Values Of Rotational Speed Research Articles

Comparative analysis of mixing distribution in aerobic stirred bioreactor for simulated yeasts and fungus broths

The study on mixing distribution for an aerobic stirred bioreactor and simulated (solutions of carboxymethylcellulose sodium salt), yeasts (S. cerevisiae) and fungus (P. chrysogenum pellets and free mycelia) broths indicated the significant variation of mixing time on the bioreactor height. The experiments suggested the possibility to reach a uniform mixing in whole bulk of the real broths for a certain value of rotation speed or biomass concentration domain. For S. cerevisiae broths the optimum rotation speed increased to 500 rpm with the biomass accumulation from 40 to 150 g/l d.w. Irrespective of their morphology, for fungus cultures the existence of optimum rotation speed (500 rpm) has been recorded only for biomass concentration below 24 g/l d.w. The influence of aeration rate depends on the apparent viscosity/biomass concentration and on the impellers and sparger positions. By increasing the apparent viscosity for simulated broths, or biomass amount for real broths, the shape of the curves describing the mixing time variation is significantly changed for all the considered positions. The intensification of the aeration induced the increase of mixing time, which reached a maximum value, decreasing then, due to the flooding phenomena. This variation became more pronounced at higher viscosities for simulated broths, at higher yeasts concentration, and at lower pellets or filamentous fungus concentration, respectively. By means of the experimental data and using MATLAB software, some mathematical correlations for mixing time have been proposed for each broth and considered position inside the bioreactor. These equations offer a good agreement with the experiment, the maximum deviation being +/-7.3% for S. cerevisiae broths.

Investigation of bilayer period and individual layer thickness of CrN/TiN superlattices by ellipsometry and X-ray techniques

CrN/TiN superlattice (SL) coatings were prepared employing reactive magnetron sputtering in unbalanced configuration. The coatings were deposited in a mixed Ar/N 2 atmosphere rotating the substrate holder, located at the centre of the deposition chamber. Through the rotation, the substrate was sequentially exposed in two diametrically located Cr and Ti targets (purity 99.95%) leading to the deposition of the CrN and TiN single layers, respectively. The deposition was carried out at various values of substrate bias voltage and substrate rotation speed. The microstructure of the SL coatings was investigated in terms of the thickness of the individual CrN and TiN single layers and the bilayer period Λ, namely the sum of the thickness of two sequentially CrN and TiN layers. Λ values were calculated employing X-ray diffraction (XRD) at both low and high diffraction angles. Moreover, the high-angle XRD patterns enabled the determination of the single CrN and TiN layer thickness. In addition, the thickness of the single layers was determined from Spectroscopic Ellipsometry using the Bruggeman effective medium approximation. The results reveal good agreement between the various techniques.

A note on the small oscillation regimes of rotating liquid bridges: Transition from surface to internal wave modes

An analysis of the small oscillation modes of rotating liquid bridges is carried out. The study is performed in the particular conditions when both surface and internal wave mode frequencies almost coincide for a certain meridional and azimuthal wave number. The critical values of the rotation speed and the natural frequencies for which this transitional condition takes place are obtained numerically as a function of the parameters characterizing the fluid configuration. The influence of both the outer bath and the liquid bridge equilibrium shape on the transition is analyzed. Analytical expressions providing the critical values of the rotation speed and the natural frequencies are obtained for cylindrical liquid bridges.

Sulfite induced autoxidation of NiII and CoII tetraglycine complexes. Spectrophotometric and rotating ring-disc voltammetric studies.

The oxidation of Ni(II) and Co(II) tetraglycine complexes in borate buffer aqueous solution, by dissolved oxygen, is strongly accelerated by sulfite. The formation of Ni(III) and Co(III) complexes with maximum absorbances at 327 and 265 nm, respectively, was followed by spectrophotometric measurements. Ni(III) formation was also characterized by voltammetry at low temperatures, whose anodic and cathodic components were observed in the recorded voltammograms. Spectra and rotating ring-disc voltammograms, recorded at various rotation speed values, showed that the Ni(III) species decomposes. The electrochemical process related to the couple Co(II)/Co(III), in a medium containing tetraglycine, was not reversible. In both Ni(II) and Co(II) complexes the metal ion oxidation in the presence of oxygen and sulfite involves the reduction of some initial Ni(III) or Co(III) by sulfite to produce the SO(3).- radical, which rapidly reacts with dissolved oxygen to produce SO(5).-, which then oxidizes Ni(II) or Co(II).

