Optimization Of Impeller Research Articles

Study of solid–liquid mixing in agitated tanks through electrical resistance tomography

Electrical resistance tomography (ERT), which is a non-intrusive flow visualization technique, was used to investigate the solid–liquid mixing in an agitated tank equipped with a top-entering axial-flow impeller. The signals obtained from eight ERT planes were utilized to reconstruct the tomograms by using the linear back projection algorithm. The ERT measurements were correlated to solid concentration profiles by which the degree of homogeneity was quantified. In this study, the effect of important parameters such as impeller type (Lightnin A100, A200, A310, and A320 impellers), impeller speed (250–800 rpm), impeller off-bottom clearance ( T/5– T/2, where T is the tank diameter), particle size (210–1500 μm), and solid concentration (5–30 wt%) on the degree of homogeneity were explored. The results showed that the degree of homogeneity in the solid–liquid mixing was improved with increasing the impeller speed. However, after reaching the maximum achievable homogeneity, further increase in impeller speed was not beneficial but might be detrimental. Hence, the measurement of the optimal impeller speed as a function of operating conditions and design parameters has vital role in achieving maximum homogeneity in a solid–liquid mixing system.

Numerical investigation of the influence of variable diffuser vane angles on the performance of a centrifugal compressor

In this study, the performance of a turbocharger compressor system for light-duty diesels, encompassing the airflow geometry from impeller inlet to volute exit, has been simulated numerically, and the effects of variable diffuser vane angles on the compressor performance and operating range have been investigated. It is found that the angle of the diffuser vane has significant influence on the compressor operating range, and optimized design of the variable diffuser vane angle can increase the stable operating range and improve the compressor efficiency significantly when compared with fixed diffuser vane angles and vaneless designs. However, changing the diffuser vane angle alone may not achieve the full control of the operating range of a compressor desired. Other technologies (e.g. variable inlet guide vanes, casing treatment, or optimum impeller design) may also be necessary to achieve the widest operating range required.

THREE DIMENSIONAL MULTI-OBJECTIVE DESIGN OPTIMIZATION OF CENTRIFUGAL COMPRESSOR IMPELLER

A method for centrifugal compressor impeller’s multi-objective design optimization was developed. The method was applied to a tested twelve radial bladed centrifugal compressor impeller, available in the open literature, as a test case characterized by three-dimensional viscous turbulent flow structure. The optimization target was to maximize the total-to-total adiabatic efficiency, and pressure ratio of the impeller at the design point, considering constant mass flow rate, rotational speed, and nearly constant torque. The aerodynamic analysis was performed using (CFX BladeGen) commercial software. This software solves the three-dimensional turbulent Navier-Stokes flow equations, with zero-equation turbulence model using finite volume method. The capabilities of the software were first validated by comparing the computed results with, an experimental data made by Mizuki [10, 11]. In this experimental work, yaw probes distributed along the impeller channel, were used to determine total and static pressures for hub and shroud. GAlib software was used to apply Genetic algorithm for handling of the optimization problem. The optimal impeller configuration, which corresponds to maximum efficiency, and maximum pressure ratio, keeping the same mass flow rate and rpm, was obtained with only 0.7% violation of the original torque value. A comparison between original and optimized impellers was made, which revealed the causes for efficiency and pressure ratio improvements.

Optimization of mixing in stirred bioreactors, 2: Selection of optimum impeller combinations for non-aerated simulated broths

Although radial impellers, especially the Rushton turbine, are widely used in stirred bioreactors, their applicability is limited by the high apparent viscosities of the broths. For optimizing mechanical mixing by selecting the appropriate impeller for a specific fermentation broth or process, the comparative analysis of the mixing efficiency, energy costs and shear effects on the biocatalysts is required. By means of this analysis, three different combinations of radial impellers for water and viscous simulated broths were selected for attaining optimum mixing in a bioreactor. The proposed impellers combinations offer the most intense and uniformly distributed mixing and the lowest specific power consumption required for reaching a maximum level of mixing time of less than one minute.

