagulasi Flokulasi Terhadap Pola Aliran dan Penyisihan TSS

Environmental pollution caused by wastewater has reached alarming levels, especially in large cities like Surabaya, where household wastewater is a major contributor. The coagulation-flocculation method is used to treat wastewater by precipitating particles from the wastewater. The use of mechanical impellers plays a crucial role in this process. This study analyzes the influence of impeller design, mixing time, and impeller rotation speed on the efficiency of Total Suspended Solid (TSS) removal and flow patterns in coagulation-flocculation. An impeller with a blade angle of 30° produces a wider and more effective flow pattern compared to a 60° angle. The number of blades and the blade angle affect TSS removal efficiency, with a 6-blade impeller at 30° angle achieving the highest efficiency. The optimal mixing time is 1 minute for coagulation and 20 minutes for flocculation. The optimal impeller rotation speed is 100 rpm for coagulation and 60 rpm for flocculation. The findings provide practical guidelines for enhancing the efficiency of domestic wastewater treatment.

The Similarity Law of Cavitation Number on Cavitation Instability in Liquid Rocket Inducer

Abstract The influence of inducer rotation speed on the propagation characteristics of rotating cavitation and on the unsteady characteristics of cavitation in rotating cavitation and cavitation surge were examined using a three-bladed inducer, which is named THK inducer, to develop the rocket engine turbopump that can operate stably over a wide operating range. The novel point of the paper is focusing on the cavitation itself, which is the cause of cavitation instabilities. The paper conducted two types of experiments using an inducer and single hydrofoils, and the dimensional and nondimensional unsteady characteristic, which is the frequency of unsteady cavitation and the Strouhal number, were evaluated. Three types of rotating cavitation and cavitation surge were observed in the inducer. For a given cavitation number, the Strouhal number of rotating cavitation and the frequency of unsteady cavitation in cavitation surge are independent of the inducer rotation speed, respectively. The characteristic of rotating cavitation corresponds to that of cavitations arising in hydrofoils, but its characteristic of cavitation surge does not correspond. The dynamic characteristic of cavitation compliance in cavitation surge is similar to that of several rocket engine turbopumps. Therefore, it was proved that rotating cavitation is a cavity oscillation and cavitation surge is a system oscillation. Additionally, in a flow field with the same flow coefficient and different impeller rotation speed, the unsteady characteristics of cavitation instabilities are equal if the cavitation number is equal, which is named the “similarity law of cavitation number on cavitation instability.”

Investigating the impact of impeller geometry for a stirred mill using the discrete element method: Effect of pin number and thickness

Vertical stirred milling is a major technique for grinding fine and ultra-fine particles. In this study, attritor designs of varying pin number and projected area were examined over a range of impeller rotational speeds using the Discrete Element Method (DEM). Analysis determined that additional pins improved the potential for effective grinding due to an increase of average collision energy. However, this was accompanied by a greater power draw. When projected area was maintained, there were fewer differences between designs, meaning that the specific configuration of the pins may not be as important. A template of the mill can be found at https://github.com/darhyme147/ligggghts_stirred_mill_template.

Experimental study of the flow of viscous Newtonian fluids in a centrifugal pump

This paper analyzes the influence of viscosity and impeller rotation speed in the calculation of the flow and in the theoretical prediction of the performance of a centrifugal pump impeller. The evaluation of the viscous effects allows the prediction of the frictional losses of the impeller and a more correct evaluation of the operating characteristics than can be obtained with a perfect fluid. The viscosity modifies the values of the velocity distribution in the channels of the impeller and the deviation of the flow at the exit of the blade. The experiments were carried out with mineral oils of different viscosities varying between 96.10-3 Pa.s and 520.10-3 Pa.s and which are represented by a perfectly newtonian behavior.