摩擦圧接における熱量の測定

In order to measure the heat input (quantity of heat) generated during friction welding, a new type calorimeter of acryl resin was developed, and applied to friction welding of a stainless steel. The heat input measured during friction welding was in good agreement with the values calculated from the measured values of friction torque, burn-off length, rotation speed and pressure. Being classified into friction and deformation heat inputs, the friction heat input was much greater than the deformation heat input through the friction and upset stages.

Compensation of Thermo-elastic Machine Tool Deformation Based on Control internal Data

The thermo-elastic behaviour of machine tool structures leads to unwanted displacements at the tool centre point (TCP) and has a significant influence on the machining accuracy. In the past, therefore, numerous direct and indirect compensation methods were developed to reduce and/or compensate the thermo-elastic displacements. The paper describes a new indirect compensation approach which allows the abandonment of all additional sensors with the exception of one environmental temperature sensor. As input control internal data of the feed drives and the main spindle are used exclusively. The rotational speed and motor current values - the latter correlate to the drive torque - represent the thermal load parameters of the machine. A combination of first and second order time delay elements describes the displacement behaviour of the machine resulting from these load parameters. The parameters of the time delay elements are determined by a systematic calibration procedure. The resulting displacements are calculated online and superposed as offset-values for the correction of the respective axis positions. Practical experiments show that with this elementary method a reduction of the thermo-elastic displacements of more than 80 % of the initial value is possible.

Disc Brake Squeal – An Experimental Approach

The phenomenon of squeal in disc brakes has been, and still is, a problem for the automotive industry. Extensive research has been done in an attempt to understand the mechanisms that cause it and in developing design procedures to reduce it to make vehicles more comfortable. Part of the research programme at Liverpool University has been the verification of finite element models of disc brakes using an experimental brake rig. Tests have been carried out on a Rover solid disc, a Mercedes solid disc and a Mercedes vented disc. The test rig houses the front knuckle in a rigid support, and the drive is to the wheel studs on the disc. There is no wheel in place. The brake calliper is mounted in the normal fashion to the knuckle. A 42 kW motor drives the disc against the action of the brake. A fixed array of 12 non-contact capacitance displacement transducers is arranged in an arc near the outer radius of the disc. These measure the axial displacement of the disc while it is rotating. During a squeal event, the measurement system records these displacements along with values of disc temperature, rotation speed, shaft torque and hydraulic pressure at a logging rate of 56 kHz. From this high definition time domain data, small time samples can be analysed using a least squares technique to determine the nature of the vibration mode at a given squeal frequency. The analysis shows that the vibration of the brake disc can take several forms. With different conditions, even on the same disc, the vibration mode can be a forward travelling wave, a backward travelling wave or a standing wave (relative to the calliper). This paper is in two parts. The first part describes the test rig and the testing procedures; the second part explains how the analysis is performed and shows some of the results from typical squeal tests.

Optimisation of the meat emulsification process using at-line human evaluations and the Simplex method

The Simplex method has been used to determine the value of process parameters, mixing duration and mixer rotation speed, that lead to a product with desired sensory characteristics at the end of the chopping step during the manufacture of meat emulsion. These characteristics are evaluated as a global index called chopping degree (CD). It is calculated using the theory of fuzzy sets on the basis of a temperature measurement and four sensory evaluations made close to the line by operators. CD value should be as close as possible to 5. The results have allowed the optimisation of intermediary sensory quality by obtaining a maximum point where CD equals 4.8. The processing conditions established at the end of the Simplex algorithm are 3 min and 2000 rpm.

Thermohydrodynamic behavior of journal bearings running under different steady conditions

In most previous investigations, journal bearing performance characteristics have been analyzed using different simplified assumptions. The purpose of this study is to eliminate most of those assumptions, using computational fluid dynamics (CFD) techniques to solve the exact governing equations. The bearing has a finite length and operates under incompressible laminar flow and steady conditions. Numerical solutions of the full three-dimensional Navier-Stokes equations, coupled with the energy equation in the lubricant field and the heat conduction equations in the bearing and the shaft are obtained. Considering the complexity of the physical geometry, conformal mapping is used to generate an orthogonal grid and the governing equations are transformed for use in the computational domain. Discretized forms of the transformed equations are obtained by control volume method and solved by SIMPLE algorithm. Cavitation effects are also considered by introducing an appropriate three-dimensional cavitation model. In order to study the effect of main parameters on thermohydrodynamic behavior of journal bearings, solutions are obtained for different values of the eccentricity and radial clearance and also for different values of the rotational speed of the shaft. To validate the computational results, comparison with the experimental data of other investigators is made, and reasonable agreement is obtained.