Improving Gas Distribution through Agitator and Gas Sparger Modification in an Autoclave Model

An experimental study of the effect of gas sparger geometry and agitator location on gas distribution in agitated systems is presented. The results have shown that varying the impeller position modified the size of low void fraction zone. The optimum impeller position for achieving a small low voidage zone without changing the flow pattern has been identified. It was found that impeller positions below or above the optimal location have a negative effect on gas dispersion while the sparger geometry did not affect significantly the overall gas distribution. Low void fraction zone could be detected by a void sensor even if not visually observed.

Optimization of the mixing in stirred bioreactors, 1. Comparative analysis of the mixing efficiency with different radial impellers for simulated broths

Although radial impellers, especially the Rushton turbine, are widely used in stirred bioreactors, their applicability is limited by the high apparent viscosities of the broth. Beside the intensification of broth circulation, the energetic efficiency and the shear effects on biocatalysts must be taken into account to select the optimum impeller or impellers combination. In this context, the paper presents a comparative study on the efficiency of seven different radial impellers for simulated broth mixing in a stirred bioreactor. The analysis was made by means of the mixing time values obtained by vertically changing the position of the pH-sensor in the broths, in correlation with the energy consumption needed for a certain level of mixing time or for the uniform distribution of the mixing intensity into the bulk volume of the broths.

Optimization of a Miniature Maglev Ventricular Assist Device for Pediatric Circulatory Support

A miniature Maglev blood pump based on magnetically levitated bearingless technology is being developed and optimized for pediatric patients. We performed impeller optimization by characterizing the hemodynamic and hemocompatibility performances using a combined computational and experimental approach. Both three-dimensional flow features and hemolytic characteristics were analyzed using computational fluid dynamics (CFD) modeling. Hydraulic pump performances and hemolysis levels of three different impeller designs were quantified and compared numerically. Two pump prototypes were constructed from the two impeller designs and experimentally tested. Comparison of CFD predictions with experimental results showed good agreement. The optimized impeller remarkably increased overall pump hydraulic output by more than 50% over the initial design. The CFD simulation demonstrated a clean and streamlined flow field in the main flow path. The numerical results by hemolysis model indicated no significant high shear stress regions. Through the use of CFD analysis and bench-top testing, the small pediatric pump was optimized to achieve a low level of blood damage and improved hydraulic performance and efficiency. The Maglev pediatric blood pump is innovative due to its small size, very low priming volume, excellent hemodynamic and hematologic performance, and elimination of seal-related and bearing-related failures due to adoption of magnetically levitated bearingless motor technology, making it ideal for pediatric applications.

Optimizing impeller geometry for performance enhancement of a centrifugal pump using the Taguchi quality concept

This article discusses a research methodology for performance enhancement of centrifugal pump through Taguchi's parametric design concept. The objective is to find an optimum impeller design and geometry that makes the pump functionally reliable for winning customer's confidence. Computational fluid dynamic (CFD) analysis has been done to know how the flow pattern changes in the impeller when the pump is required to run at different operating conditions. The streamline analysis from CFD plots gives informative pictures of the flow field, which help the designer understand how the effect of deviation made in the impeller design specifications significantly influence the pump performance. CFD results match well with the predictions of the pump performance at the duty point as regard to head, discharge, and efficiency of the prototype model. The study infers that the CFD prediction tallies with Taguchi's experimental results.

Solids motion in a conical frustum-shaped high shear mixer granulator

An experimental study has been carried out on the solids motion in a conical frustum-shaped vertical high shear mixer granulator by using the positron emission particle tracking (PEPT) technique. The mixer granulator has a vertical shaft attached to which are 4 sets of impellers at different elevations. The shaft is operated at 3, 6 and 12 Hz, which correspond to the top impeller tip speed of 2.1, 4.1 and 8.3 m/s. Particles are observed to circulate in both the horizontal and vertical directions. The period of horizontal circulation is short and is in the order of seconds, whereas that of the vertical circulation takes tens of seconds and often consists of lots of higher frequency fluctuations. There is a dominant solids motion in the tangential direction at all impeller speeds with the maximum tangential velocity 2.2–5.3 times that of the maximum axial and radial velocities. The maximum values of the three velocity components increase with increasing impeller speed, but the ratios of the maximum velocity to the tip speed decreases with increasing impeller speed, suggesting a rate-dependent behaviour. The particle flow pattern shows the presence of swirling flows at a position depending on the impeller speed. The results also suggest the existence of an optimal impeller speed that gives the best macroscopic mixing characterised by the vertical solids circulation.

Bacterial cellulose production by Gluconacetobacter hansenii in an agitated culture without living non-cellulose producing cells

Bacterial cellulose (BC) was produced by Gluconacetobacter hansenii PJK in a jar fermenter equipped with a 6 flat-blade turbine impeller and the relationship between the populations of non-cellulose producing cells ( Cel − mutants) and BC production was investigated. The population of Cel − mutants converted from cellulose producing cells ( Cel + cells) decreased as the impeller speed increased. Cel + cells seemed to be protected from the strong shear stress generated by the impeller rotating at a high speed by the BC net produced by the cells. There was an optimum impeller speed in maximizing the population of Cel + cells and BC production. The optimum impeller speed increased with ethanol supplementation to a basal medium. The by-product, water-soluble polysaccharide (WSPS), was a homopolysaccharide of glucuronic acid. WSPS production was related to the population ratio of Cel + cells to the total cells.

Mixing Time, Homogenization Energy and Residence Time Distribution in a Gas-Induced Contactor

Mixing time, homogenization energy and residence time distribution (RTD) experiments have been carried out in a gas-induced contactor in order to determine mixing characteristics of the vessel. Effects of sensor location, impeller speed, gas induction, and gassing on mixing time have been studied. Experiments on a semi-technical scale vessel have identified optimal mixing time conditions and optimal impeller speeds for most efficient homogenization energy. The effects of liquid flow rate and impeller speed on liquid phase RTD have also been investigated. The contactor mixing behaviour was modelled by a continuous stirred tank reactor (CSTR) with dead zones and bypassing. Good agreement between experimental and model results was observed. Analysis shows that contactor performance is close to that of an ideal CSTR; however, dead zones (as large as 16.7%) at low liquid flow rates and bypassing (as large as 10%) at high liquid rates need to be considered.

Suspension of buoyant particles in a three phase stirred tank

Despite many applications in the process industries, the suspension of floating particles in aerated stirred tanks has received little attention. The critical just drawdown agitator speed for different concentrations of floating particles, gas holdup and shaft power have been measured in a vessel of 0.476 m diameter with four baffles and dished base. The aspect ratio of the liquid in the tank is 1.8. Five agitator configurations, each with three impellers on a single shaft, were used in the experiments. Two impeller designs were used, a deep hollow blade (semi-ellipse) disk turbine (HEDT) and a 4-wide-blade hydrofoil impeller, the latter in either upward-pumping ( WH U ) or downward-pumping ( WH D ) mode. Polypropylene (PP) particles, 3 or 4 mm in size and density 900 kg / m 3 , were used in the suspension experiments. Results show that these solids have little effect on the relative power demand (RPD, ratio of gassed power demand to that when ungassed, i.e., RPD = P G / P U ). Agitators using the radial dispersing HEDT as the bottom impeller have a flatter RPD, than those when an up or down pumping hydrofoil is at the bottom. However, gas holdup decreases with increasing solid concentration. Among the five different impeller combinations, a downward pumping top impeller has a significantly higher just drawdown agitation speed and power consumption, so the WH D mode is not as suitable for the drawdown of floating particles. For any given upper impeller, the just drawdown agitation speeds for different combinations are almost same, though in multi-impeller stirred tanks the gas dispersion is controlled mainly by the bottom impeller. Of these impeller combinations, those using a HEDT as the bottom impeller have the flattest RPD and the highest gas holdup at a given gas flow rate and power input. The optimal impeller combination for to achieve both the drawdown of floating particles and gas dispersion is HEDT + WH D + WH U .