Particle Trajectory in Turbulent Boundary Layer at High Particle Reynolds Number

Particle Trajectory in Turbulent Boundary Layer at High Particle Reynolds Number

On Cross-Flow Fan Similarity: Effects of Casing Shape

The limited number of experimental investigations on similarity operation in the literature is not sufficient to state the validity of similarity laws for cross-flow fans. This is also due to the operating conditions occurring in practical applications, where the values of impeller size and rotational speed generally result in low Reynolds numbers and, then, in a non-negligible influence of viscous forces on performance. The analysis is further complicated by the high influence of the casing shape on performance, which can lead to induced effects on similarity operation. An experimental test program is presented in this paper, aimed at understanding the influence of Reynolds number on performance for different casing shapes. Five impellers having similar shape and different dimensions were tested, each one matched with five casings at different rotational speed. The results show that similarity laws can be applied with good approximation above critical blade Reynolds numbers of around 4000 to 15,000, depending on the geometrical characteristics of the casing. The strong scale effect, shown by some authors in the literature, is not observed in these tests.

Study of the Mass Transfer at Fluorine-Evolution Carbon Electrodes

The kinetics rate of the fluorine evolution reaction (FER) was studied in molten KF-2HF mainly by impedance spectroscopy with a rotating disk electrode in large potential and rotation speed ranges. A new model for the schematic representation of the electrode/electrolyte interface has been proposed including the presence of an intermediate layer between the electrode surface and the fluorine gas film. This layer is composed of a solid C–F compound (generated on carbon anodes surface during the electrolysis), liquid KF-2HF melt, and fluorine gas. The influence of the mass-transfer phenomenon occurring in that layer was pointed out in the low frequency part of the impedance diagrams. This intermediate layer gives also rise to a capacitive loop at very high frequency which does not vary with the applied potential and the rotating speed values. The kinetics rate of the FER is governed both by the mass transfer and the charge transfer. Finally, the influence of the C–F on the anodic overvoltage was studied. © 2000 The Electrochemical Society. All rights reserved.

Selective separation of penicillin V from phenoxyacetic acid using liquid membranes

The selective separation of Penicillin V from phenoxyacetic acid using extraction and transport through liquid membranes consisting of 1,2-dichloroethane and Amberlite LA-2 as carrier was studied. The selective separation is the result of the difference between the acidity and hydrophobicity of the two compounds. The experimental data indicated the decisive influences of pH (difference between the feed and stripping phases), carrier concentration in solvent phase (0–80 g/l Amberlite LA-2) and mixing intensity. Thus, the selectivity factor, defined as the ratio between the final mass flows of Penicillin V and phenoxyacetic acid, was enhancing by reducing the pH gradient between the aqueous solutions and by using low concentrations of carrier inside the liquid membrane, in the conditions of high stirrers rotation speed values. The selectivity factor value varied between 2.5 and 80.4.

Hydrostatic equilibrium and convective stability in the plasmasphere

It has been shown that no hydrostatic/barometric model for a rotating plasmasphere is able to fit the equatorial electron density distributions observed by the ISEE satellite for L<8, following prolonged periods of quite magnetic conditions. Indeed, it has been found that all these saturated plasma density profiles are characterized by scale heights which are independent of L, while those corresponding to any hydrostatic/barometric models are always increasing functions of L. Furthermore, all calculated barometric equatorial density profiles have a minimum value at an equatorial distance given by L o =(GM E / Ω 2R 3 E ) 1/3=6.6( Ω E / Ω) 2/3, depending on the value of the angular rotational speed, Ω: L o≤6.6 for Ω/Ω E≥1. The position of this minimum is independent of the particle velocity distribution function (VDF) assumed (i.e. on the energy spectrum of the ions and electrons); the value of the minimum density depends on the temperature and density at the low altitude reference, as well as on the kappa index of the Lorentzian VDF assumed to calculate the barometric model. There is no evidence for such a minimum value in the observed equatorial density profiles of ISEE. This is considered as a second indication that the plasmasphere is not in hydrostatic/barometric equilibrium. Next, it is shown that for L> L o all barometric models are convectively unstable with respect to interchange and quasi-interchange. Therefore, it is not surprising that observed density profiles do not fit any of the profiles corresponding to corotating barometric models. A final indication that the plasmasphere is not in hydrostatic equilibrium but in a state of continuous hydrodynamic expansion comes from the fact that the total plasma pressure at the outer edge of the magnetosphere is lower than the kinetic pressure predicted by barometric models at large radial distances. As a consequence of this pressure unbalance, the plasmasphere is expected to expand continuously like the solar corona. Evidence for such a plasmaspheric wind had already been inferred earlier from the study of the ion density profiles obtained from the OGO-5 mission.