Recent Studies on Agitated Three-Phase (Gas–Solid–Liquid) Systems in the Turbulent Regime

Earlier work using Rushton turbines and down-(MFD) and up-(MFU) pumping, 45°-pitched blade turbines at relatively low concentrations of solids of different size and density in vessels up to 1.8 m diameter enabled correlations to be developed for predicting the minimum speed for solid suspension, NJSg. Further work has been conducted with these impellers and with two modern impellers, a Scaba 6SRGT, a typical hollow-blade radial flow impeller, and a typical up-pumping, axial flow, wide-blade hydrofoil, the Lightnin’ A315, in a vessel of 0.45 m diameter with solids up to 40% by weight. The earlier correlations were validated for the new higher concentration conditions. In all cases, increases in solids concentration increased NJSg and the specific energy dissipation rate required to suspend solids, (ɛT)JSg On the other hand, the large increase (up to two orders of magnitude) in mixing time found at solids concentration >∼15% by weight in two phase systems at NJSg as compared with the case without solids, is essentially eliminated in the three-phase case. At low gassing rates, QGv (vvm), down-pumping impellers achieve suspension and relatively good vertical solids distribution at the lowest (ɛT)jsg-However, with increased QGv UP to 3 vvm, NJSg and (ɛT)JSg increase rapidly, solids maldistribution develops, the flow pattern is very unstable and gross torque fluctuations occur. For the 6SRGT, the operation is very stable and although NjSg and (ɛT)JSg are both high they are insensitive to QGv This high value of (ɛT)JSg may not be a disadvantage if high rates of gas–liquid mass transfer are required. For both the 6MFU and especially the A315(U), the flow pattern, NJSg and (ɛT)JSg are again all very insensitive to QGv and a good vertical solids distribution is maintained. For the A315(U) at high QGv values, (ɛT)JSg is the least amongst the impellers tested, so that wide-blade, up-pumping axial flow hydrofoils are considered to be the optimum impeller when just physical suspension is required or solid–liquid reactions are rate limiting.

Effect of Relative Impeller-to-Volute Position on Hydraulic Efficiency and Static Radial Force Distribution in a Circular Volute Centrifugal Pump

The hydraulic performance and radial hydraulic force characteristics of a circular volute centrifugal pump are strongly affected by the impeller to volute relative position. For a typical design configuration the geometric center of the impeller will be coincident with the volute geometric center. However, assembling a circular volute pump with the impeller center eccentric from the volute center can radically alter both the hydraulic performance and the radial hydraulic force characteristics. In particular, at the design flow coefficient an optimum impeller to volute relative position exists where the efficiency is maximized and the resultant radial force is minimized. At the optimal relative position a 5 percent and a 3.5 percent increase in the efficiency was realized compared to the centered positions for the circular and spiral volutes, respectively. In addition the nondimensional resultant radial force at the design flow coefficient was reduced from 0.045 at the centered position to 0.005 at the optimal position for the circular casing. This value of radial thrust is similar in magnitude to the radial thrust for the spiral volute operating at the design flow coefficient. By assembling a circular volute pump with the appropriate relative impeller to volute position the design simplicity of a circular volute can be utilized without compromising pump hydraulic performance or radial force characteristics as compared to a typical spiral volute. [S0098-2202(00)02303-8]

Mathematical model based estimation of volumetric oxygen transfer coefficient(s) in the production of proteolytic enzymes in Bacillus amyloliquefaciens

Alkaline protease is a class of important hydrolytic enzymes having wide applications in bioprocess industries. Their optimum pH in the alkaline range and stability at higher temperatures make them ideal in detergent and leather processing industries. These enzymes have excellent depilating capacity. The present study aims at process optimization for the production of alkaline protease from Bacillus amyloliquefaciens ATCC 23844. Information on the optimal operating temperature and pH were elicited from specific growth rates and alkaline protease yields. It was also observed that besides pH and temperature, the oxygen transfer rate is another important limiting variable for the production of protease. Volumetric oxygen transfer coefficient (kLa) was estimated at various impeller speeds and aeration rates. The optimal impeller speed and aeration rates were determined from kLa and the relative protease yield data. It was understood that the oxygen transfer rate is one of the crucial parameters for the production of proteolytic enzymes by B. amyloliquefaciens.

Minimum Power Requirements for Complete Suspension of Solid Particles in an Agitator

Abstract The suspension of solids in a liquid is an operation common to many applications of mixing in process engineering. A new concept is suggested for calculating the minimum theoretical power requirement to suspend a given amount of solids in a stirred vessel. A material balance equation, based on the effective adsorption of gold cyanide onto activated carbon and ion-exchange resin in a stirred vessel, was used to estimate mass-transfer parameters which were used to derive an optimum impeller speed. It will be demonstrated that the minimum theoretical power derived here is in agreement with other concepts proposed in the literature, and in some cases even suggest smaller minimum values. Furthermore, it will be shown that inert fines in solution can enhance the effective mass transfer, thus minimizing the power input.

Strain selection, medium development and scale-up of toyocamycin production by streptomyces chrestomyceticus

The batch productivity (QTM) of the production of the nucleoside antibiotic toyocamycin (TM) by Streptomyces chrestomyceticus was increased ten-fold by selection of a UV generated mutant, optimization of pH, increasing incubation temperature from 28 °C to 36 °C, and addition of soy oil. Initial high oxygen transfer rates stimulated QTM maxima two-fold. Antibiotic production by the mutant strain, U190, however, appeared more shear sensitive than the parent culture FCRF 341 with maximum antibiotic titer being inversely related to impellor tip velocity, Tv. For this reason, scale-up could not be done at constant P/V or constant volumetric oxygen transfer. Instead, programming of impeller speed was evaluated in order to maintain optimal impeller tip velocity during scale-up. It was found that a low constant Tv maintained in scale-up in geometrically similar vessels was most beneficial for duplication of optimal antibiotic productivity, QTM. Pilot fermentations (120 dm3 scale) were used to determine coefficients of QTM variation from oxygen uptake rate (OUR) and total CO2 evolution data for monitoring of QTM variation during scale-up to the 12,000 dm3 scale. This technique allowed for on-line prediction of antibiotic titer and QTM from fermentor exhaust gas data.

Mixing of pseudoplastic liquid in a vessel equipped with a variety of helical ribbon impellers.

A huge number of data prove that the dimensionless mixing time of pseudoplastic liquids with a helical ribbon impeller increases with an increase in the apparent Reynolds number in the laminar flow region, but starts to decrease with the Reynolds number above a certain critical Reynolds number. The mixing time is strongly affected by the liquid shear-thinning property, increasing as the liquid shear-thinning property increases. The mixing time in the laminar-flow region is correlated with liquid properties, impeller geometry and operational conditions. The optimum impeller geometry for the mixing of pseudoplastic liquids is predicted.

Mixing effects in dead end hydrogenation of oils: Sulfite oxidation model

AbstractMost industrial hydrogenators are of the dead end type where the gas is bubbled at the bottom of the apparatus, builds up a certain pressure on top of the oil, and is not recirculated. The hydrogen needed by the reaction comes partly from the fraction of the bubbles that is absorbed and partly from the gas space. It was found that sodium sulfite oxidation follows the same mixing pattern, i.e., the highest rate of oxidation always occurred in the upper half of the liquid and correlated strongly with the Reynolds number of the turbine. it is shown that for Reynolds numbers above 600 the optimum impeller position is about two thirds the liquid height measured from the bottom of the vessel. Information is given regarding the variations in selectivity, isomerization and hydrogenation of oils when the speed, relative location and dimensions of the turbine are varied.