Dynamic analysis of rotationally flexible cam mechanisms

A novel mechanism for the actuation of valves in an internal combustion (IC) engine is described. Previous publications are reviewed and it is shown that the mechanism has received very little attention, in particular no dynamic analysis of it has been published. The mechanism features a shaft driving a cam through a coupling of sufficient rotational flexibility to permit significant angular offsets to develop during the cycle. A differential equation of motion of a simplified system is derived and solved using two methods. The theory requires a knowledge of twelve fundamental system dynamic parameters from which a prediction of angular offset of the camlobe throughout the cycle is produced. A dataset was obtained from a purpose built apparatus which recorded the angular offset of the camlobe with respect to the camshaft for a range of rotational speed values. Results graphs are presented and the level of agreement between theory and experiment is discussed. The work demonstrates for the first time that useful predictions of simplified mechanism performance can be obtained from the model developed. Recommendations for further work in this area are made.

Domain growth in a multivariable nonpotential system

We present a study of dynamical scaling and domain growth in a nonpotential system that models Rayleigh–Bénard convection in a rotating cell. In d=1, dynamical scaling holds, but the nonpotential terms modify the characteristic growth law with a crossover from logarithmic to linear in time. In d=2 the nonpotential terms prevent coarsening for values of the angular rotation speed below the Küppers–Lortz instability.

The Effect of Disk Warpage/Skew on the Deflection and Vibration of a Flexible Disk Spinning Above a Baseplate and in Contact With a Point-Head

A flexible disk, with small initial warpage/skew, is spinning in close proximity to a stationary baseplate. The partial differential equation for the disk deflection is coupled to the Reynolds equation of the stabilizing air-film. Disk warpage/skew produces a small change in the deflection which rotates with the disk. These deflections are obtained by linearizing the coupled equations about the axisymmetric configuration corresponding to a perfect disk. Numerical solutions are obtained and compared for different values of rotational speed and air-film thickness. The results show that among the three skewed/warped disks modeled, the skewed disk (i.e., the plane of the disk is skewed with respect to its axis of rotation) produces the largest deflection change (axial runout). With the effect of a point-contact head included, the existence of disk warpage/skew causes the head to produce a spatially-fixed harmonically varying force. The total disk motion is determined by superposition of the deflection pattern fixed on the disk and the space-fixed head-induced vibration. The disk pitch angle variation at the head is obtained and the results are compared for various values of the rotational speed and air-film thickness.

Three‐dimensional flow modeling of a self‐wiping corotating twin‐screw extruder. Part II: The kneading section

AbstractThree‐dimensional flow simulations of kneading elements in an intermeshing corotating twin‐screw extruder are performed by solving the Navier Stokes equations with a finite element package, Sepran. Instead of using the whole geometry of the 8‐shaped barrel a simplified geometry is used, representing a large part of the geometry during the rotating action of the kneading paddle. The goal of these calculations is to study the dependence of several factors that influence mixing, such as shear rate, elongation rate, pressure, and the flow profile in the extruder on various extruder parameters, such as fluid viscosity, rotation speed, and throughput.The shear and elongation rate and the pressure drop are calculated for varying viscosities. The various stagger angles possible for disc configurations in the corotating twin‐screw extruder are modeled. The axial backflow volume is calculated for varying values of rotation speed and throughput.

The microprocessor measurement of low values of rotational speed and acceleration

An algorithm and its microprocessor implementation for the measurement of low values of rotational speed and acceleration/deceleration of rotating machinery are presented. This measuring technique was developed for the special application where the speed reference signal is derived from a pulse train at a frequency of only 1 pulse/r. This fact places severe constraints on the resolution and measuring time of the instrument because an inverse relationship exists between these two parameters. A special feature of this instrument is that it can estimate speed and rate-of-change of speed in between the speed reference pulses by extrapolation of historic data. The instrument is implemented using standard microprocessor components and supporting circuitry. >

Theoretical Calculations of the Flow Around a Rotating Circular Cylinder Placed in a Uniform Flow

The rotation of a circular cylinder placed in a uniform flow is assumed to add a circulation to the flow around the cylinder proportional to the product of the angular velocity of the cylinder and the front area between upper and lower separation points. Adding the velocity due to this induced circulation to the base velocity distribution of the non-rotating cylinder the new velocity distribution on the rotating cylinder is formed. Thwaites’ method is then used to calculate the laminar boundary layer on the upper and on the lower sides of the cylinder. The stagnation point, and the upper and lower separation points are also calculated at different values of rotational speed. The calculated lift and drag coefficients using a linear pressure distribution on the wake part of the cylinder with the calculated pressure dstribution on the front part between the two separation points show the same trend as the measured values. The torque coefficient is also calculated to estimate the necessary power required to rotate the cylinder to produce the needed lift.